Zeb1 mutant mice as a model of posterior corneal dystrophy

Atherosclerotic plaque development in mice is enhanced by myeloid ZEB1 downregulation

Accumulation of lipid-laden macrophages within the arterial neointima is a critical step in atherosclerotic plaque formation. Here, we show that reduced levels of the cellular plasticity factor ZEB1 in macrophages increase atherosclerotic plaque formation and the chance of cardiovascular events. Compared to control counterparts (Zeb1WT/ApoeKO), male mice with Zeb1 ablation in their myeloid cells (Zeb1∆M/ApoeKO) have larger atherosclerotic plaques and higher lipid accumulation in their macrophages due to delayed lipid traffic and deficient cholesterol efflux. Zeb1∆M/ApoeKO mice display more pronounced systemic metabolic alterations than Zeb1WT/ApoeKO mice, with higher serum levels of low-density lipoproteins and inflammatory cytokines and larger ectopic fat deposits. Higher lipid accumulation in Zeb1∆M macrophages is reverted by the exogenous expression of Zeb1 through macrophage-targeted nanoparticles. In vivo administration of these nanoparticles reduces atherosclerotic plaque formation in Zeb1∆M/ApoeKO mice. Finally, low ZEB1 expression in human endarterectomies is associated with plaque rupture and cardiovascular events. These results set ZEB1 in macrophages as a potential target in the treatment of atherosclerosis.

Animal Models in Eye Research: Focus on Corneal Pathologies

The eye is a complex sensory organ that enables visual perception of the world. The dysfunction of any of these tissues can impair vision. Conduction studies on laboratory animals are essential to ensure the safety of therapeutic products directly applied or injected into the eye to treat ocular diseases before eventually proceeding to clinical trials. Among these tissues, the cornea has unique homeostatic and regenerative mechanisms for maintaining transparency and refraction of external light, which are essential for vision. However, being the outermost tissue of the eye and directly exposed to the external environment, the cornea is particularly susceptible to injury and diseases. This review highlights the evidence for selecting appropriate animals to better understand and treat corneal diseases, which rank as the fifth leading cause of blindness worldwide. The development of reliable and human-relevant animal models is, therefore, a valuable research tool for understanding and translating fundamental mechanistic findings, as well as for assessing therapeutic potential in humans. First, this review emphasizes the unique characteristics of animal models used in ocular research. Subsequently, it discusses current animal models associated with human corneal pathologies, their utility in understanding ocular disease mechanisms, and their role as translational models for patients.

Zeb1 facilitates corneal epithelial wound healing by maintaining corneal epithelial cell viability and mobility

The cornea is the outmost ocular tissue and plays an important role in protecting the eye from environmental insults. Corneal epithelial wounding provokes pain and fear and contributes to the most ocular trauma emergency assessments worldwide. ZEB1 is an essential transcription factor in development; but its roles in adult tissues are not clear. We identify Zeb1 is an intrinsic factor that facilitates corneal epithelial wound healing. In this study, we demonstrate that monoallelic deletion of Zeb1 significantly expedites corneal cell death and inhibits corneal epithelial EMT-related cell migration upon an epithelial debridement. We provide evidence that Zeb1-regulation of corneal epithelial wound healing is through the repression of genes required for Tnfa-induced epithelial cell death and the induction of genes beneficial for epithelial cell migration. We suggest utilizing TNF-α antagonists would reduce TNF/TNFR1-induced cell death in the corneal epithelium and inflammation in the corneal stroma to help corneal wound healing.

Update on the genetics of corneal endothelial dystrophies

Corneal endothelial dystrophies are a heterogeneous group of diseases with different modes of inheritance and genetic basis for each dystrophy. The genes associated with these diseases encode transcription factors, structural components of the stroma and Descemet membrane, cell transport proteins, and others. Congenital hereditary endothelial dystrophy (CHED) is associated with mutations in two genes, OVOL2 and SLC4A11, for dominant and recessive forms of CHED, respectively. Mutations in three genes are known to cause posterior polymorphous corneal dystrophy (PPCD). They are OVOL2 (PPCD1), ZEB1 (PPCD3), and GRHL1 (PPCD4). The PPCD2 locus involving the collagen gene COL8A2 on chromosome 1 is disputed due to insufficient evidence. Mutations in the COL8A2 gene are associated with early-onset Fuchs’ endothelial corneal dystrophy (FECD). Several genes have been associated with the more common, late-onset FECD. Alterations in each of these genes occur in a fraction of patients, and the most prevalent genetic alteration in FECD patients across the world is a triplet repeat expansion in the TCF4 gene. Knowledge of the genetics of corneal endothelial dystrophies has considerably advanced within the last decade and has contributed to better diagnosis of these dystrophies as well as opened up the possibility of novel therapeutic approaches based on the molecular mechanisms involved. The functions of genes identified to date provide insights into the pathogenic mechanisms involved in each disorder.

Zeb1 Regulation of Wound Healing-Induced Inflammation in Alkali-Damaged Corneas

The cornea is an avascular tissue for vision clarity. Alkali burn could cause severe traumatic damage on the cornea with inflammation and neovascularization (NV), leading to vision reduction and blindness. Mechanisms underlying corneal inflammation and NV are not as clear. We previously reported that Zeb1 is an important factor in corneal NV, and we sought to clarify whether it is also involved in regulation of corneal inflammation. We analyzed the alkali burn-induced corneal inflammation and wound healing in both Zeb1^+/+ and Zeb1^−/+ littermates through a multidisciplinary approach. We provide evidence that Zeb1 forms a positive regulatory loop with Tgfb to regulate early corneal inflammation by maintenance of immune cell viability and mobility and later wound healing by activation of both Nf-κb and Tgfb-related Stat3 signaling pathways. We believe that ZEB1 is a potential therapeutic target, and inactivation of ZEB1 could be a strategy to treat severe corneal inflammation condition.

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Traumatic wound induces inflammation in the cornea, resulting in vision reduction

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Zeb1 is a key factor to retain immune cell viability, mobility, and cytokine expression

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Zeb1 regulates cytokine gene expression through both Nf-κb and Stat3 pathways

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Inactivation of ZEB1 could be a strategy to treat severe corneal inflammation condition

Zeb1 induces immune checkpoints to form an immunosuppressive envelope around invading cancer cells

The PDL1-PD1 immune checkpoint inhibits T cell activation, and its blockade is effective in a subset of patients. Studies are investigating how checkpoints are hijacked by cancer cells and why most patients remain resistant to immunotherapy. Epithelial mesenchymal transition (EMT), which drives tumor cell invasion via the Zeb1 transcription factor, is linked to immunotherapy resistance. In addition, M2-polarized tumor-associated macrophages (TAMs), which inhibit T cell migration and activation, may also cause immunotherapy resistance. How EMT in invading cancer cells is linked to therapy resistance and events driving TAM M2 polarization are therefore important questions. We show that Zeb1 links these two resistance pathways because it is required for PDL1 expression on invading lung cancer cells, and it also induces CD47 on these invading cells, which drives M2 polarization of adjacent TAMs. Resulting reprogramming of the microenvironment around invading cells shields them from the hostile inflammatory environment surrounding tumors.

