Decreased miR-208 induced ischemia myocardial and reperfusion injury by targeting p21

Aberrant expression of miR-208 was previously reported in cardiomyocytes after cardiac ischemia reperfusion (CIR) injury. However, the underlying mechanism has never been elucidated. In the current study, the relative level of miR-208 was determined in the hearts of CIR injury mice models using real time PCR. The effect of miR-208 on cardiomyocytes apoptosis was determined by Hoechst staining and annexin V-PI staining. Meanwhile, caspase3 activity was explored using an assay kit. To identify left ventricular fraction and relative wall thickness, the two-dimensional echocardiography was applied. Dual luciferase assay was applied to determine the target gene of miR-208. Compared with normal control, the level of miR-208 was significantly reduced in the hearts of CIR injury mouse models. Further studies revealed that reduction of miR-208 contributed to reactive oxygen species (ROS) production in the cardiomyocytes. We also found that inhibition of miR-208 prompted cardiomyocyte apoptosis. More importantly, the phosphorylation level of Akt and p38 was enhanced in primary cardiomyocytes transfected with miR-208 inhibitor, indicating a potential stress-response after CIR injury in primary cardiomyocytes. Dual luciferase assay and western blot analysis showed that transfection with miR-208 markedly suppressed the protein expression of p21, suggesting p21 was a target gene of miR-208. To conclude, we showed that reduced miR-208 level enhanced cardiomyocyte apoptosis mainly by targeting p21.