Suitability of Human Tenon’s Fibroblasts as Feeder Cells for Culturing Human Limbal Epithelial Stem Cells

Corneal epithelial regeneration through ex vivo expansion of limbal stem cells (LSCs) on 3T3-J2 fibroblasts has revealed some limitations mainly due to the corneal microenvironment not being properly replicated, thus affecting long term results. Insights into the feeder cells that are used to expand LSCs and the mechanisms underlying the effects of human feeder cells have yet to be fully elucidated. We recently developed a standardized methodology to expand human Tenon’s fibroblasts (TFs). Here we aimed to investigate whether TFs can be employed as feeder cells for LSCs, characterizing the phenotype of the co-cultures and assessing what human soluble factors are secreted. The hypothesis that TFs could be employed as alternative human feeder layer has not been explored yet. LSCs were isolated from superior limbus biopsies, co-cultured on TFs, 3T3-J2 or dermal fibroblasts (DFs), then analyzed by immunofluorescence (p63α), colony-forming efficiency (CFE) assay and qPCR for a panel of putative stem cell and epithelial corneal differentiation markers (KRT3). Co-cultures supernatants were screened for a set of soluble factors. Results showed that the percentage of p63α⁺LSCs co-cultured onto TFs was significantly higher than those on DFs (p?=?0.032) and 3T3-J2 (p?=?0.047). Interestingly, LSCs co-cultures on TFs exhibited both significantly higher CFE and mRNA expression levels of ΔNp63α than on 3T3-J2 and DFs (p?<?0.0001), showing also significantly greater levels of soluble factors (IL-6, HGF, b-FGF, G-CSF, TGF-β3) than LSCs on DFs. Therefore, TFs could represent an alternative feeder layer to both 3T3-J2 and DFs, potentially providing a suitable microenvironment for LSCs culture.     

A novel NIH/3T3 duplex feeder system to engineer corneal epithelial sheets with enhanced cytokeratin 15-positive progenitor populations

Corneal epithelial cell sheets co-cultivated with feeder cells are used to reconstruct the ocular surface in stem cell-depleted eyes. The present study was conducted to investigate the optimal method of using feeder cells in the interest of preserving progenitor cells in cultivated sheets. We compared the phenotype and secondary colony forming efficiency (CFE) of cell sheets that were engineered using 3T3 feeder cells as a separate layer or as a contact layer. We also devised a novel "duplex feeder" system that consists of two separate layers of feeder cells. After cells reached confluence, cells were cultured at the air-liquid interface to allow full stratification. Stratified sheets were then analyzed using immunohistochemistry and secondary colony formation. Contact feeder cultures and duplex feeder cultures yielded epithelial sheets with small, cuboid basal cells with strong expression of keratin (K)3, K12, and K 15. Furthermore, only duplex feeder layers reproduced the basal K 15, suprabasal K12 limbal phenotype where epithelial stem cells reside. A similar effect was observed when cornea stroma-derived progenitor cells were used as feeder cells. Duplex feeder sheets also produced significantly more secondary colonies than cells dissociated from single layer sheets, suggesting that the duplex feeder system produces transplantable sheets with a higher yield of progenitor cells.     

Cell size correlates with phenotype and proliferative capacity in human corneal epithelial cells

This study investigated whether cell size correlates with phenotype and proliferative capacity in human corneal epithelial cells. Primary cultured human corneal epithelial cells were sorted by flow cytometry based on forward scatter profile in comparison with the profile of beads of known size. Four fractions (A, B, C, and D) of cells ranging in size from 10 to 16, 17 to 23, 24 to 30, and >or=31 microm in diameter, respectively, were collected to evaluate their 5-bromo-2-deoxyuridine (BrdU) label retention properties, cell phenotype, and clonal growth capacity on a 3T3 fibroblast feeder layer. Among these four populations, cell size was shown to positively correlate with the expression of the differentiation markers keratin (K) 3, K12, and involucrin and inversely with the levels of stem cell-associated markers DeltaNp63 and ABCG2 and with colony-forming efficiency (CFE) and growth capacity. Population A with the smallest size, accounting for 11.0%+/-4.5% of the entire population, contained the greatest number of BrdU label-retaining slow-cycling cells, displayed the highest percentage of cells immunopositive to p63 and ABCG2 and negative to K3 and involucrin, expressed the highest levels of DeltaNp63 and ABCG2 mRNA and the lowest levels of K3, K12, and involucrin, and possessed the highest CFE and growth capacity. These findings suggest that cell size correlates with cell differentiation phenotypes and proliferative capacity in human corneal epithelial cells. The smallest cells in population A seem to be enriched for putative stem cells, and small cell size may represent one of the important properties of adult corneal epithelial stem cells.     

