Pathological molecular mechanism of symptomatic late-onset Fuchs endothelial corneal dystrophy by bioinformatic analysis

Senescent characteristics of human corneal endothelial cells upon ultraviolet-A exposure

PURPOSE

The objective of this study was to investigate the senescent phenotypes of human corneal endothelial cells (hCEnCs) upon treatment with ultraviolet (UV)-A.

METHODS

We assessed cell morphology, senescence-associated β-galactosidase (SA-β-gal) activity, cell proliferation and expression of senescence markers (p16 and p21) in hCEnCs exposed to UV-A radiation, and senescent hCEnCs induced by ionizing radiation (IR) were used as positive controls. We performed RNA sequencing and proteomics analyses to compare gene and protein expression profiles between UV-A- and IR-induced senescent hCEnCs, and we also compared the results to non-senescent hCEnCs.

RESULTS

Cells exposed to 5 J/cm2 of UV-A or to IR exhibited typical senescent phenotypes, including enlargement, increased SA-β-gal activity, decreased cell proliferation and elevated expression of p16 and p21. RNA-Seq analysis revealed that 83.9% of the genes significantly upregulated and 82.6% of the genes significantly downregulated in UV-A-induced senescent hCEnCs overlapped with the genes regulated in IR-induced senescent hCEnCs. Proteomics also revealed that 93.8% of the proteins significantly upregulated in UV-A-induced senescent hCEnCs overlapped with those induced by IR. In proteomics analyses, senescent hCEnCs induced by UV-A exhibited elevated expression levels of several factors part of the senescence-associated secretory phenotype.

CONCLUSIONS

In this study, where senescence was induced by UV-A, a more physiological stress for hCEnCs compared to IR, we determined that UV-A modulated the expression of many genes and proteins typically altered upon IR treatment, a more conventional method of senescence induction, even though UV-A also modulated specific pathways unrelated to IR.

Expression and Impact of Fibronectin, Tenascin-C, Osteopontin, and Type XIV Collagen in Fuchs Endothelial Corneal Dystrophy

Purpose

Fuchs endothelial corneal dystrophy (FECD) is characterized by Descemet's membrane (DM) abnormalities, namely an increased thickness and a progressive appearance of guttae and fibrillar membranes. The goal of this study was to identify abnormal extracellular matrix (ECM) proteins expressed in FECD DMs and to evaluate their impact on cell adhesion and migration.

Methods

Gene expression profiles from in vitro (GSE112039) and ex vivo (GSE74123) healthy and FECD corneal endothelial cells were analyzed to identify deregulated matrisome genes. Healthy and end-stage FECD DMs were fixed and analyzed for guttae size and height. Immunostaining of fibronectin, tenascin-C, osteopontin, and type XIV collagen was performed on ex vivo specimens, as well as on tissue-engineered corneal endothelium reconstructed using healthy and FECD cells. An analysis of ECM protein expression according to guttae and fibrillar membrane was performed using immunofluorescent staining and phase contrast microscopy. Finally, cell adhesion was evaluated on fibronectin, tenascin-C, and osteopontin, and cell migration was studied on fibronectin and tenascin-C.

Results

SPP1 (osteopontin), FN1 (fibronectin), and TNC (tenascin-C) genes were upregulated in FECD ex vivo cells, and SSP1 was upregulated in both in vitro and ex vivo FECD conditions. Osteopontin, fibronectin, tenascin-C, and type XIV collagen were expressed in FECD specimens, with differences in their location. Corneal endothelial cell adhesion was not significantly affected by fibronectin or tenascin-C but was decreased by osteopontin. The combination of fibronectin and tenascin-C significantly increased cell migration.

Conclusions

This study highlights new abnormal ECM components in FECD, suggests a certain chronology in their deposition, and demonstrates their impact on cell behavior.

