Effect of miR-21/TLR4/NF-κB pathway on myocardial apoptosis in rats with myocardial ischemia-reperfusion

The aim of the study was to investigate the influences of micro ribonucleic acid (miR)-21 and downstream Toll-like receptor 4 (TLR4)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway on myocardial apoptosis induced by myocardial ischemia-reperfusion (I/R) injury in rats.

Recombinant adeno-associated virus rAAV9-ZsGreen-pre-miR-21 and blank control virus were constructed. A total of 48 Sprague-Dawley (SD) rats were randomly divided into S1 group (open chest only), S2 group (transfection with blank virus + open chest), I/R1 group (transfection with blank virus + 6 d of myocardial I/R), and I/R2 group (transfection with miR-21 + 6 d of myocardial I/R). The cardiac function and myocardial infarct size of rats were evaluated in each group. Quantitative Polymerase Chain Reaction (qPCR) was applied to measure the expression level of miR-21 in the myocardium. The level of myocardial apoptosis in each group was detected through terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) staining. Western blotting was performed to determine the protein expression levels of B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein (Bax), Caspase-3, TLR4, and NF-κB in the myocardium. The content of interleukin-6 (IL-6) and IL-10 was measured using enzyme-linked immunosorbent assay (ELISA) kits.

The cardiac function of rats in I/R1 and I/R2 groups was significantly lower than that in S1 and S2 groups (p<0.01). Rats in I/R2 group had better cardiac function than those in I/R1 group (p<0.01). In I/R1 group, the level of myocardial apoptosis of rats was overtly increased compared with that in S1, S2, and I/R2 groups (p<0.01), while the expression level of miR-21 in myocardium was evidently lower than that in S1, S2, and I/R2 groups (p<0.01). Compared with S1, S2, and I/R2 groups, I/R1 group had markedly decreased Bcl-2/Bax expression level and IL-10 content and overtly elevated expression levels of Caspase-3, p-TLR4, p-NF-κB, and IL-6 content in the myocardium (p<0.01).

Myocardial I/R injury in rats leads to decreased expression of miR-21. The overexpression of miR-21 is able to effectively inhibit the TLR4/NF-κB pathway and reduce the level of myocardial apoptosis of rats and the release of inflammatory factors.