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.

Genetic background modifies vulnerability to glaucoma-related phenotypes in Lmx1b mutant mice

Variants in the LIM homeobox transcription factor 1-beta (LMX1B) gene predispose individuals to elevated intraocular pressure (IOP), a key risk factor for glaucoma. However, the effect of LMX1B mutations varies widely between individuals. To better understand the mechanisms underlying LMX1B-related phenotypes and individual differences, we backcrossed the Lmx1b^V265D (also known as Lmx1b^Icst ) allele onto the C57BL/6J (B6), 129/Sj (129), C3A/BLiA-Pde6b⁺ /J (C3H) and DBA/2J-Gpnmb⁺ (D2-G) mouse strain backgrounds. Strain background had a significant effect on the onset and severity of ocular phenotypes in Lmx1b^V265D/+ mutant mice. Mice of the B6 background were the most susceptible to developing abnormal IOP distribution, severe anterior segment developmental anomalies (including malformed eccentric pupils, iridocorneal strands and corneal abnormalities) and glaucomatous nerve damage. By contrast, Lmx1b^V265D mice of the 129 background were the most resistant to developing anterior segment abnormalities, had less severe IOP elevation than B6 mutants at young ages and showed no detectable nerve damage. To identify genetic modifiers of susceptibility to Lmx1b^V265D -induced glaucoma-associated phenotypes, we performed a mapping cross between mice of the B6 (susceptible) and 129 (resistant) backgrounds. We identified a modifier locus on Chromosome 18, with the 129 allele(s) substantially lessening severity of ocular phenotypes, as confirmed by congenic analysis. By demonstrating a clear effect of genetic background in modulating Lmx1b-induced phenotypes, providing a panel of strains with different phenotypic severities and identifying a modifier locus, this study lays a foundation for better understanding the roles of LMX1B in glaucoma with the goal of developing new treatments.

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.

Corneal Dystrophy in Dutch Belted Rabbits as a Possible Model of Thiel-Behnke Subtype of Epithelial-Stromal TGFβ-Induced Corneal Dystrophy

The International Committee for Classification of Corneal Dystrophies (IC3D) categorized corneal dystrophies in humans using anatomic, genotypic, and clinicopathologic phenotypic features. Relative to the IC3D classification, a review of the veterinary literature confirmed that corneal dystrophy is imprecisely applied to any corneal opacity and to multiple poorly characterized histologic abnormalities of the cornea in animals. True corneal dystrophy occurs in mice with targeted mutations and spontaneously in pet dogs and cats and in Dutch belted (DB) rabbits, but these instances lack complete phenotyping or genotyping. Corneal dystrophy in DB rabbits can be an important confounding finding in ocular toxicology studies but has only been described once. Therefore, the ophthalmology and pathology of corneal dystrophy in 13 DB rabbits were characterized to determine whether the findings were consistent with or a possible model of any corneal dystrophy subtypes in humans. Slit lamp and optical coherence tomography (OCT) imaging were used to characterize corneal dystrophy over 4 months in young DB rabbits. The hyperechoic OCT changes correlated with light microscopic findings in the anterior stroma, consisting of highly disordered collagen fibers and enlarged keratocytes. Histochemical stains did not reveal abnormal deposits. Small clusters of 8 to 16 nm diameter curly fibers identified by transmission electron microscopy were consistent with Thiel-Behnke (TBCD) subtype of epithelial-stromal transforming growth factor β-induced dystrophies. Sporadic corneal dystrophy in DB rabbits appears to be a potential animal model of TBCD, but genotypic characterization will be required to confirm this categorization.

Zinc finger E-box binding homeobox 1 and atherosclerosis: New insights and therapeutic potential

Zinc finger E-box binding homeobox 1 (ZEB1), an important transcription factor belonging to the ZEB family, plays a crucial role in regulating gene expression required for both normal physiological and pathological processes. Accumulating evidence has shown that ZEB1 participates in the initiation and progression of atherosclerotic cardiovascular disease. Recent studies suggest that ZEB1 protects against atherosclerosis by regulation of endothelial cell angiogenesis, endothelial dysfunction, monocyte-endothelial cell interaction, macrophage lipid accumulation, macrophage polarization, monocyte-vascular smooth muscle cell (VSMC) interaction, VSMC proliferation and migration, and T cell proliferation. In this review, we summarize the recent progress of ZEB1 in the pathogenesis of atherosclerosis and provide insights into the prevention and treatment of atherosclerotic cardiovascular disease.

Investigating the Pathogenicity of VSX1 Missense Mutations and Their Association With Corneal Disease

Purpose

Despite numerous studies associating Visual System Homeobox 1 (VSX1), with posterior polymorphous corneal dystrophy and keratoconus, its role in these diseases is unclear. Here we examine the pathogenicity of VSX1 missense mutations in vitro and in a mouse genetic model.

Methods

Vsx1 transcriptional repressor activity, protein stability, and subcellular localization activity, was examined using luciferase reporter-based assays, western blotting and immunolabeling, respectively, in transfected human embryonic kidney 293T cells. A genetic model for VSX1 p.P247R was generated to investigate pathogenicity of the mutation, in vivo. A wholemount confocal imaging approach on unfixed intact eyes was developed to examine corneal morphology, curvature, and thickness. Immunolabeling and electroretinography was used to examine retinal phenotype.

Results

A mutation corresponding to human VSX1 p.P247R led to enhanced transcriptional repressor activity, in vitro. A mouse model for VSX1 p.P247R did not have any observable corneal defect, but did exhibit an abnormal electroretinogram response characterized by a more prominent ON as opposed to OFF panretinal responsiveness. In vitro analysis of additional VSX1 missense mutations showed that they either enhanced repressor activity or did not alter activity.

Conclusions

Our results indicate that although VSX1 sequence variants can alter transcriptional activity, in the context of a mouse genetic model, at least one of these changes does not lead to corneal abnormalities. While we cannot exclude a role for VSX1 as a risk factor for corneal disease, on its own, it does not appear to play a major causative role.

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.

