Using acellular porcine limbal stroma for rabbit limbal stem cell microenvironment reconstruction

To investigate the feasibility of using acellular porcine limbal stroma for limbal stem cell microenvironment reconstruction. Limbal reconstruction was performed in rabbit partial limbal defect models. Rabbits were randomly divided into four groups: acellular porcine limbal stroma, de-epithelized rabbit limbal autograft stroma, de-epithelized porcine limbal stroma and acellular porcine corneal stroma transplantation groups. In both the acellular porcine limbal stroma and de-epithelized rabbit limbal autograft stroma groups, cornea transparency and epithelium integrity were sustained and graft rejection was not observed. The basal epithelial cells of the grafts showed the K3+/P63+/Ki67+ phenotype at postoperative month 1, but it returned to K3-/P63+/Ki67+(phenotype characteristic of limbal epithelium) by postoperative months 3 and 6. In the de-epithelized porcine limbal stroma group, acute and serious immune rejection occurred by postoperative days 8-10. The basal epithelial cells of the grafts showed the K3+/P63+/Ki67+ phenotype at postoperative month 1. In the acellular porcine corneal stroma group, there were some new vessel invasion into the peripheral cornea and mild corneal opacity. The basal epithelial cells of the grafts showed the K3+/P63+/Ki67+ phenotype at postoperative months 1, 3, and 6. In conclusion, acellular porcine limbal stroma possessed very low immunogenicity, retained a good original limbal ECM microenvironment, and thus the reconstructed rabbit limbal microenvironment maintained limbal epithelial stem cell stemness and proliferation.     

N-Cadherin is expressed by putative stem/progenitor cells and melanocytes in the human limbal epithelial stem cell niche

Corneal epithelial stem cells are known to be localized to the basal layer of the limbal epithelium, providing a model system for epithelial stem cell biology; however, the mechanisms regarding the maintenance of these stem cells in their specialized niche remain poorly understood. N-cadherin is a member of the classic cadherin family and has previously been demonstrated to be expressed by hematopoietic stem cells. In the present study, we demonstrate that N-cadherin is expressed by putative stem/progenitor cells, as well as melanocytes, in the human limbal epithelial stem cell niche. In addition, we demonstrate that upon in vitro culture using 3T3 feeder layers, loss of N-cadherin expression occurs with cell proliferation. These results indicate that N-cadherin may be a critical cell-to-cell adhesion molecule between corneal epithelial stem/progenitor cells and their corresponding niche cells in the limbal epithelium.     

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。     

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 Wnt pathway, epithelial-stromal interactions, and malignant progression in phyllodes tumours

In a previous study of phyllodes tumours, it has been shown that both the stroma and the epithelium can exhibit distinct molecular changes, suggesting that both are part of the neoplastic process. In view of this finding, it was decided to study stromal-epithelial interactions in these tumours by examining the Wnt-APC-beta-catenin pathway. Beta-catenin and cyclin D1 immunohistochemistry was performed on 119 phyllodes tumours. Eighty-six (72%) showed stromal nuclear beta-catenin localization and in 57% the staining was moderate or strong; however, of the eight malignant tumours in the series, seven showed absent or weak nuclear staining (p<0.025). In no tumour was nuclear beta-catenin staining seen in the epithelial component. Moderate or strong stromal cyclin D1 staining correlated with nuclear stromal beta-catenin staining (p<0.05). Forty-five of the tumours, including two malignant lesions, were screened for beta-catenin exon 3 mutations using SSCP and sequencing, but none was found. Loss of heterozygosity (LOH) of the marker D5S346 was used to infer APC mutation, but only one (benign) tumour showed LOH. Wnt2 and Wnt5a mRNA was localized by in situ hybridization in 13 cases (three malignant) chosen to reflect the different beta-catenin staining patterns. There was an association between strong nuclear beta-catenin staining of stromal cells and epithelial Wnt5a expression (p<0.0015). These data suggest that stromal proliferation in benign phyllodes tumours relies on abnormalities in the Wnt pathway which result not from mutation, but from Wnt5a expression in the epithelium. In the progression to malignancy, the stromal proliferation appears to become independent of the Wnt pathway and, presumably, of the epithelial component of these tumours.     

