Colocalization of increased transforming growth factor-beta-induced protein (TGFBIp) and Clusterin in Fuchs endothelial corneal dystrophy

Proteomic profiling of human corneal stroma from long-term contact lens wearers reveals activation of inflammatory responses

PURPOSE

To investigate the association between proteomic changes and potential pathogenesis in the human cornea with respect to the duration of wearing soft contact lenses (SCLs).

METHODS

A total of 96 corneal stroma samples, obtained via small incision lenticule extraction (SMILE), were equally grouped according to the duration of wearing SCL: 0Y, did not wear SCL; 5Y, wore SCL for<5 years; 5-10Y, wore SCL for 5-10 years; O10Y, wore SCL for>10 years. Liquid chromatography-tandem mass spectrometry was used to identify and quantify protein profiles in the corneal stroma. Expression levels of CO1A1, CO4A1, NFKB1, and IL6RB were determined using western blot and immunohistochemistry analysis.

RESULTS

This study quantified a total of 5,668 proteins across samples and identified 2,379 differentially expressed proteins (DEPs) with significantly increased abundance in the three SCL-wearing groups compared with that in the non-SCL-wearing group. Compared with those in the 0Y group, the molecular functions of DEPs in the 5Y, 5-10Y, and O10Y groups were mainly related to translation regulator activity, antigen binding, peptidase inhibitor activity, participation in extracellular matrix (ECM) production, complement activation, and inflammatory responses. Pathway enrichment analysis of DEPs showed that the sphingolipid, phosphatidylinositol 3-kinase-protein kinase B, and hypoxia-inducible factor-1 signaling pathways were activated in the human corneal stroma after long-term SCL use.

CONCLUSIONS

Inflammation-related proteomic components in human corneal stroma increased after long-term use of SCL and may act as an essential factor in the molecular pathogenesis of corneal stroma damage.

The soil and the seed: The relationship between Descemet's membrane and the corneal endothelium

Descemet's membrane (DM), the basement membrane of the corneal endothelium, is formed from the extracellular matrix (ECM) secreted by corneal endothelial cells. The ECM supports the growth and function of the corneal endothelial cells. Changes to DM are central to the diagnosis of the most common corneal endothelial disease, Fuchs endothelial corneal dystrophy (FECD). Changes in DM are also noted in systemic diseases such as diabetes mellitus. In FECD, the DM progressively accumulates guttae, "drop-like deposits" that disrupt the corneal endothelial cell monolayer. While the pathophysiologic changes to corneal endothelial cells in the course of FECD have been well described and reviewed, the changes to DM have received limited attention. The reciprocity of influence between the corneal endothelial cells and DM demands full attention to the latter in our search for novel treatment and preventive strategies. In this review, we discuss what is known about the formation and composition of DM and how it changes in FECD and other conditions. We review characteristics of guttae and the interplay between corneal endothelial cells and guttae, particularly as it might apply to future cell-based and genetic therapies for FECD.

Expression Pattern of Tenascin-C, Matrilin-2, and Aggrecan in Diseases Affecting the Corneal Endothelium

Purpose: The aim of this study was to examine the expression pattern of tenascin-C, matrilin-2, and aggrecan in irreversible corneal endothelial pathology such as pseudophakic bullous keratopathy (PBK) and Fuchs’ endothelial corneal dystrophy (FECD), which most frequently require corneal transplantation. Materials and methods: Histological specimens of corneal buttons removed during keratoplasty were investigated in PBK (n = 20) and FECD (n = 9) and compared to healthy control corneas (n = 10). The sections were studied by chromogenic immunohistochemistry (CHR-IHC) and submitted for evaluation by two investigators. Semiquantitative scoring (0 to 3+) was applied according to standardized methods at high magnification (400x). Each layer of the cornea was investigated; in addition, the stroma was subdivided into anterior, middle, and posterior parts for more precise analysis. In case of non-parametric distribution Mann−Whitney test was applied to compare two groups. Kruskal−Wallis and Dunn’s multiple comparisons tests have been applied for comparison of the chromogenic IHC signal intensity among corneal layers within the control and patient groups. Differences of p < 0.05 were considered as significant. Results: Significantly elevated tenascin-C immunopositivity was present in the epithelium and every layer of the stroma in both pathologic conditions as compared to normal controls. In addition, also significantly stronger matrilin-2 positivity was detected in the epithelium; however, weaker reaction was present in the endothelium in PBK cases. Minimal, but significantly elevated immunopositivity could be observed in the anterior and posterior stroma in the FECD group. Additionally, minimally, but significantly higher aggrecan immunoreaction was present in the anterior stroma in PBK and in the posterior stroma in both endothelial disorders. All three antibodies disclosed the strongest reaction in the posterior stroma either in PBK or in FECD cases. Conclusions: These extracellular matrix molecules disclosed up to moderate immunopositivity in the corneal layers in varying extents. Through their networking, bridging, and adhesive abilities these proteins are involved in corneal regeneration and tissue reorganization in endothelial dysfunction.

Potential role of extracellular granzyme B in wet age-related macular degeneration and fuchs endothelial corneal dystrophy

Age-related ocular diseases are the leading cause of blindness in developed countries and constitute a sizable socioeconomic burden worldwide. Age-related macular degeneration (AMD) and Fuchs endothelial corneal dystrophy (FECD) are some of the most common age-related diseases of the retina and cornea, respectively. AMD is characterized by a breakdown of the retinal pigment epithelial monolayer, which maintains retinal homeostasis, leading to retinal degeneration, while FECD is characterized by degeneration of the corneal endothelial monolayer, which maintains corneal hydration status, leading to corneal edema. Both AMD and FECD pathogenesis are characterized by disorganized local extracellular matrix (ECM) and toxic protein deposits, with both processes linked to aberrant protease activity. Granzyme B (GrB) is a serine protease traditionally known for immune-mediated initiation of apoptosis; however, it is now recognized that GrB is expressed by a variety of immune and non-immune cells and aberrant extracellular localization of GrB substantially contributes to various age-related pathologies through dysregulated cleavage of ECM, tight junction, and adherens junction proteins. Despite growing recognition of GrB involvement in multiple age-related pathologies, its role in AMD and FECD remains poorly understood. This review summarizes the pathophysiology of, and similarities between AMD and FECD, outlines the current knowledge of the role of GrB in AMD and FECD, as well as hypothesizes putative contributions of GrB to AMD and FECD pathogenesis and highlights the therapeutic potential of pharmacologically inhibiting GrB as an adjunctive treatment for AMD and FECD.

Clusterin, other extracellular chaperones, and eye disease

Proteostasis refers to all the processes that maintain the correct expression level, location, folding and turnover of proteins, essential to organismal survival. Both inside cells and in body fluids, molecular chaperones play key roles in maintaining proteostasis. In this article, we focus on clusterin, the first-recognized extracellular mammalian chaperone, and its role in diseases of the eye. Clusterin binds to and inhibits the aggregation of proteins that are misfolded due to mutations or stresses, clears these aggregating proteins from extracellular spaces, and facilitates their degradation. Clusterin exhibits three main homeostatic activities: proteostasis, cytoprotection, and anti-inflammation. The so-called "protein misfolding diseases" are caused by aggregation of misfolded proteins that accumulate pathologically as deposits in tissues; we discuss several such diseases that occur in the eye. Clusterin is typically found in these deposits, which is interpreted to mean that its capacity as a molecular chaperone to maintain proteostasis is overwhelmed in the disease state. Nevertheless, the role of clusterin in diseases involving such deposits needs to be better defined before therapeutic approaches can be entertained. A more straightforward case can be made for therapeutic use of clusterin based on its proteostatic role as a proteinase inhibitor, as well as its cytoprotective and anti-inflammatory properties. It is likely that clusterin works together in this way with other extracellular chaperones to protect the eye from disease, and we discuss several examples. We end this article by predicting future steps that may lead to development of clusterin as a biological drug.

