ALDH3A1 Plays a Functional Role in Maintenance of Corneal Epithelial Homeostasis

Aldehyde Dehydrogenase and Aldo-Keto Reductase Enzymes: Basic Concepts and Emerging Roles in Diabetic Retinopathy

Diabetic retinopathy (DR) is a complication of diabetes mellitus that can lead to vision loss and blindness. It is driven by various biochemical processes and molecular mechanisms, including lipid peroxidation and disrupted aldehyde metabolism, which contributes to retinal tissue damage and the progression of the disease. The elimination and processing of aldehydes in the retina rely on the crucial role played by aldehyde dehydrogenase (ALDH) and aldo-keto reductase (AKR) enzymes. This review article investigates the impact of oxidative stress, lipid-derived aldehydes, and advanced lipoxidation end products (ALEs) on the advancement of DR. It also provides an overview of the ALDH and AKR enzymes expressed in the retina, emphasizing their growing importance in DR. Understanding the relationship between aldehyde metabolism and DR could guide innovative therapeutic strategies to protect the retina and preserve vision in diabetic patients. This review, therefore, also explores various approaches, such as gene therapy and pharmacological compounds that have the potential to augment the expression and activity of ALDH and AKR enzymes, underscoring their potential as effective treatment options for DR.

Investigating the Functional Roles of Aldehyde Dehydrogenase 3A1 in Human Corneal Epithelial Cells

Aldehyde dehydrogenase 3A1 (ALDH3A1) oxidizes medium-chain aldehydes to their corresponding carboxylic acids. It is expressed at high rates in the human cornea, where it has been characterized as a multi-functional protein displaying various cytoprotective modes of action. Previous studies identified its association with the DNA damage response (DDR) pathway. Here, we utilized a stable transfected HCE-2 (human corneal epithelium) cell line expressing ALDH3A1, to investigate the molecular mechanisms underlying the cytoprotective role(s) of ALDH3A1. Our data revealed morphological differences among the ALDH3A1-expressing and the mock-transfected HCE-2 cells accompanied by differential expression of E-cadherin. Similarly, the ALDH3A1/HCE-2 cells demonstrated higher mobility, reduced proliferation, upregulation of ZEB1, and downregulation of CDK3, and p57. The expression of ALDH3A1 also affected cell cycle progression by inducing the sequestration of HCE-2 cells at the G2/M phase. Following 16 h cell treatments with either H₂O₂ or etoposide, a significantly lower percentage of ALDH3A1/HCE-2 cells were apoptotic compared to the respective treated mock/HCE-2 cells. Interestingly, the protective effect of ALDH3A1 expression under these oxidative and genotoxic conditions was accompanied by a reduced formation of γ-H2AX foci and higher levels of total and phospho (Ser15) p53. Finally, ALDH3A1 was found to be localized both in the cytoplasm and the nucleus of transfected HCE-2 cells. Its cellular compartmentalization was not affected by oxidant treatment, while the mechanism by which ALDH3A1 translocates to the nucleus remains unknown. In conclusion, ALDH3A1 protects cells from both apoptosis and DNA damage by interacting with key homeostatic mechanisms associated with cellular morphology, cell cycle, and DDR.

ETS1-HMGA2 Axis Promotes Human Limbal Epithelial Stem Cell Proliferation

Purpose

This study aimed to investigate the role and molecular mechanism of ETS1 in the proliferation and differentiation of human limbal epithelial stem cells (LESCs).

Methods

RNA-seq and quantitative real-time PCR were used to determine gene expression changes when ETS1 and HMGA2 was knocked down using short-hairpin RNAs or overexpressed by lentivirus. Immunofluorescence and flow cytometry experiments were performed to assess the roles of ETS1 and HMGA2 in LESC proliferation. ETS1-bound cis-regulatory elements and target genes in LESCs were identified using chromatin immunoprecipitation sequencing. The epigenetic features of ETS1-binding sites were assessed by the published histone modification and chromatin accessibility profiles.

Results

ETS1 was robustly expressed in LESCs but dramatically reduced on differentiation into corneal epithelial cells (CECs). ETS1 knockdown in LESCs inhibited cellular proliferation and activated CEC markers (KRT3, KRT12, CLU, and ALDH3A1). When ETS1 was overexpressed during CEC differentiation, LESC-associated genes were upregulated while CEC-associated genes were downregulated. The genome-wide binding profile of ETS1 was identified in LESCs. ETS1 occupied H3K4me3-marked promoters and H3K27ac/H3K4me1-marked enhancers. ETS1-binding sites were also enriched for chromatin accessibility signal. HMGA2 showed a consistent expression pattern with ETS1. ETS1 activates HMAG2 by binding to its promoter. Knockdown and overexpression experiments suggested that HMGA2 can promote LESC proliferation and inhibits its differentiation.

Conclusions

ETS1 promotes LESC proliferation and inhibits its differentiation via activating HMGA2.

Rumen microbiota-host transcriptome interaction mediates the protective effects of trans-10, cis-12 CLA on facilitating weaning transition of lambs

Developing alternatives to antibiotics for prevention of gastrointestinal dysbiosis in early-weaning farmed animals is urgently needed. This study was to explore the potential effects of trans-10, cis-12 conjugated linoleic acid (CLA) on maintaining ruminal homeostasis of young ruminants during the weaning transition period. Thirty neonatal lambs were selected (6 lambs per group) and euthanized for rumen microbial and epithelial analysis. The lambs were weaned at 28 d and experienced the following 5 treatments: euthanized on d 28 as the pre-weaning control (CON0), fed starter feed for 5 (CON5) or 21 (CON21) d, fed starter feed with 1% of CLA supplemented for 5 (CLA5) or 21 (CLA21) d. Results showed that the average daily weight gain and dry matter intake were significantly higher in CLA5 than CON5 group. As compared with the CON5 and CON21 group, the relative abundances of volatile fatty acid (VFA) producing bacteria including Bacteroides, Treponema, Parabacteroides and Anaerovibrio, as well as the concentrations of acetate, butyrate and total VFA were significantly increased in CLA5 and CLA21 group, respectively. Integrating microbial profiling and epithelial transcriptome results showed that 7 downregulated inflammatory signaling-related host genes IL2RA, CXCL9, CD4, CCR4, LTB, SPP1, and BCL2A1 with CLA supplementation were significantly negatively correlated with both VFA concentration and VFA producing bacteria, while 3 (GPX2, SLC27A2 and ALDH3A1) and 2 (GSTM3 and GSTA1) upregulated metabolism-related genes, significantly positively correlated with either VFA concentration or VFA producing bacteria, respectively. To confirm the effects of CLA on epithelial signal transduction, in vitro experiment was further conducted by treating rumen epithelial cells without or with IL-17A + TNF-α for 12 h after pretreatment of 100 μM CLA or not (6 replicates per treatment). The results demonstrated the anti-inflammatory effect of CLA via suppressing the protein expression of NF-кB p-p65/p65 with the activation of peroxisome proliferator-activated receptor gamma (PPARγ). In conclusion, CLA supplementation enhanced the ruminal microbiota-driven transcriptional regulation in healthy rumen epithelial development via rumen VFA production, and CLA may therefore serve as an alternative way to alleviate early-weaning stress and improve physiological and metabolic conditions of young ruminants.

