Investigation of the functional impact of CHED- and FECD4-associated SLC4A11 mutations in human corneal endothelial cells.

Mutations in the solute linked carrier family 4 member 11 (SLC4A11) gene are associated with congenital hereditary endothelial dystrophy (CHED) and Fuchs corneal endothelial dystrophy type 4 (FECD4), both characterized by corneal endothelial cell (CEnC) dysfunction and/or cell loss leading to corneal edema and visual impairment. In this study, we characterize the impact of CHED-/FECD4-associated SLC4A11 mutations on CEnC function and SLC4A11 protein localization by generating and comparing human CEnC (hCEnC) lines expressing wild type SLC4A11 (SLC4A11WT) or mutant SLC4A11 harboring CHED-/FECD4-associated SLC4A11 mutations (SLC4A11MU). SLC4A11WT and SLC4A11MU hCEnC lines were generated to express either SLC4A11 variant 2 (V2WT and V2MU) or variant 3 (V3WT and V3MU), the two major variants expressed in ex vivo hCEnC. Functional assays were performed to assess cell barrier, proliferation, viability, migration, and NH3-induced membrane conductance. We demonstrate SLC4A11-/- and SLC4A11MU hCEnC lines exhibited increased migration rates, altered proliferation and decreased cell viability compared to SLC4A11WT hCEnC. Additionally, SLC4A11-/- hCEnC demonstrated decreased cell-substrate adhesion and membrane capacitances compared to SLC4A11WT hCEnC. Induction with 10mM NH4Cl led SLC4A11WT hCEnC to depolarize; conversely, SLC4A11-/- hCEnC hyperpolarized and the majority of SLC4A11MU hCEnC either hyperpolarized or had minimal membrane potential changes following NH4Cl induction. Immunostaining of primary hCEnC and SLC4A11WT hCEnC lines for SLC4A11 demonstrated predominately plasma membrane staining with poor or partial colocalization with mitochondrial marker COX4 within a subset of punctate subcellular structures. Overall, our findings suggest CHED-associated SLC4A11 mutations likely lead to hCEnC dysfunction, and ultimately CHED, by interfering with cell migration, proliferation, viability, membrane conductance, barrier function, and/or cell surface localization of the SLC4A11 protein in hCEnC. Additionally, based on their similar subcellular localization and exhibiting similar cell functional profiles, protein isoforms encoded by SLC4A11 variant 2 and variant 3 likely have highly overlapping functional roles in hCEnC.

Lisch Epithelial Corneal Dystrophy Is Caused by Heterozygous Loss-of-Function Variants in MCOLN1.

PURPOSE: To report the genetic etiology of Lisch epithelial corneal dystrophy (LECD). DESIGN: Multicenter cohort study. METHODS: A discovery cohort of 27 individuals with LECD from 17 families, including 7 affected members from the original LECD family, 6 patients from 2 new families and 14 simplex cases, was recruited. A cohort of 6 individuals carrying a pathogenic MCOLN1 (mucolipin 1) variant was reviewed for signs of LECD. Next-generation sequencing or targeted Sanger sequencing were used in all patients to identify pathogenic or likely pathogenic variants and penetrance of variants. RESULTS: Nine rare heterozygous MCOLN1 variants were identified in 23 of 27 affected individuals from 13 families. The truncating nature of 7 variants and functional testing of 1 missense variant indicated that they result in MCOLN1 haploinsufficiency. Importantly, in the homozygous and compound-heterozygous state, 4 of 9 LECD-associated variants cause the rare lysosomal storage disorder mucolipidosis IV (MLIV). Autosomal recessive MLIV is a systemic disease and comprises neurodegeneration as well as corneal opacity of infantile-onset with epithelial autofluorescent lysosomal inclusions. However, the 6 parents of 3 patients with MLIV confirmed to carry pathogenic MCOLN1 variants did not have the LECD phenotype, suggesting MCOLN1 haploinsufficiency may be associated with reduced penetrance and variable expressivity. CONCLUSIONS: MCOLN1 haploinsufficiency is the major cause of LECD. Based on the overlapping clinical features of corneal epithelial cells with autofluorescent inclusions reported in both LECD and MLIV, it is concluded that some carriers of MCOLN1 haploinsufficiency-causing variants present with LECD.

