Limbal dermoid epithelium shares phenotypic characteristics common to both hair epidermal and limbal epithelial stem cells

Limbal Epithelial Stem Cells in the Diabetic Cornea

Continuous replenishment of the corneal epithelium is pivotal for maintaining optical transparency and achieving optimal visual perception. This dynamic process is driven by limbal epithelial stem cells (LESCs) located at the junction between the cornea and conjunctiva, which is otherwise known as the limbus. In patients afflicted with diabetes, hyperglycemia-induced impairments in corneal epithelial regeneration results in persistent epithelial and other defects on the ocular surface, termed diabetic keratopathy (DK), which progressively diminish vision and quality of life. Reports of delayed corneal wound healing and the reduced expression of putative stem cell markers in diabetic relative to healthy eyes suggest that the pathogenesis of DK may be associated with the abnormal activity of LESCs. However, the precise role of these cells in diabetic corneal disease is poorly understood and yet to be comprehensively explored. Herein, we review existing literature highlighting aberrant LESC activity in diabetes, focusing on factors that influence their form and function, and emerging therapies to correct these defects. The consequences of malfunctioning or depleted LESC stocks in DK and limbal stem cell deficiency (LSCD) are also discussed. These insights could be exploited to identify novel targets for improving the management of ocular surface complications that manifest in patients with diabetes.

Non-canonical Wnt signaling in the eye

Wnt signaling comprises a group of complex signal transduction pathways that play critical roles in cell proliferation, differentiation, and apoptosis during development, as well as in stem cell maintenance and adult tissue homeostasis. Wnt pathways are classified into two major groups, canonical (β-catenin-dependent) or non-canonical (β-catenin-independent). Most previous studies in the eye have focused on canonical Wnt signaling, and the role of non-canonical signaling remains poorly understood. Additionally, the crosstalk between canonical and non-canonical Wnt signaling in the eye has hardly been explored. In this review, we present an overview of available data on ocular non-canonical Wnt signaling, including developmental and functional aspects in different eye compartments. We also discuss important changes of this signaling in various ocular conditions, such as keratoconus, aniridia-related keratopathy, diabetes, age-related macular degeneration, optic nerve damage, pathological angiogenesis, and abnormalities in the trabecular meshwork and conjunctival cells, and limbal stem cell deficiency.

Congenital central corneal dermoid: A rare entity

BACKGROUND

To understand the pathogenesis of a central corneal dermoid (CD) in a 12-day-old child, a comparison of CD specimen was done with limbal dermoid (LD) and cadaveric corneal (CC) specimens by immuno-histochemical staining.

METHODS

The child underwent penetrating keratoplasty for visual rehabilitation. The corneal tissue was sent for histo-pathological and immunochemistry evaluation. The corneal specimen obtained was compared the origin of central CD with LD and CC based on their antigenic expression profile.

RESULTS

Clinically over a period of 75 months post operatively the child maintained a clear graft. Hematoxylin and Eosin staining of LD had a typical morphology including stratified keratinized epithelium, hair shaft with pilo sebaceous glands, eccrine sweat glands, lymphocytes, and blood vessels. Immuno-histochemical staining showed positive stain for Cytokeratin 3 epithelial marker in the epithelium of CC, LD, and CD. Smooth muscle maker (SMA) was identified in LD and CD but not in the CC as it is devoid of blood vessels. Limbal stem cell maker (P63) was detected only in LD. Vimentin, a mesenchymal stem cell marker stained positively in all three tissues of CC, LD, and CD.

CONCLUSIONS

Corneal dermoid showed positive staining for mesodermal tissue components compared to both ectodermal and mesodermal components in limbal dermoid suggesting possibly a different origin of corneal dermoid.

Expression and localization of Sox10 during hair follicle morphogenesis and induced hair cycle

Sox transcription factors play many diverse roles during development, including regulating stem cell states, directing differentiation, and influencing the local chromatin landscape. Sox10 has been implicated in the control of stem/progenitor activity and epithelial-mesenchymal transition, yet it has not been studied in relation to the hair follicle cycle or hair follicle stem cell (HFSC) control. To elucidate the role of Sox10 in hair follicle cycle control, we performed immunohistochemical and immunofluorescence analysis of its expression during hair morphogenesis, the postnatal hair cycle, and the depilation-induced murine hair follicle cycle. During hair follicle morphogenesis, Sox10 was expressed in the hair germ and peg. In telogen, we detected nuclear Sox10 in the hair bulge and germ cell cap, where HFSCs reside, while in anagen and catagen, Sox10 was detected in the epithelial portion, such as the strands of keratinocytes, the outer root sheath (ORS) in anagen, and the regressed epithelial strand of hair follicle in catagen. These results suggest that Sox10 may be involved in early hair follicle morphogenesis and postnatal follicular cycling.

The capacity of goat epidermal adult stem cells to reconstruct the damaged ocular surface of total LSCD and activate corneal genetic programs

Epidermal adult stem cells (EpiASCs) have the potential for unlimited proliferation and differentiation, however, the ability of these stem cells to activate corneal genetic programs in response to corneal stroma stimulation needs to be further validated. Herein, a feasible strategy was developed to reconstruct the damaged corneal surface in a goat model with total limbal stem cell deficiency (LSCD) by transplanting EpiASCs, which had been explanted and cultured from the skin of an adult ram goat and were then purified by selecting single cell-derived clones and cultivating them on a denuded human amniotic membrane (HAM). These artificial tissues were then successfully transplanted into ewe goats with total LSCD. Binding of EpiASCs to the base membrane of an EpiASCs-HAM-Sheet (EHS) indicated their proliferating status. After transplantation, the EpiASCs could survive in the host tissue and they reconstructed the damaged ocular surface of total LSCD. The crystal reconstructed corneal epithelium expressed CK3 and Pax-6 similar to normal corneal epithelium and expressed the Sry gene after transplantation. These results demonstrated that EpiASCs could be induced to differentiate into corneal epithelial cell types in a corneal microenvironment and had the ability to activate corneal genetic programs. This work offer a foundation for promoting tissue-engineered cornea into clinical application.