Human amniotic epithelial cells as novel feeder layers for promoting ex vivo expansion of limbal epithelial progenitor cells

Human amniotic epithelial cells (HAECs) are a unique embryonic cell source that potentially can be used as feeder layers for expanding different types of stem cells. In vivo, HAECs uniformly expressed pan-cytokeratins (pan-CK) and heterogeneously expressed vimentin (Vim). The two phenotypes expressing either pan-CK(+)/Vim(+) or pan-CK(+)/Vim(-) were maintained in serum-free media with high calcium. In contrast, all HAECs became pan-CK(+)/Vim(+) in serum-containing media, which also promoted HAEC proliferation for at least eight passages, especially supplemented with epidermal growth factor and insulin. Mitomycin C-arrested HAEC feeder layers were more effective in promoting clonal growth of human limbal epithelial progenitors than conventional 3T3 murine feeder layers. Cells in HAEC-supported clones were uniformly smaller, sustained more proliferation, and expressed less CK12 and connexin 43 but higher levels of stem cell-associated markers such as p63, Musashi-1, and ATP-binding cassette subfamily G2 than those of 3T3-supported clones. Subculturing of clonally expanded limbal progenitors from HAEC feeder layers, but not from 3T3 feeder layers, gave rise to uniformly p63-positive epithelial progenitor cells as well as nestin-positive neuronal-like progenitors. Collectively, these results indicated that HAECs can be used as a human feeder layer equivalent for more effective ex vivo expansion of adult epithelial stem cells from the human limbus. Disclosure of potential conflicts of interest is found at the end of this article.     

活体及体外条件下对角膜上皮干细胞的定位

背景：眼表存在两种形式的上皮干细胞即角膜上皮干细胞和结膜上皮干细胞,角膜上皮干细胞在角膜上皮细胞更新和角膜透明的维持方面起着重要作用。 目的：采用活体激光扫描角膜共焦显微镜和免疫荧光染色技术相结合的方法,从活体和体外层面上对角膜上皮干细胞进行定位研究。 方法：收集2009年9月至2012年9月来河南省眼科研究所就诊的单侧角膜缘干细胞缺乏患者,使用活体激光扫描角膜共焦显微镜检查患者双眼,健侧眼为对照。扫描方位依次为中央角膜及上、下、左、右方的角膜缘,记录扫描图像并分析。眼球材料来自于河南省眼库,切取角膜中央和角膜缘组织,组织包埋剂包被、冰冻切片,切片厚度5-7 μm;免疫荧光染色技术检测p63、ABCG2、K3和Connexin 43在角膜中央及角膜缘上皮层的表达。 结果与结论：共有24例患者确诊为单侧角膜缘干细胞缺乏,活体激光扫描角膜共焦显微镜下患侧眼角膜病变区可见结膜细胞及杯状细胞;角膜缘区域Vogt栅栏状结构消失,色素细胞消失,取而代之的是大量纤维瘢痕化组织。免疫荧光染色示表达ABCG2和p63的细胞主要在角膜缘上皮基底层,尤其在近结膜侧的角膜缘及角膜缘中间部表达相对较高,而中央角膜上皮层细胞不表达;K3及Connexin43在角膜缘上皮基底细胞层不表达,中央角膜上皮全层表达。通过活体激光扫描角膜共焦显微镜观察及干细胞标记物检测显示角膜上皮干细胞主要存在于角膜缘外2/3区域的Vogt栅栏基底部及钉突结构中。中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程全文链接：     

Molecular profile of organ culture-stored corneal epithelium: LGR5 is a potential new phenotypic marker of residual human corneal limbal epithelial stem cells

Long-term preservation of corneal limbal epithelium may decrease its quality and change the molecular signature of the limbal epithelial stem cells. In this study we have investigated the molecular profile of isolated corneal epithelial cells that have been in storage for an extended time. Isolated cells were characterised by the expression profile of different cytokeratins and markers of squamous metaplasia (vimentin and α?actin). Furthermore, we examined global markers of adult stem cells including p63α and ABCG2 but also LGR5 as a novel stem cell marker. Immunocytochemical staining and PCR analysis of p63α, ABCG2 and LGR5 revealed the existence of side-population cells with a stem-cell phenotype and maintenance of corneal limbal stem cell properties. LGR5 expression can be related to cellular stemness and can be considered as a new phenotypic marker of residual human corneal limbal stem cells. However, the existence of CK10 together with co-expressed α-actin and vimentin suggests that the corneas investigated were under oxidative stress and showed evidence of squamous metaplasia.     

