Evolving concepts on the pathogenic mechanisms of aniridia related keratopathy

Effect of isolated keratin 3 knockdown on gene expression of primary limbal epithelial cells without and with inflammatory stimuli

PURPOSE

Studies have shown that keratin 3 (KRT3) expression is reduced in paired box 6 (PAX6) haploinsufficient primary limbal epithelial cells (LECs). The downregulation of KRT3 expression due to PAX6 haploinsufficiency is likely a critical factor in the development and progression of aniridia associated keratopathy (AAK). In addition, the ocular surface of congenital aniridia patients exhibits an inflammatory environment. The objective of this study was to investigate the isolated effect of KRT3 knockdown, achieved via siRNA silencing in healthy LECs, on PAX6 and other related gene expressions, both under normal and inflammatory conditions.

METHODS

To achieve KRT3 knockdown, human primary LECs were transfected with KRT3 siRNA using Lipofectamine 2000. Inflammatory conditions were induced 48 hours after transfection by treating the cells with 2 mg/mL of lipopolysaccharides (LPS) or 1 ng/mL of IL-1β. Subsequently, gene and protein expression levels were analysed using qPCR, Western blotting, and ELISA.

RESULTS

Following KRT3 knockdown at protein level, there was DSG1, ADH7 and PPARγ upregulation and MAPK1 downregulation solely at transcriptional level (p ≤ 0.031). Nevertheless, IL-6 downregulation could be observed both at transcriptional and at protein levels (p ≤ 0.003). Following KRT3 siRNA knockdown, LPS induced inflammation decreased PPARγ mRNA level and IL-1β induced inflammation decreased DSG1 and ADH7 mRNA levels without changes at protein levels (p ≤ 0.014). In contrast, in control knockdown LECs, IL-1β induced inflammation significantly decreased KRT3 mRNA and protein levels and IL-6 protein level (p ≤ 0.02).

CONCLUSIONS

In normal LECs, inflammatory stimuli slow differentiation and simultaneously induce IL-6 production. These mechanisms are absent in KRT3 knockdown LECs. As a result, despite the presence of inflammation, KRT3 knockdown LECs continue their differentiation unaltered while maintaining inflammatory IL-6 protein secretion.

[Glaucoma in PAX6-related congenital aniridia: A review of the literature]

PAX6-related congenital aniridia is a genetic pan-ocular disease characterized by a partial or total absence of the iris and foveal hypoplasia. The mechanisms involved in the development of ocular hypertension and glaucoma in patients with congenital aniridia are still unknown. Many hypotheses have been proposed and the advent of new anterior segment imaging techniques has allowed the identification of various potential mechanisms: congenital trabecular dysfunction, progressive closure of the iridocorneal angle, postoperative ocular hypertension. The diagnosis must take into account the various obstacles to clinical examination (corneal opacity, obturating cataract, foveolar aplasia, significant nystagmus) and is often considered only upon detection of ocular hypertension. Glaucoma remains, along with limbal insufficiency, one of the major causes of blindness in congenital aniridia. The treatment of glaucoma in congenital aniridia is primarily medical. The benefit/risk ratio of a surgical intervention should always be thoroughly evaluated in order to not underestimate the postoperative complications associated with congenital aniridia.

Increased susceptibility of human limbal aniridia fibroblasts to oxidative stress

Aniridia-associated keratopathy originates from a haploinsufficiency of the transcription factor PAX6 (PAX6+/-). In the corneal epithelium of PAX6+/- mice, a significant increase in oxidized proteins was observed, accompanied by impaired compensation for elevated oxidative stress (OS). The extent to which limbal fibroblast cells (LFCs) are affected by an increased susceptibility to OS in cases of congenital aniridia (AN) has not been determined, yet. Our aim was to examine the impact of OS on antioxidant enzyme expression in normal and AN-LFCs. Following isolation and culture of primary LFCs (n = 8) and AN-LFCs (n = 8), cells were treated with cobalt chloride for 48 h to chemically induce hypoxic conditions and OS. Subsequently, HIF-1α/-2α, PHD1/2, Nrf2, CAT, SOD1, PRDX6, and GPX1 gene expression was examined by qPCR. SOD1, PRDX6, and GPX1 protein levels were assessed from the cell lysate by Western blot. The induction of hypoxia led to reduced HIF-1α gene expression in both fibroblast groups (p≤0.008), while the decrease in PHD1 was limited to AN-LFCs (p = 0.0007). On the other hand, under hypoxic conditions, PHD2 showed higher mRNA expression in AN-LFCs compared to normal LFCs (p = 0.013). As a result of OS, the mRNA levels of Nrf2 (p<0.0001) and the antioxidant enzymes CAT (p = 0.005), SOD1 (p = 0.005), GPX1 (p = 0.002) decreased in AN-LFCs. This was accompanied by an increased protein expression of SOD1 (p = 0.019) and PRDX6 (p=0.0009). In the normal LFC group, the induced extent of OS had no impact on the gene (p≥0.151) and protein expression (p ≥ 0.629) of antioxidant enzymes, except for the GPX1 mRNA level (p = 0.027). AN-LFCs exhibit higher susceptibility to OS than normal LFCs. Therefore, in AN-LFCs, there are sustained alterations in gene and protein expression of antioxidative enzymes even after 48 h of CoCl2 treatment.

Congenital anterior segment ocular disorders: Genotype-phenotype correlations and emerging novel mechanisms

Development of the anterior segment of the eye requires reciprocal sequential interactions between the arising tissues, facilitated by numerous genetic factors. Disruption of any of these processes results in congenital anomalies in the affected tissue(s) leading to anterior segment disorders (ASD) including aniridia, Axenfeld-Rieger anomaly, congenital corneal opacities (Peters anomaly, cornea plana, congenital primary aphakia), and primary congenital glaucoma. Current understanding of the genetic factors involved in ASD remains incomplete, with approximately 50% overall receiving a genetic diagnosis. While some genes are strongly associated with a specific clinical diagnosis, the majority of known factors are linked with highly variable phenotypic presentations, with pathogenic variants in FOXC1, CYP1B1, and PITX2 associated with the broadest spectrum of ASD conditions. This review discusses typical clinical presentations including associated systemic features of various forms of ASD; the latest functional data and genotype-phenotype correlations related to 25 ASD factors including newly identified genes; promising novel candidates; and current and emerging treatments for these complex conditions. Recent developments of interest in the genetics of ASD include identification of phenotypic expansions for several factors, discovery of multiple modes of inheritance for some genes, and novel mechanisms including a growing number of non-coding variants and alleles affecting specific domains/residues and requiring further studies.

Examination of Subbasal Nerve Plexus and Central Corneal Stromal Microstructure in Subjects With Congenital Aniridia, Using in Vivo Confocal Laser Scanning Microscopy

PURPOSE

During life up to 70% of aniridia subjects develop aniridia-associated keratopathy (AAK). AAK is characterized by limbal stem cell insufficiency, impaired corneal epithelial cell differentiation and abnormal cell adhesion, which leads to centripetal spreading vascularization, conjunctivalization, and thickening of the cornea. Our aim was to examine the subbasal nerve plexus and central corneal stromal microstructure in subjects with congenital aniridia, using in vivo confocal laser scanning microscopy CLSM.

METHODS

31 eyes of 18 patients (55.6% males, mean age: 25.22 ± 16.35 years) with congenital aniridia and 46 eyes of 29 healthy subjects (41.4% males, mean age 30 ± 14.82 years) were examined using the Rostock Cornea Module of Heidelberg Retina Tomograph-III. At the subbasal nerve plexus, corneal nerve fiber density (CNFD), corneal nerve fiber length (CNFL), corneal total branch density (CTBD), and corneal nerve fiber width (CNFW) were analyzed using ACCMetrics software. Keratocyte density in the anterior, middle and posterior stroma was assessed manually.

