Functional impact of ZEB1 mutations associated with posterior polymorphous and Fuchs' endothelial corneal dystrophies

Corneal endothelial cell morphology in children with autosomal recessive Alport syndrome: a longitudinal study

PURPOSE

To evaluate the corneal endothelial cell morphology in children with autosomal recessive Alport syndrome (ARAS).

METHODS

This is a longitudinal, prospective cohort study that evaluated pediatric patients with genetically diagnosed ARAS. Fifty-eight eyes of 29 pediatric patients (12 patients, 17 controls) underwent a full ophthalmic examination. Corneal endothelial cell density (ECD) (cells/mm²), coefficient variation (CV) of cell area (polymegathism), the percentage of hexagonal cells (HEX) (pleomorphism), and central corneal thickness (CCT) were analyzed automatically using a noncontact specular microscopy.

RESULTS

The mean ECD was 2904 ± 355.48 cell/mm² in the ARAS group and 3263.20 ± 261.71 cell/mm² in the control group (p = 0.004). In the ARAS group, the mean CV was 46.53 ± 10.43, which was significantly higher than that in controls (p = 0.026). The mean HEX was 48.86 ± 14.71 in the ARAS group and 59.06 ± 10.64 in the control group (p = 0.038). The mean CCT was 565.26 ± 39.77 µm in the ARAS group and 579.66 ± 31.65 µm in the control group (p = 0.282). The comparison of endothelial cell characteristic of the ARAS group with 1-year follow-up is as follows: The mean ECD decreased from 2904 ± 355.48 cell/mm² to 2735 ± 241.58 cell/mm² (p = 0.003). The mean CV increased from 46.53 ± 10.43 to 47.93 ± 10.50 (p = 0.471). The mean HEX decreased from 48.86 ± 14.71 to 48.50 ± 10.06 (p = 0.916). The mean CCT decreased from 565.26 ± 39.77 µm to 542.86 ± 40.39 µm (p = 0.000).

CONCLUSION

Measurement of ECD and percentage of hexagonality can also be used as an indicator of the health of the corneal endothelium. In this study, the mean ECD and HEX were significantly lower in ARAS group than in age-matched pediatric controls. Polymegathism, which reflects cellular stress, was statistically significantly higher in ARAS group. The mean ECD and CCT decreased significantly at 1-year follow-up. This study may demostrated that endothelial damages and stress in ARAS patients appear in childhood and show a rapid increase with age.

Systematic review of SLC4A11, ZEB1, LOXHD1, and AGBL1 variants in the development of Fuchs' endothelial corneal dystrophy

Introduction

The pathogenic role of variants in TCF4 and COL8A2 in causing Fuchs' endothelial corneal dystrophy (FECD) is not controversial and has been confirmed by numerous studies. The causal role of other genes, SLC4A11, ZEB1, LOXHD1, and AGBL1, which have been reported to be associated with FECD, is more complicated and less obvious. We performed a systematic review of the variants in the above-mentioned genes in FECD cases, taking into account the currently available population frequency information, transcriptomic data, and the results of functional studies to assess their pathogenicity.

Methods

Search for articles published in 2005-2022 was performed manually between July 2022 and February 2023. We searched for original research articles in peer-reviewed journals, written in English. Variants in the genes of interest identified in patients with FECD were extracted for the analysis. We classified each presented variant by pathogenicity status according to the ACMG criteria implemented in the Varsome tool. Diagnosis, segregation data, presence of affected relatives, functional analysis results, and gene expression in the corneal endothelium were taken into account. Data on the expression of genes of interest in the corneal endothelium were extracted from articles in which transcriptome analysis was performed. The identification of at least one variant in a gene classified as pathogenic or significantly associated with FECD was required to confirm the causal role of the gene in FECD.

Results

The analysis included 34 articles with 102 unique ZEB1 variants, 20 articles with 64 SLC4A11 variants, six articles with 26 LOXHD1 variants, and five articles with four AGBL1 variants. Pathogenic status was confirmed for seven SLC4A11 variants found in FECD. No variants in ZEB1, LOXHD1, and AGBL1 genes were classified as pathogenic for FECD. According to the transcriptome data, AGBL1 and LOXHD1 were not expressed in the corneal endothelium. Functional evidence for the association of LOXHD1, and AGBL1 with FECD was conflicting.

