MicroRNA-146b inhibition augments hypoxia-induced cardiomyocyte apoptosis

MicroRNAs (miRs) regulate a number of physiological and pathological processes, including myocardial chronic hypoxia. Previous studies revealed that the expression of miR-146b is increased in vitro and in vivo following the induction of hypoxia. In the present study, the role of miR-146b in hypoxic cardiomyocytes, and the mechanisms underlying its activity, were investigated. The expression of miR-146b was measured in tissue samples from patients with congenital heart disease by reverse transcription-quantitative polymerase chain reaction. The rat H9c2 cardiomyocyte cell line was transfected with an miR-146b inhibitor or the experimental controls, and the cells were maintained under hypoxic conditions for 72 h. The expression of miR-146b increased following the induction of hypoxia. Transfection with the miR-146b inhibitor enhanced the release of lactate dehydrogenase and increased hypoxia-induced apoptosis, as determined by terminal deoxynucleotidyl transferase dUTP nick-end labeling, Hoechst 33258 staining, JC-1 assay (measuring mitochondrial membrane permeability) and annexin V/propidium iodide analysis. A decreased expression of Bcl-2 was observed, whereas the expression levels of cleaved-caspase 3 and Bax were increased. Western blot analysis and a dual luciferase reporter assay confirmed that ribonuclease L is a direct target of miR-146b. Furthermore, inhibition of miR-146b increased the activation of nuclear factor-kappa B and signal transducer and activator of transcription 3. In conclusion, the inhibition of miR-146b may increase hypoxia-induced cardiomyocyte apoptosis.