Nephrin is an immunoglobulin-like protein with important structural and signaling properties in the glomerular podocyte. Nephrin expression has been recently reported in the pancreas where its function remains unknown. Recent data suggest a role for nephrin in vesicle trafficking. Our preliminary data with insulinoma cells overexpressing nephrin suggest a role for nephrin in insulin secretion. We could also show that nephrin co-localizes with an important molecule involved in insulin exocytosis in beta cells, i.e., vescicle associated membrane protein (VAMP)-2. The goal of this application is to understand the role of nephrin in the regulation of constitutive and glucose stimulated insulin secretion by pancreatic beta cells. We hypothesize that, upon glucose stimulation, nephrin contributes to insulin vesicle granules'exocytosis. To this aim, we will manipulate nephrin expression by shRNAmir technology in insulinoma cells and whole islets. We will further investigate the functional and biochemical interaction of nephrin with VAMP-2 in beta cells, and the relationship between such interaction and insulin secretion. Upon glucose stimulation, the activity of several GTPases facilitates insulin secretion: among them, dynamin has an important role in both podocytes and beta cell structural and functional integrity. Thus, we hypothesize that glucose stimulated dynamin activity is the driving force that allows nephrin to recruit more immature insulin vesicles to the plasma membrane. The short-term objectives of this grant proposal are to allow the applicant to understand how molecules that are relevant to podocyte function in diabetes may also affect pancreatic beta cell function. The outcome of the proposed research may allow the identification of a common pathogenetic pathway linking diabetes and diabetic nephropathy, and may lead to the development of a new cure for diabetes. This proposal will allow the applicant to receive training for the study of beta cell physiology through the utilization of novel techniques for beta cell imaging in vivo, study of calcium currents, insulin production and beta cell signal transduction.
The specific aims and experimental design of the proposal will support the development of her career as an independent investigator. This project fits well into the applicant's long-term goal to pursue an academic career focused on diabetes and aimed at the development of new drugs for the cure of diabetes and its complications. The environment of the Diabetes Research Institute is unique due its leadership role in the field of islet cell biology and transplantation, and because it offers the applicant the possibility to interact with key faculty members that will constantly provide intellectual and technical support.
The proposed research is relevant because it investigates how molecules that are very important for the functional integrity of the renal filtration barrier may play a role in insulin secreting cells of the pancreas. The proposed research may lead to: 1) the identification of a common pathogenetic pathway in diabetes and one of its major complication, i.e. diabetic nephropathy;2) the discovery of novel therapeutic targets for the cure of diabetes.