RESULTS

The CNFD (2.02 ± 4.08 vs 13.99 ± 6.34/mm2), CNFL (5.78 ± 2.68 vs 10.56 ± 2.82 mm/mm2) and CTBD (15.08 ± 15.62 vs 27.44 ± 15.05/mm2) were significantly lower in congenital aniridia subjects than in controls (p < 0.001 for all). CNFW was significantly higher in aniridia subjects than in controls (0.03 ± 0.004 vs 0.02 ± 0.003 mm/mm2) (p = 0.003). Keratocyte density was significantly lower in all stromal layers of aniridia subjects than in controls (p < 0.001 for all). Stromal alterations included confluent keratocytes, keratocytes with long extensions and hyperreflective dots between keratocytes in aniridia.

CONCLUSIONS

Decrease in CNFD, CNFL, and CTBD, as well as increase in CNFW well refer to the congenital aniridia-associated neuropathy. The decreased keratocyte density and the stromal alterations may be related to an increased cell death in congenital aniridia, nevertheless, stromal changes in different stages of AAK have to be further analyzed in detail.

Animal Models for Limbal Stem Cell Deficiency: A Critical Narrative Literature Review

This literature review will provide a critical narrative overview of the highlights and potential pitfalls of the reported animal models for limbal stem cell deficiency (LSCD) and will identify the neglected aspects of this research area. There exists significant heterogeneity in the literature regarding the methodology used to create the model and the predefined duration after the insult when the model is supposedly fully fit for evaluations and/or for testing various therapeutic interventions. The literature is also replete with examples wherein the implementation of a specific model varies significantly across different studies. For example, the concentration of the chemical, as well as its duration and technique of exposure in a chemically induced LSCD model, has a great impact not only on the validity of the model but also on the severity of the complications. Furthermore, while some models induce a full-blown clinical picture of total LSCD, some are hindered by their ability to yield only partial LSCD. Another aspect to consider is the nature of the damage induced by a specific method. As thermal methods cause more stromal scarring, they may be better suited for assessing the anti-fibrotic properties of a particular treatment. On the other hand, since chemical burns cause more neovascularisation, they provide the opportunity to tap into the potential treatments for anti-neovascularisation. The animal species (i.e., rats, mice, rabbits, etc.) is also a crucial factor in the validity of the model and its potential for clinical translation, with each animal having its unique set of advantages and disadvantages. This review will also elaborate on other overlooked aspects, such as the anaesthetic(s) used during experiments, the gender of the animals, care after LSCD induction, and model validation. The review will conclude by providing future perspectives and suggestions for further developments in this rather important area of research.

Early ocular surface and tear film status in congenital aniridia indicates a supportive treatment window

AIM

To evaluate changes in the ocular surface and tear film with age and mutational status in congenital aniridia.

METHODS

45 participants with congenital aniridia (89 eyes) in a prospective, cross-sectional study. Whole-exome sequencing identified the causative mutation. Examinations included slit-lamp biomicroscopy, in vivo confocal microscopy, Ocular Surface Disease Index (OSDI) score, blink rate, Schirmer I test, Oxford Staining Score (OSS), tear film break-up time (TFBUT) and Ocular Protection Index (OPI).

RESULTS

There were age-dependent increases in OSDI (β=0.34, 95% CI 0.03 to 0.66; p=0.030), blink rate (β=0.18, 95% CI 0.08 to 0.27; p<0.001) and OSS (β=0.05, 95% CI 0.03 to 0.07; p<0.001) and age-dependent reductions in tear production (β=-0.23, 95% CI -0.43 to 0.02; p=0.029) and TFBUT (β=-0.10, 95% CI -0.17 to -0.04; p<0.001). Perturbed OSDI, OSS, blink rate, tear production and TFBUT were noted after the age of ten and OSDI, OSS, blink rate and TFBUT correlated with deficient corneal nerves and limbal stem cell function. OSDI, blink rate, Schirmer, OSS, TFBUT and OPI were not associated with type of PAX6 mutation, but OSDI, OSS and blink rate associated with grade of aniridia-associated keratopathy.

CONCLUSIONS

Ocular surface damage and dry eye signs appear in congenital aniridia regardless of mutation, appearing after 10 years of age and progressing thereafter. An early treatment window may exist for therapies to protect the ocular surface homoeostasis and limbal function, to possibly delay keratopathy development and progression.

rAAV-PHP.B escapes the mouse eye and causes lethality whereas rAAV9 can transduce aniridic corneal limbal stem cells without lethality

Recently safety concerns have been raised in connection with high doses of recombinant adeno-associated viruses (rAAV). Therefore, we undertook a series of experiments to test viral capsid (rAAV9 and rAAV-PHP.B), dose, and route of administration (intrastromal, intravitreal, and intravenous) focused on aniridia, a congenital blindness that currently has no cure. The success of gene therapy for aniridia may depend on the presence of functional limbal stem cells (LSCs) in the damaged aniridic corneas and whether rAAV can transduce them. Both these concerns were unknown, and thus were also addressed by our studies. For the first time, we report ataxia and lethality after intravitreal or intrastromal rAAV-PHP.B virus injections. We demonstrated virus escape from the eye and transduction of non-ocular tissues by rAAV9 and rAAV-PHP.B capsids. We have also shown that intrastromal and intravitreal delivery of rAAV9 can transduce functional LSCs, as well as all four PAX6-expressing retinal cell types in aniridic eye, respectively. Overall, lack of adverse events and successful transduction of LSCs and retinal cells makes it clear that rAAV9 is the capsid of choice for future aniridia gene therapy. Our finding of rAAV lethality after intraocular injections will be impactful for other researchers developing rAAV-based gene therapies.

Future directions in managing aniridia-associated keratopathy

Congenital aniridia is a panocular disorder that is typically characterized by iris hypoplasia and aniridia-associated keratopathy (AAK). AAK results in the progressive loss of corneal transparency and thereby loss of vision. Currently, there is no approved therapy to delay or prevent its progression, and clinical management is challenging because of phenotypic variability and high risk of complications after interventions; however, new insights into the molecular pathogenesis of AAK may help improve its management. Here, we review the current understanding about the pathogenesis and management of AAK. We highlight the biological mechanisms involved in AAK development with the aim to develop future treatment options, including surgical, pharmacological, cell therapies, and gene therapies.

Genetic predisposition to ocular surface disorders and opportunities for gene-based therapies

The ocular surface, comprised of the corneal and conjunctival epithelium, innervation system, immune components, and tear-film apparatus, plays a key role in ocular integrity as well as comfort and vision. Gene defects may result in congenital ocular or systemic disorders with prominent ocular surface involvement. Examples include epithelial corneal dystrophies, aniridia, ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome, xeroderma pigmentosum (XP), and hereditary sensory and autonomic neuropathy. In addition, genetic factors may interact with environmental risk factors in the development of several multifactorial ocular surface disorders (OSDs) such as autoimmune disorders, allergies, neoplasms, and dry eye disease. Advanced gene-based technologies have already been introduced in disease modelling and proof-of-concept gene therapies for monogenic OSDs. For instance, patient-derived induced pluripotent stem cells have been used for modelling aniridia-associated keratopathy (AAK), XP, and EEC syndrome. Moreover, CRISPR/Cas9 genome editing has been used for disease modelling and/or gene therapy for AAK and Meesmann's epithelial corneal dystrophy. A better understanding of the role of genetic factors in OSDs may be helpful in designing personalized disease models and treatment approaches. Gene-based approaches in monogenic OSDs and genetic predisposition to multifactorial OSDs such as immune-mediated disorders and neoplasms with known or possible genetic risk factors has been seldom reviewed. In this narrative review, we discuss the role of genetic factors in monogenic and multifactorial OSDs and potential opportunities for gene therapy.