Absence of the Klotho Function Causes Cornea Degeneration with Specific Features Resembling Fuchs Endothelial Corneal Dystrophy and Bullous Keratopathy

The Klotho loss-of-function mutation is known to cause accelerated senescence in many organs, but its effects on the cornea have not been published. The present study aims to investigate the effects of the Klotho null mutation on cornea degeneration and to characterize the pathological features. Mouse corneas of Klotho homozygous, heterozygous, and wild-type mice at 8 weeks of age for both genders were subject to pathological and immunohistological examinations. The results show an irregular topography on the corneal surface with a Klotho null mutation. Histological examinations revealed a reduced corneal epithelial cell density, endothelial cell-shedding, and decreased cornea stromal layer thickness in the absence of the Klotho function. Furthermore, guttae formation and the desquamation of wing cells were significantly increased, which was comparable to the characteristics of Fuchs endothelial corneal dystrophy and bullous keratopathy. The mechanism analysis showed multi-fold abnormalities, including oxidative stress-induced cornea epithelium apoptosis and inflammation, extracellular matrix remodeling in the stroma, and a disruption of epithelial repair, presumably through the epithelial-mesenchymal transition. In conclusion, cornea degeneration was observed in the Klotho loss-of-function mutant mice. These pathological features support the use of Klotho mutant mice for investigating age-related cornea anomalies, including Fuchs endothelial corneal dystrophy, bullous keratopathy, and dry eye diseases.

Fuchs endothelial corneal dystrophy: an updated review

PURPOSE

The present review will summarize FECD-associated genes and pathophysiology, diagnosis, current  therapeutic approaches, and future treatment perspectives.

METHODS

Literature review.

RESULTS

Fuchs' endothelial corneal dystrophy (FECD) is the most common bilateral corneal dystrophy and accounts for one-third of all corneal transplants performed in the US. FECD is caused by a combination of genetic and non-heritable factors, and there are two types: early-onset FECD, which affects individuals from an early age and is usually more severe, and late-onset FECD, which is more common and typically manifests around the age of 40. The hallmark findings of FECD include progressive loss of corneal endothelial cells and the formation of focal excrescences (guttae) on the Descemet membrane. These pathophysiological changes result in progressive endothelial dysfunction, leading to a decrease in visual acuity and blindness in later stages. The present review will summarize FECD-associated genes and pathophysiology, diagnosis, current therapeutic approaches, and future treatment perspectives.

CONCLUSION

With the characterization and understanding of FECD-related genes and ongoing research into regenerative therapies for corneal endothelium, we can hope to see more significant improvements in the future in the management and care of the disease.

Systematic Review of the Diagnostic Criteria and Severity Classification for Fuchs Endothelial Corneal Dystrophy

PURPOSE

There are no defined diagnostic criteria and severity classification for Fuchs endothelial corneal dystrophy (FECD), which are required for objective standardized assessments. Therefore, we performed a systematic literature review of the current diagnosis and severity classification of FECD.

METHODS

We searched the Ovid MEDLINE and Web of Science databases for studies published until January 13, 2021. We excluded review articles, conference abstracts, editorials, case reports with <5 patients, and letters.

RESULTS

Among 468 articles identified, we excluded 173 and 165 articles in the first and second screenings, respectively. Among the 130 included articles, 61 (47%) and 99 (76%) mentioned the diagnostic criteria for FECD and described its severity classification, respectively. Regarding diagnosis, slitlamp microscope alone was the most frequently used device in 31 (51%) of 61 articles. Regarding diagnostic findings, corneal guttae alone was the most common parameter [adopted in 23 articles (38%)]. Regarding severity classification, slitlamp microscopes were used in 88 articles (89%). The original or modified Krachmer grading scale was used in 77 articles (78%), followed by Adami's classification in six (6%). Specular microscopes or Scheimpflug tomography were used in four articles (4%) and anterior segment optical coherence tomography in one (1%).

CONCLUSIONS

FECD is globally diagnosed by the corneal guttae using slitlamp examination, and its severity is predominantly determined by the original or modified Krachmer grading scale. Objective severity grading using Scheimpflug or anterior segment optical coherence tomography can be applied in the future innovative therapies such as cell injection therapy or novel small molecules.