Impact of TCF4 Repeat Number on Resolution of Corneal Edema after Descemet's Stripping Only in Fuchs Dystrophy: A Pilot Study

Purpose: To investigate whether Fuchs endothelial corneal dystrophy (FECD) genotype, specifically transcription factor 4 (TCF4) CTG triplet repeat “load” predicts time to clearance following Descemet’s Stripping Only (DSO). Methods: This prospective, interventional trial was conducted on consecutive FECD patients undergoing DSO. Genetic analysis using patients’ saliva was performed to assess the extent of CTG expansion using short tandem repeat analysis, corroborated gel electrophoresis and Sanger sequencing. Polymerase chain reaction and bidirectional Sanger sequencing was undertaken. Partial least square regression and logistic regression modelling was used to evaluate the predictive power of TCF4 repeats on corneal clearance. Results: Of 11 eyes of 11 patients, 8 showed complete corneal clearance. For these 8 patients, mean TCF4 allele repeat was 24.8 (SD: 23.7, range: 11–63) and 63.4 (SD: 30.3; range: 11–97), respectively. In total, 9/11 (81.8%) had expanded CTG repeats (>40) in one allele. In cases with an allele repeat ≥80, there was a significantly increased risk of corneal non-clearance (odds ratio 18.2, p = 0.009). Conclusion: Whilst it was not possible to predict time to corneal clearance based on CTG repeats, there is a significant correlation between allele repeats and achievement of corneal clearance.

Cigarette Smoke Triggers Loss of Corneal Endothelial Cells and Disruption of Descemet's Membrane Proteins in Mice

Purpose

To investigate changes at a molecular level in the mouse corneal endothelium (CE) exposed to chronic cigarette smoke (CS).

Methods

Pregnant mice (gestation days 18–20) were placed in a whole-body exposure smoking chamber, and a few days later pups were born. After 3.5 months of CS exposure, a ConfoScan4 scanning microscope was used to examine the corneal endothelial cells (CECs) of CS-exposed and control (Ct) mice. The CE was peeled under a microscope and maintained as four biological replicates (two male and two female) for CS-exposed and Ct mice; each replicate consisted of 16 CEs. The proteome of the CE was investigated through mass spectrometry.

Results

The CE images of CS-exposed and Ct mice revealed a difference in the shape of CECs accompanied by a nearly 10% decrease in CEC density (P < 0.00003) following CS exposure. Proteome profiling identified a total of 524 proteins exhibiting statistically significant changes in CE from CS-exposed mice. Importantly, proteins associated with Descemet's membrane (DM), including COL4α1, COL4α2, COL4α3, COL4α4, COL4α5, COL4α6, COL8α1, COL8α2, and FN1, among others, exhibited diminished protein levels in the CE of CS-exposed mice.

Conclusions

Our data confirm that exposure to CS results in reduced CEC density accompanied by diminished levels of multiple collagen and extracellular matrix proteins associated with DM.

Cell cycle re-entry and arrest in G2/M phase induces senescence and fibrosis in Fuchs Endothelial Corneal Dystrophy

Fuchs endothelial corneal dystrophy (FECD) is an age-related disease whereby progressive loss of corneal endothelial cells (CEnCs) leads to loss of vision. There is currently a lack of therapeutic interventions as the etiology of the disease is complex, with both genetic and environmental factors. In this study, we have provided further insights into the pathogenesis of the disease, showing a causal relationship between senescence and endothelial-mesenchymal transition (EMT) using in vitro and in vivo models. Ultraviolet A (UVA) light induced EMT and senescence in CEnCs. Senescent cells were arrested in G2/M phase of the cell cycle and responsible for the resulting profibrotic phenotype. Inhibiting ATR signaling and subsequently preventing G2/M arrest attenuated EMT. In vivo, UVA irradiation induced cell cycle re-entry in post mitotic CEnCs, resulting in senescence and fibrosis at 1- and 2-weeks post-UVA. Selectively eliminating senescent cells using the senolytic cocktail of dasatinib and quercetin attenuated UVA-induced fibrosis, highlighting the potential for a new therapeutic intervention for FECD.

Matrix metalloproteinases and their inhibitors in Fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) is characterized by a progressive loss of corneal endothelial cells (CECs) and an abnormal accumulation of extracellular matrix in Descemet's membrane leading to increased thickness and formation of excrescences called guttae. Extracellular matrix homeostasis is modulated by an equilibrium between matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors (TIMPs). This study aimed to investigate MMPs and TIMPs profile in FECD, taking into account cell morphology. Populations of FECD and healthy CECs were cultured and their conditioned media collected for analysis. The presence of proteases in the conditioned media was studied using a semi-quantitative proteome profiler array, and MMPs levels were assessed using quantitative assays (ELISA and quantitative antibody array). MMP activity was determined by zymography and fluorometry. The expression pattern of the membrane type 1-MMP (MT1-MMP, also known as MMP-14) was examined by immunofluorescence on ex vivo FECD and healthy explants of CECs attached to Descemet's membrane. Finally, MMPs and TIMPs protein expression was compared to gene expression obtained from previously collected data. FECD and healthy CEC populations generated cultures of endothelial, intermediate, and fibroblastic-like morphology. Various MMPs (MMP-1, -2, -3, -7, -8, -9, -10, and -12) and TIMPs (TIMP-1 to -4) were detected in both FECD and healthy CECs culture supernatants. Quantitative assays revealed a decrease in MMP-2 and MMP-10 among FECD samples. Both these MMPs can degrade the main extracellular matrix components forming guttae (fibronectin, laminin, collagen IV). Moreover, MMPs/TIMPs ratio was also decreased among FECD cell populations. Activity assays showed greater MMPs/Pro-MMPs proportions for MMP-2 and MMP-10 in FECD cell populations, although overall activities were similar. Moreover, the analysis according to cell morphology revealed among healthy CECs, both increased (MMP-3 and -13) and decreased (MMP-1, -9, -10, and -12) MMPs proteins along with increased MMPs activity (MMP-2, -3, -9, and -10) in the fibroblastic-like subgroup when compared to the endothelial subgroup. However, FECD CECs did not show similar behaviors between the different morphology subgroups. Immunostaining of MT1-MMP on ex vivo FECD and healthy explants revealed a redistribution of MT1-MMP around guttae in FECD explants. At the transcriptional level, no statistically significant differences were detected, but cultured FECD cells had a 12.2-fold increase in MMP1 and a 4.7-fold increase in TIMP3. These results collectively indicate different, and perhaps pathological, MMPs and TIMPs profile in FECD CECs compared to healthy CECs. This is an important finding suggesting the implication of MMPs and TIMPs in FECD pathophysiology.

Diseases of the corneal endothelium

The corneal endothelial monolayer and associated Descemet's membrane (DM) complex is a unique structure that plays an essential role in corneal function. Endothelial cells are neural crest derived cells that rest on a special extracellular matrix and play a major role in maintaining stromal hydration within a narrow physiologic range necessary for clear vision. A number of diseases affect the endothelial cells and DM complex and can impair corneal function and vision. This review addresses different human corneal endothelial diseases characterized by loss of endothelial function including: Fuchs endothelial corneal dystrophy (FECD), posterior polymorphous corneal dystrophy (PPCD), congenital hereditary endothelial dystrophy (CHED), bullous keratopathy, iridocorneal endothelial (ICE) syndrome, post-traumatic fibrous downgrowth, glaucoma and diabetes mellitus.

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.

Fuchs Endothelial Corneal Dystrophy: Clinical, Genetic, Pathophysiologic, and Therapeutic Aspects

Fuchs endothelial corneal dystrophy (FECD) is a bilateral corneal endothelial disorder and the most common cause of corneal transplantation worldwide. Professor Ernst Fuchs described the first 13 cases of FECD more than 100 years ago. Since then, we have seen far-reaching progress in its diagnosis and treatment. In the field of diagnostics, new technologies enable the development of more accurate classification systems and the more detailed breakdown of the genetic basis of FECD. Laboratory studies help in deciphering the molecular pathomechanisms. The development of minimally invasive surgical techniques leads to a continuous improvement of the postoperative result. This review highlights and discusses clinical, genetic, pathophysiologic, and therapeutic aspects of this common and important corneal disorder.