Novel Animal Model of Limbal Stem Cell Deficiency Induced by Forcing Eye-Open at Birth

PURPOSE

The aim of this study was to develop a rat model of limbal stem cell deficiency (LSCD) by forcing eye-open at birth (FEOB).

METHODS

A total of 200 Sprague-Dawley neonatal rats were randomly divided into the control group and the experimental group, which received eyelid open surgery on postnatal day 1 (P1). Observation time points were defined as P1, P5, P10, P15, and P30. Slit-lamp microscope and corneal confocal microscope were used to observe the clinical features of the model. The eyeballs were collected for hematoxylin and eosin staining and periodic acid-Schiff staining. Proliferating cell nuclear antigen, CD68/polymorphonuclear leukocytes, and cytokeratin 10/12/13 immunostaining were performed, while the ultrastructure of the cornea was observed by scanning electron microscopy. Real-time polymerase chain reactions (PCRs), western blot, and immunohistochemical staining of activin A receptor-like kinase-1/5 were used to analyze the possible pathogenesis.

RESULTS

FEOB could successfully induce the typical manifestations of LSCD, including corneal neovascularization, severe inflammation, and corneal opacity. In the FEOB group, goblet cells could be detected in the corneal epithelium by periodic acid-Schiff staining. The expression of cytokeratins was also different between the 2 groups. Furthermore, proliferating cell nuclear antigen immunohistochemical staining revealed the weak proliferation and differentiation ability of limbal epithelial stem cells in the FEOB group. Real-time PCRs, western blot, and immunohistochemical staining of activin A receptor-like kinase-1/activin A receptor-like kinase-5 in the FEOB group showed different expression patterns than those of the control group.

CONCLUSIONS

FEOB in rats induces ocular surface changes resembling LSCD in humans, representing a novel model of LSCD.

[Autologous serum eye drops for therapy-resistant epithelial defects of the cornea : Impact of underlying disease and simultaneous amniotic transplantation in 990 applications]

BACKGROUND

The aim of the study was to evaluate the impact of simultaneous amniotic membrane transplantation (AMT), status of the cornea (own cornea vs. graft) and underlying disease on the success and recurrence rates of autologous serum (AS) in therapy-resistant epithelial defects.

PATIENTS AND METHODS

Between 2007 and 2019, 990 treatments with AS in 703 eyes of 645 patients were retrospectively examined. The presence of erosion or ulcer, use of AMT, status of the cornea and the underlying disease were recorded. Epithelial closure rate within 4 weeks and the recurrence rate after epithelial closure were main outcome measures. The median observation period was 50 months.

RESULTS

Epithelial closure was seen in 73.6% and recurrence in 27.4%. AMT was used significantly more often for ulcers (p < 0.001) and recurrences (p = 0.048). Without AMT, there was a significantly higher epithelial closure rate (p < 0.001) and faster healing tendency (p < 0.001). There was no difference between own corneas and grafts with respect to epithelial closure rate (p = 0.47). On the grafts there was a significantly higher recurrence rate (p = 0.004) and faster recurrence (p = 0.03), especially ≤6 months after epithelial closure. The underlying diseases showed a significant difference in epithelial closure rate (p = 0.02) and recurrence rate (p < 0.001) with highest success in corneal dystrophies and lowest in congenital aniridia.

CONCLUSION

AS is an effective therapeutic option for therapy-resistant epithelial defects. There was a high success rate for the grafts but with a higher tendency to develop recurrences. In cases of simultaneous AMT, a reduced success rate can be expected, due to the higher complexity of the given situation. AS can be used successfully in various underlying diseases, with limitations in case of congenital aniridia.

[Regenerative medicine for the corneal epithelium : Cell therapy from bench to bedside]

In the case of thermal or caustic burns of the ocular surface, loss of limbal epithelial stem cells leads to compromised self-renewal of the corneal epithelium. This results in permanent loss of vision. In these situations, transplantation of cultured limbal epithelial cells on an amniotic membrane or fibrin gel as substrate (Holoclar®) can help to regenerate the corneal surface. The required cells are obtained from the healthy partner eye, if available. Adult stem cells from other parts of the body potentially serve as alternative cell sources: hair follicles, oral mucosa, mesenchymal stromal cells, or induced pluripotent stem cells (originally, e.g., skin fibroblasts). The reprogramming of such cells can be achieved with the help of transcription factors. In addition, work is being done on biosynthetic or synthetic matrices, which not only serve as substrate material for the transplantation but also support the functional properties of these cells (self-renewal, corneal epithelial-typical phenotype).

Aniridia-related keratopathy relevant cell signaling pathways in human fetal corneas

We aimed to study aniridia-related keratopathy (ARK) relevant cell signaling pathways [Notch1, Wnt/β-catenin, Sonic hedgehog (SHH) and mTOR] in normal human fetal corneas compared with normal human adult corneas and ARK corneas. We found that fetal corneas at 20 weeks of gestation (wg) and normal adult corneas showed similar staining patterns for Notch1; however 10–11 wg fetal corneas showed increased presence of Notch1. Numb and Dlk1 had an enhanced presence in the fetal corneas compared with the adult corneas. Fetal corneas showed stronger immunolabeling with antibodies against β-catenin, Wnt5a, Wnt7a, Gli1, Hes1, p-rpS6, and mTOR when compared with the adult corneas. Gene expression of Notch1, Wnt5A, Wnt7A, β-catenin, Hes1, mTOR, and rps6 was higher in the 9–12 wg fetal corneas compared with adult corneas. The cell signaling pathway differences found between human fetal and adult corneas were similar to those previously found in ARK corneas with the exception of Notch1. Analogous profiles of cell signaling pathway activation between human fetal corneas and ARK corneas suggests that there is a less differentiated host milieu in ARK.

Outcomes of Human Leukocyte Antigen-Matched Allogeneic Cultivated Limbal Epithelial Transplantation in Aniridia-Associated Keratopathy-A Single-Center Retrospective Analysis

PURPOSE

To assess the efficacy and safety of human leukocyte antigen-matched allogeneic cultivated limbal epithelial stem cell grafts in the treatment of aniridia-associated keratopathy (AAK).

METHODS

Six eyes of 6 patients with severe AAK received an allogeneic stem cell graft between January 2010 and March 2017. Anatomical and functional results were assessed at 6 months, 1 year, 2 years, and the final follow-up visit available. Safety analysis was performed by considering all perioperative and postoperative adverse events and additional surgeries required during the follow-up period.

RESULTS

The mean follow-up was 53.6 months (range 24-104 months). In most patients (80%), there was an early improvement of the keratopathy postoperatively, which slowly regressed during longer follow-up. At the final follow-up, 4 of the eyes were graded as failure and 1 eye was graded as partial success. Grading the sixth eye was not possible because of an adverse event. None of the patients maintained a total anatomical success in the long-term. Only 1 patient maintained a modest improvement in best-corrected visual acuity from hand motion to counting fingers. Four serious adverse events were recorded in 2 patients.

CONCLUSIONS

Severe AAK remains a challenging condition to manage. Transplantation of allogenic ex vivo cultivated limbal stem cells may provide a temporary improvement in ocular surface stability, but anatomical and functional results are poor in the long-term. The eyes are prone to adverse events, and any surgical treatment should take this into consideration.