Conclusion

Our analysis confirmed the causal role of SLC4A11 variants in the development of FECD. The causal role of ZEB1, LOXHD1, and AGBL1 variants in FECD has not been confirmed. Further evidence from familial cases and functional analysis is needed to confirm their causal roles in FECD.

Comparing Gene Panels for Non-Retinal Indications: A Systematic Review

Importance: The options for genetic testing continue to grow for ocular conditions, including optic atrophy, anterior segment dysgenesis, cataracts, corneal dystrophy, nystagmus, and glaucoma. Gene panels can vary in content and coverage, as we and others have evaluated in inherited retinal disease (IRD). Objective: To describe gene panel testing options for inherited eye disease phenotypes and their differences. This review is important for making diagnostic decisions. Evidence review: A licensed, certified genetic counselor (RP) used Concert Genetics and the search terms optic atrophy, corneal dystrophy, cataract, glaucoma, anterior segment dysgenesis, microphthalmia/anophthalmia, and nystagmus to identify available testing options performed by CLIA-certified commercial genetic testing laboratories. Other co-authors were surveyed with respect to genetic panels used for the indications of interest. Ophthalmic panels were then compared using Concert Genetics in addition to their own websites. Findings: Panels from each clinical category were included and summarized. This comparison highlighted the differences and similarities between panels so that clinicians can make informed decisions. Conclusions: Access to genetic testing is increasing. The diagnostic yield of genetic testing is increasing. Each panel is different, so phenotyping or characterizing clinical characteristics that may help predict a specific genotype, as well as pre-test hypotheses regarding a genotype, should shape the choice of panels.

The approach to patient clustering based on the microchip data confined to distinct loci using the combinations of variants

Fuchs' endothelial corneal dystrophy is a socially significant hereditary disease. More than a half of cases in the European population are caused by the increased number of trinucleotude repeats in the TCF4 gene. The study was aimed to develop and test the approach of dividing patients into groups based on the chip-based genotyping and genome-wide association study (GWAS) results. The analysis was conducted using FECD Genetics Multi-center Study and AREDs project datasets containing the data of 1721 clinical cases and 2408 control patients. When analyzing the GWAS results, the patients and the control group were divided into two groups by means of hierarchical clustering suggesting that patients with the increased number of repeats in the TCF4 gene are carriers of specific combinations of genomic variants (haplotypes). It was shown that individual variants cannot be used for the molecular genetic stratification of patients with the increased number of repeats in TCF4 due to inconsistent results obtained for the variants. Furthermore, the haplotype-based approach outperformed the SNPs in terms of odds ratio. The paper proposes a method that enables further search for the biologically relevant combinations of genomic variants.

Posterior Polymorphous Corneal Dystrophy in a Patient with a Novel ZEB1 Gene Mutation

Posterior polymorphous corneal dystrophy (PPCD), a rare, bilateral, autosomal-dominant, inherited corneal dystrophy, affects the Descemet membrane and corneal endothelium. We describe an unusual presentation of PPCD associated with a previously unknown genetic alteration in the ZEB1 gene. The proband is a 64-year-old woman diagnosed with keratoconus referred for a corneal endothelium study who presented endothelial lesions in both eyes suggestive of PPCD, corectopia and iridocorneal endothelial synechiae in the right eye and intrastromal segments in the left eye. The endothelial count was 825 in the right eye and 1361 in the left eye, with typical PPCD lesions visible under specular and confocal microscopy. In the next generation sequencing genetic analysis, a heterozygous c.1A > C (p.Met1Leu) mutation was found in the ZEB1 gene (TCF8). The PPCD3 subtype is associated with corneal ectasia, and both can appear due to a pathogenic mutation in the ZEB1 gene (OMIM #189909). However, our patient had a previously unreported mutation in the ZEB1 gene, which mediates the transition between cell lines and provides a pathogenic explanation for the epithelialisation of the corneal endothelium, a characteristic of PPCD.

