Deletion of the aquaporin-4 gene alters expression and phosphorylation of protective kinases in the mouse heart

Abstract

Aim. Aquaporins are channel-forming proteins highly permeable to water and some small molecular solutes. We have previously shown that aquaporin-4 knockout mice have increased tolerance to ischemia. However, the mechanism of cardioprotection was unclear. The aim of the current study was to investigate the effects of aquaporin-4 deletion on baseline expression and phosphorylation of some cardioprotective protein kinases. Methods. Proteins were extracted from hearts of aquaporin-4 knockout mice and littermate wild-type controls and analyzed with Western blot. Samples were taken from young (≤ 6 months of age), and old (≥ 1 year) mice. Results. Western blots showed three different isoforms of aquaporin-4 in wild types, likely representing M1, M23, and Mz. Total AMP-dependent kinase expression was decreased in aquaporin-4 knockout hearts by 18 ± 13% (p = 0.02), while the expression of Akt kinase, extracellular signal regulated kinase 1/2, protein kinase C-epsilon, mitogen-associated kinase P38 and C-Jun N-terminal kinase was unchanged. The phosphorylation of Akt kinase was reduced in hearts from knockout mice by 41 ± 16% (p = 0.01). No other alterations in phosphorylation were found. These effects were only detected in young mice. Conclusion. Deletion of the aquaporin-4 gene decreased AMP-dependent kinase expression and Akt kinase phosphorylation in the heart. These changes may influence energy metabolism and endogenous cardioprotection.

Key Words::

• Cardiac aquaporins
• protein kinases
• RISK pathway
• protein kinase C epsilon
• cardioprotection
• AMPK

Acknowledgements

This investigation was supported by Gjensidigestiftelsen, The Southeastern Regional Health Trust, The Jahre Foundation, The University of Oslo, and Oslo University Hospital, Ullevål, The Nansen Foundation, and the Norwegian Health Association. Lars Mariero was recipient of a medical student's scholarship from the University of Oslo and the Norwegian Research Council. We are grateful for the generous gift of AQP4 KO mice from Ole Petter Ottersen and Torgeir Holen, Centre of Molecular Biology and Neuroscience, University of Oslo.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.