OUP accepted manuscript

Oxygen uptake at the ocular surface in diabetic animals is impaired in response to central corneal injury

Poor wound healing is one of the most devastating complications in late-stage diabetic patients. The avascular cornea does not rely on circulation for its oxygen consumption, uptaking it mainly from the atmosphere. Previous studies demonstrated that oxygen uptake (O2U) in diabetic experimental animals and patients is significantly lower than in the non-diabetic condition. Our recent experiments show that upon wounding of the central cornea the O2U decreased across the ocular surface, followed by two increases at 6-24 h, and at 72 h, which appeared to be important for proper wound healing. It is however not known whether the two distinct O2U increases are maintained in diabetic ocular surface in response to corneal injury. In this study, we used an optic-fiber oxygen micro-sensor to measure O2U across the ocular surface of streptozotocin (STZ)- induced diabetic mice and age-matched control mice following injury to the central cornea. We found that the injury causes an immediate and substantial reduction of O2U across the ocular surface. O2U in non-diabetic corneas increases at 2-6 h post wounding (hpw), decreasing again before the second rise to peak at 72 hpw, especially at the limbus. O2U in the diabetic cornea decreases more markedly than that of non-diabetic control. This defective diabetic O2U persisted, precluding the two dynamic rises in O2U, leading to a failure in recovery. Altogether, our results suggest a previously unknown mechanism of a defective O2U response to injury in the diabetic ocular surface, which warrants further research and may lead to new therapeutic paths.

Limbal stem cell deficiency approaches and limbal niche restoration

Approaches to limbal stem cell deficiency remain challenging, especially in bilateral cases, where healthy limbal stem cells are not accessible. While living-related allogeneic and allogeneic limbal stem cell sources have been utilized, their dependence on immunosuppression and its associated side effects pose significant limitations. Mucosal and mesenchymal stem cells have shown potential for differentiation into limbal stem cells and promoting corneal healing, primarily when cultured on the amniotic membrane or fibrin. However, none can fully replicate the original limbus. Innovations in surgical techniques, such as simple oral mucosal transplantation and subconjunctival or intrastromal mesenchymal stem cell injections, are emerging approaches. For successful limbal regeneration, both appropriate cells and suitable scaffolds are essential. Recent studies on decellularized and acellularized limbus models have demonstrated the potential to provide a three-dimensional native structure for cell seeding, retention, and differentiation. Creating a thin, evenly decellularized scaffold is a critical step in ensuring proper corneo-limbal slope formation, facilitating cell migration to the ocular surface. Harvesting the limbus, decellularization, and cell seeding are the three main steps in limbal reconstruction. Recent studies focus on microkeratome-assisted limbal harvesting to create a thin, even, and 360-degree limbal graft. This technique helps form an attached corneo-limbal interface, facilitating limbal stem cell migration. In the second step, acellularization is performed to preserve the extracellular matrix as much as possible, maintaining hemostasis and supporting paracrine interactions. The final steps involve recellularization and transplantation onto the eye. We summarize various limbal decellularization methods, their outcomes, and their potential in limbal reconstruction. More clinical studies are needed to validate this phase of limbal deficiency treatment.

A Narrative Medicine Approach to Navigating Barriers to the Diagnosis of Pediatric Neurotrophic Keratopathy

OBJECTIVE

Neurotrophic keratopathy (NK) is a rare disease characterized by the loss of corneal innervation and increased vulnerability to injury. The diagnosis and treatment of NK can be challenging for pediatric patients and their caregivers. This study explores the experiences of caregivers navigating the diagnostic and treatment journey of pediatric patients with neurotrophic keratopathy.

DESIGN

This study is a qualitative study using semi-structured interviews.

SUBJECTS

Ten caregivers of pediatric patients with NK who had undergone corneal neurotization (CN) surgery.

METHODS

Caregivers were interviewed about their experiences related to the diagnostic process, treatment challenges, lifestyle changes, and the impact of CN surgery. Interviews were recorded, transcribed, and analyzed using an inductive-deductive approach to identify recurring themes.

