GRK2 Participates in Islet Function and Glucose-Stimulated Insulin Secretory Responses

Insulin deficiency is central to diabetes and diabetes-related cardiac dysfunction. GPCRs are known modulators of insulin secretion and a main pharmacological target in various tissues, including the heart. GPCR kinase 2 (GRK2) phosphorylates activated GPCRs, targeting receptors for recycling or degradation. Notably, we and others have shown that GRK2 can also localize to the cardiac mitochondria where it participates in substrate utilization, particularly in response to cellular stress. GRK2 is downregulated in the pancreas of diabetogenic mice, and we have shown that pancreatic loss of GRK2 impairs insulin secretion in normal and high fat diet. Mice with pancreatic-specific GRK2 KO showed glucose intolerance (AUC WT 8691 vs. KO 14766 mg/dl*min, n=22/group, p<.05) due to significant decrease in insulin secretion following glucose administration (after 15 minutes WT 2.35 vs. KO 1.616 ng/ml, N=16-19/group, P<.0001) without changes in islet size or cell distribution. Using a model of high fat diet, we observed an impairment in glucose-stimulated insulin release in pancreatic GRK2 KO animals when compared to control animals without significant changes in fasting insulin secretion or insulin sensitivity. To further dissect the role of islet GRK2 in α- or β-cells, we have constructed two novel mouse models of inducible cell type-specific GRK2 KO. Our preliminary studies reveal that β-cell GRK2 deficient animals are prone to glucose intolerance and decreased glucose-induced insulin secretion when exposed to high fat high sucrose diet. This suggests that GRK2 plays a role in islet adaptation to metabolic challenge. Further studies will delineate the mechanistic role of GRK2 in mediating metabolism and calcium influx in β-cells regulating insulin secretion, and subsequently the impact to the heart in the presence or absence of TAC. Our studies will provide new GRK2 mechanistic insight that could be explored as new pharmacological strategies to delay diabetes disease progression. Disclosure J. W. Snyder: None. S. K. Montgomery: None. N. M. Doliba: None. J. Roman: None. Y. Tian: None. P. Y. Sato: None. W. L. Holland: None. R. Choi: None. Funding National Institutes of Health (1R56HL149887) ; University of Pennsylvania Diabetes Research Center Pilot and Feasibility Grant (P30-DK019525) ; American Heart Association Scientist Development Grant (17SDG33660407)