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

Background: 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. Methodology/Principal Findings: In this manuscript we analyzed the role of PKC-alpha (PKC alpha) on endocytosis of nephrin in podocytes. We found that treatment of diabetic mice with a PKC alpha-inhibitor (GO6976) leads to preserved nephrin expression and reduced proteinuria. In vitro, we found that high glucose stimulation would induce PKC alpha protein expression in murine and human podocytes. We can demonstrate that PKC alpha mediates nephrin endocytosis in podocytes and that overexpression of PKC alpha leads to an augmented endocytosis response. After PKC-activation, we demonstrate an inducible association of PKC alpha, PICK1 and nephrin in podocytes. Moreover, we can demonstrate a strong induction of PKC alpha in podocytes of patients with diabetic nephropathy. Conclusions/Significance: We therefore conclude that activation of PKC alpha is a pathomechanistic key event during the development of diabetic nephropathy. PKC alpha is involved in reduction of nephrin surface expression and therefore PKC alpha inhibition might be a novel target molecule for anti-proteinuric therapy.