BCL-6 promotes the methylation of miR-34a by recruiting EZH2 and upregulating CTRP9 to protect ischemic myocardial injury.

Acute myocardial infarction (AMI) and the following heart failure are public health problems faced all over the globe. The current study set out to investigate the role of B-cell lymphoma 6 (BCL-6) in cardiac protection after AMI. Initially, AMI mouse models and H9c2 cell oxygen-glucose deprivation (OGD) models were established. The cell models were transfected with the vectors containing oe-BCL-6, oe-EZH2, sh-EZH2, miR-34a mimic, and miR-34a inhibitor. RT-qPCR and Western blot analysis were applied to detect the expression patterns of microRNA-34a (miR-34a), BCL-6, enhancer of zeste homolog 2 (EZH2), and C1q tumor necrosis factor-related protein 9 (CTRP9) in the treated cell models. ChIP-qPCR and co-immunoprecipitation assay were performed to detect EZH2 enrichment and H3K27me3 levels in the miR-34a promoter region and the interaction between BCL-2 and EZH2, respectively. EdU staining, TUNEL staining, and flow cytometry were performed to detect cell proliferation and apoptosis, while ELISA was conducted to detect the oxidative stress levels. It was found that miR-34a was highly expressed in heart tissues of AMI models, while BCL-6 and EZH2 were poorly expressed. BCL-2 overexpression increased the recruitment of EZH2, upregulated H3K27me3 level in the miR-34a promoter region, and inhibited the miR-34a expression. Ctrp9, the downstream negative-regulatory molecule of miR-34a, was upregulated. Besides, miR-34a/CTRP9 expression changes were found to affect cardiomyocyte apoptosis, oxidation stress, and proliferation, and prevent myocardial injury in AMI mice. Our findings indicate that BCL-6 increases the level of H3K27me3 in the promoter region of miR-34a via EZH2 recruitment and CTRP9 upregulation, which inhibits the apoptosis of myocardial cells.