Decreased FABP5 and DSG1 protein expression following PAX6 knockdown of differentiated human limbal epithelial cells

PAX6 haploinsufficiency related aniridia is characterized by disorder of limbal epithelial cells (LECs) and aniridia related keratopathy. In the limbal epithelial cells of aniridia patients, deregulated retinoic acid (RA) signaling components were identified. We aimed to visualize differentiation marker and RA signaling component expression in LECs, combining a differentiation triggering growth condition with a small interfering RNA (siRNA) based aniridia cell model (PAX6 knock down). Primary LECs were isolated from corneoscleral rims of healthy donors and cultured in serum free low Ca²⁺ medium (KSFM) and in KSFM supplemented with 0.9 mmol/L Ca²⁺. In addition, LECs were treated with siRNA against PAX6. DSG1, PAX6, KRT12, KRT 3, ADH7, RDH10, ALDH1A1, ALDH3A1, STRA6, CYP1B1, RBP1, CRABP2, FABP5, PPARG, VEGFA and ELOVL7 expression was determined using qPCR and western blot. DSG1, FABP5, ADH7, ALDH1A1, RBP1, CRABP2 and PAX6 mRNA and FABP5 protein expression increased (p ≤ 0.03), PPARG, CYP1B1 mRNA expression decreased (p ≤ 0.0003) and DSG1 protein expression was only visible after Ca²⁺ supplementation. After PAX6 knock down and Ca²⁺ supplementation, ADH7 and ALDH1A1 mRNA and DSG1 and FABP5 protein expression decreased (p ≤ 0.04), compared to Ca²⁺ supplementation alone. Using our cell model, with Ca²⁺ supplementation and PAX6 knockdown with siRNA treatment against PAX6, we provide evidence that haploinsufficiency of the master regulatory gene PAX6 contributes to differentiation defect in the corneal epithelium through alterations of RA signalling. Upon PAX6 knockdown, DSG1 differentiation marker and FABP5 RA signaling component mRNA expression decreases. A similar effect becomes apparent at protein level though differentiation triggering Ca²⁺ supplementation in the siRNA-based aniridia cell model. Expression data from this cell model and from our siRNA aniridia cell model strongly indicate that FABP5 expression is PAX6 dependent. These new findings may lead to a better understanding of differentiation processes in LECs and are able to explain the insufficient cell function in AAK.

Aniridia and the ocular surface: Medical and surgical problems and solutions

Congenital aniridia is a multisystemic genetic disease due to a mutation in PAX6 gene which severely affects the development and functionality of the human eyes. In patients affected by the mutation, aside from the absence or defects of iris tissue formation, abnormalities in position or opacities of the crystalline lens, macular hypoplasia, ocular surface disease is the main cause of visual loss and the deterioration of the quality of life of most patients. Limbal stem cell deficiency combined with tear film instability and secondary dry eye cause aniridic keratopathy which, in advanced stages, ends up in corneal opacification. In this paper, the actual knowledge about congenital aniridia keratopathy physiopathology and medical and surgical treatment options and their efficacy are discussed. Indications and results of topical treatments with artificial tears and blood-derivatives in its initial stages, and different surgical techniques as limbal stem cell transplantation, keratoplasty and keratoprostheses are reviewed. Finally, recent advances and results in regenerative medicine techniques with ex vivo stem cell cultivation or other types of cultivated cells are presented.

Pathophysiology of aniridia-associated keratopathy: Developmental aspects and unanswered questions

Aniridia, a rare congenital disease, is often characterized by a progressive, pronounced limbal insufficiency and ocular surface pathology termed aniridia-associated keratopathy (AAK). Due to the characteristics of AAK and its bilateral nature, clinical management is challenging and complicated by the multiple coexisting ocular and systemic morbidities in aniridia. Although it is primarily assumed that AAK originates from a congenital limbal stem cell deficiency, in recent years AAK and its pathogenesis has been questioned in the light of new evidence and a refined understanding of ocular development and the biology of limbal stem cells (LSCs) and their niche. Here, by consolidating and comparing the latest clinical and preclinical evidence, we discuss key unanswered questions regarding ocular developmental aspects crucial to AAK. We also highlight hypotheses on the potential role of LSCs and the ocular surface microenvironment in AAK. The insights thus gained lead to a greater appreciation for the role of developmental and cellular processes in the emergence of AAK. They also highlight areas for future research to enable a deeper understanding of aniridia, and thereby the potential to develop new treatments for this rare but blinding ocular surface disease.

An attempt to optimize the outcome of penetrating keratoplasty in congenital aniridia-associated keratopathy (AAK)

Purpose

To propose an optimized microsurgical and medical approach to reduce the risk of complications after penetrating keratoplasty (PKP) in patients with aniridia-associated keratopathy (AAK).

Methods

Retrospective observational case series of 25 PKP performed in 16 patients with AAK. Preoperative indications were endothelial decompensation and vascularized scars (68%) or graft failure (32%) due to limbal stem cell deficiency. The optimized approach included a combination of a small corneal graft size (around 7.0 mm), interrupted 10–0nylon sutures, simultaneous AMT as a patch, large bandage contact lens, temporary lateral tarsorrhaphy, postoperative autologous serum eye drops, and systemic immunosuppression. Main outcome measures included: visual acuity, transplant survival, and complications encountered during follow-up of 107 weeks on average.

Results

A complete modified keratoplasty scheme was used in 10 of 25 PKP (group 1), while at least one of the modifications was missing in the other 15 PKP (group 2). After 8 weeks of follow-up, the epithelium was closed in 23 eyes. Visual acuity improved in 19 eyes at 6 months of follow-up, and remained stable in six eyes. None of the eyes showed a decrease in visual acuity. At the last post-operative follow-up, this visual improvement persisted in 14 eyes and graft survival rate after 156 weeks (3 years) was 69% in group 1 versus 44% in group 2 (p = 0.39, log-rank test). Secondary corneal neovascularization (8%), scarring (4%), ulcer (4%), or graft rejection (8%) happened mostly in the second group which was missing at least one of the suggested modifications.

Conclusions

PKP in congenital aniridia must be considered as a high-risk keratoplasty. An optimized therapeutic approach seems to be promising in order to reduce the postoperative complication rate in these most difficult eyes.

Dysfunction of the limbal epithelial stem cell niche in aniridia-associated keratopathy

PURPOSE

Abnormalities in the limbal niche microenvironment have been suggested to be causally involved in aniridia-associated keratopathy (AAK), but histological analyses on the limbal structure and composition in AAK are lacking. Here, we investigated morphologic and molecular alterations of the limbal epithelial stem cell niche in human congenital aniridia.

METHODS

The blind, buphthalmic and painful left eye of a 16-year old girl with congenital aniridia and juvenile glaucoma had to be enucleated because of uncontrolled intraocular pressure. The diagnosis of AAK was based on classical clinical features and partial limbal stem cell deficiency in the superior half. Genetic analysis identified a large heterozygous PAX6 gene deletion encompassing exons 11-15 as well as exon 9 of the neighboring ELP4 gene. Three limbal biopsies were taken from the superior, nasal and temporal regions to isolate and cultivate limbal epithelial progenitor cells and subject them to mRNA expression analyses. The globe was vertically bisected and processed for light and transmission electron microscopy and immunohistochemistry.

RESULTS

Comparative analysis of the superior and inferior limbal zones showed a gradual degradation of palisade structures associated with the transition from a hyperplastic to an attenuated corneal epithelium, inflammatory cell infiltrations and basement membrane irregularities. The clinically unaffected inferior part revealed no distinct stem cell clusters in the preserved palisade region, but a uniform population of hyperproliferative, undifferentiated progenitor cells in the basal/suprabasal layers of limbal and corneal epithelia, which gave rise to maldifferentiated epithelial cells exhibiting a conjunctival/epidermal phenotype and nuclear-to-cytoplasmic translocation of Pax6. The structure of the limbal niche was fundamentally perturbed, showing marked alterations in extracellular matrix composition, dislocation of atypical melanocytes lacking melanosomes and melanin, aberrant Wnt/β-catenin and retinoic acid signaling, and massive immune cell infiltration.

CONCLUSIONS

Considering the limitations of a single Case study, the findings suggest that ocular surface alterations in AAK are caused by a primary dysfunction and gradual breakdown of the limbal stem cell niche through Pax6-related effects on both melanogenesis and epithelial differentiation.

