Jan Magnus Aronsen

• Veras, Ioanni; Eken, Olav Søvik; Levy, Finn Olav; Melleby, Arne Olav & Aronsen, Jan Magnus (2026). Protocol for isolation of nuclei from murine cardiac tissue for single-nucleus multiomic sequencing. STAR Protocols. 7(2). doi: 10.1016/j.xpro.2026.104615. Full text in Research Archive
• Mathiesen, Sabrina Bech; Støle, Thea Parsberg; Romaine, Andreas; Lunde, Marianne; Martinsen, Marita & Aronsen, Jan Magnus [Show all 10 contributors for this article] (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. Full text in Research Archive Show summary

  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.

• Ruud, Marianne; Frisk, Michael; Melleby, Arne Olav; Norseng, Per Andreas; Mohamed, Belal A. & Li, Jia [Show all 22 contributors for this article] (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), p. 4487–4510. doi: 10.1113/JP284566. Full text in Research Archive Show summary

  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.

• Vistnes, Maria; Erusappan, Pugazendhi Murugan; Sasi, Athiramol; Nordén, Einar Sjaastad; Bergo, Kaja Knudsen & Romaine, Andreas [Show all 22 contributors for this article] (2023). Inhibition of the extracellular enzyme A disintegrin and metalloprotease with thrombospondin motif 4 prevents cardiac fibrosis and dysfunction. Cardiovascular Research (CVR). ISSN 0008-6363. 119(10), p. 1915–1927. doi: 10.1093/cvr/cvad078. Full text in Research Archive Show summary

  Abstract Aims Heart failure is a condition with high mortality rates, and there is a lack of therapies that directly target maladaptive changes in the extracellular matrix (ECM), such as fibrosis. We investigated whether the ECM enzyme known as A disintegrin and metalloprotease with thrombospondin motif (ADAMTS) 4 might serve as a therapeutic target in treatment of heart failure and cardiac fibrosis. Methods and results The effects of pharmacological ADAMTS4 inhibition on cardiac function and fibrosis were examined in rats exposed to cardiac pressure overload. Disease mechanisms affected by the treatment were identified based on changes in the myocardial transcriptome. Following aortic banding, rats receiving an ADAMTS inhibitor, with high inhibitory capacity for ADAMTS4, showed substantially better cardiac function than vehicle-treated rats, including ∼30% reduction in E/e′ and left atrial diameter, indicating an improvement in diastolic function. ADAMTS inhibition also resulted in a marked reduction in myocardial collagen content and a down-regulation of transforming growth factor (TGF)-β target genes. The mechanism for the beneficial effects of ADAMTS inhibition was further studied in cultured human cardiac fibroblasts producing mature ECM. ADAMTS4 caused a 50% increase in the TGF-β levels in the medium. Simultaneously, ADAMTS4 elicited a not previously known cleavage of TGF-β-binding proteins, i.e. latent-binding protein of TGF-β and extra domain A-fibronectin. These effects were abolished by the ADAMTS inhibitor. In failing human hearts, we observed a marked increase in ADAMTS4 expression and cleavage activity. Conclusion Inhibition of ADAMTS4 improves cardiac function and reduces collagen accumulation in rats with cardiac pressure overload, possibly through a not previously known cleavage of molecules that control TGF-β availability. Targeting ADAMTS4 may serve as a novel strategy in heart failure treatment, in particular, in heart failure with fibrosis and diastolic dysfunction.

• Skogestad, Jonas; Albert, Ingrid; Hougen, Karina; Lothe, Gustav B; Lunde, Marianne & Eken, Olav Søvik [Show all 25 contributors for this article] (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), p. 1221–1236. doi: 10.1161/CIRCULATIONAHA.121.054168. Full text in Research Archive
• Sánchez-Pérez, Patricia; Mata, Ana; Torp, May-Kristin; López-Bernardo, Elia; Heiestad, Christina Mathisen & Aronsen, Jan Magnus [Show all 14 contributors for this article] (2023). Energy substrate metabolism, mitochondrial structure and oxidative stress after cardiac ischemia-reperfusion in mice lacking UCP3. Free Radical Biology & Medicine. ISSN 0891-5849. 205, p. 244–261. doi: 10.1016/j.freeradbiomed.2023.05.014. Full text in Research Archive Show summary

  Myocardial ischemia-reperfusion (IR) injury may result in cardiomyocyte dysfunction. Mitochondria play a critical role in cardiomyocyte recovery after IR injury. The mitochondrial uncoupling protein 3 (UCP3) has been proposed to reduce mitochondrial reactive oxygen species (ROS) production and to facilitate fatty acid oxidation. As both mechanisms might be protective following IR injury, we investigated functional, mitochondrial structural, and metabolic cardiac remodeling in wild-type mice and in mice lacking UCP3 (UCP3–KO) after IR. Results showed that infarct size in isolated perfused hearts subjected to IR ex vivo was larger in adult and old UCP3–KO mice than in equivalent wild-type mice, and was accompanied by higher levels of creatine kinase in the effluent and by more pronounced mitochondrial structural changes. The greater myocardial damage in UCP3–KO hearts was confirmed in vivo after coronary artery occlusion followed by reperfusion. S1QEL, a suppressor of superoxide generation from site IQ in complex I, limited infarct size in UCP3–KO hearts, pointing to exacerbated superoxide production as a possible cause of the damage. Metabolomics analysis of isolated perfused hearts confirmed the reported accumulation of succinate, xanthine and hypoxanthine during ischemia, and a shift to anaerobic glucose utilization, which all recovered upon reoxygenation. The metabolic response to ischemia and IR was similar in UCP3–KO and wild-type hearts, being lipid and energy metabolism the most affected pathways. Fatty acid oxidation and complex I (but not complex II) activity were equally impaired after IR. Overall, our results indicate that UCP3 deficiency promotes enhanced superoxide generation and mitochondrial structural changes that increase the vulnerability of the myocardium to IR injury.

• Lunde, Ida Gjervold; Aronsen, Jan Magnus; Melleby, Arne Olav; Strand, Mari Elen; Skogestad, Jonas & Bendiksen, Bård Andre [Show all 11 contributors for this article] (2022). Cardiomyocyte-specific overexpression of syndecan-4 in mice results in activation of calcineurin-NFAT signalling and exacerbated cardiac hypertrophy. Molecular Biology Reports. ISSN 0301-4851. 49(12), p. 11795–11809. doi: 10.1007/s11033-022-07985-y. Full text in Research Archive Show summary

  Abstract Background Cardiomyocyte hypertrophy is a hallmark of cardiac dysfunction in patients with aortic stenosis (AS), and can be triggered by left ventricular (LV) pressure overload in mice by aortic banding (AB). Syndecan-4 is a transmembrane heparan sulphate proteoglycan which is found increased in the myocardium of AS patients and AB mice. The role of syndecan-4 in cardiomyocyte hypertrophy is not well understood. Purpose of the study We developed mice with cardiomyocyte-specific overexpression of syndecan-4 ( Sdc4-Tg ) and subjected these to AB to examine the role of syndecan-4 in hypertrophy and activation of the pro-hypertrophic calcineurin-NFAT signalling pathway. Methods and results Sdc4-Tg mice showed exacerbated cardiac remodelling upon AB compared to wild type (WT). At 2–6 weeks post-AB, Sdc4-Tg and WT mice showed similar hypertrophic growth, while at 20 weeks post-AB, exacerbated hypertrophy and dysfunction were evident in Sdc4-Tg mice. After cross-breeding of Sdc4-Tg mice with NFAT-luciferase reporter mice, we found increased NFAT activation in Sdc4-Tg hearts after AB. Immunoprecipitation showed that calcineurin bound to syndecan-4 in Sdc4-Tg hearts. Isolated cardiomyocytes from Sdc4-Tg mice showed alterations in Ca 2+ fluxes, suggesting that syndecan-4 regulated Ca 2+ levels, and thereby, activating the syndecan-4-calcineurin complex resulting in NFAT activation and hypertrophic growth. Similarly, primary cardiomyocyte cultures from neonatal rats showed increased calcineurin-NFAT-dependent hypertrophic growth upon viral Sdc4 overexpression. Conclusion Our study of mice with cardiomyocyte-specific overexpression of Sdc4 have revealed that syndecan-4 is important for activation of the Ca 2+ -dependent calcineurin-NFAT signalling pathway, hypertrophic remodelling and dysfunction in cardiomyocytes in response to pressure overload.

• Skogestad, Jonas & Aronsen, Jan Magnus (2022). Regulation of Cardiac Contractility by the Alpha 2 Subunit of the Na⁺/K⁺-ATPase. Frontiers in Physiology. 13. doi: 10.3389/fphys.2022.827334. Full text in Research Archive Show summary

  Cytosolic Na + concentrations regulate cardiac excitation-contraction coupling and contractility. Inhibition of the Na + /K + -ATPase (NKA) activity increases cardiac contractility by increasing cytosolic Ca 2+ levels, as increased cytosolic Na + levels are coupled to less Ca 2+ extrusion and/or increased Ca 2+ influx from the Na + /Ca 2+ -exchanger. NKA consists of one α subunit and one β subunit, with α1 and α2 being the main α isoforms in cardiomyocytes. Substantial evidence suggests that NKAα2 is the primary regulator of cardiac contractility despite being outnumbered by NKAα1 in cardiomyocytes. This review will mainly focus on differential regulation and subcellular localization of the NKAα1 and NKAα2 isoforms, and their relation to the proposed concept of subcellular gradients of Na + in cardiomyocytes. We will also discuss the potential roles of NKAα2 in mediating cardiac hypertrophy and ventricular arrhythmias.