Limbal epithelial stem/progenitor cells attract stromal niche cells by SDF-1/CXCR4 signaling to prevent differentiation

Corneal epithelial stem cells (SCs) are an ideal model for investigating how adult lineage-committed epithelial SCs are regulated by an anatomically defined and accessible niche, that is, limbal palisades of Vogt, located between the cornea and the conjunctiva. We have used collagenase digestion to isolate the entire limbal epithelial SCs and subjacent mesenchymal cells, and we have demonstrated that their close association is crucial for promoting epithelial clonal growth, implying that the latter serves as niche cells (NCs). After their close association was disrupted by trypsin/EDTA, single SCs and NCs could reunite to generate sphere growth in three-dimensional Matrigel in the embryonic SC medium, and that such sphere growth initiated by SC-NC reunion was mediated by SDF-1 uniquely expressed by limbal epithelial progenitor cells and its receptor CXCR4, but not CXCR7, strongly expressed by limbal stromal NCs. Inhibition of CXCR4 by AMD3100 or a blocking antibody to CXCR4 but not CXCR7 disrupted their reunion and yielded separate spheres with a reduced size, while resultant epithelial spheres exhibited more corneal differentiation and a notable loss of holoclones. For the first time, these results provide strong evidence supporting that limbal SC function depends on close physical association with their native NCs via SDF-1/CXCR4 signaling. This novel in vitro model of sphere growth with NCs can be used for investigating how limbal SC self-renewal and fate decision might be regulated in the limbal niche.     

Concise review: Stem cells in the corneal stroma

The cornea is a tough transparent tissue admitting and focusing light in the eye. More than 90% of the cornea is stroma, a highly organized, transparent connective tissue maintained by keratocytes, quiescent mesenchymal cells of neural crest origin. A small population of cells in the mammalian stroma displays properties of mesenchymal stem cells, including clonal growth, multipotent differentiation, and expression of an array of stem cell-specific markers. Unlike keratocytes, the corneal stromal stem cells (CSSCs) undergo extensive expansion in vitro without loss of the ability to adopt a keratocyte phenotype. Several lines of evidence suggest CSSCs to be of neural crest lineage and not from bone marrow. CSSCs are localized in the anterior peripheral (limbal) stroma near to stem cells of the corneal epithelium. CSSCs may function to support potency of the epithelial stem cells in their unique limbal niche. On the other hand, little information is available documenting a role for CSSCs in vivo in stromal wound healing or regeneration. In vitro CSSCs reproduce the highly organized connective tissue of the stroma, demonstrating a potential use of these cells in tissue bioengineering. Direct introduction of CSSCs into the corneal stroma generated transparent tissue in a mouse model of corneal opacity. Human CSSCs injected into mice corneas did not elicit immune rejection over an extended period of time. The CSSCs therefore appear offer an opportunity to develop cell- and tissue-based therapies for irreversible corneal blindness, conditions affecting more than 10 million individuals worldwide.     

人羊膜上皮细胞体外培养重建角膜上皮的实验研究

目的: 探讨人羊膜上皮细胞(human amniotic epithelial cells, HAECs)诱导分化为角膜上皮细胞的可塑性及其重建角膜上皮的可行性。方法: 取足月产人羊膜,通过胶原酶、胰蛋白酶和EDTA消化获得HAECs,将细胞在体外培养扩增、传代,将2~3代HAECs接种于去上皮的兔角膜基质上培养,待HAECs融合形成单层后,置于插入式培养皿中进行气液界面培养14 d。对角膜基质上培养的HAECs用光镜、扫描电镜和透射电镜进行形态学及超微结构观察,以及细胞角蛋白(CK)3/12的免疫组织化学检测。结果: HAECs可在角膜基质上生长,培养1~2 d可形成单层,气液界面培养14 d可形成4~5层细胞的复层上皮,扫描电镜观察细胞表面有丰富的微绒毛,透射电镜下可见上皮细胞之间有桥粒连接,免疫组化检测复层细胞表达CK3/12,所形成的复层结构与正常角膜上皮相似。结论: HAECs有可能作为种子细胞用于组织工程角膜上皮重建。     

