背景来源于多能干细胞的视网膜色素上皮(RPE)细胞移植治疗年龄相关性黄斑变性(AMD)和视网膜色素变性(RP)是近年研究热点，但RPE体外分化诱导效率低下、成本高等一直是难以克服的障碍。研究表明，姜黄素(curcumin)可促进人胚胎干细胞(ESCs)的定向诱导分化，但其对人ESCs向RPE样细胞的定向分化的作用机制尚不清楚。
目的研究体外培养的人ESCs向视网膜色素上皮(RPE)样细胞的诱导分化过程，探讨curcumin对人ESCs向RPE细胞定向诱导效率的影响及其机制。
方法将人ESCs株进行体外培养，将处于对数生长期的ESCs传代至基质膜(Matrigel)包被的6孔板中，以mTeSR™1培养基培养至过渡融合状态后更换为含质量分数87% KnockOut™DMEM、质量分数10%血清替代物(SR)、质量分数1%非必需氨基酸和质量分数1%谷氨酰胺及青链霉素双抗的分化诱导体系，同时加入终浓度为1 μmol/L的curcumin处理24 h，对照组培养基中未加入curcumin。分别于诱导培养3周及5周时提取细胞RNA及蛋白，采用荧光定量逆转录PCR(RT-PCR)法检测诱导RPE(iRPE)细胞中干细胞标志物、RPE相关标志物及Wnt/β-catenin信号通路相关因子mRNA的相对表达水平；采用Western blot法及免疫荧光染色检测人ESCs、iRPE细胞及人RPE细胞中相关标志物蛋白的表达水平；通过细胞吞噬实验检测iRPE细胞的吞噬功能。
结果Curcumin组诱导后3周时即可见iRPE细胞色素化，随着时间延长色素化程度更高，而对照组细胞在诱导后5周时开始出现细胞色素化。RT-PCR结果显示，curcumin诱导后3周及5周，curcumin组iRPE细胞中ESCs标志物NANOG mRNA的相对表达水平明显低于对照组，差异均有统计学意义( t＝13. 086， P＝0. 022； t＝34. 186， P＝0. 004)，而RPE标志物Pax6、RX、CRALBP及RPE65 mRNA的相对表达量明显高于对照组，差异均有统计学意义(均 P<0. 01)。Western blot检测显示，CRALBP、RPE65和MITF蛋白在iRPE细胞中表达，表达强度与人RPE细胞相近，而人ESCs不表达上述蛋白。免疫荧光染色显示，iRPE细胞中Pax6、MITF和ZO-1蛋白表达阳性，分别定位于细胞质和细胞膜，可见curcumin组得到的细胞为iRPE细胞，纯化效率达到100%，体外细胞吞噬实验显示，iRPE细胞的细胞质内呈现的聚苯乙烯荧光微球接近阳性对照组，而阴性对照组iRPE细胞中未见到聚苯乙烯荧光微球。诱导培养后第3周和第5周时，curcumin组细胞中Wnt信号通路下游靶因子Lef1、MYC和TCF7，Wnt受体FZD3及Wnt配体Wnt2B和Wnt7B的mRNA相对表达水平明显高于对照组，差异均有统计学意义(均 P<0. 01)。
结论Curcumin能提高人ESCs向RPE样细胞的定向诱导效率，其主要机制可能是通过促进Wnt/β-catenin信号通路的活性，从而促进iRPE细胞的分化和成熟。
BackgroundPluripotent stem cell-derived retinal pigment epithelial (RPE) cells holds great promise for the treatment of age-related macular degeneration (AMD) and retinitis pigmentosa (RP), but the poor induction efficiency and the according high cost of RPE differentiation hindere its clinical applications. Curcumin is proved to have a promoting effect on the induced differentiation of embryonic stem cells (ESCs). However, the mechanism of curcumin on differentiation of human ESCs into RPE-like cells remains unclear.
ObjectiveThis study aimed to explore the underlying molecular mechanism of curcumin on directed differentiation of human ESCs into RPE-like cells.
MethodsHuman ESCs strains were cultured in the Matrigel-coated 6-well plate with mTeSR™1 medium until over-confluence, and basic fibroblast growth factor was withdrawn there after to induce automatic differentiation. Curcumin at the final concentration 1 μmol/L was added in the first day of differentiation for 24 hours, and the cells without curcumin in the medium served as the control group. Total RNA and protein were extracted at 3 weeks and 5 weeks after induction. RT-PCR, Western blot and immunofluorescence were performed to examine the expressions of the biomarks of stem cells and RPE cells as well as Wnt/β-catenin signaling pathway components. The endocytosis of polystyrene microsphere by induced RPE (iRPE) cells was investigated to verify their function of phagocytosis which features RPE cells.
ResultsPigmented cells were found from 3 weeks through 5 weeks after induction in the curcumin group, but only less pigmented cells were seen in the fifth week after induction in the control group. In the third and fifth week after induction, the relative expression levels of NANOG mRNA in the iRPE cells were significantly lower than those in the control group ( t=13. 086, P=0. 022; t=34. 186, P=0. 004), and the relative expression levels of Pax6, RX, CRALBP and RPE65 mRNA were higher in the curcumin group than those of the control group (all at P<0. 01). Western blot assay showed that the expressing bands for CRALBP, RPE65 and MITF enhanced in iRPE cells with a similar appearance in human RPE cells. However, these expressions were all absent in human ESCs. Immunofluorescence staining showed the positive expressions of Pax6, MITF and ZO-1 in cytoplasm of iRPE cells in the curcumin group with a purified efficacy 100%. The fluorescence dye-doped polystyrene microspheres in cytoplasm were obvious in the iRPE cells like positive controls, but the polystyrene microsphere was absent in the negative controls. From 3 weeks through 5 weeks after induced, the relative expression levels of Lef1, MYC and TCF7 mRNA (the dwnstream target genes of Wnt signaling pathway), FZD3 mRNA (Wnt receptor), Wnt2B mRNA (Wnt ligand) and Wnt7B mRNA were significantly reduced in the curcumin group compared with the control group (all at P<0. 01).
ConclusionsCurcumin promotes the differentiation of human ESCs into RPE-like cells by stimulating the activation of Wnt signaling pathway, and therefore accelerate the differentiation and mature of iRPE cells.
殷秋菊,吴一湘,于莉,等. 姜黄素对人胚胎干细胞向视网膜色素上皮样细胞定向诱导效率的促进作用[J]. 中华实验眼科杂志,2015,33(9)：774-780.
DOI:10.3760/cma.j.issn.2095-0160.2015.09.002版权归中华医学会所有。
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