Identification of lncRNAs Associated with the Pathogenesis of Diabetic Retinopathy: From Sequencing Analysis to Validation via In Vivo and In Vitro Experiments

This study is aimed at screening for differentially expressed long noncoding RNAs (lncRNAs) associated with the pathogenesis of diabetic retinopathy and verifying the role of lncZNRD1 in high glucose-induced injury of retinal microvascular endothelial cells. The retinal tissues of normal and diabetic rats were collected for high-throughput sequencing of differentially expressed lncRNAs. Retinal microvascular endothelial cells were treated with 50 mM glucose for 4 h, 8 h, 24 h, 48 h, and 72 h. Our results showed that compared with the control group, there were 736 differentially expressed lncRNAs in the retina tissue of the model group, including 226 upregulated genes and 736 downregulated genes. Based on the differentially expressed lncRNAs, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that the ErbB signaling pathway, transforming growth factor- (TGF-) β signaling pathway, PI3K − Akt signaling pathway, cyclic adenosine 3,5-monophosphate (cAMP) signaling pathway, mitogen-activated protein kinase (MAPK) signaling pathway, and hypoxia-inducible factor-1 (HIF-1) signaling pathway were likely involved in the regulation of diabetic retinopathy. Compared with the control group, the expression of lncZNRD1-AS1 was significantly increased in retinal microvascular endothelial cells after treatment with high glucose for 24 h. Silencing lncZNRD1 promoted high glucose-induced apoptosis of microvascular endothelial cells. Additionally, silencing lncZNRD1 increased the expression levels of ALDH7A1 and ALDH3A2. In conclusion, lncZNRD1-AS1 demonstrated potentially beneficial function against high glucose-induced retina cell injury by regulating ALDH7A1 and ALDH3A2 expressions.

Relationship between Aldehyde Dehydrogenase, PD-L1 and Tumor-Infiltrating Lymphocytes with Pathologic Response and Survival in Breast Cancer

Aldehyde dehydrogenase 1A1 (ALDH1A1) is a cancer stem cell (CSC) marker related to clinical outcomes in breast cancer (BC). The aim of this study was to analyze the relationship between ALDH1A1, programmed death ligand 1 (PD-L1) and tumor-infiltrating lymphocytes (TILs) in triple negative (TN) and human epidermal growth factor receptor 2-positive (HER2+) BC tumors, and its association with clinicopathological characteristics and outcomes. A retrospective, historical cohort study of patients diagnosed with early or locally advanced BC treated with neoadjuvant chemotherapy was conducted. ALDH1A1, PD-L1 expression and TILs were assessed using immunohistochemistry. A total of 75 patients were analyzed (42.7% TN, 57.3% HER2+ tumors). ALDH1A1+ was related to HTILs (p = 0.005) and PD-L1+ tumors (p = 0.004). ALDH1A1+ tumors presented higher CD3+ (p = 0.008), CD4+ (p = 0.005), CD8+ (p = 0.003) and CD20+ (p = 0.006) TILs. ALDH1A1+ (p = 0.018), PD-L1+ (p = 0.004) and HTILs (p < 0.001) were related to smaller tumors. ALDH1A1+ was related to pathologic complete response (pCR) (p = 0.048). At the end of the follow-up (54.4 [38.3−87.6] months), 47 patients (62.7%) remained disease-free, and 20 (26.7%) had died. HTILs were related to improved disease-free survival (p = 0.027). ALDH1A1+ was related to PD-L1+ and HITLs, that might be related to higher pCR rates with neoadjuvant therapy.

Localization of phosphatidylinositol phosphate 5 kinase γ, phospholipase β3 and diacylglycerol kinase ζ in corneal epithelium in comparison with conjunctival epithelium of mice

