( Z* l; E- w" K8 V: R6.4非神经干细胞移植治疗脑梗死9 B5 q6 t! l' [- g/ Y
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由于自体干细胞及修复能力有限,利用干细胞横向分化特性,使非神经干细胞在一定条件下诱导分化为神经干细胞,使非神经干细胞治疗脑缺血成为可能。骨髓干细胞具有分布广、来源丰富和体外分离培养技术成熟等优势,是较为理想的非神经干细胞来源。骨髓干细胞证实至少存在三个干细胞群:造血干细胞、间质干细胞和内皮干细胞。研究发现骨髓干细胞具有全能性,特定环境可以分化为多种组织细胞。研究证明骨髓干细胞能分化成神经细胞或胶质细胞等[20~24],植入组神经功能恢复明显好于对照组,说明骨髓干细能在受体脑内成活迁移,并能参与神经功能重建。关于骨髓中何种细胞分化为神经细胞待进一步研究[25]。动员自身骨髓干细胞向脑缺血损伤区趋化、归巢、分化和促进血管新生,更符合机体自身反应性修复机制,方法简便,安全有效、无创、可操作且避免细胞移植免疫排斥,应用价值高。& e2 f& J1 }3 i
3 n0 Y0 o; {+ X/ T 干细胞移植对脑梗塞的功能改善有一定疗效已得到公认,但作用机制未明。部分学者认为干细胞移植分化为神经组织,替代损伤细胞,重建了神经环路。也有部分学者认为目前没有足够证据显示干细胞以这种方式起作用。目前干细胞移植后表达NeuN,MAP-2(microtubule associated protein-2)和GFAP的细胞仅有1%,2%,5%,且无法证明它们是否具有正常细胞功能,也无法确定这些细胞是否与其它细胞建立联系[26]。一个更合理的假设是移植的干细胞与宿主相互作用而分泌一些细胞因子和或神经递质来促进神经功能恢复。此外,Chen[24]等还发现干细胞可促进缺血区脑血管的形成。2 e- K4 l9 d2 {4 \* P! r. M
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干细胞的来源、分离、培养及鉴定还有许多工作要做,干细胞诱导、分化及迁移机制有待进一步研究; 目前建立的干细胞系绝大多数来源于鼠,而鼠与人之间存在着明显的种属差异;免疫反应;怎样控制细胞的增殖,部分移植的干细胞发展成脑瘤[28];在移植过程中,注意移植病原体;干细胞转染范围的非选择性表达及转基因表达的原位调节;利用胚胎干细胞存在着社会学及伦理学方面的问题等。通过细胞培养技术及基因组的研究,如DNA微列阵技术,进一步明确成体干细胞确切位置,可以设计药物特异性地激活这些细胞。进一步认识干细胞的本质和控制分化基因,通过调控靶基因,可以从干细胞诱导产生特定的分化细胞来满足各种需要。横向分化的发现对干细胞的研究和应用具有重要意义,人们可望从自体中分离诱导出干细胞,有可能解决干细胞的来源问题。随着科学技术的发展,上述存在的问题将逐步解决,干细胞的应用将有广阔的前景。 ) D( d, T% f* G( ?$ l 【参考文献】/ j& {, M& M* Y! M8 k0 o
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