• Manfra, Ornella; Calamera, Gaia; Froese, Alexander; Arunthavarajah, Dulasi; Surdo, Nicoletta C. & Meier, Silja [Show all 14 contributors for this article] (2022). CNP regulates cardiac contractility and increases cGMP near both SERCA and TnI: difference from BNP visualized by targeted cGMP biosensors. Cardiovascular Research (CVR). ISSN 0008-6363. 118(6), p. 1506–1519. doi: 10.1093/cvr/cvab167. Full text in Research Archive Show summary

  Abstract Aims Guanylyl cyclase-B (GC-B; natriuretic peptide receptor-B, NPR-B) stimulation by C-type natriuretic peptide (CNP) increases cGMP and causes a lusitropic and negative inotropic response in adult myocardium. These effects are not mimicked by NPR-A (GC-A) stimulation by brain natriuretic peptide (BNP), despite similar cGMP increase. More refined methods are needed to better understand the mechanisms of the differential cGMP signalling and compartmentation. The aim of this work was to measure cGMP near proteins involved in regulating contractility to understand compartmentation of cGMP signalling in adult cardiomyocytes. Methods and results We constructed several fluorescence resonance energy transfer (FRET)-based biosensors for cGMP subcellularly targeted to phospholamban (PLB) and troponin I (TnI). CNP stimulation of adult rat cardiomyocytes increased cGMP near PLB and TnI, whereas BNP stimulation increased cGMP near PLB, but not TnI. The phosphodiesterases PDE2 and PDE3 constrained cGMP in both compartments. Local receptor stimulation aided by scanning ion conductance microscopy (SICM) combined with FRET revealed that CNP stimulation both in the t-tubules and on the cell crest increases cGMP similarly near both TnI and PLB. In ventricular strips, CNP stimulation, but not BNP, induced a lusitropic response, enhanced by inhibition of either PDE2 or PDE3, and a negative inotropic response. In cardiomyocytes from heart failure rats, CNP increased cGMP near PLB and TnI more pronounced than in cells from sham-operated animals. Conclusion These targeted biosensors demonstrate that CNP, but not BNP, increases cGMP near TnI in addition to PLB, explaining how CNP, but not BNP, is able to induce lusitropic and negative inotropic responses.

• Støle, Thea Parsberg; Lunde, Marianne; Shen, Xin; Martinsen, Marita; Lunde, Per Kristian & Li, Jia [Show all 12 contributors for this article] (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. Full text in Research Archive Show summary

  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.

• Robinson, Emma L.; Drawnel, Faye M.; Mehdi, Saher; Archer, Caroline R.; Liu, Wei & Okkenhaug, Hanneke [Show all 15 contributors for this article] (2022). MSK-Mediated Phosphorylation of Histone H3 Ser28 Couples MAPK Signalling with Early Gene Induction and Cardiac Hypertrophy. Cells. 11(4). doi: 10.3390/cells11040604. Full text in Research Archive Show summary

  Heart failure is a leading cause of death that develops subsequent to deleterious hypertrophic cardiac remodelling. MAPK pathways play a key role in coordinating the induction of gene expression during hypertrophy. Induction of the immediate early gene (IEG) response including activator protein 1 (AP-1) complex factors is a necessary and early event in this process. How MAPK and IEG expression are coupled during cardiac hypertrophy is not resolved. Here, in vitro, in rodent models and in human samples, we demonstrate that MAPK-stimulated IEG induction depends on the mitogen and stress-activated protein kinase (MSK) and its phosphorylation of histone H3 at serine 28 (pH3S28). pH3S28 in IEG promoters in turn recruits Brg1, a BAF60 ATP-dependent chromatin remodelling complex component, initiating gene expression. Without MSK activity and IEG induction, the hypertrophic response is suppressed. These studies provide new mechanistic insights into the role of MAPK pathways in signalling to the epigenome and regulation of gene expression during cardiac hypertrophy.

• Wanichawan, Pimthanya; Skogestad, Jonas; Lunde, Marianne; Støle, Thea Parsberg; Stensland, Maria & Nyman, Tuula Anneli [Show all 10 contributors for this article] (2021). Design of a proteolytically stable sodium-calcium exchanger 1 activator peptide for in vivo studies. Frontiers in Pharmacology. 12(638646). doi: 10.3389/fphar.2021.638646. Full text in Research Archive Show summary

  The cardiac sodium–calcium exchanger (NCX1) is important for normal Na + - and Ca 2+ -homeostasis and cardiomyocyte relaxation and contraction. It has been suggested that NCX1 activity is reduced by phosphorylated phospholemman (pSer68-PLM); however its direct interaction with PLM is debated. Disruption of the potentially inhibitory pSer68-PLM-NCX1 interaction might be a therapeutic strategy to increase NCX1 activity in cardiac disease. In the present study, we aimed to analyze the binding affinities and kinetics of the PLM-NCX1 and pSer68-PLM-NCX1 interactions by surface plasmon resonance (SPR) and to develop a proteolytically stable NCX1 activator peptide for future in vivo studies. The cytoplasmic parts of PLM (PLM cyt ) and pSer68-PLM (pSer68-PLM cyt ) were found to bind strongly to the intracellular loop of NCX1 (NCX1 cyt ) with similar K D values of 4.1 ± 1.0 nM and 4.3 ± 1.9 nM, but the PLM cyt -NCX1 cyt interaction showed higher on/off rates. To develop a proteolytically stable NCX1 activator, we took advantage of a previously designed, high-affinity PLM binding peptide (OPT) that was derived from the PLM binding region in NCX1 and that reverses the inhibitory PLM (S68D)-NCX1 interaction in HEK293. We performed N- and C-terminal truncations of OPT and identified PYKEIEQLIELANYQV as the minimum sequence required for pSer68-PLM binding. To increase peptide stability in human serum, we replaced the proline with an N-methyl-proline (NOPT) after identification of N-terminus as substitution tolerant by two-dimensional peptide array analysis. Mass spectrometry analysis revealed that the half-life of NOPT was increased 17-fold from that of OPT. NOPT pulled down endogenous PLM from rat left ventricle lysate and exhibited direct pSer68-PLM binding in an ELISA-based assay and bound to pSer68-PLM cyt with a K D of 129 nM. Excess NOPT also reduced the PLM cyt -NCX1 cyt interaction in an ELISA-based competition assay, but in line with that NCX1 and PLM form oligomers, NOPT was not able to outcompete the physical interaction between endogenous full length proteins. Importantly, cell-permeable NOPT-TAT increased NCX1 activity in cardiomyocytes isolated from both SHAM-operated and aorta banded heart failure (HF) mice, indicating that NOPT disrupted the inhibitory pSer68-PLM-NCX1 interaction. In conclusion, we have developed a proteolytically stable NCX1-derived PLM binding peptide that upregulates NCX1 activity in SHAM and HF cardiomyocytes.

• Frisk, Michael; Le, Christopher; Shen, Xin; Røe, Åsmund Treu; Hou, Yufeng & Manfra, Ornella [Show all 24 contributors for this article] (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), p. 405–419. doi: 10.1016/j.jacc.2020.11.044. Full text in Research Archive Show summary

  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.

• Carlson, Cathrine Rein; Aronsen, Jan Magnus; Dahl, Anna Bergan; Moutty, Marie Christine; Lunde, Marianne & Lunde, Per Kristian [Show all 22 contributors for this article] (2021). AKAP18δ Anchors and Regulates CaMKII Activity at Phospholamban-SERCA2 and RYR. Circulation Research. ISSN 0009-7330. 130(1), p. 27–44. doi: 10.1161/CIRCRESAHA.120.317976. Full text in Research Archive Show summary

  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.

• Danielsen, Tore Kristian; Sadredini, Mani; Manotheepan, Ravinea; Aronsen, Jan Magnus; Frisk, Michael & Haugsten, Marie Hansen [Show all 13 contributors for this article] (2021). Exercise training stabilizes RyR2-dependent Ca2+ release in post-infarction heart failure. Frontiers in Cardiovascular Medicine. 7. doi: 10.3389/fcvm.2020.623922. Full text in Research Archive Show summary

  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 < 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.

• Rønning, Sissel Beate; Carlson, Cathrine Rein; Aronsen, Jan Magnus; Pisconti, Addolorata; Høst, Vibeke & Lunde, Marianne [Show all 11 contributors for this article] (2020). Syndecan-4–/– Mice Have Smaller Muscle Fibers, Increased Akt/mTOR/S6K1 and Notch/HES-1 Pathways, and Alterations in Extracellular Matrix Components. Frontiers in Cell and Developmental Biology. doi: 10.3389/fcell.2020.00730. Full text in Research Archive Show summary

  Background: Extracellular matrix (ECM) remodeling is essential for skeletal muscle development and adaption in response to environmental cues such as exercise and injury. The cell surface proteoglycan syndecan-4 has been reported to be essential for muscle differentiation, but few molecular mechanisms are known. Syndecan-4–/– mice are unable to regenerate damaged muscle, and display deficient satellite cell activation, proliferation, and differentiation. A reduced myofiber basal lamina has also been reported in syndecan-4–/– muscle, indicating possible defects in ECM production. To get a better understanding of the underlying molecular mechanisms, we have here investigated the effects of syndecan-4 genetic ablation on molecules involved in ECM remodeling and muscle growth, both under steady state conditions and in response to exercise. Methods: Tibialis anterior (TA) muscles from sedentary and exercised syndecan-4–/– and WT mice were analyzed by immunohistochemistry, real-time PCR and western blotting. Results: Compared to WT, we found that syndecan-4–/– mice had reduced body weight, reduced muscle weight, muscle fibers with a smaller cross-sectional area, and reduced expression of myogenic regulatory transcription factors. Sedentary syndecan-4–/– had also increased mRNA levels of syndecan-2, decorin, collagens, fibromodulin, biglycan, and LOX. Some of these latter ECM components were reduced at protein level, suggesting them to be more susceptible to degradation or less efficiently translated when syndecan-4 is absent. At the protein level, TRPC7 was reduced, whereas activation of the Akt/mTOR/S6K1 and Notch/HES-1 pathways were increased. Finally, although exercise induced upregulation of several of these components in WT, a further upregulation of these molecules was not observed in exercised syndecan-4–/– mice. Conclusion: Altogether our data suggest an important role of syndecan-4 in muscle development.