Keratitis Fugax Hereditaria Associated With a Novel NLRP3 Mutation in a Non-Finnish Patient.

PURPOSE: The aim of this study was to report a novel heterozygous variant c.1712G>T (p.Gly571Val) in the nucleotide-binding domain, leucine-rich repeat family, pyrin domain-containing 3 gene ( NLRP3 ) in a previously unreported non-Finnish individual with keratitis fugax hereditaria (KFH). METHODS: Ophthalmologic examination of the proband was performed with slit-lamp biomicroscopy and anterior segment optical coherence tomography. Saliva was collected as a source of DNA, after which targeted exome sequencing of candidate genes was performed using a commercially available panel. Identified presumed pathogenic variants were confirmed by Sanger sequencing. RESULTS: Slit-lamp examination of the 52-year-old female proband revealed peripheral arcus-like degeneration and bilateral central corneal opacification, observed on anterior segment optical coherence tomography to involve the anterior half of the corneal stroma. Examination of the proband's parents revealed clear corneas in each eye. Genetic testing of the proband identified the presence of a novel heterozygous NLRP3 missense mutation (c.1712G>T, p.Gly571Val), which was confirmed by Sanger sequencing. This mutation was absent in the proband's parents. CONCLUSIONS: Although KFH has been reported only in individuals of Finnish descent and only in association with a missense mutation in exon 1 of NLRP3 , we report an individual of non-Finnish descent with KFH associated with a novel heterozygous variant in exon 2 of NLRP3 . Thus, ophthalmologists should be aware of the ethnic and genetic heterogeneity associated with KFH.

Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis.

Purpose: Pre-Descemet corneal dystrophy (PDCD) with X-linked ichthyosis (XLI) is associated with mutations in or deletions of the steroid sulfatase gene (STS). As only three cases of genetically confirmed PDCD associated with XLI have been reported, we sought to expand our understanding of the genetic basis of PDCD by screening STS in two previously unreported families. Materials and Methods: The affected individuals underwent cutaneous and slit-lamp examinations. Saliva samples collected from each affected individual served as a source of DNA for the amplification of the 10 coding exons of STS and flanking DNA markers. Results: The slit-lamp examination of three affected men (two of whom were brothers) from two families revealed bilateral punctate posterior corneal stromal opacities anterior to the Descemet membrane. Cutaneous examination demonstrated dry, coarse, scaly ichthyotic changes characteristic of XLI in all individuals. Genetic examination of the STS locus on the X chromosome in Case 1 revealed a deletion that spanned across DNA markers DXS1130-DXS237, which includes all the coding exons (exons 1-10) of STS. Genetic screening of Cases 2 and 3 revealed a partial deletion of the STS locus involving exons 1-7 and flanking DNA marker DXS1130 on the X chromosome. Conclusions: PDCD with XLI may be associated with either partial or complete deletion of STS. Despite the identification of point mutations, partial deletion, and complete deletion of STS in different affected families reported to date, there was no apparent difference in the affected phenotype between the families, suggesting that the identified variants likely all resulted in loss of function of steroid sulfatase.

Novel DCN Mutation in Armenian Family With Congenital Stromal Corneal Dystrophy.

