Glucagon Receptor Signaling Is Essential for Control of Murine Hepatocyte Survival

Background & AimsGlucagon action in the liver is essential for control of glucose homeostasis and the counterregulatory response to hypoglycemia. Because receptors for the related peptides glucagon-like peptide-1 and glucagon-like peptide-2 regulate β-cell and enterocyte apoptosis, respectively, we examined whether glucagon receptor (Gcgr) signaling modulates hepatocyte survival.MethodsThe importance of the Gcgr for hepatocyte cell survival was examined using Gcgr+/+ and Gcgr−/− mice in vivo, and murine hepatocyte cultures in vitro.ResultsGcgr−/− mice showed enhanced susceptibility to experimental liver injury induced by either Fas Ligord activation or a methionine- and choline-deficient diet. Restoration of hepatic Gcgr expression in Gcgr−/− mice attenuated the development of hepatocellular injury. Furthermore, exogenous glucagon administration reduced Jo2-induced apoptosis in wild-type mice and decreased caspase activation in fibroblasts expressing a heterologous Gcgr and in primary murine hepatocyte cultures. The anti-apoptotic actions of glucagon were independent of protein kinase A, phosphatioylinositol-3K, and mitogen-activated protein kinase, and were mimicked by the exchange protein directly activated by the cyclic AMP agonist 8-(4-chloro-phenylthio)-2′-O-methyladerosine-3′, 5′-cyclic monophosphate-cAMP.ConclusionsThese findings extend the essential actions of the Gcgr beyond the metabolic control of glucose homeostasis to encompass the regulation of hepatocyte survival.