• Louwe, Maria Cornelia; Olsen, Maria Belland; Kaasbøll, Ole Jørgen; Yang, Kuan; Fosshaug, Linn Elisabeth Lillerud & Alfsnes, Katrine [Show all 25 contributors for this article] (2020). Absence of NLRP3 Inflammasome in Hematopoietic Cells Reduces Adverse Remodeling After Experimental Myocardial Infarction. JACC: Basic to Translational Science. ISSN 2452-302X. 5(12), p. 1210–1224. doi: 10.1016/j.jacbts.2020.09.013. Full text in Research Archive Show summary

  An inflammatory response is required for tissue healing after a myocardial infarction (MI), but the process must be balanced to prevent maladaptive remodeling. This study shows that improved survival and cardiac function following MI, in mice deficient for the NLRP3 inflammasome, can be recapitulated in wild-type mice receiving bone marrow from Nlrp3−/− mice. This suggests that NLRP3 activation in hematopoietic cells infiltrating in the myocardium increases mortality and late ventricular remodeling. Our data should encourage performing clinical trials directly targeting NLRP3 inflammasome and their inflammatory cytokines (interleukin-1β and -18) in MI patients.

• Tazmini, Kiarash; Frisk, Michael; Lewalle, Alexandre; Laasmaa, Martin; Morotti, Stefano & Lipsett, David Bruce [Show all 16 contributors for this article] (2020). Hypokalemia promotes arrhythmia by distinct mechanisms in atrial and ventricular myocytes. Circulation Research. ISSN 0009-7330. 126(7), p. 889–906. doi: 10.1161/CIRCRESAHA.119.315641. Full text in Research Archive Show summary

  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 [Show all 16 contributors for this article] (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), p. 752–764. doi: 10.1093/cvr/cvy257. Full text in Research Archive Show summary

  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 [Show all 10 contributors for this article] (2019). Cardiomyocyte substructure reverts to an immature phenotype during heart failure. Journal of Physiology. ISSN 0022-3751. 597(7), p. 1833–1853. doi: 10.1113/JP277273. Full text in Research Archive Show summary

  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.

• Mohammadzadeh, Naiyereh; Lunde, Ida Gjervold; Andenæs, Kine; Strand, Mari Elen; Aronsen, Jan Magnus & Skrbic, Biljana [Show all 15 contributors for this article] (2019). The extracellular matrix proteoglycan lumican improves survival and counteracts cardiac dilatation and failure in mice subjected to pressure overload. Scientific Reports. 9:9206, p. 1–13. doi: 10.1038/s41598-019-45651-9. Full text in Research Archive Show summary

  Left ventricular (LV) dilatation is a key step in transition to heart failure (HF) in response to pressure overload. Cardiac extracellular matrix (ECM) contains fibrillar collagens and proteoglycans, important for maintaining tissue integrity. Alterations in collagen production and cross-linking are associated with cardiac LV dilatation and HF. Lumican (LUM) is a collagen binding proteoglycan with increased expression in hearts of patients and mice with HF, however, its role in cardiac function remains poorly understood. To examine the role of LUM in pressure overload induced cardiac remodeling, we subjected LUM knock-out (LUMKO) mice to aortic banding (AB) and treated cultured cardiac fibroblasts (CFB) with LUM. LUMKO mice exhibited increased mortality 1–14 days post-AB. Echocardiography revealed increased LV dilatation, altered hypertrophic remodeling and exacerbated contractile dysfunction in surviving LUMKO 1–10w post-AB. LUMKO hearts showed reduced collagen expression and cross-linking post-AB. Transcriptional profiling of LUMKO hearts by RNA sequencing revealed 714 differentially expressed transcripts, with enrichment of cardiotoxicity, ECM and inflammatory pathways. CFB treated with LUM showed increased mRNAs for markers of myofibroblast differentiation, proliferation and expression of ECM molecules important for fibrosis, including collagens and collagen cross-linking enzyme lysyl oxidase. In conclusion, we report the novel finding that lack of LUM attenuates collagen cross-linking in the pressure-overloaded heart, leading to increased mortality, dilatation and contractile dysfunction in mice.

• Espe, Emil Knut Stenersen; Aronsen, Jan Magnus; Norden, Einar Sjaastad; Zhang, Lili & Sjaastad, Ivar (2019). Regional right ventricular function in rats: a novel magnetic resonance imaging method for measurement of right ventricular strain. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 318(1), p. 143–153. doi: 10.1152/ajpheart.00357.2019. Full text in Research Archive Show summary

  The function of the right ventricle (RV) is linked to clinical outcome in many cardiovascular diseases, but its role in experimental heart failure remains largely unexplored due to difficulties in measuring RV function in vivo. We aimed to advance RV imaging by establishing phase-contrast MRI (PC-MRI) as a robust method for measuring RV function in rodents. A total of 46 Wistar-Hannover rats with left ventricular (LV) myocardial infarction and 10 control rats (sham) were examined 6 wk after surgery. Using a 9.4-T preclinical MRI system, we utilized PC-MRI to measure strain/strain rate in the RV free wall under isoflurane anesthesia. Cine MRI was used to measure RV volumes. LV end-diastolic pressure (LVEDP) was measured and used to identify pulmonary congestion. The infarct rats were divided into two groups: those with signs of pulmonary congestion (PC), with LVEDP ≥ 15 mmHg ( n = 26) and those without signs of pulmonary congestion (NPC), with LVEDP < 15 mmHg ( n = 20). The NPC rats exhibited preserved RV strains/strain rates, whereas the PC rats exhibited reduced strains/strain rates (26–48% lower than sham). Of the strain parameters, longitudinal strain and strain rate exhibited the highest correlations to LVEDP and lung weight (rho = 0.65–0.72, P < 0.001). Basal longitudinal strain was most closely associated with signs of pulmonary congestion and indexes of RV remodeling. Longitudinal RV strain had higher area under the curve than ejection fraction for detecting subtle RV dysfunction (area under the curve = 0.85 vs. 0.67). In conclusion, we show for the first time that global and regional RV myocardial strain can be measured robustly in rodents. Reduced RV strain was closely associated with indexes of pulmonary congestion and molecular markers of RV remodeling. NEW & NOTEWORTHY Global and regional right ventricular myocardial strain can be measured with high reproducibility and low interobserver variability in rodents using tissue phase mapping MRI. Reduced right ventricular strain was associated with indexes of pulmonary congestion and molecular markers of right ventricular remodeling. Regional strain in the basal myocardium was considerably higher than in the apical myocardium.

• Mathiesen, Sabrina Bech; Lunde, Marianne; Aronsen, Jan Magnus; Romaine, Andreas; Kaupang, Anita & Martinsen, Marita [Show all 11 contributors for this article] (2019). The cardiac syndecan-4 interactome reveals a role for syndecan-4 in nuclear translocation of muscle LIM protein (MLP). Journal of Biological Chemistry. ISSN 0021-9258. 294(22), p. 8717–8731. doi: 10.1074/jbc.RA118.006423. Full text in Research Archive Show summary

  Costameres are signaling hubs at the sarcolemma and important contact points between the extracellular matrix and cell interior, sensing and transducing biomechanical signals into a cellular response. The transmembrane proteoglycan syndecan-4 localizes to these attachment points and has been shown to be important in the initial stages of cardiac remodeling, but its mechanistic function in the heart remains insufficiently understood. Here, we sought to map the cardiac interactome of syndecan-4 to better understand its function and downstream signaling mechanisms. By combining two different affinity purification methods with MS analysis, we found that the cardiac syndecan-4 interactome consists of 21 novel and 29 previously described interaction partners. Nine of the novel partners were further validated to bind syndecan-4 in HEK293 cells (i.e. CAVIN1/PTRF, CCT5, CDK9, EIF2S1, EIF4B, MPP7, PARVB, PFKM, and RASIP). We also found that 19 of the 50 interactome partners bind differently to syndecan-4 in the left ventricle lysate from aortic-banded heart failure (ABHF) rats compared with SHAM-operated animals. One of these partners was the well-known mechanotransducer muscle LIM protein (MLP), which showed direct and increased binding to syndecan-4 in ABHF. Nuclear translocation is important in MLP-mediated signaling, and we found less MLP in the nuclear-enriched fractions from syndecan-4-/- mouse left ventricles but increased nuclear MLP when syndecan-4 was overexpressed in a cardiomyocyte cell line. In the presence of a cell-permeable syndecan-4-MLP disruptor peptide, the nuclear MLP level was reduced. These findings suggest that syndecan-4 mediates nuclear translocation of MLP in the heart

• Mcginley, Gary George; Bendiksen, Bård Andre; Zhang, Lili; Aronsen, Jan Magnus; Norden, Einar Sjaastad & Sjaastad, Ivar [Show all 7 contributors for this article] (2019). Accelerated magnetic resonance imaging tissue phase mapping of the rat myocardium using compressed sensing with iterative soft-thresholding. PLOS ONE. 14:e0218874(7), p. 1–17. doi: 10.1371/journal.pone.0218874. Full text in Research Archive Show summary

  Introduction Tissue Phase Mapping (TPM) MRI can accurately measure regional myocardial velocities and strain. The lengthy data acquisition, however, renders TPM prone to errors due to variations in physiological parameters, and reduces data yield and experimental throughput. The purpose of the present study is to examine the quality of functional measures (velocity and strain) obtained by highly undersampled TPM data using compressed sensing reconstruction in infarcted and non-infarcted rat hearts. Methods Three fully sampled left-ventricular short-axis TPM slices were acquired from 5 non-infarcted rat hearts and 12 infarcted rat hearts in vivo. The datasets were used to generate retrospectively (simulated) undersampled TPM datasets, with undersampling factors of 2, 4, 8 and 16. Myocardial velocities and circumferential strain were calculated from all datasets. The error introduced from undersampling was then measured and compared to the fully sampled data in order to validate the method. Finally, prospectively undersampled data were acquired and compared to the fully sampled datasets. Results Bland Altman analysis of the retrospectively undersampled and fully sampled data revealed narrow limits of agreement and little bias (global radial velocity: median bias = -0.01 cm/s, 95% limits of agreement = [-0.16, 0.20] cm/s, global circumferential strain: median bias = -0.01%strain, 95% limits of agreement = [-0.43, 0.51] %strain, all for 4x undersampled data at the mid-ventricular level). The prospectively undersampled TPM datasets successfully demonstrated the feasibility of method implementation. Conclusion Through compressed sensing reconstruction, highly undersampled TPM data can be used to accurately measure the velocity and strain of the infarcted and non-infarcted rat myocardium in vivo, thereby increasing experimental throughput and simultaneously reducing error introduced by physiological variations over time.