PURPOSE: Congenital stromal corneal dystrophy (CSCD) is a rare congenital, dominantly inherited disorder characterized by diffuse stromal opacification associated with mutations in the decorin gene ( DCN ). As only 5 families with genetically confirmed CSCD have been reported, the identification of a novel pedigree provides the opportunity to better characterize the phenotype and genetic basis. METHODS: An Armenian family with individuals in 4 consecutive generations demonstrated clinical features consistent with CSCD. Consented individuals underwent slit lamp examination, optical coherence tomography, and confocal microscopy. Genomic DNA was collected from saliva and all coding and adjacent intronic regions of DCN were sequenced. In silico analysis was performed for identified mutation(s). Excised corneal tissue underwent light, electron microscopic, and immunohistochemical evaluation. RESULTS: Affected individuals demonstrated bilateral, diffuse, panstromal corneal opacification. Three of the 6 individuals diagnosed with CSCD underwent genetic analysis; all demonstrated a novel heterozygous frameshift deletion in exon 8 of DCN (p.His317Thrfs*11), predicted to cause a 33 amino acid truncation and to be damaging and disease causing by SIFT and MutationTaster. Light and electron microscopic examination of an excised cornea demonstrated increased corneal thickness, stromal scarring, keratocyte loss, and an irregularity of lamellar collagen spacing and fibril formation. Immunofluorescent examination demonstrated increased DCN immunostaining, predominantly in the widened interlamellar spaces. CONCLUSIONS: We report only the sixth pedigree with genetically confirmed CSCD, associated with a novel DCN frameshift mutation. The clinical evaluation, multimodal imaging, and histopathologic assessment in this family with CSCD broaden our understanding of this rare corneal disease.

Confirmation of association of TGFBI p.Ser591Phe mutation with variant lattice corneal dystrophy.

PURPOSE: To provide the initial confirmation of the c.1772C>T (p.Ser591Phe) mutation in the transforming growth factor-ß-induced (TGFBI) gene as being associated with variant lattice corneal dystrophy (LCD). METHODS: Ophthalmologic examination of the proband was performed with slit lamp biomicroscopy. Saliva was collected as a source of DNA for screening all 17 exons of TGFBI, after which three family members were selectively screened for variants in exon 13. Rosetta-based structure prediction was used to calculate changes in TGFBI protein (TGFBIp) stability secondary to the c.1772C>T (p.Ser591Phe) missense mutation. RESULTS: Slit lamp examination of the 38-year-old proband revealed a clear cornea right eye and unilateral, discrete, and branching lattice lines in the anterior and mid-stroma of the central cornea left eye. Screening of TGFBI in the proband revealed a heterozygous missense mutation in exon 13 (c.1772C>T (p.Ser591Phe)) that was also identified in her affected mother but not in her brother or maternal grandmother. Calculated energy change in Rosetta (ΔΔG) for the TGFBIp variant p.Ser591Phe was 23.5, indicating a thermodynamic destabilization resulting from energetic frustration. CONCLUSIONS: The p.Ser591Phe mutation in TGFBI is associated with an unilateral variant of LCD. Rosetta-predicted stability changes indicate that the p.Ser591Phe variant is destabilizing, which is consistent with other observations for LCD-causing mutations.

Confirmation of PRDX3 c.568G>C as the Genetic Basis of Punctiform and Polychromatic Pre-Descemet Corneal Dystrophy.

PURPOSE: The aim of this study was to report the results of screening peroxiredoxin 3 (PRDX3) and PDZ domain-containing protein 8 (PDZD8) in a previously unreported pedigree with punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD) to confirm that the PRDX3 mutation c.568G>C is the genetic basis of PPPCD. METHODS: Ophthalmologic examination of the proband and her affected father was performed with slit lamp biomicroscopy. Saliva was collected from the proband as a source of DNA, after which screening for PRDX3 and PDZD8 was performed. RESULTS: Slit lamp examination of the proband revealed polychromatic deposits diffusely distributed at the pre-Descemet level in both corneas and anterior subcapsular in the crystalline lens of both eyes. The proband's father also demonstrated diffuse pre-Descemetic polychromatic deposits in both eyes but no lenticular deposits. Screening of PRDX3 in the proband demonstrated the c.568G>C (p.Asp190His) variant previously associated with PPPCD and failed to identify any variants in PDZD8. CONCLUSIONS: We report the initial confirmation of PRDX3 as the genetic basis of PPPCD in a previously unreported pedigree and expand the phenotype of PPPCD to include polychromatic lenticular deposits.

Corneal ectasia associated with posterior lamellar opacification.

