WNK1 activity modulates biophysical properties of glomerular podocytes through regulation of non-muscle myosin II activation

Podocytes are terminally differentiated arborized cells that adhere to and cover glomerular capillaries. Extensive interdigitation of cell extensions with neighboring podocytes structurally form the slit diaphragm, the sieve that retains proteins in the blood while allowing filtrate through for excretion. A common feature of disease progression in chronic kidney disease is loss of podocyte structural complexity and adhesion strength, and resultant elevated proteinuria from filtration failure. Various models of cell injury have reduced capacity to spread and generate traction force. Cell structure and adhesive properties require concerted activities of the actomyosin and focal adhesions, which are dynamically regulatable components of the cell cytoskeleton that are responsive to matrix stiffness. Non-muscle myosin IIs (NMIIs) require RLC phosphorylation-regulated myosin head conformational changes for actin-activated ATPase reactions. Given the importance of myosins in determining cell structure and function, information on basic fundamental properties of podocytes at the level of actomyosin regulation is necessary to understand dysregulation involved in podocyte injury. We previously reported that with-no-lysine (WNK)1 kinase is expressed in podocytes and that chemical inhibition of WNK activity affects mouse glomerular stiffness and podocyte foot process structure, directly causing a reduction in slit diaphragm density. We determined that WNK1 activity and expression contributes to podocyte membrane blebbing, lamellipodia formation and cell migration, processes that all require NMII activity. Herein, we report differential expression and distribution of NMIIA and NMIIB in healthy and diseased podocytes, and evidence of a WNK1-NMIIB signaling axis in glomerular podocytes that contributes to regulation of cell motility and morphology. Collectively, the results support understanding of a potential targetable mechanism necessary for foot process formation and maintenance.