William Edward Louch

• Erdal, Magnhild Sekse; Qi, Jing; Erusappan, Pugazendhi Murugan; Schubert, Mario; Koser, Franziska & Basson, Adelle [Vis alle 23 forfattere av denne artikkelen] (2026). Biallelic titin truncation disrupts sarcomere assembly and function in patient-derived iPSC cardiomyocytes. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 218, s. 130–136. doi: 10.1016/j.yjmcc.2026.08.001.
• Becker, Victoria; Kavaliauskiene, Simona; Morgenroth, Daniel; Mahat, Sudip; Louch, William Edward & Johansen, Ida Beitnes [Vis alle 7 forfattere av denne artikkelen] (2026). Bent out of shape: The impact of deviating heart morphology on cardiac function in Atlantic salmon (Salmo salar L.). Aquaculture. ISSN 0044-8486. 622. doi: 10.1016/j.aquaculture.2026.744076. Fulltekst i vitenarkiv
• Li, Jia; Sundnes, Joakim; Erdal, Magnhild Sekse; Hou, Yufeng; Norseng, Per Andreas & Linke, Wolfgang A. [Vis alle 8 forfattere av denne artikkelen] (2026). β-Adrenergic stimulation recruits additional contracting sarcomeres in cardiomyocytes. Cardiovascular Research (CVR). ISSN 0008-6363. 122(9), s. 1127–1129. doi: 10.1093/cvr/cvag083. Fulltekst i vitenarkiv
• halvorsen, pia skovholt; Mahat, Sudip; Larsen, Simen Westegaard; Sørgaard, Tuva M.G.; Becker, Victoria & Morgenroth, Daniel [Vis alle 12 forfattere av denne artikkelen] (2026). The influence of egg incubation and rearing temperature on heart morphology and function in farmed Atlantic salmon (Salmo salar). Aquaculture. ISSN 0044-8486. 617. doi: 10.1016/j.aquaculture.2026.743755. Fulltekst i vitenarkiv
• Espe, Emil Knut Stenersen; Louch, William Edward; Smith, Godfrey L & Stokke, Mathis Korseberg (2026). The border zone after myocardial infarction: clarification of terminology and proposal for a new definition. Cardiovascular Research (CVR). ISSN 0008-6363. 122(3), s. 297–300. doi: 10.1093/cvr/cvag023. Fulltekst i vitenarkiv
• Jæger, Karoline Horgmo; Louch, William Edward & Tveito, Aslak (2025). Reduced gap junction coupling amplifies the effects of cardiomyocyte variability and destabilizes the heartbeat. Physiological Reports. 13(13). doi: 10.14814/phy2.70461. Fulltekst i vitenarkiv Vis sammendrag

  Cardiomyocytes exhibit significant cell-to-cell variability due to differences in protein expression and post-translational modifications in the cell membrane and the intracellular machinery. Resulting variability in action potential propagation and configuration is proposed to promote arrhythmia. However, such effects may be suppressed by tight electrical coupling of cells in the healthy heart, but not during pathological conditions where gap junction function is impaired. To investigate this, we employed a cell-based mathematical model of cardiac electrophysiology, in which we systematically modified properties of individual cells and intercellular electrical connectivity (gap junctions). Despite the inclusion of marked variation in properties between cells, we observed electrical homogeneity when cells were well coupled. In contrast, lower and/or more variable gap junction connectivity resulted in nonhomogeneous action potential configuration and irregular timing of the depolarizing and repolarizing electrical wavefronts. Pro-arrhythmic early after depolarizations also occurred under these conditions. These effects were effectively dampened in highly coupled cells. Nevertheless, differences in calcium homeostasis were not negated by gap junction coupling, indicating a limit to which electrical connections can homogenize mechanical function. Our findings underscore the critical role of intercellular coupling in maintaining cardiac stability and highlight the importance of studying cardiomyocytes within a syncytium rather than in isolation.

• Mathiesen, Sabrina Bech; Støle, Thea Parsberg; Romaine, Andreas; Lunde, Marianne; Martinsen, Marita & Aronsen, Jan Magnus [Vis alle 10 forfattere av denne artikkelen] (2025). Syndecan-4 interacts directly with β-parvin and regulates the ILK-PINCH-β-parvin complex, the β-parvin-β-PIX-Rac1 axis, and cardiomyocyte geometry in a sex-dependent manner. Frontiers in Cell and Developmental Biology. 13. doi: 10.3389/fcell.2025.1569185. Fulltekst i vitenarkiv Vis sammendrag

  Syndecan-4 is a ubiquitously expressed transmembrane proteoglycan that links the extracellular matrix to intracellular protein networks. It is located at stress-sensing structures in cardiomyocytes, including costameres and Z-discs, and in male mice, it is involved in the hypertrophic response to cardiac pressure overload. We have recently found female syndecan-4 KO cardiomyocytes, without challenge, to be smaller in area. Smaller cardiomyocytes with elongation defects have been observed in animal models with β-parvin deficiency, where the loss of this mechano-sensor disrupts the guanine nucleotide exchange factor (GEF) β-PIX-GTPase Rac1 axis, which is essential for proper cell elongation. β-parvin, together with integrin-linked kinase (ILK) and particularly interesting new cysteine-histidine-rich protein (PINCH), constitutes the IPP complex (ILK-PINCH-parvin), which is part of the integrin consensus adhesome. Interestingly, in a previous large cardiac interactome study, we have identified β-parvin, as well as ILK, β-PIX, and Rac1 as potential syndecan-4 partners. To better understand the syndecan-4-β-parvin association, we mapped their interaction and investigated the effect of syndecan-4 ablation on the IPP complex, the β-parvin-β-PIX-Rac1 axis, and cardiomyocyte geometry in both females and males. Interestingly, genetic ablation of syndecan-4 resulted in shorter cardiomyocytes in females only. The syndecan-4-β-parvin interaction was mapped to accessible sequences within the N-terminal, linker, and CH2 domains of β-parvin and the unique variable C2 cytoplasmic region of syndecan-4. Syndecan-4 ablation resulted in lower levels of membrane-localized β-parvin in both sexes and sex-specific differences in its associated partners ILK and PINCH, suggesting that syndecan-4 is linked to integrin signaling through the IPP complex. Finally, Rac1, known for its involvement in cell size regulation, and some of its regulators, β-PIX, RhoGDIα, and the serine/threonine kinase PAK, showed sex-specific alterations following syndecan-4 ablation. Altogether, our data suggest that syndecan-4 binds directly to β-parvin and regulates cardiomyocyte length, the IPP complex, and the β-parvin-β-PIX-Rac1 in a sex-dependent manner. These findings highlight a sex-specific role for syndecan-4 in cardiomyocyte structure, offering new insight into the molecular basis for sex differences in cardiac biology.

• Branovets, Jelena; Laasmaa, Martin; Stolova, Jekaterina; Shen, Xin; Rätsepso, Triinu & Bernasconi, Romain [Vis alle 13 forfattere av denne artikkelen] (2025). Lifelong creatine deficiency leads to augmented sarcoplasmic reticulum calcium release but not heart failure. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 329(2), s. H471–H489. doi: 10.1152/ajpheart.00106.2025. Fulltekst i vitenarkiv Vis sammendrag

  Previous studies have suggested that reduced creatine kinase (CK) activity may lead to heart failure. Here, we studied calcium handling in the hearts of creatine-deficient arginine-glycine amidino-transferase knockout (AGAT KO) mice with lifelong inhibition of CK. In contrast to failing cardiomyocytes, AGAT KO cardiomyocytes exhibited larger calcium transients due to more readily firing RyR clusters releasing more calcium from the SR. Thus, lifelong creatine deficiency does not lead to the phenotype observed in heart failure.

• Gonano, Luis A.; Kinns, Alycia M.; Dahl, Anna Bergan; Louch, William Edward & Jones, Peter P. (2025). Interplay Between Ryanodine Receptor Arrangement and Function: Implications for (Patho)physiological Control of Calcium Release. Circulation Research. ISSN 0009-7330. 137(6), s. 902–923. doi: 10.1161/circresaha.125.325387. Fulltekst i vitenarkiv Vis sammendrag

  Calcium release through the cardiac RyR2 (type-2 ryanodine receptor) is essential for cardiac contraction. RyR2 dysfunction is associated with a spectrum of cardiac pathologies, most notably arrhythmias. While excessive RyR2 activity was historically seen as the driver of arrhythmia, it is now clear that inadequate calcium release is equally detrimental. This homeostatic balance of activity requires precise tuning, which is provided by a swathe of regulating factors spanning posttranslational modifications, protein-protein interactions, and the more recently identified positioning of individual RyR2 channels within the cell. This review summarizes how too much, or too little, calcium release can lead to arrhythmia and explores how the multitude of regulating factors work synergistically to set and modify RyR2 physiologically and become impaired in disease. Finally, we examine how RyR2-targeted pharmacological approaches can therapeutically rebalance calcium handling and inhibit arrhythmia.

• Dahl, Anna Bergan; Carlson, Cathrine Rein; Laasmaa, Martin; Subramanian, Hariharan; Basson, Adelle & Li, Jia [Vis alle 16 forfattere av denne artikkelen] (2025). Activated CaMKIIδ translocates to the RyR nanodomain in cardiomyocytes. Cardiovascular Research (CVR). ISSN 0008-6363. 121(14), s. 2177–2188. doi: 10.1093/cvr/cvaf187. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Aims The heartbeat is triggered by the coordinated release of Ca2+ from the ryanodine receptor type-2 (RyR) in cardiomyocytes. Phosphorylation of RyR by Ca2+/calmodulin-dependent kinase IIδ (CaMKIIδ) fine-tunes this process in health, while hyperphosphorylation causes excessive, pathological Ca2+ release. We investigated how CaMKIIδ is spatially recruited and anchored to RyRs to achieve this functional regulation. Methods and results We employed confocal and dSTORM microscopy to investigate the macro- and nanoscale distribution of CaMKIIδ across cardiomyocytes, respectively. We linked positional rearrangement of the kinase during β-adrenergic stimulation (isoproterenol, Iso) to alterations in RyR phosphorylation and function (Ca2+ sparks), and the requirement of the CaMKIIδ anchoring protein AKAP18δ by knockdown/knockout. Confocal microscopy revealed that macroscale CaMKIIδ localization was not markedly altered during Iso-treatment, although a narrowing of its distribution around the Z-lines occurred, where the RyR reside. Higher resolution dSTORM imaging confirmed that local mobilization of CaMKIIδ by Iso decreased the distance from Z-lines and RyRs to the nearest CaMKIIδ by 28 and 12%, respectively. Functionally, kinase translocation into the RyR nanodomain was accompanied by increased channel phosphorylation and Ca2+ spark frequency. These actions were dependent on CaMKIIδ activity, since kinase translocation, RyR phosphorylation, and activation were all mimicked by the upstream activator of CaMKIIδ (8-CPT) and prevented by direct CaMKIIδ inhibitors (AIP, N1 peptide). A critical role of AKAP18δ in this mechanism was supported by immunoprecipitation experiments, which showed greater kinase binding to AKAP18δ during Iso-stimulation. Furthermore, loss of AKAP18δ by viral-mediated AKAP18δ knockdown or knockout prevented CaMKIIδ translocation to Z-lines. Microtubular disruption also blocked CaMKIIδ translocation. Conclusion Collectively, our results indicate that nanoscale movement of CaMKIIδ is closely associated with RyR activation following β-adrenergic stimulation. This translocation depends on an intact microtubular network and kinase binding to AKAP18δ.

• Delgadillo-Silva, Luis Fernando; Dakessian, Karen; Provencher-Girard, Audrey; Louch, William Edward & Rutter, Guy A. (2025). ER calcium stores contribute to glucose-induced Ca2+ waves and intercellular connectivity in mouse pancreatic islets. Cell Calcium. ISSN 0143-4160. 133. doi: 10.1016/j.ceca.2025.103093. Fulltekst i vitenarkiv Vis sammendrag

  Defective insulin secretion is a hallmark of diabetes mellitus. Glucose-induced Ca2+ oscillations are critical for the stimulation of insulin secretion, though the mechanisms through which these propagate across the islet are poorly understood. Here, we use beta cell-targeted GCaMP6f to explore the role of endoplasmic reticulum (ER) Ca2+ mobilization in response to submaximal (11 mM) or hyperglycemic (25 mM) glucose, mimicking diabetes. Inhibition of inositol 1,4,5-trisphosphate (IP3) receptors, and other ion channels, with 2-aminoethoxydiphenyl borate (2-APB), had minimal effects on the initial peak or intercellular connectivity provoked by 11 mM glucose. However, 2-APB lowered subsequent glucose-induced cytosolic Ca2+increases and connectivity at both 11 and 25 mM glucose. Unexpectedly, the activation of IP3 receptors with the muscarinic acetylcholine receptor agonist carbachol had minimal impact on the initial peak elicited by 11 mM glucose, but Ca2+ waves at 11 and 25 mM glucose were more poorly coordinated. To determine whether ER calcium mobilization was sufficient to initiate Ca2+ waves we next blocked sarco(endo)plasmic Ca2+ ATPase (SERCA) pumps with thapsigargin, whilst preventing plasma membrane depolarization with the KATP-channel opener, diazoxide. Under these conditions, an initial cytosolic Ca2+increase was followed by secondary Ca2+ waves that subsided slowly. The application of carbachol alongside diazoxide still enhanced Ca2+dynamics, though activity was uncoordinated. After genetic deletion of SERCA2 in beta cells, Ca2+wave frequency, but not connectivity, were lowered. Our results show that ER Ca2+ mobilization plays a relatively minor role in the initiation and propagation of Ca2+ waves in response to glucose but is needed for sustained Ca2+waves.

• Clowsley, Alexander H.; Meletiou, Anna; Janicek, Radoslav; Bokhobza, Alexandre F. E.; Lučinskaitė, Evelina & Bleuer, Gabriela [Vis alle 10 forfattere av denne artikkelen] (2025). MINFLUX microscopy resolves subunits of the cardiac ryanodine receptor and its 3D orientation in cells. Nature Communications. 17(1). doi: 10.1038/s41467-025-67801-6. Fulltekst i vitenarkiv Vis sammendrag

  The cardiac ryanodine receptor (RyR2) constitutes the molecular basis of the process of calcium-induced calcium release where activation of RyR2s can be locally regenerative. Here, we present purely optical data of RyR2 distribution with sub-molecular resolution by applying 3D MINFLUX microscopy. Using single-domain antibodies and DNA-PAINT we determine the location of individual RyR2 subunits with high precision (~3 nm) and resolve the 3D orientations of RyR2s in-situ. We measured labeling efficiencies of ~50%, implying RyR2 tetramer detection probability approaching 95%. In HEK293 cells, RyR2 expression was dense, with some clusters containing several hundred RyR2s. Ventricular myocytes from mice contained large clusters containing many tens of close-packed RyR2s, resolving apparent discrepancies between electron microscopy and previous super-resolution microscopy data. The methodology developed here reveals the full 3D morphological complexity of RyR2 channels and is applicable to other multi-subunit complexes in a variety of cell types.

• Huse, Camilla; Murphy, Sarah Louise Mikalsen; Yang, Kuan; Balzer, Nora Reka; Stokke, Mathis Korseberg & Anstensrud, Anne Kristine [Vis alle 27 forfattere av denne artikkelen] (2025). The effects of interleukin-6-receptor inhibition on monocytes in STEMI: a substudy of the ASSAIL-MI trial. EBioMedicine. 121, s. 105960–105960. doi: 10.1016/j.ebiom.2025.105960. Fulltekst i vitenarkiv
• halvorsen, pia skovholt; Mahat, Sudip; Becker, Victoria; Kavaliauskiene, Simona; Sørgaard, Tuva M.G. & Morgenroth, Daniel [Vis alle 10 forfattere av denne artikkelen] (2025). Functional and structural cardiac remodelling in farmed Atlantic salmon (Salmo salar). Aquaculture. ISSN 0044-8486. 614. doi: 10.1016/j.aquaculture.2025.743496. Fulltekst i vitenarkiv Vis sammendrag

  Cardiac performance is key for survival and fitness, particularly during energetically demanding and stressful events such as migration in the wild and stressful handling and crowding in aquaculture. Heart morphology is well-known to be altered in farmed salmon, yet the functional consequences remain unknown. Cardiac morphology, structure and function were compared between seawater-ready wild and farmed Atlantic salmon (Salmo salar) smolts by morphological and histological assessment, and echocardiography. In line with previous research, farmed hearts had rounder and less symmetrical ventricles with enlarged bulbi. Morphological deviations were present in a staggering 76 % of farmed smolts but were completely absent in the wild population. Echocardiography revealed reduced atrial area and E/A ratio in farmed individuals, indicating larger reliance on atrial contraction under rest. Histological analyses showed a relatively thicker compact myocardium, due to cardiomyocyte widening in farmed fish — features consistent with hypertrophic remodelling. Collectively, these findings confirm consistent structural remodelling in farmed salmon hearts and reveal functional adaptations to altered cardiac morphology. Most likely, these physiological alterations are shaped by selective breeding and rearing conditions and may influence cardiac performance under routine aquaculture conditions.