Maternal finger-prick allogenic blood for persistent corneal epithelial defects

This is a case of a 17-year-old patient with aniridia-related keratopathy and persistent epithelial defect (PED) treated successfully using maternal finger-prick blood (FPB). Maternal allogenic FPB treatment was initiated to the patient who was non-compliant with the use of autologous FPB. The PED was successfully managed with maternal FPB treatment with rapid and complete closure of the epithelial defect. Additionally, there was immediate and sustained symptomatic improvement to pain and recovery of vision in the only seeing eye. There was no immunological reaction to allogenic blood. Maternal finger-prick allogenic blood could serve as a potential alternative to serum eye drops or autologous FPB in the management of refractory PED, particularly in reference to the paediatric or the vulnerable age group. Further studies are required to confirm the role of allogenic blood in the treatment of PED.

Congenital aniridia - A comprehensive review of clinical features and therapeutic approaches

Congenital aniridia is a rare genetic eye disorder with total or partial absence of the iris from birth. In most cases the genetic origin of aniridia is a mutation in the PAX6 gene, leading to involvement of most eye structures. Hypoplasia of the fovea is usually present and is associated with reduced visual acuity and nystagmus. Aniridia-associated keratopathy, glaucoma, and cataract are serious and progressive complications that can further reduce visual function. Treatment of the ocular complications of aniridia is challenging and has a high risk of side effects. New approaches such as stem cell therapy may, however, offer better prognoses. We describe the various ocular manifestations of aniridia, with a special focus on conditions that commonly require treatment. We also review the growing literature reporting systemic manifestations of the disease.

Quantitative Analysis of the Association Between Follow-Up Duration and Severity of Limbal Stem Cell Deficiency or Visual Acuity in Aniridia

Purpose

This study aimed to quantitatively analyze the association between follow-up duration and the severity of limbal stem cell deficiency (LSCD) or visual acuity in patients with aniridia.

Methods

A total of 52 eyes of 27 patients with aniridia were enrolled at Osaka University Hospital. Medical records were retrospectively reviewed to obtain information on the severity of LSCD and corrected distance visual acuity (CDVA). LSCD severity was based on a modified severity grading scale. We used an ordered logistic regression model to examine the association between follow-up duration and LSCD severity, and a linear regression model with a generalized linear mixed model for the association between follow-up duration and visual acuity.

Results

The mean follow-up duration was 5.2 ± 6.3 years. The mean age at the last follow-up visit was 40.5 ± 18.9 years. The mean CDVA was 1.52 ± 1.09 logMAR. At the last follow-up, 1 examined eye (1.9%) was categorized as stage 0, 7 (13.5%) as Ia, 9 (17.3%) as Ib, 5 (9.6%) as Ic, 2 (3.8%) as IIb, 12 (23.1%) as IIc, and 11 (21.2%) as III. Five eyes (9.6%) were unclassifiable. There was a significant association between follow-up duration and LSCD severity (odds ratio per +1 year, 1.41; P < 0.001). CDVA significantly decreased as follow-up duration increased. Each increase of 1 year in the follow-up duration was associated with a mean difference of +0.021 logMAR (95% confidence interval [CI] 0.01–0.03; P < 0.001).

Conclusions

We quantitatively demonstrate that LSCD severity and visual impairment significantly progress as follow-up duration increases.

Single-cell transcriptomics identifies limbal stem cell population and cell types mapping its differentiation trajectory in limbal basal epithelium of human cornea

PURPOSE

This study aimed to uncover novel cell types in heterogenous basal limbus of human cornea for identifying LSC at single cell resolution.

METHODS

Single cells of human limbal basal epithelium were isolated from young donor corneas. Single-cell RNA-Sequencing was performed using 10x Genomics platform, followed by clustering cell types through the graph-based visualization method UMAP and unbiased computational informatic analysis. Tissue RNA in situ hybridization with RNAscope, immunofluorescent staining and multiple functional assays were performed using human corneas and limbal epithelial culture models.

RESULTS

Single-cell transcriptomics of 16,360 limbal basal cells revealed 12 cell clusters belonging to three lineages. A smallest cluster (0.4% of total cells) was identified as LSCs based on their quiescent and undifferentiated states with enriched marker genes for putative epithelial stem cells. TSPAN7 and SOX17 are discovered and validated as new LSC markers based on their exclusive expression pattern and spatial localization in limbal basal epithelium by RNAscope and immunostaining, and functional role in cell growth and tissue regeneration models with RNA interference in cultures. Interestingly, five cell types/states mapping a developmental trajectory of LSC from quiescence to proliferation and differentiation are uncovered by Monocle3 and CytoTRACE pseudotime analysis. The transcription factor networks linking novel signaling pathways are revealed to maintain LSC stemness.

CONCLUSIONS

This human corneal scRNA-Seq identifies the LSC population and uncovers novel cell types mapping the differentiation trajectory in heterogenous limbal basal epithelium. The findings provide insight into LSC concept and lay the foundation for understanding the corneal homeostasis and diseases.

Abnormal neovascular and proliferative conjunctival phenotype in limbal stem cell deficiency is associated with altered microRNA and gene expression modulated by PAX6 mutational status in congenital aniridia

PURPOSE

To evaluate conjunctival cell microRNA (miRNAs) and mRNA expression in relation to observed phenotype of progressive limbal stem cell deficiency in a cohort of subjects with congenital aniridia with known genetic status.

METHODS

Using impression cytology, bulbar conjunctival cells were sampled from 20 subjects with congenital aniridia and 20 age and sex-matched healthy control subjects. RNA was extracted and miRNA and mRNA analyses were performed using microarrays. Results were related to severity of keratopathy and genetic cause of aniridia.

RESULTS

Of 2549 miRNAs, 21 were differentially expressed in aniridia relative to controls (fold change ≤ -1.5 or ≥ +1.5). Among these miR-204-5p, an inhibitor of corneal neovascularization, was downregulated 26.8-fold in severely vascularized corneas. At the mRNA level, 539 transcripts were differentially expressed (fold change ≤ -2 or ≥ +2), among these FOSB and FOS were upregulated 17.5 and 9.7-fold respectively, and JUN by 2.9-fold, all being components of the AP-1 transcription factor complex. Pathway analysis revealed enrichment of PI3K-Akt, MAPK, and Ras signaling pathways in aniridia. For several miRNAs and transcripts regulating retinoic acid metabolism, expression levels correlated with keratopathy severity and genetic status.

CONCLUSION

Strong dysregulation of key factors at the miRNA and mRNA level suggests that the conjunctiva in aniridia is abnormally maintained in a pro-angiogenic and proliferative state, and these changes are expressed in a PAX6 mutation-dependent manner. Additionally, retinoic acid metabolism is disrupted in severe, but not mild forms of the limbal stem cell deficiency in aniridia.

Germline CRISPR/Cas9-Mediated Gene Editing Prevents Vision Loss in a Novel Mouse Model of Aniridia

Aniridia is a rare eye disorder, which is caused by mutations in the paired box 6 (PAX6) gene and results in vision loss due to the lack of a long-term vision-saving therapy. One potential approach to treating aniridia is targeted CRISPR-based genome editing. To enable the Pax6 small eye (Sey) mouse model of aniridia, which carries the same mutation found in patients, for preclinical testing of CRISPR-based therapeutic approaches, we endogenously tagged the Sey allele, allowing for the differential detection of protein from each allele. We optimized a correction strategy in vitro then tested it in vivo in the germline of our new mouse to validate the causality of the Sey mutation. The genomic manipulations were analyzed by PCR, as well as by Sanger and next-generation sequencing. The mice were studied by slit lamp imaging, immunohistochemistry, and western blot analyses. We successfully achieved both in vitro and in vivo germline correction of the Sey mutation, with the former resulting in an average 34.8% ± 4.6% SD correction, and the latter in restoration of 3xFLAG-tagged PAX6 expression and normal eyes. Hence, in this study we have created a novel mouse model for aniridia, demonstrated that germline correction of the Sey mutation alone rescues the mutant phenotype, and developed an allele-distinguishing CRISPR-based strategy for aniridia.

