Metformin inhibits hepatic gluconeogenesis in mice independently of the LKB1/AMPK pathway via a decrease in hepatic energy state
Marc Foretz, … , Fabrizio Andreelli, Benoit Viollet
Marc Foretz, … , Fabrizio Andreelli, Benoit Viollet
Published June 23, 2010
Citation Information: J Clin Invest. 2010;120(7):2355-2369. https://doi.org/10.1172/JCI40671.
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Research Article

Metformin inhibits hepatic gluconeogenesis in mice independently of the LKB1/AMPK pathway via a decrease in hepatic energy state

Abstract

Metformin is widely used to treat hyperglycemia in individuals with type 2 diabetes. Recently the LKB1/AMP-activated protein kinase (LKB1/AMPK) pathway was proposed to mediate the action of metformin on hepatic gluconeogenesis. However, the molecular mechanism by which this pathway operates had remained elusive. Surprisingly, here we have found that in mice lacking AMPK in the liver, blood glucose levels were comparable to those in wild-type mice, and the hypoglycemic effect of metformin was maintained. Hepatocytes lacking AMPK displayed normal glucose production and gluconeogenic gene expression compared with wild-type hepatocytes. In contrast, gluconeogenesis was upregulated in LKB1-deficient hepatocytes. Metformin decreased expression of the gene encoding the catalytic subunit of glucose-6-phosphatase (G6Pase), while cytosolic phosphoenolpyruvate carboxykinase (Pepck) gene expression was unaffected in wild-type, AMPK-deficient, and LKB1-deficient hepatocytes. Surprisingly, metformin-induced inhibition of glucose production was amplified in both AMPK- and LKB1-deficient compared with wild-type hepatocytes. This inhibition correlated in a dose-dependent manner with a reduction in intracellular ATP content, which is crucial for glucose production. Moreover, metformin-induced inhibition of glucose production was preserved under forced expression of gluconeogenic genes through PPARγ coactivator 1α (PGC-1α) overexpression, indicating that metformin suppresses gluconeogenesis via a transcription-independent process. In conclusion, we demonstrate that metformin inhibits hepatic gluconeogenesis in an LKB1- and AMPK-independent manner via a decrease in hepatic energy state.

Authors

Marc Foretz, Sophie Hébrard, Jocelyne Leclerc, Elham Zarrinpashneh, Maud Soty, Gilles Mithieux, Kei Sakamoto, Fabrizio Andreelli, Benoit Viollet

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Figure 7

Effects of metformin on AMPK activation in WT and Lkb1-KO hepatocytes.

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Effects of metformin on AMPK activation in WT and Lkb1-KO hepatocytes. ...
After attachment, WT and LKB1-deficient primary hepatocytes were cultured for 16 hours in M199 medium containing 100 nM dex. Hepatocytes were then incubated in glucose-free DMEM containing lactate/pyruvate (10:1 mM) and 100 nM dex alone or with 100 μM Bt2-cAMP and with or without 0.25, 0.5, 1, or 2 mM metformin. After 8 hours, cells were harvested for Western blot analysis and measurement of LKB1 activity. (A) The level of LKB1 protein was assessed by immunoblot analysis using anti-LKB1 antibodies. β-Actin was immunoblotted as a loading control. (B) LKB1 activity was assessed following its immunoprecipitation and assayed with the LKBtide peptide. Assays were performed on hepatocyte extracts from 3 independent experiments. (C) Immunoblots were performed against phospho-AMPKα (Thr172), AMPKα, phospho-ACC (Ser79), ACC, CRTC2, G6Pase, and PEPCK. Blots are representative of 3 independent experiments.