Cardioprotective mechanism of microRNA for targeting bnip3 in ischemic myocardium

Abstract

Heart failure is the leading cause of death worldwide, and the death of cardiomyocytes contributes to the progression of heart failure through the functional demise of the myocardium. Major cell death mechanisms, including autophagy, apoptosis, and necrosis, have been identified to be involved in the death of cardiomyocytes. Bcl-2 E1B 19-KDa interacting protein 3 (bnip3), which triggers mitochondrial dysfunction via mitochondrial outer membrane permeabilization (MOMP), has been implicated in all of those cell death mechanisms of cardiomyocytes, suggesting that its modulation may be a therapeutically viable approach to prevent excessive cardiac cell death in cardiovascular diseases (CVDs). MicroRNAs (miRNAs or miRs) are small, non-coding RNAs that function as important post-transcriptional regulators by binding to target mRNAs and subsequently suppressing target gene translation. Accumulating data indicate that miRNAs play important roles in the development of diseases, including CVDs; thus, the miRNA-mediated modulation of bnip3 may serve as an effective therapeutic strategy for improving cardiomyocyte survival. In this study, miRNA-182 was screened as a miRNA that targets bnip3, and its effects on the apoptosis, necrosis, and autophagy of cardiomyocytes under hypoxic conditions were investigated. miRNA-182 inhibited increases in intracellular calcium and mitochondrial fragmentation directly through bnip3 expression. Additionally, after screening a few hundred small molecules for the ability to enhance miRNA-182 expression, the GSK-3β inhibitor kenpaullone was identified as an inducer of endogenous miRNA-182. Further examination suggested that the transcription factors β-catenin and sp-1 were involved in the kenpaullone-induced up-regulation of miRNA-182. Kenpaullone repressed mitochondrial fragmentation, ROS production, and apoptotic pathway activation.

Furthermore, miRNA-182 and kenpaullone both independently reduced fibrosis and apoptosis in an ischemic reperfusion heart model in vivo, resulting in improved cardiac function, connexin 43 expression, and microvessel density. The results of this study strongly suggest that the miRNA-mediated down-regulation of bnip3 can be an effective therapeutic strategy for enhancing cardiomyocyte survival in ischemic heart disease. In addition, this finding provides empirical proof of a novel concept: a small molecule drug that targets a specific miRNA (SMIR) to treat myocardial infarction.