• Parvan, Reza; Becker, Victoria; Milad, Hosseinpour,; Yousef, Moradi,; Louch, William Edward & Cataliotti, Alessandro [Vis alle 9 forfattere av denne artikkelen] (2025). Prognostic and predictive microRNA panels for heart failure patients with reduced or preserved ejection fraction: a meta-analysis of Kaplan–Meier-based individual patient data. BMC Medicine. 23. doi: 10.1186/s12916-025-04238-0. Fulltekst i vitenarkiv Vis sammendrag

  Cardiac troponins and natriuretic peptides are benchmark biomarkers for heart failure (HF) with reduced ejection fraction (HFrEF) but have limited prognostic performance for HF patients with preserved ejection fraction (HFpEF). Non-coding RNA-based biomarkers represent an innovative approach to risk-stratify patients and might address the unmet need for minimally invasive prognostic and predictive tools for HF development and HF-related outcomes. Our aim is to investigate the prognostic performance and risk stratification potential of circulating panels of microRNAs (miRNAs) in HFrEF and HFpEF. A systematic search on PubMed, Web of Science, and Scopus databases was performed for studies reporting miRNAs as prognostic biomarkers in HF patients. A total of 22 studies pooling 5736 participants were included for quantitative analysis. KM-based individual patient data (IPD) analysis was performed in 12 studies (5064 participants). KM-based IPD analysis in HFrEF allowed the identification of a panel of four miRNAs (miR-27a-3p, miR-129-5p, miR-145-5p, and miR-590-3p) predicting the risk of all-cause death with hazard ratio (HR) 4.26 [2.68–6.76]. MiR-122-5p and miR-423-5p predicted cardiovascular death of HFrEF patients (HR 3.61 [2.67–4.87]). In HFpEF, miR-19a-3p predicted all-cause death of HFpEF patients with HR 2.23 [1.16–4.27]. Moreover, a panel of eight miRNAs (miR-17-5p, miR-20a-5p, miR-21, miR-23, miR-27, miR-106b-5p, miR-210, and miR-221) showed significant association with HF incidence (HR 2.14 [1.81–2.53]). A comprehensive meta-analysis of KM-based IPD enabled the identification of unique miRNA panels predicting the incidence and severity of HFrEF and HFpEF, supporting the clinical usefulness of miRNA profiling for tailored healthcare and risk stratification in HF patients. Nonetheless, more rigorously designed longitudinal studies are needed to validate the clinical application of miRNAs as prognostic and predictive biomarkers.

• Rugolo, Ilde; Shen, Xin; Støle, Thea Parsberg; Dahl, Anna Bergan; Manfra, Ornella & Lunde, Marianne [Vis alle 12 forfattere av denne artikkelen] (2025). Identification of a Small Secretoneurin Derivative That Inhibits CaMKIIδ Activity. Journal of Cellular and Molecular Medicine. ISSN 1582-1838. 29(20). doi: 10.1111/jcmm.70900. Fulltekst i vitenarkiv Vis sammendrag

  ABSTRACT Ventricular arrhythmias, a major cause of sudden cardiac death, are driven by Ca 2+ imbalance in cardiac myocytes, often linked to the overactivation of CaMKIIδ (Ca 2+ /calmodulin‐dependent protein kinase II delta). As such, inhibiting CaMKIIδ represents a promising therapeutic strategy. Based on our previous finding that native secretoneurin (SN) is a weak CaMKIIδ inhibitor, we aimed to develop a more potent derivative of SN to effectively counter aberrant Ca 2+ handling and arrhythmia risk. Various regions of SN were tested for CaMKII binding, identifying the core region as the sequence with the strongest binding capacity. This region was subsequently optimised with two phenylalanine substitutions, resulting in the SN derivative SN‐db‐short. Structural homology modeling and ELISA‐based assays revealed that SN‐db‐short bound both the substrate‐binding (S‐site) region of CaMKIIδ, in addition to the ATP‐binding region, with 8‐fold stronger binding compared to SN. Surface plasmon resonance experiments confirmed that SN‐db‐short exhibited a higher association rate and affinity for CaMKIIδ compared to SN. Consistent with only a partial calmodulin binding motif, SN‐db‐short showed no calmodulin binding, indicating selective CaMKIIδ inhibition. In functional studies, SN‐db‐short inhibited CaMKIIδ‐mediated phosphorylation of ryanodine receptor 2 and appeared more effective than SN in reducing the incidence of Ca 2+ sparks and Ca 2+ waves. SN‐db‐short also more markedly inhibited CaMKIIδ phosphorylation of phospholamban, slowed Ca 2+ reuptake, and reduced the magnitude of Ca 2+ transients during isoproterenol stimulation. SN‐db‐short effectively inhibits CaMKIIδ and significantly counters aberrant Ca 2+ handling in cardiomyocytes. Thus, this optimised peptide holds therapeutic potential for reducing the risk of ventricular arrhythmias.

• Handegard, Vilde; Lunde, Per Kristian; Frisk, Michael; Seynnes, Olivier R.; Ørtenblad, N. & Louch, William Edward [Vis alle 8 forfattere av denne artikkelen] (2025). Myofiber structure, sarcoplasmic reticulum Ca2+ handling, and contractile function after muscle-damaging exercise in humans. Physiological Reports. 13(3). doi: 10.14814/phy2.70204. Fulltekst i vitenarkiv Vis sammendrag

  Exercise-induced muscle damage (EIMD) is characterized by a severe and prolonged decline in force-generating capacity. However, the precise cellular mechanisms underlying the observed long-lasting decline in force-generating capacity associated with EIMD are still unclear. We investigated in vivo force generation and ex vivo Ca2+-activated force generation, Ca2+ sensitivity, and myofiber Ca2+ handling systems (SR and t-tubules) in human biceps brachii before and 2, 48, and 96 h after eccentrically muscle-damaging contractions and in non-exercised control arm. The force-generating capacity declined by 50 ± 13% 3 h after exercise and was still not recovered after 96 h. The force-Ca relationship of skinned myofibers revealed an impaired maximal Ca2+-activated force in MHC I-fibers, but not MHC II-fibers 48 h after exercise. Further, Ca2+ sensitivity was increased in MHC II-fibers, which was reversed after incubation with a strong reductant. There was a biphasic increase in SERCA sulfonylation, and a parallel reduction in the SR Ca2+ uptake rate, with no effects on SR vesicle leak or SR vesicle Ca2+ release rate. T-tubules showed a progressive increase in the density of longitudinal tubules by 96 h after exercise. In conclusion, MHC II-fiber Ca2+ sensitivity was increased 48 h after exercise, attributed to changes in the REDOX status. 96 h after exercise SR vesicle Ca2+ uptake was impaired, and an increased number of longitudinal tubules were observed. These alterations may contribute to the impaired force generation evident at the late stage of recovery.

• Nordén, Einar Sjaastad; Bendiksen, Bård Andre; Bergo, Kaja Knudsen; Espe, Emil Knut Stenersen; Mcginley, Gary George & Hasic, Almira [Vis alle 17 forfattere av denne artikkelen] (2024). Sacubitril/valsartan preserves regional cardiac function following myocardial infarction in rats. ESC Heart Failure. doi: 10.1002/ehf2.15145. Fulltekst i vitenarkiv Vis sammendrag

  Aims Sacubitril/valsartan (Sac/Val) is used for treatment of heart failure. The effect of Sac/Val on regional dysfunction following myocardial infarction (MI) remains uncertain. This study aimed at understanding the effects of Sac/Val on regional function after MI. Methods and results MI or sham surgery was performed in Sprague–Dawley rats. Animals were randomized to treatment with Sac/Val, valsartan (Val) or vehicle (Veh). Magnetic resonance imaging was used to acquire left ventricular volumes and strain. Left ventricular tissue was obtained for wesern blotting, PCR and Masson's trichrome staining. Isolated cardiac fibroblasts were cultured with Veh, atrial natriuretic peptide (ANP), adrenomedullin (ADM) and sacubitrilat, and collagen expression assessed with droplet digital PCR. Results Sac/Val reduced ventricular end-diastolic volume by 18% compared with Veh, and preserved circumferential systolic strain in the zone proximal to infarction compared with sham after 42 days of treatment (peak strain ± SEM: sham: −0.19 ± 0.01%; Sac/Val: −0.14 ± 0.02%; Val: −0.10 ± 0.02%; Veh: −0.10 ± 0.02%). Masson's trichrome staining demonstrated lower fibrotic deposition in the intermediate zone with Sac/Val treatment than Veh (sham: 2.29 ± 0.17%; Sac/Val: 2.31 ± 0.27%; Val: 3.22 ± 0.60%; Veh: 4.14 ± 0.48%). The amounts of the pro-apoptotic caspase 3 cleavage fragments p19/17 were 89% higher in Val than sham, with Sac/Val showing no significant increase compared with sham. Collagen expression in human fibroblast culture was lower in cells co-treated with sacubitrilat and ANP, an effect not observed with sacubitrilat/ADM co-treatment. Conclusions Sac/Val preserves in vivo myocardial function in the region most proximal to MI in rats and reduces left ventricular dilatation. These effects may be related to a reduction in both fibrosis and pro-apoptotic signalling.

• Zhang, Xianwei; Wu, Yixuan; Smith, Charlotte E.R.; Louch, William Edward; Morotti, Stefano & Dobrev, Dobromir [Vis alle 8 forfattere av denne artikkelen] (2024). Enhanced Ca²⁺-Driven Arrhythmogenic Events in Female Patients With Atrial Fibrillation: Insights From Computational Modeling. JACC: Clinical Electrophysiology. ISSN 2405-500X. doi: 10.1016/j.jacep.2024.07.020. Fulltekst i vitenarkiv
• Becker, Victoria; Kavaliauskiene, Simona; Sandblom, Erik; Zena, Lucas A.; Gräns, Albin & Louch, William Edward [Vis alle 9 forfattere av denne artikkelen] (2024). Echocardiography - a non-invasive alternative for assessing cardiac morphology and function in Atlantic salmon (Salmo salar L.). Aquaculture. ISSN 0044-8486. 592. doi: 10.1016/j.aquaculture.2024.741223. Fulltekst i vitenarkiv Vis sammendrag

  Cardiac-related mortality is increasing in farmed salmon. Non-invasive tools for examining and screening for cardiac morphology and function are limited, and most common methodologies are lethal, time-consuming, and immobile. Echocardiography has previously been tested as a non-invasive, quick, and portable alternative, though its implementation is minimal. Improvements in echocardiographic techniques during the last decade have enabled more refined assessments of structure and function and hold potential for use in fish farms. Utilising a compact, transportable ultrasound system, we examined the applicability of echocardiography in Atlantic salmon (Salmo salar L.). Several protocols and projections were tested, and intra- and inter-variation for both operators (image acquisition) and observers (image analysis) were assessed. In addition, the accuracy of cardiac structure/function measurements was compared with standard methods. In general, high accuracy and reproducibility of cardiac dimensions and functional parameters were found within the same and between different observers analysing the same dataset (intra- and inter-observer). Measurements between recordings of the same operator (intra-operator) and between different operators (inter-operator) were less accurate and repeatable but comparable to observations in previous human and mammalian studies. Cardiac output was slightly higher when measured with echocardiography compared to transit time flow probe. Yet, a strong correlation exists between the two methods. Furthermore, morphology measured in excised hearts ex vivo was comparable to echocardiography measurements and strongly correlated. Thus, ultrasound presents a highly feasible, non-invasive, and swift alternative to current methods for detailed cardiac assessment of salmon hearts.

• Juncos, Juan Xavier Masjoan; Nadeem, Fahad; Shakil, Shazia; El-Husari, Malik; Zafar, Iram & Louch, William Edward [Vis alle 10 forfattere av denne artikkelen] (2024). Myocardial SERCA2 Protects Against Cardiac Damage and Dysfunction Caused by Inhaled Bromine. Journal of Pharmacology and Experimental Therapeutics. ISSN 0022-3565. 390(1), s. 146–158. doi: 10.1124/jpet.123.002084. Fulltekst i vitenarkiv Vis sammendrag

  Myocardial sarcoendoplasmic reticulum calcium ATPase 2 (SERCA2) activity is critical for heart function. We have demonstrated that inhaled halogen (chlorine or bromine) gases inactivate SERCA2, impair calcium homeostasis, increase proteolysis, and damage the myocardium ultimately leading to cardiac dysfunction. To further elucidate the mechanistic role of SERCA2 in halogen-induced myocardial damage, we used bromine-exposed cardiac-specific SERCA2 knockout (KO) mice [tamoxifen-administered SERCA2 (flox/flox) Tg (αMHC-MerCreMer) mice] and compared them to the oil-administered controls. We performed echocardiography and hemodynamic analysis to investigate cardiac function 24 hours after bromine (600 ppm for 30 minutes) exposure and measured cardiac injury markers in plasma and proteolytic activity in cardiac tissue and performed electron microscopy of the left ventricle (LV). Cardiac-specific SERCA2 knockout mice demonstrated enhanced toxicity to bromine. Bromine exposure increased ultrastructural damage, perturbed LV shape geometry, and demonstrated acutely increased phosphorylation of phospholamban in the KO mice. Bromine-exposed KO mice revealed significantly enhanced mean arterial pressure and sphericity index and decreased LV end diastolic diameter and LV end systolic pressure when compared with the bromine-exposed control FF mice. Strain analysis showed loss of synchronicity, evidenced by an irregular endocardial shape in systole and irregular vector orientation of contractile motion across different segments of the LV in KO mice, both at baseline and after bromine exposure. These studies underscore the critical role of myocardial SERCA2 in preserving cardiac ultrastructure and function during toxic halogen gas exposures.

• Ruud, Marianne; Frisk, Michael; Melleby, Arne Olav; Norseng, Per Andreas; Mohamed, Belal A. & Li, Jia [Vis alle 22 forfattere av denne artikkelen] (2024). Regulation of cardiomyocyte t-tubule structure by preload and afterload: Roles in cardiac compensation and decompensation. Journal of Physiology. ISSN 0022-3751. 602(18), s. 4487–4510. doi: 10.1113/JP284566. Fulltekst i vitenarkiv Vis sammendrag

  Mechanical load is a potent regulator of cardiac structure and function. Although high workload during heart failure is associated with disruption of cardiomyocyte t-tubules and Ca2+ homeostasis, it remains unclear whether changes in preload and afterload may promote adaptive t-tubule remodelling. We examined this issue by first investigating isolated effects of stepwise increases in load in cultured rat papillary muscles. Both preload and afterload increases produced a biphasic response, with the highest t-tubule densities observed at moderate loads, whereas excessively low and high loads resulted in low t-tubule levels. To determine the baseline position of the heart on this bell-shaped curve, mice were subjected to mildly elevated preload or afterload (1 week of aortic shunt or banding). Both interventions resulted in compensated cardiac function linked to increased t-tubule density, consistent with ascension up the rising limb of the curve. Similar t-tubule proliferation was observed in human patients with moderately increased preload or afterload (mitral valve regurgitation, aortic stenosis). T-tubule growth was associated with larger Ca2+ transients, linked to upregulation of L-type Ca2+ channels, Na+–Ca2+ exchanger, mechanosensors and regulators of t-tubule structure. By contrast, marked elevation of cardiac load in rodents and patients advanced the heart down the declining limb of the t-tubule–load relationship. This bell-shaped relationship was lost in the absence of electrical stimulation, indicating a key role of systolic stress in controlling t-tubule plasticity. In conclusion, modest augmentation of workload promotes compensatory increases in t-tubule density and Ca2+ cycling, whereas this adaptation is reversed in overloaded hearts during heart failure progression.

