Podocytic PKC-Alpha Is Regulated in Murine and Human Diabetes and Mediates Nephrin Endocytosis

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Abstract
Microalbuminuria is an early lesion during the development of diabetic nephropathy. The loss of high molecular weight proteins in the urine is usually associated with decreased expression of slit diaphragm proteins. Nephrin, is the major component of the glomerular slit diaphragm and loss of nephrin has been well described in rodent models of experimental diabetes as well as in human diabetic nephropathy. In this manuscript we analyzed the role of PKC-alpha (PKCα) on endocytosis of nephrin in podocytes. We found that treatment of diabetic mice with a PKCα-inhibitor (GÖ6976) leads to preserved nephrin expression and reduced proteinuria. In vitro, we found that high glucose stimulation would induce PKCα protein expression in murine and human podocytes. We can demonstrate that PKCα mediates nephrin endocytosis in podocytes and that overexpression of PKCα leads to an augmented endocytosis response. After PKC-activation, we demonstrate an inducible association of PKCα, PICK1 and nephrin in podocytes. Moreover, we can demonstrate a strong induction of PKCα in podocytes of patients with diabetic nephropathy. We therefore conclude that activation of PKCα is a pathomechanistic key event during the development of diabetic nephropathy. PKCα is involved in reduction of nephrin surface expression and therefore PKCα inhibition might be a novel target molecule for anti-proteinuric therapy.