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.     

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。     

The porcine limbal epithelial stem cell niche as a new model for the study of transplanted tissue-engineered human limbal epithelial cells

Transparency of the human cornea is dependent upon the integrity of its epithelium and hence a population of limbal epithelial stem cells (LESCs). We have previously shown that LESCs reside in limbal epithelial crypts at the periphery of the human cornea. In this study the anatomy and functionality of the porcine limbus was evaluated for the first time as a novel model of the human limbus. Scanning electron microscopy, confocal microscopy, and histology revealed common structures in the porcine and human limbus in terms of the location and topography of palisades of Vogt and limbal epithelial crypts. Epithelial cells harvested from crypt regions achieved higher colony forming efficiency than cultures established from the noncrypt regions and central cornea. Also, expression of the putative SC markers p63α and integrin β1 brightness was higher in the basal layer of the crypt regions, as shown by immunocytochemistry. De-epithelialized porcine corneas were used as an in vitro organ culture model to study the fate of transplanted human epithelium cultured from the limbus. Multilayered epithelium was observed after ～1 week. Subsequently, wounds were inflicted on the central corneal epithelium. The wounded tissue healed within 5-7 days, and multilayering of the central corneal epithelium was re-established. The transplanted epithelia were repeatedly wounded at least four times and the wounds healed by 1 week. Putative SC marker expression of the transplanted epithelia was confirmed using immunohistochemistry. These results demonstrate that the porcine limbus shares features with the human limbus and as such provides a suitable model for the study of cultured limbal epithelial cell transplantation. These data have significant clinical value as this model can provide information on LESC fate post-transplantation and their ability to respond to injury, which is not possible to study in patients.     

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：     

Wnt信号通路调控角膜缘干细胞治疗角膜缘干细胞缺乏症

文题释义： Wnt信号通路：Wnt信号通路是一条高度保守的信号通路,在干细胞调控中发挥重要作用。当细胞外Wnts与细胞膜上特异性受体Frizzled蛋白结合导致GSK3β失活,β-catenin在胞质中积累继而向胞核转位,标志着Wnt通路被激活。β-catenin在细胞核中与转录因子Tcf /LEF结合启动下游基因而发挥功能。 角膜缘干细胞：角膜缘为角膜和结膜、巩膜交界部分,角膜缘干细胞存在于角膜缘的Vogt栅栏结构中,属于单能干细胞,在角膜损伤修复中发挥重要作用。角膜缘干细胞缺乏是由于眼表各类损伤(化学伤、严重的感染等)或者基质微环境异常(先天性无虹膜、放射线所致角膜病)导致角膜上皮被结膜上皮侵犯和替代。 背景：Wnt信号通路在干细胞的调控中发挥重要作用,但是其对于角膜缘干细胞的调控作用尚不十分明确。 目的：探讨Wnt信号通路对角膜缘干细胞的调控作用及其在角膜缘干细胞缺乏症治疗中的疗效。 方法：大鼠角膜缘组织中依次加入Dispase和Trypsin/EDTA进行消化,将消化后的角膜缘干细胞悬液接种于3D-Matrigel微环境中培养,实验组培养体系中加入Wnt信号通路激活剂氯化锂(500 μmol/L),对照组不加氯化锂,培养第7天qRT-PCR检测角膜缘干细胞中p63α、CK12、CEBPδ和Ki67的表达,免疫荧光染色检测角膜缘干细胞中β-catenin的表达。采用碱烧伤法建立大鼠角膜缘干细胞缺乏模型,治疗组大鼠结膜下注射激活了Wnt信号通路的角膜缘干细胞,对照组大鼠结膜下注射等量PBS,随后每天使用裂隙灯观察,治疗后第4天取角膜缘组织进行免疫荧光染色、苏木精-伊红染色。 结果与结论：①角膜缘干细胞在3D-Matrigel培养微环境中呈球形聚集生长,对照组角膜缘干细胞中β-catenin呈阴性,实验组角膜缘干细胞中β-catenin在细胞浆和细胞核内聚集;②qRT-PCR结果显示：对照组与实验组之间干性指标p63α、CK12和功能指标CEBPδ差异均无显著性意义(P > 0.05);实验组增殖指标Ki-67较对照组水平明显升高,差异有显著性意义(P < 0.05);③建立大鼠角膜缘干细胞缺乏模型,治疗组大鼠角膜组织混浊评分较对照组明显减低,差异有显著性意义(P < 0.05),角膜组织苏木精-伊红染色可见治疗组大鼠角膜上皮细胞排列整齐,细胞大小较均一,修复情况较良好,免疫荧光结果显示治疗组大部分角膜上皮细胞中β-catenin在细胞浆以及细胞核内聚集,而对照组角膜上皮细胞中β-catenin仅是弱阳性,未见在胞浆聚集或者进核;④结果表明,Wnt信号通路的激活增强了角膜缘干细胞的增殖能力,同时能够维持细胞干性,角膜缘干细胞进入干细胞自我更新状态;激活Wnt信号通路后的角膜缘干细胞可促进角膜缘干细胞缺乏模型大鼠角膜上皮的修复,减轻角膜混浊程度;通过调控Wnt信号通路改变角膜缘干细胞的功能特性可能成为治疗角膜缘干细胞缺乏症的新途径。 ORCID: 0000-0003-0698-3653(韩波) 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     

