Role of GPR40 in the regulation of insulin secretion

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DESCRIPTION (provided by applicant): Fatty acids acutely stimulate insulin secretion, but chronically impair pancreatic beta-cell function, a phenomenon likely to play a role in the pathogenesis of type 2 diabetes mellitus. Recently, a G-protein-coupled receptor specifically expressed on the surface of beta cells has been proposed as a long-chain fatty acid receptor. This challenges the current dogma that the effects of fatty acids on insulin secretion are mediated by their transmembrane transport and intracellular metabolism. The overall objective of the work described in this proposal is to define the role of the G-protein coupled receptor GPR40 in pancreatic beta-cell function. We have obtained preliminary data showing that gpr40 -/- mice develop glucose intolerance, and that islets isolated from these mice have defective fatty-acid potentiation of insulin secretion. Based on these preliminary findings, our hypothesis is that GPR40 plays an essential role in the regulation of insulin secretion by long-chain fatty acids. Specific aim 1 is to assess whether targeted deletion of gpr40 affects glucose homeostasis and insulin secretion in mice and precipitates the onset of diabetes upon high-fat feeding. We hypothesize that the lack of GPR40 will impair glucose homeostasis in vivo. Our preliminary findings support this hypothesis, but need to be further substantiated by measuring insulin secretion in response to various secretagogues as well as insulin sensitivity in vivo at different ages. We further hypothesize that the absence of GPR40 will precipitate the onset of diabetes in the context of high-fat diet-induced insulin resistance. Specific aim 2 is to determine whether loss of function of GPR40 impairs fuel metabolism and insulin secretion in isolated mouse islets. We hypothesize that islets isolated from gpr40 KO mice will have defective insulin secretion in response to FA. Our preliminary data showing impairment of FA-induced insulin release support this hypothesis, but need to be further substantiated by measuring insulin secretion in response to a variety of nutrient and non-nutrient stimuli and performing a comprehensive assessment of glucose and FA metabolism in islets from gpr40 -/- mice. As an alternative approach, we will knock down GPR40 expression in isolated adult mouse islets by RNA silencing using adenoviral technology.