Abstract

Objective. Nephrin, an immunoglobulin-like-protein essential for the function of the glomerular podocyte and regulated in diabetic nephropathy, is also expressed in pancreatic β-cells, where its function remains unknown. The aim of this study was to investigate whether diabetes modulates nephrin expression in human pancreatic islets and to explore the role of nephrin in β-cell function.

Research Design and Methods. Nephrin expression in human pancreas and in MIN6 insulinoma cells was studied by Western-Blot, PCR, confocal microscopy, subcellular fractionation and immunogold-labeling. Islets from diabetic (n=5) and non-diabetic (n=7) patients were compared. Stable transfection and siRNA knockdown in MIN-6 cells/human islets were utilized to study nephrin function in vitro and in vivo after transplantation in diabetic immunodeficient mice. Live imaging of GFP-nephrin transfected cells was utilized to study nephrin endocytosis.

Results. Nephrin was found at the plasma membrane and on insulin vesicles. Nephrin expression was decreased in islets from diabetic patients when compared to non-diabetic controls. Nephrin transfection in MIN-6 cells/pseudoislets resulted in higher glucose-stimulated insulin release in vitro and in vivo after transplantation into immunodeficient diabetic mice. Nephrin gene silencing abolished stimulated insulin release. Confocal imaging of GFP-nephrin transfected cells revealed nephrin endocytosis upon glucose stimulation. Actin stabilization prevented nephrin trafficking as well as nephrin positive effect on insulin release.

Conclusions. Our data suggest that nephrin is an active component of insulin vesicle machinery that may affect vesicle-actin interaction and mobilization to the plasma membrane. Development of drugs targeting nephrin may represent a novel approach to treat diabetes.