Mechanisms of myocardial repair by cell-based therapy

虽然众所周知，骨髓细胞(BMC)移植到缺血心脏可以诱导血管生成，改善心肌梗死后的心功能，但确切的机制尚不清楚。我们验证了BMCs产生的细胞因子在这种基于细胞的治疗中起关键作用的假设。成年雄性Wistar大鼠的BMCs在常氧(20%O2)和低氧(1%O2)条件下培养24小时。EL ISA和Western blotting分析表明，BMC可产生多种细胞因子，包括血管内皮细胞生长因子、IL-1β、血小板衍生生长因子和胰岛素样生长因子1，部分细胞因子在低氧刺激下明显增强。与空白对照相比，常氧或低氧条件下培养的BMCs培养上清液可显著抑制体外培养的成年大鼠心肌细胞的凋亡(p&lt；0.05)，并增强其收缩功能(p&lt；0.05)。采用大鼠急性心肌梗死模型，于心肌梗死后第0天心肌内注射骨髓细胞培养上清液或对照培养液，然后于心肌梗死后第2、4、6天腹腔注射。与对照组相比，在常氧和低氧条件下培养的BMCs培养上清液均可显著增加梗死心肌微血管密度，缩小心肌纤维化面积，从而显著改善梗死后7d的心功能(p&lt；0.05)。这些结果表明，BMCs产生多种细胞因子，这些细胞因子通过直接保护心肌细胞免受缺血损伤，诱导治疗性血管生成，抑制心肌梗死心脏重构，从而改善梗死心脏的功能。

While it is well known that the implantation of bone marrow cells (BMCs) into ischemic hearts can induce angiogenesis and improve cardiac function after myocardial infarction, the precise mechanisms remain unclear. We tested the hypothesis that cytokines produced by BMCs play a key role in this cell-based therapy.BMCs from adult male Wistar rats were cultured under normoxic (20% O2) or hypoxic (1% O2) conditions for 24 hours. ELISA and Western blotting analysis showed that various cytokines, including vascular endothelial growth factor, IL-1β, platelet-derived growth factor, and insulin-like growth factor 1, were produced from BMCs, and that some were enhanced significantly by hypoxia stimulation. Compared with a control blank medium, the supernatant of BMCs cultured under normoxic or hypoxic conditions significantly inhibited apoptosis (p<0.05), and increased the contractive function of isolated adult rat cardiomyocytes in vitro (p<0.05). Using a rat model of acute myocardial infarction, we injected the supernatant of BMCs or control medium intramyocardially on day 0, and then intraperitoneally on days 2, 4, and 6 after infarction. Compared with the control medium, administering the supernatant of BMCs cultured under both normoxic or hypoxic significantly increased the microvessel density and decreased the fibrotic area in the infarcted myocardium, which contributed to a significant improvement in cardiac function at days 7 after infarction (p<0.05).These results show that various cytokines were produced from BMCs, and these cytokines contributed to functional improvement of the infarcted heart, by directly protecting cardiomyocytes against ischemic injury, inducing therapeutic angiogenesis, and inhibiting remodeling of the infarcted heart.