• Lauritzen, Knut Husø; Yang, Kuan; Frisk, Michael; Louwe, Maria Cornelia; Olsen, Maria Belland & Ziegler, Mathias [Vis alle 11 forfattere av denne artikkelen] (2024). Apigenin inhibits NLRP3 inflammasome activation in monocytes and macrophages independently of CD38. Frontiers in Immunology. 15. doi: 10.3389/fimmu.2024.1497984. Fulltekst i vitenarkiv Vis sammendrag

  Introduction: CD38, a regulator of intracellular calcium signalling, is highly expressed in immune cells. Mice lacking CD38 are very susceptible to acute bacterial infections, implicating CD38 in innate immune responses. The effects of CD38 inhibition on NLRP3 inflammasome activation in human primary monocytes and monocyte-derived macrophages have not been investigated. Apigenin is a naturally occurring flavonoid known to inhibit CD38. However, apigenin has also been proposed to inhibit the extracellular ATP receptor P2XR7, an upstream activator of NLRP3. In this study we aimed to investigate whether apigenin attenuates NLRP3 inflammasome activation in human monocytes and monocyte-derived macrophages through CD38 inhibition. Methods: LPS-primed human monocytes and monocyte-derived macrophages were treated with apigenin, the CD38 inhibitor 78c, antagonists of CD38 second messengers (8-br-ADPR and 8-br-cADPR) or the ATP hydrolase, apyrase, prior to NLRP3 activation with ATP, monosodium urate crystals (MSU) or nigericin. IL-1β and TNF secretion and mRNA expression, as well as N-terminal gasdermin-D formation were quantified. Ca2+ mobilization was determined by live confocal microscopy. NLRP3 activity was also compared in WT and CD38-/- mouse bone marrow-derived macrophages (BMDMs) with and without CD38 inhibitors. Results: Apigenin significantly inhibited IL-1β release from LPS-primed monocytes and macrophages activated with ATP, MSU, or nigericin. CD38 inhibition with 78c also attenuated NLRP3-dependent IL-1β release. Apigenin was a potent inhibitor of Ca2+ flux from the endoplasmic reticulum to the cytosol in human monocyte-derived macrophages. Apyrase attenuated IL-1β release induced by ATP or MSU, but not by nigericin. However, the NLRP3 inflammasome is not compromised in CD38-/- bone marrow-derived macrophages compared to corresponding WT cells, and apigenin moderated IL-1β release in both genotypes. Discussion: Our data support that apigenin attenuates NLRP3 activation independently of CD38. Our results also suggest that MSU crystals activate NLRP3 through autocrine or paracrine ATP signalling.

• Stokke, Mathis Korseberg; Louch, William Edward & Smith, Godfrey L (2024). Electrophysiological tolerance: a new concept for understanding the electrical stability of the heart. Europace. ISSN 1099-5129. 26(11), s. 1–6. doi: 10.1093/europace/euae282. Fulltekst i vitenarkiv Vis sammendrag

  The co-ordinated electrical activity of ∼2 billion cardiac cells ensures stability of the heartbeat. Indeed, the remarkably low incidence (<1%) of ventricular arrhythmias in the healthy heart is only possible when the electrical event across this syncytium is closely controlled. In contrast, the diseased myocardium is associated with increased electrophysiological heterogeneity, unstable rhythm, and increased incidence of lethal arrhythmias. But what is the link between cellular and tissue level heterogeneity? Recent research has shown the existence of considerable cellular heterogeneity even in the healthy heart, suggesting that cell-to-cell variability in electrical (e.g. action potential duration) and mechanical performance (e.g. twitch amplitude) is a normal property. This observation has been previously unappreciated because the aggregated function in the form of QT-interval and cardiac output varies <1% on a beat-to-beat basis. This article describes the underlying cellular variability that is tolerated—and perhaps needed—by different regions of the heart for normal function and indicates why this variability is not apparent in function at the chamber and organ level. Thus, in contrast to the current dominant view, this article postulates that heterogeneity is normal and potentially endows various functional benefits. This new view of how the component parts of the heart come together to function also suggests novel mechanisms for cardiac pathologies, namely that dysfunction may emerge from changes in the extent and/or nature of heterogeneity. Once understood, restoring normal forms of heterogeneity could be a novel approach to treatment.

• Støle, Thea Parsberg; Lunde, Marianne; Gehmlich, Katja; Christensen, Geir; Louch, William Edward & Carlson, Cathrine Rein (2024). Exploring Syndecan-4 and MLP and Their Interaction in Primary Cardiomyocytes and H9c2 Cells. Cells. 13(11). doi: 10.3390/cells13110947. Fulltekst i vitenarkiv Vis sammendrag

  The transmembrane proteoglycan syndecan-4 is known to be involved in the hypertrophic response to pressure overload. Although multiple downstream signaling pathways have been found to be involved in this response in a syndecan-4-dependent manner, there are likely more signaling components involved. As part of a larger syndecan-4 interactome screening, we have previously identified MLP as a binding partner to the cytoplasmic tail of syndecan-4. Interestingly, many human MLP mutations have been found in patients with hypertrophic (HCM) and dilated cardiomyopathy (DCM). To gain deeper insight into the role of the syndecan-4–MLP interaction and its potential involvement in MLP-associated cardiomyopathy, we have here investigated the syndecan-4–MLP interaction in primary adult rat cardiomyocytes and the H9c2 cell line. The binding of syndecan-4 and MLP was analyzed in total lysates and subcellular fractions of primary adult rat cardiomyocytes, and baseline and differentiated H9c2 cells by immunoprecipitation. MLP and syndecan-4 localization were determined by confocal microscopy, and MLP oligomerization was determined by immunoblotting under native conditions. Syndecan-4–MLP binding, as well as MLP self-association, were also analyzed by ELISA and peptide arrays. Our results showed that MLP-WT and syndecan-4 co-localized in many subcellular compartments; however, their binding was only detected in nuclear-enriched fractions of isolated adult cardiomyocytes. In vitro, syndecan-4 bound to MLP at three sites, and this binding was reduced in some HCM-associated MLP mutations. While MLP and syndecan-4 also co-localized in many subcellular fractions of H9c2 cells, these proteins did not bind at baseline or after differentiation into cardiomyocyte-resembling cells. Independently of syndecan-4, mutated MLP proteins had an altered subcellular localization in H9c2 cells, compared to MLP-WT. The DCM- and HCM-associated MLP mutations, W4R, L44P, C58G, R64C, Y66C, K69R, G72R, and Q91L, affected the oligomerization of MLP with an increase in monomeric at the expense of trimeric and tetrameric recombinant MLP protein. Lastly, two crucial sites for MLP self-association were identified, which were reduced in most MLP mutations. Our data indicate that the syndecan-4–MLP interaction was present in nuclear-enriched fractions of isolated adult cardiomyocytes and that this interaction was disrupted by some HCM-associated MLP mutations. MLP mutations were also linked to changes in MLP oligomerization and self-association, which may be essential for its interaction with syndecan-4 and a critical molecular mechanism of MLP-associated cardiomyopathy.

• Rudsari, Hamid Khoshfekr; O'Hern, Colin; Ural, Evran E.; Damrath, Martin; Neeb, Emily & Zoofaghari, Mohammad [Vis alle 11 forfattere av denne artikkelen] (2023). Human Heart Organoid-derived Extracellular Vesicles for Cardiac Intercellular Communication. I Eckford, Andrew & Noel, Adam (Red.), The 10th Annual ACM International Conference on Nanoscale Computing and Communication. Association for Computing Machinery (ACM). ISSN 9798400700347. s. 122–128. doi: 10.1145/3576781.3608718. Fulltekst i vitenarkiv
• Gamage, Thilini Hansamali Gamage Yaddehi; Grabmayr, Herwig; Horvath, Ferdinand; Fahrner, Marc; Misceo, Doriana & Louch, William Edward [Vis alle 21 forfattere av denne artikkelen] (2023). A single amino acid deletion in the ER Ca2+ sensor STIM1 reverses the in vitro and in vivo effects of the Stormorken syndrome-causing R304W mutation. Science Signaling. ISSN 1945-0877. 16(771). doi: 10.1126/scisignal.add0509. Fulltekst i vitenarkiv
• Perdreau-Dahl, Harmonie; Lipsett, David Bruce; Frisk, Michael; Kermani, Fatemeh; Carlson, Cathrine Rein & Brech, Andreas [Vis alle 19 forfattere av denne artikkelen] (2023). BIN1, Myotubularin, and Dynamin-2 Coordinate T-Tubule Growth in Cardiomyocytes. Circulation Research. ISSN 0009-7330. 132(11), s. E188–E205. doi: 10.1161/CIRCRESAHA.122.321732. Fulltekst i vitenarkiv
• Laasmaa, Martin; Branovets, Jelena; Stolova, Jekaterina; Shen, Xin; Rätsepso, Triinu & Balodis, Mihkel Jaan [Vis alle 11 forfattere av denne artikkelen] (2023). Cardiomyocytes from female compared to male mice have larger ryanodine receptor clusters and higher calcium spark frequency. Journal of Physiology. ISSN 0022-3751. 601(18), s. 4033–4052. doi: 10.1113/JP284515. Fulltekst i vitenarkiv Vis sammendrag

  Sex differences in cardiac physiology are receiving increased attention as it has become clear that men and women have different aetiologies of cardiac disease and require different treatments. There are experimental data suggesting that male cardiomyocytes exhibit larger Ca2+ transients due to larger Ca2+ sparks and a higher excitation–contraction coupling gain; in addition, they exhibit a larger response to adrenergic stimulation with isoprenaline (ISO). Here, we studied whether there are sex differences relating to structural organization of the transverse tubular network and ryanodine receptors (RyRs). Surprisingly, we found that female cardiomyocytes exhibited a higher spark frequency in a range of spark magnitudes. While overall RyR expression and phosphorylation were the same, female cardiomyocytes had larger but fewer RyR clusters. The density of transverse t-tubules was the same, but male cardiomyocytes had more longitudinal t-tubules. The Ca2+ transients were similar in male and female cardiomyocytes under control conditions and in the presence of ISO. The synchrony of the Ca2+ transients was similar between sexes as well. Overall, our data suggest subtle sex differences in the Ca2+ influx and efflux pathways and their response to ISO, but these differences are balanced, resulting in similar Ca2+ transients in field-stimulated male and female cardiomyocytes. The higher spark frequency in female cardiomyocytes is related to the organization of RyRs into larger, but fewer clusters.

• Li, Jia; Sundnes, Joakim; Hou, Yufeng; Laasmaa, Martin; Ruud, Marianne & Unger, Andreas [Vis alle 19 forfattere av denne artikkelen] (2023). Stretch Harmonizes Sarcomere Strain Across the Cardiomyocyte. Circulation Research. ISSN 0009-7330. 133(3), s. 255–270. doi: 10.1161/CIRCRESAHA.123.322588. Fulltekst i vitenarkiv Vis sammendrag

  BACKGROUND: Increasing cardiomyocyte contraction during myocardial stretch serves as the basis for the Frank-Starling mechanism in the heart. However, it remains unclear how this phenomenon occurs regionally within cardiomyocytes, at the level of individual sarcomeres. We investigated sarcomere contractile synchrony and how intersarcomere dynamics contribute to increasing contractility during cell lengthening. METHODS: Sarcomere strain and Ca2+ were simultaneously recorded in isolated left ventricular cardiomyocytes during 1 Hz field stimulation at 37 °C, at resting length and following stepwise stretch. RESULTS: We observed that in unstretched rat cardiomyocytes, differential sarcomere deformation occurred during each beat. Specifically, while most sarcomeres shortened during the stimulus, ≈10% to 20% of sarcomeres were stretched or remained stationary. This nonuniform strain was not traced to regional Ca2+ disparities but rather shorter resting lengths and lower force production in systolically stretched sarcomeres. Lengthening of the cell recruited additional shortening sarcomeres, which increased contractile efficiency as less negative, wasted work was performed by stretched sarcomeres. Given the known role of titin in setting sarcomere dimensions, we next hypothesized that modulating titin expression would alter intersarcomere dynamics. Indeed, in cardiomyocytes from mice with titin haploinsufficiency, we observed greater variability in resting sarcomere length, lower recruitment of shortening sarcomeres, and impaired work performance during cell lengthening. CONCLUSIONS: Graded sarcomere recruitment directs cardiomyocyte work performance, and harmonization of sarcomere strain increases contractility during cell stretch. By setting sarcomere dimensions, titin controls sarcomere recruitment, and its lowered expression in haploinsufficiency mutations impairs cardiomyocyte contractility.

• Skogestad, Jonas; Albert, Ingrid; Hougen, Karina; Lothe, Gustav B; Lunde, Marianne & Eken, Olav Søvik [Vis alle 25 forfattere av denne artikkelen] (2023). Disruption of Phosphodiesterase 3A Binding to SERCA2 Increases SERCA2 Activity and Reduces Mortality in Mice with Chronic Heart Failure. Circulation. ISSN 0009-7322. 147(16), s. 1221–1236. doi: 10.1161/CIRCULATIONAHA.121.054168. Fulltekst i vitenarkiv
• Hou, Yufeng; Laasmaa, Martin; Li, Jia; Shen, Xin; Manfra, Ornella & Nordén, Einar Sjaastad [Vis alle 12 forfattere av denne artikkelen] (2023). Live-cell photoactivated localization microscopy correlates nanoscale ryanodine receptor configuration to calcium sparks in cardiomyocytes. Nature Cardiovascular Research. 2(3), s. 251–267. doi: 10.1038/s44161-022-00199-2. Fulltekst i vitenarkiv
• Manfra, Ornella; Louey, Samantha; Jonker, Sonnet S.; Perdreau-Dahl, Harmonie; Frisk, Michael & Giraud, George D. [Vis alle 8 forfattere av denne artikkelen] (2023). Augmenting workload drives T-tubule assembly in developing cardiomyocytes. Journal of Physiology. ISSN 0022-3751. doi: 10.1113/JP284538. Fulltekst i vitenarkiv Vis sammendrag

  Contraction of cardiomyocytes is initiated at subcellular elements called dyads, where L-type Ca2+ channels in t-tubules are located within close proximity to ryanodine receptors in the sarcoplasmic reticulum. While evidence from small rodents indicates that dyads are assembled gradually in the developing heart, it is unclear how this process occurs in large mammals. We presently examined dyadic formation in fetal and newborn sheep (Ovis aries), and the regulation of this process by fetal cardiac workload. By employing advanced imaging methods, we demonstrated that t-tubule growth and dyadic assembly proceed gradually during fetal sheep development, from 93 days of gestational age until birth (147 days). This process parallels progressive increases in fetal systolic blood pressure, and includes step-wise colocalization of L-type Ca2+ channels and the Na+/Ca2+ exchanger with ryanodine receptors. These proteins are upregulated together with the dyadic anchor junctophilin-2 during development, alongside changes in the expression of amphiphysin-2 (BIN1) and its partner proteins myotubularin and dynamin-2. Increasing fetal systolic load by infusing plasma or occluding the post-ductal aorta accelerated t-tubule growth. Conversely, reducing fetal systolic load with infusion of enalaprilat, an angiotensin converting enzyme inhibitor, blunted t-tubule formation. Interestingly, altered t-tubule densities did not relate to changes in dyadic junctions, or marked changes in the expression of dyadic regulatory proteins, indicating that distinct signals are responsible for maturation of the sarcoplasmic reticulum. In conclusion, augmenting blood pressure and workload during normal fetal development critically promotes t-tubule growth, while additional signals contribute to dyadic assembly.

• Lunde, Per Kristian; Manfra, Ornella; Støle, Thea Parsberg; Lunde, Marianne; Martinsen, Marita & Carlson, Cathrine Rein [Vis alle 7 forfattere av denne artikkelen] (2023). Polyarginine Cell-Penetrating Peptides Bind and Inhibit SERCA2. Cells. 12(19). doi: 10.3390/cells12192358. Fulltekst i vitenarkiv Vis sammendrag

  Cell-penetrating peptides (CPPs) are short peptide sequences that have the ability to cross the cell membrane and deliver cargo. Although it is critical that CPPs accomplish this task with minimal off-target effects, such actions have in many cases not been robustly screened. We presently investigated whether the commonly used CPPs TAT and the polyarginines Arg9 and Arg11 exert off-target effects on cellular Ca2+ homeostasis. In experiments employing myocytes and homogenates from the cardiac left ventricle or soleus muscle, we observed marked inhibition of Ca2+ recycling into the sarcoplasmic reticulum (SR) following incubation with polyarginine CPPs. In both tissues, the rate of SR Ca2+ leak remained unchanged, indicating that protracted Ca2+ removal from the cytosol stemmed from inhibition of the SR Ca2+ ATPase 2 (SERCA2). No such inhibition occurred following treatment with TAT, or in preparations from the SERCA1-expressing extensor digitorum longus muscle. Experiments in HEK cells overexpressing individual SERCA isoforms confirmed that polyarginine incubation specifically inhibited the activity of SERCA2a and 2b, but not SERCA1 or 3. The attenuation of SERCA2 activity was not dependent on the presence of phospholamban, and ELISA-based analyses rather revealed direct interaction between the polyarginines and the actuator domain of the protein. Surface plasmon resonance experiments confirmed strong binding within this region of SERCA2, and slow dissociation between the two species. Based on these observations, we urge caution when employing polyarginine CPPs. Indeed, as SERCA2 is expressed in diverse cell types, the wide-ranging consequences of SERCA2 binding and inhibition should be anticipated in both experimental and therapeutic settings.

