Mesenchymal stem cell exosomes alleviate ischemic myocardial injury by miR-125b-5p/BTG2 pathway

MicroRNAs mediate the protective effects of bone marrow mesenchymal stem cell-derived exosomes (BMSC-Exos) against myocardial injury. This study aimed to elucidate the specific role of exosomal miR-125b-5p in ischemic myocardial injury, focusing on its regulatory interaction with B-cell translocation gene 2 (BTG2). Murine BMSCs were transfected with miR-125b-5p inhibitor or negative-control (NC) oligonucleotides and then used to generate miR-125b-5p-knockdown (miR-125b-5p^KD)-Exos or NC-Exos under hypoxic condition. In vivo, myocardial infarction (MI) was induced by LAD ligation, followed by intramyocardial injection with 50 μl of PBS, or containing 200 μg of NC-Exos, or miR-125b-5p^KD-Exos. In vitro, HL-1 cells were treated with NC-Exos or miR-125b-5p^KD-Exos at a final concentration of 50 μg/ml under hypoxia/serum-deprived (HSD) condition. Cell apoptosis, inflammation, fibrosis, cardiac function and BTG2 expression were assessed. Exosomes uptake was detected by fluorescence microscopy after exosomes labeled with DiD dye were injected into ischemic myocardium or co-cultured with HL-1 cells under HSD condition. Dual-luciferase reporter assay was applied to validate miR-125b-5p/BTG2 interaction. When compared with group MI, treatment with NC-Exos significantly alleviated the inflammatory response (inflammation score: 1.70 ± 0.37 vs. 3.47 ± 0.22, P < 0.01), inhibited cardiac fibrosis (fibrotic area ratio: 15.98% ± 2.79% vs. 31.55% ± 3.54%, P < 0.01), and improved cardiac function (ejection fraction: 49.48% ± 6.43% vs. 29.35% ± 5.79%, P < 0.01 and fractional shortening: 30.88% ± 3.70% vs. 16.15 ± 2.72%, P < 0.01). NC-Exos reduced the cell apoptosis by 41.5% in vivo (18.00% ± 3.74% vs. 30.75% ± 3.86%, P < 0.01) when compared with group MI and by 52.2% in vitro (10.48% ± 1.80% vs. 21.93% ± 1.76%, P < 0.001) when compared with group HSD. Treatment with NC-Exos also resulted in remarkable down-regulation of BTG2 expression. The knockdown of miR-125b-5p weakened these protective effects of NC-Exos. The effective uptake of DiD-labeled exosomes by ischemic myocardium and HL-1 cells were confirmed by fluorescence microscopy. Dual-luciferase reporter assay further confirmed that BTG2 is the target of miR-125b-5p. BMSC-derived exosomes confer cardioprotection, at least in part, by transferring miR-125b-5p into cardiomyocytes to target BTG2.