Oxidative Stress and Cellular Protein Accumulation Are Present in Keratoconus, Macular Corneal Dystrophy, and Fuchs Endothelial Corneal Dystrophy

The aim of the study was to investigate oxidative stress as well as cellular protein accumulation in corneal diseases including keratoconus (KC), macular corneal dystrophy (MCD), and Fuchs endothelial corneal dystrophy (FECD) at their primary affecting sites. Corneal buttons from KC, MCD, and FECD patients, as well as healthy controls, were analyzed immunohistochemically to evaluate the presence of oxidative stress and the function of the proteostasis network. 4-Fydroxynonenal (4-HNE) was used as a marker of oxidative stress, whereas the levels of catalase and heat-shock protein 70 (HSP70) were analyzed to evaluate the response of the antioxidant defense system and molecular chaperones, respectively. Sequestosome 1 (SQSTM1) levels were determined to assess protein aggregation and the functionality of autophagic degradation. Basal epithelial cells of the KC samples showed increased levels of oxidative stress marker 4-HNE and antioxidant enzyme catalase together with elevated levels of HSP70 and accumulation of SQSTM1. Corneal stromal cells and endothelial cells from MCD and FECD samples, respectively, showed similarly increased levels of these markers. All corneal diseases showed the presence of oxidative stress and activation of the molecular chaperone response to sustain protein homeostasis. However, the accumulation of protein aggregates suggests insufficient function of the protective mechanisms to limit the oxidative damage and removal of protein aggregates via autophagy. These results suggest that oxidative stress has a role in KC, MCD, and FECD at the cellular level as a secondary outcome. Thus, antioxidant- and autophagy-targeted therapies could be included as supporting care when treating KC or corneal dystrophies.

Intergenic variants, rs1200114 and rs1200108 are genetically associated along with a decreased ATP1B1 expression in Fuchs Endothelial Corneal Dystrophy

Fuchs endothelial corneal dystrophy (FECD) is an age-related, bilateral corneal condition, characterized by apoptosis of the terminally differentiated endothelial cells. A genome-wide association study (GWAS) conducted in the European population in 2017, identified a new single nucleotide polymorphism (SNP), rs1200114 in the intergenic region between long intergenic non-protein coding RNA 970 (LINC00970) and ATPase Na+/K+ transporting subunit beta 1 (ATP1B1). The major focus of the current study is to understand the genetic association of this intergenic variant, rs1200114 with FECD in the Indian population. Sanger sequencing followed by statistical analysis indicated a significant difference in the allelic frequency between controls and cases (P = 0.01) with the minor allele 'G' of rs1200114 imparting a 1.64 fold increased risk for the disease. Luciferase reporter assay revealed no significant difference in the luciferase activity between allele 'A' and 'G' of rs1200114. However, quantitative RT-PCR assay revealed lower expression of ATP1B1 in FECD subjects compared with controls (P = 0.007). Therefore, to find whether another nearby SNP imparts regulatory effect, tag SNP association analysis was carried out; which revealed a significant association of another SNP, rs1200108, present in the intergenic region between LINC00970 and ATP1B1 with FECD (P = 0.009). The protective allele 'A' of rs1200108 displayed reduced reporter activity as opposed to the risk allele 'G' (P = 0.014). Furthermore, haplotype 'A-A' of rs1200108 - rs1200114 was present at a higher frequency in control subjects, suggesting it as a protective haplotype. Altogether, this study inferred the genetic association of rs1200114 and rs1200108 along with the decreased expression of ATP1B1 related to FECD pathogenesis in the Indian population.

Cell derived matrices from bovine corneal endothelial cells as a model to study cellular dysfunction

PURPOSE

Fuchs endothelial corneal dystrophy (FECD) is a progressive corneal disease that impacts the structure and stiffness of the Descemet's membrane (DM), the substratum for corneal endothelial cells (CECs). These structural alterations of the DM could contribute to the loss of the CECs resulting in corneal edema and blindness. Oxidative stress and transforming growth factor-β (TGF-β) pathways have been implicated in endothelial cell loss and endothelial to mesenchymal transition of CECs in FECD. Ascorbic acid (AA) is found at high concentrations in FECD and its impact on CEC survival has been investigated. However, how TGF-β and AA effect the composition and rigidity of the CEC's matrix remains unknown.