Limbal epithelial side-population cells have stem cell-like properties, including quiescent state

Corneal epithelial (CE) stem cells are believed to reside in the basal layer of the limbal epithelium but remain poorly understood due to the lack of an accepted in vivo reconstitution assay as well as definitive markers for epithelial stem cells. It has been reported that side-population (SP) cells with the ability to efflux the DNA-binding dye Hoechst 33342 have stem cell-like properties and that the SP phenotype accurately represents a quiescent and immature stem cell population in the adult bone marrow. In the present study, we investigated whether SP cells isolated from the limbal epithelium have stem cell-like properties. SP cells, separated by fluorescence-activated cell sorting, comprise approximately 0.4% of all limbal epithelial cells and have markedly higher expression of the stem cell markers ABCG2, Bmi-1, and nestin but no expression of markers for differentiated CE cells compared with non-SP cells. Cell-cycle and telomerase activity analyses revealed that SP cells are growth arrested and reside in the quiescent state. Moreover, limbal epithelial SP cells did not demonstrate proliferative capabilities under typical in vitro epithelial cell culture conditions using 3T3 feeder layers. These findings present the possibility that quiescent limbal epithelial SP cells may represent an extremely immature stem cell population compared with currently defined epithelial stem or progenitor cells.     

体外培养人角膜缘上皮细胞抑制激活态角膜基质细胞的生长

背景：角膜受到损伤后,角膜基质细胞激活转变为成纤维细胞,引起角膜基质瘢痕化,导致视力下降甚至丧失。 目的：观察角膜不同部位上皮细胞与角膜基质细胞的相互作用,探索角膜缘上皮细胞群能否抑制激活态角膜基质细胞的生长。 方法：采用酶消化及机械外力相结合的方法获取人角膜中央、角膜旁中央及角膜缘处角膜上皮细胞与浅层角膜基质细胞,进行体外培养。相差显微镜下观察细胞形态及生长变化。待培养角膜上皮细胞与基质细胞发生接触抑制时,记作“0 周”,采用免疫荧光染色技术检测培养细胞中PCNA及p63蛋白的表达。 结果与结论：培养的角膜上皮细胞与成纤维细胞发生接触抑制时,两种细胞间有明显分界线。角膜缘组上皮细胞中PCNA及p63蛋白均有较高的表达;角膜旁中央组PCNA有较高的表达,p63蛋白阴性表达;角膜中央组PCNA表达较低,p63蛋白阴性表达;从鉴定结果中可以得出只有角膜缘组中存在一定比例的角膜缘上皮干细胞。角膜缘组上皮细胞逐渐包围并化解成纤维细胞,在相互作用4周后,成纤维细胞聚集成死细胞团,缺乏角膜缘干细胞的中央组及旁中央组中成纤维细胞生长面积增加,上皮细胞生长受到抑制甚至死亡。说明体外培养的角膜缘上皮细胞群可以抑制激活态角膜基质细胞的生长。     

Intrastromal invasion by limbal epithelial cells is mediated by epithelial-mesenchymal transition activated by air exposure