脱细胞猪角膜基质的基底膜在修复兔角膜损伤中的作用

目的 探讨脱细胞角膜基质支架材料表面保存基底膜样结构对修复角膜损伤的必要性. 方法 将采用反复冻融及酶消化法制备的脱细胞猪角膜基质,移植到兔角膜损伤模型上,通过大体及组织学分别观察材料表面基底膜结构的有无对修复兔角膜基质损伤的影响. 结果 脱细胞猪角膜基质材料表面有基底膜的实验组（n=8）兔角膜损伤全部修复,无穿孔,支架材料与受体角膜整合.材料表面无基底膜的对照组（n=8）中,有6例植入的支架材料溶解,兔角膜穿孔.两组结果比较差异有显著统计学意义. 结论 脱细胞角膜基质支架材料表面具有基底膜样结构,有利于形成正常角膜上皮屏障,从而防止了生物材料的过快降解,有利于材料与宿主基质的整合和改建.     

In vitro phenotypic characterization of human limbal epithelial cells

INTRODUCTION: Human limbal epithelial cells (huLEC) have been used for clinical purposes in ocular surface diseases to promote rapid re-epithelisation and restore corneal epithelium integrity. However, in Mexico this technique has not been fully developed. This study was conducted to characterize the huLEC phenotype expanded in vitro using a cell culture technique. MATERIAL AND METHODS: Cells were obtained from limbal tissue, cultured in KSFM medium and analyzed for the expression of vimentin, K, K19, p63, K12, by flow cytometry and immuno-fluorescence. RESULTS: The phenotype of cultured cells was vimentin+K+K19+ p63+K12-. CONCLUSIONS: Our results suggest that under these culture conditions huLEC maintained their stem cell phenotype. This culture technique could be used for clinical purposes in Mexico.     

脱细胞猪角膜表面基底膜成分的检测

背景：前期实验显示脱细胞猪角膜具有良好的组织相容性,可以支持角膜细胞和皮肤上皮细胞的生长。 目的：检测脱细胞猪角膜是否保存了利于角膜上皮细胞生长的重要组织结构—基底膜。 方法：利用荧光抗体对脱细胞猪角膜表面的基底膜成分(层粘蛋白和Ⅳ型胶原)进行免疫组织化学检测,荧光显微镜下观察脱细胞猪角膜表面是否保存了基底膜成分。 结果与结论：免疫荧光染色显示脱细胞猪角膜前基质表面层粘蛋白和Ⅳ型胶原呈阳性表达,与新鲜猪角膜表面基底膜的荧光表达相同,表明脱细胞猪角膜保存了利于角膜上皮细胞生长的基底膜。     

Reconstruction of damaged corneas by transplantation of autologous limbal epithelial cells