Post-Translational Modification of ZEB Family Members in Cancer Progression

Post-translational modification (PTM), the essential regulatory mechanisms of proteins, play essential roles in physiological and pathological processes. In addition, PTM functions in tumour development and progression. Zinc finger E-box binding homeobox (ZEB) family homeodomain transcription factors, such as ZEB1 and ZEB2, play a pivotal role in tumour progression and metastasis by induction epithelial-mesenchymal transition (EMT), with activation of stem cell traits, immune evasion and epigenetic reprogramming. However, the relationship between ZEB family members' post-translational modification (PTM) and tumourigenesis remains largely unknown. Therefore, we focussed on the PTM of ZEBs and potential therapeutic approaches in cancer progression. This review provides an overview of the diverse functions of ZEBs in cancer and the mechanisms and therapeutic implications that target ZEB family members' PTMs.

CK2 and the Hallmarks of Cancer

Cancer is a leading cause of death worldwide. Casein kinase 2 (CK2) is commonly dysregulated in cancer, impacting diverse molecular pathways. CK2 is a highly conserved serine/threonine kinase, constitutively active and ubiquitously expressed in eukaryotes. With over 500 known substrates and being estimated to be responsible for up to 10% of the human phosphoproteome, it is of significant importance. A broad spectrum of diverse types of cancer cells has been already shown to rely on disturbed CK2 levels for their survival. The hallmarks of cancer provide a rationale for understanding cancer’s common traits. They constitute the maintenance of proliferative signaling, evasion of growth suppressors, resisting cell death, enabling of replicative immortality, induction of angiogenesis, the activation of invasion and metastasis, as well as avoidance of immune destruction and dysregulation of cellular energetics. In this work, we have compiled evidence from the literature suggesting that CK2 modulates all hallmarks of cancer, thereby promoting oncogenesis and operating as a cancer driver by creating a cellular environment favorable to neoplasia.

Expression and Function of ZEB1 in the Cornea

ZEB1 is an important transcription factor for epithelial to mesenchymal transition (EMT) and in the regulation of cell differentiation and transformation. In the cornea, ZEB1 presents in all three layers: the epithelium, the stroma and the endothelium. Mutations of ZEB1 have been linked to multiple corneal genetic defects, particularly to the corneal dystrophies including keratoconus (KD), Fuchs endothelial corneal dystrophy (FECD), and posterior polymorphous corneal dystrophy (PPCD). Accumulating evidence indicates that dysfunction of ZEB1 may affect corneal stem cell homeostasis, and cause corneal cell apoptosis, stromal fibrosis, angiogenesis, squamous metaplasia. Understanding how ZEB1 regulates the initiation and progression of these disorders will help us in targeting ZEB1 for potential avenues to generate therapeutics to treat various ZEB1-related disorders.

[Molecular genetic aspects of Fuchs' endothelial corneal dystrophy pathogenesis]

Fuchs' corneal dystrophy (FCD) is a common bilateral non-inflammatory endothelial pathology. It is a multigenic disorder with various expressivity, penetrance and population prevalence. This review discusses corneal endothelium pump function, FCD pathogenesis and its known genetic factors.

Multifaceted actions of Zeb2 in postnatal neurogenesis from the ventricular-subventricular zone to the olfactory bulb

The transcription factor Zeb2 controls fate specification and subsequent differentiation and maturation of multiple cell types in various embryonic tissues. It binds many protein partners, including activated Smad proteins and the NuRD co-repressor complex. How Zeb2 subdomains support cell differentiation in various contexts has remained elusive. Here, we studied the role of Zeb2 and its domains in neurogenesis and neural differentiation in the young postnatal ventricular-subventricular zone (V-SVZ), in which neural stem cells generate olfactory bulb-destined interneurons. Conditional Zeb2 knockouts and separate acute loss- and gain-of-function approaches indicated that Zeb2 is essential for controlling apoptosis and neuronal differentiation of V-SVZ progenitors before and after birth, and we identified Sox6 as a potential downstream target gene of Zeb2. Zeb2 genetic inactivation impaired the differentiation potential of the V-SVZ niche in a cell-autonomous fashion. We also provide evidence that its normal function in the V-SVZ also involves non-autonomous mechanisms. Additionally, we demonstrate distinct roles for Zeb2 protein-binding domains, suggesting that Zeb2 partners co-determine neuronal output from the mouse V-SVZ in both quantitative and qualitative ways in early postnatal life.