Mitotic polarization of transcription factors during asymmetric division establishes fate of forming cancer cells

A model of K-Ras-initiated lung cancer was used to follow the transition of precancerous adenoma to adenocarcinoma. In hypoxic, Tgf-β1-rich interiors of adenomas, we show that adenoma cells divide asymmetrically to produce cancer-generating cells highlighted by epithelial mesenchymal transition and a CD44/Zeb1 loop. In these cells, Zeb1 represses the Smad inhibitor Zeb2/Sip1, causing Pten loss and launching Tgf-β1 signaling that drives nuclear translocation of Yap1. Surprisingly, the nuclear polarization of transcription factors during mitosis establishes parent and daughter fates prior to cytokinesis in sequential asymmetric divisions that generate cancer cells from precancerous lesions. Mutation or knockdown of Zeb1 in the lung blocked the production of CD44^hi, Zeb1^hi cancer-generating cells from adenoma cells. A CD44/Zeb1 loop then initiates two-step transition of precancerous cells to cancer cells via a stable intermediate population of cancer-generating cells. We show these initial cancer-generating cells are independent of cancer stem cells generated in tumors by p53-regulated reprogramming of existing cancer cells.

Transition from premalignant lesion to cancer cell highlights tumor initiation. Here, the authors use a model of K-Ras-initiated lung cancer to document two successive asymmetric divisions, each driven by mitotic polarization of key transcription factors, which lead to generation of initial cancer cells.

Elucidating the molecular basis of PPCD: Effects of decreased ZEB1 expression on corneal endothelial cell function

PURPOSE

To investigate the functional role that the zinc e-box binding homeobox 1 (ZEB1) gene, which underlies the genetic basis of posterior polymorphous corneal dystrophy 3 (PPCD3), plays in corneal endothelial cell proliferation, apoptosis, migration, and barrier function.

METHODS

A human corneal endothelial cell line (HCEnC-21T) was transfected with siRNA targeting ZEB1 mRNA. Cell proliferation, apoptosis, migration, and barrier assays were performed: Cell proliferation was assessed with cell counting using a hemocytometer; cell apoptosis, induced by either ultraviolet C (UVC) radiation or doxorubicin treatment, was quantified by measuring cleaved caspase 3 (cCASP3) protein levels; and cell migration and barrier function were monitored with electric cell-substrate impedance sensing (ECIS).

RESULTS

ZEB1 knockdown in HCEnC-21T cells transfected with siRNA targeting ZEB1 did not result in a significant difference in cell proliferation when compared with control. Although knockdown of ZEB1 in HCEnC-21T cells sensitized the cells to UV-induced apoptosis, ZEB1 knockdown did not alter the cells' susceptibility to doxorubicin-induced apoptosis, as measured with cCASP3 protein levels, compared with controls. Similarly, no difference was observed in cell migration following ZEB1 knockdown. However, cell barrier function increased significantly following ZEB1 knockdown.

CONCLUSIONS

The corneal endothelium in PPCD3 is characterized by morphologic, anatomic, and molecular features that are more consistent with an epithelial-like rather than an endothelial-like phenotype. Although these characteristics have been well documented, we demonstrate for the first time that susceptibility to UV-induced apoptosis and cell barrier function are significantly altered in the setting of reduced ZEB1. The significance of an altered cellular response to apoptotic stimuli and increased cell barrier function in the pathobiology of PPCD remains to be fully elucidated.

microRNA-204 modulates chemosensitivity and apoptosis of prostate cancer cells by targeting zinc-finger E-box-binding homeobox 1 (ZEB1)

Epigenetic gene inactivation by microRNAs (miRNAs) is crucial in malignant transformation, prevention of apoptosis, development of drug resistance, and metastasis. miR-204 dysregulation has been reported in prostate cancer (PC). It is considered to exert tumor suppressor functions and is associated with the development of chemoresistance. However, the detailed mechanisms underlying the role of miR-204 in PC, particularly in chemoresistance, remain to be fully elucidated. In this study, analysis using miRNA microarray showed that miR-204 is downregulated in chemoresistant PC tissues with respect to its expression in chemosensitive PC tissues and benign prostatic hyperplasia tissues. Microarray results were validated via qPCR. The changes in miR-204 expression levels were also observed in vitro. Forced overexpression of miR-204 evidently attenuated docetaxel chemoresistance and promoted apoptosis in PC-3-R cells, whereas miR-204 knockdown effectively reduced docetaxel-induced cell death and inhibited cell apoptosis. Mechanistically, miR-204 directly targets the 3'-untranslated region of zinc-finger E-box-binding homeobox 1 (ZEB1) and inhibits its protein expression via translational repression. Furthermore, suppression of ZEB1 could effectively improve miR-204 deficiency-triggered chemoresistance in PC cells. Our results collectively indicate that miR-204 expression is downregulated in chemoresistant PC tissues and cells and that miR-204/ZEB1 could potentially be used as adjunct therapy for patients with advanced/chemoresistant PC.

Agenesis of the corpus callosum, developmental delay, autism spectrum disorder, facial dysmorphism, and posterior polymorphous corneal dystrophy associated with ZEB1 gene deletion

We report on a girl diagnosed prenatally with agenesis of the corpus callosum (ACC) on fetal ultrasound and MRI. On postnatal follow-up she was noted to have developmental delay, facial dysmorphism, autism spectrum disorder, and posterior polymorphous corneal dystrophy (PPD). Array-comparative genomic hybridization analysis (Array-CGH) showed a 2.05 Mb de novo interstitial deletion at 10p11.23p11.22. The deleted region overlaps 1 OMIM Morbid Map gene, ZEB1 (the zinc finger E-box binding homeobox transcription factor 1), previously associated with posterior polymorphous corneal dystrophy type 3 (PPCD3). To our best knowledge this is the first reported case with a deletion of the ZEB1 gene in an individual with ACC and PPD, showing that the haploinsufficiency of the ZEB1 is likely the cause of our patient's phenotype.

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.

ZEB1 Regulates Multiple Oncogenic Components Involved in Uveal Melanoma Progression

Human uveal melanoma (UM) is a major ocular malignant tumor with high risk of metastasis and requires multiple oncogenic factors for progression. ZEB1 is a zinc finger E-box binding transcription factor known for participating epithelial-mesenchymal transition (EMT), a critical cellular event for metastasis of malignant tumors of epithelium origin. ZEB1 is also expressed in UM and high expression of ZEB1 correlates with UM advancement, but has little effect on cell morphology. We show that spindle UM cells can become epithelioid but not vice versa; and ZEB1 exerts its tumorigenic effects by promoting cell dedifferentiation, proliferation, invasiveness, and dissemination. We provide evidence that ZEB1 binds not only to repress critical genes involving in pigment synthesis, mitosis, adherent junctions, but also to transactivate genes involving in matrix degradation and cellular locomotion to propel UM progression towards metastasis. We conclude that ZEB1 is a major oncogenic factor required for UM progression and could be a potential therapeutic target for treating UM in the clinic.

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.