• Skogestad, Jonas; Aronsen, Jan Magnus; Tovsrud, Nils; Wanichawan, Pimthanya; Hougen, Karina & Stokke, Mathis Korseberg [Show all 10 contributors for this article] (2019). Coupling of the Na+/K+-ATPase to Ankyrin B controls Na+/Ca2+ exchanger activity in cardiomyocytes. Cardiovascular Research (CVR). ISSN 0008-6363. 116(1), p. 78–90. doi: 10.1093/cvr/cvz087. Full text in Research Archive
• 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. Full text in Research Archive
• Sokolova, Marina; Sjaastad, Ivar; Louwe, Maria Cornelia; Alfsnes, Katrine; Aronsen, Jan Magnus & Zhang, Lili [Show all 15 contributors for this article] (2019). NLRP3 inflammasome promotes myocardial remodeling during diet-induced obesity. Frontiers in Immunology. 10:1621(JULY), p. 1–13. doi: 10.3389/fimmu.2019.01621. Full text in Research Archive Show summary

  Background: Obesity is an increasingly prevalent metabolic disorder in the modern world and is associated with structural and functional changes in the heart. The NLRP3 inflammasome is an innate immune sensor that can be activated in response to endogenous danger signals and triggers activation of interleukin (IL)-1β and IL-18. Increasing evidence points to the involvement of the NLRP3 inflammasome in obesity-induced inflammation and insulin resistance, and we hypothesized that it also could play a role in the development of obesity induced cardiac alterations. Methods and Results: WT, Nlrp3−/−, and ASC−/− (Pycard−/−) male mice were exposed to high fat diet (HFD; 60 cal% fat) or control diet for 52 weeks. Cardiac structure and function were evaluated by echocardiography and magnetic resonance imaging, respectively. Whereas, NLRP3 and ASC deficiency did not affect the cardiac hypertrophic response to obesity, it was preventive against left ventricle concentric remodeling and impairment of diastolic function. Furthermore, whereas NLRP3 and ASC deficiency attenuated systemic inflammation in HFD fed mice; long-term HFD did not induce significant cardiac fibrosis or inflammation, suggesting that the beneficial effects of NLRP3 inflammasome deficiency on myocardial remodeling at least partly reflect systemic mechanisms. Nlrp3 and ASC (Pycard) deficient mice were also protected against obesity-induced systemic metabolic dysregulation, as well as lipid accumulation and impaired insulin signaling in hepatic and cardiac tissues. Conclusions: Our data indicate that the NLRP3 inflammasome modulates cardiac concentric remodeling in obesity through effects on systemic inflammation and metabolic disturbances, with effect on insulin signaling as a potential mediator within the myocardium.

• Kolstad, Terje; Brink, Jonas van den; MacQuaide, Niall; Lunde, Per; Frisk, Michael & Aronsen, Jan [Show all 12 contributors for this article] (2018). Ryanodine Receptor Dispersion Disrupts Ca2+-Release in Failing Cardiac Myocytes. eLIFE. 7. doi: 10.7554/eLife.39427. Full text in Research Archive
• Melleby, Arne Olav; Romaine, Andreas; Aronsen, Jan Magnus; Veras, Ioanni; Zhang, Lili & Sjaastad, Ivar [Show all 8 contributors for this article] (2018). A novel method for high precision aortic constriction that allows for generation of specific cardiac phenotypes in mice. Cardiovascular Research (CVR). ISSN 0008-6363. doi: 10.1093/cvr/cvy141. Full text in Research Archive Show summary

  Aims Generation of reproducible cardiac disease phenotypes in mice is instrumental for investigating mechanisms leading to heart failure (HF). For decades, suture-based thoracic aortic constriction has been the preferred method for increasing left ventricular (LV) afterload in rodents, but the degree of stenosis resulting from this method is variable. In an effort to improve this methodology, we subjected mice to constriction of the ascending aorta using o-rings with fixed inner diameters (IDs). Methods and results Mice of C57BL/6J and FVB/N background were subjected to constriction of the ascending aorta using o-rings with fixed IDs of 0.71, 0.66, and 0.61 mm. O-ring aortic banding resulted in 98.7% survival 2 weeks post-surgery, with very low intra- and inter-surgeon variation. When using the narrowest o-ring (0.61 mm), mice developed hypertrophy within 1 week. Over 20 weeks, the mice gradually developed reduced LV ejection fraction (LVEF) and dilatation with increased left atrial dimensions and lung weight, indicating congestion. When using o-rings with IDs of 0.66 mm and 0.71 mm, the mice developed hypertrophy, but maintained a compensated state with stabilized LVEF 8–20 weeks post-surgery. The up-regulation of signature genes associated with HF, hypertrophy, fibrosis, and the level of activation of MAPK and NFAT signalling pathways corresponded to the degree of stenosis. Conclusion Here, we introduce a novel method for high precision aortic constriction in mice with high intra- and inter-surgeon reproducibility and low post-operative mortality that allows generation of specific cardiac disease phenotypes.

• Smyrnias, Ioannis; Goodwin, Normann; Wachten, Dagmar; Skogestad, Jonas; Aronsen, Jan Magnus & Robinson, Emma Louise [Show all 13 contributors for this article] (2018). Contractile responses to endothelin-1 are regulated by PKC phosphorylation of cardiac myosin binding protein-C in rat ventricular myocytes. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 117, p. 1–18. doi: 10.1016/j.yjmcc.2018.02.012. Full text in Research Archive
• Skogestad, Jonas & Aronsen, Jan Magnus (2018). Hypokalemia-induced arrhythmias and heart failure: New insights and implications for therapy. Frontiers in Physiology. 9:1500, p. 1–11. doi: 10.3389/fphys.2018.01500. Full text in Research Archive Show summary

  Routine use of diuretics and neurohumoral activation make hypokalemia (serum K+ < 3. 5 mM) a prevalent electrolyte disorder among heart failure patients, contributing to the increased risk of ventricular arrhythmias and sudden cardiac death in heart failure. Recent experimental studies have suggested that hypokalemia-induced arrhythmias are initiated by the reduced activity of the Na+/K+-ATPase (NKA), subsequently leading to Ca2+ overload, Ca2+/Calmodulin-dependent kinase II (CaMKII) activation, and development of afterdepolarizations. In this article, we review the current mechanistic evidence of hypokalemia-induced triggered arrhythmias and discuss how molecular changes in heart failure might lower the threshold for these arrhythmias. Finally, we discuss how recent insights into hypokalemia-induced arrhythmias could have potential implications for future antiarrhythmic treatment strategies.

• Kolstad, Terje R Selnes; Brink, Jonas van Den; Macquaide, Niall; Lunde, Per Kristian; Frisk, Michael & Aronsen, Jan Magnus [Show all 13 contributors for this article] (2018). Ryanodine receptor dispersion disrupts Ca2+ release in failing cardiac myocytes. eLIFE. 7. doi: 10.7554/eLife.39427. Full text in Research Archive Show summary

  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.

• Andenæs, Kine; Lunde, Ida Gjervold; Mohammadzadeh, Naiyereh; Dahl, Christen Peder; Aronsen, Jan Magnus & Strand, Mari Elen [Show all 11 contributors for this article] (2018). The extracellular matrix proteoglycan fibromodulin is upregulated in clinical and experimental heart failure and affects cardiac remodeling. PLOS ONE. 13(7), p. 1–20. doi: 10.1371/journal.pone.0201422. Full text in Research Archive Show summary

  Pressure overload of the heart leads to cardiac remodeling that may progress into heart failure, a common, morbid and mortal condition. Increased mechanistic insight into remodeling is instrumental for development of novel heart failure treatment. Cardiac remodeling comprises cardiomyocyte hypertrophic growth, extracellular matrix alterations including fibrosis, and inflammation. Fibromodulin is a small leucine-rich proteoglycan that regulates collagen fibrillogenesis. Fibromodulin is expressed in the cardiac extracellular matrix, however its role in the heart remains largely unknown. We investigated fibromodulin levels in myocardial biopsies from heart failure patients and mice, subjected fibromodulin knock-out (FMOD-KO) mice to pressure overload by aortic banding, and overexpressed fibromodulin in cultured cardiomyocytes and cardiac fibroblasts using adenovirus. Fibromodulin was 3-10-fold upregulated in hearts of heart failure patients and mice. Both cardiomyocytes and cardiac fibroblasts expressed fibromodulin, and its expression was increased by pro-inflammatory stimuli. Without stress, FMOD-KO mice showed no cardiac phenotype. Upon aortic banding, left ventricles of FMOD-KO mice developed mildly exacerbated hypertrophic remodeling compared to wild-type mice, with increased cardiomyocyte size and altered infiltration of leukocytes. There were no differences in mortality, left ventricle dilatation, dysfunction or expression of heart failure markers. Although collagen amount and cross-linking were comparable in FMOD-KO and wild-type, overexpression of fibromodulin in cardiac fibroblasts in vitro decreased their migratory capacity and expression of fibrosis-associated molecules, i.e. the collagen-cross linking enzyme lysyl oxidase, transglutaminase 2 and periostin. In conclusion, despite a robust fibromodulin upregulation in clinical and experimental heart failure, FMOD-KO mice showed a relatively mild hypertrophic phenotype. In cultured cardiac fibroblasts, fibromodulin has anti-fibrotic effects.