Corneal thinning and cornea guttata in patients with mutations in TGFB2

OBJECTIVE

Human genome-wide association studies and animal models suggest a role for TGFB2 in contributing to the corneal thickness phenotype. No specific mutations, however, have been reported in this gene that affect corneal thickness. We sought to determine if haploinsufficiency of TGFB2 in humans associated with Loeys-Dietz syndrome type 4 is associated with corneal thinning.

DESIGN

Observational cohort study of families with Loeys-Dietz syndrome type 4, caused specifically by TGFB2 mutations, in a tertiary care setting.

PARTICIPANTS

Three probands with pathogenic mutations in TGFB2 and family members underwent comprehensive ophthalmic examination.

METHODS

Clinical assessment included Scheimpflug imaging, specular microscopy, and slit-lamp biomicroscopy. We measured visual acuity, axial length, refractive error, and central corneal thickness.

RESULTS

Clinical evaluation of 2 probands identified corneal thinning and cornea guttata, despite a young age and distinct mutations in TGFB2 (c.905G>A, p.Arg302His; c.988C>A, p.Arg330Ser). In the third family, corneal thinning co-segregated with a TGFB2 mutation (c.1103G>A, p.Gly368Glu), although without apparent guttae.

CONCLUSIONS

In this series, participants with TGFB2 mutations associated with Loeys-Dietz syndrome type 4 demonstrated decreased corneal thickness, and in 2 cases with splice site mutations, also demonstrated cornea guttata. The data demonstrate the importance of considering distinct phenotype-genotype correlations within this condition.

Distinct ocular surface soluble factor profile in human corneal dystrophies

PURPOSE

Corneal dystrophies (CD) are classified as rare eye diseases that results in visual impairment and requires corneal transplant in advanced stages. Ocular surface inflammatory status in different types of CD remains underexplored. Hence, we studied the levels of tear soluble factors in the tears of patients with various types of corneal dystrophies.

METHODS

17 healthy subjects and 30 CD subjects (including epithelial, stromal and endothelial CD) were included in the study. Schirmer's strips were used to collect the tear fluid in all subjects. 27 soluble factors including cytokines, chemokines, soluble cell adhesion molecules and growth factors were measured in the eluted tears by multiplex ELISA or single analyte sandwich ELISA.

RESULTS

Percentages of subjects with detectable levels of tear soluble factors were significantly higher in CD compared to controls. Significant higher level of IL-2 was observed in both epithelial and stromal CD. IL-4, TGFβ1 and IgE were significantly higher in stromal CD. VCAM, IL-13 and Fractalkine were significantly elevated in epithelial and macular CD. IL-1α, IL-8, IL-12, ANG, Eotaxin, MCP1, RANTES, ICAM1, L-selectin and P-selectin were significantly higher in epithelial CD. TGFBIp was significantly elevated in lattice CD and endothelial CD.

CONCLUSION

Distinct set of the tear soluble factors were dysregulated in various types of CD. Increase in tear inflammatory factors was observed in majority of the CD subjects depending on their sub-types. This suggests a plausible role of aberrant inflammation in CD pathobiology. Hence, modulating inflammation could be a potential strategy in improving the prognosis of CD.

The serine protease HtrA1 cleaves misfolded transforming growth factor β-induced protein (TGFBIp) and induces amyloid formation

The serine protease high-temperature requirement protein A1 (HtrA1) is associated with protein-misfolding disorders such as Alzheimer's disease and transforming growth factor β-induced protein (TGFBIp)-linked corneal dystrophy. In this study, using several biochemical and biophysical approaches, including recombinant protein expression, LC-MS/MS and 2DE analyses, and thioflavin T (ThT) fluorescence assays for amyloid fibril detection, and FTIR assays, we investigated the role of HtrA1 both in normal TGFBIp turnover and in corneal amyloid formation. We show that HtrA1 can cleave WT TGFBIp but prefers amyloidogenic variants. Corneal TGFBIp is extensively processed in healthy people, resulting in C-terminal degradation products spanning the FAS1-4 domain of TGFBIp. We show here that HtrA1 cleaves the WT FAS1-4 domain only inefficiently, whereas the amyloidogenic FAS1-4 mutations transform this domain into a considerably better HTRA1 substrate. Moreover, HtrA1 cleavage of the mutant FAS1-4 domains generated peptides capable of forming in vitro amyloid aggregates. Significantly, these peptides have been previously identified in amyloid deposits in vivo, supporting the idea that HtrA1 is a causative agent for TGFBIp-associated amyloidosis in corneal dystrophy. In summary, our results indicate that TGFBIp is an HtrA1 substrate and that some mutations in the gene encoding TGFBIp cause aberrant HtrA1-mediated processing that results in amyloidogenesis in corneal dystrophies.

Activation of PINK1-Parkin-Mediated Mitophagy Degrades Mitochondrial Quality Control Proteins in Fuchs Endothelial Corneal Dystrophy

Corneal endothelium (CE) is a monolayer of mitochondria-rich cells, critical for maintaining corneal transparency compatible with clear vision. Fuchs endothelial corneal dystrophy (FECD) is a heterogeneous, genetically complex disorder, where oxidative stress plays a key role in the rosette formation during the degenerative loss of CE. Increased mitochondrial fragmentation along with excessive mitophagy activation has been detected in FECD; however, the mechanism of aberrant mitochondrial dynamics in CE cell loss is poorly understood. Here, the role of oxidative stress in mitophagy activation in FECD is investigated. Immunoblotting of FECD ex vivo specimens revealed an accumulation of PINK1 and phospho-Parkin (Ser65) along with loss of total Parkin and total Drp1. Similarly, modeling of rosette formation with menadione (MN), led to phospho-Parkin accumulation in fragmented mitochondria resulting in mitophagy-induced mitochondrial clearance, albeit possibly in a PINK1-independent manner. Loss of PINK1, phospho-Drp1, and total Drp1 was prominent after MN-induced oxidative stress, but not after mitochondrial depolarization by carbonyl cyanide m-chlorophenyl hydrazone. Moreover, MN-induced mitophagy led to degradation of Parkin along with sequestration of Drp1 and PINK1 that was rescued by mitophagy inhibition. This study shows that in FECD, intracellular oxidative stress induces Parkin-mediated mitochondrial fragmentation where endogenous Drp1 and PINK1 are sequestered and degraded by mitophagy during degenerative loss of post-mitotic cells of ocular tissue.

Reduced expression of apolipoprotein E and immunoglobulin heavy constant gamma 1 proteins in Fuchs endothelial corneal dystrophy

BACKGROUND

Fuchs endothelial corneal dystrophy (FECD) is a progressive and potentially a sight threatening disease, and a common indication for corneal grafting in the elderly. Aberrant thickening of Descemet's membrane, formation of microscopic excrescences (guttae) and gradual loss of corneal endothelial cells are the hallmarks of the disease. The aim of this study was to identify differentially abundant proteins between FECD-affected and unaffected Descemet's membrane.

METHODS

Label-free quantitative proteomics using nanoscale ultra-performance liquid chromatography-mass spectrometry (nUPLC-MS^E ) was employed on affected and unaffected Descemet's membrane extracts, and interesting findings were further investigated using quantitative reverse transcription-polymerase chain reaction and immunohistochemical techniques.

RESULTS

Quantitative proteomics revealed significantly lower abundance of apolipoprotein E (APOE) and immunoglobulin heavy constant gamma 1 protein (IGHG1) in affected Descemet's membrane. The difference in the distribution of APOE between affected and unaffected Descemet's membrane and of IGHG1 detected by immunohistochemistry support their down-regulation in the disease. Comparative gene expression analysis showed significantly lower APOE mRNA levels in FECD-affected than unaffected corneal endothelium. IGHG1 gene is expressed at extremely low levels in the corneal endothelium, precluding relative expression analysis.

CONCLUSIONS

This is the first study to report comparative proteomics of Descemet's membrane tissue, and implicates dysregulation of APOE and IGHG1 proteins in the pathogenesis of Fuchs endothelial corneal dystrophy.

Regional variability in corneal endothelial cell density between guttae and non-guttae areas in Fuchs endothelial corneal dystrophy

OBJECTIVE

To assess the regional variability of corneal endothelial cell density (ECD) between guttae and non-guttae areas in subjects with Fuchs endothelial corneal dystrophy (FECD) using non-contact specular microscopy and confocal microscopy.