HCE-T cell line lacks cornea-specific differentiation markers compared to primary limbal epithelial cells and differentiated corneal epithelium

PURPOSE

Human corneal epithelial cell-transformed (HCE-T) cell line is used as a widely accepted barrier model for pharmacological investigations in the context of eye application. The differentiation of (limbal) corneal epithelial into mature corneal epithelium coincides with the expression of established differentiation markers. If these differentiation mechanisms are disturbed, it will lead to ocular surface disease. In this study, we want to compare the expression of differentiation markers in the HCE-T cell line to differentiated primary epithelial cells (pCECs) and primary limbal epithelial cell (LEC) culture. This is necessary in order to decide whether HCE-T cells could be a tool to study the differentiation process and its regulatory networks in corneal epithelium.

METHODS

Primary limbal epithelial cells (LECs) for cell culture and primary corneal epithelial cells (pCECs) as differentiated tissue samples were obtained from the limbus or central cornea region of corneal donors. HCE-T cell line was purchased from RIKEN Institute RCB-2280.Expression levels of conjunctival- and corneal-specific keratin and adhesion markers (KRT3, KRT12, KRT13, KRT19, DSG1), stem cell and differentiation markers (PAX6, ABCG2, ADH7, TP63, ALDH1A1), and additional (unvalidated) putative differentiation and stem cell markers (CTSV, SPINK7, DKK1) were analyzed with qPCR. Additionally, KRT3, KRT12, DSG1, and PAX6 protein levels were analyzed with Western blot.

RESULTS

KRT3, KRT12, DSG1, PAX6, ADH7, and ALDH1A1 mRNA expressions were higher in LECs and magnitudes higher in pCECs compared to HCE-T cells. KRT3, KRT12, PAX6, ALDH1A1, ADH7, TP63, and CTSV mRNAs have shown increasing mRNA expression from HCE-T < HCE-T cultured in keratinocyte serum-free medium (KSFM) < LEC < to pCEC.KRT3 and KRT12 protein expressions were only slightly increased in LEC compared to HCE-T samples, and the strongest signals were seen in pCEC samples. DSG1 protein expression was only detected in pCECs. PAX6 protein expression was hardly detected in HCE-T cells, and no difference could be seen between LECs and pCECs.

CONCLUSIONS

The HCE-T cell line is even less differentiated than LECs regarding the investigated markers and therefore might also lack the ability to express differentiation markers at protein level. Hence, this cell line is not suitable to study corneal differentiation processes. Primary LECs in the way cultured here are not an ideal system compared to differentiated epithelium in organ culture but should be preferred to HCE-T cells if corneal differentiation markers are investigated. Other cell models or differentiation protocols should be developed in the future to gain new tools for research on ocular surface diseases.

Human aniridia limbal epithelial cells lack expression of keratins K3 and K12

Aniridia is a rare disease of the eye that affects the iris, lens and the cornea. In about 90% of the cases, patients showed a loss of PAX6 function. Patients with aniridia often develop aniridia-related keratopathy (ARK), due to limbal stem cell insufficiency. The aim of this study was to determine the differentiation status of limbal epithelial cells (LECs) in patients with ARK. Epithelial cells were isolated from the limbus region of two patients with aniridia and cultured in KSFM medium supplemented with EGF and BPE. Normal cells were obtained from limbus region of cadaveric control patients. Cells were analyzed with RT-PCR, qPCR and Western blot to evaluate expression of the developmental transcription factor, PAX6, potential stem cell markers, ΔNp63α and ABCG2, and corneal differentiation markers, keratin 12 (K12) and K3. Conjunctival differentiation markers, keratin 13 (K13) and K19 were also investigated. Cells were immunostained to evaluate K3, PAX6, and p63α protein expression. Protein coding sequence of PAX6 from patient LEC-cDNA was cloned and sequenced. RT-PCR showed that K3 and K12 transcripts were absent from patient cells, but present in healthy control preparations. Transcription levels of PAX6, ABCG2, and p63α of aniridia patients show no differences compared to normal control cells. Western blot showed reduced PAX6, protein levels in aniridia-LECs compared to control-LECs. Immunostaining also showed reduced PAX6 and K3 expression in aniridia-LECs compared to control-LECs. One aniridia patient showed a loss of stop codon in half of the cloned transcripts. In the second aniridia patient mRNA degradation through nonsense mediated decay seems to be very likely since we could not identify the mutation c.174C > T (Refseq. NM_000280), or misspliced transcripts in cDNA. We identified decreased PAX6 protein levels in aniridia patients in addition to decreased K12 mRNA levels compared to control cells. This result indicates an altered differentiation of limbal epithelial cells of aniridia patients. Further studies are necessary to evaluate the mechanism of differentiation of limbal epithelial cells in aniridia.

Clinical and morphological manifestations of aniridia-associated keratopathy on anterior segment optical coherence tomography and in vivo confocal microscopy

PURPOSE

The study aimed to evaluate clinical and morphological changes in the limbal palisades of Vogt (POV) at different stages of aniridia-associated keratopathy (AAK) and to assess possible utility of anterior segment optical coherence tomography (AS-OCT) for the visualization of limbal progenitor structures as it correlates to laser scanning confocal microscopy (LSCM) data.

METHODS

The study involved 32 patients (59 eyes) with congenital aniridia. AAK stage was defined based on biomicroscopy. Assessment of limbal zone and detection of POVs in identical areas was performed by LSCM (HRT3) and AS-OCT (RTVue XR Avanti) using 3D Cornea (En Face mode) and Cornea Cross Line protocols.

RESULTS

Intact and changed POVs were found in 8/8 stage 0 eyes, in 1/21 stage I and 2/13 stage II eyes. Spearman's correlation coefficient in assessing the consistency of the POV diagnostic results by LSCM and AS-OCT for the inferior limbus was r_S = 0.85 (P < 0.05), for the superior limbus - r_S = 0.53 (P < 0.05). AS-OCT was less sensitive for detection of partially present POVs in superior limbus. The negative correlation between AAK stage and POV preservation was determined (r_S = -0.5, P < 0.05). There was no correlation between AAK stage and patient age (r_S = 0.235, P = 0.209). Three patients with PAX6 3' deletion showed stage 0 AAK with intact or slightly disturbed POVs morphology and transparent cornea.

CONCLUSION

AS-OCT may be an additional diagnostic tool for POV visualization in vivo in aniridic patients. Its diagnostic accuracy is subject to selection of anatomic region, nystagmus and the degree of POV degradation.

Corneal epithelial stem cells and their niche at a glance

The corneal epithelium acts as a protective barrier on the anterior ocular surface and is essential for maintaining transparency of the cornea and thus visual acuity. During both homeostasis and repair, the corneal epithelium is maintained by self-renewing stem cells, which persist throughout the lifetime of the organism. Importantly, as in other self-renewing tissues, the functional activity of corneal epithelial stem cells (CSCEs) is tightly regulated by the surrounding microenvironment, or niche, which provides a range of cues that maintain the stem cell population. This Cell Science at a Glance article and the accompanying poster will therefore aim to summarise our current understanding of the corneal epithelial stem cell niche and its role in regulating stem cell activity during homeostasis, repair and disease.

[Diagnostic capabilities of optical coherence tomography and confocal laser scanning microscopy in studying manifestations of aniridia-associated keratopathy]

AIM

to investigate the possible use of anterior segment optical coherence tomography (AS-OCT) and laser scanning confocal microscopy (LSCM) for visualization of limbal progenitor structures and epithelial changes at different stages of aniridia-associated keratopathy (AAK) and to analyze genotype-phenotype correlations of corneal damage.