BACKGROUND: Stevens-Johnson syndrome, ocular pemphigoid, and thermal or chemical burns can cause scarring and opacification of the cornea and loss of vision. Transplantation of epithelial cells from the limbus of the contralateral cornea can restore useful vision. However, this procedure requires a large limbal graft from the healthy eye and is not possible in patients who have bilateral lesions. METHODS: We took specimens of limbal epithelial cells from the healthy contralateral eyes of six patients with severe unilateral corneal disease. The epithelial cells were cultured and expanded on amniotic membrane. The amniotic membrane, together with the sheet of limbal epithelial cells, was transplanted to the denuded corneal surface of the damaged eye after superficial keratectomy to remove fibrovascular ingrowth. The mean (+/-SD) follow-up period was 15+/-2 months. RESULTS: Complete reepithelialization of the corneal surface occurred within two to four days of transplantation in all six eyes receiving transplants. By one month, the ocular surface was covered with corneal epithelium, and the clarity of the cornea was improved. In five of the six eyes receiving transplants (83 percent), the mean visual acuity improved from 20/112 to 20/45. In one patient with a chemical burn who had total opacification of the cornea, the acuity improved from the ability to count fingers at 40 cm to 20/200. No patient had recurrent neovascularization or inflammation in the transplanted area during the follow-up period. CONCLUSIONS: Transplantation of autologous limbal epithelial cells cultured on amniotic membrane is a simple and effective method of reconstructing the corneal surface and restoring useful vision in patients with unilateral deficiency of limbal epithelial cells.     

Morphological and Autoradiographic Studies on the Corneal and Limbal Epithelium of Rabbits

The investigation was centered on the morphological features of the conjunctiva–cornea transition (limbus) of the rabbit eye and the proliferative behavior of its epithelium. The eyes were processed for examination with light and electron microscopy, as well as for autoradiography after intravitreal injection of [³H]thymidine ([³H]TdR). At the sites of extraocular muscle insertion, the vascularization of the stroma extended to the peripheral cornea, and the limbal epithelium was thin with its basal stratum made up by clear cuboidal cells. In between the muscle insertions, the cuboidal clear cells, as well as the stroma blood vessels, were scarce. At the light microscope level, the basement membrane was distinct in the cornea but not in the limbus or the conjunctiva. Autoradiographs demonstrated that, at the limbus, the basal cells migrated very quickly to the suprabasal region and remained there up to the 28‐day interval. Labeled cells were identified in all epithelial layers of the cornea, including the basal one, at 21 and 28 days but not in the limbal basal clear cells. The rate of renewal of conjunctival epithelium was similar to that observed for the transition with scarce clear cells. The high‐resolution autoradiographs demonstrated that the basal cuboidal clear limbal cells exhibit a quick renewal and that they are not label‐retaining cells. These latter ones were detected all over the corneal epithelium and in the suprabasal layers of the limbus up to 28 days, in physiological conditions, without the need of stimulation by damage to the corneal epithelium. Anat Rec, 291:191–203, 2008. © 2008 Wiley‐Liss, Inc.     

Down-regulation of Pax6 is associated with abnormal differentiation of corneal epithelial cells in severe ocular surface diseases

Pax6 is the universal master control gene for eye morphogenesis. Other than retina and lens, Pax6 also expressed in the ocular surface epithelium from early gestation until the postnatal stage, in which little is known about the function of Pax6. In this study, corneal pannus tissues from patients with ocular surface diseases such as Stevens-Johnson syndrome (SJS), chemical burn, aniridia and recurrent pterygium were investigated. Our results showed that normal ocular surface epithelial cells expressed Pax6. However, corneal pannus epithelial cells from the above patients showed a decline or absence of Pax6 expression, accompanied by a decline or absence of K12 keratin but an increase of K10 keratin and filaggrin expression. Pannus basal epithelial cells maintained nuclear p63 expression and showed activated proliferation, evidenced by positive Ki67 and K16 keratin staining. On 3T3 fibroblast feeder layers, Pax6 immunostaining was negative in clones generated from epithelial cells harvested from corneal pannus from SJS or aniridia, but positive in those from the normal limbal epithelium; whereas western blots showed that some epithelial clones expanded from pannus retained Pax6 expression. Transient transfection of an adenoviral vector carrying EGFP-Pax6 transgenes into these Pax6(-) clones increased both Pax6 and K12 keratin expression. These results indicate that Pax6 helps to maintain the normal corneal epithelial phenotype postnatally, and that down-regulation of Pax6 is associated with abnormal epidermal differentiation in severe ocular surface diseases. Reintroduction of activation of the Pax6 gene might be useful in treating squamous metaplasia of the ocular surface epithelium.     