BACKGROUND: Concomitant corneal ectasia and posterior lamellar corneal opacification is rare, and the genetic relationship between these two conditions is unclear. We report the genetic and clinical characterization of this phenotype in three unrelated individuals. MATERIALS AND METHODS: One previously reported affected individual and two unreported, unrelated, affected individuals were recruited for the study. Subjects and unaffected relatives underwent slit lamp examination, refraction, and multi-modal imaging. Saliva samples were obtained from two of the three affected individuals, from which DNA was extracted. Sanger sequencing was performed to identify mutations in genes associated with posterior amorphous corneal dystrophy (PACD), brittle cornea syndrome (BCS), and posterior polymorphous corneal dystrophy (PPCD), while copy number variation (CNV) analysis was used to identify CNV in the PACD locus. RESULTS: Affected individuals demonstrated bilateral corneal steepening, stromal thinning and lamellar posterior corneal opacification. Corneal topography and tomography revealed conical or globular corneal steepening and decreased thickness. Anterior segment optical coherence tomography demonstrated hyperreflectivity of the posterior stroma in each of the affected individuals. Genetic testing did not detect a heterozygous deletion involving the PACD locus on chromosome 12 or a pathogenic mutation in the genes associated with BCS or PPCD. CONCLUSIONS: Corneal ectasia may be associated with posterior lamellar stromal opacification that appears consistent with PACD. However, genetic testing for PACD as well as BCS and PPCD in affected individuals fails to reveal pathogenic deletions or mutations, indicating that other genetic factors are involved.

Identification of A Novel TGFBI Gene Mutation (p.Serine524Cystine) Associated with Late Onset Recurrent Epithelial Erosions and Bowman Layer Opacities.

BACKGROUND: Most transforming growth factor beta-induced (TGFBI) corneal dystrophies are associated with a characteristic phenotype, clinical course, and a conserved mutation in the TGFBI gene. However, we report a novel TGFBI missense mutation associated with a late-onset, variant Bowman layer dystrophy. METHODS: Participants underwent slit-lamp examination and multimodal imaging. Polymerase chain reaction amplification and Sanger sequencing were performed on saliva-derived genomic DNA to screen TGFBI exons 4 and 12 as well as COL17A1 exon 46. PolyPhen-2 and SIFT were used to predict the functional impact of any identified variants. RESULTS: A 56-year-old Thai woman reported a four-year history of decreased vision and intermittent eye irritation, suggestive of recurrent epithelial erosions, in both eyes. Slit-lamp exam revealed bilateral, irregular, limbal-sparing Bowman layer opacities, which were also noted on anterior segment optical coherence tomography. Phototherapeutic keratectomy was performed in the right eye, improving the best-corrected visual acuity from 20/50 to 20/30. Sequencing of the TGFBI gene revealed a novel heterozygous, missense mutation in exon 12 (c.1571 C > G; p.Ser524Cys), which was present in an affected son and absent in an unaffected son, and was predicted to be damaging by PolyPhen-2 and SIFT. The patient was diagnosed with a variant Bowman layer dystrophy given the late onset of an atypical phenotype and the identification of a novel TGFBI mutation. CONCLUSIONS: A novel TGFBI missense mutation is associated with a late-onset Bowman layer dystrophy. Given the atypical clinical appearance and course, molecular genetic analysis was utilized to establish a definitive diagnosis.

Energy Shortage in Human and Mouse Models of SLC4A11-Associated Corneal Endothelial Dystrophies.