• Aronsen, Jan Magnus; Espe, Emil Knut Stenersen; Young-Halvorsen, Kristine Skårdal; Hasic, Almira; Zhang, Lili & Sjaastad, Ivar (2017). Noninvasive stratification of postinfarction rats based on the degree of cardiac dysfunction using magnetic resonance imaging and echocardiography. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 312(5), p. H932–H942. doi: 10.1152/ajpheart.00668.2016. Full text in Research Archive
• Romaine, Andreas; Sørensen, Ida Wiig; Zeltz, Cedric; Lu, Ning; Erusappan, Pugazendhi Murugan & Melleby, Arne Olav [Show all 15 contributors for this article] (2017). Overexpression of integrin α11 induces cardiac fibrosis in mice. Acta Physiologica Scandinavica. ISSN 0001-6772. 222:e13025(2), p. 1–17. doi: 10.1111/apha.12932. Full text in Research Archive
• Espe, Emil Knut Stenersen; Aronsen, Jan Magnus; Eriksen, Morten; Sejersted, Ole M; Zhang, Lili & Sjaastad, Ivar (2017). Regional dysfunction after myocardial infarction in rats. Circulation Cardiovascular Imaging. ISSN 1941-9651. 10(9), p. e005997–e005997. doi: 10.1161/CIRCIMAGING.116.005997. Full text in Research Archive
• Espe, Emil Knut Stenersen; Young-Halvorsen, Kristine Skårdal; Aronsen, Jan Magnus; Zhang, Lili & Sjaastad, Ivar (2017). A semiautomatic method for rapid segmentation of velocity-encoded myocardial magnetic resonance imaging data. Magnetic Resonance in Medicine. ISSN 0740-3194. 78(3), p. 1199–1207. doi: 10.1002/mrm.26486. Full text in Research Archive
• Thienpont, Bernard; Aronsen, Jan Magnus; Robinson, Emma Louise; Okkenhaug, Hanneke; Loche, Elena & Ferrini, Arianna [Show all 14 contributors for this article] (2017). The H3K9 dimethyltransferases EHMT1/2 protect against pathological cardiac hypertrophy. Journal of Clinical Investigation. ISSN 0021-9738. 127(1), p. 335–348. doi: 10.1172/JCI88353. Full text in Research Archive
• Meier, Silja; Andressen, Kjetil Wessel; Aronsen, Jan Magnus; Sjaastad, Ivar; Hougen, Karina & Skomedal, Tor [Show all 10 contributors for this article] (2017). PDE3 inhibition by C-type natriuretic peptide-induced cGMP enhances cAMP-mediated signaling in both non-failing and failing hearts. European Journal of Pharmacology. ISSN 0014-2999. 812, p. 174–183. doi: 10.1016/j.ejphar.2017.07.014. Full text in Research Archive
• Dhondup, Yangchen; Sjaastad, Ivar; Sandanger, Øystein; Aronsen, Jan Magnus; Ahmed, Muhammad Shakil & Attramadal, Håvard [Show all 14 contributors for this article] (2017). Toll-like receptor 9 promotes survival in SERCA2a KO heart failure mice. Mediators of Inflammation. ISSN 0962-9351. 2017:9450439, p. 1–11. doi: 10.1155/2017/9450439. Full text in Research Archive Show summary

  Aim. Inflammation is important in heart failure (HF). The role of the immune receptor toll-like receptor 9 (TLR9) in HF is not understood and not investigated in diastolic HF. We investigated the role of TLR9 in a murine diastolic HF model caused by cardiomyocyte SERCA2a excision. Methods and Results. We crossed SERCA2a KO and TLR9 KO mice to generate four mouse lines. Tamoxifen-induced cardiomyocyte SERCA2a gene excision was carried out in mice, causing diastolic HF. After 7.6 weeks, cardiac functions and dimensions were analyzed by echocardiography and heart tissues were processed. HF mice depleted of TLR9 demonstrated reduced survival compared to SERC2a KO mice, with a median life expectancy of 58 days compared to 63 days. Both HF groups displayed increased left atrium size, lung weight, fetal gene expressions, monocyte/macrophage infiltration, and fibrosis. However, there were no significant differences between the groups. Conclusion. In mice with SERCA2a KO-induced diastolic HF, the absence of TLR9 reduced median life expectancy. The cause remains elusive, as all investigated HF parameters were unaltered. Still, these findings support a salutary role of TLR9 in some subsets of HF conditions and underline the importance for future studies on the mechanisms of TLR9 in diastolic HF.

• Gattoni, Sara; Røe, Åsmund Treu; Aronsen, Jan Magnus; Sjaastad, Ivar; Louch, William Edward & Smith, Nicolas P. [Show all 7 contributors for this article] (2017). Compensatory and decompensatory alterations in cardiomyocyte Ca2+ dynamics in hearts with diastolic dysfunction following aortic banding. Journal of Physiology. ISSN 0022-3751. 595(12), p. 3867–3889. doi: 10.1113/JP273879. Full text in Research Archive
• Landfors, Miriam; Johansen, Jostein; Aronsen, Jan Magnus; Vågbø, Cathrine Broberg; Doré, Louis C. & He, Chuan [Show all 13 contributors for this article] (2017). Genome-wide profiling of DNA 5-hydroxymethylcytosine during rat Sertoli cell maturation. Cell Discovery. ISSN 2056-5968. 3. doi: 10.1038/celldisc.2017.13. Full text in Research Archive Show summary

  Sertoli cells have dual roles during the cells’ lifetime. In the juvenile mammal, Sertoli cells proliferate and create the structure of the testis, and during puberty they cease to proliferate and take on the adult role of supporting germ cells through spermatogenesis. Accordingly, many genes expressed in Sertoli cells during testis formation are repressed during spermatogenesis. 5-Hydroxymethylcytosine (5hmC) is a DNA modification enzymatically generated from 5mC and present in all investigated mammalian tissues at varying levels. Using mass spectrometry and immunofluorescence staining we identified a substantial Sertoli cell-specific global 5hmC increase during rat puberty. Chemical labeling, pull-down and sequencing of 5hmC-containing genomic DNA from juvenile and adult rat Sertoli cells revealed that genes that lose or gain 5hmC belong to different functional pathways and mirror the functions of the cells in the two different states. Loss of 5hmC is associated with genes involved in development and cell structure, whereas gain of 5hmC is associated with genes involved in cellular pathways pertaining to the function of the adult Sertoli cells. This redistribution during maturation shows that 5hmC is a dynamic nucleotide modification, correlated to gene expression.

• Røe, Åsmund Treu; Aronsen, Jan Magnus; Young-Halvorsen, Kristine Skårdal; Hamdani, Nazha; Linke, Wolfgang A. & Danielsen, Håvard Emil [Show all 9 contributors for this article] (2017). Increased passive stiffness promotes diastolic dysfunction despite improved Ca2+ handling during left ventricular concentric hypertrophy. Cardiovascular Research (CVR). ISSN 0008-6363. 113(10), p. 1161–1172. doi: 10.1093/cvr/cvx087. Full text in Research Archive
• Aronsen, Jan Magnus; Louch, William Edward & Sjaastad, Ivar (2016). Cardiomyocyte Ca2+ dynamics: Clinical perspectives. Scandinavian Cardiovascular Journal. ISSN 1401-7431. 50(2), p. 65–77. doi: 10.3109/14017431.2015.1136079. Full text in Research Archive
• Hortemo, Kristin Halvorsen; Lunde, Per Kristian; Anonsen, Jan Haug; Kvaløy, Heidi; Munkvik, Morten & Rehn, Tommy Aune [Show all 10 contributors for this article] (2016). Exercise training increases protein O-GlcNAcylation in rat skeletal muscle. Physiological Reports. 4(18), p. e12896–e12896. doi: 10.14814/phy2.12896. Full text in Research Archive Show summary

  Protein O‐GlcNAcylation has emerged as an important intracellular signaling system with both physiological and pathophysiological functions, but the role of protein O‐GlcNAcylation in skeletal muscle remains elusive. In this study, we tested the hypothesis that protein O‐GlcNAcylation is a dynamic signaling system in skeletal muscle in exercise and disease. Immunoblotting showed different protein O‐GlcNAcylation pattern in the prototypical slow twitch soleus muscle compared to fast twitch EDL from rats, with greater O‐GlcNAcylation level in soleus associated with higher expression of the modulating enzymes O‐GlcNAc transferase (OGT), O‐GlcNAcase (OGA), and glutamine fructose‐6‐phosphate amidotransferase isoforms 1 and 2 (GFAT1, GFAT2). Six weeks of exercise training by treadmill running, but not an acute exercise bout, increased protein O‐GlcNAcylation in rat soleus and EDL. There was a striking increase in O‐GlcNAcylation of cytoplasmic proteins ~50 kDa in size that judged from mass spectrometry analysis could represent O‐GlcNAcylation of one or more key metabolic enzymes. This suggests that cytoplasmic O‐GlcNAc signaling is part of the training response. In contrast to exercise training, postinfarction heart failure (HF) in rats and humans did not affect skeletal muscle O‐GlcNAcylation level, indicating that aberrant O‐GlcNAcylation cannot explain the skeletal muscle dysfunction in HF. Human skeletal muscle displayed extensive protein O‐GlcNAcylation that by large mirrored the fiber‐type‐related O‐GlcNAcylation pattern in rats, suggesting O‐GlcNAcylation as an important signaling system also in human skeletal muscle.