Eyeing the Extracellular Matrix in Vascular Development and Microvascular Diseases and Bridging the Divide between Vascular Mechanics and Function

The extracellular matrix (ECM) is critical in all aspects of vascular development and health: supporting cell anchorage, providing structure, organization and mechanical stability, and serving as a sink for growth factors and sustained survival signals. Abnormal changes in ECM protein expression, organization, and/or properties, and the ensuing changes in vascular compliance affect vasodilator responses, microvascular pressure transmission, and collateral perfusion. The changes in microvascular compliance are independent factors initiating, driving, and/or exacerbating a plethora of microvascular diseases of the eye including diabetic retinopathy (DR) and vitreoretinopathy, retinopathy of prematurity (ROP), wet age-related macular degeneration (AMD), and neovascular glaucoma. Congruently, one of the major challenges with most vascular regenerative therapies utilizing localized growth factor, endothelial progenitor, or genetically engineered cell delivery, is the regeneration of blood vessels with physiological compliance properties. Interestingly, vascular cells sense physical forces, including the stiffness of their ECM, through mechanosensitive integrins, their associated proteins and the actomyosin cytoskeleton, which generates biochemical signals that culminate in a rapid expression of matricellular proteins such as cellular communication network 1 (CCN1) and CCN2 (aka connective tissue growth factor or CTGF). Loss or gain of function of these proteins alters genetic programs of cell growth, ECM biosynthesis, and intercellular signaling, that culminate in changes in cell behavior, polarization, and barrier function. In particular, the function of the matricellular protein CCN2/CTGF is critical during retinal vessel development and regeneration wherein new blood vessels form and invest a preformed avascular neural retina following putative gradients of matrix stiffness. These observations underscore the need for further in-depth characterization of the ECM-derived cues that dictate structural and functional properties of the microvasculature, along with the development of new therapeutic strategies addressing the ECM-dependent regulation of pathophysiological stiffening of blood vessels in ischemic retinopathies.

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.

Potential Protective and Therapeutic Roles of the Nrf2 Pathway in Ocular Diseases: An Update

Nuclear factor- (erythroid-derived 2-) like 2 (Nrf2) is a regulator of many processes of life, and it plays an important role in antioxidant, anti-inflammatory, and antifibrotic responses and in cancer. This review is focused on the potential mechanism of Nrf2 in the occurrence and development of ocular diseases. Also, several Nrf2 inducers, including noncoding RNAs and exogenous compounds, which control the expression of Nrf2 through different pathways, are discussed in ocular disease models and ocular cells, protecting them from dysfunctional changes. Therefore, Nrf2 might be a potential target of protecting ocular cells from various stresses and preventing ocular diseases.

Ultraviolet A light induces DNA damage and estrogen-DNA adducts in Fuchs endothelial corneal dystrophy causing females to be more affected

Fuchs endothelial corneal dystrophy (FECD) is a leading cause of corneal endothelial (CE) degeneration resulting in impaired visual acuity. It is a genetically complex and age-related disorder, with higher incidence in females. In this study, we established a nongenetic FECD animal model based on the physiologic outcome of CE susceptibility to oxidative stress by demonstrating that corneal exposure to ultraviolet A (UVA) recapitulates the morphological and molecular changes of FECD. Targeted irradiation of mouse corneas with UVA induced reactive oxygen species (ROS) production in the aqueous humor, and caused greater CE cell loss, including loss of ZO-1 junctional contacts and corneal edema, in female than male mice, characteristic of late-onset FECD. UVA irradiation caused greater mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) damage in female mice, indicative of the sex-driven differential response of the CE to UVA, thus accounting for more severe phenotype in females. The sex-dependent effect of UVA was driven by the activation of estrogen-metabolizing enzyme CYP1B1 and formation of reactive estrogen metabolites and estrogen-DNA adducts in female but not male mice. Supplementation of N-acetylcysteine (NAC), a scavenger of reactive oxygen species (ROS), diminished the morphological and molecular changes induced by UVA in vivo. This study investigates the molecular mechanisms of environmental factors in FECD pathogenesis and demonstrates a strong link between UVA-induced estrogen metabolism and increased susceptibility of females for FECD development.