METHODS

In this study, we investigated the effect of AA, TGF-β1 and TGF-β3 on the deposition, ultrastructure, stiffness, and composition of the extracellular matrix (ECM) secreted by primary bovine corneal endothelial cells (BCECs).

RESULTS

Immunofluorescence and electron microscopy post-decellularization demonstrated a robust deposition and distinct structure of ECM in response to treatments. AFM measurements showed that the modulus of the matrix in BCECs treated with TGF-β1 and TGF-β3 was significantly lower than the controls. There was no difference in the stiffness of the matrix between the AA-treated cell and controls. Gene Ontology analysis of the proteomics results revealed that AA modulates the oxidative stress pathway in the matrix while TGF-β induces the expression of matrix proteins collagen IV, laminin, and lysyl oxidase homolog 1.

CONCLUSIONS

Molecular pathways identified in this study demonstrate the differential role of soluble factors in the pathogenesis of FECD.

MiR-302a Regenerates Human Corneal Endothelial Cells against IFN-γ-Induced Cell Death

Damage to human corneal endothelial cells (hCECs) leads to bullous keratopathy because these cells cannot be regenerated in vivo. In this study, we investigated the protective role of microRNA (miR)-302a against interferon-γ (IFN-γ)-induced senescence and cell death of hCECs. Cultured hCECs were transfected with miR-302a and treated with IFN-γ (20 ng/mL) to evaluate the protective effect of miR-302a on IFN-γ-induced cell death. Senescence was evaluated by the senescence-associated β-galactosidase (SA-β-gal) assay, and the secretion of senescence-associated secretory phenotype (SASP) factors was analyzed. Mitochondrial function and endoplasmic reticulum (ER) stress were assessed. We revealed that miR-302a enhanced the cell viability and proliferation of hCECs and that IFN-γ increased the cell size, the number of SA-β-gal-positive cells, and SASP factors, and arrested the cell cycle, which was eliminated by miR-302a. miR-302a ameliorated mitochondrial oxidative stress and ER stress levels which were induced by IFN-γ. IFN-γ decreased the mitochondrial membrane potential and promoted autophagy, which was eliminated by miR-302a. The in vivo study showed that regeneration of rat CECs was promoted in the miR-302a group by inhibiting IFN-γ and enhancing mitochondrial function. In conclusion, miR-302a eliminated IFN-γ-induced senescence and cellular damage by regulating the oxidative and ER stress, and promoting the proliferation of CECs. Therefore, miR-302a may be a therapeutic option to protect hCECs against IFN-γ-induced stress.

Beneficial Effects of Polydeoxyribonucleotide (PDRN) in an In Vitro Model of Fuchs Endothelial Corneal Dystrophy

Fuchs endothelial corneal dystrophy (FECD) is a bilateral, hereditary syndrome characterized by progressive irreversible injury in the corneal endothelium; it is the most frequent cause for corneal transplantation worldwide. Oxidative stress induces the apoptosis of corneal endothelial cells (CECs), and has a crucial function in FECD pathogenesis. The stimulation of the adenosine A_2A receptor (A_2Ar) inhibits oxidative stress, reduces inflammation and modulates apoptosis. Polydeoxyribonucleotide (PDRN) is a registered drug that acts through adenosine A_2Ar. Thus, the goal of this study was to assess the effect of PDRN in an in vitro FECD model. Human Corneal Endothelial Cells (IHCE) were challenged with H₂O₂ (200 μM) alone or in combination with PDRN (100 μg/mL), PDRN plus ZM241385 (1 μM) as an A_2Ar antagonist, and CGS21680 (1 μM) as a well-known A_2Ar agonist. H₂O₂ reduced the cells’ viability and increased the expression of the pro-inflammatory markers NF-κB, IL-6, IL-1β, and TNF-α; by contrast, it decreased the expression of the anti-inflammatory IL-10. Moreover, the pro-apoptotic genes Bax, Caspase-3 and Caspase-8 were concurrently upregulated with a decrease of Bcl-2 expression. PDRN and CGS21680 reverted the negative effects of H₂O₂. Co-incubation with ZM241385 abolished the effects of PDRN, indicating that A_2Ar is involved in the mode of action of PDRN. These data suggest that PDRN defends IHCE cells against H₂O₂-induced damage, potentially as a result of its antioxidant, anti-inflammatory and antiapoptotic properties, suggesting that PDRN could be used as an FECD therapy.