MATERIAL AND METHODS

Thirty-four patients (63 eyes) with congenital aniridia (CA) were subjected to epithelial cell density measurement in the central cornea as well as epithelial surface assessment with limbal palisades of Vogt (POV) detection in the corresponding sites of the two corneas. For that, LSCM (HRT3) and AS-OCT (RTVue XR Avanti) were performed. Central corneal and epithelial thicknesses were measured using the Pachymetry protocol.

RESULTS

There has been found an increase in the central corneal thickness (CCT) of CA patients, which correlated with the stage of AAK, and a decrease in the central epithelial thickness as compared with healthy subjects (p<0.05). The difference between the basal and wing epithelial cells density in eyes with stages I and II AAK and normal cells density at stage 0 AAK was statistically significant (p<0.05). Intact or disturbed POV were detected in all patients with PAX6 3' deletion. At that, AS-OCT findings highly agreed with LSCM images for both the inferii (r_S=0.85, p<0.05) and superior limbi (r_S=0.53, p<0.05). A negative correlation was established between the stage of AAK and in vivo morphology of POV (r_S=-0.5, p<0.05). However, no correlation was found between the stage of AAK and patient's age (r_S=0.169, p=0.174).

CONCLUSION

AS-OCT and LSCM are both important diagnostic tools for corneal surface monitoring in patients with limbal stem cells deficiency.

Long-term results of allogenic penetrating limbo-keratoplasty: 20 years of experience

AimThe objective of the study was to evaluate the long-term results of allogenic penetrating limbo-keratoplasy. This method allows simultaneous transplantation of a corneal graft and limbal stem cells of the donor by means of eccentric trephination of the donor button.MethodThe data of 192 consecutive cases of allogenic penetrating limbo-keratoplasty from 1995 to 2015 were reviewed. These had been performed exclusively in eyes with complete failure of the limbal stem cells, in combination with deep corneal scarring. Indications were predominantly eye burns, inflammatory conditions, and congenital aniridia. Graft survival and rejection rates were assessed using Kaplan-Meier analysis.ResultsFollow-up averaged 2.1±2.2 years. Median graft survival was 3.4 years in eye burns, 3.9 years in inflammatory disease, and 3.2 years in congenital aniridia. Median survival was 3.9 years in the heterogenous group of other indications.ConclusionAllogenic limbo-keratoplasty is a suitable option used to treat patients with bilateral complete failure of the limbal stem cells and deep opacification of the central cornea. The main reasons for graft failure are the loss of graft-limbal stem cell functioning and endothelial graft rejection.

Boston type 1 keratoprosthesis from patient selection through postoperative management: a review for the keratoprosthetic surgeon

For the anterior segment surgeon, the implantation of Boston type 1 keratoprosthesis is a multistep process that begins with careful patient selection. Success depends on thorough preoperative evaluation, detailed surgical planning, and frequent postoperative follow-up. New practice patterns have emerged for each of these phases as the international experience with keratoprosthesis grows. This review details special considerations that can improve outcomes and also allow surgeons to consider its use in challenging patient populations at each step.

Congenital Aniridia and the Ocular Surface

Aniridia is a congenital pan-ocular disorder caused by haplo-insufficiency of Pax6, a crucial gene for proper development of the eye. Aniridia affects a range of eye structures, including the cornea, iris, anterior chamber angle, lens, and fovea. The ocular surface, in particular, can be severely affected by a progressive pathology termed aniridia-associated keratopathy (AAK), markedly contributing to impaired vision. The purpose of this review is to provide an update of the current knowledge of the genetic, clinical, micro-morphological, and molecular aspects of AAK. We draw upon material presented in the literature and from our own observations in large aniridia cohorts. We summarize signs and symptoms of AAK, describe current options for management, and discuss the latest research findings that may lead to better diagnosis and new treatment or prevention strategies for this debilitating ocular surface condition.

Limbal Stem Cell Deficiency: Current Treatment Options and Emerging Therapies

Severe ocular surface disease can result in limbal stem cell deficiency (LSCD), a condition leading to decreased visual acuity, photophobia, and ocular pain. To restore the ocular surface in advanced stem cell deficient corneas, an autologous or allogenic limbal stem cell transplantation is performed. In recent years, the risk of secondary LSCD due to removal of large limbal grafts has been significantly reduced by the optimization of cultivated limbal epithelial transplantation (CLET). Despite the great successes of CLET, there still is room for improvement as overall success rate is 70% and visual acuity often remains suboptimal after successful transplantation. Simple limbal epithelial transplantation reports higher success rates but has not been performed in as many patients yet. This review focuses on limbal epithelial stem cells and the pathophysiology of LSCD. State-of-the-art therapeutic management of LSCD is described, and new and evolving techniques in ocular surface regeneration are being discussed, in particular, advantages and disadvantages of alternative cell scaffolds and cell sources for cell based ocular surface reconstruction.

Keratopathy, cataract, and dry eye in a survey of aniridia subjects

Purpose

To determine the prevalence of keratopathy, cataract, and dry eye in a group of individuals with aniridia.

Methods

We reviewed survey data from the Aniridia Foundation International (AFI) registry, which included 99 subjects who self-reported on corneal disease, cataract, and dry eye disease.

Results

The average age of respondents was 25.3±18.6 years, with a range of 0 to 67. Of 99 subjects, 46% stated they have corneal disease, 32% stated they did not, and 22% were unsure. The average age of diagnosis of keratopathy was 20.0±12.2 years. Keratolimbal allograft was reported in 20% and penetrating keratoplasty in 9%. Cataract was reported in 65%, with an average age of 9.4±14.0 years at time of diagnosis, and cataract surgery was reported in 32%. The average age of subjects at the time of cataract and corneal surgery was 28.4±13.7 and 33.5±11.4 years, respectively. Symptomatic dry eye was reported in 56% of subjects, with an average age at diagnosis of 23.8±13.3 years.

Conclusion

There is a high prevalence of corneal disease in aniridia, with diagnosis in late childhood or early adulthood in nearly one-half of subjects, often requiring corneal surgery. Cataract and dry eye are commonly associated with aniridia. Although aniridia subjects may have been aware of the diagnosis of cataract at an early age, they usually were treated for cataract and keratopathy as adults.

Treatment of congenital aniridia associated with subluxated infantile cataract

A 5 year old boy was presented at Eye clinic University clinical center Tuzla with congenital aniridia in both eyes. Clinical examination revealed visual acuity of 0,08 without correction in right and 0.7 with -5.0 Dsph and -1.0 Dcyl Axx 109° in left eye. Opthalmologic examination showed bilateral aniridia associated with moderate cataract in the right and incipient cataract in the left eye. In the right eye, zonular weakness with incipient capsular displacement and esotropia of Δ6º, were noted. The patient underwent phacoemulsification, implantation of capsular tension ring and Artificial Iris implant in the capsular bag. Phacoemulsification went uneventful and early postoperative recovery was successful with no signs of aniridia-associated keratopathy development and normal values of intra ocular pressure. Patient was not motivated for operation of the left eye and it was corrected with soft contact lens. Six month after the operation visual acuity in the right eye improved to 0.9 with +1.25Dsph and maintained stable in left eye, with complete elimination of esotropia and signs of binocular vision restoration. Small incision cataract extraction with IOL and Artificial Iris implantation in one procedure can be used to correct congenital aniridia and cataract with significant visual function improvement.