Purpose: To elucidate the molecular events in solute carrier family 4 member 11 (SLC4A11)-deficient corneal endothelium that lead to the endothelial dysfunction that characterizes the dystrophies associated with SLC4A11 mutations, congenital hereditary endothelial dystrophy (CHED) and Fuchs endothelial corneal dystrophy 4. Methods: Comparative transcriptomic analysis (CTA) was performed in primary human corneal endothelial cells (pHCEnC) and murine corneal endothelial cells (MCEnC) with normal and reduced levels of SLC4A11 (SLC4A11 KD pHCEnC) and Slc4a11 (Slc4a11-/- MCEnC), respectively. Validation of differentially expressed genes was performed using immunofluorescence staining of CHED corneal endothelium, as well as western blot and quantitative PCR analysis of SLC4A11 KD pHCEnC and Slc4a11-/- MCEnC. Functional analyses were performed to investigate potential functional changes associated with the observed transcriptomic alterations. Results: CTA revealed inhibition of cell metabolism and ion transport function as well as mitochondrial dysfunction, leading to reduced adenosine triphosphate (ATP) production, in SLC4A11 KD pHCEnC and Slc4a11-/- MCEnC. Co-localization of SNARE protein STX17 with mitochondria marker COX4 was observed in CHED corneal endothelium, as was activation of AMPK-p53/ULK1 in both SLC4A11 KD pHCEnC and Slc4a11-/- MCEnC, providing additional evidence of mitochondrial dysfunction and mitophagy. Reduced Na+-dependent HCO3- transport activity and altered NH4Cl-induced membrane potential changes were observed in Slc4a11-/- MCEnC. Conclusions: Reduced steady-state ATP levels and subsequent activation of the AMPK-p53 pathway provide a link between the metabolic functional deficit and transcriptome alterations, as well as evidence of insufficient ATP to maintain the Na+/K+-ATPase corneal endothelial pump as the cause of the edema that characterizes SLC4A11-associated corneal endothelial dystrophies.

Phenotypic and functional characterization of corneal endothelial cells during in vitro expansion.

The advent of cell culture-based methods for the establishment and expansion of human corneal endothelial cells (CEnC) has provided a source of transplantable corneal endothelium, with a significant potential to challenge the one donor-one recipient paradigm. However, concerns over cell identity remain, and a comprehensive characterization of the cultured CEnC across serial passages has not been performed. To this end, we compared two established CEnC culture methods by assessing the transcriptomic changes that occur during in vitro expansion. In confluent monolayers, low mitogenic culture conditions preserved corneal endothelial cell state identity better than culture in high mitogenic conditions. Expansion by continuous passaging induced replicative cell senescence. Transcriptomic analysis of the senescent phenotype identified a cell senescence signature distinct for CEnC. We identified activation of both classic and new cell signaling pathways that may be targeted to prevent senescence, a significant barrier to realizing the potential clinical utility of in vitro expansion.

Identification of a Novel Missense KRT12 Mutation in a Vietnamese Family with Meesmann Corneal Dystrophy.

Meesmann epithelial corneal dystrophy (MECD) is a rare dominantly inherited disorder that is characterized by corneal epithelial microcysts and is associated with mutations in the keratin 3 (KRT3) and keratin 12 (KRT12) genes. In this study, we report a novel mutation in the KRT12 gene in a Vietnamese pedigree with MECD. Slit-lamp examination was performed on each of the 7 recruited members of a Vietnamese family to identify characteristic features of MECD. After informed consent was obtained from each individual, genomic DNA was isolated from saliva samples and screening of KRT3and KRT12 genes was performed by Sanger sequencing. The proband, a 31-year-old man, complained of a 1-year history of eye irritation and photophobia. Slit-lamp examination revealed intraepithelial microcysts involving only the corneal periphery in each eye with clear central corneas and no stromal or endothelial involvement. Three family members demonstrated similar intraepithelial microcysts, but with diffuse involvement, extended from limbus to limbus. Sanger sequencing of KRT3 (exon 7) and KRT12 (exons 1 and 6) in the proband revealed a novel heterozygous KRT12 variant (c.1273G>A [p.Glu425Lys]) that was present in the three affected family members but was absent in the three family members with clear corneas. This study is the first report of a Vietnamese family affected with MECD, associated with an atypical peripheral corneal epithelial phenotype in the proband and a novel mutation in KRT12.

Punctiform and Polychromatic Pre-Descemet Corneal Dystrophy: Clinical Evaluation and Identification of the Genetic Basis.