MAIN OUTCOMES

Caregiver experiences and perceptions of diagnostic delays, information-seeking behaviors, lifestyle changes, and the effects of CN surgery on corneal health and quality of life.

RESULTS

Five key themes emerged from the analysis: (1) Delays in diagnosis due to insufficient specialist knowledge; (2) Caregivers' proactive efforts in seeking information; (3) Substantial lifestyle changes required by NK; (4) The impact of CN surgery on corneal health and quality of life; and (5) Variability in healthcare experiences, highlighting the need for effective communication. Caregivers expressed frustration with diagnostic delays and highlighted their reliance on external support networks.

CONCLUSIONS

This study illustrates the need for enhanced awareness among clinicians about NK and the benefits of narrative medicine in fostering caregiver-provider relationships. The challenges reported by families navigating NK inform strategies that may improve diagnosis and treatment of NK.

Delayed Periocular and Anterior Segment Complications Following Locally Administered Chemotherapy for Vitreous Seeding in Retinoblastoma

BACKGROUND

Long-term follow-up is essential for retinoblastoma survivors, as treatment-related sequelae can emerge years after therapy.

METHODS

This case series reviews 67 eyes treated with periocular and/or intravitreal chemotherapy from 2005 through 2020.

RESULTS

Periocular chemotherapy was associated with orbital fibrosis in 79.1% of cases, with risk increasing concomitantly with the number of injections. Cataracts developed in 19.4% of eyes, with 10 out of 13 requiring cataract extraction. Other complications included chronic conjunctivitis and limbal stem cell deficiency (3% each), while strabismus was observed in 29.9% of which 7.5% underwent strabismus surgery. Comparative analyses of periocular and anterior segment complications from other retrospective studies are included to contextualize our findings.

CONCLUSIONS

Understanding these long-term sequelae is crucial for appropriately following and managing retinoblastoma survivors who were treated during this era. We highlight the importance of vigilant surveillance as treatment protocols continue to evolve.

Classification and treatment approach of chemical burn associated Limbal stem cell deficiency: based on novel global consensus

PURPOSE

To evaluate the severity distribution of chemical burn-induced Limbal stem cell deficiency (LSCD) according to the novel global consensus classification and to compare the treatment approach, before and after the global consensus.

METHODS

Medical records of 127 eyes of 109 patients with LSCD were included. LSCD stages were categorized according to the global consensus classification published by "International LSCD Working Group".

RESULTS

The mean age was 37.5 ± 16.5(6-75). The distribution of LSCD stage according to the global consensus scale was as follows: Stage 1A in 5 eyes(3.9%);Stage 1B in 16 eyes(12.6%);Stage 1C in 4 eyes(3.2%);Stage 2A in 15 eyes(11.8%);Stage 2B in 36 eyes(28.3%);Stage 3 in 51 eyes(40.2%). A total of 88(69.3%) eyes underwent surgery for LSCD. Of these, 80 had surgery prior to the publication of the global consensus (before October 2020), 58(72.5%) had preoperative severe (≥ Stage 2B) LSCD and 22(27.5%) had preoperative early stage (≤ Stage 2A) LSCD. As of October 2020, all 8 eyes that underwent surgery had preoperative severe (≥ Stage 2B) LSCD, as recommended by global consensus.

CONCLUSION

Recently, a global consensus has been established on both the classification and the management of LSCD. This study is one of the first to present small-scale epidemiological data on the severity distribution of LSCD in the light of the global consensus. It was observed that surgery was performed on 27.5% of the eyes that were not recommended for surgery according to this new consensus. With the increasing awareness of this consensus, it might be possible to avoid unnecessary surgical intervention.

Development and characterization of a preclinical mouse model of alkali-induced limbal stem cell deficiency

PURPOSE

Limbal stem cell deficiency (LSCD) secondary to ocular surface alkali burn is a blinding condition that features corneal conjunctivalization. Mechanistic insights into its pathophysiology are lacking. Here, we developed a mouse model that recapitulates human disease to comprehensively delineate the clinicopathological features of a conjunctivalized cornea.