• Shen, Xin; Brink, Jonas van den; Bergan-Dahl, Anna; Kolstad, Terje; Norden, Einar & Hou, Yufeng [Vis alle 11 forfattere av denne artikkelen] (2022). Prolonged β-adrenergic stimulation disperses ryanodine receptor clusters in cardiomyocytes. eLIFE. 11. doi: 10.7554/eLife.77725. Fulltekst i vitenarkiv Vis sammendrag

  Ryanodine Receptors (RyRs) exhibit dynamic arrangements in cardiomyocytes, and we previously showed that 'dispersion' of RyR clusters disrupts Ca2+ homeostasis during heart failure (HF) (Kolstad et al., eLife, 2018). Here, we investigated whether prolonged β-adrenergic stimulation, a hallmark of HF, promotes RyR cluster dispersion, and examined the underlying mechanisms. We observed that treatment of healthy rat cardiomyocytes with isoproterenol for 1 hour triggered progressive fragmentation of RyR clusters. Pharmacological inhibition of CaMKII reversed these effects, while cluster dispersion was reproduced by specific activation of CaMKII, and in mice with constitutively active Ser2814-RyR. A similar role of protein kinase A (PKA) in promoting RyR cluster fragmentation was established by employing PKA activation or inhibition. Progressive cluster dispersion was linked to declining Ca2+ spark fidelity and magnitude, and slowed release kinetics from Ca2+ propagation between more numerous RyR clusters. In healthy cells, this served to dampen the stimulatory actions of β-adrenergic stimulation over the longer term, and protect against pro-arrhythmic Ca2+ waves. However, during HF, RyR dispersion was linked to impaired Ca2+ release. Thus, RyR localization and function are intimately linked via channel phosphorylation by both CaMKII and PKA which, while finely tuned in healthy cardiomyocytes, underlies impaired cardiac function during pathology.ADD A COMMENT +Open annotations. The current annotation count on this page is 0.Data availability

• Zhang, Xianwei; Ni, Haibo; Morotti, Stefano; Smith, Charlotte E. R.; Sato, Daisuke & Louch, William Edward [Vis alle 8 forfattere av denne artikkelen] (2022). Mechanisms of spontaneous Ca2+ release-mediated arrhythmia in a novel 3D human atrial myocyte model: I. Transverse-axial tubule variation. Journal of Physiology. ISSN 0022-3751. doi: 10.1113/JP283363. Fulltekst i vitenarkiv
• Zhang, Xianwei; Smith, Charlotte E. R.; Morotti, Stefano; Edwards, Andrew; Sato, Daisuke & Louch, William Edward [Vis alle 8 forfattere av denne artikkelen] (2022). Mechanisms of spontaneous Ca²⁺ release-mediated arrhythmia in a novel 3D human atrial myocyte model: II Ca²⁺-handling protein variation. Journal of Physiology. ISSN 0022-3751. doi: 10.1113/JP283602. Fulltekst i vitenarkiv
• Mesa, María Hernández; Brink, Jonas van Den; Louch, William Edward; McCabe, Kimberly J. & Rangamani, Padmini (2022). Nanoscale organization of ryanodine receptor distribution and phosphorylation pattern determines the dynamics of calcium sparks. PLoS Computational Biology. ISSN 1553-734X. 18(6). doi: 10.1371/journal.pcbi.1010126. Fulltekst i vitenarkiv Vis sammendrag

  Super-resolution imaging techniques have provided a better understanding of the relationship between the nanoscale organization and function of ryanodine receptors (RyRs) in cardiomyocytes. Recent data have indicated that this relationship is disrupted in heart failure (HF), as RyRs are dispersed into smaller and more numerous clusters. However, RyRs are also hyperphosphorylated in this condition, and this is reported to occur preferentially within the cluster centre. Thus, the combined impact of RyR relocalization and sensitization on Ca 2+ spark generation in failing cardiomyocytes is likely complex and these observations suggest that both the nanoscale organization of RyRs and the pattern of phosphorylated RyRs within clusters could be critical determinants of Ca 2+ spark dynamics. To test this hypothesis, we used computational modeling to quantify the relationships between RyR cluster geometry, phosphorylation patterns, and sarcoplasmic reticulum (SR) Ca 2+ release. We found that RyR cluster disruption results in a decrease in spark fidelity and longer sparks with a lower amplitude. Phosphorylation of some RyRs within the cluster can play a compensatory role, recovering healthy spark dynamics. Interestingly, our model predicts that such compensation is critically dependent on the phosphorylation pattern, as phosphorylation localized within the cluster center resulted in longer Ca 2+ sparks and higher spark fidelity compared to a uniformly distributed phosphorylation pattern. Our results strongly suggest that both the phosphorylation pattern and nanoscale RyR reorganization are critical determinants of Ca 2+ dynamics in HF.

• Genst, Erwin De; Foo, Kylie S.; Xiao, Yao; Rohner, Eduarde; Vries, Emma de & Sohlmér, Jesper [Vis alle 21 forfattere av denne artikkelen] (2022). Blocking phospholamban with VHH intrabodies enhances contractility and relaxation in heart failure. Nature Communications. 13(1). doi: 10.1038/s41467-022-29703-9. Fulltekst i vitenarkiv Vis sammendrag

  Abstract The dysregulated physical interaction between two intracellular membrane proteins, the sarco/endoplasmic reticulum Ca 2+ ATPase and its reversible inhibitor phospholamban, induces heart failure by inhibiting calcium cycling. While phospholamban is a bona-fide therapeutic target, approaches to selectively inhibit this protein remain elusive. Here, we report the in vivo application of intracellular acting antibodies (intrabodies), derived from the variable domain of camelid heavy-chain antibodies, to modulate the function of phospholamban. Using a synthetic VHH phage-display library, we identify intrabodies with high affinity and specificity for different conformational states of phospholamban. Rapid phenotypic screening, via modified mRNA transfection of primary cells and tissue, efficiently identifies the intrabody with most desirable features. Adeno-associated virus mediated delivery of this intrabody results in improvement of cardiac performance in a murine heart failure model. Our strategy for generating intrabodies to investigate cardiac disease combined with modified mRNA and adeno-associated virus screening could reveal unique future therapeutic opportunities.

• Frisk, Michael; Norseng, Per Andreas; Espe, Emil Knut Stenersen & Louch, William Edward (2022). Tubulator: an automated approach to analysis of t-tubule and dyadic organization in cardiomyocytes. Philosophical Transactions of the Royal Society of London. Biological Sciences. ISSN 0962-8436. 377(1864). doi: 10.1098/rstb.2021.0468. Fulltekst i vitenarkiv Vis sammendrag

  During cardiac disease, t-tubules and dyads are remodelled and disrupted within cardiomyocytes, thereby reducing cardiac performance. Given the pathological implications of such dyadic remodelling, robust and versatile tools for characterizing these sub-cellular structures are needed. While analysis programs for continuous and regular structures such as rodent ventricular t-tubules are available, at least in two dimensions, these approaches are less appropriate for assessment of more irregular structures, such as dyadic proteins and non-rodent t-tubules. Here, we demonstrate versatile, easy-to-use software that performs such analyses. This software, called Tubulator, enables automated analysis of t-tubules and dyadic proteins alike, in both tissue sections and isolated myocytes. The program measures densities of subcellular structures and proteins in individual cells, quantifies their distribution into transversely and longitudinally oriented elements, and supports detailed co-localization analyses. Importantly, Tubulator provides tools for three-dimensional assessment and rendering of image stacks, extending examinations from the single plane to the whole-myocyte level. To provide insight into the consequences of dyadic organization for synchrony of Ca2+ handling, Tubulator also creates ‘distance maps', by calculating the distance from all cytosolic positions to the nearest t-tubule and/or dyad. In conclusion, this freely accessible program provides detailed automated analysis of the three-dimensional nature of dyadic and t-tubular structures. This article is part of the theme issue ‘The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health, and disease’.

• Dibb, Katharine; Louch, William Edward & Trafford, Andrew (2022). Cardiac transverse tubules in physiology and heart failure. Annual Review of Physiology. ISSN 0066-4278. doi: 10.1146/annurev-physiol-061121-040148. Fulltekst i vitenarkiv
• Rypdal, Karoline Bjarnesdatter; Melleby, Arne Olav; Robinson, Emma Louise; Li, Jia; Palmero, Sheryl & E., Seifert Deborah [Vis alle 20 forfattere av denne artikkelen] (2022). ADAMTSL3 knock-out mice develop cardiac dysfunction and dilatation with increased TGFβ signalling after pressure overload. Communications Biology. 5(1). doi: 10.1038/s42003-022-04361-1. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Heart failure is a major cause of morbidity and mortality worldwide, and can result from pressure overload, where cardiac remodelling is characterized by cardiomyocyte hypertrophy and death, fibrosis, and inflammation. In failing hearts, transforming growth factor (TGF)β drives cardiac fibroblast (CFB) to myofibroblast differentiation causing excessive extracellular matrix production and cardiac remodelling. New strategies to target pathological TGFβ signalling in heart failure are needed. Here we show that the secreted glycoprotein ADAMTSL3 regulates TGFβ in the heart. We found that Adamtsl3 knock-out mice develop exacerbated cardiac dysfunction and dilatation with increased mortality, and hearts show increased TGFβ activity and CFB activation after pressure overload by aortic banding. Further, ADAMTSL3 overexpression in cultured CFBs inhibits TGFβ signalling, myofibroblast differentiation and collagen synthesis, suggesting a cardioprotective role for ADAMTSL3 by regulating TGFβ activity and CFB phenotype. These results warrant future investigation of the potential beneficial effects of ADAMTSL3 in heart failure.

• Shen, Xin; Brink, Jonas van den; Dahl, Anna; Kolstad, Terje R Selnes; Nordén, Einar Sjaastad & Hou, Yufeng [Vis alle 15 forfattere av denne artikkelen] (2022). Prolonged β-adrenergic stimulation disperses ryanodine receptor clusters in cardiomyocytes and has implications for heart failure. eLIFE. 11. doi: 10.7554/eLife.77725. Fulltekst i vitenarkiv Vis sammendrag

  Ryanodine receptors (RyRs) exhibit dynamic arrangements in cardiomyocytes, and we previously showed that ‘dispersion’ of RyR clusters disrupts Ca 2+ homeostasis during heart failure (HF) (Kolstad et al., eLife, 2018). Here, we investigated whether prolonged β-adrenergic stimulation, a hallmark of HF, promotes RyR cluster dispersion and examined the underlying mechanisms. We observed that treatment of healthy rat cardiomyocytes with isoproterenol for 1 hr triggered progressive fragmentation of RyR clusters. Pharmacological inhibition of Ca 2+ /calmodulin-dependent protein kinase II (CaMKII) reversed these effects, while cluster dispersion was reproduced by specific activation of CaMKII, and in mice with constitutively active Ser2814-RyR. A similar role of protein kinase A (PKA) in promoting RyR cluster fragmentation was established by employing PKA activation or inhibition. Progressive cluster dispersion was linked to declining Ca 2+ spark fidelity and magnitude, and slowed release kinetics from Ca 2+ propagation between more numerous RyR clusters. In healthy cells, this served to dampen the stimulatory actions of β-adrenergic stimulation over the longer term and protect against pro-arrhythmic Ca 2+ waves. However, during HF, RyR dispersion was linked to impaired Ca 2+ release. Thus, RyR localization and function are intimately linked via channel phosphorylation by both CaMKII and PKA, which, while finely tuned in healthy cardiomyocytes, underlies impaired cardiac function during pathology.

• Rixon, Chloe Louise; Andreassen, Kristine; Shen, Xin; Erusappan, Pugazendhi Murugan; Almaas, Vibeke Marie & Palmero, Sheryl [Vis alle 14 forfattere av denne artikkelen] (2022). Lumican accumulates with fibrillar collagen in fibrosis in hypertrophic cardiomyopathy. ESC Heart Failure. doi: 10.1002/ehf2.14234. Fulltekst i vitenarkiv Vis sammendrag

  Aims Familial hypertrophic cardiomyopathy (HCM) is the most common form of inherited cardiac disease. It is characterized by myocardial hypertrophy and diastolic dysfunction, and can lead to severe heart failure, arrhythmias, and sudden cardiac death. Cardiac fibrosis, defined by excessive accumulation of extracellular matrix (ECM) components, is central to the pathophysiology of HCM. The ECM proteoglycan lumican is increased during heart failure and cardiac fibrosis, including HCM, yet its role in HCM remains unknown. We provide an in-depth assessment of lumican in clinical and experimental HCM.<p> <p>Methods Left ventricular (LV) myectomy specimens were collected from patients with hypertrophic obstructive cardiomyopathy (n = 15), and controls from hearts deemed unsuitable for transplantation (n = 8). Hearts were harvested from a mouse model of HCM; Myh6 R403Q mice administered cyclosporine A and wild-type littermates (n = 8–10). LV tissues were analysed for mRNA and protein expression. Patient myectomy or mouse mid-ventricular sections were imaged using confocal microscopy, direct stochastic optical reconstruction microscopy (dSTORM), or electron microscopy. Human foetal cardiac fibroblasts (hfCFBs) were treated with recombinant human lumican (n = 3) and examined using confocal microscopy.<p> <p>Results Lumican mRNA was increased threefold in HCM patients (P < 0.05) and correlated strongly with expression of collagen I (R² = 0.60, P < 0.01) and III (R² = 0.58, P < 0.01). Lumican protein was increased by 40% in patients with HCM (P < 0.01) and correlated with total (R² = 0.28, P = 0.05) and interstitial (R² = 0.30, P < 0.05) fibrosis. In mice with HCM, lumican mRNA increased fourfold (P < 0.001), and lumican protein increased 20-fold (P < 0.001) in insoluble ECM lysates. Lumican and fibrillar collagen were located together throughout fibrotic areas in HCM patient tissue, with increased co-localization measured in patients and mice with HCM (patients: +19%, P < 0.01; mice: +13%, P < 0.01). dSTORM super-resolution microscopy was utilized to image interstitial ECM which had yet to undergo overt fibrotic remodelling. In these interstitial areas, collagen I deposits located closer to ( 15 nm, P < 0.05), overlapped more frequently with (+7.3%, P < 0.05) and to a larger degree with (+5.6%, P < 0.05) lumican in HCM. Collagen fibrils in such deposits were visualized using electron microscopy. The effect of lumican on collagen fibre formation was demonstrated by adding lumican to hfCFB cultures, resulting in thicker (+53.8 nm, P < 0.001), longer (+345.9 nm, P < 0.001), and fewer ( 8.9%, P < 0.001) collagen fibres. <p>Conclusions The ECM proteoglycan lumican is increased in HCM and co-localizes with fibrillar collagen throughout areas of fibrosis in HCM. Our data suggest that lumican may promote formation of thicker collagen fibres in HCM.

• Louch, William Edward; Perdreau-Dahl, Harmonie & Edwards, Andrew (2022). Image-Driven Modeling of Nanoscopic Cardiac Function: Where Have We Come From, and Where Are We Going? Frontiers in Physiology. 13, s. 1–21. doi: 10.3389/fphys.2022.834211. Fulltekst i vitenarkiv Vis sammendrag

  Complementary developments in microscopy and mathematical modeling have been critical to our understanding of cardiac excitation–contraction coupling. Historically, limitations imposed by the spatial or temporal resolution of imaging methods have been addressed through careful mathematical interrogation. Similarly, limitations imposed by computational power have been addressed by imaging macroscopic function in large subcellular domains or in whole myocytes. As both imaging resolution and computational tractability have improved, the two approaches have nearly merged in terms of the scales that they can each be used to interrogate. With this review we will provide an overview of these advances and their contribution to understanding ventricular myocyte function, including exciting developments over the last decade. We specifically focus on experimental methods that have pushed back limits of either spatial or temporal resolution of nanoscale imaging (e.g., DNA-PAINT), or have permitted high resolution imaging on large cellular volumes (e.g., serial scanning electron microscopy). We also review the progression of computational approaches used to integrate and interrogate these new experimental data sources, and comment on near-term advances that may unify understanding of the underlying biology. Finally, we comment on several outstanding questions in cardiac physiology that stand to benefit from a concerted and complementary application of these new experimental and computational methods.

• Støle, Thea Parsberg; Lunde, Marianne; Shen, Xin; Martinsen, Marita; Lunde, Per Kristian & Li, Jia [Vis alle 12 forfattere av denne artikkelen] (2022). The female syndecan-4^−/− heart has smaller cardiomyocytes, augmented insulin/pSer473-Akt/pSer9-GSK-3β signaling, and lowered SCOP, pThr308-Akt/Akt and GLUT4 levels. Frontiers in Cell and Developmental Biology. 10. doi: 10.3389/fcell.2022.908126. Fulltekst i vitenarkiv Vis sammendrag

  Background: In cardiac muscle, the ubiquitously expressed proteoglycan syndecan-4 is involved in the hypertrophic response to pressure overload. Protein kinase Akt signaling, which is known to regulate hypertrophy, has been found to be reduced in the cardiac muscle of exercised male syndecan-4 −/− mice. In contrast, we have recently found that pSer473-Akt signaling is elevated in the skeletal muscle ( tibialis anterior, TA) of female syndecan-4 −/− mice. To determine if the differences seen in Akt signaling are sex specific, we have presently investigated Akt signaling in the cardiac muscle of sedentary and exercised female syndecan-4 −/− mice. To get deeper insight into the female syndecan-4 −/− heart, alterations in cardiomyocyte size, a wide variety of different extracellular matrix components, well-known syndecan-4 binding partners and associated signaling pathways have also been investigated. Methods: Left ventricles (LVs) from sedentary and exercise trained female syndecan-4 −/− and WT mice were analyzed by immunoblotting and real-time PCR. Cardiomyocyte size and phosphorylated Ser473-Akt were analyzed in isolated adult cardiomyocytes from female syndecan-4 −/− and WT mice by confocal imaging. LV and skeletal muscle (TA) from sedentary male syndecan-4 −/− and WT mice were immunoblotted with Akt antibodies for comparison. Glucose levels were measured by a glucometer, and fasting blood serum insulin and C-peptide levels were measured by ELISA. Results: Compared to female WT hearts, sedentary female syndecan-4 −/− LV cardiomyocytes were smaller and hearts had higher levels of pSer473-Akt and its downstream target pSer9-GSK-3β. The pSer473-Akt inhibitory phosphatase PHLPP1/SCOP was lowered, which may be in response to the elevated serum insulin levels found in the female syndecan-4 −/− mice. We also observed lowered levels of pThr308-Akt/Akt and GLUT4 in the female syndecan-4 −/− heart and an increased LRP6 level after exercise. Otherwise, few alterations were found. The pThr308-Akt and pSer473-Akt levels were unaltered in the cardiac and skeletal muscles of sedentary male syndecan-4 −/− mice. Conclusion: Our data indicate smaller cardiomyocytes, an elevated insulin/pSer473-Akt/pSer9-GSK-3β signaling pathway, and lowered SCOP, pThr308-Akt/Akt and GLUT4 levels in the female syndecan-4 −/− heart. In contrast, cardiomyocyte size, and Akt signaling were unaltered in both cardiac and skeletal muscles from male syndecan-4 −/− mice, suggesting important sex differences.