DESIGN

Retrospective chart review from 2009 to 2014 at the Massachusetts Eye and Ear Infirmary.

PARTICIPANTS

One hundred fifteen eyes of 73 subjects with FECD.

METHODS

Subjects with FECD underwent same-day specular and confocal microscopy in the same eye. Clinical stage of disease was documented on the day of image acquisition. Regional variability of ECD associated with guttae and non-guttae areas was assessed. Manual endothelial cell counts were performed.

RESULTS

Thirty-two percent of subjects had high quality endothelial images by both specular and confocal microscopy. Of these subjects, 83% were classified clinically as early-stage FECD. There was a significant association between stage of disease and the ability to obtain high quality specular images (χ²; p = 0.0012). There was no difference in mean ECD derived from specular (1363 ± 594 cells/mm²) or confocal (1391 ± 493 cells/mm²; p = 0.75) images. There was a statistically significant decrease of 31.8 ± 21.7% in mean ECD in areas surrounding guttae (1296 ± 560 cells/mm²) compared to non-guttae areas (1926 ± 674 cells/mm²; p < 0.0001) as determined by confocal microscopy.

CONCLUSION

These findings support confocal microscopy as an alternative to specular microscopy for evaluating the corneal endothelium of patients with FECD, especially those with advanced disease. Confocal microscopy also revealed regional differences in ECD in guttae and non-guttae areas in patients with FECD.

REVIEW: Current understanding of the pathogenesis of Fuchs' endothelial corneal dystrophy

Fuchs' endothelial corneal dystrophy (FECD) is the most prominent reason for corneal-endothelial transplantations across the globe. The disease pathophysiology manifests through a combination of various genetic and non-heritable factors. This review provides a comprehensive list of known genetic players that cause FECD, and discusses the prominent pathological features that participate in disease progression, such as channel dysfunction, abnormal extracellular matrix deposition, RNA toxicity, oxidative stress, and apoptosis. Although current practices to correct visual acuity involve surgical intervention, this review also discusses the scope of various non-surgical therapeutics to remedy FECD.

The Human Eye Proteome Project: Updates on an Emerging Proteome

The human eye is a complex organ consisting of multiple compartments with unique and specialized properties that reflect their varied functions. Although there have been advancements in ocular imaging and therapeutics over the past decade, the pathogenesis of many common eye diseases remains poorly understood. Proteomics is an invaluable tool to gain insight into pathogenesis, diagnosis, and treatment of eye diseases. By 2013, when the Human Eye Proteome Project (also known as the EyeOme) was founded, there were 4842 nonredundant proteins identified in the human eye. Twenty-three recent papers on the human eye proteome were identified in PubMed searches. These papers were used to compile an updated resource of 9782 nonredundant proteins in the human eye. This updated catalogue sheds light on the molecular makeup of previously undescribed proteomes within the human eye, including optic nerve, sclera, iris, and ciliary body, while adding additional proteins to previously characterized proteomes such as aqueous humor, lens, vitreous, retina, and retinal pigment epithelium/choroid. Although considerable advances have been made to characterize the complete proteome of the human eye, additional high-quality data are needed to confirm and quantify previously discovered eye proteins in both health and disease.

A Rabbit Corneal Endothelial Dysfunction Model Using Endothelial-Mesenchymal Transformed Cells

Unlike humans, rabbit corneal endothelial wounds are known to spontaneously heal. The current study was aimed to develop a new rabbit bullous keratopathy model using corneal endothelial cells that were induced to undergo endothelial-mesenchymal transformation (EMT). EMT was induced in rabbit corneal endothelial cells (RCECs) by culturing with TGFβ and basic FGF Supplemented Medium. The corneal endothelia in recipient rabbits were mechanically scraped from the corneal endothelial surface inside an 8 mm mark. Then, a suspension of EMT-induced RCECs (EMT-RCECs) was injected into the anterior chamber. Eyes injected with freshly isolated RCECs (Fresh RCECs group) and eyes that were scraped without injection of cells (Scrape group) were used as controls. Immediately following operation, subepithelial and stromal edema was observed with increased central corneal thickness and corneal opacity in all groups. In the EMT-RCECs group, bullous keratopathy persisted for 42 days up to the end of the study. In the Fresh-RCECs and Scrape groups, corneal transparency and thickness recovered by 7 days after treatment and was maintained up to 42 days. The activated fibroblast marker, α-SMA, was observed spanning from corneal endothelium to corneal stroma in the EMT-RCECs group. Interestingly, α-SMA was upregulated in the Scrape-group as well. In all groups, there was no damage to other intraocular structures, and intraocular pressure was normal throughout the observation period. Transplanting a fresh donor cornea effectively treated corneal edema due to bullous keratopathy. This model is a promising tool for pre-clinical trials in the development of new therapies against corneal endothelial dysfunction.

Fuchs Endothelial Corneal Dystrophy Through the Prism of Oxidative Stress

The corneal endothelium (CE) is vital for maintaining the water balance and clarity of the cornea. The CE is a cell layer that is particularly susceptible to aging because of its postmitotic arrest, high metabolic activity involving pumping of ions, and lifelong exposure to ultraviolet light. Despite gradual age-related cell loss, a sufficient number of CE cells are preserved during the lifespan of an individual. However, in conditions such as Fuchs endothelial corneal dystrophy (FECD), permanent loss of CE cells leads to corneal edema and loss of vision requiring corneal transplantation. FECD is a genetic and oxidative stress disorder manifested by abnormal cell-matrix interactions and expedited cellular aging culminating in cellular death. Because the endothelium has minimal replicative capacity in vivo and an inability to replace its genome, it is particularly prone to cumulative DNA damage acquired throughout life. In FECD, the underlying genetic defects make the CE genome even more vulnerable to this damage, to the point of causing mitochondrial dysfunction, mitochondrial membrane potential loss, and excessive mitophagy activation. Endogenous and exogenous intracellular stressors alter the synthetic footprint of CE cells, leading to endothelial-mesenchymal transition and secretion of aberrant extracellular matrix (in the form of guttae), resembling scar formation in other organs. In turn, the guttae or endothelial scars contribute to a vicious cycle of FECD pathogenesis and, by further inducing endothelial-mesenchymal transition and oxidant-antioxidant imbalance, perpetuate the molecular changes of the degenerating endothelium.

NQO1 downregulation potentiates menadione-induced endothelial-mesenchymal transition during rosette formation in Fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) is a genetic and oxidative stress disorder of post-mitotic human corneal endothelial cells (HCEnCs), which normally exhibit hexagonal shape and form a compact monolayer compatible with normal corneal functioning and clear vision. FECD is associated with increased DNA damage, which in turn leads to HCEnC loss, resulting in the formation rosettes and aberrant extracellular matrix (ECM) deposition in the form of pro-fibrotic guttae. Since the mechanism of ECM deposition in FECD is currently unknown, we aimed to investigate the role of endothelial-mesenchymal transition (EMT) in FECD using a previously established cellular in vitro model that recapitulates the characteristic rosette formation, by employing menadione (MN)-induced oxidative stress. We demonstrate that MN treatment alone, or a combination of MN and TGF-β1 induces reactive oxygen species (ROS), cell death, and EMT in HCEnCs during rosette formation, resulting in upregulation of EMT- and FECD-associated markers such as Snail1, N-cadherin, ZEB1, and transforming growth factor-beta-induced (TGFβI), respectively. Additionally, FECD ex vivo specimens displayed a loss of organized junctional staining of plasma membrane-bound N-cadherin, with corresponding increase in fibronectin and Snail1 compared to ex vivo controls. Addition of N-acetylcysteine (NAC) downregulated all EMT markers and abolished rosette formation. Loss of NQO1, a metabolizing enzyme of MN, led to greater increase in intracellular ROS levels as well as a significant upregulation of Snail1, fibronectin, and N-cadherin compared to normal cells, indicating that NQO1 regulates Snail1-mediated EMT. This study provides first line evidence that MN-induced oxidative stress leads to EMT in corneal endothelial cells, and the effect of which is further potentiated when redox cycling activity of MN is enhanced by the absence of NQO1. Given that NAC inhibits Snail-mediated EMT, this may be a potential therapeutic intervention for FECD.