Rapid tissue engineering of biomimetic human corneal limbal crypts with 3D niche architecture

Limbal epithelial stem cells are responsible for the maintenance of the human corneal epithelium and these cells reside in a specialised stem cell niche. They are located at the base of limbal crypts, in a physically protected microenvironment in close proximity to a variety of neighbouring niche cells. Design and recreation of elements of various stem cell niches have allowed researchers to simplify aspects of these complex microenvironments for further study in vitro. We have developed a method to rapidly and reproducibly create bioengineered limbal crypts (BLCs) in a collagen construct using a simple one-step method. Liquid is removed from collagen hydrogels using hydrophilic porous absorbers (HPAs) that have custom moulded micro-ridges on the base. The resulting topography on the surface of the thin collagen constructs resembles the dimensions of the stromal crypts of the human limbus. Human limbal epithelial cells seeded onto the surface of the constructs populate these BLCs and form numerous layers with a high proportion of the cells lining the crypts expressing putative stem cell marker, p63α. The HPAs are produced using a moulding process that is flexible and can be adapted depending on the requirements of the end user. Creation of defined topographical features using this process could be applicable to numerous tissue-engineering applications where varied 3-dimensional niche architectures are required.     

A dual-layer silk fibroin scaffold for reconstructing the human corneal limbus

Membranes prepared from Bombyx mori silk fibroin have shown potential as a substrate for human limbal epithelial (L-EC) and stromal cell cultivation. Here we present fibroin as a dual-layer construct containing both an epithelium and underlying stroma for corneolimbal reconstruction. We have compared the growth and phenotype of L-EC on non-porous versus porous fibroin membranes. Furthermore, we have compared the growth of limbal mesenchymal stromal cells (L-MSC) in either serum-supplemented medium or the MesenCult-XF(?) culture system within fibroin fibrous mats. The co-culture of L-EC and L-MSC in fibroin dual-layer constructs was also examined. L-EC on porous membranes displayed a squamous monolayer; in contrast, L-EC on non-porous fibroin appeared cuboidal and stratified. Both constructs maintained evidence of corneal phenotype (cytokeratin 3/12) and distribution of ΔNp63(+) progenitor cells. L-MSC cultivated within fibroin fibrous mats in serum-supplemented medium contained less than 64% of cells expressing the characteristic MSC phenotype of CD73(+)CD90(+)CD105(+) after two weeks, compared with over 81% in MesenCult-XF(?) medium. Dual-layer fibroin scaffolds consisting of L-EC and L-MSC maintained a similar phenotype as on the separate layers. These results support the feasibility of a 3D engineered limbus constructed from B.?mori silk fibroin, and warrant further studies into the potential benefits it offers to corneolimbal tissue regeneration.     

Differentiation of human embryonic stem cells into corneal epithelial-like cells by in vitro replication of the corneal epithelial stem cell niche

Human embryonic stem cells (hESCs) are pluripotent cells capable of differentiating into any cell type of the body. It has long been known that the adult stem cell niche is vital for the maintenance of adult stem cells. The cornea at the front of the eye is covered by a stratified epithelium that is renewed by stem cells located at its periphery in a region known as the limbus. These so-called limbal stem cells are maintained by factors within the limbal microenvironment, including collagen IV in basement membrane and limbal fibroblasts in the stroma. Because this niche is very specific to the stem cells (rather than to the more differentiated cells) of the corneal epithelium, it was hypothesized that replication of these factors in vitro would result in hESC differentiation into corneal epithelial-like cells. Indeed, here we show that culturing of hESC on collagen IV using medium conditioned by the limbal fibroblasts results in the loss of pluripotency and differentiation into epithelial-like cells. Further differentiation results in the formation of terminally differentiated epithelial-like cells not only of the cornea but also of skin. Scanning electron microscopy shows that some differences exist between hESC-derived and adult limbal epithelial-like cells, necessitating further investigation using in vivo animal models of limbal stem cell deficiency. Such a model of hESC differentiation is useful for understanding the early events of epithelial lineage specification and to the eventual potential application of epithelium differentiated from hESC for clinical conditions of epithelial stem cell loss. 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：     

