ATP-sensitive potassium (KATP) channels in pancreatic b-cells couple blood glucose concentrations to membrane excitability thus control insulin secretion. The b-cell KATP channel is a complex of four sulfonylurea receptor 1 and four inwardly rectifying potassium channel Kir6.2 subunits. Mutations in the channel genes that lead to loss of channel function have been known for quite some time to underlie the insulin secretion disease congenital hyperinsulinism. More recently, gain-of-function channel mutations have been discovered as a major cause of neonatal diabetes. The long-term goal of our research is to understand regulation of b-cell KATP channels, how this regulation is perturbed by channel mutations to cause disease and how we may manipulate channel regulation to combat insulin secretion disease. Work supported by this grant to date has identified several novel mechanisms by which channel mutations cause abnormal insulin secretion. Among these, defective channel biogenesis and trafficking that results in reduced surface channel expression levels is the most prevalent in mutations associated with congenital hyperinsulinism. Interestingly, our recent work found many neonatal diabetes mutations also affect channel biogenesis and surface expression. Of significance, we have identified a group of mutations whose trafficking defects could be corrected pharmacologically by sulfonylureas, drugs commonly used to treat type II diabetes. These findings underscore the importance of channel biogenesis and trafficking, which in turn control surface channel expression, in b-cell function and the potential of manipulating these cellular events to treat insulin secretion disease. In this renewal application, we will build up on these findings and further investigate the biogenesis and trafficking regulation of KATP channels in b-cells. Using a combination of molecular, biochemical, cell biological and electrophysiological approaches we will (1) delineate the biogenesis and trafficking pathways of KATP channels in b-cells, (2) determine how channel mutations alter channel expression and gating to cause b-cell dysfunction and disease, and (3) elucidate the mechanism by which sulfonylureas rescue channel biogenesis/trafficking defects and assess the utility of sulfonylureas in restoring mutant channel expression and function in b-cells. The proposed studies will better our understanding of how regulation of KATP channel trafficking contributes to regulation of insulin secretion. This information is critical for our long-term goal of integrating all aspects of KATP channel regulation to fully understand the role of these channels in b-cell function under physiological and pathological conditions.
Abnormal insulin secretion results in life-threatening diseases such as diabetes and hyperinsulinism. We propose to study how mutations in the KATP channel, a key molecule involved in regulation of insulin secretion, affect channel properties to cause disease and how we can correct channel defects caused by mutations. These studies are highly relevant to human health and may lead to novel therapeutic strategies for these devastating diseases.
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