METHODS

LSCD was induced in the right eyes of 6-8-week-old C57BL/6 male and female mice (n = 151) by topical administration of 0.25N sodium hydroxide on the cornea. Uninjured left eyes served as controls. Clinical, histological, phenotypic, molecular, and immunological assessments were performed at multiple time-points over 6-months.

RESULTS

Clinically, alkali burn caused persistent corneal opacity (p = 0.0014), increased punctate staining (p = 0.0002), and reduced epithelial thickness (p = 0.0082) compared to controls. Total LSCD was confirmed in corneal whole mounts by loss of K12 protein (p < 0.0001) and mRNA expression (p = 0.0090). Instead, K8+, K13+, K15+ and MUC5AC+ conjunctival epithelia prevailed. 20 % of injured corneas developed islands of K12+ epithelia, suggesting epithelial transdifferentiation. Squamous metaplasia was detected in 50 % of injured corneas. Goblet cell density peaked early post-injury but decreased over time (p = 0.0047). Intraepithelial corneal basal nerve density remained reduced even at 6-months post-injury (p = 0.0487).

CONCLUSIONS

We developed and comprehensively characterized a preclinical mouse model of alkali-induced LSCD. Understanding the pathophysiological processes that transpire on the ocular surface in LSCD is key to discovering, testing, and advancing biological and pharmacological interventions that can be dispensed prior to or in conjunction with stem cell therapy to rehabilitate the cornea and restore vision.

Targeting limbal epithelial stem cells: master conductors of corneal epithelial regeneration from the bench to multilevel theranostics

The cornea is the outermost layer of the eye and plays an essential role in our visual system. Limbal epithelial stem cells (LESCs), which are localized to a highly regulated limbal niche, are the master conductors of corneal epithelial regeneration. Damage to LESCs and their niche may result in limbal stem cell deficiency (LSCD), a disease confused ophthalmologists so many years and can lead to corneal conjunctivalization, neovascularization, and even blindness. How to restore the LESCs function is the hot topic for ocular scientists and clinicians around the world. This review introduced LESCs and the niche microenvironment, outlined various techniques for isolating and culturing LESCs used in LSCD research, presented common diseases that cause LSCD, and provided a comprehensive overview of both the diagnosis and multiple treatments for LSCD from basic research to clinical therapies, especially the emerging cell therapies based on various stem cell sources. In addition, we also innovatively concluded the latest strategies in recent years, including exogenous drugs, tissue engineering, nanotechnology, exosome and gene therapy, as well as the ongoing clinical trials for treating LSCD in recent five years. Finally, we highlighted challenges from bench to bedside in LSCD and discussed cutting-edge areas in LSCD therapeutic research. We hope that this review could pave the way for future research and translation on treating LSCD, a crucial step in the field of ocular health.

Limbal stem cell therapy

PURPOSE OF REVIEW

To highlight the progress and future direction of limbal stem cell (LSC) therapies for the treatment of limbal stem cell deficiency (LSCD).

RECENT FINDINGS

Direct LSC transplantation have demonstrated good long-term outcomes. Cultivated limbal epithelial transplantation (CLET) has been an alternative to treat severe to total LSCD aiming to improve the safety and efficacy of the LSC transplant. A prospective early-stage uncontrolled clinical trial shows the feasibility and safety of CLET manufactured under xenobiotic free conditions. Other cell sources for repopulating of the corneal epithelium such as mesenchymal stem cells (MSCs) and induced pluripotent stem cells are being investigated. The first clinical trials of using MSCs showed short-term results, but long-term efficacy seems to be disappointing. A better understanding of the niche function and regulation of LSC survival and proliferation will lead to the development of medical therapies to rejuvenate the residual LSCs found in a majority of eyes with LSCD in vivo. Prior efforts have been largely focused on improving LSC transplantation. Additional effort should be placed on improving the accuracy of diagnosis and staging of LSCD, and implementing standardized outcome measures which enable comparison of efficacy of different LSCD treatments for different severity of LSCD. The choice of LSCD treatment will be customized based on the severity of LSCD in the future.