The Genetics and Pathophysiology of IC3D Category 1 Corneal Dystrophies: A Review

Corneal dystrophies are a group of inherited disorders affecting the cornea, many of which lead to visual impairment. The International Committee for Classification of Corneal Dystrophies has established criteria to clarify the status of the various corneal dystrophies, which include the knowledge of the underlying genetics. In this review, we discuss the International Committee for Classification of Corneal Dystrophies category 1 (second edition) corneal dystrophies, for which a clear genetic link has been established. We highlight the various mechanisms underlying corneal dystrophy pathology, including structural disorganization, instability or maladhesion, aberrant protein stability and deposition, abnormal cellular proliferation or apoptosis, and dysfunction of normal enzymatic processes. Understanding these genetic mechanisms is essential for designing targets for therapeutic intervention, especially in the age of gene therapy and gene editing.

Association of a Chromosomal Rearrangement Event with Mouse Posterior Polymorphous Corneal Dystrophy and Alterations in Csrp2bp, Dzank1, and Ovol2 Gene Expression

We have previously described a mouse model of human posterior polymorphous corneal dystrophy (PPCD) and localized the causative mutation to a 6.2 Mbp region of chromosome 2, termed Ppcd1. We now show that the gene rearrangement linked to mouse Ppcd1 is a 3.9 Mbp chromosomal inversion flanked by 81 Kbp and 542 bp deletions. This recombination event leads to deletion of Csrp2bp Exons 8 through 11, Dzank1 Exons 20 and 21, and the pseudogene Znf133. In addition, we identified translocation of novel downstream sequences to positions adjacent to Csrp2bp Exon 7 and Dzank1 Exon 20. Twelve novel fusion transcripts involving Csrp2bp or Dzank1 linked to downstream sequences have been identified. Eight are expressed at detectable levels in PPCD1 but not wildtype eyes. Upregulation of two Csrp2bp fusion transcripts, as well as upregulation of the adjacent gene, Ovol2, was observed. Absence of the PPCD1 phenotype in animals haploinsufficient for Csrp2bp or both Csrp2bp and Dzank1 rules out haploinsufficiency of these genes as a cause of mouse PPCD1. Complementation experiments confirm that PPCD1 embryonic lethality is due to disruption of Csrp2bp expression. The ocular expression pattern of Csrp2bp is consistent with a role for this protein in corneal development and pathogenesis of PPCD1.

ZEB1: at the crossroads of epithelial-mesenchymal transition, metastasis and therapy resistance

Zinc finger E-box binding homeobox 1 (ZEB1) is a transcription factor that promotes tumor invasion and metastasis by inducing epithelial-mesenchymal transition (EMT) in carcinoma cells. EMT not only plays an important role in embryonic development and malignant progression, but is also implicated in cancer therapy resistance. It has been hypothesized that carcinoma cells that have undergone EMT acquire cancer stem cell properties including self-renewal, chemoresistance and radioresistance. However, our recent data indicate that ZEB1 regulates radioresistance in breast cancer cells through an EMT-independent mechanism. In this Perspective, we review different mechanisms by which ZEB1 regulates tumor progression and treatment resistance. Based on studies by us and others, we propose that it is specific EMT inducers like ZEB1, but not the epithelial or mesenchymal state itself, that dictate cancer stem cell properties.

Heterozygous deletions at the ZEB1 locus verify haploinsufficiency as the mechanism of disease for posterior polymorphous corneal dystrophy type 3

A substantial proportion of patients with posterior polymorphous corneal dystrophy (PPCD) lack a molecular diagnosis. We evaluated 14 unrelated probands who had a clinical diagnosis of PPCD who were previously determined to be negative for mutations in ZEB1 by direct sequencing. A combination of techniques was used including whole-exome sequencing (WES), single-nucleotide polymorphism (SNP) array copy number variation (CNV) analysis, quantitative real-time PCR, and long-range PCR. Segregation of potentially pathogenic changes with disease was confirmed, where possible, in family members. A putative run of homozygosity on chromosome 10 was identified by WES in a three-generation PPCD family, suggestive of a heterozygous deletion. SNP array genotyping followed by long-range PCR and direct sequencing to define the breakpoints confirmed the presence of a large deletion that encompassed multiple genes, including ZEB1. Identification of a heterozygous deletion spanning ZEB1 prompted us to further investigate potential CNVs at this locus in the remaining probands, leading to detection of two additional heterozygous ZEB1 gene deletions. This study demonstrates that ZEB1 mutations account for a larger proportion of PPCD than previously estimated, and supports the hypothesis that haploinsufficiency of ZEB1 is the underlying molecular mechanism of disease for PPCD3.

miR-128 modulates chemosensitivity and invasion of prostate cancer cells through targeting ZEB1

OBJECTIVE

Recent reports strongly suggest the profound role of miRNAs in cancer therapeutic response and progression, including invasion and metastasis. The sensitivity to therapy and invasion is the major obstacle for successful treatment in prostate cancer. We aimed to investigate the regulative effect of miR-128/zinc-finger E-box-binding homeobox 1 axis on prostate cancer cell chemosensitivity and invasion.

METHODS

The miR-128 expression pattern of prostate cancer cell lines and tissues was detected by real-time reverse transcriptase-polymerase chain reaction, while the mRNA and protein expression levels of zinc-finger E-box-binding homeobox 1 were measured by real-time reverse transcriptase-polymerase chain reaction and western blot assay, respectively. Dual-luciferase reporter gene assay was used to find the direct target of miR-128. Furthermore, prostate cancer cells were treated with miR-128 mimic or zinc-finger E-box-binding homeobox 1-siRNA, and then the cells' chemosensitivity and invasion were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and transwell assay, respectively.

RESULTS

We found miR-128 expression obviously decreased in prostate cancer tissues compared with paired normal tissues. Restored miR-128 expression sensitized prostate cancer cells to cisplatin and inhibited the invasion. Furthermore, there was an inverse expression pattern between miR-128 and zinc-finger E-box-binding homeobox 1 in prostate cancer cells and tissues, and zinc-finger E-box-binding homeobox 1 was identified as a direct target of miR-128 in prostate cancer. Knockdown of zinc-finger E-box-binding homeobox 1 expression efficiently sensitized prostate cancer cells to cisplatin and inhibited the invasion. However, ectopic zinc-finger E-box-binding homeobox 1 expression impaired the effects of miR-128 on chemosensitivity and invasion in prostate cancer cells.

CONCLUSIONS

miR-128 functions as a potential cancer suppressor in prostate cancer progression and rational therapeutic strategies for prostate cancer would be developed based on miR-128/zinc-finger E-box-binding homeobox 1 axis.

Different thresholds of ZEB1 are required for Ras-mediated tumour initiation and metastasis

Ras pathway mutation is frequent in carcinomas where it induces expression of the transcriptional repressor ZEB1. Although ZEB1 is classically linked to epithelial-mesenchymal transition and tumour metastasis, it has an emerging second role in generation of cancer-initiating cells. Here we show that Ras induction of ZEB1 is required for tumour initiation in a lung cancer model, and we link this function to repression Pten, whose loss is critical for emergence of cancer-initiating cells. These two roles for ZEB1 in tumour progression can be distinguished by their requirement for different levels of ZEB1. A lower threshold of ZEB1 is sufficient for cancer initiation, whereas further induction is necessary for tumour metastasis.