A novel role for CRIM1 in the corneal response to UV and pterygium development

Pterygium is a pathological proliferative condition of the ocular surface, characterised by formation of a highly vascularised, fibrous tissue arising from the limbus that invades the central cornea leading to visual disturbance and, if untreated, blindness. Whilst chronic ultraviolet (UV) light exposure plays a major role in its pathogenesis, higher susceptibility to pterygium is observed in some families, suggesting a genetic component. In this study, a Northern Irish family affected by pterygium but reporting little direct exposure to UV was identified carrying a missense variant in CRIM1 NM_016441.2: c.1235 A > C (H412P) through whole-exome sequencing and subsequent analysis. CRIM1 is expressed in the developing eye, adult cornea and conjunctiva, having a role in cell differentiation and migration but also in angiogenesis, all processes involved in pterygium formation. We demonstrate elevated CRIM1 expression in pterygium tissue from additional individual Northern Irish patients compared to unaffected conjunctival controls. UV irradiation of HCE-S cells resulted in an increase in ERK phosphorylation and CRIM1 expression, the latter further elevated by the addition of the MEK1/2 inhibitor, U0126. Conversely, siRNA knockdown of CRIM1 led to decreased UV-induced ERK phosphorylation and increased BCL2 expression. Transient expression of the mutant H412P CRIM1 in corneal epithelial HCE-S cells showed that, unlike wild-type CRIM1, it was unable to reduce the cell proliferation, increased ERK phosphorylation and apoptosis induced through a decrease of BCL2 expression levels. We propose here a series of intracellular events where CRIM1 regulation of the ERK pathway prevents UV-induced cell proliferation and may play an important role in the in the pathogenesis of pterygium.

Double limbal dermoid with Tessier's paramedian facial cleft

We report the case of mandibulofacial dysostosis in a 9-year-old Indian boy presenting with unilateral double limbal dermoid in superotemporal and superonasal quadrants, high arched palate, and paramedian cleft in the right side of the nose with abnormal dentition. A multidisciplinary approach to treatment was advised. The dermoid cysts were excised surgically with a reconstruction of the ocular surface using multilayered amniotic membrane transplantation.

New Grading System for Limbal Dermoid: A Retrospective Analysis of 261 Cases Over a 10-Year Period

Purpose:

To establish a new scoring system for limbal dermoid, in order to unify the diagnostic criteria and assess the prognosis.

Methods:

A retrospective study was conducted on 261 patients with limbal dermoid. The basic information, clinical features, and pathology of dermoids were recorded, and the prognosis at 1 year after keratoplasty was assessed at follow-up. A new visual scoring system was created for the area of corneal involvement, the area of conjunctival involvement, and the surface shape.

Results:

There were 154 females and 107 males with mean age of 4 ± 3 years at surgery. After scoring, 59% (136) of patients were classified as grade I, 26% (60) as grade II, and 14% (33) as grade III. The pathological results were 124 dermoid cases, 76 lipodermoid, 5 complex choristoma, and 10 epibulbar osseous choristoma. Moreover, patients with lower clinical scores presented a better prognosis; the mean logarithm of the minimum angle of resolution (logMAR) best-corrected visual acuity in grade I patients was 0.38 ± 0.05, which was better than the grade II value of 0.61 ± 0.09 (P < 0.05) and the grade III value of 0.94 ± 0.11 (P < 0.001).

Conclusions:

New grading systems for limbal dermoid were useful for clinical diagnosis and may have prognostic value in predicting visual acuity. A lower-grade dermoid exhibited better vision postoperatively.

Differentiation of human limbal-derived induced pluripotent stem cells into limbal-like epithelium

Limbal epithelial stem cell (LESC) deficiency (LSCD) leads to corneal abnormalities resulting in compromised vision and blindness. LSCD can be potentially treated by transplantation of appropriate cells, which should be easily expandable and bankable. Induced pluripotent stem cells (iPSCs) are a promising source of transplantable LESCs. The purpose of this study was to generate human iPSCs and direct them to limbal differentiation by maintaining them on natural substrata mimicking the native LESC niche, including feederless denuded human amniotic membrane (HAM) and de-epithelialized corneas. These iPSCs were generated with nonintegrating vectors from human primary limbal epithelial cells. This choice of parent cells was supposed to enhance limbal cell differentiation from iPSCs by partial retention of parental epigenetic signatures in iPSCs. When the gene methylation patterns were compared in iPSCs to parental LESCs using Illumina global methylation arrays, limbal-derived iPSCs had fewer unique methylation changes than fibroblast-derived iPSCs, suggesting retention of epigenetic memory during reprogramming. Limbal iPSCs cultured for 2 weeks on HAM developed markedly higher expression of putative LESC markers ABCG2, ΔNp63α, keratins 14, 15, and 17, N-cadherin, and TrkA than did fibroblast iPSCs. On HAM culture, the methylation profiles of select limbal iPSC genes (including NTRK1, coding for TrkA protein) became closer to the parental cells, but fibroblast iPSCs remained closer to parental fibroblasts. On denuded air-lifted corneas, limbal iPSCs even upregulated differentiated corneal keratins 3 and 12. These data emphasize the importance of the natural niche and limbal tissue of origin in generating iPSCs as a LESC source with translational potential for LSCD treatment.