MMP9 and Myocardial fibrosis: For example, exercise can promote the release of exosomes containing high levels of miR-455, miR-29b, miR-323-5p, and miR-466 by cardiomyocytes, and the miRNAs in these exosomes can inhibit MMP-9 activity and block ECM remodeling, thereby reducing myocardial fibrosis in db/db mice (88).