• Young-Halvorsen, Kristine Skårdal; Espe, Emil Knut Stenersen; Zhang, Lili; Aronsen, Jan Magnus & Sjaastad, Ivar (2016). Three-directional evaluation of mitral flow in the rat heart by phase-contrast cardiovascular magnetic resonance. PLOS ONE. 11(3). doi: 10.1371/journal.pone.0150536. Full text in Research Archive Show summary

  Purpose Determination of mitral flow is an important aspect in assessment of cardiac function. Traditionally, mitral flow is measured by Doppler echocardiography which suffers from several challenges, particularly related to the direction and the spatial inhomogeneity of flow. These challenges are especially prominent in rodents. The purpose of this study was to establish a cardiovascular magnetic resonance (CMR) protocol for evaluation of three-directional mitral flow in a rodent model of cardiac disease. Materials and Methods Three-directional mitral flow were evaluated by phase contrast CMR (PC-CMR) in rats with aortic banding (AB) (N = 7) and sham-operated controls (N = 7). Peak mitral flow and deceleration rate from PC-CMR was compared to conventional Doppler echocardiography. The accuracy of PC-CMR was investigated by comparison of spatiotemporally integrated mitral flow with left ventricular stroke volume assessed by cine CMR. Results PC-CMR portrayed the spatial distribution of mitral flow and flow direction in the atrioventricular plane throughout diastole. Both PC-CMR and echocardiography demonstrated increased peak mitral flow velocity and higher deceleration rate in AB compared to sham. Comparison with cine CMR revealed that PC-CMR measured mitral flow with excellent accuracy. Echocardiography presented significantly lower values of flow compared to PC-CMR. Conclusions For the first time, we show that PC-CMR offers accurate evaluation of three-directional mitral blood flow in rodents. The method successfully detects alterations in the mitral flow pattern in response to cardiac disease and provides novel insight into the characteristics of mitral flow.

• Sadredini, Mani; Danielsen, Tore Kristian; Aronsen, Jan Magnus; Manotheepan, Ravinea; Hougen, Karina & Sjaastad, Ivar [Show all 7 contributors for this article] (2016). Beta-adrenoceptor stimulation reveals Ca2+ waves and sarcoplasmic reticulum Ca2+ depletion in left ventricular cardiomyocytes from post-infarction rats with and without heart failure. PLOS ONE. 11(4). doi: 10.1371/journal.pone.0153887. Full text in Research Archive Show summary

  Abnormal cellular Ca2+ handling contributes to both contractile dysfunction and arrhythmias in heart failure. Reduced Ca2+ transient amplitude due to decreased sarcoplasmic reticulum Ca2+ content is a common finding in heart failure models. However, heart failure models also show increased propensity for diastolic Ca2+ release events which occur when sarcoplasmic reticulum Ca2+ content exceeds a certain threshold level. Such Ca2+ release events can initiate arrhythmias. In this study we aimed to investigate if both of these aspects of altered Ca2+ homeostasis could be found in left ventricular cardiomyocytes from rats with different states of cardiac function six weeks after myocardial infarction when compared to sham-operated controls. Video edge-detection, whole-cell Ca2+ imaging and confocal linescan imaging were used to investigate cardiomyocyte contractile properties, Ca2+ transients and Ca2+ waves. In baseline conditions, i.e. without beta-adrenoceptor stimulation, cardiomyocytes from rats with large myocardial infarction, but without heart failure, did not differ from sham-operated animals in any of these aspects of cellular function. However, when exposed to beta-adrenoceptor stimulation, cardiomyocytes from both non-failing and failing rat hearts showed decreased sarcoplasmic reticulum Ca2+ content, decreased Ca2+ transient amplitude, and increased frequency of Ca2+ waves. These results are in line with a decreased threshold for diastolic Ca2+ release established by other studies. In the present study, factors that might contribute to a lower threshold for diastolic Ca2+ release were increased THR286 phosphorylation of Ca2+/calmodulin-dependent protein kinase II and increased protein phosphatase 1 abundance. In conclusion, this study demonstrates both decreased sarcoplasmic reticulum Ca2+ content and increased propensity for diastolic Ca2+ release events in ventricular cardiomyocytes from rats with heart failure after myocardial infarction, and that these phenomena are also found in rats with large myocardial infarctions without heart failure development. Importantly, beta-adrenoceptor stimulation is necessary to reveal these perturbations in Ca2+ handling after a myocardial infarction.

• Hafver, Tandekile Lubelwana; Hodne, Kjetil; Wanichawan, Pimthanya; Aronsen, Jan Magnus; Dalhus, Bjørn & Lunde, Per Kristian [Show all 14 contributors for this article] (2016). Protein phosphatase 1c associated with the cardiac sodium calcium exchanger 1 regulates its activity by dephosphorylating Serine 68-phosphorylated phospholemman. Journal of Biological Chemistry. ISSN 0021-9258. 291(9), p. 4561–4579. doi: 10.1074/jbc.M115.677898. Full text in Research Archive Show summary

  The sodium (Na+)-calcium (Ca2+) exchanger 1 (NCX1) is an important regulator of intracellular Ca2+ homeostasis. Serine 68 phosphorylated phospholemman (pSer-68-PLM) inhibits NCX1 activity. In the context of Na+/K+ ATPase (NKA) regulation, pSer-68-PLM is dephosphorylated by protein phosphatase 1 (PP1). PP1 also associates with NCX1, however, the molecular basis of this association is unknown. In the present study, we aimed to analyze the mechanisms of PP1 targeting to the NCX1-pSer-68-PLM complex and hypothesized that a direct and functional NCX1-PP1 interaction is a prerequisite for pSer-68-PLM dephosphorylation. Using a variety of molecular techniques, we show that PP1 catalytic subunit (PP1c) co-localized, co-fractionated, and co-immunoprecipitated with NCX1 in rat cardiomyocytes, left ventricle lysates and HEK293 cells. Bioinformatic analysis, immunoprecipitations, mutagenesis, pull-down experiments and peptide arrays constrained PP1c anchoring to the K-I/V-F-F motif in the first Ca2+ binding domain (CBD1) in NCX1. This binding site is also partially in agreement with the extended PP1 binding motif; K-I/V-F-F-X5-8-Φ1Φ2-X8-9-R. The cytosolic loop of NCX1, containing the K-I/V-F-F motif, had no effect on PP1 activity in an in vitro assay. Dephosphorylation of pSer-68-PLM in HEK293 cells was not observed when NCX1 was absent, when the K-I/V-F-F motif was mutated or when the PLM and PP1c binding sites were separated (mimicking calpain cleavage of NCX1). Co-expression of PLM and NCX1 inhibited NCX1 current (both modes). Moreover, co-expression of PLM with NCX1-(F407P) (mutated K-I/V-F-F motif) resulted in NCX1 current being completely abolished. In conclusion, NCX1 is a substrate-specifying PP1c regulator protein, indirectly regulating NCX1 activity through pSer-68-PLM dephosphorylation.

• Frisk, Michael; Ruud, Marianne; Espe, Emil Knut Stenersen; Aronsen, Jan Magnus; Røe, Åsmund Treu & Zhang, Lili [Show all 11 contributors for this article] (2016). Elevated ventricular wall stress disrupts cardiomyocyte t-tubule structure and calcium homeostasis. Cardiovascular Research (CVR). ISSN 0008-6363. doi: 10.1093/cvr/cvw111. Full text in Research Archive Show summary

  Aims Invaginations of the cellular membrane called t-tubules are essential for maintaining efficient excitation–contraction coupling in ventricular cardiomyocytes. Disruption of t-tubule structure during heart failure has been linked to dyssynchronous, slowed Ca2+ release and reduced power of the heartbeat. The underlying mechanism is, however, unknown. We presently investigated whether elevated ventricular wall stress triggers remodelling of t-tubule structure and function. Methods and results MRI and blood pressure measurements were employed to examine regional wall stress across the left ventricle of sham-operated and failing, post-infarction rat hearts. In failing hearts, elevated left ventricular diastolic pressure and ventricular dilation resulted in markedly increased wall stress, particularly in the thin-walled region proximal to the infarct. High wall stress in this proximal zone was associated with reduced expression of the dyadic anchor junctophilin-2 and disrupted cardiomyocyte t-tubular structure. Indeed, local wall stress measurements predicted t-tubule density across sham and failing hearts. Elevated wall stress and disrupted cardiomyocyte structure in the proximal zone were also associated with desynchronized Ca2+ release in cardiomyocytes and markedly reduced local contractility in vivo. A causative role of wall stress in promoting t-tubule remodelling was established by applying stretch to papillary muscles ex vivo under culture conditions. Loads comparable to wall stress levels observed in vivo in the proximal zone reduced expression of junctophilin-2 and promoted t-tubule loss. Conclusion Elevated wall stress reduces junctophilin-2 expression and disrupts t-tubule integrity, Ca2+ release, and contractile function. These findings provide new insight into the role of wall stress in promoting heart failure progression.

• Dhondup, Yangchen; Sjaastad, Ivar; Scott, Helge; Sandanger, Øystein; Zhang, Lili & Haugstad, Solveig Bjærum [Show all 17 contributors for this article] (2015). Sustained toll-like receptor 9 activation promotes systemic and cardiac inflammation, and aggravates diastolic heart failure in SERCA2a KO Mice. PLOS ONE. 10:e0139715(10). doi: 10.1371/journal.pone.0139715. Full text in Research Archive Show summary

  Aim Cardiac inflammation is important in the pathogenesis of heart failure. However, the consequence of systemic inflammation on concomitant established heart failure, and in particular diastolic heart failure, is less explored. Here we investigated the impact of systemic inflammation, caused by sustained Toll-like receptor 9 activation, on established diastolic heart failure. Methods and Results Diastolic heart failure was established in 8–10 week old cardiomyocyte specific, inducible SERCA2a knock out (i.e., SERCA2a KO) C57Bl/6J mice. Four weeks after conditional KO, mice were randomized to receive Toll-like receptor 9 agonist (CpG B; 2μg/g body weight) or PBS every third day. After additional four weeks, echocardiography, phase contrast magnetic resonance imaging, histology, flow cytometry, and cardiac RNA analyses were performed. A subgroup was followed, registering morbidity and death. Non-heart failure control groups treated with CpG B or PBS served as controls. Our main findings were: (i) Toll-like receptor 9 activation (CpG B) reduced life expectancy in SERCA2a KO mice compared to PBS treated SERCA2a KO mice. (ii) Diastolic function was lower in SERCA2a KO mice with Toll-like receptor 9 activation. (iii) Toll-like receptor 9 stimulated SERCA2a KO mice also had increased cardiac and systemic inflammation. Conclusion Sustained activation of Toll-like receptor 9 causes cardiac and systemic inflammation, and deterioration of SERCA2a depletion-mediated diastolic heart failure.