Corneal epithelial stem cells are located in the basal layer of the limbus between the cornea and the conjunctiva. Regulation of these limbal epithelial progenitor cells by the stromal niche dictates corneal surface health. To further characterize this process, limbal explants were cultured at the air-fluid interface, termed air-lifting, to stimulate the niche. As compared to submerged cultures, air-lifting significantly promoted epithelial stratification, migration, proliferation, and intrastromal invasion by limbal epithelial cells. Epithelial intrastromal invasion was noted when the limbal, but not corneal, epithelium was recombined with the limbal stroma containing live, but not dead, cells. Invading limbal basal cells displayed up-regulated nuclear expression of p63 and Ki67, down-regulated E-cadherin and cornea-specific keratin 3, and switched expression of beta-catenin from intercellular junctions to the nucleus and cytoplasm, indicating the activation of the Wnt/beta-catenin pathway. Invaded cells isolated by collagenase from the stroma of air-lifted, but not submerged, explants showed vivid clonal growth on 3T3 fibroblast feeder layers and complete epithelial-mesenchymal transition by expressing nuclear p63 and cytoplasmic S100A4. These findings collectively suggest that epithelial-mesenchymal transition via the Wnt/beta-catenin pathway influences the fate of limbal epithelial cells, likely to be progenitor cells, between regeneration and fibrosis when the stromal niche is activated.     

Characterisation of Human Limbal Side Population Cells Isolated Using an Optimised Protocol From an Immortalised Epithelial Cell Line and Primary Limbal Cultures

The challenges in limbal stem cell biology largely remain in the process of identification, isolation and expansion of these adult corneal epithelial stem cells of the eye. Due to the absence of specific limbal stem cell markers, identification and isolation of putative limbal stem cells is a complicated task. The side population assay is an isolation method that utilises the ability of stem cells to efflux the DNA-binding dye Hoechst 33342 (or other vital dyes) combined with dual wavelength flow cytometry and is a valuable strategy to enrich for limbal stem cells. This assay has been used to successfully identify stem/ progenitor cell populations in a variety of tissues and cell lines. Here we optimise this assay to identify SP cell populations in both primary human limbal epithelial cultures and in an established human corneal epithelial cell line. The limbal SP fraction showed higher expression of ATP-binding cassette sub-family G member 2 (ABCG2), ΔNp63—a common limbal stem cell marker and the stem cell marker Sox2 compared to non-SP cells (NSP).     

A new isolation method of human limbal progenitor cells by maintaining close association with their niche cells

In human corneal epithelium, self-renewal and fate decision of stem cells are highly regulated in a niche microenvironment called palisades of Vogt in the limbus. Herein, we discovered that digestion with dispase, which cleaves off the basement membrane, did not remove the entire basal epithelial progenitor cells. In contrast, digestion with collagenase isolated on cluster consisting of not only entire epithelial progenitor cells but also their closely associated mesenchymal cells because of better preservation of some basement membrane matrix. Collagenase isolated more basal epithelial progenitor cells, which were p63α+ and small in the size (8 μm in diameter), and generated significantly more holoclones and meroclones on 3T3 fibroblast feeder layers than dispase. Further, collagenase isolated more small pan-cytokeratin-/p63α-/vimentin+ cells with the size as small as 5 μm in diameter and heterogeneously expressing vimentin, Oct4, Sox2, Nanog, Rex1, Nestin, N-cadherin, SSEA4, and CD34. Maintenance of close association between them led to clonal growth in a serum-free, low-calcium medium, whereas disruption of such association by trypsin/EDTA resulted in no clonal growth unless cocultured with 3T3 fibroblast feeder layers. Similarly, on epithelially denuded amniotic membrane, maintenance of such association led to consistent and robust epithelial outgrowth, which was also abolished by trypsin/EDTA. Epithelial outgrowth generated by collagenase-isolated clusters was significantly larger in diameter and its single cells yielded more holoclones on 3T3 fibroblast feeder layers than that from dispase-isolated sheets. This new isolation method can be used for exploring how limbal epithelial stem cells are regulated by their native niche cells.     

The effect of micropores in the surface of temperature-responsive culture inserts on the fabrication of transplantable canine oral mucosal epithelial cell sheets

Primary canine oral mucosal epithelial cells were cultured on temperature-responsive dishes and cell culture inserts to fabricate transplantable epithelial cell sheets. When 3T3 feeder layers and fetal bovine serum were eliminated from dish culture, the harvested cell sheets became significantly more fragile. In contrast, when epithelial cells were cultured on inserts having submicron-scale pores, cell sheet fragility was eliminated. Keratin expression profiles showed no differences among the harvested cell sheets, but the expression of p63, a putative stem/progenitor marker, was strongly dependent on the presence of 3T3 feeder layers and serum. These results suggest that the maintenance of stem/progenitor cells is influenced by the apical/basal supply of nutrients as well as culture supplements.     