A review of the clinical and genetic aspects of aniridia

Aniridia classically presents with a bilateral congenital absence or malformation of the irides, foveal hypoplasia, and nystagmus, and patients tend to develop visually significant pre-senile cataracts and keratopathy. Additionally, they are at high risk for developing glaucoma. Classic aniridia can be genetically defined as the presence of a PAX6 gene deletion or loss-of-function mutation that results in haploinsufficiency. Variants of aniridia, which include a condition previously referred to as autosomal dominant keratitis, are likely due to PAX6 mutations that lead to partial loss of PAX6 function. Aniridia-associated keratopathy (AAK) is a progressive and potentially debilitating problem affecting aniridic patients. The current treatments for AAK are to replace the limbal stem cells through keratolimbal allograft (KLAL) with or without subsequent keratoplasty for visual rehabilitation, or to implant a Boston type 1 keratoprosthesis. Future therapies for AAK may be aimed at the genetic modification of corneal limbal stem cells.

Differentiation and molecular profiling of human embryonic stem cell-derived corneal epithelial cells

It has been suggested that the isolation of scalable populations of limbal stem cells may lead to radical changes in ocular therapy. In particular, the derivation and transplantation of corneal stem cells from these populations may result in therapies providing clinical normality of the diseased or damaged cornea. Although feasible in theory, the lack of donor material in sufficient quantity and quality currently limits such a strategy. A potential scalable source of corneal cells could be derived from pluripotent stem cells (PSCs). We developed an in vitro and serum-free corneal differentiation model which displays significant promise. Our stepwise differentiation model was designed with reference to development and gave rise to cells which displayed similarities to epithelial progenitor cells which can be specified to cells displaying a corneal epithelial phenotype. We believe our approach is novel, provides a robust model of human development and in the future, may facilitate the generation of corneal epithelial cells that are suitable for clinical use. Additionally, we demonstrate that following continued cell culture, stem cell-derived corneal epithelial cells undergo transdifferentiation and exhibit squamous metaplasia and therefore, also offer an in vitro model of disease.

The developmental regulator Pax6 is essential for maintenance of islet cell function in the adult mouse pancreas

The transcription factor Pax6 is a developmental regulator with a crucial role in development of the eye, brain, and olfactory system. Pax6 is also required for correct development of the endocrine pancreas and specification of hormone producing endocrine cell types. Glucagon-producing cells are almost completely lost in Pax6-null embryos, and insulin-expressing beta and somatostatin-expressing delta cells are reduced. While the developmental role of Pax6 is well-established, investigation of a further role for Pax6 in the maintenance of adult pancreatic function is normally precluded due to neonatal lethality of Pax6-null mice. Here a tamoxifen-inducible ubiquitous Cre transgene was used to inactivate Pax6 at 6 months of age in a conditional mouse model to assess the effect of losing Pax6 function in adulthood. The effect on glucose homeostasis and the expression of key islet cell markers was measured. Homozygous Pax6 deletion mice, but not controls, presented with all the symptoms of classical diabetes leading to severe weight loss requiring termination of the experiment five weeks after first tamoxifen administration. Immunohistochemical analysis of the pancreata revealed almost complete loss of Pax6 and much reduced expression of insulin, glucagon, and somatostatin. Several other markers of islet cell function were also affected. Notably, strong upregulation in the number of ghrelin-expressing endocrine cells was observed. These findings demonstrate that Pax6 is essential for adult maintenance of glucose homeostasis and function of the endocrine pancreas.

Surgical and visual outcomes of the type I Boston Keratoprosthesis for the management of aniridic fibrosis syndrome in congenital aniridia

PURPOSE

To report the clinical features and surgical management of aniridic fibrosis syndrome using the type I Boston Keratoprosthesis (KPro).

DESIGN

Interventional case series.

METHODS

Retrospective chart review of 9 eyes in 9 patients with congenital aniridia that developed aniridic fibrosis syndrome.

RESULTS

All patients had clinical diagnosis of congenital aniridia. Previously, all patients had undergone cataract surgery with posterior chamber intraocular lens (IOL) implantation and 7 patients had existing tube shunts. In all cases, fibrosis presented as progressive retrocorneal and retrolenticular membrane formation causing displacement of the IOL and secondary corneal decompensation. Two eyes had tractional folds in the retina with posterior extension of the membrane. The management included IOL explantation in 7 of 9 cases, removal of fibrosis with pars plana vitrectomy in all 9 patients, and implantation of a type I Boston KPro in all eyes. At a mean final follow-up of 26.1 months (range 6 to 48 months), vision remained improved in all patients. No patient had recurrence of the fibrotic membrane after KPro implantation.

CONCLUSION

This study represents another case series describing aniridic fibrosis syndrome and the largest study to report utilization of the type I Boston KPro in such patients. As the fibrosis can cause IOL dislocation, corneal decompensation, hypotony, and retinal detachment, monitoring for aniridic fibrosis syndrome in congenital aniridia with early surgical intervention is recommended. Type I Boston KPro may be considered in the surgical treatment of this condition.

Pathologic epithelial and anterior corneal nerve morphology in early-stage congenital aniridic keratopathy

OBJECTIVE

To document the clinical and morphologic corneal findings in the early stages of congenital aniridic keratopathy in Swedish families.

DESIGN

Prospective, observational, comparative case series.

PARTICIPANTS

A total of 16 eyes of 16 subjects with congenital aniridic keratopathy and a clear central cornea, and 6 eyes from 6 healthy controls (unaffected relatives). Nine of the 16 eyes with aniridia came from 5 families with a documented familial history of aniridia.

METHODS

Detailed ophthalmic examinations included best spectacle-corrected visual acuity (BSCVA), tear film production, tear break-up time (BUT), corneal touch sensitivity, intraocular pressure measurement, ultrasound pachymetry, slit-lamp biomicroscopy, and laser scanning in vivo confocal microscopy (IVCM).

MAIN OUTCOME MEASURES

Confirmed stage of aniridic keratopathy, clinical parameters of cornea and tear film (visual acuity, sensitivity, corneal thickness, tear production, and BUT), and the morphologic status of corneal epithelium, sub-basal nerves, and limbal palisades of Vogt.

RESULTS

In early-stage aniridic keratopathy, BSCVA and tear BUT were reduced relative to controls (P < 0.001 for both), and corneal thickness was increased (P=0.01). Inflammatory dendritic cells were present in the central epithelium in aniridia, with significantly increased density relative to controls (P = 0.001). Discrete focal opacities in the basal epithelial region were present in 5 of 11 aniridia cases with an otherwise clear cornea. Opacities were associated with dendritic cells and harbored structures presumed to be goblet cells. Sub-basal nerves were extremely dense in 3 aniridia cases, and a prominent whorl pattern of nerves and epithelial cells was observed in 1 case. Normal limbal palisade morphology was absent in aniridia but present in controls.

CONCLUSIONS

Early-stage aniridic keratopathy is characterized by the development of focal opacities in the basal epithelium, altered sub-basal nerves, infiltration of the central epithelium by dendritic cells, tear film instability, and increased corneal thickness and degradation of limbal palisade architecture. These findings may help to elucidate the pathogenesis of aniridic keratopathy.

Concise review: limbal stem cell deficiency, dysfunction, and distress

The cornea is the clear tissue at the front of the eye that transmits light to the retina at the back of the eye. The cornea is covered by an epithelium and surrounded by a narrow band of tissue known as the limbus. The limbus has two important roles in maintaining a healthy corneal epithelium. First, stem cells for the corneal epithelium reside at the limbus and not in the cornea. Second, the limbus acts as a barrier separating the clear avascular corneal epithelium from the surrounding vascular conjunctival tissue. A failure of these limbal functions can result in the painful and blinding disease of limbal stem cell deficiency. In this disease, the corneal epithelium cannot be maintained by the stem cells, and the corneal surface becomes replaced by hazy conjunctival tissue. There are many causes of limbal stem cell deficiency, such as burns to the eye, inflammatory diseases, and hereditary diseases. Current understanding of the pathophysiology of the disease is discussed here. In particular, understanding whether the limbal stem cells are lost or become dysfunctional or indeed whether the limbal microenvironment is disturbed is important when developing appropriate management strategies for the disease.