The Molecular Basis of Fuchs' Endothelial Corneal Dystrophy

Fuchs' endothelial corneal dystrophy (FECD) is a common disease resulting from corneal endothelial cell dysfunction. It is inherited in an autosomal dominant fashion with incomplete penetrance, and with a female bias. Approximately half of cases occur sporadically, and the remainder are familial. Early and late-onset forms of the disease exist. A review of the literature has revealed more than 15 genes harbouring mutations and/or single nucleotide polymorphisms associated with FECD. The proteins encoded by these genes cover a wide range of endothelial function, including transcription regulation, DNA repair, mitochondrial DNA mutations, targeting of proteins to the cell membrane, deglutamylation of proteins, extracellular matrix secretion, formation of cell-cell and cell-extracellular matrix junctions, water pump, and apoptosis. These genetic variations will form the platform for the further understanding of the pathological basis of the disease, and the development of targeted treatments. This review aims to summarise known genetic variations associated with FECD, discuss any known molecular effects of the variations, how these provide opportunities for targeted therapies, and what therapies are currently in development.

The utility of massively parallel sequencing for posterior polymorphous corneal dystrophy type 3 molecular diagnosis

The aim of this study was to identify the molecular genetic cause of disease in posterior polymorphous corneal dystrophy (PPCD) probands of diverse origin and to assess the utility of massively parallel sequencing in the detection of ZEB1 mutations. We investigated a total of 12 families (five British, four Czech, one Slovak and two Swiss). Ten novel and two recurrent disease-causing mutations in ZEB1, were identified in probands by Sanger (n = 5), exome (n = 4) and genome (n = 3) sequencing. Sanger sequencing was used to confirm the mutations detected by massively parallel sequencing, and to perform segregation analysis. Genome sequencing revealed that one proband harboured a novel ∼0.34 Mb heterozygous de novo deletion spanning exons 1-7 and part of exon 8. Transcript analysis confirmed that the ZEB1 transcript is detectable in blood-derived RNA samples and that the disease-associated variant c.482-2A>G leads to aberrant pre-mRNA splicing. De novo mutations, which are a feature of PPCD3, were found in the current study with an incidence rate of at least 16.6%. In general, massively parallel sequencing is a time-efficient way to detect PPCD3-associated mutations and, importantly, genome sequencing enables the identification of full or partial heterozygous ZEB1 deletions that can evade detection by both Sanger and exome sequencing. These findings contribute to our understanding of PPCD3, for which currently, 49 pathogenic variants have been identified, all of which are predicted to be null alleles.

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.

Analysis of candidate genes ZEB1 and LOXHD1 in late-onset Fuchs' endothelial corneal dystrophy in an Indian cohort

BACKGROUND

Fuchs' endothelial corneal dystrophy (FECD) is a complex degenerative disease of the corneal endothelium with genetic predisposition. Pathogenic rare variants have been identified in SLC4A11, LOXHD1, ZEB1, and AGBL1. Association of single nucleotide polymorphisms (SNPs) and CTG trinucleotide repeat expansions in the intron of TCF4 gene to FECD has been studied across multiple ethnicities. Recently, genome-wide association studies have also identified KANK4, LAMC1, and ATP1B1 as novel loci for FECD. Here, we report the contribution of ZEB1 and LOXHD1 genes in our sporadic late-onset FECD cohort.

