Metformin attenuates angiotensin II‐induced TGFβ1 expression by targeting hepatocyte nuclear factor‐4‐α

Background and Purpose Metformin, a small molecule, antihyperglycaemic agent, is a well‐known activator of AMP‐activated protein kinase (AMPK) and protects against cardiac fibrosis. However, the underlying mechanisms remain elusive. TGFβ1 is a key cytokine mediating cardiac fibrosis. Here, we investigated the effects of metformin on TGFβ1 production induced by angiotensin II (AngII) and the underlying mechanisms. Experimental Approach Wild‐type and AMPKα2 −/− C57BL/6 mice were injected s.c. with metformin or saline and infused with AngII (3 mg·kg −1 ·day −1 ) for 7 days. Adult mouse cardiac fibroblasts (CFs) were isolated for in vitro experiments. Key Results In CFs, metformin inhibited AngII‐induced TGFβ1 expression via AMPK activation. Analysis using bioinformatics predicted a potential hepatocyte nuclear factor 4α (HNF4α)‐binding site in the promoter region of the Tgfb1 gene. Overexpressing HNF4α increased TGFβ1 expression in CFs. HNF4α siRNA attenuated AngII‐induced TGFβ1 production and cardiac fibrosis in vitro and in vivo . Metformin inhibited the AngII‐induced increases in HNF4α protein expression and binding to the Tgfb1 promoter in CFs. In vivo , metformin blocked the AngII‐induced increase in cardiac HNF4α protein levels in wild‐type mice but not in AMPKα2 −/− mice. Consequently, metformin inhibited AngII‐induced TGFβ1 production and cardiac fibrosis in wild‐type mice but not in AMPKα2 −/− mice. Conclusions and Implications HNF4α mediates AngII‐induced TGFβ1 transcription and cardiac fibrosis. Metformin inhibits AngII‐induced HNF4α expression via AMPK activation, thus decreasing TGFβ1 transcription and cardiac fibrosis. These findings reveal a novel antifibrotic mechanism of action of metformin and identify HNF4α as a new potential therapeutic target for cardiac fibrosis. Linked Articles This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc