Multiple roles of Pax6 in postnatal cornea development.

Mammalian corneal development is a multistep process, including formation of the corneal epithelium (CE), endothelium and stroma during embryogenesis, followed by postnatal stratification of the epithelial layers and continuous renewal of the epithelium to replace the outermost corneal cells. Here, we employed the Cre-loxP system to conditionally deplete Pax6 proteins in two domains of ocular cells, i.e., the ocular surface epithelium (cornea, limbus and conjunctiva) (OSE) or postnatal CE via K14-cre or Aldh3-cre, respectively. Earlier and broader inactivation of Pax6 in the OSE resulted in thickened OSE with CE and limbal cells adopting the conjunctival keratin expression pattern. More restricted depletion of Pax6 in postnatal CE resulted in an abnormal cornea marked by reduced epithelial thickness despite increased epithelial cell proliferation. Immunofluorescence studies revealed loss of intermediate filament Cytokeratin 12 and diffused expression of adherens junction components, together with reduced tight junction protein, Zonula occludens-1. Furthermore, the expression of Cytokeratin 14, a basal cell marker in apical layers, indicates impaired differentiation of CE cells. Collectively, our data demonstrate that Pax6 is essential for maintaining proper differentiation and strong intercellular adhesion in postnatal CE cells, whereas limbal Pax6 is required to prevent the outgrowth of conjunctival cells to the cornea.

Immortalization effect of SV40T lentiviral vectors on canine corneal epithelial cells.

BACKGROUND: Primary canine corneal epithelial cells (CCECs) easily become senescent, and cell proliferation is limited. Therefore, sampling for experimentation requires a large number of animals, which is problematic in terms of animal welfare and fails to maintain the stability of the cells for in vitro analyses. RESULTS: In this study, CCECs were separated and purified by trypsin and dispase II enzymatic analysis. Next, the cells were immortalized by transfection with a lentiviral vector expressing Simian vacuolating virus 40 large T (SV40T). The immortalized canine corneal epithelial cell line (CCEC-SV40T) was established by serial passages and monoclonal selection. The biological characteristics of CCEC-SV40T cells were evaluated based on the cell proliferation rate, cell cycle pattern, serum dependence, karyotype, and cytokeratin 12 immunofluorescence detection. In addition, we infected CCEC-SV40T cells with Staphylococcus pseudintermedius (S. pseudintermedius) and detected the inflammatory response of the cells. After the CCEC-SV40T cells were passaged continuously for 40 generations, the cells grew in a cobblestone pattern, which was similar to CCECs. The SV40T gene and cytokeratin 12 can be detected in each generation. CCEC-SV40T cells were observed to have a stronger proliferation capacity than CCECs. CCEC-SV40T cells maintained the same diploid karyotype and serum-dependent ability as CCECs. After CCEC-SV40T cells were infected with S. pseudintermedius, the mRNA expression levels of NLRP3, Caspase-1 and proinflammatory cytokines, including IL-1ß, IL-6, IL-8 and TNF-α, were upregulated, and the protein levels of MyD88, NLRP3 and the phosphorylation of Iκbα and p65 were upregulated. CONCLUSIONS: In conclusion, the CCEC-SV40T line was successfully established and can be used for in vitro studies, such as research on corneal diseases or drug screening.

Conditional Deletion of AP-2ß in the Periocular Mesenchyme of Mice Alters Corneal Epithelial Cell Fate and Stratification.

The cornea is an anterior eye structure specialized for vision. The corneal endothelium and stroma are derived from the periocular mesenchyme (POM), which originates from neural crest cells (NCCs), while the stratified corneal epithelium develops from the surface ectoderm. Activating protein-2ß (AP-2ß) is highly expressed in the POM and important for anterior segment development. Using a mouse model in which AP-2ß is conditionally deleted in the NCCs (AP-2ß NCC KO), we investigated resulting corneal epithelial abnormalities. Through PAS and IHC staining, we observed structural and phenotypic changes to the epithelium associated with AP-2ß deletion. In addition to failure of the mutant epithelium to stratify, we also observed that Keratin-12, a marker of the differentiated epithelium, was absent, and Keratin-15, a limbal and conjunctival marker, was expanded across the central epithelium. Transcription factors PAX6 and P63 were not observed to be differentially expressed between WT and mutant. However, growth factor BMP4 was suppressed in the mutant epithelium. Given the non-NCC origin of the epithelium, we hypothesize that the abnormalities in the AP-2ß NCC KO mouse result from changes to regulatory signaling from the POM-derived stroma. Our findings suggest that stromal pathways such as Wnt/ß-Catenin signaling may regulate BMP4 expression, which influences cell fate and stratification.

Expansion of Human Limbal Epithelial Stem/Progenitor Cells Using Different Human Sera: A Multivariate Statistical Analysis.

Transplantation of human cultured limbal epithelial stem/progenitor cells (LESCs) has demonstrated to restore the integrity and functionality of the corneal surface in about 76% of patients with limbal stem cell deficiency. However, there are different protocols for the expansion of LESCs, and many of them use xenogeneic products, being a risk for the patients' health. We compared the culture of limbal explants on the denuded amniotic membrane in the culture medium-supplemental hormone epithelial medium (SHEM)-supplemented with FBS or two differently produced human sera. Cell morphology, cell size, cell growth rate, and the expression level of differentiation and putative stem cell markers were examined. Several bioactive molecules were quantified in the human sera. In a novel approach, we performed a multivariate statistical analysis of data to investigate the culture factors, such as differently expressed molecules of human sera that specifically influence the cell phenotype. Our results showed that limbal cells cultured with human sera grew faster and contained similar amounts of small-sized cells, higher expression of the protein p63α, and lower of cytokeratin K12 than FBS cultures, thus, maintaining the stem/progenitor phenotype of LESCs. Furthermore, the multivariate analysis provided much data to better understand the obtaining of different cell phenotypes as a consequence of the use of different culture methodologies or different culture components.

Keratin 12 missense mutation induces the unfolded protein response and apoptosis in Meesmann epithelial corneal dystrophy.

Meesmann epithelial corneal dystrophy (MECD) is a rare autosomal dominant disorder caused by dominant-negative mutations within the KRT3 or KRT12 genes, which encode the cytoskeletal protein keratins K3 and K12, respectively. To investigate the pathomechanism of this disease, we generated and phenotypically characterized a novel knock-in humanized mouse model carrying the severe, MECD-associated, K12-Leu132Pro mutation. Although no overt changes in corneal opacity were detected by slit-lamp examination, the corneas of homozygous mutant mice exhibited histological and ultrastructural epithelial cell fragility phenotypes. An altered keratin expression profile was observed in the cornea of mutant mice, confirmed by western blot, RNA-seq and quantitative real-time polymerase chain reaction. Mass spectrometry (MS) and immunohistochemistry demonstrated a similarly altered keratin profile in corneal tissue from a K12-Leu132Pro MECD patient. The K12-Leu132Pro mutation results in cytoplasmic keratin aggregates. RNA-seq analysis revealed increased chaperone gene expression, and apoptotic unfolded protein response (UPR) markers, CHOP and Caspase 12, were also increased in the MECD mice. Corneal epithelial cell apoptosis was increased 17-fold in the mutant cornea, compared with the wild-type (P < 0.001). This elevation of UPR marker expression was also observed in the human MECD cornea. This is the first reporting of a mouse model for MECD that recapitulates the human disease and is a valuable resource in understanding the pathomechanism of the disease. Although the most severe phenotype is observed in the homozygous mice, this model will still provide a test-bed for therapies not only for corneal dystrophies but also for other keratinopathies caused by similar mutations.

Human aniridia limbal epithelial cells lack expression of keratins K3 and K12.

Aniridia is a rare disease of the eye that affects the iris, lens and the cornea. In about 90% of the cases, patients showed a loss of PAX6 function. Patients with aniridia often develop aniridia-related keratopathy (ARK), due to limbal stem cell insufficiency. The aim of this study was to determine the differentiation status of limbal epithelial cells (LECs) in patients with ARK. Epithelial cells were isolated from the limbus region of two patients with aniridia and cultured in KSFM medium supplemented with EGF and BPE. Normal cells were obtained from limbus region of cadaveric control patients. Cells were analyzed with RT-PCR, qPCR and Western blot to evaluate expression of the developmental transcription factor, PAX6, potential stem cell markers, ΔNp63α and ABCG2, and corneal differentiation markers, keratin 12 (K12) and K3. Conjunctival differentiation markers, keratin 13 (K13) and K19 were also investigated. Cells were immunostained to evaluate K3, PAX6, and p63α protein expression. Protein coding sequence of PAX6 from patient LEC-cDNA was cloned and sequenced. RT-PCR showed that K3 and K12 transcripts were absent from patient cells, but present in healthy control preparations. Transcription levels of PAX6, ABCG2, and p63α of aniridia patients show no differences compared to normal control cells. Western blot showed reduced PAX6, protein levels in aniridia-LECs compared to control-LECs. Immunostaining also showed reduced PAX6 and K3 expression in aniridia-LECs compared to control-LECs. One aniridia patient showed a loss of stop codon in half of the cloned transcripts. In the second aniridia patient mRNA degradation through nonsense mediated decay seems to be very likely since we could not identify the mutation c.174C > T (Refseq. NM_000280), or misspliced transcripts in cDNA. We identified decreased PAX6 protein levels in aniridia patients in addition to decreased K12 mRNA levels compared to control cells. This result indicates an altered differentiation of limbal epithelial cells of aniridia patients. Further studies are necessary to evaluate the mechanism of differentiation of limbal epithelial cells in aniridia.

Mutation analysis of TGFBI and KRT12 in a case of concomitant keratoconus and granular corneal dystrophy.

PURPOSE: This study is to summarize the concurrent keratoconus (KC) and granular corneal dystrophy (GCD) phenotype and identify the underlying genetic cause in a 23-year-old male patient. METHODS: A detailed family history and clinical data from the patient and his parents were collected by ophthalmologic examination. The candidate genes were captured and sequenced by targeted next-generation sequencing, and the results were confirmed by Sanger sequencing. RESULTS: The proband was clinically diagnosed as a case of concurrent KC and GCD, which is a very rare presentation. His father and grandmother were diagnosed as GCD in both eyes. There was no character of KC in his father's and grandmother's eyes. A heterozygous TGFBI mutation in exon 4 (c.370G > A) was identified in the proband, which was predicted to generate a missense mutation (p.R124H). The mutation also existed in his father and grandmother. A heterozygous KRT12 mutation in exon 8 (c.1456-1457ins GTA) was identified in the proband, which was predicted to generate an insert mutation and created a premature termination codon. The mutation did not exist in his father and grandmother. The two mutations did not exist in his mother and 200 unrelated normal controls. CONCLUSIONS: KC can co-exist with GCD. The missense mutation (c.370G > A) in the TGFBI gene and insert mutation (c.1456-1457ins GAT) in the KRT12 gene were identified in a 23-year-old male patient with concurrent KC and GCD.

CRISPR/Cas9 DNA cleavage at SNP-derived PAM enables both in vitro and in vivo KRT12 mutation-specific targeting.

CRISPR/Cas9-based therapeutics hold the possibility for permanent treatment of genetic disease. The potency and specificity of this system has been used to target dominantly inherited conditions caused by heterozygous missense mutations through inclusion of the mutated base in the short-guide RNA (sgRNA) sequence. This research evaluates a novel approach for targeting heterozygous single-nucleotide polymorphisms (SNPs) using CRISPR/Cas9. We determined that a mutation within KRT12, which causes Meesmann's epithelial corneal dystrophy (MECD), leads to the occurrence of a novel protospacer adjacent motif (PAM). We designed an sgRNA complementary to the sequence adjacent to this SNP-derived PAM and evaluated its potency and allele specificity both in vitro and in vivo. This sgRNA was found to be highly effective at reducing the expression of mutant KRT12 mRNA and protein in vitro. To assess its activity in vivo we injected a combined Cas9/sgRNA expression construct into the corneal stroma of a humanized MECD mouse model. Sequence analysis of corneal genomic DNA revealed non-homologous end-joining repair resulting in frame-shifting deletions within the mutant KRT12 allele. This study is the first to demonstrate in vivo gene editing of a heterozygous disease-causing SNP that results in a novel PAM, further highlighting the potential for CRISPR/Cas9-based therapeutics.

Remodeling of epithelial cells and basement membranes in a corneal deficiency model with long-term follow-up.

The ocular surface consists of the cornea, conjunctiva, and the limbus that is located in the transitional zone between the cornea and conjunctiva. The corneal epithelial cells are generated through the mitosis of corneal epithelial stem cells in the limbus. This study investigated a rabbit corneal deficiency model prepared by the surgical removal of the corneal and limbal epithelia, which express cytokeratin 12 (K12). After the surgery, K13-expressing conjunctival epithelium migrated onto the corneal surface and completely covered the surface, leading to neovascularization and corneal opacification. However, at 24 and 48 weeks after the surgery, K12-expressing cornea-like cells reappeared on the model ocular surface. These cells formed an island surrounded by invaded conjunctiva and were isolated from the limbus. Interestingly, in the 24-week model surface, α1(IV) and α2(IV) collagen chains, which are normally found in the basement membrane of the native limbus and conjunctiva, and not in the cornea, were continuously deposited throughout the entire basement membrane, including the basement membrane under cornea-like cells. By contrast, in the 48-week model surface, α1(IV) and α2(IV) collagen chains were absent from the basement membrane beneath the central part of cornea-like cells and were localized below the invaded conjunctiva and the transitional zone between cornea-like cells and the invaded conjunctiva, which had similar distribution to the native ocular basement membrane. Moreover, K12, K14, p63, vimentin, and α1(IV) and α2(IV) collagen chains, which are colocalized in the native limbus, were all present at the transitional zone of the 48-week model surface. Therefore, a limbus-like structure appeared to be reconstructed on the surface of the 48-week model as a stem cell niche. This study should aid in the understanding of human corneal deficiency, the correlation between the epithelial cell phenotype and the composition of the basement membrane, and the epithelial stem cell niche.

Identification of presumed pathogenic KRT3 and KRT12 gene mutations associated with Meesmann corneal dystrophy.

PURPOSE: To report potentially pathogenic mutations in the keratin 3 (KRT3) and keratin 12 (KRT12) genes in two individuals with clinically diagnosed Meesmann corneal dystrophy (MECD). METHODS: Slit-lamp examination was performed on the probands and available family members to identify characteristic features of MECD. After informed consent was obtained, saliva samples were obtained as a source of genomic DNA, and screening of KRT3 and KRT12 was performed. Potentially pathogenic variants were screened for in 200 control chromosomes. PolyPhen-2, SIFT, and PANTHER were used to predict the functional impact of identified variants. Short tandem repeat genotyping was performed to confirm paternity. RESULTS: Slit-lamp examination of the first proband demonstrated bilateral, diffusely distributed, clear epithelial microcysts, consistent with MECD. Screening of KRT3 revealed a heterozygous missense variant in exon 1, c.250C>T (p.(Arg84Trp)), which has a minor allele frequency of 0.0076 and was not identified in 200 control chromosomes. In silico analysis with PolyPhen-2 and PANTHER predicted the variant to be damaging to protein function; however, SIFT analysis predicted tolerance of the variant. The second proband demonstrated bilateral, diffusely distributed epithelial opacities that appeared gray-white on direct illumination and translucent on retroillumination. Neither parent demonstrated corneal opacities. Screening of KRT12 revealed a novel heterozygous insertion/deletion variant in exon 6, c.1288_1293delinsAGCCCT (p.(Arg430_Arg431delinsSerPro)). This variant was not present in either of the proband's parents or in 200 control chromosomes and was predicted to be damaging by PolyPhen-2, PANTHER, and SIFT. Haplotype analysis confirmed paternity of the second proband, indicating that the variant arose de novo. CONCLUSIONS: We present a novel KRT12 mutation, representing the first de novo mutation and the first indel in KRT12 associated with MECD. In addition, we report a variant of uncertain significance in KRT3 in an individual with MECD. Although the potential pathogenicity of this variant is unknown, it is the first variant affecting the head domain of K3 to be reported in an individual with MECD and suggests that disease-causing variants associated with MECD may not be restricted to primary sequence alterations of either the helix-initiation or helix-termination motifs of K3 and K12.

In Vivo Confocal Microscopy 1 Year after Autologous Cultured Limbal Stem Cell Grafts.

PURPOSE: To correlate clinical, impression cytologic, and in vivo confocal microscopy findings on the corneal surface after cultured limbal stem cell transplantation. DESIGN: Prospective, interventional, noncomparative, masked case series. PARTICIPANTS: Thirteen patients with limbal stem cell deficiency after unilateral (9 eyes) or bilateral (2 eyes) chemical burn, liquid nitrogen injury (1 eye), or herpes simplex virus infection (1 eye). METHODS: Limbal cells were harvested from healthy or less affected eyes, cultured on 3T3 cells and fibrin glue, and transplanted to the patient's injured eye. Patients underwent clinical examination and impression cytologic examination of the central cornea before and 1 year after intervention. In vivo confocal microscopy scans were obtained in all corneal quadrants after 1 year. The interexamination agreement was established by calculation of the Cohen's κ coefficient. MAIN OUTCOME MEASURES: Results of surgery were assessed considering clinical signs (successful: restoration of transparent, avascular, and stable corneal epithelium without neovascularization in central corneal surface; partially successful: recurrence of superficial neovascularization; failed: recurrent epithelial defects, pannus, and inflammation), phenotype of cells covering the corneal surface (conjunctivalized corneal surface: cytokeratin 12 [cK12]-negative and mucin 1 [MUC1]-positive cells; mixed epithelium: cK12-positive and MUC1-positive cells; corneal epithelium: cK12-positive and MUC1-negative cells), and cell morphologic features (corneal epithelium: multilayered polygonal and flat cells with hyperreflective nuclei; conjunctival epithelium: stratified cuboidal or polygonal cells, hyperreflective cytoplasm, and barely defined borders; epithelial transition: transition of epithelial cells from the cornea to the conjunctiva over the corneal surface). RESULTS: We found a moderate to substantial degree of concordance between confocal microscopy and clinical evaluation (κ = 0.768) and between confocal microscopy and impression cytologic analysis (κ = 0.629). Confocal microscopy showed that 46.2% of patients exhibited corneal epithelium in the central and peripheral cornea, 30.8% showed an irregular mixed corneal and conjunctival epithelium, and 23.0% showed conjunctival epithelium. Palisades of Vogt were absent in all (100.0%) patients, and the cornea-conjunctiva epithelial transition localized approximately 1 mm internally on the cornea. CONCLUSIONS: Confocal microscopy provides objective measures of the corneal epithelium and may significantly improve the evaluation of outcomes after cultured limbal stem cell graft.

Comparison of techniques for corneal epithelium cell culture for the collection of conditioned medium.

PURPOSES: To determine the best protocol in obtaining the higher yield of conditioned culture medium to be used for the bone marrow mesenchymal stem cell differentiation into corneal epithelial cells, five techniques for the primary culture of human corneal epithelial cells were evaluated. METHODS: The studied culture techniques of corneal epithelial cells were: explants in culture flasks with and without hydrophilic surface treatment, on amniotic membrane, with enzymatic digestion, and by corneal scraping. The conditioned culture medium collected from these cultures was used to differentiate human bone marrow mesenchymal stem cells into corneal epithelial cells, which were characterized using flow cytometry with pan-cytokeratin and the corneal-specific markers, cytokeratin 3 and cytokeratin 12. RESULTS: The culture technique using flasks with hydrophilic surface treatment resulted in the highest yield of conditioned culture medium. Flasks without surface treatment resulted to a very low success rate. Enzymatic digestion and corneal scraping showed contamination with corneal fibroblasts. The culture on amniotic membranes only allowed the collection of culture medium during the 1st cell confluence. The effectiveness of cell differentiation was confirmed by cytometry analysis using the collected conditioned culture medium, as demonstrated by the expressions of cytokeratin 3 (95.3%), cytokeratin 12 (93.4%), and pan-cytokeratin (95.3%). CONCLUSION: The culture of corneal epithelial cell explants in flasks with hydrophilic surface treatment is the best technique for collecting a higher yield of conditioned culture medium to be used to differentiate mesenchymal stem cells.

Ex vivo expanded autologous limbal epithelial cells on amniotic membrane using a culture medium with human serum as single supplement.

In patients with limbal stem cell deficiency (LSCD), transplantation of ex vivo expanded human limbal epithelial cells (HLECs) can restore the structural and functional integrity of the corneal surface. However, the protocol for cultivation and transplantation of HLECs differ significantly, and in most protocols growth additives such as cholera toxins, exogenous growth factors, hormones and fetal calf serum are used. In the present article, we compare for the first time human limbal epithelial cells (HLECs) cultivated on human amniotic membrane (HAM) in a complex medium (COM) including fetal bovine serum to a medium with human serum as single growth supplement (HSM), and report on our first examinations of HLECs expanded in autologous HSM and used for transplant procedures in patients with LSCD. Expanded HLECs were examined by genome-wide microarray, RT-PCR, Western blotting, and for cell viability, morphology, expression of immunohistochemical markers and colony forming efficiency. Cultivation of HLECs in HSM produced a multilayered epithelium where cells with markers associated with LESCs were detected in the basal layers. There were few transcriptional differences and comparable cell viability between cells cultivated in HSM and COM. The p63 gene associated with LESCs were expressed 3.5 fold more in HSM compared to COM, and Western blotting confirmed a stronger p63α band in HSM cultures. The cornea-specific keratin CK12 was equally found in both culture conditions, while there were significantly more CK3 positive cells in HSM. Cells in epithelial sheets on HAM remaining after transplant surgery of patients with LSCD expressed central epithelial characteristics, and dissociated cells cultured at low density on growth-arrested fibroblasts produced clones containing 21 ± 12% cells positive for p63α (n = 3). In conclusion, a culture medium without growth additives derived from animals or from animal cell cultures and with human serum as single growth supplement may serve as an equivalent replacement for the commonly used complex medium for ex vivo expansion of HLECs on HAM.

Pluripotin enhances the expansion of rabbit limbal epithelial stem/progenitor cells in vitro.

This study was designed to demonstrate the effects of pluripotin on the proliferation, senescence and colony formation efficiency of rabbit limbal epithelial cells (RLECs) in vitro. Rabbit primary limbal epithelial cells were harvested and cultured in the presence of pluripotin. The cell proliferation was measured using the 3-(4,5)-dimethylthiahiazo(-z-y1)-3 5-di-phenytetrazoliumromide (MTT) assay and was also observed by confocal microscopy with Ki67 staining, whereas cell senescence was detected by senescence-associated ß-galactosidase (SA-ß-gal) staining. The colony morphology, colony-forming efficiency and colony size were observed and compared. The characteristics of the proliferating cells were examined by immunofluorescent staining using antibodies against deltaNP63, ABCG2 and Keratin 3/12. The results showed that pluripotin significantly promoted the proliferation of RLECs and increased the dividing cells with positive Ki67 staining at the concentrations lower than 400 nM. The colony-forming efficiency increased from 13.5% in the control cells to 26.4% in the 200 or 400 nM pluripotin-treated cells. The number of colonies of moderate size (600-900 µm) increased significantly in the presence of pluripotin (above 60.0% at 200 nM or 400 nM) compared with the untreated normal cells (18.6%), whereas the number of small-sized colonies (<600 µm) decreased from 79.5% for the control cells to lower than 35.0% at 200 nM or 400 nM pluripotin. Moreover, the cells treated with pluripotin stained negative with SA-ß-gal, while the untreated cells showed visible positive staining. Immunofluorescent staining suggested that the pluripotin treatment resulted in higher positive staining for the limbal stem cell markers (deltaNP63 and ABCG2) and down-regulated of differentiated corneal epithelial cell marker (Keratin 3/12). This study confirmed that the small molecular compound pluripotin promoted the proliferation of rabbit limbal epithelial cells by improving the expansion of limbal stem/progenitor cells in vitro.

Keratin 13 is a more specific marker of conjunctival epithelium than keratin 19.

PURPOSE: To evaluate the expression patterns of cytokeratin (K) 12, 13, and 19 in normal epithelium of the human ocular surface to determine whether K13 could be used as a marker for conjunctival epithelium. METHODS: Total RNA was isolated from the human conjunctiva and central cornea. Those transcripts that had threefolds or higher expression levels in the conjunctiva than the cornea were identified using microarray technique. Expression levels of three known signature genes and of two conjunctival genes, K13 and K19 were confirmed by using quantitative real-time PCR (qRT-PCR). Protein expression of K12, K13, and K19 was confirmed by immunostaining with specific antibodies on histologic sections of human sclerocornea that contained the conjunctiva, limbus, and cornea and on impression cytology (IC) specimens of the cornea and conjunctiva from normal donors. Double staining of K13/K12 and K19/K12 on histologic sections and IC specimens was performed. RESULTS: There were 337 transcripts that were preferentially expressed in the conjunctiva. K13 and K19 were among the top twenty transcripts in the conjunctiva and this preferential expression pattern of K13 and K19 was confirmed by qRT-PCR. Immunohistochemical studies showed that K13 was expressed at the posterior limbal epithelium and conjunctival epithelium but was totally absent in the cornea. K12 was expressed in the corneal and anterior limbal epithelia except for the basal layer and was absent from the conjunctiva. In contrast, K19 was detected in the corneal, limbal and conjunctival epithelia. Immunostaining of the IC specimens showed K12(+) epithelial cells in the corneal region, K13(+) cells in the conjunctival area, and K19(+) cells in the corneal and conjunctival specimens. Expression of K13 and K12 on the ocular surface was mutually exclusive on both the histologic and IC samples using double immunostaining. CONCLUSIONS: K13 is more specific to the conjunctival epithelial cells than K19 and potentially could be used as a marker to identify conjunctival epithelial cells in limbal stem cell deficiency.

Limbal fibroblast conditioned media: a non-invasive treatment for limbal stem cell deficiency.

PURPOSE: Limbal fibroblasts are known to regulate the maintenance and differentiation of the corneal epithelium including the limbal epithelial stem cells. This study examined the effect of limbal fibroblast conditioned media in a mouse model of limbal stem cell deficiency. METHODS: Limbal stem cell deficiency was created in C57/Bl6 mice by performing a limbus to limbus epithelial debridement. The mice were treated topically for 3 weeks with conditioned media derived from human limbal fibroblasts. The control mice were treated with skin fibroblast conditioned media or Dulbecco's serum-free medium. RESULTS: The mice treated with limbal fibroblast conditioned media demonstrated substantial growth of corneal type epithelial cells on the corneal surface with less conjunctival goblet cells. By contrast, the control treated corneas were found to be covered primarily by conjunctival type epithelium. CONCLUSIONS: Cell culture media conditioned by limbal fibroblasts appear to contain factor(s) that are therapeutically beneficial in a model of limbal stem cell deficiency. The current results further support the notion that the essential limbal stem cell niche is provided by limbal fibroblasts and suggest a new, non-invasive option in the treatment of limbal stem cell deficiency.

Coexistence of Meesmann Corneal Dystrophy and a Pseudo-Unilateral Lattice Corneal Dystrophy in a Patient With a Novel Pathogenic Variant in the Keratin K3 Gene: A Case Report.

PURPOSE: This study aims to clinically and genetically report a case of coexisting Meesmann corneal dystrophy (MECD) and pseudo-unilateral lattice corneal dystrophy (LCD). METHODS: Clinical characterization was supported by a complete ophthalmological evaluation, including visual acuity measurement and slit-lamp examination. Molecular diagnosis was performed by whole-exome sequencing analyzing the gelsolin, keratin K3 (KRT3), keratin K12, and transforming growth factor-beta-induced genes. RESULTS: A 57-year-old woman presented with recurrent corneal erosions over 17 years and visual impairment in both eyes. Ophthalmological evaluation revealed multiple central tiny cysts in the epithelium of both eyes and lattice linear lesions only in the right cornea. In both eyes, a corneal posterior crocodile shagreen degeneration could also be observed. These findings were compatible with a MECD and a unilateral LCD. Molecular analysis identified the novel heterozygous nucleotide substitution c.1492G>A (amino acid change p.Glu498Lys) in the KRT3 gene, in cosegregation with the MECD familial phenotype. However, no genetic evidence supported the unique LCD phenotype observed in the patient. CONCLUSIONS: To the best of our knowledge, this is the first report of a pseudo-unilateral LCD in a patient with coexistent MECD. Moreover, the genetic analysis showed a novel mutation in the previously MECD-associated gene KRT3.

Identification of a novel mutation in the cornea specific keratin 12 gene causing Meesmann's corneal dystrophy in a German family.

PURPOSE: To report a novel missense mutation of the cornea specific keratin 12 (KRT12) gene in two generations of a German family diagnosed with Meesmann;s corneal dystrophy. METHODS: Ophthalmologic examination of the proband and sequencing of keratin 3 (KRT3) and KRT12 of the proband and three other family members were performed. Restriction enzyme analysis was used to confirm the detected mutation in affected individuals of the family. RESULTS: Slit-lamp biomicroscopy of the proband revealed multiple intraepithelial microcysts comparable to a Meesmann dystrophy phenotype. A novel heterozygous A-->G transversion at the first nucleotide position of codon 129 (ATG>GTG, M129V) in exon 1 of KRT12 was detected in the proband, her two affected sons but not in her unaffected husband or 50 control individuals. CONCLUSIONS: We have identified a novel missense mutation within the highly conserved helix-initiation motif of KRT12 causing Meesmann;s corneal dystrophy in a German family.

Long-term phenotypic study after allogeneic cultivated corneal limbal epithelial transplantation for severe ocular surface diseases.

PURPOSE: To determine the long-term epithelial lineage of origin of surgically removed grafts after allogeneic cultivated corneal limbal epithelial transplantation (CLET). DESIGN: Interventional case reports. PARTICIPANTS: We studied 2 eyes from 2 patients with total corneal stem cell destruction; 1 eye was from a patient with Stevens-Johnson syndrome and 1 eye had sustained chemical injury. METHODS: Allogeneic cultivated corneal limbal epithelial sheets on human amniotic membrane (AM) were transplanted onto the ocular surface. Regrafting (1 eye, 42 months later) or penetrating keratoplasty (1 eye, 75 months later) were performed after the initial transplantation procedure for further visual rehabilitation. MAIN OUTCOME MEASURES: The excised grafts were subjected to clinical evaluation and to light- and transmission electron microscopy (TEM) examination and to immunohistochemical analysis. RESULTS: In clinically conjunctival grafts, TEM and immunohistochemical analysis disclosed only small areas where the original cultivated corneal epithelial cells persisted. Neighboring conjunctival epithelial cells had apparently invaded a large portion of the corneal surface (keratin 3/12(-), Muc5ac(+)). In clinically corneal grafts, transplanted allogeneic cultivated corneal epithelial cells clearly survived for a long period of time (keratin 3/12(+), Muc5ac(-)); there was no infiltration by inflammatory cells, nor was there dissolution of the AM substrate. CONCLUSIONS: We theorize that the process of graft opacification after allogeneic CLET is responsible for the loss of transplanted cultivated corneal epithelial cells and that this is followed by conjunctival cell invasion onto the corneal surface. The results of this study confirmed that in the clinically evaluated corneal graft, transplanted cultivated corneal epithelial cells indeed survived for a long period of time on the corneal surface and maintained ocular surface integrity, even though the transplanted cells were allogeneic.

Development of the cornea of true moles (Talpidae): morphogenesis and expression of PAX6 and cytokeratins.

Corneal development and structure were studied in the Iberian mole Talpa occidentalis, which has permanently closed eyelids, and the European mole Talpa europaea, in which the eyes are open. The vertebrate cornea typically maintains a three-layered structure - a stratified epithelium with protective and sensory function, an avascular, hypocellular, collagenous stroma, and an endothelium with both barrier and transport functions that regulates corneal hydration, hence maintaining transparency. Compared to mouse, both mole species had significant corneal specializations, but the Iberian mole had the most divergent phenotype, with no endothelium and a flattened monolayer epithelium. Nevertheless, normal epithelial cell junctions were observed and corneal transparency was maintained. Corneas of European moles have a dysmorphic phenotype that recapitulates the human disorder keratoconus for which no mouse model exists. Mole corneas are vascularized - a situation only previously observed in the manatee Trichechus- and have non-radial patterns of corneal innervation indicative of failure of corneal epithelial cell migration. The transcription factor Pax6 is required for corneal epithelial differentiation in mice, but was found to be dispensable in moles, which had mosaic patterns of PAX6 localization uniquely restricted, in European moles, to the apical epithelial cells. The apparently stalled or abnormal differentiation of corneas in adult moles is supported by their superficial similarity to the corneas of embryonic or neonatal mice, and their abnormal expression of cytokeratin-12 and cytokeratin-5. European moles seem to have maintained some barrier/protective function in their corneas. However, Iberian moles show a more significant corneal regression likely related to the permanent eyelid fusion. In this mole species, adaptation to the arid, harder, Southern European soils could have favoured the transfer of these functions to the permanently sealed eyelids.