Exercise Mitigates Cardiac Dysfunction Post-MI in Ovariectomized Mice via miR-21/Sox7-Mediated Suppression of Cardiac Fibroblast Activation

Background: Postmenopausal women have higher risks of myocardial infarction (MI) and subsequent cardiac dysfunction. Exercise is widely recognized to protect the cardiovascular system, but its molecular mechanisms in postmenopausal MI remain not fully understood. This study explored the effects and mechanism of swimming exercise against cardiac dysfunction in ovariectomized (OVX) mice post-MI. Methods: OVX mice were subjected to a 3-week swimming training before MI induction via permanent ligation of left anterior descending artery. Cardiac systolic function was evaluated by echocardiography. Masson, HE, WGA staining, RT-qPCR, and Western blotting were combined to detect the extent of cardiomyocyte hypertrophy, myocardial fibrosis, and apoptosis. To explore the key exercise-effectors, we detected microRNAs (miR-21, miR-146a, miR-155) in serum samples of elderly post-MI women subsequent to exercise rehabilitation training. miR-21 expression was further investigated in heart sample of OVX plus MI mice. The role of miR-21 in vivo was elucidated through miR-21 knockout mice model and AAV9-mediated miR-21 overexpression mice model. The function of miR-21 in vitro were evaluated in cardiac fibroblasts isolated from OVX mice and treated with TGF-β to induce its activation. miR-21 targets were revealed by microarray analysis and verified by luciferase reporter and functional rescue assays. Results: Swimming significantly improved cardiac function in OVX mice post-MI, alleviated cardiomyocyte hypertrophy, reduced myocardial fibrosis, and inhibited apoptosis. miR-21 expression was downregulated by exercise training both in heart of OVX mice post-MI and in serum of elderly women after MI. miR-21 knockout mimicked swimming’s cardioprotective effects towards OVX mice post-MI, while miR-21 overexpression abolished these effects. The overexpression of miR-21 promoted the TGF-β-induced differentiation of cardiac fibroblasts into myofibroblasts and their proliferation, whereas its inhibition blocked TGF-β’s pro-fibrotic role. Microarray analysis and luciferase assays identified Sox7 as a direct miR-21 target, and Sox7 knockdown reversed anti-fibrotic effect of inhibiting miR-21. Conclusion: Swimming protects against post-MI cardiac dysfunction in OVX mice by downregulating myocardial miR-21, thereby upregulating its target gene Sox7 and inhibiting cardiac fibroblast activation. miR-21 and its downstream target Sox7 contributes to cardioprotective effects of swimming, offering a potential target for postmenopausal MI treatment.