Extracellular Matrix and Integrin Expression Profiles in Fuchs Endothelial Corneal Dystrophy Cells and Tissue Model

Primary corneal endothelial cell (CEC) cultures and 3D-engineered tissue models were used to study the aberrant deposition of extracellular matrix (ECM) in a vision impairing pathology known as Fuchs endothelial corneal dystrophy (FECD). CECs were isolated from excised Descemet membranes of patients with end-stage FECD. CECs isolated from healthy corneas served as controls. Microarray gene profiling was performed on postconfluent cultures of healthy and FECD cells. Protein expression analyses were conducted on tissue models that were engineered by seeding an endothelium on previously devitalized human stromal carriers. The engineered endothelia were kept in culture for 1-3 weeks to reform the endothelial monolayer. Protein expression of integrin subunits α4, α6, αv, and β1, as well as laminin, type IV collagen, fibronectin, clusterin, and transforming growth factor β-induced protein (TGFβIp) was then assessed by immunofluorescence. Microarray analysis showed nonstatistical twofold downregulation of collagen-coding genes (COL4A4, COL8A2, and COL21A1) and a twofold upregulation of the COL6A1, laminin α3 gene LAMA3, and integrin subunit α10 gene ITGA10 in FECD cells. Fibronectin type III domain containing 4 (FNDC4) and integrin β5 (ITGB5) genes was significantly upregulated in FECD cells. Immunostainings demonstrated that the protein expression of the integrin subunits α4, α6, αv, and β1, type IV collagen, as well as laminin remained similar between native and engineered endothelia. TGFβIp expression was found on the stromal side of both FECD and healthy Descemet's membrane, and only one out of three FECD specimens was positive for the clusterin protein. Interestingly, the ECM protein fibronectin was also found to have a stronger presence on engineered FECD tissues, a result consistent with the native FECD specimens. To conclude, this study allowed to identify fibronectin deposition as one of the first steps in the pathogenesis of FECD, as defined by our engineered tissue model. This opens the way to an entirely new perspective for in vitro pharmacological testing of new therapies for FECD, the leading indication for corneal transplantation in North America.

Activation of TGF-β signaling induces cell death via the unfolded protein response in Fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) is a slowly progressive bilateral disease of corneal endothelium in which accumulation of extracellular matrix (ECM) and loss of corneal endothelial cells (CECs) are phenotypic features. The corneal endothelium maintains corneal transparency by regulating water hydration; consequently, corneal endothelial dysfunction causes serious vision loss. The only therapy for corneal haziness due to corneal endothelial diseases, including FECD, is corneal transplantation using donor corneas, and no pharmaceutical treatment is available. We provide evidence that the expression levels of transforming growth factor-β (TGF-β) isoforms and TGF-β receptors are high in the corneal endothelium of patients with FECD. A cell model based on patients with FECD shows that TGF-β signaling induced a chronic overload of ECM proteins to the endoplasmic reticulum (ER), thereby enhancing the formation of unfolded protein and triggering the intrinsic apoptotic pathway through the unfolded protein response (UPR). We propose that inhibition of TGF-β signaling may represent a novel therapeutic target that suppresses cell loss as well as the accumulation of ECM in FECD.

Evaluation of Retinal and Choroidal Thickness in Fuchs' Uveitis Syndrome

Purpose. We aimed to investigate retinal and choroidal thickness in the eyes of patients with Fuchs' uveitis syndrome (FUS). Methods. Fifteen patients with unilateral FUS and 20 healthy control subjects were enrolled. Spectral domain optical coherence tomography (Spectralis HRA+OCT, 870 nm; Heidelberg Engineering, Heidelberg, Germany) was used to obtain retinal and choroidal thickness measurements. The retinal nerve fiber layer (RNFL) thickness, macular thickness, and choroidal thickness of the eyes with FUS were compared with the unaffected eye and the eyes of healthy control subjects. Results. The mean choroidal thickness at fovea and at each point within the horizontal nasal and temporal quadrants at 500 μm intervals to a distance of 1500 µm from the foveal center was significantly thinner in the affected eye of FUS patients compared with the unaffected eye of FUS patients or the eyes of healthy control subjects. However, there were no significant differences in RNFL or macular thickness between groups. Conclusions. Affected eyes in patients with FUS tend to have thinner choroids as compared to eyes of unaffected fellow eyes and healthy individuals, which might be a result of the chronic inflammation associated with the disease.

Genetics in Keratoconus: where are we?

Keratoconus (KC) is a non-inflammatory thinning and protrusion of the cornea in which the cornea assumes a conical shape. Complex etiology of this condition at present remains an enigma. Although environmental factors have been involved in KC pathogenesis, strong underlining genetic susceptibility has been proven. The lack of consistent findings among early genetic studies suggested a heterogeneity and complex nature of the genetic contribution to the development of KC. Recently, genome-wide linkage studies (GWLS) and genome-wide association studies (GWAS) were undertaken. Next-generation sequencing (NGS)-based genomic screens are also currently being carried out. Application of these recently developed comprehensive genetic tools led to a much greater success and increased reproducibility of genetic findings in KC. Involvement of the LOX gene identified through GWLS has been confirmed in multiple cohorts of KC patients around the world. KC susceptibility region located at the 2q21.3 chromosomal region near the RAB3GAP1 gene identified through GWAS was independently replicated. Rare variants in the ZNF469 gene (mutated in corneal dystrophy Brittle Cornea Syndrome) and in the TGFBI gene (mutated in multiple corneal epithelial–stromal TGFBI dystrophies) have been repeatedly identified in familial and sporadic KC patients of different ethnicities. Additional comprehensive strategies using quantitative endophenotypes have been successfully employed to bring further understanding to the genetics of KC. Additional genetic determinants including the COL5A1 gene have been identified in the GWAS of KC-related trait central corneal thickness. These recent discoveries confirmed the importance of the endophenotype approach for studying complex genetic diseases such as KC and showed that different connective tissue disorders may have the same genetic determinants.

Menadione-Induced DNA Damage Leads to Mitochondrial Dysfunction and Fragmentation During Rosette Formation in Fuchs Endothelial Corneal Dystrophy

AIMS

Fuchs endothelial corneal dystrophy (FECD), a leading cause of age-related corneal edema requiring transplantation, is characterized by rosette formation of corneal endothelium with ensuing apoptosis. We sought to determine whether excess of mitochondrial reactive oxygen species leads to chronic accumulation of oxidative DNA damage and mitochondrial dysfunction, instigating cell death.

RESULTS

We modeled the pathognomonic rosette formation of postmitotic corneal cells by increasing endogenous cellular oxidative stress with menadione (MN) and performed a temporal analysis of its effect in normal (HCEnC, HCECi) and FECD (FECDi) cells and ex vivo specimens. FECDi and FECD ex vivo specimens exhibited extensive mtDNA and nDNA damage as detected by quantitative PCR. Exposure to MN triggered an increase in mitochondrial superoxide levels and led to mtDNA and nDNA damage, while DNA amplification was restored with NAC pretreatment. Furthermore, MN exposure led to a decrease in ΔΨm and adenosine triphosphate levels in normal cells, while FECDi exhibited mitochondrial dysfunction at baseline. Mitochondrial fragmentation and cytochrome c release were detected in FECD tissue and after MN treatment of HCEnCs. Furthermore, cleavage of caspase-9 and caspase-3 followed MN-induced cytochrome c release in HCEnCs.

INNOVATION

This study provides the first line of evidence that accumulation of oxidative DNA damage leads to rosette formation, loss of functionally intact mitochondria via fragmentation, and subsequent cell death during postmitotic cell degeneration of ocular tissue.

CONCLUSION

MN induced rosette formation, along with mtDNA and nDNA damage, mitochondrial dysfunction, and fragmentation, leading to activation of the intrinsic apoptosis via caspase cleavage and cytochrome c release. Antioxid. Redox Signal. 24, 1072-1083.

