骨髓间充质干细胞移植促进脊髓损伤修复的机制

Mechanism of bone mesenchymal stem cells transplantation promoting recovery of injured spinal cord

目的研究骨髓问充质干细胞（BMSCs）移植对损伤脊髓神经功能恢复的影响及其机制。方法采用纽约大学脊髓重物坠落仪制作大鼠脊髓损伤模型。脊髓损伤后7d，在损伤中心周围移植BMSCs（BMSCs组）或注射PBS（PBS组）。采用BBB评分评价大鼠脊髓功能。测定脊髓空洞体积，透射电镜观察脊髓损伤中心轴突的数量。采用绿色荧光蛋白（GFP）转基因大鼠的BMSCs示踪移植细胞，观察BMSCs移植后在脊髓中的存活及向神经细胞分化的情况。采用脊髓埋管模型，研究BMSCs移植对损伤脊髓轴突再生的影响。结果BMSCs组BBB评分显著高于PBS组，而其脊髓空洞体积明显小于PBS组。电镜下可见，在脊髓损伤中心BMSCs组的轴突数量明显多于PBS组。细胞移植后4周，在脊髓损伤中心周围可见大量BMSCs-GFP细胞。免疫荧光染色结果表明，脊髓移植的BMSCs并不表达神经元、星形胶质细胞和少突胶质细胞的表面标志性蛋白。脊髓埋管实验发现，在种有BMSCs的导管内可见有NF阳性的神经纤维的长入，而未种有BMSCs组的导管内未见神经纤维的生长。结论脊髓损伤后进行BMSCs移植可促进损伤脊髓功能的恢复，其机制与BMSCs移植促进神经元轴突再生的作用有关。

Objective To investigate the effects of bone mesenchymal stem cells （BMSCs） transplantation on the neurological function recovery of injured spinal cord and the underlying mechanism. Methods Rats were subjected to contusive spinal cord injury by using NYU spinal cord contusive impac- tor system （ NYC Impactor）. Seven days after spinal cord injury, the transplantation of BMSCs （ BMSCs group） or injection of PBS （ PBS group） was performed around the epicenter of injured spinal cord in rats. Basso-Beattie-Bresnahan （BBB） score was used to evaluate the function of spinal cord. The cavity volume of the injured spinal cord was measured and the axons in the injury center of spinal cord were ex- amined under transmission electron microscopy. The BMSCs of the green fluorescent protein （ GFP ） transgenic rats were used to trace the transplanted cells and the survivor of BMSCs in the injured spinal cord and their differentiation into neural ceils were observed. A mini-channel implantation model was em- ployed to further investigate the role of BMSCs transplantation on the axonal regeneration. Results The BMSCs group showed a higher BBB score and a smaller lesion volume as compared with the PBS group. Transmission electron microscopy examination displayed that the number of axons in the BMSCs group was far more than that in the PBS group. A great number of BMSCs-GFP were founded around the center of the injured spinal cord at 4 weeks after BMSCs transplantation. Immunohistochemistry showed that the im- planted BMSCs-GFP did not express the surface marker of neurons, astrocytes and oligodendrocytes. In the mini-channel implantation model, NF-positive nerve fibers grew into the BMSCs-seeded channel, while there were no nerve fibers in the channel without seeding of BMSCs. Conclusions The BMSCs transplantation for the injured spinal cord promotes its functional recovery, and the related mechanism is in correlation with BMSCs transplantation inducing axonal regeneration.