SUMMARY

New approaches for managing different stages of LSCD are being developed. This concise review summarizes the progresses in LSC therapies for LSCD, underlying mechanisms, limitations, and future areas of development.

Correlation Between Anterior Chamber Angle Status and Limbal Stem Cell Deficiency in Primary Angle-Closure Glaucoma

PURPOSE

To investigate the correlation between the opening and closing states of anterior chamber angle (ACA) and the density of limbal epithelial basal cells (LEBCs) in subjects with primary angle-closure glaucoma (PACG).

DESIGN

Cross-sectional observational study.

METHODS

A total of 54 eyes of 29 patients diagnosed with PACG were included in the study. Fifty-four eyes from normal subjects were included as control. Automatic evaluation system for ultrasound biomicroscopy images of anterior chamber angle was used to assist ophthalmologists in identifying the opening or closing state of ACA, and the in vivo confocal microscopy (IVCM) was used to evaluate the density of LEBCs in different directions.

RESULTS

(1) The average density of LEBCs in the superior, inferior, nasal, and temporal limbus of the eyes in the PACG group was lower than that in the control group, and this pattern did not align with the density distribution observed in the control group. (2) In the early, moderate and advanced PACG, the density of LEBCs corresponding to the closed angle was lower than that in the control group (P < .05). Compared with the density of LEBCs corresponding to the closed angle and the open angle, the closed angle of PACG in the early, moderate and advanced stages was less than that in the open angle (P < .05 in the early and moderate stages; advanced stage P > .05). (3) The basal cell density was processed by dimensionless analysis. In the data calculated by averaging and minimizing, both closed angle dimensionless values were smaller than the open angle (P < .05). (4) Comparative analysis was conducted among the normal, open-angle, and closed-angle conditions in the superior, inferior, nasal, and temporal limbus. In the early stage of PACG, significant differences were observed in 4 limbal regions (P < .05), while in the moderate PACG stage, this difference was noted in 3 limbal regions (P < .05). In advanced PACG, 2 limbal regions exhibited significant differences (P < .05). These findings suggest that during the early PACG stage, angle closure is the predominant influencing factor on LEBCs density, while in the advanced stage, the decrease in density is attributed to a combination of angle closure and the natural progression of the disease.

CONCLUSIONS

There is a significant correlation between anterior chamber angle status and LEBCs. Advanced PACG and angle closure should be highly suspected of the occurrence of limbal stem cell deficiency (LSCD).

Corneal injury repair and the potential involvement of ZEB1

The cornea, consisting of three cellular and two non-cellular layers, is the outermost part of the eyeball and frequently injured by external physical, chemical, and microbial insults. The epithelial-to-mesenchymal transition (EMT) plays a crucial role in the repair of corneal injuries. Zinc finger E-box binding homeobox 1 (ZEB1), an important transcription factor involved in EMT, is expressed in the corneal tissues. It regulates cell activities like migration, transformation, and proliferation, and thereby affects tissue inflammation, fibrosis, tumor metastasis, and necrosis by mediating various major signaling pathways, including transforming growth factor (TGF)-β. Dysfunction of ZEB1 would impair corneal tissue repair leading to epithelial healing delay, interstitial fibrosis, neovascularization, and squamous cell metaplasia. Understanding the mechanism underlying ZEB1 regulation of corneal injury repair will help us to formulate a therapeutic approach to enhance corneal injury repair.

Unveiling the landscape of post-keratoplasty keratitis: a comprehensive epidemiological analysis in a tertiary center

PURPOSE

The present study aimed to epidemiologically evaluate patients with infectious keratitis following corneal transplantation.

METHODS

This retrospective study analyzed medical records of patients who underwent keratoplasty from March 2014 to March 2022 at a tertiary center. A total of seventy-five patients were evaluated. The data were classified based on culture results, the type of microorganisms involved, treatment requirements, and the type of primary keratoplasty performed.