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

PURPOSE

To assess the impact of zinc finger E-box binding homeobox 1 (ZEB1) gene mutations associated with posterior polymorphous corneal dystrophy 3 (PPCD3) and Fuchs' endothelial corneal dystrophy (FECD).

METHODS

Thirteen of the 27 previously reported ZEB1 truncating mutations associated with PPCD3 and the six previously reported ZEB1 missense mutations associated with FECD were generated and transiently transfected into a corneal endothelial cell line. Protein abundance was determined by immunoblotting, while intracellular localization was determined by fluorescence confocal microscopy.

RESULTS

Three of the 13 ZEB1 truncated mutants, and none of the missense mutants, showed significant decrease in mutant ZEB1 protein levels. Predominant nuclear localization was observed for truncated ZEB1 mutant proteins with a predicted molecular weight of less than 92 kilodaltons. The two largest mutant proteins that lacked a putative nuclear localization signal (NLS), p.(Ser638Cysfs*5) and p.(Gln884Argfs*37), primarily localized to the cytoplasm, while the NLS-containing mutant proteins, p.(Glu997Alafs*7) and p.(Glu1039Glyfs*6), primarily localized to the nucleus. All the missense ZEB1 mutant proteins were exclusively present in the nucleus.

CONCLUSIONS

ZEB1 truncating mutations result in a significant decrease and/or impaired nuclear localization of the encoded protein, indicating that ZEB1 haploinsufficiency in PPCD3 may result from decreased protein production and/or impaired cellular localization. Conversely, as the reported ZEB1 missense mutations do not significantly impact protein abundance or nuclear localization, the effect of these mutations on ZEB1 function and their relationship to FECD, if any, remain to be elucidated.

Classification of posterior polymorphous corneal dystrophy as a corneal ectatic disorder following confirmation of associated significant corneal steepening

IMPORTANCE

The identification of steep corneal curvatures in a significant percentage of patients with posterior polymorphous corneal dystrophy (PPCD) confirms this previously reported association and suggests a role for the ZEB1 protein in keratocyte function.

OBJECTIVE

To determine whether PPCD is characterized by significant corneal steepening.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional study at university-based and private ophthalmology practices of 38 individuals (27 affected and 11 unaffected) from 23 families with PPCD.

EXPOSURE

Slitlamp examination and corneal topographic imaging were performed for individuals with PPCD and unaffected family members. Saliva or blood samples were obtained from each individual for DNA isolation and ZEB1 sequencing. Corneal ZEB1 expression was measured using immunohistochemistry.

MAIN OUTCOMES AND MEASURES

Percentage of individuals affected with PPCD and controls with an average keratometric value greater than 48.0 diopters (D) in each eye; the mean keratometric value averaged for both eyes of individuals with PPCD and controls; and the correlation of ZEB1 mutation with keratometric value.

RESULTS

ZEB1 coding region mutations were identified in 7 of the 27 affected individuals. Ten of the 38 individuals (26.3%) had average keratometric values greater than 48.0 D OU: 10 of 27 individuals with PPCD (37.0%; 6 of 7 individuals with ZEB1 mutations [85.7%] and 4 of 20 individuals without ZEB1 mutations [20.0%]) and 0 of 11 unaffected individuals (P = .04 for unaffected vs affected individuals; P = .004 for individuals with PPCD with vs without ZEB1 mutation). The mean keratometric value of each eye of affected individuals (48.2 D) was significantly greater than that of each eye of unaffected family members (44.1 D) (P = .03). Affected individuals with ZEB1 mutations demonstrated a mean keratometric value of 53.3 D, which was significantly greater than that of affected individuals without ZEB1 mutations (46.5 D; P = .004). Fluorescence immunohistochemistry demonstrated ZEB1 expression in keratocyte nuclei.

CONCLUSIONS AND RELEVANCE

Abnormally steep corneal curvatures are identified in 37% of all individuals with PPCD and 86% of affected individuals with PPCD secondary to ZEB1 mutations. ZEB1 is present in keratocyte nuclei, suggesting a role for ZEB1 in keratocyte function. Therefore, ZEB1 may play a role in both corneal stromal and endothelial development and function, and PPCD should be considered both an endothelial dystrophy and an ectatic disorder.

Preliminary identification of differentially expressed tear proteins in keratoconus

PURPOSE

To examine the proteins differentially expressed in the tear film of people with keratoconus and normal subjects.

METHODS

Unstimulated tears from people with keratoconus (KC) and controls (C) were collected using a capillary tube. Tear proteins from people with KC and controls were partitioned using a novel in-solution electrophoresis, Microflow 10 (ProteomeSep), and analyzed using linear ion trap quadrupole fourier transform mass spectrometry. Spectral counting was used to quantify the individual tear proteins.

RESULTS

Elevated levels of cathepsin B (threefold) were evident in the tears of people with KC. Polymeric immunoglobulin receptor (ninefold), fibrinogen alpha chain (eightfold), cystatin S (twofold), and cystatin SN (twofold) were reduced in tears from people with KC. Keratin type-1 cytoskeletal-14 and keratin type-2 cytoskeletal-5 were present only in the tears of people with KC.

CONCLUSIONS

The protein changes in tears, that is, the decrease in protease inhibitors and increase in proteases, found in the present and other previously published studies reflect the pathological events involved in KC corneas. Further investigations into tear proteins may help elucidate the underlying molecular mechanisms of KC, which could result in better treatment options.

Transcriptome-guided functional analyses reveal novel biological properties and regulatory hierarchy of human embryonic stem cell-derived ventricular cardiomyocytes crucial for maturation

Human (h) embryonic stem cells (ESC) represent an unlimited source of cardiomyocytes (CMs); however, these differentiated cells are immature. Thus far, gene profiling studies have been performed with non-purified or non-chamber specific CMs. Here we took a combinatorial approach of using systems biology to guide functional discoveries of novel biological properties of purified hESC-derived ventricular (V) CMs. We profiled the transcriptomes of hESCs, hESC-, fetal (hF) and adult (hA) VCMs, and showed that hESC-VCMs displayed a unique transcriptomic signature. Not only did a detailed comparison between hESC-VCMs and hF-VCMs confirm known expression changes in metabolic and contractile genes, it further revealed novel differences in genes associated with reactive oxygen species (ROS) metabolism, migration and cell cycle, as well as potassium and calcium ion transport. Following these guides, we functionally confirmed that hESC-VCMs expressed I_KATP with immature properties, and were accordingly vulnerable to hypoxia/reoxygenation-induced apoptosis. For mechanistic insights, our coexpression and promoter analyses uncovered a novel transcriptional hierarchy involving select transcription factors (GATA4, HAND1, NKX2.5, PPARGC1A and TCF8), and genes involved in contraction, calcium homeostasis and metabolism. These data highlight novel expression and functional differences between hESC-VCMs and their fetal counterparts, and offer insights into the underlying cell developmental state. These findings may lead to mechanism-based methods for in vitro driven maturation.

