Oxidative stress and cardiomyocyte apoptosis contributed to the progression of doxorubicin (Dox)-induced cardiotoxicity. Recent studies identified microRNA-22 (miR-22) as a cardiac- and skeletal muscle-enriched microRNA that functioned as a key regulator in stress-induced cardiac injury. The present study aimed to investigate the role and possible mechanism of miR-22 on Dox-induced oxidative stress and cardiomyocyte apoptosis. Mice were exposed to reduplicative injections of Dox (i.p., 4 mg/kg) weekly for consecutive 4 weeks to generate Dox-induced cardiotoxicity. Herein, we found that miR-22 level was significantly increased in murine hearts subjected to chronic Dox treatment. MiR-22 inhibition attenuated oxidative stress and cardiomyocyte apoptosis in vivo and in vitro, thereby preventing Doxinduced cardiac dysfunction. Mechanistically, we observed that miR-22 directly bound to the 3'-UTR of Sirt1 and caused SIRT1 downregulation. Conversely, miR-22 antagomir upregulated SIRT1 expression and SIRT1 inhibitor abolished the beneficial effects of miR-22 antagomir. In conclusion, miR-22 inhibition prevented oxidative stress and cardiomyocyte apoptosis via upregulating SIRT1 and miR-22 might be a new target for treating Dox-induced cardiotoxicity. (C) 2019 Elsevier Inc. All rights reserved.