Metformin Inhibits Hepatic Gluconeogenesis Through AMP-Activated Protein Kinase–Dependent Regulation of the Orphan Nuclear Receptor SHP

Abstract

OBJECTIVE—Metformin is an antidiabetic drug commonly used to treat type 2 diabetes. The aim of the study was to determine whether metformin regulates hepatic gluconeogenesis through the orphan nuclear receptor small heterodimer partner (SHP; NR0B2). RESEARCH DESIGN AND METHODS—We assessed the regulation of hepatic SHP gene expression by Northern blot analysis with metformin and adenovirus containing a constitutive active form of AMP-activated protein kinase (AMPK) (Ad-AMPK) and evaluated SHP, PEPCK, and G6Pase promoter activities via transient transfection assays in hepatocytes. Knockdown of SHP using siRNA SHP was conducted to characterize the metformininduced inhibition of hepatic gluconeogenic gene expression in hepatocytes, and metformin– and adenovirus SHP (Ad-SHP)– mediated hepatic glucose production was measured in B6- Lepob/ob mice. RESULTS—Hepatic SHP gene expression was induced by metformin, 5-aminoimidazole-4-carboxamide-1- -D-ribofuranoside (AICAR), and Ad-AMPK. Metformin-induced SHP gene expression was abolished by adenovirus containing the dominant negative form of AMPK (Ad-DN-AMPK), as well as by compound C. Metformin inhibited hepatocyte nuclear factor-4 – or FoxA2- mediated promoter activity of PEPCK and G6Pase, and the inhibition was blocked with siRNA SHP. Additionally, SHP knockdown by adenovirus containing siRNA SHP inhibited metformin- mediated repression of cAMP/dexamethasone-induced hepatic gluconeogenic gene expression. Furthermore, oral administration of metformin increased SHP mRNA levels in B6- Lepob/ob mice. Overexpression of SHP by Ad-SHP decreased blood glucose levels and hepatic gluconeogenic gene expression in B6-Lepob/ob mice. CONCLUSIONS—We have concluded that metformin inhibits hepatic gluconeogenesis through AMPK-dependent regulation of SHP. Diabetes 57:306–314, 2008