• Sommese, Leandro M.; Racioppi, María Florencia; Shen, Xin; Orlowski, Alejandro; Valverde, Carlos A. & Louch, William Edward [Vis alle 8 forfattere av denne artikkelen] (2022). Discordant Ca²⁺ release in cardiac myocytes: characterization and susceptibility to pharmacological RyR2 modulation. Pflügers Archiv: European Journal of Physiology. ISSN 0031-6768. doi: 10.1007/s00424-022-02678-8. Fulltekst i vitenarkiv
• Edwards, Andrew; Mørk, Halvor; Stokke, Mathis; Lipsett, David; Sjaastad, Ivar & Richard, Sylvain [Vis alle 8 forfattere av denne artikkelen] (2021). Sarcoplasmic Reticulum Calcium Release Is Required for Arrhythmogenesis in the MouseData_Sheet_1.pdf. Frontiers in Physiology. 129247113307196118101757330290951073619410426311810310255549995881112965921565931388107972921061031069987209102119109419102782. doi: 10.3389/fphys.2021.74473010.3389/fphys.2021.744730.s001. Fulltekst i vitenarkiv
• Zhou, Junlan; Singh, Neha; Monnier, Chloe; Marszalec, William; Li, Gaoyang & Jin, Jing [Vis alle 15 forfattere av denne artikkelen] (2021). Phosphatidylinositol-4,5-Bisphosphate Binding to Amphiphysin-II Modulates T-Tubule Remodeling: Implications for Heart Failure. Frontiers in Physiology. 12:782767, s. 1–14. doi: 10.3389/fphys.2021.782767. Fulltekst i vitenarkiv Vis sammendrag

  BIN1 (amphyphysin-II) is a structural protein involved in T-tubule (TT) formation and phosphatidylinositol-4,5-bisphosphate (PIP2) is responsible for localization of BIN1 to sarcolemma. The goal of this study was to determine if PIP2-mediated targeting of BIN1 to sarcolemma is compromised during the development of heart failure (HF) and is responsible for TT remodeling. Immunohistochemistry showed co-localization of BIN1, Cav1.2, PIP2, and phospholipase-Cβ1 (PLCβ1) in TTs in normal rat and human ventricular myocytes. PIP2 levels were reduced in spontaneously hypertensive rats during HF progression compared to age-matched controls. A PIP Strip assay of two native mouse cardiac-specific isoforms of BIN1 including the longest (cardiac BIN1 #4) and shortest (cardiac BIN1 #1) isoforms as well human skeletal BIN1 showed that all bound PIP2. In addition, overexpression of all three BIN1 isoforms caused tubule formation in HL-1 cells. A triple-lysine motif in a short loop segment between two helices was mutated and replaced by negative charges which abolished tubule formation, suggesting a possible location for PIP2 interaction aside from known consensus binding sites. Pharmacological PIP2 depletion in rat ventricular myocytes caused TT loss and was associated with changes in Ca 2+ release typically found in myocytes during HF, including a higher variability in release along the cell length and a slowing in rise time, time to peak, and decay time in treated myocytes. These results demonstrate that depletion of PIP2 can lead to TT disruption and suggest that PIP2 interaction with cardiac BIN1 is required for TT maintenance and function.

• Beverborg, Niels Grote; Spater, Daniela; Knoll, Ralph; Hidalgo, Alejandro; Yeh, Steve T & Elbeck, Zaher [Vis alle 27 forfattere av denne artikkelen] (2021). Phospholamban antisense oligonucleotides improve cardiac function in murine cardiomyopathy. Nature Communications. 12(1), s. 5180–5180. doi: 10.1038/s41467-021-25439-0. Fulltekst i vitenarkiv
• Yamakawa, Sean; Wu, Daniel; Dasgupta, Mona; Pedamallu, Havisha; Gupta, Binita & Modi, Rishi [Vis alle 20 forfattere av denne artikkelen] (2021). Role of t-tubule remodeling on mechanisms of abnormal calcium release during heart failure development in canine ventricle. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 320(4), s. H1658–H1669. doi: 10.1152/AJPHEART.00946.2020. Fulltekst i vitenarkiv
• Frisk, Michael; Le, Christopher; Shen, Xin; Røe, Åsmund Treu; Hou, Yufeng & Manfra, Ornella [Vis alle 24 forfattere av denne artikkelen] (2021). Etiology-dependent impairment of diastolic cardiomyocyte calcium homeostasis in heart failure with preserved ejection fraction. Journal of the American College of Cardiology. ISSN 0735-1097. 77(4), s. 405–419. doi: 10.1016/j.jacc.2020.11.044. Fulltekst i vitenarkiv Vis sammendrag

  Background Whereas heart failure with reduced ejection fraction (HFrEF) is associated with ventricular dilation and markedly reduced systolic function, heart failure with preserved ejection fraction (HFpEF) patients exhibit concentric hypertrophy and diastolic dysfunction. Impaired cardiomyocyte Ca2+ homeostasis in HFrEF has been linked to disruption of membrane invaginations called t-tubules, but it is unknown if such changes occur in HFpEF. Objectives This study examined whether distinct cardiomyocyte phenotypes underlie the heart failure entities of HFrEF and HFpEF. Methods T-tubule structure was investigated in left ventricular biopsies obtained from HFrEF and HFpEF patients, whereas cardiomyocyte Ca2+ homeostasis was studied in rat models of these conditions. Results HFpEF patients exhibited increased t-tubule density in comparison with control subjects. Super-resolution imaging revealed that higher t-tubule density resulted from both tubule dilation and proliferation. In contrast, t-tubule density was reduced in patients with HFrEF. Augmented collagen deposition within t-tubules was observed in HFrEF but not HFpEF hearts. A causative link between mechanical stress and t-tubule disruption was supported by markedly elevated ventricular wall stress in HFrEF patients. In HFrEF rats, t-tubule loss was linked to impaired systolic Ca2+ homeostasis, although diastolic Ca2+ removal was also reduced. In contrast, Ca2+ transient magnitude and release kinetics were largely maintained in HFpEF rats. However, diastolic Ca2+ impairments, including reduced sarco/endoplasmic reticulum Ca2+-ATPase activity, were specifically observed in diabetic HFpEF but not in ischemic or hypertensive models. Conclusions Although t-tubule disruption and impaired cardiomyocyte Ca2+ release are hallmarks of HFrEF, such changes are not prominent in HFpEF. Impaired diastolic Ca2+ homeostasis occurs in both conditions, but in HFpEF, this mechanism for diastolic dysfunction is etiology-dependent.

• Rohner, Eduarde; Witman, Nevin; Sohlmer, Jesper; Genst, Erwin De; Louch, William Edward & Sahara, Makoto [Vis alle 7 forfattere av denne artikkelen] (2021). An mRNA assay system demonstrates proteasomal-specific degradation contributes to cardiomyopathic phospholamban null mutation. Molecular medicine (Cambridge, Mass. Print). ISSN 1076-1551. 27(1). doi: 10.1186/s10020-021-00362-8. Fulltekst i vitenarkiv Vis sammendrag

  Background The human L39X phospholamban (PLN) cardiomyopathic mutant has previously been reported as a null mutation but the detailed molecular pathways that lead to the complete lack of detectable protein remain to be clarified. Previous studies have shown the implication between an impaired cellular degradation homeostasis and cardiomyopathy development. Therefore, uncovering the underlying mechanism responsible for the lack of PLN protein has important implications in understanding the patient pathology, chronic human calcium dysregulation and aid the development of potential therapeutics. Methods A panel of mutant and wild-type reporter tagged PLN modified mRNA (modRNA) constructs were transfected in human embryonic stem cell-derived cardiomyocytes. Lysosomal and proteasomal chemical inhibitors were used together with cell imaging and protein analysis tools in order to dissect degradation pathways associated with expressed PLN constructs. Transcriptional profiling of the cardiomyocytes transfected by wild-type or L39X mutant PLN modRNA was analysed with bulk RNA sequencing. Results Our modRNA assay system revealed that transfected L39X mRNA was stable and actively translated in vitro but with only trace amount of protein detectable. Proteasomal inhibition of cardiomyocytes transfected with L39X mutant PLN modRNA showed a fourfold increase in protein expression levels. Additionally, RNA sequencing analysis of protein degradational pathways showed a significant distinct transcriptomic signature between wild-type and L39X mutant PLN modRNA transfected cardiomyocytes. Conclusion Our results demonstrate that the cardiomyopathic PLN null mutant L39X is rapidly, actively and specifically degraded by proteasomal pathways. Herein, and to the best of our knowledge, we report for the first time the usage of modified mRNAs to screen for and illuminate alternative molecular pathways found in genes associated with inherited cardiomyopathies.

• Kobirumaki-Shimozawa, Fuyu; Shimozawa, Togo; Oyama, Kotaro; Baba, Shunsuke; Li, Jia & Nakanishi, Tomohiro [Vis alle 10 forfattere av denne artikkelen] (2021). Synchrony of sarcomeric movement regulates left ventricular pump function in the in vivo beating mouse heart. The Journal of General Physiology. ISSN 0022-1295. 153(11). doi: 10.1085/jgp.202012860. Fulltekst i vitenarkiv Vis sammendrag

  Sarcomeric contraction in cardiomyocytes serves as the basis for the heart’s pump functions. It has generally been considered that in cardiac muscle as well as in skeletal muscle, sarcomeres equally contribute to myofibrillar dynamics in myocytes at varying loads by producing similar levels of active and passive force. In the present study, we expressed α-actinin–AcGFP in Z-disks to analyze dynamic behaviors of sequentially connected individual sarcomeres along a myofibril in a left ventricular (LV) myocyte of the in vivo beating mouse heart. To quantify the magnitude of the contribution of individual sarcomeres to myofibrillar dynamics, we introduced the novel parameter “contribution index” (CI) to measure the synchrony in movements between a sarcomere and a myofibril (from −1 [complete asynchrony] to 1 [complete synchrony]). First, CI varied markedly between sarcomeres, with an average value of ∼0.3 during normal systole. Second, when the movements between adjacent sarcomeres were asynchronous (CI &amp;lt; 0), a sarcomere and the ones next to the adjacent sarcomeres and farther away moved in synchrony (CI &amp;gt; 0) along a myofibril. Third, when difference in LV pressure in diastole and systole (ΔLVP) was lowered to &amp;lt;10 mm Hg, diastolic sarcomere length increased. Under depressed conditions, the movements between adjacent sarcomeres were in marked asynchrony (CI, −0.3 to −0.4), and, as a result, average CI was linearly decreased in association with a decrease in ΔLVP. These findings suggest that in the left ventricle of the in vivo beating mouse heart, (1) sarcomeres heterogeneously contribute to myofibrillar dynamics due to an imbalance of active and passive force between neighboring sarcomeres, (2) the force imbalance is pronounced under depressed conditions coupled with a marked increase in passive force and the ensuing tug-of-war between sarcomeres, and (3) sarcomere synchrony via the distal intersarcomere interaction regulates the heart's pump function in coordination with myofibrillar contractility.

• Edwards, Andrew G.; Mørk, Halvor Kjeang; Stokke, Mathis Korseberg; Lipsett, David Bruce; Sjaastad, Ivar & Richard, Sylvain [Vis alle 8 forfattere av denne artikkelen] (2021). Sarcoplasmic Reticulum Calcium Release Is Required for Arrhythmogenesis in the Mouse. Frontiers in Physiology. 12, s. 1–13. doi: 10.3389/fphys.2021.744730. Fulltekst i vitenarkiv Vis sammendrag

  Dysfunctional sarcoplasmic reticulum Ca 2+ handling is commonly observed in heart failure, and thought to contribute to arrhythmogenesis through several mechanisms. Some time ago we developed a cardiomyocyte-specific inducible SERCA2 knockout mouse, which is remarkable in the degree to which major adaptations to sarcolemmal Ca 2+ entry and efflux overcome the deficit in SR reuptake to permit relatively normal contractile function. Conventionally, those adaptations would also be expected to dramatically increase arrhythmia susceptibility. However, that susceptibility has never been tested, and it is possible that the very rapid repolarization of the murine action potential (AP) allows for large changes in sarcolemmal Ca 2+ transport without substantially disrupting electrophysiologic stability. We investigated this hypothesis through telemetric ECG recording in the SERCA2-KO mouse, and patch-clamp electrophysiology, Ca 2+ imaging, and mathematical modeling of isolated SERCA2-KO myocytes. While the SERCA2-KO animals exhibit major (and unique) electrophysiologic adaptations at both the organ and cell levels, they remain resistant to arrhythmia. A marked increase in peak L-type calcium ( I CaL ) current and slowed I CaL decay elicited pronounced prolongation of initial repolarization, but faster late repolarization normalizes overall AP duration. Early afterdepolarizations were seldom observed in KO animals, and those that were observed exhibited a mechanism intermediate between murine and large mammal dynamical properties. As expected, spontaneous SR Ca 2+ sparks and waves were virtually absent. Together these findings suggest that intact SR Ca 2+ handling is an absolute requirement for triggered arrhythmia in the mouse, and that in its absence, dramatic changes to the major inward currents can be resisted by the substantial K + current reserve, even at end-stage disease.

• Setterberg, Ingunn Elise; Le, Christopher; Frisk, Michael; Li, Jia & Louch, William Edward (2021). The physiology and pathophysiology of T-tubules in the heart. Frontiers in Physiology. 12:718404, s. 1–21. doi: 10.3389/fphys.2021.718404. Fulltekst i vitenarkiv Vis sammendrag

  In cardiomyocytes, invaginations of the sarcolemmal membrane called t-tubules are critically important for triggering contraction by excitation-contraction (EC) coupling. These structures form functional junctions with the sarcoplasmic reticulum (SR), and thereby enable close contact between L-type Ca 2+ channels (LTCCs) and Ryanodine Receptors (RyRs). This arrangement in turn ensures efficient triggering of Ca 2+ release, and contraction. While new data indicate that t-tubules are capable of exhibiting compensatory remodeling, they are also widely reported to be structurally and functionally compromised during disease, resulting in disrupted Ca 2+ homeostasis, impaired systolic and/or diastolic function, and arrhythmogenesis. This review summarizes these findings, while highlighting an emerging appreciation of the distinct roles of t-tubules in the pathophysiology of heart failure with reduced and preserved ejection fraction (HFrEF and HFpEF). In this context, we review current understanding of the processes underlying t-tubule growth, maintenance, and degradation, underscoring the involvement of a variety of regulatory proteins, including junctophilin-2 (JPH2), amphiphysin-2 (BIN1), caveolin-3 (Cav3), and newer candidate proteins. Upstream regulation of t-tubule structure/function by cardiac workload and specifically ventricular wall stress is also discussed, alongside perspectives for novel strategies which may therapeutically target these mechanisms.

