The regulator of G protein signaling RGS9 supports insulin secretion in male mouse islets

Objectives Regulators of G protein signaling (RGS) proteins terminate G protein-coupled receptor signaling and regulate multiple aspects of pancreatic islet function. Although RGS9 is highly enriched in human and rodent islets, its cellular localization and physiological role remain largely unknown. Here, we investigated the expression of Rgs9 in mouse islets and its contribution to insulin secretion. Methods Rgs9 expression was characterized by RNA in situ hybridization and fluorescence-activated cell sorting coupled with quantitative PCR. Rgs9 function was investigated by shRNA-mediated knockdown in wild-type and Dishevelled, Egl-10 and Pleckstrin (DEP) domain-deficient Rgs9 mutant (Rgs9ΔDEP/ΔDEP) mouse pseudo-islets. Results Rgs9 was detected throughout the endocrine pancreas but was enriched in β and δcells, with the Rgs9-1 isoform representing the predominant splice variant in mouse islets. Rgs9 knockdown in mouse pseudo-islets impaired glucose- and KCl-stimulated insulin secretion without affecting insulin content. In contrast, Rgs9ΔDEP/ΔDEP mouse islets failed to reproduce this phenotype. Further characterization of the mutant mice revealed persistent expression of Rgs9 transcripts, which when knocked down impaired both glucose- and KCl-stimulated insulin secretion. Conclusions These data indicate that RGS9 supports glucose-stimulated insulin secretion. Given that RGS9 acts exclusively on Gαi/o, our results further suggest that RGS9 in β cells dampens inhibitory signaling to promote insulin secretion. Finally, the Rgs9ΔDEP/ΔDEP mutant does not represent a complete loss-of-function in islets likely due to the retention of the GTPase-activating protein (GAP) activity in the absence of the DEP domain.