• Ottesen, Anett Hellebø; Louch, William Edward; Carlson, Cathrine Rein; Landsverk, Ole J. B.; Kurola, Jouni & Johansen, Rune Forstrøm [Show all 18 contributors for this article] (2015). Secretoneurin is a novel prognostic cardiovascular biomarker associated with cardiomyocyte calcium handling. Journal of the American College of Cardiology. ISSN 0735-1097. 65(4), p. 339–351. doi: 10.1016/j.jacc.2014.10.065. Full text in Research Archive
• Lauritzen, Knut Husø; Kleppa, Liv; Aronsen, Jan Magnus; Eide, Lars; Carlsen, Harald & Haugen, Øyvind Pernell [Show all 12 contributors for this article] (2015). Impaired dynamics and function of mitochondria caused by mtDNA toxicity leads to heart failure. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 309(3), p. H434–H449. doi: 10.1152/ajpheart.00253.2014. Full text in Research Archive
• Hortemo, Kristin Halvorsen; Aronsen, Jan Magnus; Lunde, Ida Gjervold; Sjaastad, Ivar; Lunde, Per Kristian & Sejersted, Ole M (2015). Exhausting treadmill running causes dephosphorylation of sMLC2 and reduced level of myofilament MLCK2 in slow twitch rat soleus muscle. Physiological Reports. 3(2). doi: 10.14814/phy2.12285. Full text in Research Archive Show summary

  Myosin light chain 2 (MLC2) is a small protein in the myosin complex, regulating muscle contractile function by modulating Ca2+ sensitivity of myofilaments. MLC2 can be modified by phosphorylation and O-GlcNAcylation, two reversible and dynamic posttranslational modifications. The slow isoform of MLC2 (sMLC2) is dephosphorylated in soleus muscle during in situ loaded shortening contractions, which correlates with reduction in shortening capacity. Here, we hypothesize that exhausting in vivo treadmill running induces dephosphorylation of MLC2 in slow twitch soleus, but not in fast twitch EDL muscle, and that there are reciprocal changes in MLC2 O-GlcNAcylation. At rest, both phosphorylation and O-GlcNAcylation of MLC2 were lower in slow than fast twitch muscles. One bout of exhausting treadmill running induced dephosphorylation of sMLC2 in soleus, paralleled by reduced levels of the kinase MLCK2 associated to myofilaments, suggesting that the acute reduction in phosphorylation is mediated by dissociation of MLCK2 from myofilaments. O-GlcNAcylation of MLC2 did not change significantly, and seems of limited importance in the regulation of MLC2 phosphorylation during in vivo running. After 6 weeks of treadmill running, the dephosphorylation of sMLC2 persisted in soleus along with reduction in MLCK2 both in myofilament- and total protein fraction. In EDL on the contrary, phosphorylation of MLC2 was not altered after one exercise bout or after 6 weeks of treadmill running. Thus, in contrast to fast twitch muscle, MLC2 dephosphorylation occurs in slow twitch muscle during in vivo exercise and may be linked to reduced myofilament-associated MLCK2 and reduced shortening capacity.

• Espe, Emil Knut Stenersen; Aronsen, Jan Magnus; Eriksen, Guro Søe; Zhang, Lili; Smiseth, Otto A. & Edvardsen, Thor [Show all 8 contributors for this article] (2015). Assessment of regional myocardial work in rats. Circulation Cardiovascular Imaging. ISSN 1941-9651. 8. doi: 10.1161/CIRCIMAGING.114.002695. Full text in Research Archive

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• Haraldsrud, Andreas; Maasø, Arnt; Lerheim, Birgitte; Gregers, Tone Fredsvik; Mirmotahari, Omid & Aronsen, Jan Magnus [Show all 8 contributors for this article] (2024). Rart eller innovativt? Å finne kreativitet i undervisningen. Full text in Research Archive
• Aronsen, Jan Magnus; Skogestad, Jonas; Albert, Ingrid; Melleby, Arne Olav & Carlson, Cathrine Rein (2023). Response by Aronsen et al to Letter Regarding Article, "Disruption of Phosphodiesterase 3A Binding to SERCA2 Increases SERCA2 Activity and Reduces Mortality in Mice With Chronic Heart Failure". Circulation. ISSN 0009-7322. 148(10), p. 857–858. doi: 10.1161/CIRCULATIONAHA.123.065884. Full text in Research Archive
• Tonne, Hilde; Ruud, Kenneth; Aronsen, Jan Magnus; Aamot, Eli; Melleby, Karianne & Hansen, Mette Halskov [Show all 11 contributors for this article] (2022). Statsråden omtaler situasjonen som «alvorlig». Realiteten er at det er en oppkonstruert krise. Full text in Research Archive
• Aronsen, Jan Magnus; Sørensen, Erik Øiolf; Daugstad, Karoline; Nacey, Susan Lee; Tafintseva, Valeria & Beyer, Audun [Show all 21 contributors for this article] (2022). Infrastruktur og tjenester for FAIR forskningsdata – Status og forslag til videre arbeid : Sluttrapport fra utredningsgruppen 15.3.2022. Full text in Research Archive Show summary

  Denne rapporten er en av flere leveranser fra utredningen «Felles infrastruktur og tjenester for FAIR forskningsdata», på oppdrag fra Digitaliseringsstyret for høyere utdanning og forskning. Rapporten publiseres på nettstedet openscience.no som er under utvikling som et samlingssted for informasjon om åpen forskning. Hovedredaktør for nettstedet er Sikt – Kunnskapssektorens tjenesteleverandør, og redaksjonsrådet har også medlemmer fra UHR og fra Forskningsrådet. Hovedmålgruppe for nettstedet er de norske forskningsinstitusjonene. Rapporten retter seg mot både forskningsinstitusjoner i universitets- og høyskolesektoren, helsesektoren og instituttsektoren, myndighetsorganer, finansiører og de enkelte forskningsmiljøene.

• Aronsen, Jan Magnus; Smedt, Koenraad De; Heggland, Ingrid; Dingsør, Liv; Tronstad, Stein & Pedersen, Ole Petter [Show all 8 contributors for this article] (2020). Hvordan få økt deling og gjenbruk av forskningsdata? Full text in Research Archive
• Rønning, Sissel Beate; Carlson, Cathrine Rein; Aronsen, Jan Magnus; Høst, Vibeke; Pisconti, Addolorate & Lunde, Marianne [Show all 11 contributors for this article] (2019). Extracellular Matrix remodeling and multiple signaling pathways are regulated by syndecan-4 during myogenesis. Full text in Research Archive
• Bratland-Sanda, Solfrid; Blikstad-Balas, Marte; Moor, Katrien De; Eriksen, Marianne Hem; Falkum, Ingrid Lossius & Holmen, Heidi [Show all 7 contributors for this article] (2018). Akademia må satse på undervisningskarrierer. Full text in Research Archive
• Aronsen, Jan Magnus & Jensenius, Alexander Refsum (2018). «Røvertidsskriftene» er bare toppen av isfjellet. Full text in Research Archive Show summary

  Staten betaler for ny kunnskap, gir den bort gratis, og kjøper den deretter tilbake av internasjonale forlag.

• Aronsen, Jan Magnus; Jensenius, Alexander Refsum; Emblem, Kyrre Eeg; Storeng, Katerini Tagmatarchi; Enberg, Katja & Knutsen, Carl Henrik [Show all 7 contributors for this article] (2017). Kvalitetsparadokset i den norske forskningspolitikken. Full text in Research Archive Show summary

  De fleste insentivene norske forskere opplever i sin hverdag, er preget av kortsiktige resultater og målstyring mot kvantitet heller enn kvalitet. Dette er et kvalitetsparadoks i norsk forskningspolitikk. skriver flere medlemmer i Akademiet for yngre forskere.