Therapeutic contact lens for Fuchs endothelial corneal dystrophy: Monitoring with Scheimpflug tomopraphy

Purpose

This case report demonstrates the effectiveness of a combined unique soft contact lens design and hypertonic saline at reducing corneal edema symptoms. In addition, this case shows that using tomographic data is invaluable for detecting and monitoring of these presentations.

Observations

A 61 year old patient diagnosed with Fuchs endothelial corneal dystrophy (FECD) presented with complaints over the past year of intermittent blurry, foggy vision upon awakening and glare while driving. Slit lamp examination showed no signs of corneal edema. Data acquired from the Scheimpflug tomographer revealed subclinical signs, including increased corneal thickness, displacement of the thinnest point of the cornea, focal posterior depression, elevated densinometry, "camel's back" sign, irregular isopachs, and a plane slope of pachymetry progression in both eyes. The patient was fit with Therapeutic Hyper-CL™ soft contact lenses for eight days extended wear and instilled 5% sodium chloride six times a day. Visual acuity improved in the right and left eye from 0.5(-2) and 0.5(+1) to 0.4(+2) and 0.3(-1), respectively. Corneal thickness at the thinnest point decreased from 650μm to 632μm-632μm and 604μm in the right and left eye respectively and a significant decrease in total densinometry was noted from 34.7 to 33.8 standardized grayscale units (GSU) to 23.1 and 24 GSU, in the right and left eye respectively. The patient reported a decrease in symptoms and his 8-item Contact Lens Dry Eye Questionnaire (CLDEQ-8) score was 19 after treatment.

Conclusions and importance

Treatment for one week with Therapeutic Hyper-CL™ soft contact lenses combined with 5% sodium chloride decreased corneal edema signs and symptoms. Tomographic data facilitated diagnosis and monitoring of improvement.

Oxidative Stress Induces a Breakdown of the Cytoskeleton and Tight Junctions of the Corneal Endothelial Cells

Purpose: To investigate the impact of oxidative stress, which is a hallmark of Fuchs dystrophy, on the barrier function of the corneal endothelial cells. Methods: Experiments were carried out with cultured bovine and porcine corneal endothelial cells. For oxidative stress, cells were supplemented with riboflavin (Rf) and exposed to UV-A (15-30 min) to induce Type-1 photochemical reactions that release H₂O₂. The effect of the stress on the barrier function was assayed by transendothelial electrical resistance (TER) measurement. In addition, the associated changes in the organization of the microtubules, perijunctional actomyosin ring (PAMR), and ZO-1 were evaluated by immunocytochemistry, which was also repeated after direct exposure to H₂O₂ (100 μM, 1 h). Results: Exposure to H₂O₂ led to the disassembly of microtubules and the destruction of PAMR. In parallel, the contiguous locus of ZO-1 was disrupted, marking a loss of barrier integrity. Accordingly, a sustained loss in TER was induced when cells in the Rf-supplemented medium were exposed to UV-A. However, the addition of catalase (7,000 U/mL) to rapidly decompose H₂O₂ limited the loss in TER. Furthermore, the adverse effects on microtubules, PAMR, and ZO-1 were suppressed by including catalase, ascorbic acid (1 mM; 30 min), or pretreatment with p38 MAP kinase inhibitor (SB-203580; 10 μM, 1 h). Conclusions: Acute oxidative stress induces microtubule disassembly by a p38 MAP kinase-dependent mechanism, leading to the destruction of PAMR and loss of barrier function. The response to oxidative stress is reminiscent of the (TNF-α)-induced breakdown of barrier failure in the corneal endothelium.

