LAUSR

OBJECTIVE Myocardial infarction (MI), which causes irreversible damage and loss of cardiomyocytes, is the most important cause of death in the world. MicroRNA is an important regulator of physiological and pathological activities of cardiovascular system. The aim of this research was to study the effect of microRNA-323-3p (miR-323-3p) on MI and its underlying mechanisms of action. MATERIALS AND METHODS A rat model of MI was established to measure the expression of miR-323-3p, Bax, Bcl-2, SOD1, and SOD2 in ischemic myocardial tissue, and the cardiac function of rats were tested at seventh day after MI. H9c2 cells were divided into control group, miRNA negative control (NC) transfection group, miR-323-3p mimic (miR-323-3p min) transfection group, and then, treated with H2O2. Oxidative stress and apoptosis of H9c2 cells were observed by Western blot, Real Time-Polymerase Chain Reaction (RT-PCR), flow cytometry, SOD activity assay, TUNEL staining, DHR dye assay, etc. RESULTS: The level of miR-323-3p was decreased in ischemic myocardium, as well as H2O2-treated H9c2 cells. MiR-323-3p overexpression greatly decreased the level of Bax and increased the levels of SOD1, SOD2, and Bcl-2. After treated with miR-323-3p mimic, TUNEL positive cells were greatly reduced, and apoptosis rate of H9c2 cells was greatly decreased. Moreover, SOD levels significantly increased, while ROS production decreased after treatment of miR-323-3p. After intravenous injection of miR-323-3p agomir in rats with MI, the cardiac function of the rats was significantly improved. Western blot and Luciferase reporter gene experiments illustrated that miR-323-3p acts by targeting TGF-β2. CONCLUSIONS MiR-323-3p was downregulated in ischemic myocardium and H2O2-treated H9c2 cells, and miR-323-3p overexpression reduced oxidative stress and apoptosis of cardiomyocytes. The protective function was achieved via regulation of TGF-β2/JNK pathway.