BACKGROUND:Stem cels have multi-directional differentiation and self-replication abilities, under certain conditions, which can differentiate into myocardial cels to repair the damaged myocardium. OBJECTIVE: To investigate the effects of transplantation of umbilical cord mesenchymal stem cels derived at different gestational weeks on infarct size and angiogenesis in the infarct region of experimental rabbits with myocardial infarction. METHODS: Ten ful-term umbilical cord samples and 10 umbilical cord samples of aborted fetuses at 10-12 gestation weeks were selected to in vitro isolate umbilical cord mesenchymal stem cels that were subjected to BrdU labeling. HLA-G expression was detected in the cels. Thirty white rabbits were selected to make myocardial infarction models, and 2 weeks after modeling, the model rabbits were randomized into aborted cel transplantation group, ful-term cel transplantation group and control group (n=10 per group). Then, BrdU-labeled cels were injected correspondingly into the infarct region of rabbits in the two cel transplantation groups. Rabbits in the control group were subjected to an equal volume of serum-free. Four weeks after transplantation, heart function of rabbits was monitored using electrocardiogram, and myocardial tissues were taken to measure infarct size and blood capilary density. RESULTS AND CONCLUSION: HLA-G expression was different in different sources of umbilical cord mesenchymal stem cels: high HLA-G expression was found in the aborted umbilical cord mesenchymal stem cels, and meanwhile, low HLA-G expression was found in the ful-term umbilical cord mesenchymal stem cels. Compared with the control group, the left ventricular end-diastolic volume and left ventricular ejection fraction of aborted and ful-term cel transplantation groups were significantly improved, especialy in the aborted cel transplantation group (P < 0.05). BrdU-positive cels were found in the infarct site in both transplantation groups. Compared with the control group, the infarct size and capilary density were improved most significantly in the aborted cel transplantation group folowed by the ful-term cel transplantation group (P < 0.05). Electrocardiogram findings showed significant improvement in both cel transplantation groups compared with the control group (P < 0.05), especialy in the aborted cel transplantation group. These findings indicate that umbilical cord mesenchymal stem cels derived at low gestational weeks improve the heart function more significantly than the ful-term umbilical cord mesenchymal stem cels, which have the potential to become a better source of cardiomyocytes for transplantation.%背景：干细胞有多向分化和自我复制能力，在一定条件下可以分化为心肌细胞，修复受损心肌。目的：观察不同孕周人脐带间充质干细胞移植对实验兔心肌梗死面积、梗死区新生血管的影响。方法：①选取足月胎儿脐带和孕10-12周流产胎儿脐带各10根，体外分离培养脐带间充质干细胞并行BrdU标记，检测HLA-G在细胞中的表达。②30只大白兔建立心肌梗死动物模型，建模成功2周后随机分为3组：流产细胞移植组、足月细胞移植组、对照组各10只。将BrdU标记的人脐带间充质干细胞分别注射于对应各组实验兔的心肌梗死区，对照组注射等量的无血清培养基。③移植治疗4周后监测实验兔的心脏功能和心电图，取心肌组织检测心肌梗死面积、毛细血管密度。结果与结论：①HLA-G在孕10-12周流产胎儿及足月分娩胎儿的脐带间充质干细胞中分别呈高表达及低表达。②足月细胞移植组和流产细胞移植组左室舒张末容积均小于对照组(P <0.05)，左心室射血分数均大于对照组(P <0.05)，流产细胞移植组左室舒张末容积小于足月细胞移植组(P <0.05)，左心室射血分数大于足月细胞移植组(P <0.05)。③两组实验兔模型的心肌梗死区均有BrdU示踪细胞；流产细胞移植组和足月细胞移植组的心肌梗死面积小于对照组(P <0.05)，流产细胞移植组的心肌梗死面积小于足月细胞移植组(P <0.05)。④流产细胞移植组和足月细胞移植组毛细血管密度均明显高于对照组(P <0.05)，流产细胞移植组较足月细胞移植组增加更为明显(P <0.05)。⑤在心电图方面，流产细胞移植组和足月细胞移植组与对照组相比均明显改善(P <0.05)，流产细胞移植组较足月细胞移植组改善更为明显。⑥结果表明来源于小孕周胎儿脐带组织的间充质干细胞能更好地改善心脏功能，有潜力成为心肌细胞移植的更理想来源。
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