Based on the theory that the phosphoinositide (PI) signal is involved in the physiology of cornea and conjunctiva, we examined the localization in the mouse anterior ocular epithelia of immunoreactivities for phosphatidylinositol 4-phosphate 5-kinase (PIP5K), phospholipase C (PLC) and diacylglycerol kinase (DGK), enzymes that work sequentially in PI cycle. Immunoreactivity for PIP5Kγ in the corneal epithelium, including the limbus, was distinct in adults in contrast to faint or negligible immunoreactivity in the conjunctival epithelium in neonatal mice. This adult localization pattern was first recognized at the postnatal time of eyelid opening. Immunoreactivity for PLCβ3 was rather equally distinct throughout the entire corneal and conjunctival epithelia in adults. DGKζ-immunoreactive nuclei were mainly localized in the basal half domain of the corneal epithelium but in both basal and apical domains of the conjunctival epithelium in adults. This nuclear immunoreactivity was at weak or negligible levels in the peripheral and limbus cornea and in a considerable portion of the bulbar conjunctival epithelium continuous with the limbus. The adult patterns for PLCβ3 and DGKζ were already present at birth. The present findings suggest the following possibilities on the functional significance of the three enzyme molecules. PIP5Kγ is involved in cornea-specific functions such as bright-field vision, including corneal transparency, and in the stability of epithelial junctions, for which there seems to be a much higher requirement in the corneal epithelium than in the conjunctival epithelium. PLCβ3 is involved from birth in as-yet undefined functions exerted ubiquitously from birth in both corneal and conjunctival epithelia. DGKζ is involved in regulation from birth of the transcription in epithelial cells, including apoptosis as well as regulation of mitosis of epithelial cells in both cornea and conjunctiva, with the transcription involvement more apparent in the conjunctiva, although it does not work in stem cells of the corneal limbus.

Aldehyde Dehydrogenases Expression in Corneal Epithelial Cells with Limbal Stem Cell Deficiency

Purpose: The purpose of the present study is to investigate the expression of aldehyde dehydrogenases (ALDHs) in rabbit corneas with limbal stem cell deficiency (LSCD) and corneas treated with cultured autologous oral mucosa epithelial cell sheet CAOMECS designed to reconstruct the ocular surface with LSCD. Methods: New Zealand white rabbit autologous oral mucosal epithelial cells were isolated from a buccal biopsy and cultured to be grafted back onto corneas of rabbit model of LSCD. Immunofluorescent staining and Western blot analysis were used to compare the expression of ALDH1A1 and ALDH1A3 in healthy, LSCD-diseased, CAOMECS treated corneas. Human oral mucosal and corneal epithelial cells (OMECS and CECs) were cultured and treated with retinoic acid (RA) to further investigate the expression of ALDHs. Results: In healthy corneas, ALDH1A1 and ALDH1A3 were markedly expressed in basal cells of corneal epithelium. In LSCD diseased corneas, ALDH1A1 and ALDH1A3 were markedly expressed in the conjunctivalized apical epithelial cells, the goblet cells, and the stroma. CAOMECS grafted corneas showed a decreased expression of ALDHs as compared to LSCD diseased corneas. Western blot analysis confirmed the up regulation of ALDH1A1 and ALDH1A3 expression in LSCD-diseased corneal epithelial cells. CAOMECS expressed low levels of ALDH1A1 and ALDH1A3, as compared to diseased CECs (D-CEC). When ALDH1A3 was up regulated by retinoic acid treatment in OMECS, Pax-6 expression was down regulated, suggesting a decrease in regenerative capacity when ALDH enzymes are up regulated. Conclusions: These findings report for the first time the up regulation of ALDH1A1 and ALDH1A3 in rabbit corneas with LSCD and document that CAOMECS grafting used to reconstruct corneal epithelium may reduce the expression levels of ALDH enzymes.

ALDH3A1 driving tumor metastasis is mediated by p53/BAG1 in lung adenocarcinoma

Lung adenocarcinoma (LUAD) is a lethal malignancy with metastasis, a major tumor feature that predominantly correlated with progression, but the molecules that mediated tumor metastasis remain elusive. To declare the critical regulatory genes, RNA sequencing data in LUAD patients was acquired from The Cancer Genome Atlas (TCGA) and found that ALDH3A1 was distinctly highly expressed in LUAD patients with metastasis (M1) compared with those without metastasis (M0), linked to the property of cancer stem cell and epithelial-mesenchymal transition (EMT). Besides, high ALDH3A1 expression predicted a poor prognosis. Knockdown of ALDH3A1 showed decreased proliferation, migration, and invasion in A549 cell line. Furthermore, BAG1 was regulated by ALDH3A1 through p53, enhanced cell proliferation, and predicted clinical prognosis. Our findings collectively uncovered a novel mechanism that orchestrates tumor cells' metastasis, and decreasing ALDH3A1 represented a potential therapeutic target for reprogramming metastasis.

