Gαo Represses Insulin Secretion by Reducing Vesicular Docking in Pancreatic β-Cells

OBJECTIVE Pertussis toxin uncoupling-based studies have shown that Gal and G alpha o can inhibit insulin secretion in pancreatic beta-cells. Yet it is unclear whether G alpha i and G alpha o operate through identical mechanisms and how these G-protein-mediated signals inhibit insulin secretion in vivo. Our objective is to examine whether/how G alpha o regulates islet development and insulin secretion in beta-cells. RESEARCH DESIGN AND METHODS Immunoassays were used to analyze the G alpha o expression in mouse pancreatic cells. G alpha o was specifically inactivated in pancreatic progenitor cells by pancreatic cell-specific gene deletion. Hormone expression and insulin secretion in response to different stimuli were assayed in vivo and in vitro. Electron microscope and total internal reflection fluorescence-based assays were used to evaluate how G alpha o regulates insulin vesicle docking and secretion in response to glucose stimulation. RESULTS Islet cells differentiate properly in G alpha o(-/-) mutant mice. G alpha o inactivation significantly enhances insulin secretion both in vivo and in isolation. G alpha o nullizygous beta-cells contain an increased number of insulin granules docked on the cell plasma membrane, although the total number of vesicles per beta-cell remains unchanged. CONCLUSIONS-G alpha o is not required for endocrine islet cell differentiation, but it regulates the number of insulin vesicles docked on the beta-cell membrane. Diabetes 59:2522-2529, 2010