miR-21 enhances the protective effect of loperamide on rat cardiomyocytes against hypoxia/reoxygenation, reactive oxygen species production and apoptosis via regulating Akap8 and Bard1 expression

Effective therapies to reduce ischemia/reperfusion and hypoxia/reoxygenation injury are currently lacking. Furthermore, the effects of loperamide and microRNA (miR)-21 on hypoxia/reoxygenation injury of cardiomyocytes have remained to be elucidated. Therefore, the present study aimed to investigate the effect of loperamide and miR-21 on cardiomyocytes during hypoxia/reoxygenation injury, and to explore the underlying molecular mechanisms. H9c2 rat cardiomyocytes were pre-treated with loperamide prior to hypoxia/reoxygenation. The viability of H9c2 cells was measured with a cell counting kit 8 and apoptosis was detected with an Annexin V-phycoerythrin/7-aminoactinomycin D apoptosis kit. Furthermore, reactive oxygen species were detected with a specific kit. Genes regulated by miR-21 were screened with an mRNA chip and confirmed using reverse-transcription quantitative polymerase chain reaction analysis. The direct targeting relationship of miR-21 with certain mRNAs was then confirmed using a Dual-Luciferase Reporter Assay system. The results indicated that the apoptotic rate and reactive oxygen species levels in rat cardiomyocytes were markedly increased after hypoxia/reoxygenation treatment. Pre-treatment with loperamide significantly protected H9c2 cells against apoptosis and reactive oxygen species production after hypoxia/reoxygenation. The protection was markedly decreased by miR-21 inhibitor and enhanced by miR-21 mimics. Screening for genes associated with cardiomyocyte apoptosis revealed that the relative expression of A-kinase anchoring protein 8 (Akap8) and BRCA1 associated RING domain 1 (Bard1) was consistent with the experimental results on apoptosis and reactive oxygen species. Compared with the group treated by hypoxia/reoxygenation alone, pre-treatment with loperamide markedly decreased the expression of BRCA1-interacting protein C-terminal helicase 1, Akap8 and Bard1 after hypoxia/reoxygenation. The decrease in the expression of Akap8 and Bard1 was markedly attenuated by miR-21 inhibitor and enhanced by miR-21 mimics. miR-21 mimics directly targeted the 3-untranslated region (UTR) of Akap8 and Bard1 mRNA to thereby decrease their expression. In conclusion, the protection of rat cardiomyocytes against hypoxia/reoxygenation-induced apoptosis and reactive oxygen species production by loperamide was markedly enhanced by miR-21. miR-21 directly targets the 3-UTR of Akap8 and Bard1 mRNA and enhances the inhibitory effects of loperamide on Akap8 and Bard1 expression in rat cardiomyocytes after hypoxia/reoxygenation.