Uncovering Two Novel Diabetes Drug Targets in the IDG

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Project Summary/Abstract Nearly 10% of the world has diabetes and this number is projected to increase. Type 2 diabetes occurs when beta cells fail to produce sufficient insulin in the face of insulin resistance. Current therapies are inadequate and many patients eventually become insulin dependent. Though we now have many forms of short and long acting insulins, insulin still has a small therapeutic window with a high chance of hyperglycemia and hypoglycemia with just slight errors in dosing. Therefore, new therapies are needed. Our long term goal is to find new therapeutic targets in the pancreatic beta cell to improve overall function and survival. In this R03, we propose to study beta-cell specific knockout mice of the two IDG-eligible genes. One is an endoplasmic reticulum (ER) resident protein that has been linked to ER stress. The second is a GPCR. Notably, both ER stress and GPCRs have been fertile grounds for development of diabetes drugs so these studies could have future therapeutic relevance. We hypothesize that loss of the ER protein will trigger ER stress in the pancreatic beta cell, resulting in beta cell death, while loss of the GPCR in beta cells will result in defective glucose stimulated insulin secretion (GSIS) due to reduced Gq signaling. Aim 1: Characterize the glucose homeostasis of a beta cell-specific knockout mouse of this ER resident protein with a focus on the unfolded protein response. Because of a potential role in ER stress in other tissues, we hypothesize that loss of this gene in the beta cell will result in ER stress and beta cell death, resulting in diabetes. We will perform glucose tolerance testing of these mice with concomitant measurement of basal and stimulated plasma insulin levels. We will study insulin secretion by islet perifusion. We will measure beta cell mass using a novel digital PCR assay and beta cell death using immunostaining. Finally, we will measure markers of the unfolded protein response. Aim 2: Characterize the glucose homeostasis of a beta cell-specific GPCR knockout mouse with a focus on insulin secretion. Given the Gq coupling of this GPCR and the known role of Gq in insulin secretion, we hypothesize the major defect in these beta cell specific knockouts will be in insulin secretion. We will also ask if a natural ligand of this GPCR, which appears to be normally expressed in the islet, can stimulate insulin secretion. The expected outcomes of this R03 proposal will be the identification of two new targets for diabetes therapeutics aimed at improving pancreatic beta cell function. This grant will also allow us to develop a pipeline to study additional IDG genes in vivo in the beta cell as the collection of IDG knockout mice expands.