RESULTS

Seventy-five patients were evaluated in this study, with a mean age of 45.9 years (22-95 years). The mean duration between the first surgery and the incidence of infectious keratitis was 1.43 years, and most cases occurred in the first year (56.2%). Bacterial and fungal keratitis in 2.17%, 1.39%, and 1.26% of cases undergoing penetrating keratoplasty (PK), endothelial keratoplasty (EK), and anterior lamellar keratoplasty (ALK) occurred, respectively. Streptococcus viridans (9.3%) and Staphylococcus aureus (6.6%) had the highest prevalence. Across various smear and culture results (gram-positive, gram-negative, fungal, and negative culture), no significant differences were found in endophthalmitis rates (P = 0.797) and the necessity for tectonic grafts (P = 0.790). Similarly, the choice of surgical method (PK, ALK, EK) showed no significant impact on the need for tectonic grafts (P = 0.45) or the rate of endophthalmitis (P = 0.55).

CONCLUSIONS

The incidence of keratitis after a corneal graft was 1.7%, with Streptococcus viridans and Staphylococcus aureus the most common microorganisms. The rate of endophthalmitis associated with post-keratoplasty keratitis was 0.053%. There was no correlation between the necessity for a tectonic graft or the incidence of endophthalmitis and the type of microorganisms involved.

The Potential Reversible Transition between Stem Cells and Transient-Amplifying Cells: The Limbal Epithelial Stem Cell Perspective

Stem cells (SCs) undergo asymmetric division, producing transit-amplifying cells (TACs) with increased proliferative potential that move into tissues and ultimately differentiate into a specialized cell type. Thus, TACs represent an intermediary state between stem cells and differentiated cells. In the cornea, a population of stem cells resides in the limbal region, named the limbal epithelial stem cells (LESCs). As LESCs proliferate, they generate TACs that move centripetally into the cornea and differentiate into corneal epithelial cells. Upon limbal injury, research suggests a population of progenitor-like cells that exists within the cornea can move centrifugally into the limbus, where they dedifferentiate into LESCs. Herein, we summarize recent advances made in understanding the mechanism that governs the differentiation of LESCs into TACs, and thereafter, into corneal epithelial cells. We also outline the evidence in support of the existence of progenitor-like cells in the cornea and whether TACs could represent a population of cells with progenitor-like capabilities within the cornea. Furthermore, to gain further insights into the dynamics of TACs in the cornea, we outline the most recent findings in other organ systems that support the hypothesis that TACs can dedifferentiate into SCs.

SinCMat: A single-cell-based method for predicting functional maturation transcription factors

A major goal of regenerative medicine is to generate tissue-specific mature and functional cells. However, current cell engineering protocols are still unable to systematically produce fully mature functional cells. While existing computational approaches aim at predicting transcription factors (TFs) for cell differentiation/reprogramming, no method currently exists that specifically considers functional cell maturation processes. To address this challenge, here, we develop SinCMat, a single-cell RNA sequencing (RNA-seq)-based computational method for predicting cell maturation TFs. Based on a model of cell maturation, SinCMat identifies pairs of identity TFs and signal-dependent TFs that co-target genes driving functional maturation. A large-scale application of SinCMat to the Mouse Cell Atlas and Tabula Sapiens accurately recapitulates known maturation TFs and predicts novel candidates. We expect SinCMat to be an important resource, complementary to preexisting computational methods, for studies aiming at producing functionally mature cells.

Eyes open on stem cells

Recently, the murine cornea has reemerged as a robust stem cell (SC) model, allowing individual SC tracing in living animals. The cornea has pioneered seminal discoveries in SC biology and regenerative medicine, from the first corneal transplantation in 1905 to the identification of limbal SCs and their transplantation to successfully restore vision in the early 1990s. Recent experiments have exposed unexpected properties attributed to SCs and progenitors and revealed flexibility in the differentiation program and a key role for the SC niche. Here, we discuss the limbal SC model and its broader relevance to other tissues, disease, and therapy.