Culture of corneal endothelial cells obtained by descemetorhexis of corneas with Fuchs endothelial corneal dystrophy

Currently, endothelial keratoplasty is the gold standard for the surgical treatment of Fuchs endothelial corneal dystrophy (FECD). Despite the remarkable success in terms of surgical outcomes, a shortage of corneal donor tissue poses a limitation to performing endothelial keratoplasty in many parts of the world. Cell therapy is a potential alternative strategy to keratoplasty and is currently under investigation. Considering that corneas with FECD may contain relatively healthy endothelial cells, samples obtained by descemetorhexis of eyes undergoing EK for FECD can be used for ex vivo expansion of endothelial cells as an autologous cell culture. In this study, we established corneal endothelial cell cultures derived from 40 patients that underwent endothelial keratoplasty for advanced FECD. Several parameters were evaluated including patient characteristics such as age, gender, and endothelial cell density as well as various processing and cell culture protocols based on different combinations of shipping temperatures, stabilization periods and treatment methods for corneal endothelial cell dissociation. FECD cultures were classified into three groups as: (i) no cells, (ii) cell cultures with endothelial-like morphology or (iii) cell cultures with fibroblast-like features. Our data seem to suggest that some factors can influence FECD cell culture characteristics including young age, high paracentral endothelial cell density, low shipping temperature and short stabilization period prior to cell isolation. Treatment with type 1 collagenase for cell isolation can delay endothelial-to-mesenchymal transition, but does not increase proliferative capacity. Although heterologous corneal endothelial cultures from healthy donors have shown encouraging outcomes, the feasibility of autologous cell therapy as a potential treatment for FECD remains challenging. Low initial cell concentration as well as endothelial to mesenchymal transition are the main obstacles to the application of FECD cultures in the clinical setting.

Incorporating Differential Gene Expression Analysis with Predictive Biomarkers to Identify Novel Therapeutic Drugs for Fuchs Endothelial Corneal Dystrophy

Purpose

Based on the differential gene expression analysis for predictive biomarkers with RNA-Sequencing data from Fuchs endothelial corneal dystrophy (FECD) patients, we are aiming to evaluate the efficacy of Library of Integrated Network-based Cellular Signatures (LINCS) perturbagen prediction software to identify novel pharmacotherapeutic targets that can revert the pathogenic gene expression signatures and reverse disease phenotype in FECD.

Methods

A publicly available RNA-seq dataset was used to compare corneal endothelial specimens from controls and patients with FECD. Based on the differential gene expression analysis for predictive biomarkers, we evaluated the efficacy of LINCS perturbagen prediction software to identify novel therapeutic targets that can revert the pathogenic gene expression signatures and reverse disease phenotypes in FECD.

Results

The RNA-seq dataset of the corneal endothelial cells from FECD patients revealed the differential gene expression signatures of FECD. Many of the differential expressed genes are related to canonical pathways of the FECD pathogenesis, such as extracellular matrix reorganization and immunological response. The expression levels of genes VSIG2, IL18, and ITGB8 were significantly increased in FECD compared with control. Meanwhile, the expression levels of CNGA3, SMOX, and CERS1 were significantly lower in the FECD than in control. We employed LINCS L1000 Characteristic Direction Signature Search Engine (L1000-CDS2) to investigate pathway-based molecular treatment. L1000-CDS2 predicted that small molecule drugs such as histone deacetylase (HDAC) inhibitors might be a potential candidate to reverse the pathological gene expression signature in FECD.

Conclusions

Based on differential gene expression signatures, several candidate drugs have been identified to reverse the disease phenotypes in FECD. Gene expression signature with LINCS small molecule prediction software can discover novel preclinical drug candidates for FECD.

Fuchs endothelial corneal dystrophy: The vicious cycle of Fuchs pathogenesis

Fuchs endothelial corneal dystrophy (FECD) is the most common primary corneal endothelial dystrophy and the leading indication for corneal transplantation worldwide. FECD is characterized by the progressive decline of corneal endothelial cells (CECs) and the formation of extracellular matrix (ECM) excrescences in Descemet's membrane (DM), called guttae, that lead to corneal edema and loss of vision. FECD typically manifests in the fifth decades of life and has a greater incidence in women. FECD is a complex and heterogeneous genetic disease where interaction between genetic and environmental factors results in cellular apoptosis and aberrant ECM deposition. In this review, we will discuss a complex interplay of genetic, epigenetic, and exogenous factors in inciting oxidative stress, auto(mito)phagy, unfolded protein response, and mitochondrial dysfunction during CEC degeneration. Specifically, we explore the factors that influence cellular fate to undergo apoptosis, senescence, and endothelial-to-mesenchymal transition. These findings will highlight the importance of abnormal CEC-DM interactions in triggering the vicious cycle of FECD pathogenesis. We will also review clinical characteristics, diagnostic tools, and current medical and surgical management options for FECD patients. These new paradigms in FECD pathogenesis present an opportunity to develop novel therapeutics for the treatment of FECD.

