To investigate the effect of overexpressed microRNA-27a-3p (miR-27a-3p) on viral myocarditis (VMC) cell injury and its mechanisms.

Primary cardiomyocytes of rats were infected with Coxsackie B3 virus (CVB3) to establish VMC cell model (CVB3 group) . Normal cardiomyocytes as control (con) , and the miR-NC, miR-27a-3p mimics, si-NC, and si-Sema7A were transfected into CVB3-infected cardiomyocytes respectively, which were named as CVB3+miR-NC, CVB3+miR-27a-3p, CVB3+si-NC, and CVB3+si-Sema7A group. The miR-27a-3p mimics and pcDNA, miR-27a-3p mimics and pcDNA-Sema7A were co-transfected into CVB3-infected cardiomyocytes, respectively, and named as CVB3+miR-27a-3p+pcDNA and CVB3+miR-27a-3p+pcDNA-Sema7A group. Real-time quantitative polymerase chain reaction (qRT-PCR) and Western blot were used to detect the expression levels of miR-27a-3p and Sema7A in cells. Flow cytometry was used to detect the apoptotic rate of cardiomyocytes after overexpression of miR-27a-3p or knock-down Sema7A. The levels of tumor necrosis factor-α (TNF-α) and interleukin (IL) -1 in the cells were detected by enzyme-linked immunosorbent assay (ELISA) . The targeting relationship between miR-27a-3p and Sema7A was verified by dual luciferase reporter gene assay. The expression of Bax, cleaved caspase-3 and Bcl-2 protein was detected by Western blot.

Compared with Con group, the expression level of miR-27a-3p in CVB3 group was significantly decreased (1.01±0.09 vs 0.42±0.04, P < 0.05) , and the mRNA and protein levels of Sema7A were significantly increased (1.02±0.09 vs 2.15±0.21, P < 0.05, 0.43±0.04 vs 0.94±0.09, P < 0.05) , the levels of TNF-α and IL-1 were significantly increased [ (403.56±38.16) pg/mL vs (1156.48±63.59) pg/mL, (29.45±3.54) pg/mL vs (136.57±12.47) pg/mL, P < 0.05], the apoptosis rate was increased significantly (5.36±0.54 vs 24.58±2.14, P < 0.05) , the expression levels of Bax and cleaved caspase-3 were increased significantly (P < 0.05) , and the expression level of Bcl-2 was decreased significantly (P < 0.05) . Compared with the CVB3+miR-NC group, the levels of TNF-α and IL-1 in the CVB3+miR-27a-3p group were significantly reduced [ (1187.69± 71.42) pg/mL vs (516.28±48.31) pg/mL, (147.25±14.05) pg/mL vs (43.68±5.02) pg/mL, P < 0.05], the apoptosis rate was decreased [ (26.38±2.55) ﹪ vs (10.24± 1.15) ﹪, P < 0.05], the expression levels of Bax and cleaved caspase-3 were decreased (P < 0.05) , and the expression level of Bcl-2 was increased (P < 0.05) . Double luciferase reporting experiments confirmed that miR-27a-3p could target Sema7A expression. Sema7A overexpression could reverse the effect of miR-27a-3p overexpression on CVB3- induced VMC cell injury.

Overexpression of miR-27a-3p can reduce the expression of inflammatory factors and inhibit apoptosis in VMC cells, thereby reducing myocardial injury. The mechanism may be related to the targeted regulation of the expression of Sema7A.