The Ets transcription factor EHF as a regulator of cornea epithelial cell identity

The cornea is the clear, outermost portion of the eye composed of three layers: an epithelium that provides a protective barrier while allowing transmission of light into the eye, a collagen-rich stroma, and an endothelium monolayer. How cornea development and aging is controlled is poorly understood. Here we characterize the mouse cornea transcriptome from early embryogenesis through aging and compare it with transcriptomes of other epithelial tissues, identifying cornea-enriched genes, pathways, and transcriptional regulators. Additionally, we profiled cornea epithelium and stroma, defining genes enriched in these layers. Over 10,000 genes are differentially regulated in the mouse cornea across the time course, showing dynamic expression during development and modest expression changes in fewer genes during aging. A striking transition time point for gene expression between postnatal days 14 and 28 corresponds with completion of cornea development at the transcriptional level. Clustering classifies co-expressed, and potentially co-regulated, genes into biologically informative categories, including groups that exhibit epithelial or stromal enriched expression. Based on these findings, and through loss of function studies and ChIP-seq, we show that the Ets transcription factor EHF promotes cornea epithelial fate through complementary gene activating and repressing activities. Furthermore, we identify potential interactions between EHF, KLF4, and KLF5 in promoting cornea epithelial differentiation. These data provide insights into the mechanisms underlying epithelial development and aging, identifying EHF as a regulator of cornea epithelial identity and pointing to interactions between Ets and KLF factors in promoting epithelial fate. Furthermore, this comprehensive gene expression data set for the cornea is a powerful tool for discovery of novel cornea regulators and pathways.

Analysis of the role of ZEB1 in the pathogenesis of posterior polymorphous corneal dystrophy

PURPOSE

To determine how nonsense mutations in the transcription factor ZEB1 lead to the development of posterior polymorphous corneal dystrophy type 3 (PPCD3).

METHODS

Whole-cell extracts were obtained from cultured human corneal epithelial cells (HCEpCs) as a source of ZEB1 protein. DNA-binding assays were performed using the whole-cell extract and oligonucleotide probes consisting of the two conserved E2-box motifs and surrounding nucleotides upstream of COL4A3. ZEB1 and COL4A3 mRNA expression in primary human corneal endothelial cells (HCEnCs) was assayed in both PPCD3 and control corneas by RT-PCR. Immunohistochemistry was used to localize ZEB1 and COL4A3 expression in normal human cornea.

RESULTS

Electromobility shift assays (EMSAs) and competition EMSAs demonstrated binding of protein(s) in the cultured HCEpCs to the E2-box motifs in the probes. The supershift EMSA confirmed that ZEB1, demonstrated to be present in the whole-cell extracts, binds to both the proximal and distal E2-box motifs in the COL4A3 promoter region. Both COL4A3 and ZEB1 are expressed in normal HCEnCs, although in PPCD3, ZEB1 expression is decreased and COL4A3 expression is increased compared with levels of both genes in healthy control corneas.

CONCLUSIONS

Inversely related HCEnC expression levels of ZEB1 and COL4A3 in PPCD3 indicate that ZEB1-mediated alterations in COL4A3 expression are most likely associated with the pathogenesis of this corneal endothelial dystrophy. However, the demonstration of COL4A3 expression in healthy adult primary HCEnCs suggests that PPCD3 is more likely to involve an alteration in the timing and/or degree of COL4A3 expression than to result from the dichotomous change implied by the previously proposed ectopic expression model.

Posterior polymorphous dystrophy associated with nonkeratoconic steep corneal curvatures

PURPOSE

To report a case series of eyes with posterior polymorphous corneal dystrophy and steep nonkeratoconic corneas.

METHODS

Retrospective, descriptive, nonrandomized case series.

RESULTS

Thirty-five eyes of 18 patients (14 cases from 6 families and 4 isolated cases) with diffuse posterior polymorphous corneal dystrophy had mean topographic simulated keratometry readings of 52.21 diopters (D), with a range of 46.47 D to 59.86 D and an SD of 3.69 D, with no slit-lamp or topographic findings suggestive of keratoconus.

CONCLUSIONS

The patients in this series demonstrate diffuse posterior polymorphous corneal dystrophy and nonkeratoconic steep corneas.

A noncoding point mutation of Zeb1 causes multiple developmental malformations and obesity in Twirler mice

Heterozygous Twirler (Tw) mice develop obesity and circling behavior associated with malformations of the inner ear, whereas homozygous Tw mice have cleft palate and die shortly after birth. Zeb1 is a zinc finger protein that contributes to mesenchymal cell fate by repression of genes whose expression defines epithelial cell identity. This developmental pathway is disrupted in inner ears of Tw/Tw mice. The purpose of our study was to comprehensively characterize the Twirler phenotype and to identify the causative mutation. The Tw/+ inner ear phenotype includes irregularities of the semicircular canals, abnormal utricular otoconia, a shortened cochlear duct, and hearing loss, whereas Tw/Tw ears are severely malformed with barely recognizable anatomy. Tw/+ mice have obesity associated with insulin-resistance and have lymphoid organ hypoplasia. We identified a noncoding nucleotide substitution, c.58+181G>A, in the first intron of the Tw allele of Zeb1 (Zeb1^Tw). A knockin mouse model of c.58+181G>A recapitulated the Tw phenotype, whereas a wild-type knockin control did not, confirming the mutation as pathogenic. c.58+181G>A does not affect splicing but disrupts a predicted site for Myb protein binding, which we confirmed in vitro. In comparison, homozygosity for a targeted deletion of exon 1 of mouse Zeb1, Zeb1^ΔEx1, is associated with a subtle abnormality of the lateral semicircular canal that is different than those in Tw mice. Expression analyses of E13.5 Twirler and Zeb1^ΔEx1 ears confirm that Zeb1^ΔEx1 is a null allele, whereas Zeb1^Tw RNA is expressed at increased levels in comparison to wild-type Zeb1. We conclude that a noncoding point mutation of Zeb1 acts via a gain-of-function to disrupt regulation of Zeb1^Tw expression, epithelial-mesenchymal cell fate or interactions, and structural development of the inner ear in Twirler mice. This is a novel mechanism underlying disorders of hearing or balance.