Clusterin in the eye: An old dog with new tricks at the ocular surface

The multifunctional protein clusterin (CLU) was first described in 1983 as a secreted glycoprotein present in ram rete testis fluid that enhanced aggregation ('clustering') of a variety of cells in vitro. It was also independently discovered in a number of other systems. By the early 1990s, CLU was known under many names and its expression had been demonstrated throughout the body, including in the eye. Its homeostatic activities in proteostasis, cytoprotection, and anti-inflammation have been well documented, however its roles in health and disease are still not well understood. CLU is prominent at fluid-tissue interfaces, and in 1996 it was demonstrated to be the most highly expressed transcript in the human cornea, the protein product being localized to the apical layers of the mucosal epithelia of the cornea and conjunctiva. CLU protein is also present in human tears. Using a preclinical mouse model for desiccating stress that mimics human dry eye disease, the authors recently demonstrated that CLU prevents and ameliorates ocular surface barrier disruption by a remarkable sealing mechanism dependent on attainment of a critical all-or-none concentration in the tears. When the CLU level drops below the critical all-or-none threshold, the barrier becomes vulnerable to desiccating stress. CLU binds selectively to the ocular surface subjected to desiccating stress in vivo, and in vitro to LGALS3 (galectin-3), a key barrier component. Positioned in this way, CLU not only physically seals the ocular surface barrier, but it also protects the barrier cells and prevents further damage to barrier structure. CLU depletion from the ocular surface epithelia is seen in a variety of inflammatory conditions in humans and mice that lead to squamous metaplasia and a keratinized epithelium. This suggests that CLU might have a specific role in maintaining mucosal epithelial differentiation, an idea that can now be tested using the mouse model for desiccating stress. Most excitingly, the new findings suggest that CLU could serve as a novel biotherapeutic for dry eye disease.

Fuchs endothelial corneal dystrophy: current perspectives

Fuchs endothelial corneal dystrophy (FECD) is the most common corneal dystrophy and frequently results in vision loss. Hallmarks of the disease include loss of corneal endothelial cells and formation of excrescences of Descemet's membrane. Later stages involve all layers of the cornea. Impairment of endothelial barrier and pump function and cell death from oxidative and unfolded protein stress contribute to disease progression. The genetic basis of FECD includes numerous genes and chromosomal loci, although alterations in the transcription factor 4 gene are associated with the majority of cases. Definitive treatment of FECD is corneal transplantation. In this paper, we highlight advances that have been made in understanding FECD's clinical features, pathophysiology, and genetics. We also discuss recent advances in endothelial keratoplasty and potential future treatments.

Abnormal regulation of extracellular matrix and adhesion molecules in corneas of patients with keratoconus

AIM

To identify changes in the expression of genes coding for extracellular matrix (ECM) proteins in patients with non-inflammatory corneal disorder keratoconus (KC), patients with corneal scarring, and normal controls.

MATERIALS AND METHODS

Total RNA extracted from corneal tissue of 13 KC patients, 2 patients with corneal scaring and 4 normal controls was analyzed using Human Extracellular Matrix & Adhesion Molecules Profiler PCR Array. Statistically significant changes in gene expression were identified using the Data Analysis software.

RESULTS

Comparison of KC and control corneas with thresholds of 1.5 or greater fold change and a p-value of 0.05 or lower, revealed 21 differentially expressed genes, 16 genes were downregulated and 5 were upregulated. Among transcripts downregulated in KC patients we identified THBS1, ADAMTS1, SPP1, several collagens and integrins. We found TGFBI (BIGH3) gene was the most significantly upregulated transcript.

CONCLUSION

Development of keratoconus results in deregulation of gene expression of extracellular matrix and adhesion molecules.

CLINICAL SIGNIFICANCE

Downregulation of collagens and upregulation of TGFBI repeatedly identified in KC patients may be used as clinical markers of the disease.

Fuchs Corneal Dystrophy

Fuchs corneal dystrophy (FCD) is a hereditary, progressive disease of the posterior cornea which results in excrescences of Descemet membrane, endothelial cell loss, corneal edema, and, in late stages, bullous keratopathy. Structural changes are noted principally in Descemet membrane and the endothelium, with thickening of Descemet membrane, loss of barrier function, and increased corneal hydration, although secondary effects occur throughout all layers. Multiple chromosomal loci and, more recently, causal genetic mutations have been identified for this complex disorder, including in TCF8, SLC4A11, LOXHD1, and AGBL1. A trinucleotide repeat in TCF4 correlates strongly with disease status and interacts in common pathways with previously identified genes. Dysregulation of pathways involving oxidative stress and apoptosis, epithelial-to-mesenchymal transition, microRNA, mitochondrial genes, and unfolded protein response has been implicated in FCD pathogenesis.

Lysosomal trafficking of TGFBIp via caveolae-mediated endocytosis

Transforming growth factor-beta-induced protein (TGFBIp) is ubiquitously expressed in the extracellular matrix (ECM) of various tissues and cell lines. Progressive accumulation of mutant TGFBIp is directly involved in the pathogenesis of TGFBI-linked corneal dystrophy. Recent studies reported that mutant TGFBIp accumulates in cells; however, the trafficking of TGFBIp is poorly understood. Therefore, we investigated TGFBIp trafficking to determine the route of its internalization and secretion and to elucidate its roles in the pathogenesis of granular corneal dystrophy type 2 (GCD2). Our data indicate that newly synthesized TGFBIp was secreted via the endoplasmic reticulum/Golgi-dependent secretory pathway, and this secretion was delayed in the corneal fibroblasts of patients with GCD2. We also found that TGFBIp was internalized by caveolae-mediated endocytosis, and the internalized TGFBIp accumulated after treatment with bafilomycin A1, an inhibitor of lysosomal degradation. In addition, the proteasome inhibitor MG132 inhibits the endocytosis of TGFBIp. Co-immunoprecipitation revealed that TGFBIp interacted with integrin α_Vβ₃. Moreover, treatment with arginine-glycine-aspartic acid (RGD) tripeptide suppressed the internalization of TGFBIp. These insights on TGFBIp trafficking could lead to the identification of novel targets and the development of new therapies for TGFBI-linked corneal dystrophy.

Transcript profile of cellular senescence-related genes in Fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) is a genetically heterogeneous disease. Hypothesizing that cellular senescence may be relevant in FECD pathogenesis, genetically undifferentiated late-onset FECD endothelial samples were analyzed to identify common changes of specific senescence-related transcripts. Total RNA was extracted from 21 FECD endothelial samples retrieved from patients undergoing lamellar keratoplasty due to clinically diagnosed end-stage FECD and from 12 endothelial samples retrieved from normal autopsy eyes. Taqman low density array (TLDA) cards were used to analyze differential expression of 89 cellular senescence-related transcripts. Result validation was performed using individual real-time PCR assays. TLDA-analysis demonstrated differential expression of 31 transcripts (fold-change >1.5; p < 0.05). Thereof, 27 showed significant up-regulation and 4 significant down-regulation. Markedly elevated mRNA-levels of the constitutively active and reactive oxygen species-generating enzyme NOX4 were found in all evaluable FECD samples. In addition, increased expression of CDKN2A and its transcriptional activators ETS1 and ARHGAP18 (SENEX) along with decreased expression of CDKN2A inhibitor ID1 were detected in FECD samples. Consistent over-expression of NOX4 in FECD endothelial samples suggests a role as pathogenic factor and as a potential new treatment target in FECD. Transcriptional up-regulation of the CDKN2A-pathway provides further evidence for increased cellular senescence in FECD endothelium.

Proteomics of Fuchs' endothelial corneal dystrophy support that the extracellular matrix of Descemet's membrane is disordered

Fuchs' endothelial corneal dystrophy (FECD) is a major corneal disorder affecting the innermost part of the cornea, leading to visual impairment. As the morphological changes in FECD are mainly observed in the extracellular matrix of the Descemet's membrane/endothelial layer, we determined the protein profiles of diseased and control tissues using two relative quantitation MS methods. The first quantitation method, based on the areas of the extracted ion chromatograms, quantified the 51 and 48 most abundant proteins of the Descemet's membrane/endothelial layer in patient and control tissues, respectively, of which 10 were significantly regulated. The results indicated that the level of type VIII collagen was unaltered even though the protein previously has been shown to be implicated in familial early-onset forms of the disease. Using the second relative quantitation method, iTRAQ, we identified 22 differentially regulated proteins, many of which are extracellular proteins known to be involved in proper assembly of the basement membrane in other tissues. In total, 26 differentially regulated proteins were identified, of which 6 proteins were regulated in both methods. These results support that the morphological changes observed in FECD are caused in part by an aberrant assembly of the extracellular matrix within the Descemet's membrane/endothelial layer.