Surgical Management of Bilateral Limbal Stem Cell Deficiency

At the age of 43 years-old, a man was left with bilateral limbal stem cell deficiency after an ocular alkaline burn with lime, which resulted in corneal opacification. After multiple unsuccessful surgical attempts to restore vision, including penetrating keratoplasties and Boston keratoprosthesis, visual acuity was counting fingers in the left eye. At 73 years of age, the patient underwent another surgery in his left eye. Cauterization of neovessels and removal of the vascular pannus were followed by partial excision of Tenon's capsule. Penetrating keratoplasty was followed by an intrastromal injection of anti-VEGF (vascular endothelial growth factor), and the ocular surface was covered with amniotic membrane. Postoperatively, the graft was clear with no signs of inflammation; vision improved to 20/50 and remained stable throughout the following two years. Herein we describe some adjunctive procedures that might have delayed failure and rejection of the corneal graft. This case demonstrates the difficulties in treating bilateral limbal stem cell deficiency in a tertiary eye care center with no capacity to perform stem cell therapy.

Wnt activation as a potential therapeutic approach to treat partial limbal stem cell deficiency

Limbal epithelial stem/progenitor cells (LSCs) are adult stem cells located at the limbus, tightly regulated by their niche involving numerous signaling pathways, such as Wnt. Wnt proteins are secreted morphogens that play critical roles in embryonic development, stem cell proliferation, self-renewal, tissue regeneration, and remodeling in adults. It has been shown that a small molecule Wnt mimic could improve LSCs expansion ex vivo. Damage to the LSCs and/or their niche can lead to limbal stem cell deficiency (LSCD), a condition that can cause corneal blindness and is difficult to treat. This study explored if repopulating residual LSCs in partial LSCD through Wnt activation could be a novel therapeutic approach. To mimic LSCD due to a chemical injury, single cultured LSCs were exposed to various concentrations of sodium hydroxide. A progressive loss of the LSCs phenotype was observed: the percentage of p63bright cells and cytokeratin (K)14+ cells decreased while the percentage of K12+ increased. Wnt activation was attained by treating the LSCs with lithium chloride (LiCl) and a small-molecule Wnt mimic, respectively. After 18 h of treatment, LSCs proliferation was increased, and the LSCs phenotype was recovered, while the untreated cells did not proliferate and lost their phenotype. The percentage of p63bright cells was significantly higher in the Wnt mimic-treated cells compared with untreated cells, while the percentage of K12+ cells was significantly lower. These findings suggest that local Wnt activation may rescue LSCs upon alkaline injury.

Wound-Healing Effects of Mesenchymal Stromal Cell Secretome in the Cornea and the Role of Exosomes

Mesenchymal stromal/stem cells (MSCs) and their secreted factors have been shown to have immunomodulatory and regenerative effects. In this study, we investigated human bone-marrow-derived MSC secretome (MSC-S) for the treatment of corneal epithelial wounds. Specifically, we evaluated the role of MSC extracellular vesicles (EV)/exosomes in mediating the wound-healing effects of the MSC-S. In vitro studies using human corneal epithelial cells showed that MSC-CM increased cell proliferation in HCEC and HCLE cells, while EV-depleted MSC-CM showed lower cell proliferation in both cell lines compared to the MSC-CM group. In vitro and in vivo experiments revealed that 1X MSC-S consistently promoted wound healing more effectively than 0.5X MSC-S, and MSC-CM promoted wound healing in a dose-dependent manner, while exosome deprivation delayed wound healing. We further evaluated the incubation period of MSC-CM on corneal wound healing and showed that MSC-S collected for 72 h is more effective than MSC-S collected for 48 h. Finally, we evaluated the stability of MSC-S under different storage conditions and found that after one cycle of freeze-thawing, MSC-S is stable at 4 °C for up to 4 weeks. Collectively, we identified the following: (i) MSC-EV/Exo as the active ingredient in MSC-S that mediates the wound-healing effects in the corneal epithelium, providing a measure to optimize its dosing for a potential clinical product; (ii) Treatment with EV/Exo-containing MSC-S resulted in an improved corneal barrier and decreased corneal haze/edema relative to EV/Exo-depleted MSC-S; (iii) The stability of MSC-CM for up to 4 weeks showed that the regular storage condition did not significantly impact its stability and therapeutic functions.

