胚胎干细胞微环境增强人角膜缘干细胞的干性和抑制凋亡的机制

摘要

背景 成体干细胞的命运与其生存的微环境密切相关.研究表明,胚胎干细胞(ESCs)微环境能增强人角膜缘干细胞(LSCs)的干性,其作用机制是研究热点. 目的 探讨干细胞微环境增强LSCs的干性及其抑制细胞凋亡的分子机制.方法将129小鼠ES细胞株(E14细胞)分别用CnT-20培养液和CnT-20+体积分数20％ ES(ESC-CM)培养液进行培养和传代.采用新鲜供体人角膜缘组织块培养法,分别用CnT-20培养液和ESC-CM培养液培养和传代LSCs,细胞经固定后于光学显微镜下观察细胞克隆形态并计算克隆形成率(CFE).ESC-CM培养组细胞分别转染端粒酶逆转录酶(TERT) siRNA(19-25nt siRNA)或siRNA(sc37007),流式细胞仪检测转染前后细胞凋亡、线粒体膜电位的改变;采用免疫荧光技术和流式细胞技术检测siRNA转染前后细胞中端粒酶的表达和活性氧簇(ROS)的产生情况;采用RT-PCR、免疫荧光技术和Western blot法检测细胞中干细胞标志物p63、三磷酸腺苷结合转运蛋白G超家族成员2(ABCG2)、整合素β1(integrin β1)和细胞分化标志物细胞角蛋白3(CK3) mRNA及其蛋白的表达;采用Western blot法检测细胞中黏着斑激酶(FAK)、Akt和糖原合成酶激酶3β(GSK3β)及其磷酸化蛋白以及p21蛋白的改变. 结果 ESC-CM培养组LSCs可传至第8代,CFE为(7.6±0.6)％,CnT-20培养组传至第6代,CFE为(5.6±0.6)％,差异有统计学意义(t=4.454,P=0.011);ESC-CM培养组第2、3、4、5、6代LSCs的凋亡百分比均明显低于CnT-20培养组,差异均有统计学意义(均P＜0.05);siRNA-F转染细胞的凋亡率为(7.7±1.3)％,明显低于siRNA-TERT转染细胞的(32.3±3.1)％,差异有统计学意义(t=-12.588,P=0.000).ESC-CM培养组与CnT-20培养组的原代LSCs 中干细胞标志物mRNA及其蛋白、TERT蛋白的相对表达量差异均无统计学意义(均P＞0.05),但ESC-CM培养组CK3 mRNA及其蛋白的相对表达量均明显低于CnT-20培养组,差异均有统计学意义(均P＜0.01);ESCCM培养组第2代细胞中干细胞标志物蛋白及TERT蛋白表达量均明显高于CnT-20培养组,差异均有统计学意义(均P＜0.01).siRNA-TERT转染组细胞端粒酶活性为(4.83±0.67)％,明显低于siRNA-F转染组的(46.71±1.22)％,差异有统计学意义(t=52.116,P=0.000).ESC-CM培养组培养液中添加了FAK抑制剂和GSK3β抑制剂以及转染TERT-siRNA后,细胞中pFAK、pAkt、pGSK3β的表达明显减弱,而p21的表达增强.ESC-CM培养组第2代LSCs及siRNA-F转染组细胞的线粒体膜电位明显高于CnT-20培养组和siRNA-TERT 转染组,差异均有统计学意义(均P＜0.01);ESC-CM培养组原代和第2代细胞中及siRNA-F转染组细胞中ROS表达比例均明显低于CnT-20培养组及siRNA-TERT转染组,差异均有统计学意义(均P＜0.01). 结论 ESC-CM培养体系可促进LSCs干性的维持,抑制细胞凋亡,其机制可能与端粒酶-p21-线粒体通路及FAK/Wnt 信号通路的激活有关.%Background The fate of adult stem cells is associated with its surrounding microenviroment.Our previous work found that embryonic stem cells (ESCs) micro-environment enhance the stemness of human limbal stem cells (LSCs),but its mechanism has not been elucidated.Objective This study was to explore the molecular mechanism of ESC micro-environment enhancing the stemness and inhibiting the apoptosis of LSCs.Methods Human LSCs were cultured by explant culture method with CnT-20 medium and CnT-20+20％ ES culture supernatant (ESC-CM),respectively.Colony formation assay was used to analyze the proliferation ability of cells.Telomerase reverse transcriptase (TERT) siRNA (19-25nt siRNA) or siRNA (sc-37007) was transfected into the cells of ESCCM group.Apoptosis and mitochondrial membrane potential were assayed by flow cytometry,and the expressions of telomerase and reactive oxygen species (ROS) in TERT siRNA-or siRNA-F-transfected cells by immunofluorescence and flow cytomery.RT-PCR,immunofluorescence staining and Western blot were employed to determine the expressions of p63,ATP-binding cassette transporer G2 (ABCG2),integrin β1 mRNA and proteins and cytokeratin 3 (C K3) in the cells.The levels of focal adhesion kinase (FAK),Akt,glycogen synthase kinase 3β (GSK3β) and p21 protein and phosphorylation proteins in the cells were detected by Western blot.Results The LSCs presented an increased proliferative capacity and passaged to the eighth generation with the colony-forming efficiency (CFE) of (7.6±0.6) ％ in ESC-CM group,but the cells to the sixth generation with the CFE of (5.6±0.6)％,showing a significant difference between them (t =4.454,P =0.011).The apoptotic rates of the cells from 2 through 6 generations were lower in the ESC-CM group than those in the CnT-20 group (all at P＜0.05).The apoptotic rate of the cells was (7.67± 1.31)％ in the siRNA-F transfected group,which was significantly lower than (32.33 ±3.13)％in the siRNA-TERT transfected group (t =-12.588,P =0.000).No significant differences were seen in the expression levels of p63,ABCG2,integrin β1 mRNA and proteins and TERT protein in the primary cells between the ESC-CM group and the CnT-20 group (all at P＞0.05),but significantly declined expressions of CK3 mRNA and protein were found in the ESC-CM group compared with the CnT-20 group (all at P＜0.01).However,the expressions of p63,ABCG2,integrin β1 mRNA and proteins and TERT protein in the second generation of the cells were significantly higher in the ESC-CM group compared with the CnT-20 group (all at P＜0.01).The telomerase activity was (4.83±0.67) ％ in the siRNA-TERT transfected group,which was significantly lower than (46.71±1.22) ％ of the siRNA-F transfected group (t =52.116,P =0.000).The expression of pFAK,pAkt,pGSK3β proteins were weakened,but the expression of p21 was increased in the ESC-CM group after addition of FAK inhibitor,GSK3β inhibitor and TERT-siRNA transfected group.Mitochondrial membrane potential in the second generation of cells was elevated in the ESC-CM group in comparison with the CnT-20 group and the siRNA-TERT transfected group (all at P＜0.01),and the rates of ROS positively reaction was lower in the ESC-CM group and the siRNA-F transfected group than those of the CnT-20 group and siRNA-TERT transfected group (all at P＜0.01).Conclusions ESC-CM culture system can effectively keep the stemness of LSCs and inhibit apoptosis.ESC-CM culture system plays functions probably via telomerase-p21-mitochondrial axis and the activation of the FAK/Wnt signaling pathways.