MATERIALS AND METHODS

In the experimental study, coding regions of ZEB1 and LOXHD1 were screened by Sanger DNA sequencing in 52 late-onset and 5 early-onset FECD cases of Indian origin, recruited at a tertiary eye care center. Further, bioinformatics analysis was done.

RESULTS

One reported missense mutation, c.2522A>C; p.(Q841P), and one variant of uncertain significance (VUS), c.619A>G; p.(S207G), were identified in the ZEB1 gene. One VUS, c.6413G>Ap.(R2138Q), was observed in LOXHD1. A 3D structural bioinformatic analysis of the missense variant in LOXHD1 predicted the variant to affect the structure-function relationship of the protein.

DISCUSSION

While mutations in ZEB1 contributed to 2% of the late-onset FECD cases, the exact role of the two VUS identified in ZEB1 and LOXHD1 in FECD pathogenesis needs to be studied.

CK2 blockade causes MPNST cell apoptosis and promotes degradation of β-catenin

Malignant peripheral nerve sheath tumors (MPNSTs) are soft tissue sarcomas that are a major cause of mortality of Neurofibromatosis type 1 (NF1) patients. MPNST patients have few therapeutic options available and only complete surgical resection can be curative. MPNST formation and survival are dependent on activated β-catenin signaling. The goal of this study was to determine if inhibition of the CK2 enzyme can be therapeutically exploited in MPNSTs, given CK2's role in mainta ining oncogenic phenotypes including stabilization of β-catenin. We found that CK2α is over-expressed in MPNSTs and is critical for maintaining cell survival, as the CK2 inhibitor, CX-4945 (Silmitasertib), and shRNA targeting CK2α each significantly reduce MPNST cell viability. These effects were preceded by loss of critical signaling pathways in MPNSTs, including destabilization of β-catenin and TCF8. CX-4945 administration in vivo slowed tumor growth and extends survival time. We conclude that CK2 inhibition is a promising approach to blocking β-catenin in MPNST cells, although combinatorial therapies may be required for maximal efficacy.

Transcriptomic Profiling of Posterior Polymorphous Corneal Dystrophy

Purpose

To investigate the molecular basis of posterior polymorphous corneal dystrophy (PPCD) by examining the PPCD transcriptome and the effect of decreased ZEB1 expression on corneal endothelial cell (CEnC) gene expression.

Methods

Next-generation RNA sequencing (RNA-seq) analyses of corneal endothelium from two PPCD-affected individuals (one with PPCD3 and one of unknown genetic cause) compared with two age-matched controls, and primary human CEnC (pHCEnC) transfected with siRNA-mediated ZEB1 knockdown. The expression of selected differentially expressed genes was validated by quantitative polymerase chain reaction (qPCR) and/or assessed by in situ hybridization in the corneal endothelium of four independent cases of PPCD (one with PPCD3 and three of unknown genetic cause).

Results

Expression of 16% and 46% of the 104 protein-coding genes specific to ex vivo corneal endothelium was lost in the endothelium of two individuals with PPCD. Thirty-two genes associated with ZEB1 and 3 genes (BMP4, CCND1, ZEB1) associated with OVOL2 were differentially expressed in the same direction in both individuals with PPCD. Immunohistochemistry staining and RNA-seq analyses demonstrated variable expression of type IV collagens in PPCD corneas. Decreasing ZEB1 expression in pHCEnC altered expression of 711 protein-coding genes, many of which are associated with canonical pathways regulating various cellular processes.

Conclusions

Identification of the altered transcriptome in PPCD and in a cell-based model of PPCD provided insight into the molecular alterations characterizing PPCD. Further study of the differentially expressed genes associated with ZEB1 and OVOL2 is expected to identify candidate genes for individuals with PPCD and without a ZEB1 or OVOL2 mutation.

Confirmation of the OVOL2 Promoter Mutation c.-307T>C in Posterior Polymorphous Corneal Dystrophy 1

Purpose

To identify the genetic basis of posterior polymorphous corneal dystrophy (PPCD) in families mapped to the PPCD1 locus and in affected individuals without ZEB1 coding region mutations.