Characterization of Porcine Ocular Surface Epithelial Microenvironment

The porcine ocular surface is used as a model of the human ocular surface; however, a detailed characterization of the porcine ocular surface has not been documented. This is due, in part, to the scarcity of antibodies produced specifically against the porcine ocular surface cell types or structures. We performed a histological and immunohistochemical investigation on frozen and formalin-fixed, paraffin-embedded ocular surface tissue from domestic pigs using a panel of 41 different antibodies related to epithelial progenitor/differentiation phenotypes, extracellular matrix and associated molecules, and various niche cell types. Our observations suggested that the Bowman's layer is not evident in the cornea; the deep invaginations of the limbal epithelium in the limbal zone are analogous to the limbal interpalisade crypts of human limbal tissue; and the presence of goblet cells in the bulbar conjunctiva. Immunohistochemistry analysis revealed that the epithelial progenitor markers cytokeratin (CK)15, CK14, p63α, and P-cadherin were expressed in both the limbal and conjunctival basal epithelium, whereas the basal cells of the limbal and conjunctival epithelium did not stain for CK3, CK12, E-cadherin, and CK13. Antibodies detecting marker proteins related to the extracellular matrix (collagen IV, Tenascin-C), cell-matrix adhesion (β-dystroglycan, integrin α3 and α6), mesenchymal cells (vimentin, CD90, CD44), neurons (neurofilament), immune cells (HLA-ABC; HLA-DR, CD1, CD4, CD14), vasculature (von Willebrand factor), and melanocytes (SRY-homeobox-10, human melanoma black-45, Tyrosinase) on the normal human ocular surface demonstrated similar immunoreactivity on the normal porcine ocular surface. Only a few antibodies (directed against N-cadherin, fibronectin, agrin, laminin α3 and α5, melan-A) appeared unreactive on porcine tissues. Our findings characterize the main immunohistochemical properties of the porcine ocular surface and provide a morphological and immunohistochemical basis useful to research using porcine models. Furthermore, the analyzed porcine ocular structures are similar to those of humans, confirming the potential usefulness of pig eyes to study ocular surface physiology and pathophysiology.

Concise Review: Bioengineering of Limbal Stem Cell Niche

The corneal epithelium is composed of nonkeratinized stratified squamous cells and has a significant turnover rate. Limbal integrity is vital to maintain the clarity and avascularity of the cornea as well as regeneration of the corneal epithelium. Limbal epithelial stem cells (LESCs) are located in the basal epithelial layer of the limbus and preserve this homeostasis. Proper functioning of LESCs is dependent on a specific microenvironment, known as the limbal stem cell niche (LSCN). This structure is made up of various cells, an extracellular matrix (ECM), and signaling molecules. Different etiologies may damage the LSCN, leading to limbal stem cell deficiency (LSCD), which is characterized by conjunctivalization of the cornea. In this review, we first summarize the basics of the LSCN and then focus on current and emerging bioengineering strategies for LSCN restoration to combat LSCD.

Corneal stem cells niche and homeostasis impacts in regenerative medicine; concise review