Review of application of mass spectrometry for analyses of anterior eye proteome

Proteins have important functional roles in the body, which can be altered in disease states. The eye is a complex organ rich in proteins; in particular, the anterior eye is very sophisticated in function and is most commonly involved in ophthalmic diseases. Proteomics, the large scale study of proteins, has greatly impacted our knowledge and understanding of gene function in the post-genomic period. The most significant breakthrough in proteomics has been mass spectrometric identification of proteins, which extends analysis far beyond the mere display of proteins that classical techniques provide. Mass spectrometry functions as a “mass analyzer” which simplifies the identification and quantification of proteins extracted from biological tissue. Mass spectrometric analysis of the anterior eye proteome provides a differential display for protein comparison of normal and diseased tissue. In this article we present the key proteomic findings in the recent literature related to the cornea, aqueous humor, trabecular meshwork, iris, ciliary body and lens. Through this we identified unique proteins specific to diseases related to the anterior eye.

The genetics of Fuchs' corneal dystrophy

Fuchs' corneal dystrophy (FCD) is a common late-onset genetic disorder of the corneal endothelium. It causes loss of endothelial cell density and excrescences in the Descemet membrane, eventually progressing to corneal edema, necessitating corneal transplantation. The genetic basis of FCD is complex and heterogeneous, demonstrating variable expressivity and incomplete penetrance. To date, three causal genes, ZEB1, SLC4A11 and LOXHD1, have been identified, representing a small proportion of the total genetic load of FCD. An additional four loci have been localized, including a region on chromosome 18 that is potentially responsible for a large proportion of all FCD cases. The elucidation of the causal genes underlying these loci will begin to clarify the pathogenesis of FCD and pave the way for the emergence of nonsurgical treatments.

The Human Eye Proteome Project: perspectives on an emerging proteome

There are an estimated 285 million people with visual impairment worldwide, of whom 39 million are blind. The pathogenesis of many eye diseases remains poorly understood. The human eye is currently an emerging proteome that may provide key insight into the biological pathways of disease. We review proteomic investigations of the human eye and present a catalogue of 4842 nonredundant proteins identified in human eye tissues and biofluids to date. We highlight the need to identify new biomarkers for eye diseases using proteomics. Recent advances in proteomics do now allow the identification of hundreds to thousands of proteins in tissues and fluids, characterization of various PTMs and simultaneous quantification of multiple proteins. To facilitate proteomic studies of the eye, the Human Eye Proteome Project (HEPP) was organized in September 2012. The HEPP is one of the most recent components of the Biology/Disease-driven Human Proteome Project (B/D-HPP) whose overarching goal is to support the broad application of state-of-the-art measurements of proteins and proteomes by life scientists studying the molecular mechanisms of biological processes and human disease. The large repertoire of investigative proteomic tools has great potential to transform vision science and enhance understanding of physiology and disease processes that affect sight.

Association of TCF4 and CLU polymorphisms with Fuchs' endothelial dystrophy and implication of CLU and TGFBI proteins in the disease process

Fuchs' endothelial dystrophy (FED) is a disease affecting the corneal endothelium. Recent studies reported significant association of polymorphisms in the TCF4 (transcription factor 4) gene, and a borderline association of PTPRG (protein tyrosine phosphatase, receptor type, G) variants with late-onset FED in Caucasians from the United States. Association of TCF4 has also been reported in the Chinese population. We aimed to determine association of the reported polymorphisms in TCF4 and PTPRG, and association of polymorphisms in the candidate genes ZEB1 (zinc-finger E-box binding homoebox 1), COL8A2 (collagen, type VIII, alpha 2), TGFBI (transforming growth factor, β-induced) and CLU (clusterin) in Australian cases. We also compared the expression of TGFBI and CLU proteins between FED and normal whole corneas. In all, 30 single-nucleotide polymorphisms (SNPs) from the candidate genes were genotyped in 103 cases and 275 controls. Each SNP and haplotype was assessed for association with the disease. SNP analysis identified an association of TCF4 (rs613872 (P=5.25 × 10(-15), OR=4.05), rs9954153 (P=3.37 × 10(-7), OR=2.58), rs2286812 (P=4.23 × 10(-6), OR=2.55) and rs17595731 (P=3.57 × 10(-5), OR=3.79)), CLU (rs17466684; P=0.003, OR=1.85) and one haplotype of TGFBI SNPs (P=0.011, OR=2.29) with FED in Caucasian Australians. No evidence for genetic association of PTPRG, ZEB1 and COL8A2 was found. Immunohistochemistry showed differential expression of CLU and TGFBI proteins in FED-affected compared with normal corneas. In conclusion, variation in TCF4, CLU and TGFBI, but not PTPRG, ZEB1 and COL8A2 genes are associated with FED in Caucasian Australian cases. Differential expression of CLU and TGFBI proteins in FED-affected corneas provides novel insights into the disease mechanism.

An Arg124His mutation in TGFBI associated to Avellino corneal dystrophy in a Chinese pedigree

PURPOSE

To identify the gene mutation underlying Avellino corneal dystrophy in a four-generation Chinese pedigree.

METHODS

Patients from the affected family underwent detailed clinical examination involving slit-lamp photography and confocal microscopy. Genomic DNA extracted from peripheral leukocytes was amplified using touch-down PCR for gene scanning. Two-point linkage analysis and haplotyping were performed to map the relevant chromosome region. The candidate gene in this region was sequenced to screen out the disease-causing mutation.

RESULTS

Patients in the pedigree were diagnosed with Avellino corneal dystrophy. Using linkage analysis, the responsible gene was mapped to chromosome 5q31.2 with a maximum LOD (log odds) score (Z(max)) of 3.23 at D5S479 (θ(max)=0.0). Haplotypes constructed from 11 microstallite markers identified the disease-linked chromosome region as being below D5S808. Sequencing of TGFBI (transforming growth factor-beta induced gene), a known gene in this region, revealed a heterozygous transition (c.418 G>A) in exon 4 resulting in Arg124His (R124H) being co-segregated with the disease in affected family members but not in the unaffected members or the 50 unrelated controls.

CONCLUSIONS

Our study demonstrated that a G>A transition in Arg124His of TGFBI was responsible for Avellino corneal dystrophy in a Chinese pedigree. This result further supports the importance of TGFBIp in maintaining transparency of the cornea.

Culture of human corneal endothelial cells isolated from corneas with Fuchs endothelial corneal dystrophy

The purpose of this study was to assess the feasibility of initiating primary cultures of corneal endothelial cells from patients suffering from Fuchs endothelial corneal dystrophy (FECD; MIM# 1036800). We also evaluated which conditions yielded the best results for culture. Twenty-nine patients undergoing Descemet stripping automated endothelial keratoplasty consented to the use of their excised Descemet's membrane for this study. Out of the 29 specimens, 18 successfully initiated a culture. Cell morphology varied between endothelial (rounded, slightly elongated cells, n = 12) and fibroblastic-like (thin and very elongated cells, n = 6). These differences in cell morphology were also observed with the normal human corneal endothelial cell cultures. The cultures that initially presented an endothelial morphology maintained their shape in subcultures. Clusterin expression was similar in FECD and normal endothelial cells. Transmission electron microscopy of FECD Descemet's membranes showed a high degree of various abnormalities generally found in this disease, such as a thickened Descemet's membrane, presence of a posterior banded layer, presence of a fibrillar layer and striated bodies of various sizes and periodicities. Patient's age was predictive of culture success, all younger FECD donors generating cultures of endothelial morphology. The absence of a fibrillar layer was also a factor associated with greater success. Culture success was not dependent on specimen size, specimen pigmentation, or patient's preoperative central corneal thickness. In conclusion, this paper shows for the first time that central Descemet's membranes of patients suffering from FECD possess proliferative endothelial cells that can be isolated and cultured without viral transduction, opening the way for new in vitro studies of this disease.