Methods

The promoter, 5’ UTR, and coding regions of OVOL2 was screened in the PPCD family in which linkage analysis established the PPCD1 locus and in 26 PPCD probands who did not harbor a ZEB1 mutation. Copy number variation (CNV) analysis in the PPCD1 and PPCD3 intervals was performed on DNA samples from eight probands using aCGH. Luciferase reporter assays were performed in human corneal endothelial cells to determine the impact of the identified potentially pathogenic variants on OVOL2 promoter activity.

Results

OVOL2 mutation analysis in the first PPCD1-linked family demonstrated segregation of the c.-307T>C variant with the affected phenotype. In the other 26 probands screened, one heterozygous coding region variant and five promoter region heterozygous variants were identified, though none are likely pathogenic based on allele frequency. Array CGH in the PPCD1 and PPCD3 loci excluded the presence of CNV involving either OVOL2 or ZEB1, respectively. The c.-307T>C variant demonstrated increased promoter activity in corneal endothelial cells when compared to the wild-type sequence as has been demonstrated previously in another cell type.

Conclusions

Previously identified as the cause of PPCD1, the OVOL2 promoter variant c.-307T>C was herein identified in the original family that established the PPCD1 locus. However, the failure to identify presumed pathogenic coding or non-coding OVOL2 or ZEB1 variants, or CNV involving the PPCD1 and PPCD3 loci in 26 other PPCD probands suggests that other genetic loci may be involved in the pathogenesis of PPCD.

Biomechanical relationships between the corneal endothelium and Descemet's membrane

The posterior face of the cornea consists of the corneal endothelium, a monolayer of cuboidal cells that secrete and attach to Descemet's membrane, an exaggerated basement membrane. Dysfunction of the endothelium compromises the barrier and pump functions of this layer that maintain corneal deturgesence. A large number of corneal endothelial dystrophies feature irregularities in Descemet's membrane, suggesting that cells create and respond to the biophysical signals offered by their underlying matrix. This review provides an overview of the bidirectional relationship between Descemet's membrane and the corneal endothelium. Several experimental methods have characterized a richly topographic and compliant biophysical microenvironment presented by the posterior surface of Descemet's membrane, as well as the ultrastructure and composition of the membrane as it builds during a lifetime. We highlight the signaling pathways involved in the mechanotransduction of biophysical cues that influence cell behavior. We present the specific example of Fuchs' corneal endothelial dystrophy as a condition in which a dysregulated Descemet's membrane may influence the progression of disease. Finally, we discuss some disease models and regenerative strategies that may facilitate improved treatments for corneal dystrophies.

Investigating the Molecular Basis of PPCD3: Characterization of ZEB1 Regulation of COL4A3 Expression

PURPOSE

To investigate the role of the zinc finger e-box binding homeobox 1 (ZEB1) transcription factor in posterior polymorphous corneal dystrophy 3 by demonstrating its ability to regulate type IV collagen gene transcription via binding to putative E2 box motifs.

METHODS

Putative E2 box motifs were identified by in silico analysis within the promoter region of collagen, type IV, alpha3 (COL4A3) and collagen, type IV, alpha4 (COL4A4). To test the ability of ZEB1 to bind to each identified E2 box, electrophoretic mobility shift assays were performed by incubating ZEB1-enriched nuclear extracts with DIG-labeled probes containing one of each of the identified E2 box motifs. Dual-luciferase reporter assays were performed to test the effects of ZEB1 on the luciferase activity of COL4A3 and cadherin 1 (CDH1) promoter constructs, and to determine the effect of a ZEB1 truncating mutation on CDH1 promoter activity.

RESULTS

ZEB1 exhibited binding to six of the nine COL4A3 E2 box probes, whereas no binding was observed for either of the two COL4A4 E2 box probes. ZEB1 overexpression resulted in reduced activity of the COL4A3 promoter construct containing all identified E2 box motifs, whereas a truncating ZEB1 mutation led to the loss of ZEB1-dependent repression of the CDH1 promoter.

