Mechanisms of myocardial repair by cell-based therapy

骨髓细胞（bone marrow cells，BMCs）移植到缺血心脏可以诱导血管新生，改善心肌梗死后的心功能，但其确切机制尚不清楚。将成年雄性Wistar大鼠的BMCs分别在常氧（20%O2）和低氧（1%O2）条件下培养24小时，观察BMCs的增殖、分化和凋亡情况。ELISA和Western blotting分析显示，BMCs可产生多种细胞因子，包括血管内皮生长因子、IL-1β、血小板源性生长因子和胰岛素样生长因子1，低氧刺激可显著增强某些细胞因子的表达。与空白对照组相比，常氧和低氧培养的BMCs上清均能显著抑制离体成年大鼠心肌细胞的凋亡（p<0.05），并增强心肌细胞的收缩功能（p<0.05）。使用大鼠急性心肌梗死模型，我们在梗死后第0天心肌内注射BMCs上清液或对照培养基，然后在梗死后第2、4和6天腹腔内注射。与对照组相比，常氧或低氧培养的BMCs上清液均可显著增加梗死心肌的微血管密度，减少梗死心肌的纤维化面积，这有助于梗死后第7天心功能的显著改善这些结果表明，多种细胞因子由BMC产生，并且这些细胞因子有助于梗塞心脏的功能改善，通过直接保护心肌细胞免受缺血性损伤、诱导治疗性血管生成和抑制梗塞心脏的重塑。

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.