MiR-21 participates in LPS-induced myocardial injury by targeting Bcl-2 and CDK6

Objective: This study aimed to investigate the relationship between miR-21 and lipopolysaccharide (LPS)-induced myocardial injury and its molecular and regulatory mechanisms. Methods: We constructed LPS-mediated myocardial injury model using C57BL/6J mice and H9c2 cells. In-vivo, in-vitro, RIP and dual-luciferase reporter assays were used to determine the effect of miR-21 on myocardial injury. Results: In-vivo and in-vitro results showed that the expression of miR-21 was increased in LPS-treated H9c2 cells and myocardial tissues of mice, and the pro-inflammatory cytokines (IL-1β, IL-6, IL-8 and TNF-α) and NF-κB pathway were activated in LPS-treated H9c2 cells. Besides, the B-cell lymphoma-2 (Bcl-2) and cyclin-dependent kinase 6 (CDK6) expression levels decreased, while Bax and cleaved caspase 9 levels increased in LPS-treated H9c2 cells. Inhibition of miR-21 could suppress LPS-induced apoptosis, inflammatory reactions and NF-κB activation to attenuate LPS-induced myocardial injury in H9c2 cells, and effectively improve survival of mice with sepsis. Most importantly, Bcl-2 and CDK6 were found to be the direct target of miR-21 using dual-luciferase reporter and RNA immunoprecipitation assays. Further gain-of-function assay demonstrated that Bcl-2 or CDK6 over-expression promoted the protective effects of miR-21 inhibitor on LPS-mediated myocardial cells. Conclusion: Our findings revealed that the down-regulation or antagonism of miR-21 protects myocardial cells against LPS-induced apoptosis and inflammation through up-regulating Bcl-2 and CDK6 expression, which provided a new insight for prevention and treatment of myocardial injury.