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

Metformin, a small molecule antihyperglycaemic agent, is well-known as an AMP-activated protein kinase (AMPK) activator and protects against cardiac fibrosis. However, the underlying mechanisms remain elusive. Transforming growth factor-β1 (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 subcutaneously injected 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. Bioinformatics analysis 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 AMPKα2-/- mice. As the consequence, metformin inhibited AngII-induced TGFβ1 production and cardiac fibrosis in wild-type mice but not AMPKα2-/- mice. Conclusions and Implications HNF4α mediated AngII-induced TGFβ1 transcription and cardiac fibrosis. Metformin inhibited 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.