The limbal stem cells niche (LSCN) is an optimal microenvironment that provides the limbal epithelial stem cells (LESCs) and strictly regulates their proliferation and differentiation. Disturbing the LSCN homeostasis can lead to limbal stem cell dysfunction (LSCD) and subsequent ocular surface aberrations, such as corneal stromal inflammation, persistent epithelial defects, corneal neovascularisation, lymphangiogenesis, corneal opacification, and conjunctivalization. As ocular surface disorders are considered the second main cause of blindness, it becomes crucial to explore different therapeutic strategies for restoring the functions of the LSCN. A major limitation of corneal transplantation is the current shortage of donor tissue to meet the requirements worldwide. In this context, it becomes mandatory to find an alternative regenerative medicine, such as using cultured limbal epithelial/stromal stem cells, inducing the production of corneal like cells by using other sources of stem cells, and using tissue engineering methods aiming to produce the three-dimensional (3D) printed cornea. Limbal epithelial stem cells have been considered the magic potion for eye treatment. Epithelial and stromal stem cells in the limbal niche hold the responsibility of replenishing the corneal epithelium. These stem cells are being used for transplantation to maintain corneal epithelial integrity and ultimately sustain optimal vision. In this review, we summarised the characteristics of the LSCN and their current and future roles in restoring corneal homeostasis in eyes with LSCD.

Diagnostic Algorithm for Surgical Management of Limbal Stem Cell Deficiency

BACKGROUND

Limbal stem cell deficiency (LCSD) presents several challenges. Currently, there is no clearly defined systematic approach to LSCD diagnosis that may guide surgical tactics.

METHODS

The medical records of 34 patients with LSCD were analyzed. Diagnostic modalities included standard (visometry, tonometry, visual field testing, slit-lamp biomicroscopy with corneal fluorescein staining, Schirmer test 1, ultrasonography) and advanced ophthalmic examination methods such as anterior segment optical coherence tomography, in vivo confocal microscopy, impression cytology, and enzyme-linked immunoassay.

RESULTS

Standard ophthalmological examination was sufficient to establish the diagnosis of LSCD in 20 (58.8%) cases, whereas advanced evaluation was needed in 14 (41.2%) cases. Depending on the results, patients with unilateral LSCD were scheduled to undergo glueless simple limbal epithelial transplantation (G-SLET) or simultaneous G-SLET and lamellar keratoplasty. Patients with bilateral LSCD with normal or increased corneal thickness were enrolled in the paralimbal oral mucosa epithelium transplantation (pLOMET) clinical trial.

CONCLUSIONS

Based on the diagnostic and surgical data analyzed, the key points in LSCD diagnosis were identified, helping to guide the surgeon in selecting the appropriate surgical procedure. Finally, we proposed a novel step-by-step diagnostic algorithm and original surgical guidelines for the treatment of patients with LSCD.

Corneal regeneration: insights in epithelial stem cell heterogeneity and dynamics

The discovery of slow-cycling cells at the corneal periphery three decades ago established the limbus as the putative corneal stem cell niche. Since then, studies have underscored the importance of the limbal stem cells in maintaining the health and function of the ocular surface. Advancements in our understanding of stem cell biology have been successfully translated into stem cell therapies for corneal diseases. Here, we review recent developments in mouse genetics, intravital imaging, and single-cell genomics that have revealed an underappreciated complexity of the limbal stem cells, from their molecular identity, function, and interactions with their niche environment. Continued efforts to elucidate stem cell dynamics of this extraordinary tissue are critical for not only understanding stem cell biology but also for advancing therapeutic innovation and development.

Therapeutic Strategies for Restoring Perturbed Corneal Epithelial Homeostasis in Limbal Stem Cell Deficiency: Current Trends and Future Directions

Limbal stem cells constitute an important cell population required for regeneration of the corneal epithelium. If insults to limbal stem cells or their niche are sufficiently severe, a disease known as limbal stem cell deficiency occurs. In the absence of functioning limbal stem cells, vision-compromising conjunctivalization of the corneal epithelium occurs, leading to opacification, inflammation, neovascularization, and chronic scarring. Limbal stem cell transplantation is the standard treatment for unilateral cases of limbal stem cell deficiency, but bilateral cases require allogeneic transplantation. Herein we review the current therapeutic utilization of limbal stem cells. We also describe several limbal stem cell markers that impact their phenotype and function and discuss the possibility of modulating limbal stem cells and other sources of stem cells to facilitate the development of novel therapeutic interventions. We finally consider several hurdles for widespread adoption of these proposed methodologies and discuss how they can be overcome to realize vision-restoring interventions.