PURPOSE: This study reports the clinical features and genetic bases of 3 previously unreported families with punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD). DESIGN: Observational case series. METHODS: Full ophthalmic assessment was performed for members of 3 unreported families with PPPCD. Structural and biomechanical alterations of the cornea were screened. Whole exome sequencing (WES) was performed in the first family. Novel or rare variants that segregated with the affected status were screened in the other 2 families using Sanger sequencing. Identified variants that segregated with the affected status in all families were characterized by using in silico prediction tools and/or in vitro splice assays. Additionally, 2 previously reported PPPCD families were screened for variants identified in the 3 unreported PPPCD families. RESULTS: PPPCD was diagnosed in 12 of the 21 examined members of the 3 unreported families. The only refractive, topographic, or biomechanical abnormality associated with PPPCD was a significantly increased corneal stiffness. WES and Sanger sequencing identified 2 variants that segregated with the affected status in all 3 families: a rare intronic PDZD8 c.872+10A>T variant and a novel missense PRDX3 c.568G>C (p.Asp190His) variant. The same PRDX3 variant was identified in the previously reported PPPCD family expressing the common PPPCD phenotype and was predicted by in silico prediction tools to be damaging to protein function. CONCLUSIONS: PPPCD is associated with an alteration of corneal biomechanics and a novel missense variant in PRDX3. Screening of additional families will determine whether all families demonstrate a PRDX3 variant or whether locus heterogeneity may exist for PPPCD.

ZEB1 insufficiency causes corneal endothelial cell state transition and altered cellular processing.

The zinc finger e-box binding homeobox 1 (ZEB1) transcription factor is a master regulator of the epithelial to mesenchymal transition (EMT), and of the reverse mesenchymal to epithelial transition (MET) processes. ZEB1 plays an integral role in mediating cell state transitions during cell lineage specification, wound healing and disease. EMT/MET are characterized by distinct changes in molecular and cellular phenotype that are generally context-independent. Posterior polymorphous corneal dystrophy (PPCD), associated with ZEB1 insufficiency, provides a new biological context in which to understand and evaluate the classic EMT/MET paradigm. PPCD is characterized by a cadherin-switch and transition to an epithelial-like transcriptomic and cellular phenotype, which we study in a cell-based model of PPCD generated using CRISPR-Cas9-mediated ZEB1 knockout in corneal endothelial cells (CEnCs). Transcriptomic and functional studies support the hypothesis that CEnC undergo a MET-like transition in PPCD, termed endothelial to epithelial transition (EnET), and lead to the conclusion that EnET may be considered a corollary to the classic EMT/MET paradigm.

Alterations in GRHL2-OVOL2-ZEB1 axis and aberrant activation of Wnt signaling lead to altered gene transcription in posterior polymorphous corneal dystrophy.

Mutations associated with posterior polymorphous corneal dystrophy (PPCD) have been identified in three genes: ZEB1 (zinc-finger E-box binding homeobox 1) associated with sub-type PPCD3; OVOL2 (ovol-like zinc finger 2) associated with sub-type PPCD1; and GRHL2 (grainyhead like transcription factor 2) associated with sub-type PPCD4. Each of these genes encodes a transcription factor that regulates cell-state transitions. While the discovery of these PPCD-associated genes has greatly expanded our knowledge of the genetic basis of PPCD, the molecular mechanisms via which mutations in these genes lead to indistinguishable disease phenotypes have yet to be elucidated. To characterize the gene expression profiles of the genetic sub-types of PPCD, RNA-seq was performed on corneal endothelium derived from an individual with PPCD1 who harbors a c.-307T > C OVOL2 promoter mutation. Transcriptomic analysis of this and previously-reported RNA-seq data from two individuals with PPCD (the first with PPCD3 associated with a ZEB1 truncating mutation (c.1381delinsGACGAT) and the second with genetically unresolved PPCD in which ZEB1 coding region, OVOL2 promoter and GRHL2 promoter, exon 1, and intron 1 mutations were excluded) revealed: OVOL2 expression increased in PPCD1 (259 fold), unchanged in PPCD3 and slightly increased in genetically unresolved PPCD (from 0 TPM to 0.86 TPM, undefined fold change); ZEB1 expression decreased in PPCD1 (-5.9 fold), PPCD3 (-3.95 fold) and genetically unresolved PPCD (-3.96 fold); and GRHL2 expression increased in PPCD1 (333.5 fold), slightly increased (from 0 TPM to 0.67 TPM, undefined fold change) in PPCD3 and increased in genetically unresolved PPCD (1853 fold). Additionally, as the majority of pedigrees affected with PPCD remain genetically unresolved, we screened the promoter, exon 1, and intron 1 regions of GRHL2 in 24 PPCD probands who do not harbor a ZEB1 or OVOL2 mutation. GRHL2 screening did not identify any novel or rare GRHL2 variant in these 24 individuals. As ZEB1 can act as an activator or repressor of downstream target gene expression depending on Wnt signaling pathway activation or deactivation, we also sought to determine whether or not Wnt signaling is active in PPCD by performing immunohistochemistry in corneal tissue sections derived from an individual affected with PPCD3 and from an individual with genetically unresolved PPCD. Immunohistochemistry results demonstrated corneal endothelial nuclear accumulation of S552 phos-ß-catenin and cytosolic localization of S33/37/T42 non-phosphorylated ß-catenin in PPCD, indicating aberrant activation of Wnt signaling, which was not observed in control corneal endothelium. These findings suggest that alterations in the ZEB1-OVOL2-GRHL2 axis (caused by PPCD-associated mutations) lead to changes in corneal endothelial cell state and molecular pathways, including the aberrant activation of the Wnt signaling pathway.