Survival of cultured allogeneic limbal epithelial cells following corneal repair

In this study a technique for determining donor cell fate following corneal grafting was evaluated. Patients treated for limbal deficiency with allogeneic cultured corneal epithelial cells were studied to determine the fate of the grafted cells. The technique was evaluated initially through the use of donor eyes and then applied to the clinical analysis of 7 patients who had received a cultured corneal epithelial allograft. Cells removed from the cornea and any retrieved tissue were analyzed via polymerase chain reaction (PCR) genotyping to determine the origin of the cells populating the patients' healed cornea. A mixture of genotypes was detected in a cornea retrieved from a patient following a fully penetrating keratoplasty who had received a mixture of allogeneic tissue. Donor cells were no longer detected on the corneal surface of all 7 cases beyond 28 weeks postgraft. At these later time points, only patient genotype could be detected. These results demonstrate that PCR genotyping can be used to determine the origin of cells populating the surface of the cornea following the grafting of cultured allogeneic cells and demonstrates that transplanted cultured limbal epithelial cells do not persist on the surface of the host cornea for more than 28 weeks.     

CD18 and ICAM-1-dependent corneal neovascularization and inflammation after limbal injury

Extensive limbal injury is a leading cause of irreversible blindness. The destruction of corneal limbal stem cells often results in corneal neovascularization and an optically inferior epithelium. Previous work has shown that the neovascularization after limbal injury is vascular endothelial growth factor (VEGF)-dependent, with much of the VEGF emanating from the inflammatory cells that invade the cornea. Using a relevant mouse model of limbal injury, we examined the role of CD18 and intercellular adhesion molecule-1 (ICAM-1) in limbal injury-induced neovascularization. The results show that CD18- and ICAM-1-deficient mice developed 35% (n = 5, P = 0.003) and 36% (n = 5, P = 0.002) less neovascularization than strain-specific normal controls, respectively. The corneal neutrophil counts were similarly reduced by 51% (n = 5, P < 0.003) and 46% (n = 5, P < 0.006), respectively. When VEGF mRNA levels were analyzed, they were reduced by 66% (n = 3, P = 0.004) and 48% (n = 3, P = 0.024), respectively. Taken together, these data identify CD-18 and ICAM-1 as mediators of the inflammatory and VEGF-dependent corneal neovascularization that follows limbal injury. The targeting of CD18 and ICAM-1 may prove useful in the treatment of inflammation-associated neovascularization in the cornea and elsewhere.     

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.     

脱细胞猪角膜基质支架的制备及其生物相容性

BACKGROUND: Studies have found that a variety of biological materials can be used for preparing corneal stroma scaffolds that have good biocompatibility, but research on preparation and biocompatibility of the acellular porcine corneal stroma scaffold is little. OBJECTIVE: To explore the preparation and biocompatibility of the acellular porcine corneal stroma scaffold. METHODS: Acellular porcine corneal stroma scaffold and its extract were prepared. Well-grown human corneal stromal cells were selected and cultured in the extract of acellular porcine corneal stroma scaffold (experimental group) or in the complete medium (control group), respectively. After 1, 2 and 3 days of culture, the proliferation ability of human corneal stromal cells was detected by MTT assay. In the meanwhile, human corneal cells were directly seeded onto the acellular porcine corneal stroma scaffold, and then the cell growth on the scaffold was detected using immunochemical method. RESULTS AND CONCLUSION: The number of human corneal stromal cells was in a rise with time in the two groups, and absorbance values had no significant difference between two groups at different time points of culture. Human corneal stromal cells grew well on the scaffold, and were positive for cell integrin β1, vimentin, aldehyde dehydrogenase 3A1, as well as CD34, CDK2 and K-Ras. These results show that the acellular porcine corneal stroma scaffold has no cytotoxicity, and has good biocompatibility.