• Carlson, Cathrine Rein; Aronsen, Jan Magnus; Dahl, Anna Bergan; Moutty, Marie Christine; Lunde, Marianne & Lunde, Per Kristian [Vis alle 22 forfattere av denne artikkelen] (2021). AKAP18δ Anchors and Regulates CaMKII Activity at Phospholamban-SERCA2 and RYR. Circulation Research. ISSN 0009-7330. 130(1), s. 27–44. doi: 10.1161/CIRCRESAHA.120.317976. Fulltekst i vitenarkiv Vis sammendrag

  Background: The sarcoplasmic reticulum (SR) Ca2+-ATPase 2 (SERCA2) mediates Ca2+ reuptake into SR and thereby promotes cardiomyocyte relaxation, whereas the ryanodine receptor (RYR) mediates Ca2+ release from SR and triggers contraction. Ca2+/CaMKII (CaM [calmodulin]-dependent protein kinase II) regulates activities of SERCA2 through phosphorylation of PLN (phospholamban) and RYR through direct phosphorylation. However, the mechanisms for CaMKIIδ anchoring to SERCA2-PLN and RYR and its regulation by local Ca2+ signals remain elusive. The objective of this study was to investigate CaMKIIδ anchoring and regulation at SERCA2-PLN and RYR. Methods: A role for AKAP18δ (A-kinase anchoring protein 18δ) in CaMKIIδ anchoring and regulation was analyzed by bioinformatics, peptide arrays, cell-permeant peptide technology, immunoprecipitations, pull downs, transfections, immunoblotting, proximity ligation, FRET-based CaMKII activity and ELISA-based assays, whole cell and SR vesicle fluorescence imaging, high-resolution microscopy, adenovirus transduction, adenoassociated virus injection, structural modeling, surface plasmon resonance, and alpha screen technology. Results: Our results show that AKAP18δ anchors and directly regulates CaMKIIδ activity at SERCA2-PLN and RYR, via 2 distinct AKAP18δ regions. An N-terminal region (AKAP18δ-N) inhibited CaMKIIδ through binding of a region homologous to the natural CaMKII inhibitor peptide and the Thr17-PLN region. AKAP18δ-N also bound CaM, introducing a second level of control. Conversely, AKAP18δ-C, which shares homology to neuronal CaMKIIα activator peptide (N2B-s), activated CaMKIIδ by lowering the apparent Ca2+ threshold for kinase activation and inducing CaM trapping. While AKAP18δ-C facilitated faster Ca2+ reuptake by SERCA2 and Ca2+ release through RYR, AKAP18δ-N had opposite effects. We propose a model where the 2 unique AKAP18δ regions fine-tune Ca2+-frequency-dependent activation of CaMKIIδ at SERCA2-PLN and RYR. Conclusions: AKAP18δ anchors and functionally regulates CaMKII activity at PLN-SERCA2 and RYR, indicating a crucial role of AKAP18δ in regulation of the heartbeat. To our knowledge, this is the first protein shown to enhance CaMKII activity in heart and also the first AKAP (A-kinase anchoring protein) reported to anchor a CaMKII isoform, defining AKAP18δ also as a CaM-KAP.

• Sadredini, Mani; Haugsten, Marie Hansen; Frisk, Michael; Louch, William E.; Lehnart, Stephan E. & Sjaastad, Ivar [Vis alle 7 forfattere av denne artikkelen] (2021). CaMKII inhibition has dual effects on spontaneous Ca²⁺release and Ca²⁺ alternans in ventricular cardiomyocytes from mice with a gain-of-function RyR2 mutation. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 321(2), s. H446–H460. doi: 10.1152/ajpheart.00011.2021. Fulltekst i vitenarkiv
• Danielsen, Tore Kristian; Sadredini, Mani; Manotheepan, Ravinea; Aronsen, Jan Magnus; Frisk, Michael & Haugsten, Marie Hansen [Vis alle 13 forfattere av denne artikkelen] (2021). Exercise training stabilizes RyR2-dependent Ca2+ release in post-infarction heart failure. Frontiers in Cardiovascular Medicine. 7. doi: 10.3389/fcvm.2020.623922. Fulltekst i vitenarkiv Vis sammendrag

  Aim: Dysfunction of the cardiac ryanodine receptor (RyR2) is an almost ubiquitous finding in animal models of heart failure (HF) and results in abnormal Ca 2+ release in cardiomyocytes that contributes to contractile impairment and arrhythmias. We tested whether exercise training (ET), as recommended by current guidelines, had the potential to stabilize RyR2-dependent Ca 2+ release in rats with post-myocardial infarction HF. Materials and Methods: We subjected male Wistar rats to left coronary artery ligation or sham operations. After 1 week, animals were characterized by echocardiography and randomized to high-intensity interval ET on treadmills or to sedentary behavior (SED). Running speed was adjusted based on a weekly VO 2max test. We repeated echocardiography after 5 weeks of ET and harvested left ventricular cardiomyocytes for analysis of RyR2-dependent systolic and spontaneous Ca 2+ release. Phosphoproteins were analyzed by Western blotting, and beta-adrenoceptor density was quantified by radioligand binding. Results: ET increased VO 2max in HF-ET rats to 127% of HF-SED ( P &amp;lt; 0.05). This coincided with attenuated spontaneous SR Ca 2+ release in left ventricular cardiomyocytes from HF-ET but also reduced Ca 2+ transient amplitude and slowed Ca 2+ reuptake during adrenoceptor activation. However, ventricular diameter and fractional shortening were unaffected by ET. Analysis of Ca 2+ homeostasis and major proteins involved in the regulation of SR Ca 2+ release and reuptake could not explain the attenuated spontaneous SR Ca 2+ release or reduced Ca 2+ transient amplitude. Importantly, measurements of beta-adrenoceptors showed a normalization of beta 1 -adrenoceptor density and beta 1 :beta 2 -adrenoceptor ratio in HF-ET. Conclusion: ET increased aerobic capacity in post-myocardial infarction HF rats and stabilized RyR2-dependent Ca 2+ release. Our data show that these effects of ET can be gained without major alterations in SR Ca 2+ regulatory proteins and indicate that future studies should include upstream parts of the sympathetic signaling pathway.

• Tazmini, Kiarash; Fraz, Mai; Nymo, Ståle Haugset; Stokke, Mathis Korseberg; Louch, William Edward & Øie, Erik (2020). Potassium infusion increases the likelihood of conversion of recent-onset atrial fibrillation- A single-blinded, randomized clinical trial. American Heart Journal. ISSN 0002-8703. 221, s. 114–124. doi: 10.1016/j.ahj.2019.12.014. Fulltekst i vitenarkiv Vis sammendrag

  Background The optimal antiarrhythmic management of recent-onset atrial fibrillation (ROAF) or atrial flutter is controversial and there is a considerable variability in clinical treatment strategies. It is not known if potassium infusion has the potential to convert ROAF or atrial flutter to sinus rhythm (SR). Therefore, we aimed to investigate if patients with ROAF or atrial flutter and plasma-potassium levels ≤4.0 mmol/L have increased probability to convert to SR if the plasma-potassium level is increased towards the upper reference range (4.1-5.0 mmol/L). Methods In a placebo-controlled, single-blinded trial, patients with ROAF or atrial flutter and plasma-potassium ≤4.0 mmol/L presenting between April 2013 and November 2017 were randomized to receive potassium chloride (KCl) infusion (n = 60) or placebo (n = 53). Patients in the KCl group received infusions at one of three different rates: 9.4 mmol/h (n = 11), 12 mmol/h (n = 19), or 15 mmol/h (n = 30). Results There was no statistical difference in the number of conversions to SR between the KCl group and placebo [logrank test, P = .29; hazard ratio (HR) 1.20 (CI 0.72-1.98)]. However, KCl-infused patients who achieved an above-median hourly increase in plasma-potassium (>0.047 mmol/h) exhibited a significantly higher conversion rate compared with placebo [logrank P = .002; HR 2.40 (CI 1.36-4.21)] and KCl patients with below-median change in plasma-potassium [logrank P < .001; HR 4.41 (CI 2.07-9.40)]. Due to pain at the infusion site, the infusion was prematurely terminated in 10 patients (17%). Conclusions Although increasing plasma-potassium levels did not significantly augment conversion of ROAF or atrial flutter to SR in patients with potassium levels in the lower-normal range, our results indicate that this treatment may be effective when a rapid increase in potassium concentration is tolerated and achieved.

• Altara, Raffaele; Silva, Gustavo Jose Justo; Frisk, Michael; Spelta, Francesco; Zouein, Fouad A. & Louch, William Edward [Vis alle 8 forfattere av denne artikkelen] (2020). Cardioprotective Effects of the Novel Compound Vastiras in a Preclinical Model of End-Organ Damage. Hypertension. ISSN 0194-911X. 75(5), s. 1195–1204. doi: 10.1161/HYPERTENSIONAHA.120.14704. Fulltekst i vitenarkiv
• Rubinstein, Jack; Woo, Jessica G.; Garcia, Anastacia M.; Tarek, Alsaied; Li, Jia & Lunde, Per Kristian [Vis alle 13 forfattere av denne artikkelen] (2020). Probenecid improves cardiac function in subjects with a fontan circulation and augments cardiomyocyte calcium homeostasis. Pediatric Cardiology. ISSN 0172-0643. doi: 10.1007/s00246-020-02427-7. Fulltekst i vitenarkiv Vis sammendrag

  Subjects with functionally univentricular circulation who have completed staged single ventricle palliation, with the final stage culminating in the Fontan procedure, are often living into adulthood. However, high morbidity and mortality remain prevalent in these patients, as diastolic and systolic dysfunction of the single systemic ventricle are linked to Fontan circulatory failure. We presently investigated the effects of probenecid in post-Fontan patients. Used for decades for the treatment of gout, probenecid has been shown in recent years to positively influence cardiac function via effects on the Transient Receptor Potential Vanilloid 2 (TRPV2) channel in cardiomyocytes. Indeed, we observed that probenecid improved cardiac function and exercise performance in patients with a functionally univentricular circulation. This was consistent with our findings from a retrospective cohort of patients with single ventricle physiology where TRPV2 expression was increased. Experiments in isolated cardiomyocytes associated these positive actions to augmentation of diastolic calcium homeostasis.

• Longobardi, S.; Lewalle, A.; Coveney, S.; Sjaastad, Ivar; Espe, Emil Knut Stenersen & Louch, William Edward [Vis alle 9 forfattere av denne artikkelen] (2020). Predicting left ventricular contractile function via Gaussian process emulation in aortic-banded rats: Aortic banded rat heart simulations. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. ISSN 1364-503X. 378(2173). doi: 10.1098/rsta.2019.0334. Fulltekst i vitenarkiv
• Shiferaw, Yohannes; Aistrup, Gary L.; Louch, William Edward & Wasserstrom, J. A. (2020). Remodeling Promotes Proarrhythmic Disruption of Calcium Homeostasis in Failing Atrial Myocytes. Biophysical Journal. ISSN 0006-3495. 118(2), s. 476–491. doi: 10.1016/j.bpj.2019.12.012. Fulltekst i vitenarkiv
• Longobardi, Stefano; Lewalle, Alexandre; Coveney, Sam; Sjaastad, Ivar; Espe, Emil Knut Stenersen & Louch, William Edward [Vis alle 9 forfattere av denne artikkelen] (2020). Predicting left ventricular contractile function via Gaussian process emulation in aortic-banded rats. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. ISSN 1364-503X. 378(2173), s. 20190334–20190334. doi: 10.1098/rsta.2019.0334. Fulltekst i vitenarkiv Vis sammendrag

  Cardiac contraction is the result of integrated cellular, tissue and organ function. Biophysical in silico cardiac models offer a systematic approach for studying these multi-scale interactions. The computational cost of such models is high, due to their multi-parametric and nonlinear nature. This has so far made it difficult to perform model fitting and prevented global sensitivity analysis (GSA) studies. We propose a machine learning approach based on Gaussian process emulation of model simulations using probabilistic surrogate models, which enables model parameter inference via a Bayesian history matching (HM) technique and GSA on whole-organ mechanics. This framework is applied to model healthy and aortic-banded hypertensive rats, a commonly used animal model of heart failure disease. The obtained probabilistic surrogate models accurately predicted the left ventricular pump function (R2 = 0.92 for ejection fraction). The HM technique allowed us to fit both the control and diseased virtual bi-ventricular rat heart models to magnetic resonance imaging and literature data, with model outputs from the constrained parameter space falling within 2 SD of the respective experimental values. The GSA identified Troponin C and cross-bridge kinetics as key parameters in determining both systolic and diastolic ventricular function. This article is part of the theme issue ‘Uncertainty quantification in cardiac and cardiovascular modelling and simulation’.

• Kobirumaki-Shimozawa, Fuyu; Nakanishi, Tomohiro; Shimozawa, Togo; Terui, Takako; Oyama, Kotaro & Li, Jia [Vis alle 9 forfattere av denne artikkelen] (2020). Real-Time in vivo Imaging of Mouse Left Ventricle Reveals Fluctuating Movements of the Intercalated Discs. Nanomaterials. 10:532(3), s. 1–115. doi: 10.3390/nano10030532. Fulltekst i vitenarkiv Vis sammendrag

  Myocardial contraction is initiated by action potential propagation through the conduction system of the heart. It has been thought that connexin 43 in the gap junctions (GJ) within the intercalated disc (ID) provides direct electric connectivity between cardiomyocytes (electronic conduction). However, recent studies challenge this view by providing evidence that the mechanosensitive cardiac sodium channels Nav1.5 localized in perinexii at the GJ edge play an important role in spreading action potentials between neighboring cells (ephaptic conduction). In the present study, we performed real-time confocal imaging of the CellMask-stained ID in the living mouse heart in vivo. We found that the ID structure was not rigid. Instead, we observed marked flexing of the ID during propagation of contraction from cell to cell. The variation in ID length was between ~30 and ~42 μm (i.e., magnitude of change, ~30%). In contrast, tracking of α-actinin-AcGFP revealed a comparatively small change in the lateral dimension of the transitional junction near the ID (i.e., magnitude of change, ~20%). The present findings suggest that, when the heart is at work, mechanostress across the perinexii may activate Nav1.5 by promoting ephaptic conduction in coordination with electronic conduction, and, thereby, efficiently transmitting excitation-contraction coupling between cardiomyocytes.

• Juncos, Juan Xavier Masjoan; Shakil, Shazia; Bradley, Wayne E.; Wei, Chih-Chang; Zafar, Iram & Powell, Pamela [Vis alle 12 forfattere av denne artikkelen] (2020). Chronic cardiac structural damage, diastolic and systolic dysfunction following acute myocardial injury due to bromine exposure in rats. Archives of Toxicology. ISSN 0340-5761. s. 1–15. doi: 10.1007/s00204-020-02919-8. Fulltekst i vitenarkiv Vis sammendrag

  Accidental bromine spills are common and its large industrial stores risk potential terrorist attacks. The mechanisms of bromine toxicity and effective therapeutic strategies are unknown. Our studies demonstrate that inhaled bromine causes deleterious cardiac manifestations. In this manuscript we describe mechanisms of delayed cardiac effects in the survivors of a single bromine exposure. Rats were exposed to bromine (600 ppm for 45 min) and the survivors were sacrificed at 14 or 28 days. Echocardiography, hemodynamic analysis, histology, transmission electron microscopy (TEM) and biochemical analysis of cardiac tissue were performed to assess functional, structural and molecular effects. Increases in right ventricular (RV) and left ventricular (LV) end-diastolic pressure and LV end-diastolic wall stress with increased LV fibrosis were observed. TEM images demonstrated myofibrillar loss, cytoskeletal breakdown and mitochondrial damage at both time points. Increases in cardiac troponin I (cTnI) and N-terminal pro brain natriuretic peptide (NT-proBNP) reflected myofibrillar damage and increased LV wall stress. LV shortening decreased as a function of increasing LV end-systolic wall stress and was accompanied by increased sarcoendoplasmic reticulum calcium ATPase (SERCA) inactivation and a striking dephosphorylation of phospholamban. NADPH oxidase 2 and protein phosphatase 1 were also increased. Increased circulating eosinophils and myocardial 4-hydroxynonenal content suggested increased oxidative stress as a key contributing factor to these effects. Thus, a continuous oxidative stress-induced chronic myocardial damage along with phospholamban dephosphorylation are critical for bromine-induced chronic cardiac dysfunction. These findings in our preclinical model will educate clinicians and public health personnel and provide important endpoints to evaluate therapies.

• Tazmini, Kiarash; Frisk, Michael; Lewalle, Alexandre; Laasmaa, Martin; Morotti, Stefano & Lipsett, David Bruce [Vis alle 16 forfattere av denne artikkelen] (2020). Hypokalemia promotes arrhythmia by distinct mechanisms in atrial and ventricular myocytes. Circulation Research. ISSN 0009-7330. 126(7), s. 889–906. doi: 10.1161/CIRCRESAHA.119.315641. Fulltekst i vitenarkiv Vis sammendrag

  Rationale: Hypokalemia occurs in up to 20% of hospitalized patients and is associated with increased incidence of ventricular and atrial fibrillation. It is unclear whether these differing types of arrhythmia result from direct and perhaps distinct effects of hypokalemia on cardiomyocytes. Objective: To investigate proarrhythmic mechanisms of hypokalemia in ventricular and atrial myocytes. Methods and Results: Experiments were performed in isolated rat myocytes exposed to simulated hypokalemia conditions (reduction of extracellular [K+] from 5.0 to 2.7 mmol/L) and supported by mathematical modeling studies. Ventricular cells subjected to hypokalemia exhibited Ca2+ overload and increased generation of both spontaneous Ca2+ waves and delayed afterdepolarizations. However, similar Ca2+-dependent spontaneous activity during hypokalemia was only observed in a minority of atrial cells that were observed to contain t-tubules. This effect was attributed to close functional pairing of the Na+-K+ ATPase and Na+-Ca2+ exchanger proteins within these structures, as reduction in Na+ pump activity locally inhibited Ca2+ extrusion. Ventricular myocytes and tubulated atrial myocytes additionally exhibited early afterdepolarizations during hypokalemia, associated with Ca2+ overload. However, early afterdepolarizations also occurred in untubulated atrial cells, despite Ca2+ quiescence. These phase-3 early afterdepolarizations were rather linked to reactivation of nonequilibrium Na+ current, as they were rapidly blocked by tetrodotoxin. Na+ current-driven early afterdepolarizations in untubulated atrial cells were enabled by membrane hyperpolarization during hypokalemia and short action potential configurations. Brief action potentials were in turn maintained by ultra-rapid K+ current (IKur); a current which was found to be absent in tubulated atrial myocytes and ventricular myocytes. Conclusions: Distinct mechanisms underlie hypokalemia-induced arrhythmia in the ventricle and atrium but also vary between atrial myocytes depending on subcellular structure and electrophysiology.