An immunoprotective privilege of corneal epithelial stem cells against Th17 inflammatory stress by producing glial cell-derived neurotrophic factor

Adult stem cells are well known for their self-renewal and regenerative capacity. The mechanisms protecting these cells from inflammatory damage have not been well elucidated. This study investigated the immunoprotective properties of corneal epithelial stem cells from inflammation by producing glial cell-derived neurotrophic factor (GDNF). Primary human limbal epithelial cells (HLECs) cultured from limbal explants were treated with interleukin (IL)-17A, tumor necrosis factor (TNF)-α, or hyperosmotic media, with or without GDNF or nuclear factor kappa B (NF-κB) inhibitor (NF-κB-I) for 4-48 hours. Inflammatory mediators and Th17-inducing cytokines were determined by real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and immunobead assays. NF-κB activation was detected by p65 phosphorylation, immunostaining and Western blotting. GDNF and its receptor, GDNF family receptor α-1, were exclusively immunolocalized in the basal layer of limbal epithelium, whereas IL-17 receptor was negative in these cells. Exogenous IL-17A stimulated the expression and production of inflammatory cytokines (TNF-α, IL-6, and IL-1β) and chemokine IL-8 by HLECs. Th17-inducing cytokines, transforming growth factor (TGF)-β1, IL-6, IL-23, and IL-1β, were significantly increased at mRNA and protein levels by HLECs exposed to TNF-α or hyperosmotic media. IL-17 activated NF-κB by p65 phosphorylation at serine 536 and nuclear translocation. GDNF or NF-κB-I blocked IL-17-induced NF-κB p65 activation and production of inflammatory mediators. Furthermore, GDNF suppressed the production of Th17-inducing cytokines through inhibiting NF-κB activation. These findings demonstrate that limbal progenitor cell-produced neurotrophic factor GDNF suppresses IL-17-mediated inflammation via NF-κB signaling pathway. This may represent a unique immunoprotective property of limbal stem cells against inflammatory challenges on the ocular surface.     

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     

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).     

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.     

Beta-catenin abnormalities and associated insulin-like growth factor overexpression are important in phyllodes tumours and fibroadenomas of the breast

The aim of this study was to assess the expression of IGF-I and IGF-II in phyllodes tumours and fibroadenomas and to see if there is any correlation between nuclear beta-catenin expression and IGF-I and IGF-II expression in these tumours. In a previous study, it has been shown that Wnt signalling is important in the pathogenesis of phyllodes tumours of the breast. Epithelial Wnt5a overexpression and stromal Wnt2 overexpression were associated with abnormal, nuclear localization of beta-catenin in the stromal cells of these tumours. However, not all tumours with beta-catenin accumulation showed Wnt overexpression. One other possible cause of beta-catenin accumulation is overexpression of insulin-like growth factors (IGFs), as both IGF-I and IGF-II have been shown to stabilize beta-catenin. In this study, 30 fibroadenomas of the breast were assessed for beta-catenin expression using immunohistochemistry and the results were compared with previous data from 119 phyllodes tumours. In situ hybridization was used to assess IGF-I and IGF-II expression in 23 phyllodes tumours and 16 fibroadenomas. Nineteen phyllodes tumours (83%) showed widespread overexpression of IGF-II and 5/23 (22%) showed widespread overexpression of IGF-I. IGF-I expression correlated with nuclear beta-catenin staining in phyllodes tumours. Malignant phyllodes tumours showed no or little IGF-I expression. There was a degree of nuclear beta-catenin expression in the stroma (weak in 33%, moderate in 27%, and strong in 40%) in all fibroadenomas and nuclear beta-catenin staining correlated with IGF-I overexpression. Extensive IGF-II overexpression was also found in the majority of fibroadenomas (12/16). These results support the hypothesis that IGF-I and IGF-II overexpression may be important in the pathogenesis of fibroepithelial neoplasms of the breast and that IGF-I overexpression is likely to be contributing to the nuclear beta-catenin localization observed in the tumours.