Metformin attenuates cardiac fibrosis by inhibiting the TGFβ1–Smad3 signalling pathway

AIMS: The mechanism of the cardioprotective action of metformin is incompletely understood. We determined the role of metformin in cardiac fibrosis and investigated the mechanism. METHODS AND RESULTS: Ten-week-old male mice (C57BL/6) were subjected to left ventricular pressure overload by transverse aortic constriction. Mice received metformin (200 mg/kg/day) or normal saline for 6 weeks. Metformin inhibited cardiac fibrosis (fibrosis area/total heart area: 0.6 +/- 0.3 vs. 3.6 +/- 0.9%, P < 0.01) induced by pressure overload and improved cardiac diastolic function (left ventricular end-diastolic pressure: 5.2 +/- 0.9 vs. 11.0 +/- 1.6 mmHg, P < 0.05). Metformin inhibited the pressure overload-induced transforming growth factor (TGF)-beta(1) production in mouse hearts and the TGF-beta(1)-induced collagen synthesis in cultured adult mouse cardiac fibroblasts (CFs). Metformin suppressed the phosphorylation of Smad3 in response to TGF-beta(1) in CFs. Metformin also inhibited the nuclear translocation and transcriptional activity of Smad3 in CFs. CONCLUSION: Metformin inhibited cardiac fibrosis induced by pressure overload in vivo and inhibited collagen synthesis in CFs probably via inhibition of the TGF-beta(1)-Smad3 signalling pathway. These findings provide a new mechanism for the cardioprotective effects of metformin.