改良组织块培养法体外培养人角膜上皮干细胞

文题释义：角膜上皮干细胞：属于单能干细胞,具有细胞周期长、低分化状态、增殖潜力大、不对称分裂等特点,定位于角膜缘基底细胞层,又称之为角膜缘干细胞,对角膜上皮细胞更新及维持角膜透明起着重要作用。角膜缘干细胞的体外培养方法：主要包括酶消化培养法和组织块培养法。酶消化培养法是利用DispaseⅡ酶破坏角膜缘上皮细胞与基底膜之间的半桥粒连接,然后剥取角膜缘上皮层,再使用胰酶将其消化为单个细胞进行培养。组织块培养法没有经过酶的双重消化,将剖取的角膜缘组织块进行贴壁,细胞游离出组织块进行贴壁生长,需要一个漫长的过程。  摘要背景：角膜上皮干细胞定位于角膜缘,又称之为角膜缘干细胞,临床上由于眼表严重热烧伤、化学性烧伤、慢性炎症等原因引起的角膜缘干细胞缺乏或功能障碍治疗较为棘手。目前利用组织工程技术体外培养角膜上皮干细胞并进行临床移植成为新型有效的治疗方向。目的：探讨在无血清培养条件下采用改良组织块培养法培养人角膜上皮干细胞的可行性。方法：人角膜缘组织来自河南省眼库,植片直径小于8 mm角膜移植术后的供者剩余眼球材料,手术显微镜下剖取角膜缘上皮层外2/3区域,采用2种方法培养人角膜上皮干细胞,常规组织块培养组是将组织块上皮面向上贴壁,加入K-SFM培养液后置于 37 ℃、体积分数为5%CO₂细胞培养箱中培养;改良组织块培养组是先将组织块浸泡于K-SFM培养液中,置于细胞培养箱中孵育12 h,然后组织块上皮面向下贴壁培养。组织块周边有细胞游离出贴壁生长记作“培养第1天”,每日相差显微镜下观察细胞生长变化。利用免疫荧光染色技术检测改良组织块培养第5,10,14天时原代细胞中p63及K3的表达。结果与结论：①改良组织块培养组出膜时间明显短于常规组织块培养组(P < 0.05),出膜率明显高于常规组织块培养组(P < 0.05);②改良组织块培养组细胞生长状态良好,培养第10天可见小体积细胞较多,聚集成灶状分布;培养第14天可见细胞克隆灶,克隆灶内细胞体积较小,形态均一;③培养第5天,K3表达量较多,p63表达量较少;培养第10天,K3和p63表达量均增多;培养第14天,K3表达量未见明显增多,p63表达量明显增多;④在无血清培养条件下,改良组织块培养法能显著促进角膜上皮干细胞的游离,提高体外培养细胞数量,为人角膜缘上皮组织片的构建提供种子细胞。ORCID: 0000-0001-8370-174X(许中中) 中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

人卵巢癌细胞株侧群细胞的生物学特征

目的 研究人卵巢癌细胞株细胞中乳腺癌耐药蛋白与侧群细胞表型的关系,并探讨侧群细胞在卵巢癌病理牛理中的作用以及卵巢癌细胞株在卵巢癌肿瘤干细胞研究中的应用. 方法 利用流式细胞术从人卵巢浆液腺癌细胞株OVCAR3中分离排斥双苯酰亚胺(Hoechst 33342)染色的侧群细胞以及能被其染色的非侧群细胞,比较两个亚群的细胞集落形成率,并检验其在软琼脂平板生长的能力.同时以免疫印迹和免疫荧光染色检测两种细胞的乳腺癌耐药蛋白表达情况. 结果 OVCAR3细胞株中排斥Hoechst 33342的细胞占2.0%,此活动对维拉帕米(verapamil)敏感.侧群细胞和非侧群细胞克隆形成率分别为46.17%±23.27%和6.17%±3.06%,侧群细胞克隆形成率高于非侧群细胞(P<0.05),并能在软琼脂平板中生长、形成球形的细胞集落.侧群细胞表达乳腺癌耐药蛋白. 结论 人卵巢浆液腺癌细胞株中存在排斥Hoechst 33342染色、对维拉帕米敏感的侧群细胞,是维持细胞株的主要因素,其表型与乳腺癌耐药蛋白相关.OVCAR3可用于卵巢癌肿瘤干细胞的研究.