An alpha 2 collagen VIII transgenic knock-in mouse model of Fuchs endothelial corneal dystrophy shows early endothelial cell unfolded protein response and apoptosis

Fuchs endothelial corneal dystrophy (FECD) is a leading indication for corneal transplantation. FECD is characterized by progressive alterations in endothelial cell morphology, excrescences (guttae) and thickening of the endothelial basement membrane and cell death. Ultimately, these changes lead to corneal edema and vision loss. Due to the lack of vision loss in early disease stages and the decades long disease course, early pathophysiology in FECD is virtually unknown as studies of pathologic tissues have been limited to end-stage tissues obtained at transplant. The first genetic defect shown to cause FECD was a point mutation causing a glutamine to lysine substitution at amino acid position 455 (Q455K) in the alpha 2 collagen 8 gene (COL8A2) which results in an early onset form of the disease. Homozygous mutant knock-in mice with this mutation (Col8a2(Q455K/Q455K)) show features strikingly similar to human disease, including progressive alterations in endothelial cell morphology, cell loss and basement membrane guttae. Ultrastructural analysis shows the predominant defect as dilated endoplasmic reticulum (ER), suggesting ER stress and unfolded protein response (UPR) activation. Immunohistochemistry, western blotting, quantitative reverse transcriptase polymerase chain reaction and terminal deoxynucleotidyl transferase 2-deoxyuridine, 5-triphosphate nick end-labeling analyses support UPR activation and UPR-associated apoptosis in the Col8a2(Q455K/Q455K) mutant corneal endothelium. This study confirms the Q455K substitution in the COL8A2 gene as being sufficient to cause FECD in the first mouse model of this disease and supports the role of the UPR and UPR-associated apoptosis in the pathogenesis of FECD caused by COL8A2 mutations.

Gene therapy in the cornea: 2005--present

Successful restoration of vision in human patients with gene therapy affirmed its promise to cure ocular diseases and disorders. The efficacy of gene therapy is contingent upon vector and mode of therapeutic DNA introduction into targeted cells/tissues. The cornea is an ideal tissue for gene therapy due to its ease of access and relative immune-privilege. Considerable progress has been made in the field of corneal gene therapy in last 5 years. Several new gene transfer vectors, techniques and approaches have evolved. Although corneal gene therapy is still in its early stages of development, the potential of gene-based interventions to treat corneal abnormalities has begun to surface. Identification of next generation viral and nanoparticle vectors, characterization of delivered gene levels, localization, and duration in the cornea, and significant success in controlling corneal disorders, particularly fibrosis and angiogenesis, in experimental animal disease models, with no major side effects have propelled gene therapy a step closer toward establishing gene-based therapies for corneal blindness. Recently, researchers have assessed the delivery of therapeutic genes for corneal diseases and disorders due to trauma, infections, chemical, mechanical, and surgical injury, and/or abnormal wound healing. This review provides an update on the developments in gene therapy for corneal diseases and discusses the barriers that hinder its utilization for delivering genes in the cornea.

Molecular bases of corneal endothelial dystrophies

The phrase "corneal endothelial dystrophies" embraces a group of bilateral corneal conditions that are characterized by a non-inflammatory and progressive degradation of corneal endothelium. Corneal endothelial cells exhibit a high pump site density and, along with barrier function, are responsible for maintaining the cornea in its natural state of relative dehydration. Gradual loss of endothelial cells leads to an insufficient water outflow, resulting in corneal edema and loss of vision. Since the pathologic mechanisms remain largely unknown, the only current treatment option is surgical transplantation when vision is severely impaired. In the past decade, important steps have been taken to understand how endothelial degeneration progresses on the molecular level. Studies of affected multigenerational families and sporadic cases identified genes and chromosomal loci, and revealed either Mendelian or complex disorder inheritance patterns. Mutations have been detected in genes that carry important structural, metabolic, cytoprotective, and regulatory functions in corneal endothelium. In addition to genetic predisposition, environmental factors like oxidative stress were found to be involved in the pathogenesis of endotheliopathies. This review summarizes and crosslinks the recent progress on deciphering the molecular bases of corneal endothelial dystrophies.

Fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) is characterized by progressive loss of corneal endothelial cells, thickening of Descement's membrane and deposition of extracellular matrix in the form of guttae. When the number of endothelial cells becomes critically low, the cornea swells and causes loss of vision. The clinical course of FECD usually spans 10-20 years. Corneal transplantation is currently the only modality used to restore vision. Over the last several decades genetic studies have detected several genes, as well as areas of chromosomal loci associated with the disease. Proteomic studies have given rise to several hypotheses regarding the pathogenesis of FECD. This review expands upon the recent findings from proteomic and genetic studies and builds upon recent advances in understanding the causes of this common corneal disorder.

Evidence of oxidative stress in the pathogenesis of fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) is a progressive, blinding disease characterized by corneal endothelial (CE) cell apoptosis. Corneal transplantation is the only measure currently available to restore vision in these patients. Despite the identification of some genetic factors, the pathophysiology of FECD remains unclear. In this study, we observed a decrease in the antioxidant response element-driven antioxidants in FECD corneal endothelium. We further demonstrated that nuclear factor erythroid 2-related factor 2, a transcription factor known to bind the antioxidant response element and activate antioxidant defense, is down-regulated in FECD endothelium. Importantly, we detected significantly higher levels of oxidative DNA damage and apoptosis in FECD endothelium compared with normal controls and pseudophakic bullous keratopathy (iatrogenic CE cell loss) specimens. A marker of oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine, colocalized to mitochondria, indicating that the mitochondrial genome is the specific target of oxidative stress in FECD. Oxidative DNA damage was not detected in pseudophakic bullous keratopathy corneas, whereas it colocalized with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells in FECD samples. Ex vivo, oxidative stress caused characteristic morphological changes and apoptosis of CE, suggestive of findings that characterize FECD in vivo. Together, these data suggest that suboptimal nuclear factor erythroid 2-related factor 2-regulated defenses may account for oxidant-antioxidant imbalance in FECD, which in turn leads to oxidative DNA damage and apoptosis. This study provides evidence that oxidative stress plays a key role in FECD pathogenesis.

Retrocorneal membranes: a comparative immunohistochemical analysis of keratocytic, endothelial, and epithelial origins

PURPOSE

To determine through the use of immunohistochemistry the origins of retrocorneal cellular and fibrillar membranes.

DESIGN

Retrospective, clinicopathologic study using surgically removed human corneal tissues.

METHODS

Clinical records of patients' ocular diseases and surgical procedures were reviewed. Immunohistochemical staining was performed on 5 enucleated control globes, 32 penetrating keratoplasty specimens, and 6 Descemet stripping endothelial keratoplasty specimens to analyze: (1) the normal corneal epithelium, stroma, and endothelium; and (2) stromal scars, endothelial abnormalities, and retrocorneal membranes. Paraffin sections were stained with hematoxylin and eosin, periodic acid-Schiff, and Masson trichrome methods, and immunohistochemical analyses were performed with commonly available monoclonal and polyclonal antibodies for various cytokeratins (CKs), CD34, alpha-smooth muscle actin (SMA), and vimentin.

RESULTS

Five subtypes among 28 retrocorneal membranes were characterized. Twelve fibrous (keratocytic) membranes of stromal origin had coarse collagen and immunostained negatively for all CKs, but strongly for vimentin and alpha-SMA, the last the only marker of diagnostic value. Nine metaplastic endothelium-derived membranes produced delicate collagenous matrices and immunoreacted with CK7, vimentin, and alpha-SMA. Two epithelial multilaminar or monolaminar membranes reacted with CK cocktail and wide-spectrum CK, mildly with CK7 (not observed in orthotopic surface epithelium), and negatively for alpha-SMA and vimentin. The final 2 categories were indeterminate or non-immunoreactive (3 specimens) and mixed (2 specimens).

CONCLUSIONS

Immunohistochemistry can diagnose retrocorneal membranes of different provenances reliably in most cases. Clinical correlations established that these membranes develop after serious inflammatory disorders, prolonged wounding or ulcerations, and multiple surgeries (an average of 3.4 per patient).