A multi-ethnic genome-wide association study implicates collagen matrix integrity and cell differentiation pathways in keratoconus

Keratoconus is characterised by reduced rigidity of the cornea with distortion and focal thinning that causes blurred vision, however, the pathogenetic mechanisms are unknown. It can lead to severe visual morbidity in children and young adults and is a common indication for corneal transplantation worldwide. Here we report the first large scale genome-wide association study of keratoconus including 4,669 cases and 116,547 controls. We have identified significant association with 36 genomic loci that, for the first time, implicate both dysregulation of corneal collagen matrix integrity and cell differentiation pathways as primary disease-causing mechanisms. The results also suggest pleiotropy, with some disease mechanisms shared with other corneal diseases, such as Fuchs endothelial corneal dystrophy. The common variants associated with keratoconus explain 12.5% of the genetic variance, which shows potential for the future development of a diagnostic test to detect susceptibility to disease.

Association with Corneal Remodeling Related Genes, ALDH3A1, LOX, and SPARC Genes Variations in Korean Keratoconus Patients

Purpose

To determine whether the cornea remodeling-related genes aldehyde dehydrogenase 3A1 (ALDH3A1), lysyl oxidase (LOX), and secreted protein acidic and rich in cysteine (SPARC) were potential susceptibility candidate genes for keratoconus in Korean patients, we investigated the associations of single nucleotide polymorphisms (SNPs) in these three genes in Korean patients with keratoconus.

Methods

Genomic DNA was extracted from blood samples of unrelated patients with keratoconus and healthy control individuals. For screening of genetic variations, all exons from the entire coding regions of the ALDH3A1, LOX, and SPARC genes were directly sequenced to determine the presence of mutations. Control individuals were selected from the general population without keratoconus.

Results

In this study, we detected nine SNPs in ALDH3A1, four SNPs in LOX, and 18 SNPs in SPARC. rs116992290, IVS3-62c>t, rs116962241, and rs2228100 in ALDH3A1 and rs2956540 and rs1800449 in LOX were significantly different between patient and control groups. In the SPARC gene, the distribution of the *G allele of EX10+225 T>G (p = 0.018; odds ratio, 1.869) was strongly associated with the risk of keratoconus in the Korean population. In haplotype analysis, C-G of rs2956540-rs2288393 in LOX (p = 0.046) and C-C-G and G-G-G of rs60610024-rs2228100-rs57555435 (p = 0.021 and p < 0.001), G-A of IVS3-62 a>g - rs116962241 in ALDH3A1 (p = 0.048) predisposed significantly to keratoconus. After cross-validation consistency and permutation tests, two locus model was the best SNP variations interaction pattern.

Conclusions

Our results suggested that genetic variations in ALDH3A1, LOX, and SPARC genes were associated with a predisposition for keratoconus in Korean individuals. Moreover, variations in ALDH3A1and LOX may serve as strong biomarkers for keratoconus.

Features of p53 protein distribution in the corneal epithelium and corneal tear film

Tumor suppressor protein p53 is the key factor in the regulation of cell proliferation. Its concentration is low in the cytoplasm of most cell types. However, in corneal epithelium cells, abnormally high p53 content is detected. The aim of the present study was to characterize p53 distribution in the corneal epithelium. For this purpose, immunohistochemistry, western blot analysis and electronic microscope examinations were performed. A low level of p53 was identified in the lens, iris and retina; by contrast, a significantly high concentration of this protein was observed in the corneal epithelium. In opposite, MDM2 was identified in the lens, iris and retina while it is completely absent in the corneal epithelium. In addition, we found a significant amount of exosomes and other microvesicles containing p53 in the corneal mucin layer. We thus hypothesize that a significantly high level of p53 was caused by a combination of absents of MDM2 in parallel with p53 microvesicles storage.