Analyzing pre-symptomatic tissue to gain insights into the molecular and mechanistic origins of late-onset degenerative trinucleotide repeat disease

How genetic defects trigger the molecular changes that cause late-onset disease is important for understanding disease progression and therapeutic development. Fuchs' endothelial corneal dystrophy (FECD) is an RNA-mediated disease caused by a trinucleotide CTG expansion in an intron within the TCF4 gene. The mutant intronic CUG RNA is present at one-two copies per cell, posing a challenge to understand how a rare RNA can cause disease. Late-onset FECD is a uniquely advantageous model for studying how RNA triggers disease because: (i) Affected tissue is routinely removed during surgery; (ii) The expanded CTG mutation is one of the most prevalent disease-causing mutations, making it possible to obtain pre-symptomatic tissue from eye bank donors to probe how gene expression changes precede disease; and (iii) The affected tissue is a homogeneous single cell monolayer, facilitating accurate transcriptome analysis. Here, we use RNA sequencing (RNAseq) to compare tissue from individuals who are pre-symptomatic (Pre_S) to tissue from patients with late stage FECD (FECD_REP). The abundance of mutant repeat intronic RNA in Pre_S and FECD_REP tissue is elevated due to increased half-life in a corneal cells. In Pre_S tissue, changes in splicing and extracellular matrix gene expression foreshadow the changes observed in advanced disease and predict the activation of the fibrosis pathway and immune system seen in late-stage patients. The absolute magnitude of splicing changes is similar in pre-symptomatic and late stage tissue. Our data identify gene candidates for early drivers of disease and biomarkers that may represent diagnostic and therapeutic targets for FECD. We conclude that changes in alternative splicing and gene expression are observable decades prior to the diagnosis of late-onset trinucleotide repeat disease.

Molecular Mechanisms of Fuchs and Congenital Hereditary Endothelial Corneal Dystrophies

The cornea, the eye's outermost layer, protects the eye from the environment. The cornea's innermost layer is an endothelium separating the stromal layer from the aqueous humor. A central role of the endothelium is to maintain stromal hydration state. Defects in maintaining this hydration can impair corneal clarity and thus visual acuity. Two endothelial corneal dystrophies, Fuchs Endothelial Corneal Dystrophy (FECD) and Congenital Hereditary Endothelial Dystrophy (CHED), are blinding corneal diseases with varied clinical presentation in patients across different age demographics. Recessive CHED with an early onset (typically age: 0-3 years) and dominantly inherited FECD with a late onset (age: 40-50 years) have similar phenotypes, although caused by defects in several different genes. A range of molecular mechanisms have been proposed to explain FECD and CHED pathology given the involvement of multiple causative genes. This critical review provides insight into the proposed molecular mechanisms underlying FECD and CHED pathology along with common pathways that may explain the link between the defective gene products and provide a new perspective to view these genetic blinding diseases.

Corneal injury: Clinical and molecular aspects

Currently, over 10 million people worldwide are affected by corneal blindness. Corneal trauma and disease can cause irreversible distortions to the normal structure and physiology of the cornea often leading to corneal transplantation. However, donors are in short supply and risk of rejection is an ever-present concern. Although significant progress has been made in recent years, the wound healing cascade remains complex and not fully understood. Tissue engineering and regenerative medicine are currently at the apex of investigation in the pursuit of novel corneal therapeutics. This review uniquely integrates the clinical and cellular aspects of both corneal trauma and disease and provides a comprehensive view of the most recent findings and potential therapeutics aimed at restoring corneal homeostasis.