CONCLUSIONS

COL4A3 gene expression is negatively regulated by ZEB1 binding to E2 box motifs in the COL4A3 promoter region. Therefore, the altered expression of type IV collagens, particularly COL4A3, in the corneal endothelium in individuals with PPCD3 is likely due to reduced transcriptional repression in the setting of a single functional ZEB1 allele.

Autosomal-Dominant Corneal Endothelial Dystrophies CHED1 and PPCD1 Are Allelic Disorders Caused by Non-coding Mutations in the Promoter of OVOL2

Congenital hereditary endothelial dystrophy 1 (CHED1) and posterior polymorphous corneal dystrophy 1 (PPCD1) are autosomal-dominant corneal endothelial dystrophies that have been genetically mapped to overlapping loci on the short arm of chromosome 20. We combined genetic and genomic approaches to identify the cause of disease in extensive pedigrees comprising over 100 affected individuals. After exclusion of pathogenic coding, splice-site, and copy-number variations, a parallel approach using targeted and whole-genome sequencing facilitated the identification of pathogenic variants in a conserved region of the OVOL2 proximal promoter sequence in the index families (c.−339_361dup for CHED1 and c.−370T>C for PPCD1). Direct sequencing of the OVOL2 promoter in other unrelated affected individuals identified two additional mutations within the conserved proximal promoter sequence (c.−274T>G and c.−307T>C). OVOL2 encodes ovo-like zinc finger 2, a C2H2 zinc-finger transcription factor that regulates mesenchymal-to-epithelial transition and acts as a direct transcriptional repressor of the established PPCD-associated gene ZEB1. Interestingly, we did not detect OVOL2 expression in the normal corneal endothelium. Our in vitro data demonstrate that all four mutated OVOL2 promoters exhibited more transcriptional activity than the corresponding wild-type promoter, and we postulate that the mutations identified create cryptic cis-acting regulatory sequence binding sites that drive aberrant OVOL2 expression during endothelial cell development. Our data establish CHED1 and PPCD1 as allelic conditions and show that CHED1 represents the extreme of what can be considered a disease spectrum. They also implicate transcriptional dysregulation of OVOL2 as a common cause of dominantly inherited corneal endothelial dystrophies.

Association of ZEB1 and TCF4 rs613872 changes with late onset Fuchs endothelial corneal dystrophy in patients from northern India

PURPOSE

Fuchs endothelial corneal dystrophy (FECD) results in loss of vision associated with progressive corneal edema and loss of corneal transparency. The aim of the study was to evaluate changes in ZEB1, COL8A2, SLC4A11, and TCF4 rs613872 and correlate them with clinical findings.

METHODS

Eighty-two patients with clinically diagnosed FECD and 143 controls were recruited during the period 2007-2012. Clinical details, pedigree information up to three generations, and 5 ml of blood samples were collected. Histopathological and transmission electron microscopy studies were performed on host corneal buttons from patients who underwent keratoplasty. Genomic DNA from blood was processed for PCR amplification followed by direct sequencing to screen genetic changes in the candidate genes. The pathogenic nature of the genetic variants was assessed using Sorting Intolerant From Tolerant (SIFT) and MutationTaster.

RESULTS

The mean age at the onset of symptoms was 59.14±1.41years, the male to female ratio was 1:1.5, and the mean specular count (endothelial cell density) was 1629±93.62 cells/mm(2) with a mean central corneal thickness (CCT) of 617.30±15.73 µm. ZEB1 showed a novel variant IVS2+276 C/T in 14% of the cases, a novel nonsense p.Leu947stop mutation in one patient, two novel missense mutations (p.Glu733Lys, p.Ala818Val) in one patient each, and one novel synonymous variation (p.Ser234Ser) in two patients. Reported mutation p.Gln840Pro and five polymorphisms were also identified. The TCF4 single nucleotide polymorphism (SNP) rs613872 was significantly higher in patients with FECD.

CONCLUSIONS

This is the first report of genetic variations in ZEB1 and TCF4 SNP rs613872 in patients with FECD from northern India that suggests a possible role in disease pathogenesis and the regulation of endothelial cell density.