Aldehyde dehydrogenase 3A1 confers oxidative stress resistance accompanied by altered DNA damage response in human corneal epithelial cells

Aldehyde dehydrogenase 3A1 is constitutively expressed in a taxon-specific manner in the cornea, where, due to its high abundance, it has been characterized as a corneal crystallin. ALDH3A1 has been proposed to be a multifaceted protein that protects cellular homeostasis through several modes of action. The present study examines the mechanisms by which ALDH3A1 exerts its cytoprotective role under conditions of oxidative stress. To this end, we have utilized an isogenic HCE-2 (human corneal epithelium) cell line pair differing in the expression of ALDH3A1. Single cell gel electrophoresis assay and H2DCFDA analysis revealed that the expression of ALDH3A1 protected HCE-2 cells from H₂O₂-, tert-butyl peroxide- and etoposide-induced oxidative and genotoxic effects. Furthermore, comparative qPCR analysis revealed that a panel of cell cycle (Cyclins B1, B2, D, E), apoptosis (p53, BAX, BCL-2, BCL-XL) and DNA damage response (DNA-PK, NBS1) genes were up-regulated in the ALDH3A1 expressing HCE-2 cells. Moreover, the expression profile of a variety of DNA damage signaling (DDS)-related genes, was investigated (under normal and oxidative stress conditions) by utilizing the RT² profiler™ PCR array in both isogenic HCE-2 cell lines. Our results demonstrated that several genes associated with ATM/ATR signaling, cell cycle regulation, apoptosis and DNA damage repair were differentially expressed under all conditions tested. In conclusion, this study suggests that ALDH3A1 significantly contributes to the antioxidant defense of corneal homeostasis by maintaining DNA integrity possibly through altering the expression of specific DDS-related genes. Further studies will shed light on the precise role(s) of this multifunctional protein.

Oxidative stress in corneal injuries of different origin: Utilization of 3D human corneal epithelial tissue model

The purpose of the current work was to utilize a three dimensional (3D) corneal epithelial tissue model to study dry eye disease and oxidative stress-related corneal epithelial injuries for the advancement of ocular therapeutics. Air-liquid interface cultures of normal human corneal epithelial cells were used to produce 3D corneal epithelial tissues appropriate for physiologically relevant exposure to environmental factors. Oxidative stress was generated by exposing the tissues to non-toxic doses of ultraviolet radiation (UV), hydrogen peroxide, vesicating agent nitrogen mustard, or desiccating conditions that stimulated morphological, cellular, and molecular changes relevant to dry eye disease. Corneal specific responses, including barrier function, tissue viability, reactive oxygen species (ROS) accumulation, lipid peroxidation, cytokine release, histology, and gene expression were evaluated. 3D corneal epithelial tissue model structurally and functionally reproduced key features of molecular responses of various types of oxidative stress-induced ocular damage. The most pronounced effects for different treatments were: UV irradiation - intracellular ROS accumulation; hydrogen peroxide exposure - barrier impairment and IL-8 release; nitrogen mustard exposure - lipid peroxidation and IL-8 release; desiccating conditions - tissue thinning, a decline in mucin expression, increased lipid peroxidation and IL-8 release. Utilizing a PCR gene array, we compared the effects of corneal epithelial damage on the expression of 84 oxidative stress-responsive genes and found specific molecular responses for each type of damage. The topical application of lubricant eye drops improved tissue morphology while decreasing lipid peroxidation and IL-8 release from tissues incubated at desiccating conditions. This model is anticipated to be a valuable tool to study molecular mechanisms of corneal epithelial damage and aid in the development of therapies against dry eye disease, oxidative stress- and vesicant-induced ocular injuries.

Spatiotemporally Controlled Ablation of Klf5 Results in Dysregulated Epithelial Homeostasis in Adult Mouse Corneas

Purpose

Corneal epithelial (CE) homeostasis requires coordination between proliferation and differentiation. Here we examine the role of cell proliferation regulator Krüppel-like factor 5 (Klf5) in adult mouse CE homeostasis.