• Aronsen, Jan Magnus; Lind, Guro Elisabeth; Helland, Ingeborg Palm; Schomacker, Anders & Enberg, Katja (2017). Gode nyheter om unge forskeres karriereveier. Full text in Research Archive
• Rønning, Sissel Beate; Carlson, Cathrine Rein; Aronsen, Jan Magnus; Høst, Vibeke; Liland, Kristian Hovde & Stang, Espen [Show all 10 contributors for this article] (2017). Syndecan-4 is a skeletal muscle regenerator and is important for normal skeletal muscle fibre development. Full text in Research Archive
• Aronsen, Jan Magnus; Lind, Guro Elisabeth; Helland, Ingeborg Palm; Schomacker, Anders; Enberg, Katja & Hølleland, Herdis (2017). Karriereveier for økt forskningskvalitet. Full text in Research Archive
• Lipsett, David Bruce; Frisk, Michael; Aronsen, Jan Magnus; Sejersted, Ole M; Sjaastad, Ivar & Christensen, Geir Arve [Show all 7 contributors for this article] (2016). Sarcolemmal structure and function revert to an immature phenotype in failing cardiomyocytes. Full text in Research Archive
• Ruud, Marianne; Frisk, Michael; Aronsen, Jan Magnus; Dahl, Christen Peder; Jølle, Guro Five & Aakhus, Svend [Show all 15 contributors for this article] (2016). Mechanical load regulates cardiomyocyte t-tubular structure and Ca2+ homeostasis. Full text in Research Archive
• Marshall, Serena; Børstad, Mira Halvorsen; Skogestad, Jonas; Albert, Ingrid; Lothe, Gustav B & Espe, Emil Knut Stenersen [Show all 10 contributors for this article] (2016). SERCA2 activation is beneficial in chronic heart disease. Full text in Research Archive
• Skårdal, Kristine; Espe, Emil Knut Stenersen; Bendiksen, Bård Andre; Aronsen, Jan Magnus; Zhang, Lili & Sjaastad, Ivar (2016). Parametrizing active and passive diastolic function non-invasively using phase contrast MRI. Full text in Research Archive
• Lipsett, David Bruce; Frisk, Michael; Aronsen, Jan Magnus; Singh, Neha; Sejersted, Ole M & Sjaastad, Ivar [Show all 9 contributors for this article] (2016). BIN1 triggers t-tubule development in cardiomyocytes. Full text in Research Archive
• Kolstad, Terje R Selnes; Macquaide, Niall; Hake, Johan; Aronsen, Jan Magnus; Frisk, Michael & Sjaastad, Ivar [Show all 8 contributors for this article] (2016). Dispersion of ryanodine receptor clusters disrupts calcium sparks in failing cardiomyocyte. Full text in Research Archive
• Røe, Åsmund Treu; Ruud, Marianne; Espe, Emil Knut Stenersen; Aronsen, Jan Magnus; Sejersted, Ole M & Sjaastad, Ivar [Show all 7 contributors for this article] (2016). Elevated ventricular wall stress disrupts diastolic Calcium homeostasis of the cardiomyocyte. Full text in Research Archive
• Mohammadzadeh, Naiyereh; Engebretsen, Kristin; Lunde, Ida Gjervold; Sjaastad, Ivar; Strand, Mari Elen & Marstein, Henriette [Show all 14 contributors for this article] (2016). Lack of the extracellular matrix proteoglycan lumican leads to ventricular dilatation, attenuated hypertrophy and contractile dysfunction in response to pressure overload. Full text in Research Archive
• Norden, Einar Sjaastad; Bergo, Kaja Knudsen; Zhang, Lili; Aronsen, Jan Magnus; Hasic, Almira & Hussain, I. [Show all 8 contributors for this article] (2016). Anti-hypertrophic effects of LCZ696 in chronic cardiac pressure overload. Full text in Research Archive
• Aronsen, Jan Magnus; Skogestad, Jonas; Hougen, Karina; Lunde, Marianne; Lothe, Gustav B & Albert, Ingrid [Show all 13 contributors for this article] (2016). Physical coupling of PDE3A regulates SERCA2 activity in cardiomyocytes. Full text in Research Archive
• Albert, Ingrid; Skogestad, Jonas; Carlson, Cathrine Rein; Lunde, Marianne; Marshall, Serena & Lunde, Per Kristian [Show all 8 contributors for this article] (2016). Development of PDE3A-SERCA2 disruptor agents for SERCA2 activation. Full text in Research Archive
• Mohammadzadeh, Naiyereh; Engebretsen, Kristin V Thunheim; Lunde, Ida Gjervold; Sjaastad, Ivar; Strand, Mari Elen & Marstein, Henriette [Show all 14 contributors for this article] (2016). Lack of the extracellular matrix proteoglycan lumican leads to cardiac dysfunction in response to pressure overload. Full text in Research Archive
• Marstein, Henriette; Lunde, Per Kristian; Aronsen, Jan Magnus & Sjaastad, Ivar (2016). Inhibition of Alkbh7 regulates cardiac metabolism. Full text in Research Archive
• Aronsen, Jan Magnus; Singbrant, Sofie; Christensen, Geir Arve & Iversen, Per Ole (2016). Evidence for splenic stress-induced erythropoiesis in mice with post-infarction heart failure. Full text in Research Archive
• Rønning, Sissel Beate; Carlson, Cathrine Rein; Høst, Vibeke; Aronsen, Jan Magnus; Liland, Kristian Hovde & Stang, Espen [Show all 9 contributors for this article] (2016). Syndecan-4 is important for normal skeletal muscle fibre development. Full text in Research Archive
• Strand, Mari Elen; Aronsen, Jan Magnus; Skrbic, Biljana; Gelazauskaite, Monika; Sjaastad, Ivar & Christensen, Geir Arve [Show all 7 contributors for this article] (2016). The heparanase-syndecan-4 axis in the heart: upregulation in response to immune activation indicates a role in cardiac inflammation. Full text in Research Archive
• Kolstad, Terje R Selnes; Macquaide, Niall; Hake, Johan; Aronsen, Jan Magnus; Frisk, Michael & Sjaastad, Ivar [Show all 8 contributors for this article] (2016). Super-resolution imaging reveals dispersion of ryanodine receptor clusters during heart failure. Full text in Research Archive
• Skogestad, Jonas; Albert, Ingrid; Marshall, Serena; Børstad, Mira Halvorsen; Lothe, Gustav B & Sejersted, Ole M [Show all 8 contributors for this article] (2016). Phosphodiesterase 2 regulates Na+/K+-ATPase activity in adult cardiomyocytes. Full text in Research Archive
• Strand, Mari Elen; Aronsen, Jan Magnus; Skrbic, Biljana; Gelazaukaite, Monika; Sjaastad, Ivar & Christensen, Geir Arve [Show all 7 contributors for this article] (2016). The heparanase-syndecan-4 axis in the heart: upregulation in response to immune activation indicates a role in cardiac inflammation. Full text in Research Archive
• Ruud, Marianne; Frisk, Michael; Espe, Emil Knut Stenersen; Aronsen, Jan Magnus; Zhang, Lili & Norseng, Per Andreas [Show all 10 contributors for this article] (2016). Elevated ventricular wall stress disrupts cardiomyocyte t-tubular structure and Ca2+ homeostasis. Full text in Research Archive
• Tazmini, Kiarash; Frisk, Michael; Lipsett, David Bruce; Aronsen, Jan Magnus; Sjaastad, Ivar & Øie, Erik [Show all 7 contributors for this article] (2016). Pro-arrhythmic consequences of hypokalemia in atrial cardiomyocytes. Full text in Research Archive
• Frisk, Michael; Aronsen, Jan Magnus; Dahl, Christen Peder; Lunde, Ida Gjervold; Jølle, Guro Five & Almaas, Victor [Show all 13 contributors for this article] (2015). Maintained cardiomyocyte t-tubule structure and function in patients with non-dilated hypertrophy. Full text in Research Archive
• Mohammadzadeh, Naiyereh; Andenæs, Kine; Engebretsen, Kristin V.; Lunde, Ida Gjervold; Sjaastad, Ivar & Marstein, Henriette [Show all 12 contributors for this article] (2015). The role of lumican in Cardiac pressure overload. Full text in Research Archive
• Marshall, Serena; Aronsen, Jan Magnus; Skogestad, Jonas; Albert, Ingrid; Lothe, Gustav B & Lunde, Per Kristian [Show all 13 contributors for this article] (2015). Dual PDE3A coupling to AKAP18 and SERCA2 Controls SERCA2 Activity in adult cardiomyocytes. Full text in Research Archive
• Meier, Silja; Andressen, Kjetil Wessel; Aronsen, Jan Magnus; Sjaastad, Ivar; Skomedal, Tor & Osnes, Jan-Bjørn [Show all 9 contributors for this article] (2015). Enhancement of cAMP-mediated inotropic responses by CNP is regulated differently by PDE2 in normal and failing hearts. BMC Pharmacology and Toxicology. 16, p. A66–A66. doi: 10.1186/2050-6511-16-S1-A66. Full text in Research Archive
• Aronsen, Jan Magnus; Skogestad, Jonas; Hougen, Karina; Lunde, Marianne; Lothe, Gustav B & Albert, Ingrid [Show all 12 contributors for this article] (2015). Physical coupling between SERCA2 and PDE3A regulates SERCA2 activity in cardiomyocytes. Full text in Research Archive
• Espe, Emil Knut Stenersen; Aronsen, Jan Magnus; Skårdal, Kristine; Zhang, Lili & Sjaastad, Ivar (2015). Noninvasive detection of congestive heart failure in postinfarction rats. Full text in Research Archive
• Lothe, Gustav B; Marshall, Serena; Albert, Ingrid; Børstad, Mira Halvorsen; Skogestad, Jonas & Hougen, Karina [Show all 9 contributors for this article] (2015). Phosphodiesterase 1 regulates SERCA2 activity in adult cardiomyocytes. Full text in Research Archive
• Albert, Ingrid; Børstad, Mira Halvorsen; Carlson, Cathrine Rein; Calejo, Anna; Skogestad, Jonas & Lunde, Marianne [Show all 10 contributors for this article] (2015). Development of SERCA2 activating agents. Full text in Research Archive
• Tazmini, Kiarash; Frisk, Michael; Aronsen, Jan Magnus; Sjaastad, Ivar; Øie, Eric & Louch, William Edward (2015). Pro-arrhythmic consequences of hypokalemia in atrial cardiomyocytes. Full text in Research Archive
• Ruud, Marianne; Frisk, Michael; Norseng, Per Andreas; Røe, Åsmund Treu; Espe, Emil Knut Stenersen & Aronsen, Jan Magnus [Show all 10 contributors for this article] (2015). Regulation of cardiomyocyte t-tubule organization and density by ventricular wall stress. Biophysical Journal. ISSN 0006-3495. 108, p. 443a–443a. Full text in Research Archive
• Sadredini, Mani Nikoo; Danielsen, Tore Kristian; Aronsen, Jan Magnus; Manotheepan, Ravinea; Hougen, Karina & Sjaastad, Ivar [Show all 7 contributors for this article] (2015). Beta-adrenoreceptor stimulation reveals Ca2+ overload paradox in left ventricular cardiomyocytes from post-infarction rats with and without heart failure. Full text in Research Archive
• Aronsen, Jan Magnus; Smedt, Koenraad De; Heggland, Ingrid; Dingsør, Liv; Tronstad, Stein & Pedersen, Ole Petter [Show all 10 contributors for this article] (2021). Hvordan skal vi dele forskningsdata? Utredning og anbefalinger om lisensiering og tilgjengeliggjøring. Norges forskningsråd. ISSN 9788212039018. Full text in Research Archive
• Aronsen, Jan Magnus (2018). Molecular mediators of chronic heart disease. Universitetet i Oslo. ISSN 9788283772050. Full text in Research Archive

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