Overexpression of microRNA-378 attenuates ischemia-induced apoptosis by inhibiting caspase-3 expression in cardiac myocytes

MicroRNAs (miRNAs) are a novel class of powerful, endogenous regulators of gene expression. In an intact rat model of myocardial ischemia caused by coronary artery ligation, this study identified 17 miRNAs that changed more than 1.5-fold in the myocardium subjected to 4-h ischemia. Using miRNA microarray analysis, most of these aberrantly expressed miRNAs were confirmed by quantitative RT-PCR. MiR-378, a significantly down-regulated miRNA, was selected for further function study. In serum deprived rat H9c2 cardiomyocytes exposed to hypoxia (1% O-2), miR-378 expression was down-regulated as well. The overexpression of miR-378 resulting from miR-378 mimic transfection significantly enhanced cell viability, reduced lactate dehydrogenase release, and inhibited apoptosis and necrosis. By contrast, miR-378 deficiency resulting from miR-378 inhibitor transfection aggravated the hypoxia-induced apoptosis and cell injury. In accordance, miR-378 inhibitor caused significant apoptosis and cell injury to cardiomyocytes cultured under normoxia. Using bioinformatic algorithms, caspase-3, a key apoptosis executioner, was predicted as a putative target of miR-378. The quantitative RT-PCR showed no effects of miR-378 mimic or inhibitor on caspase-3 mRNA level. However, the amount of caspase-3 proteins was reduced by miR-378 mimic, whereas increased by miR-378 inhibitor. Furthermore, the luciferase reporter assay confirmed caspase-3 to be a target of miR-378, and the apoptosis and cell injury caused by miR-378 inhibitor in both normoxic and hypoxic cells were abolished by a caspase-3 inhibitor. This study first showed that miR-378 inhibited caspase-3 expression and attenuated ischemic injury in cardiomyocytes. It may represent a potential novel treatment for apoptosis and ischemic heart disease.