Twirler (Tw) mice have a combination of abnormalities that includes cleft palate, malformations of the inner ear, hearing loss, vestibular dysfunction, obesity, and lymphoid hypoplasia. In this study, we show that the underlying mutation affects the Zeb1 gene. Zeb1 was already known to encode a protein normally expressed in mesenchymal cells, where it represses expression of genes that are uniquely expressed in epithelial cells. The Tw mutation is a rare example of a single-nucleotide substitution in a region of a gene that does not encode protein, promoter, or splice sites, so we engineered a mouse model with the mutation that confirmed its causative role. The Tw mutation disrupts a consensus DNA binding site sequence for the Myb family of regulatory proteins. We conclude that this mutation leads to abnormal expression of Zeb1, structural malformations of the inner ear, and a loss of hearing and balance function. A similar mechanism may underlie other features of Twirler, such as obesity and cleft palate.

Cell type-specific transcriptome analysis reveals a major role for Zeb1 and miR-200b in mouse inner ear morphogenesis

Cellular heterogeneity hinders the extraction of functionally significant results and inference of regulatory networks from wide-scale expression profiles of complex mammalian organs. The mammalian inner ear consists of the auditory and vestibular systems that are each composed of hair cells, supporting cells, neurons, mesenchymal cells, other epithelial cells, and blood vessels. We developed a novel protocol to sort auditory and vestibular tissues of newborn mouse inner ears into their major cellular components. Transcriptome profiling of the sorted cells identified cell type-specific expression clusters. Computational analysis detected transcription factors and microRNAs that play key roles in determining cell identity in the inner ear. Specifically, our analysis revealed the role of the Zeb1/miR-200b pathway in establishing epithelial and mesenchymal identity in the inner ear. Furthermore, we detected a misregulation of the ZEB1 pathway in the inner ear of Twirler mice, which manifest, among other phenotypes, malformations of the auditory and vestibular labyrinth. The association of misregulation of the ZEB1/miR-200b pathway with auditory and vestibular defects in the Twirler mutant mice uncovers a novel mechanism underlying deafness and balance disorders. Our approach can be employed to decipher additional complex regulatory networks underlying other hearing and balance mouse mutants.

Differential epithelial and stromal protein profiles in keratoconus and normal human corneas

The purpose of the study was to identify epithelial and stromal proteins that exhibit up- or down-regulation in keratoconus (KC) vs. normal human corneas. Because previous proteomic studies utilized whole human corneas or epithelium alone, thereby diluted the specificity of the proteome of each tissue, we selectively analyzed the epithelium and stromal proteins. Individual preparations of epithelial and stromal proteins from KC and age-matched normal corneas were analyzed by two independent methods, i.e., a shotgun proteomic using a Nano-Electrospray Ionization Liquid Chromatography Tandem Mass Spectrometry [Nano-ESI-LC-MS (MS)(2)] and two-dimensional-difference gel electrophoresis (2D-DIGE) coupled with mass spectrometric methods. The label-free Nano-ESI-LC-MS (MS)(2) method identified 104 epithelial and 44 stromal proteins from both normal and KC corneas, and also quantified relative changes in levels of selected proteins, in both the tissues using spectral counts in a proteomic dataset. Relative to normal corneal epithelial proteins, six KC epithelial proteins (lamin-A/C, keratin type I cytoskeletal 14, tubulin beta chain, heat shock cognate 71 kDa protein, keratin type I cytoskeletal 16 and protein S100-A4) exhibited up-regulation and five proteins (transketolase, pyruvate kinase, 14-3-3 sigma isoform, phosphoglycerate kinase 1, and NADPH dehydrogenase (quinone) 1) showed down-regulation. A similar relative analysis showed that three KC stromal proteins (decorin, vimentin and keratocan) were up-regulated and five stromal proteins (TGF-betaig h3 (Bigh3), serotransferrin, MAM domain-containing protein 2 and isoforms 2C2A of collagen alpha-2[VI] chain) were down-regulated. The 2D-DIGE-mass spectrometry followed by Decyder software analysis showed that relative to normal corneas, the KC corneal epithelium exhibited up-regulation of four proteins (serum albumin, keratin 5, L-lactate dehydrogenase and annexin A8) and down-regulation of four proteins (FTH1 [Ferritin heavy chain protein 1], calpain small subunit 1, heat shock protein beta 1 and annexin A2). A similar relative analysis of stroma by this method also showed up-regulation of aldehyde dehydrogenase 3A1 (ALDH3A1), keratin 12, apolipoprotein A-IV precursor, haptoglobin precursor, prolipoprotein and lipoprotein Gln in KC corneas. Together, the results suggested that the Nano-ESI-LC-MS(MS)(2) method was superior than the 2D-DIGE method as it identified a greater number of proteins with altered levels in KC corneas. Further, the epithelial and stromal structural proteins of KC corneas exhibited altered levels compared to normal corneas, suggesting that they are affected due to structural remodeling during KC development and progression. Additionally, because several epithelial and stromal enzymes exhibited up- or down-regulation in the KC corneas relative to normal corneas, the two layers of KC corneas were under metabolic stress to adjust their remodeling.

The PPCD1 mouse: characterization of a mouse model for posterior polymorphous corneal dystrophy and identification of a candidate gene

The PPCD1 mouse, a spontaneous mutant that arose in our mouse colony, is characterized by an enlarged anterior chamber resulting from metaplasia of the corneal endothelium and blockage of the iridocorneal angle by epithelialized corneal endothelial cells. The presence of stratified multilayered corneal endothelial cells with abnormal patterns of cytokeratin expression are remarkably similar to those observed in human posterior polymorphous corneal dystrophy (PPCD) and the sporadic condition, iridocorneal endothelial syndrome. Affected eyes exhibit epithelialized corneal endothelial cells, with inappropriate cytokeratin expression and proliferation over the iridocorneal angle and posterior cornea. We have termed this the “mouse PPCD1” phenotype and mapped the mouse locus for this phenotype, designated “Ppcd1”, to a 6.1 Mbp interval on Chromosome 2, which is syntenic to the human Chromosome 20 PPCD1 interval. Inheritance of the mouse PPCD1 phenotype is autosomal dominant, with complete penetrance on the sensitive DBA/2J background and decreased penetrance on the C57BL/6J background. Comparative genome hybridization has identified a hemizygous 78 Kbp duplication in the mapped interval. The endpoints of the duplication are located in positions that disrupt the genes Csrp2bp and 6330439K17Rik and lead to duplication of the pseudogene LOC100043552. Quantitative reverse transcriptase-PCR indicates that expression levels of Csrp2bp and 6330439K17Rik are decreased in eyes of PPCD1 mice. Based on the observations of decreased gene expression levels, association with ZEB1-related pathways, and the report of corneal opacities in Csrp2bp^{tm1a(KOMP)Wtsi} heterozygotes and embryonic lethality in nulls, we postulate that duplication of the 78 Kbp segment leading to haploinsufficiency of Csrp2bp is responsible for the mouse PPCD1 phenotype. Similarly, CSRP2BP haploinsufficiency may lead to human PPCD.

