CD38-mediated Ca 2+ signaling contributes to glucagon-induced hepatic gluconeogenesis

Abstract

CD38 is a multifunctional enzyme for the synthesis of Ca 2+ second messengers. Glucagon promotes hepatic glucose production through Ca 2+ signaling in the fasting condition. In this study, we investigated the role of CD38 in the glucagon signaling of hepatocytes. Here, we show that glucagon induces cyclic ADP-ribose (cADPR) production and sustained Ca 2+ increases via CD38 in hepatocytes. 8-Br-cADPR, an antagonistic cADPR analog, completely blocked glucagon-induced Ca 2+ increases and phosphorylation of cAMP response element-binding protein (CREB). Moreover, glucagon-induced sustained Ca 2+ signals and translocation of CREB-regulated transcription coactivator 2 to the nucleus were absent and glucagon-induced glucose production and expression of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (Pck1) are remarkably reduced in hepatocytes from CD38 -/- mice. Furthermore, in the fasting condition, CD38 -/- mice have decreased blood glucose and hepatic expression of G6Pase and Pck1 compared to wild type mice. Our data suggest that CD38/cADPR-mediated Ca 2+ signals play a key role in glucagon-induced gluconeogenesis in hepatocytes, and that the signal pathway has significant clinical implications in metabolic diseases, including type 2 diabetes.