Description
Evidence for reduced expression of cyclin-G associated kinase (GAK) in glomeruli of chronic kidney disease patients was observed in the Nephroseq human database and was found to be associated with the decline in kidney function. To examine the role of GAK, a protein that functions to uncoat clathrin during endocytosis, we generated podocyte-specific Gak knockout mice (Gak KO) which developed progressive proteinuria and kidney failure with global glomerulosclerosis. We isolated glomeruli from the mutant mice to perform messenger RNA profiling and unearthed evidence for dysregulated podocyte calpain protease activity as an important contributor to this process. Treatment with calpain inhibitor III specifically inhibited calpain-1/-2 activities, mitigated the degree of proteinuria and glomerulosclerosis, and led to a striking increase in survival in the Gak KO mice. Podocyte-specific deletion of Capns1, essential for calpain-1 and calpain-2 activities, also improved proteinuria and glomerulosclerosis in Gak KO mice. Increased podocyte calpain activity mediated proteolysis of IkB resulted in increased NF-kBp65 induced Gadd45b expression in the Gak KO mice. Our results suggest that loss of podocyte associated Gak induces glomerular injury secondary to calcium dysregulation and aberrant calpain activation, which when inhibited, can provide a protective role.
Overall Design
The freshly glomeruli samples were isolated from the Control mice and Gak KO mice at 3 weeks of age for the microRNA analysis. Each sample contained 3 mice in order to get the sufficient glomeruli samples, and 2 independent experiments were analyzed and summarized.
Curator
xm_li