• Røe, Åsmund Treu; Ruud, Marianne; Espe, Emil Knut Stenersen; Manfra, Ornella; Longobardi, S & Aronsen, Jan Magnus [Vis alle 16 forfattere av denne artikkelen] (2019). Regional diastolic dysfunction in post-infarction heart failure: role of local mechanical load and SERCA expression. Cardiovascular Research (CVR). ISSN 0008-6363. 115(4), s. 752–764. doi: 10.1093/cvr/cvy257. Fulltekst i vitenarkiv Vis sammendrag

  Aims: Regional heterogeneities in contraction contribute to heart failure with reduced ejection fraction (HFrEF). We aimed to determine whether regional changes in myocardial relaxation similarly contribute to diastolic dysfunction in post-infarction HFrEF, and to elucidate the underlying mechanisms. Methods and results: Using the magnetic resonance imaging phase-contrast technique, we examined local diastolic function in a rat model of post-infarction HFrEF. In comparison with sham-operated animals, post-infarction HFrEF rats exhibited reduced diastolic strain rate adjacent to the scar, but not in remote regions of the myocardium. Removal of Ca2+ within cardiomyocytes governs relaxation, and we indeed found that Ca2+ transients declined more slowly in cells isolated from the adjacent region. Resting Ca2+ levels in adjacent zone myocytes were also markedly elevated at high pacing rates. Impaired Ca2+ removal was attributed to a reduced rate of Ca2+ sequestration into the sarcoplasmic reticulum (SR), due to decreased local expression of the SR Ca2+ ATPase (SERCA). Wall stress was elevated in the adjacent region. Using ex vivo experiments with loaded papillary muscles, we demonstrated that high mechanical stress is directly linked to SERCA down-regulation and slowing of relaxation. Finally, we confirmed that regional diastolic dysfunction is also present in human HFrEF patients. Using echocardiographic speckle-tracking of patients enrolled in the LEAF trial, we found that in comparison with controls, post-infarction HFrEF subjects exhibited reduced diastolic train rate adjacent to the scar, but not in remote regions of the myocardium. Conclusion: Our data indicate that relaxation varies across the heart in post-infarction HFrEF. Regional diastolic dysfunction in this condition is linked to elevated wall stress adjacent to the infarction, resulting in down-regulation of SERCA, disrupted diastolic Ca2+ handling, and local slowing of relaxation.

• Lipsett, David Bruce; Frisk, Michael; Aronsen, Jan Magnus; Norden, Einar Sjaastad; Buonarati, Olivia R. & Cataliotti, Alessandro [Vis alle 10 forfattere av denne artikkelen] (2019). Cardiomyocyte substructure reverts to an immature phenotype during heart failure. Journal of Physiology. ISSN 0022-3751. 597(7), s. 1833–1853. doi: 10.1113/JP277273. Fulltekst i vitenarkiv Vis sammendrag

  Reactivation of the fetal gene programme has been implicated as a driver of pathological cardiac remodelling. Here we examined whether pathological remodelling of cardiomyocyte substructure and function during heart failure (HF) reflects a reversion to an immature phenotype. Using scanning electron microscopy, we observed that Z‐grooves and t‐tubule openings at the cell surface appeared gradually during cardiac development, and disappeared during HF. Confocal and super‐resolution imaging within the cell interior revealed similar structural parallels; disorganization of t‐tubules in failing cells was strikingly reminiscent of the late stages of postnatal development, with fewer transverse elements and a high proportion of longitudinal tubules. Ryanodine receptors (RyRs) were observed to be laid down in advance of developing t‐tubules and similarly ‘orphaned’ in HF, although RyR distribution along Z‐lines was relatively sparse. Indeed, nanoscale imaging revealed coordinated packing of L‐type Ca2+ channels and RyRs into dyadic junctions during development, and orderly unpacking during HF. These findings support a ‘last in, first out’ paradigm, as the latest stages of dyadic structural development are reversed during disease. Paired imaging of t‐tubules and Ca2+ showed that the disorganized arrangement of dyads in immature and failing cells promoted desynchronized and slowed Ca2+ release in these two states. However, while developing cells exhibited efficient triggering of Ca2+ release at newly formed dyads, dyadic function was impaired in failing cells despite similar organization of Ca2+ handling proteins. Thus, pathologically deficient Ca2+ homeostasis during HF is only partly linked to the re‐emergence of immature subcellular structure, and additionally reflects lost dyadic functionality.

• Colli, Dylan; Blood, S Ryan; Sankarankutty, Aparna C; Sachse, Frank B.; Frisk, Michael & Louch, William Edward [Vis alle 7 forfattere av denne artikkelen] (2019). A Matched-Filter-Based Algorithm for Subcellular Classification of T-System in Cardiac Tissues. Biophysical Journal. ISSN 0006-3495. 116(8), s. 1386–1393. doi: 10.1016/j.bpj.2019.03.010. Fulltekst i vitenarkiv
• Ahmad, Shama; Juncos, Juan Xavier Masjoan; Ahmad, Aftab; Zaky, Ahmed; Wei, Chih-Chang & Louch, William Edward [Vis alle 14 forfattere av denne artikkelen] (2019). Bromine-inhalation mimics ischemia-reperfusion cardiomyocyte injury and calpain activation in rats. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 316(1), s. H212–H223. doi: 10.1152/ajpheart.00652.2017. Fulltekst i vitenarkiv
• Laasmaa, Martin; Lu, Pengfei; Veletic, Mladen; Louch, William Edward; Bergsland, Jacob & Balasingham, Ilangko [Vis alle 7 forfattere av denne artikkelen] (2019). Energy-efficiency of Cardiomyocyte Stimulation with Rectangular Pulses. Scientific Reports. 9:13307, s. 1–9. doi: 10.1038/s41598-019-49791-w. Fulltekst i vitenarkiv Vis sammendrag

  In cardiac pacemaker design, energy expenditure is an important issue. This work aims to explore whether varying stimulation pulse configuration is a viable optimization strategy for reducing energy consumption by the pacemaker. A single cardiomyocyte was used as an experimental model. Each cardiomyocyte was stimulated with different stimulation protocols using rectangular waveforms applied in varying number, in short succession. The amplitude, the width of each pulse, and the interval between consecutive pulses were modified. The application of multiple pulses in a short sequence led to a reduction of the threshold voltage required for stimulation when compared to a single pulse. However, none of the employed multi-pulse sequences reduced the overall energy expenditure of cell stimulation when compared to a single pulse stimulation. Among multiple pulse protocols, a combination of two short pulses (1 ms) separated with a short interval (0.5 ms) had the same energy requirements as a single short pulse (1 ms), but required the application of significantly less voltage. While increasing the number of consecutive pulses does not reduce the energy requirements of the pacemaker, the reduction in threshold voltage can be considered in practice if lower stimulation voltages are desired.

• Tazmini, Kiarash; Nymo, Ståle Haugset; Louch, William Edward; Ranhoff, Anette Hylen & Øie, Erik (2019). Electrolyte imbalances in an unselected population in an emergency department: A retrospective cohort study. PLOS ONE. 14(4). doi: 10.1371/journal.pone.0215673. Fulltekst i vitenarkiv Vis sammendrag

  Background: Although electrolyte imbalances (EIs) are common in the emergency department (ED), few studies have examined the occurrence of such conditions in an unselected population. Objectives: To investigate the frequency of EI among adult patients who present to the ED, with regards to type and severity, and the association with age and sex of the patient, hospital length of stay (LOS), readmission, and mortality. Methods: A retrospective cohort study. All patients ≥18 years referred for any reason to the ED between January 1, 2010, and December 31, 2015, who had measured blood electrolytes were included. In total, 62 991 visits involving 31 966 patients were registered. Results: EIs were mostly mild, and the most common EI was hyponatremia (glucose-corrected) (24.6%). Patients with increasing severity of EI had longer LOS compared with patients with normal electrolyte measurements. Among all admitted patients, there were 12928 (20.5%) readmissions within 30 days from discharge during the study period. Hyponatremia (glucose-corrected) was associated with readmission, with an adjusted odds ratio (OR) of 1.25 (95% CI, 1.18–1.32). Hypomagnesemia and hypocalcemia (albumin-corrected) were also associated with readmission, with ORs of 1.25 (95% CI, 1.07–1.45) and 1.22 (95% CI, 1.02–1.46), respectively. Dysnatremia, dyskalemia, hypercalcemia, hypermagnesemia, and hyperphosphatemia were associated with increased in-hospital mortality, whereas all EIs except hypophosphatemia were associated with increased 30-day and 1-year mortality. Conclusions: EIs were common and increasing severity of EIs was associated with longer LOS and increased in-hospital, 30-days and 1-year mortality. EI monitoring is crucial for newly admitted patients, and up-to-date training in EI diagnosis and treatment is essential for ED physicians.

• Lu, Pengfei; Veletic, Mladen; Laasmaa, Martin; Vendelin, Marko; Louch, William Edward & Halvorsen, Per Steinar [Vis alle 8 forfattere av denne artikkelen] (2019). Multi-nodal nano-actuator pacemaker for energy-efficient stimulation of cardiomyocytes. Nano Communication Networks. ISSN 1878-7789. 22:100270, s. 1–11. doi: 10.1016/j.nancom.2019.100270. Fulltekst i vitenarkiv Vis sammendrag

  There is continuous interest in maximizing the longevity of implantable pacemakers, which are effective in remedying and managing patients with arrhythmic heart disease. This paper accordingly first proposes miniature actuating nanomachines that inter-connect with individual cardiomyocytes and then deeply explores their energy expenditure when performing basic cardiomyocyte stimulation tasks. Since evoked electrical impulses from a number of actuated cardiomyocytes could coordinate contraction throughout the remaining heart muscle and lead to a heart beat, the miniature actuating nanomachines acting synchronously form a conceptual multi-nodal nano-actuator pacemaker network. Rectangular-, sine-, half-sine-, and sawtooth stimulation pulses with varying configurations are considered for actuation of a single isolated in-silico cardiomyocyte by each of the nanomachines. Computer optimization methods with energy consumption as a cost function are utilized to configure preferable stimulation signals in terms of numbers of stimulation sessions/pulses, pulse amplitudes, and duration. In addition, the simulation data are compared with experimental data obtained using in-vitro mouse cardiomyocytes. Among the considered waveforms, half-sine pulses that lead to actuation of a single cardiomyocyte consume minimum energy. None of the used sequences with multiple stimulation pulses reduces the overall energy expenditure of cell stimulation when compared to a single pulse stimulation.

• Skogestad, Jonas; Lines, Glenn; Louch, William Edward; Sejersted, Ole M; Sjaastad, Ivar & Aronsen, Jan Magnus (2019). Evidence for heterogeneous subsarcolemmal Na+ Levels in rat ventricular myocytes. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 316(5). doi: 10.1152/ajpheart.00637.2018. Fulltekst i vitenarkiv
• Goodridge, Jodie; Jacobs, Benedikt Marcel; Sætersmoen, Michelle Lu; Clement, Dennis; Hammer, Quirin & Clancy, Trevor [Vis alle 24 forfattere av denne artikkelen] (2019). Remodeling of secretory lysosomes during education tunes functional potential in NK cells. Nature Communications. 10:14, s. 1–15. doi: 10.1038/s41467-019-08384-x. Fulltekst i vitenarkiv Vis sammendrag

  Inhibitory signaling during natural killer (NK) cell education translates into increased responsiveness to activation; however, the intracellular mechanism for functional tuning by inhibitory receptors remains unclear. Secretory lysosomes are part of the acidic lysosomal compartment that mediates intracellular signalling in several cell types. Here we show that educated NK cells expressing self-MHC specific inhibitory killer cell immunoglobulin-like receptors (KIR) accumulate granzyme B in dense-core secretory lysosomes that converge close to the centrosome. This discrete morphological phenotype is independent of transcriptional programs that regulate effector function, metabolism and lysosomal biogenesis. Meanwhile, interference of signaling from acidic Ca2+ stores in primary NK cells reduces target-specific Ca2+-flux, degranulation and cytokine production. Furthermore, inhibition of PI(3,5)P2 synthesis, or genetic silencing of the PI(3,5)P2-regulated lysosomal Ca2+-channel TRPML1, leads to increased granzyme B and enhanced functional potential, thereby mimicking the educated state. These results indicate an intrinsic role for lysosomal remodeling in NK cell education.

• Ottesen, Anett Hellebø; Carlson, Cathrine Rein; Eken, Olav Søvik; Sadredini, Mani; Myhre, Peder Langeland & Shen, Xin [Vis alle 24 forfattere av denne artikkelen] (2019). Secretoneurin Is an Endogenous Calcium/Calmodulin-Dependent Protein Kinase II Inhibitor That Attenuates Ca2+-Dependent Arrhythmia. Circulation: Arrhythmia and Electrophysiology. ISSN 1941-3149. 12(4). doi: 10.1161/CIRCEP.118.007045. Fulltekst i vitenarkiv Vis sammendrag

  Background: Circulating SN (secretoneurin) concentrations are increased in patients with myocardial dysfunction and predict poor outcome. Because SN inhibits CaMKIIδ (Ca2+/calmodulin-dependent protein kinase IIδ) activity, we hypothesized that upregulation of SN in patients protects against cardiomyocyte mechanisms of arrhythmia. Methods: Circulating levels of SN and other biomarkers were assessed in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT; n=8) and in resuscitated patients after ventricular arrhythmia–induced cardiac arrest (n=155). In vivo effects of SN were investigated in CPVT mice (RyR2 [ryanodine receptor 2]-R2474S) using adeno-associated virus-9–induced overexpression. Interactions between SN and CaMKIIδ were mapped using pull-down experiments, mutagenesis, ELISA, and structural homology modeling. Ex vivo actions were tested in Langendorff hearts and effects on Ca2+ homeostasis examined by fluorescence (fluo-4) and patch-clamp recordings in isolated cardiomyocytes. Results: SN levels were elevated in patients with CPVT and following ventricular arrhythmia–induced cardiac arrest. In contrast to NT-proBNP (N-terminal pro-B-type natriuretic peptide) and hs-TnT (high-sensitivity troponin T), circulating SN levels declined after resuscitation, as the risk of a new arrhythmia waned. Myocardial pro-SN expression was also increased in CPVT mice, and further adeno-associated virus-9–induced overexpression of SN attenuated arrhythmic induction during stress testing with isoproterenol. Mechanistic studies mapped SN binding to the substrate binding site in the catalytic region of CaMKIIδ. Accordingly, SN attenuated isoproterenol induced autophosphorylation of Thr287-CaMKIIδ in Langendorff hearts and inhibited CaMKIIδ-dependent RyR phosphorylation. In line with CaMKIIδ and RyR inhibition, SN treatment decreased Ca2+ spark frequency and dimensions in cardiomyocytes during isoproterenol challenge, and reduced the incidence of Ca2+ waves, delayed afterdepolarizations, and spontaneous action potentials. SN treatment also lowered the incidence of early afterdepolarizations during isoproterenol; an effect paralleled by reduced magnitude of L-type Ca2+ current. Conclusions: SN production is upregulated in conditions with cardiomyocyte Ca2+ dysregulation and offers compensatory protection against cardiomyocyte mechanisms of arrhythmia, which may underlie its putative use as a biomarker in at-risk patients.

