SMAD3 and Myocardial fibrosis: Although previous studies have demonstrated that particulate matter exposure activated the ROS/TGF-β1/Smad3 signaling pathway to induce myocardial fibrosis (21), our study explained that PM2.5 exposure not only increased cardiomyocyte and fibrosis levels by TGF-β, but also promotes this outcome through macrophage–sEV secretions.