Testosterone enhances GLP-1 efficacy at the plasma membrane and endosomes to augment insulin secretion in male pancreatic β cells

Early studies showing binding of testosterone to a nuclear protein in prostate led to the establishment of a paradigm in which the androgen receptor (AR) is a nuclear ligand-activated transcription factor.1 We showed that, unlike in classical androgen target tissues, AR is localized outside the nucleus in pancreatic insulin-producing β-cells, where it signals in the presence of ligand.2 Activation of the β cell AR by the active metabolite of testosterone, dihydrotestosterone (DHT), enhances glucose-stimulated insulin secretion (GSIS) from cultured male mouse and human islets. We reported that DHT potentiates GSIS by amplifying the insulinotropic action of glucagon-like peptide-1 (GLP-1).2 Accordingly, when exposed to a western diet, male mice with conditional elimination of the AR in β-cells (βARKO) exhibit defective GSIS, leading to hypoinsulinemia and hyperglycemia.2 Here, we show that activation of the β cell AR amplifies the insulinotropic effect of islet-derived but not gut-derived GLP-1. In insulin-secreting INS1 cells expressing cAMP sensors, DHT selectively enhances the ability of GLP-1, but not that of glucose-dependent insulinotropic polypeptide (GIP) or glucagon, to produce cAMP and to potentiate GSIS. Notably, DHT enhances GLP-1 production of cAMP at the plasma membrane and endosomes. Accordingly, in male mouse and human islets, the insulinotropic effect of DHT is abolished following inhibition of the membrane and endosomal cAMP-dependent protein kinase A (PKA) and exchange protein activated by cAMP islet 2 (EPAC2) pathways. This study provides a novel paradigm in which membrane localization of a nuclear receptor allows interaction with and sensitization of a G protein-coupled receptor.