• Kolstad, Terje; Brink, Jonas van den; MacQuaide, Niall; Lunde, Per; Frisk, Michael & Aronsen, Jan [Vis alle 12 forfattere av denne artikkelen] (2018). Ryanodine Receptor Dispersion Disrupts Ca2+-Release in Failing Cardiac Myocytes. eLIFE. 7. doi: 10.7554/eLife.39427. Fulltekst i vitenarkiv
• Gamage, Thilini Hansamali Gamage Yaddehi; Gunnes, Gjermund; Lee, Robert Hugh; Louch, William Edward; Holmgren, Asbjørn & Bruton, Joseph D. [Vis alle 19 forfattere av denne artikkelen] (2018). STIM1 R304W causes muscle degeneration and impaired platelet activation in mice. Cell Calcium. ISSN 0143-4160. 76, s. 87–100. doi: 10.1016/j.ceca.2018.10.001. Fulltekst i vitenarkiv Vis sammendrag

  STIM1 and ORAI1 regulate store-operated Ca2+ entry (SOCE) in most cell types, and mutations in these proteins have deleterious and diverse effects. We established a mouse line expressing the STIM1 R304 W gain-of-function mutation causing Stormorken syndrome to explore effects on organ and cell physiology. While STIM1 R304 W was lethal in the homozygous state, surviving mice presented with reduced growth, skeletal muscle degeneration, and reduced exercise endurance. Variable STIM1 expression levels between tissues directly impacted cellular SOCE capacity. In contrast to patients with Stormorken syndrome, STIM1 was downregulated in fibroblasts from Stim1R304W/R304W mice, which maintained SOCE despite constitutive protein activity. In studies using foetal liver chimeras, STIM1 protein was undetectable in homozygous megakaryocytes and platelets, resulting in impaired platelet activation and absent SOCE. These data indicate that downregulation of STIM1 R304 W effectively opposes the gain-of-function phenotype associated with this mutation, and highlight the importance of STIM1 in skeletal muscle development and integrity.

• Shen, Xin; Brink, Jonas van den; Hou, Yufeng; Colli, Dylan; Le, Christopher & Kolstad, Terje R Selnes [Vis alle 12 forfattere av denne artikkelen] (2018). 3D dSTORM imaging reveals novel detail of ryanodine receptor localization in rat cardiac myocytes. Journal of Physiology. ISSN 0022-3751. 597(2), s. 399–418. doi: 10.1113/JP277360. Fulltekst i vitenarkiv Vis sammendrag

  Cardiomyocyte contraction is dependent on Ca2+ release from ryanodine receptors (RyRs). However, the precise localization of RyRs remains unknown, due to shortcomings of imaging techniques which are diffraction limited or restricted to 2D. We aimed to determine the 3D nanoscale organization of RyRs in rat cardiomyocytes by employing direct stochastic optical reconstruction microscopy (dSTORM) with phase ramp technology. Initial observations at the cell surface showed an undulating organization of RyR clusters, resulting in their frequent overlap in the z‐axis and obscured detection by 2D techniques. Non‐overlapping clusters were imaged to create a calibration curve for estimating RyR number based on recorded fluorescence blinks. Employing this method at the cell surface and interior revealed smaller RyR clusters than 2D estimates, as erroneous merging of axially aligned RyRs was circumvented. Functional groupings of RyR clusters (Ca2+ release units, CRUs), contained an average of 18 and 23 RyRs at the surface and interior, respectively, although half of all CRUs contained only a single ‘rogue’ RyR. Internal CRUs were more tightly packed along z‐lines than surface CRUs, contained larger and more numerous RyR clusters, and constituted ∼75% of the roughly 1 million RyRs present in an average cardiomyocyte. This complex internal 3D geometry was underscored by correlative imaging of RyRs and t‐tubules, which enabled quantification of dyadic and non‐dyadic RyR populations. Mirroring differences in CRU size and complexity, Ca2+ sparks originating from internal CRUs were of longer duration than those at the surface. These data provide novel, nanoscale insight into RyR organization and function across cardiomyocytes.

• Ghali, Rana; Raffaele, Altara; Louch, William Edward; Cataliotti, Alessandro; Mallat, Ziad & Kaplan, Abdullah [Vis alle 8 forfattere av denne artikkelen] (2018). IL-33 (interleukin 33)/sST2 (soluble suppression of tumorigenicity 2) axis in hypertension and heart failure. Hypertension. ISSN 0194-911X. 72(4), s. 818–828. doi: 10.1161/HYPERTENSIONAHA.118.11157. Fulltekst i vitenarkiv
• Foo, Kylie S.; Lehtinen, Miia L.; Leung, Chuen Yan; Lian, Xiaojun; Xu, Jiejia & Keung, Wendy [Vis alle 20 forfattere av denne artikkelen] (2018). Human ISL1+ ventricular progenitors self-assemble into an in vivo functional heart patch and preserve cardiac function post infarction. Molecular Therapy. ISSN 1525-0016. 26(7), s. 1644–1659. doi: 10.1016/j.ymthe.2018.02.012. Fulltekst i vitenarkiv Vis sammendrag

  The generation of human pluripotent stem cell (hPSC)-derived ventricular progenitors and their assembly into a 3-dimensional in vivo functional ventricular heart patch has remained an elusive goal. Herein, we report the generation of an enriched pool of hPSC-derived ventricular progenitors (HVPs), which can expand, differentiate, self-assemble, and mature into a functional ventricular patch in vivo without the aid of any gel or matrix. We documented a specific temporal window, in which the HVPs will engraft in vivo. On day 6 of differentiation, HVPs were enriched by depleting cells positive for pluripotency marker TRA-1-60 with magnetic-activated cell sorting (MACS), and 3 million sorted cells were sub-capsularly transplanted onto kidneys of NSG mice where, after 2 months, they formed a 7 mm × 3 mm × 4 mm myocardial patch resembling the ventricular wall. The graft acquired several features of maturation: expression of ventricular marker (MLC2v), desmosomes, appearance of T-tubule-like structures, and electrophysiological action potential signature consistent with maturation, all this in a non-cardiac environment. We further demonstrated that HVPs transplanted into un-injured hearts of NSG mice remain viable for up to 8 months. Moreover, transplantation of 2 million HVPs largely preserved myocardial contractile function following myocardial infarction. Taken together, our study reaffirms the promising idea of using progenitor cells for regenerative therapy.

• Kolstad, Terje R Selnes; Brink, Jonas van Den; Macquaide, Niall; Lunde, Per Kristian; Frisk, Michael & Aronsen, Jan Magnus [Vis alle 13 forfattere av denne artikkelen] (2018). Ryanodine receptor dispersion disrupts Ca2+ release in failing cardiac myocytes. eLIFE. 7. doi: 10.7554/eLife.39427. Fulltekst i vitenarkiv Vis sammendrag

  Reduced cardiac contractility during heart failure (HF) is linked to impaired Ca2+ release from Ryanodine Receptors (RyRs). We investigated whether this deficit can be traced to nanoscale RyR reorganization. Using super-resolution imaging, we observed dispersion of RyR clusters in cardiomyocytes from post-infarction HF rats, resulting in more numerous, smaller clusters. Functional groupings of RyR clusters which produce Ca2+ sparks (Ca2+ release units, CRUs) also became less solid. An increased fraction of small CRUs in HF was linked to augmented ‘silent’ Ca2+ leak, not visible as sparks. Larger multi-cluster CRUs common in HF also exhibited low fidelity spark generation. When successfully triggered, sparks in failing cells displayed slow kinetics as Ca2+ spread across dispersed CRUs. During the action potential, these slow sparks protracted and desynchronized the overall Ca2+ transient. Thus, nanoscale RyR reorganization during HF augments Ca2+ leak and slows Ca2+ release kinetics, leading to weakened contraction in this disease.

• Hou, Yufeng; Le, Christopher; Soeller, Christian & Louch, William Edward (2018). Protocol for the isolation and super-resolution dSTORM imaging of RyR2 in Cardiac myocytes. Bio-protocol. doi: 10.21769/BioProtoc.2952. Fulltekst i vitenarkiv Vis sammendrag

  Heart failure is associated with low cardiac output (CO) and low brain perfusion that imposesa significant risk for accelerated brain ageing and Alzheimer’s disease (AD) development. Al-though clinical heart failure can emerge several years following acute myocardial infarction(AMI), the impact of AMI on cerebral blood flow (CBF) at early stages and up to 30 daysfollowing MI is unknown. Sixteen months old male mice underwent left anterior descending(LAD) coronary artery ligation. Hemodynamics analyses were performed at baseline and atdays 1, 7, and 30 post-MI. Left ventricular (LV) ejection fraction (EF), LV volumes, CO, andright common carotid artery (RCCA) diameter were recorded by echocardiography. RCCAflow (RCCA FL) was measured by Doppler echocardiography. LV volumes consistently in-creased (P<0.0012) and LV systolic function progressively deteriorated (P<0.0001) post-MI.CO and RCCA FL showed a moderate but significant decrease over the course of MI withsimilar fluctuation pattern such that both variables were decreased at day 1, increased atday 7, and decreased at 30 days post-MI. Correlation and regression analyses between COand RCCA FL showed a strong correlation with significance at baseline and day 30 post-MI(R=0.71,P=0.03, andR=0.72,P=0.03, respectively). Days 1 and 7 analyses betweenCO and RCCA FL showed moderate correlation with non-significance post-MI (R=0.51,P=0.2, andR=0.56,P=0.12, respectively). In summary, CBF significantly decreased fol-lowing AMI and remained significantly decreased for up to 30 days, suggesting a potentialrisk for brain damage that could contribute to cognitive dysfunction later in life.

• Jones, Peter; Macquaide, Niall & Louch, William Edward (2018). Dyadic Plasticity in Cardiomyocytes. Frontiers in Physiology. doi: 10.3389/fphys.2018.01773. Fulltekst i vitenarkiv Vis sammendrag

  Contraction of cardiomyocytes is dependent on sub-cellular structures called dyads, where invaginations of the surface membrane (t-tubules) form functional junctions with the sarcoplasmic reticulum (SR). Within each dyad, Ca2+ entry through t-tubular L-type Ca2+ channels (LTCCs) elicits Ca2+ release from closely apposed Ryanodine Receptors (RyRs) in the SR membrane. The efficiency of this process is dependent on the density and macroscale arrangement of dyads, but also on the nanoscale organization of LTCCs and RyRs within them. We presently review accumulating data demonstrating the remarkable plasticity of these structures. Dyads are known to form gradually during development, with progressive assembly of both t-tubules and junctional SR terminals, and precise trafficking of LTCCs and RyRs. While dyads can exhibit compensatory remodeling when required, dyadic degradation is believed to promote impaired contractility and arrythmogenesis in cardiac disease. Recent data indicate that this plasticity of dyadic structure/function is dependent on the regulatory proteins junctophilin-2, amphiphysin-2 (BIN1), and caveolin-3, which critically arrange dyadic membranes while stabilizing the position and activity of LTCCs and RyRs. Indeed, emerging evidence indicates that clustering of both channels enables “coupled gating”, implying that nanoscale localization and function are intimately linked, and may allow fine-tuning of LTCC-RyR crosstalk. We anticipate that improved understanding of dyadic plasticity will provide greater insight into the processes of cardiac compensation and decompensation, and new opportunities to target the basic mechanisms underlying heart disease.

• Maleckar, Molly; Edwards, Andrew; Louch, William & Lines, Glenn (2017). Studying dyadic structure–function relationships: a review of current modeling approaches and new insights into ca2+ (mis) handling. Clinical Medicine Insights: Cardiology. 11, s. 1179546817698602–1179546817698602. Fulltekst i vitenarkiv
• Maleckar, Molly; Edwards, Andrew; Louch, William & Lines, Glenn (2017). Studying dyadic structure-function relationships: a review of current modeling approaches and new insights into Ca2+ (mis)handling. Clinical Medicine Insights: Cardiology. 11, s. 1–11. doi: 10.1177/1179546817698602. Fulltekst i vitenarkiv
• Ottesen, Anett Hellebø; Carlson, Cathrine Rein; Louch, William Edward; Dahl, Mai Britt; Sandbu, Ragnhild Askeland & Johansen, Rune Forstrøm [Vis alle 15 forfattere av denne artikkelen] (2017). Glycosylated Chromogranin A in Heart Failure: Implications for Processing and Cardiomyocyte Calcium Homeostasis. Circulation: Heart Failure. ISSN 1941-3289. 10(2). doi: 10.1161/CIRCHEARTFAILURE.116.003675. Fulltekst i vitenarkiv Vis sammendrag

  Background—Chromogranin A (CgA) levels have previously been found to predict mortality in heart failure (HF), but currently no information is available regarding CgA processing in HF and whether the CgA fragment catestatin (CST) may directly influence cardiomyocyte function. Methods and Results—CgA processing was characterized in postinfarction HF mice and in patients with acute HF, and the functional role of CST was explored in experimental models. Myocardial biopsies from HF, but not sham-operated mice, demonstrated high molecular weight CgA bands. Deglycosylation treatment attenuated high molecular weight bands, induced a mobility shift, and increased shorter CgA fragments. Adjusting for established risk indices and biomarkers, circulating CgA levels were found to be associated with mortality in patients with acute HF, but not in patients with acute exacerbation of chronic obstructive pulmonary disease. Low CgA-to-CST conversion was also associated with increased mortality in acute HF, thus, supporting functional relevance of impaired CgA processing in cardiovascular disease. CST was identified as a direct inhibitor of CaMKIIδ (Ca2+/calmodulin-dependent protein kinase IIδ) activity, and CST reduced CaMKIIδ-dependent phosphorylation of phospholamban and the ryanodine receptor 2. In line with CaMKIIδ inhibition, CST reduced Ca2+ spark and wave frequency, reduced Ca2+ spark dimensions, increased sarcoplasmic reticulum Ca2+ content, and augmented the magnitude and kinetics of cardiomyocyte Ca2+ transients and contractions. Conclusions—CgA-to-CST conversion in HF is impaired because of hyperglycosylation, which is associated with clinical outcomes in acute HF. The mechanism for increased mortality may be dysregulated cardiomyocyte Ca2+ handling because of reduced CaMKIIδ inhibition.

• Maleckar, Mary Margot Catherine; Edwards, Andrew; Louch, William Edward & Lines, Glenn Terje (2017). Studying dyadic structure-function relationships: A review of current modeling approaches and new insights into Ca2+(mis)handling. Clinical Medicine Insights: Cardiology. 11, s. 1–11. doi: 10.1177/1179546817698602. Fulltekst i vitenarkiv

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• Praetorius, Helle & Louch, William Edward (2022). Europhysiology 2022: Let’s meet for real. Acta Physiologica. ISSN 1748-1708. 235(2). doi: 10.1111/apha.13825. Fulltekst i vitenarkiv
• Louch, William Edward (2022). A TRP to the emergency room: Understanding arrhythmia in the ageing heart. Cardiovascular Research (CVR). ISSN 0008-6363. 118(4), s. 932–933. doi: 10.1093/cvr/cvac017. Fulltekst i vitenarkiv
• Louch, William Edward; Ullrich, Nina D; Navedo, Manuel F & Macquaide, Niall (2022). Editorial: Nanodomain regulation of muscle physiology and alterations in disease. Frontiers in Physiology. 13. doi: 10.3389/fphys.2022.1092304. Fulltekst i vitenarkiv
• Setterberg, Ingunn E.; Le, Christopher; Frisk, Michael; Perdreau-Dahl, Harmonie; Li, Jia & Louch, William E. (2021). Corrigendum: The Physiology and Pathophysiology of T-Tubules in the Heart (Frontiers in Physiology, (2021), 12, (718404), 10.3389/fphys.2021.718404). Frontiers in Physiology. 12. doi: 10.3389/fphys.2021.790227. Fulltekst i vitenarkiv
• Shen, Xin; Kolstad, Terje; Brink, Jonas van den; Frisk, Michael; Hou, Yufeng & Norden, Einar [Vis alle 9 forfattere av denne artikkelen] (2020). 3D Dstorm Imaging Reveals Camkii-Dependent Dispersal of Ryanodine Receptor Clusters in Failing Rat Cardiomyocytes. Fulltekst i vitenarkiv
• Louch, William Edward (2020). A horse of a different colour: Distinct mechanisms of HFpEF and HFrEF. Journal of Physiology. ISSN 0022-3751. doi: 10.1113/JP280691. Fulltekst i vitenarkiv
• Frisk, Michael; Lipsett, David Bruce & Louch, William Edward (2019). Reply to Crocini et al., Journal of Physiology, 2019, JP-LE-2019-278018. Journal of Physiology. ISSN 0022-3751. 597(11), s. 2967–2968. Fulltekst i vitenarkiv
• Frisk, Michael; Lipsett, David Bruce & Louch, William Edward (2019). Reply from M. Frisk, D. B. Lipsett and W. E. Louch. Journal of Physiology. ISSN 0022-3751. 597(11), s. 2967–2968. doi: 10.1113/JP278067. Fulltekst i vitenarkiv
• Louch, William Edward (2019). Channel surfing: New Insights into plasticity of excitation-contraction coupling. Journal of Physiology. ISSN 0022-3751. 597(8), s. 2119–2120. Fulltekst i vitenarkiv
• Bie, P.; Brandes, Ralf P.; Deuchars, S.A.; Eisner, David A; Fandrey, J. & Hecker, Marcus [Vis alle 9 forfattere av denne artikkelen] (2018). Bringing European physiologists together. Acta Physiologica. ISSN 1748-1708. 222(4). doi: 10.1111/apha.13043. Fulltekst i vitenarkiv

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