BMAL1 attenuates myocardial infarction-induced fibrosis via suppressing p-SMAD3/SMAD3 in TGF-β1 pathway

Cardiac function is markedly impaired as a result of myocardial fibrosis, a major pathological consequence that develops after myocardial infarction (MI). While BMAL1 (Brain and Muscle ARNT-like protein 1), a core circadian rhythm regulator, has been implicated in various cardiovascular pathologies, its role in post-MI cardiac fibrosis remains unclear. This study aimed to elucidate the role and underlying molecular mechanisms of BMAL1 in cardiac fibrosis. MI was induced in mice by permanent ligation of the left anterior descending coronary artery, and TGF-β1 was used to induce fibroblast activation in vitro. BMAL1 expression was manipulated through adeno-associated virus 9 (AAV9) overexpression and small interfering RNA (siRNA) knockdown. Our findings revealed a downregulation of BMAL1 expression in both infarcted myocardial tissue and TGF-β1-treated cardiac fibroblasts. In vivo, AAV9-mediated BMAL1 overexpression in MI mice significantly improved cardiac function and reduced myocardial fibrotic area. At the cellular level, BMAL1 overexpression effectively inhibited TGF-β1-induced fibroblast activation and extracellular matrix (ECM) deposition. Conversely, BMAL1 knockdown exacerbated fibroblast activation. Mechanistically, we demonstrated that BMAL1 suppresses the TGF-β1/SMAD3 signaling cascade by enhancing SMAD7 expression, reducing the expression of fibrosis-related genes. Collectively, our findings reveal BMAL1 as a critical negative regulator of post-MI myocardial fibrosis by inhibiting the TGF-β1/SMAD3 pathway mediated by SMAD7. Targeting BMAL1 may offer a novel therapeutic approach for improving cardiac remodeling following MI.