Genetics of corneal endothelial dystrophies

The corneal endothelium maintains the level of hydration in the cornea. Dysfunction of the endothelium results in excess accumulation of water in the corneal stroma, leading to swelling of the stroma and loss of transparency. There are four different corneal endothelial dystrophies that are hereditary, progressive, non-inflammatory disorders involving dysfunction of the corneal endothelium. Each of the endothelial dystrophies is genetically heterogeneous with different modes of transmission and/or different genes involved in each subtype. Genes responsible for disease have been identified for only a subset of corneal endothelial dystrophies. Knowledge of genes involved and their function in the corneal endothelium can aid understanding the pathogenesis of the disorder as well as reveal pathways that are important for normal functioning of the endothelium.

Zeb1 represses Mitf and regulates pigment synthesis, cell proliferation, and epithelial morphology

PURPOSE

Epithelial-mesenchymal transition (EMT) is important in fibrotic responses, formation of cancer stem cells, and acquisition of a metastatic phenotype. Zeb1 represses epithelial specification genes to enforce epithelial-mesenchymal phenotypic boundaries during development, and it is one of several E-box-binding repressors whose overexpression triggers EMT. The purpose of this study was to investigate the potential role for Zeb1 in EMT leading to the dedifferentiation of retinal pigment epithelial (RPE) cells.

METHODS

Real-time PCR was used to examine mRNA expression during RPE dedifferentiation in primary cultures of RPE cells from Zeb1(+/-) mice and after knockdown of Zeb1 by lentivirus shRNA. Chromatin immunoprecipitation was used to detect Zeb1 at gene promoters in vivo.

RESULTS

Zeb1 is overexpressed during RPE dedifferentiation. Heterozygous mutation or shRNA knockdown to prevent this overexpression eliminates the onset of proliferation, loss of epithelial morphology, and pigment, which characterizes RPE dedifferentiation. Zeb1 binds to the Mitf A promoter in vivo, and Zeb1 mutation or shRNA knockdown derepresses the gene. The authors link Zeb1 expression to cell-cell contact and demonstrate that forcing dedifferentiated RPE cells to adopt cell-cell only contacts via sphere formation reverses the overexpression of Zeb1 and reprograms RPE cells back to a pigmented phenotype.

CONCLUSIONS

Overexpression of the EMT transcription factor Zeb1 has an important role in RPE dedifferentiation via its regulation of Mitf. Expression of Zeb1 and, in turn, RPE dedifferentiation, is linked to cell-cell contact, and these contacts can be used to diminish Zeb1 expression and reprogram dedifferentiated RPE cells.

Corneal dystrophies

The term corneal dystrophy embraces a heterogenous group of bilateral genetically determined non-inflammatory corneal diseases that are restricted to the cornea. The designation is imprecise but remains in vogue because of its clinical value. Clinically, the corneal dystrophies can be divided into three groups based on the sole or predominant anatomical location of the abnormalities. Some affect primarily the corneal epithelium and its basement membrane or Bowman layer and the superficial corneal stroma (anterior corneal dystrophies), the corneal stroma (stromal corneal dystrophies), or Descemet membrane and the corneal endothelium (posterior corneal dystrophies). Most corneal dystrophies have no systemic manifestations and present with variable shaped corneal opacities in a clear or cloudy cornea and they affect visual acuity to different degrees. Corneal dystrophies may have a simple autosomal dominant, autosomal recessive or X-linked recessive Mendelian mode of inheritance. Different corneal dystrophies are caused by mutations in the CHST6, KRT3, KRT12, PIP5K3, SLC4A11, TACSTD2, TGFBI, and UBIAD1 genes. Knowledge about the responsible genetic mutations responsible for these disorders has led to a better understanding of their basic defect and to molecular tests for their precise diagnosis. Genes for other corneal dystrophies have been mapped to specific chromosomal loci, but have not yet been identified. As clinical manifestations widely vary with the different entities, corneal dystrophies should be suspected when corneal transparency is lost or corneal opacities occur spontaneously, particularly in both corneas, and especially in the presence of a positive family history or in the offspring of consanguineous parents. Main differential diagnoses include various causes of monoclonal gammopathy, lecithin-cholesterol-acyltransferase deficiency, Fabry disease, cystinosis, tyrosine transaminase deficiency, systemic lysosomal storage diseases (mucopolysaccharidoses, lipidoses, mucolipidoses), and several skin diseases (X-linked ichthyosis, keratosis follicularis spinolosa decalvans). The management of the corneal dystrophies varies with the specific disease. Some are treated medically or with methods that excise or ablate the abnormal corneal tissue, such as deep lamellar endothelial keratoplasty (DLEK) and phototherapeutic keratectomy (PTK). Other less debilitating or asymptomatic dystrophies do not warrant treatment. The prognosis varies from minimal effect on the vision to corneal blindness, with marked phenotypic variability.

Changes in the localization of collagens IV and VIII in corneas obtained from patients with posterior polymorphous corneal dystrophy

Posterior polymorphous corneal dystrophy (PPCD) is a hereditary bilateral disorder affecting primarily the endothelium and Descemet's membrane (DM). The aim of this study was to determine the changes in the presence and localization of the alpha1-alpha6 collagen IV chains and alpha1, alpha2 collagen VIII chains in Czech patients with PPCD. Twelve corneal buttons from ten PPCD patients who underwent corneal grafting, as well as eight unaffected corneas, were used. Enzymatic indirect immunohistochemistry was performed on cryosections using antibodies against the alpha1-alpha6 collagen IV chains and alpha1, alpha2 collagen VIII chains. The intensity of the signal was examined separately in the basal membrane of the epithelium (BME), stroma and DM. More than 50% of PPCD specimens exhibited positivity for alpha1 and alpha2 collagen IV chains in the BME and in the posterior stroma, while no staining was detected in these areas in control specimens. The signal for the alpha1 and alpha2 collagen IV chains was more intense in DM of PPCD corneas compared to controls and it was shifted from the stromal side (in control tissue) to the endothelial side of DM (in the patients). A less intensive signal in PPCD corneas for the alpha3 and alpha5 chains in DM and an accumulation of alpha3-alpha5 in the posterior stroma in diseased corneas were the only differences in staining for the alpha3-alpha6 collagen IV chains. The alpha1 collagen VIII chain was detected on both the endothelial and the stromal sides of DM in 90% of patients with PPCD, compared with the prevailing localization on the stromal side of DM in control corneas. A change in the localization of the alpha2 collagen VIII chain in DM from vertically striated features in control specimens to double line positivity in the DM of PPCD corneas and positive staining in the posterior collagenous layer of four patients were also detected. In three PPCD patients a fibrous pannus located under the BME, positive for alpha1-alpha3, alpha5 collagen IV chains and alpha1 collagen VIII chain, was observed. The increased expression of the alpha1, alpha2 collagen IV and alpha1 collagen VIII chains and the change in their localization in DM may contribute to the increased endothelial proliferative capacity observed in PPCD patients.