Mina Martine Frey

• Frey, Mina Martine; Izadpanah, Negar Zohoorian; Skauli, Nadia; Ottersen, Ole Petter & Amiry-Moghaddam, Mahmood (2025). Are diurnal variations in glymphatic clearance driven by circadian regulation of Aquaporin-4 expression? Fluids and Barriers of the CNS. 22(1), p. 1–11. doi: 10.1186/s12987-025-00676-3. Full text in Research Archive Show summary

  Aquaporin-4 (AQP4) is a key astrocytic water channel protein predominantly localized to perivascular endfeet, where it is believed to play a crucial role in brain fluid homeostasis and glymphatic waste clearance. Previous studies have suggested that the perivascular expression of AQP4 is regulated by circadian rhythms and peaks during the sleep phase, potentially influencing glymphatic function. However, direct evidence supporting circadian regulation of AQP4 remains limited. Here, we investigated AQP4 expression and perivascular distribution in the hippocampus and neocortex of mice at mid rest (day) and mid active phase (night). We employed quantitative immunogold electron microscopy (EM), in addition to immunofluorescence confocal microscopy, Western blotting, and qPCR to assess AQP4 localization and expression at the mRNA and protein levels. Our findings revealed no significant differences in AQP4 perivascular localization, total protein levels, or mRNA expression between day and night. Furthermore, the expression of key dystrophin-associated protein complex (DAPC) components, which anchor AQP4 to astrocytic endfeet, also remained largely unchanged. These results challenge the hypothesis that AQP4 localization is regulated by circadian rhythms and suggest that previously reported circadian differences in glymphatic function are mediated by factors other than AQP4 expression. This study highlights the need for further research into the mechanisms governing glymphatic function.

• Bojarskaite, Laura; Nafari, Sahar; Ravnanger, Anne Katrine; Frey, Mina Martine; Skauli, Nadia & Åbjørsbråten, Knut Sindre [Show all 13 contributors for this article] (2024). Role of aquaporin-4 polarization in extracellular solute clearance. Fluids and Barriers of the CNS. 21(1). doi: 10.1186/s12987-024-00527-7. Full text in Research Archive Show summary

  Waste from the brain has been shown to be cleared via the perivascular spaces through the so-called glymphatic system. According to this model the cerebrospinal fluid (CSF) enters the brain in perivascular spaces of arteries, crosses the astrocyte endfoot layer, flows through the parenchyma collecting waste that is subsequently drained along veins. Glymphatic clearance is dependent on astrocytic aquaporin-4 (AQP4) water channels that are highly enriched in the endfeet. Even though the polarized expression of AQP4 in endfeet is thought to be of crucial importance for glymphatic CSF influx, its role in extracellular solute clearance has only been evaluated using non-quantitative fluorescence measurements. Here we have quantitatively evaluated clearance of intrastriatally infused small and large radioactively labeled solutes in mice lacking AQP4 (Aqp4–/–) or lacking the endfoot pool of AQP4 (Snta1–/–). We confirm that Aqp4–/– mice show reduced clearance of both small and large extracellular solutes. Moreover, we find that the Snta1–/– mice have reduced clearance only for the 500 kDa [3H]dextran, but not 0.18 kDa [3H]mannitol suggesting that polarization of AQP4 to the endfeet is primarily important for clearance of large, but not small molecules. Lastly, we observed that clearance of 500 kDa [3H]dextran increased with age in adult mice. Based on our quantitative measurements, we confirm that presence of AQP4 is important for clearance of extracellular solutes, while the perivascular AQP4 localization seems to have a greater impact on clearance of large versus small molecules.

• Zahl, Soulmaz; Skauli, Nadia; Stahl, Katja; Prydz, Agnete; Frey, Mina Martine & Dissen, Erik [Show all 8 contributors for this article] (2023). Aquaporin-9 in the Brain Inflammatory Response: Evidence from Mice Injected with the Parkinsonogenic Toxin MPP⁺. Biomolecules. 13(4). doi: 10.3390/biom13040588. Full text in Research Archive Show summary

  More than 20 years have passed since the first demonstration of Aquaporin-9 (AQP9) in the brain. Yet its precise localization and function in brain tissue remain unresolved. In peripheral tissues, AQP9 is expressed in leukocytes where it is involved in systemic inflammation processes. In this study, we hypothesized that AQP9 plays a proinflammatory role in the brain, analogous to its role in the periphery. We also explored whether Aqp9 is expressed in microglial cells, which would be supportive of this hypothesis. Our results show that targeted deletion of Aqp9 significantly suppressed the inflammatory response to the parkinsonian toxin 1-methyl-4-phenylpyridinium (MPP+). This toxin induces a strong inflammatory response in brain. After intrastriatal injections of MPP+, the increase in transcript levels of proinflammatory genes was less pronounced in AQP9−/− mice compared with wild-type controls. Further, in isolated cell subsets, validated by flow cytometry we demonstrated that Aqp9 transcripts are expressed in microglial cells, albeit at lower concentrations than in astrocytes. The present analysis provides novel insight into the role of AQP9 in the brain and opens new avenues for research in the field of neuroinflammation and chronic neurodegenerative disease.

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