Crystalline Keratopathy in Post-LASIK Ectasia: A Case Report.

PURPOSE: To report an unusual case of bilateral crystalline keratopathy presenting several years after a laser in situ keratomileusis (LASIK) procedure. METHODS: Case report and review of the literature. RESULTS: A healthy 42-year-old woman with post-LASIK ectasia, treated with long-term corneoscleral contact lenses, developed new-onset crystalline keratopathy in both eyes. Anterior segment optical coherence tomography demonstrated bilaterally symmetric paracentral rings of hyperreflectivity, involving the LASIK corneal flaps. There was good clearance of the corneoscleral contact lenses with no corneal-lens touch in all quadrants. There was no evidence of infectious or systemic etiologies. Genetic testing for the UBIAD1 gene for Schnyder corneal dystrophy was negative. Continued clinical observations have exhibited progressive corneal crystalline deposition, yet the patient has remained visually asymptomatic. CONCLUSIONS: This is the first known reported case of significantly delayed progressive noninfectious crystalline keratopathy in post-LASIK ectasia. The pathophysiology of this condition remains elusive to date and highlights the challenges of noninvasive diagnostic techniques and yet the utility of molecular genetic analysis in elucidating the etiology of this unique clinical presentation.

Epithelial Recurrent Erosion Dystrophy Secondary to COL17A1 c.3156C>T Mutation in a Non-white Family.

PURPOSE: To report the identification of the collagen, type XVII, alpha 1 (COL17A1) c.3156C>T mutation associated with epithelial recurrent erosion dystrophy (ERED) in a Thai family. METHODS: Slit-lamp examination was performed to determine the affected status of each member of a Thai family, with multiple members demonstrating scattered Bowman layer opacities. After genomic deoxyribonucleic acid (DNA) was isolated from saliva, polymerase chain reaction (PCR) amplification and Sanger sequencing were performed to screen COL17A1 and exons 4 and 12 of the transforming growth factor ß-induced gene. RESULTS: The 67-year-old proband and her 4 siblings were examined by slit-lamp biomicroscopy, which identified bilateral subepithelial opacities in the proband and in one of the 4 siblings. In both the proband and the affected sister, screening of the COL17A1 gene identified a heterozygous c.3156C>T synonymous mutation that has been previously demonstrated to introduce a cryptic splice donor site, likely leading to aberrant splicing of COL17A1. This mutation was not identified in the unaffected siblings, and no mutations were identified in exons 4 and 12 of the transforming growth factor ß-induced gene in any of the screened family members. CONCLUSIONS: ERED associated with a COL17A1 mutation has been previously reported in only 6 families, all white. Identification of the c.3156C>T mutation, previously identified in 5 of these 6 families, in the Thai family we report indicates conservation of the genetic basis of ERED across different races and underscores the importance of ophthalmologists around the globe being familiar with ERED, which has only recently become a recognized corneal dystrophy.

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.

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.