Methods

Klf5 was ablated in a spatiotemporally restricted manner by inducing Cre expression in 8-week-old ternary transgenic Klf5LoxP/LoxP/Krt12rtTA/rtTA/Tet-O-Cre (Klf5Δ/ΔCE) mouse CE by administering doxycycline via chow. Normal chow-fed ternary transgenic siblings served as controls. The control and Klf5Δ/ΔCE corneal (1) histology, (2) cell proliferation, and (3) Klf5-target gene expression were examined using (1) periodic acid Schiff reagent-stained sections, (2) Ki67 expression, and (3) quantitative PCR and immunostaining, respectively. The effect of KLF4, KLF5, and OCT1 on gastrokine-1 (GKN1) promoter activity was determined by transient transfection in human skin keratinocyte NCTC-2544 cells.

Results

Klf5 expression was decreased to 23% of the controls in Klf5Δ/ΔCE corneas, which displayed increased fluorescein uptake, downregulation of tight junction proteins Tjp1 and Gkn1, desmosomal Dsg1a, and basement membrane Lama3 and Lamb1, suggesting defective permeability barrier. In transient transfection assays, KLF5 and OCT1 synergistically stimulated GKN1 promoter activity. Klf5Δ/ΔCE CE displayed significantly fewer cell layers and Ki67+ proliferative cells coupled with significantly decreased cyclin-D1, and elevated phospho(Ser-10) p27/Kip1 expression. Expression of Krt12, E-cadherin, and β-catenin remained unaltered in Klf5Δ/ΔCE corneas.

Conclusions

Klf5 contributes to adult mouse CE homeostasis by promoting (1) permeability barrier function through upregulation of Tjp1, Gkn1, Dsg1a, Lama3, and Lamb1, and (2) basal cell proliferation through upregulation of cyclin-D1 and suppression of phospho(Ser-10) p27/Kip1, without significantly affecting the expression of epithelial markers Krt12, E-cadherin, and β-catenin.

KLF4 Plays an Essential Role in Corneal Epithelial Homeostasis by Promoting Epithelial Cell Fate and Suppressing Epithelial-Mesenchymal Transition

Purpose

The purpose of this study was to test the hypothesis that KLF4 promotes corneal epithelial (CE) cell fate by suppressing the epithelial–mesenchymal transition (EMT), using spatiotemporally regulated CE-specific ablation of Klf4 in Klf4^Δ/ΔCE (Klf4^LoxP/LoxP/Krt12^rtTA/rtTA/Tet-O-Cre) mice.

Methods

CE-specific ablation of Klf4 was achieved by feeding Klf4^Δ/ΔCE mice with doxycycline chow. The wild-type (WT; normal chow-fed littermates) and the Klf4^Δ/ΔCE histology was compared by hematoxylin and eosin–stained sections; EMT marker expression was quantified by quantitative PCR, immunoblots, and immunofluorescent staining; and wound healing rate was measured by CE debridement using Algerbrush. KLF4 and EMT markers were quantified in human corneal limbal epithelial (HCLE) cells undergoing TGF-β1–induced EMT by quantitative PCR, immunoblots, and immunofluorescent staining.

Results

The epithelial markers E-cadherin, Krt12, claudin-3, and claudin-4 were down-regulated, whereas the mesenchymal markers vimentin, β-catenin, survivin, and cyclin-D1 and the EMT transcription factors Snail, Slug, Twist1, Twist2, Zeb1, and Zeb2 were up-regulated in the Klf4^Δ/ΔCE corneas. The Klf4^Δ/ΔCE cells migrated faster, filling 93% of the debrided area within 16 hours compared with 61% in the WT. After 7 days of wounding, the Klf4^Δ/ΔCE cells that filled the gap failed to regain epithelial characteristics, as they displayed abnormal stratification; down-regulation of E-cadherin and Krt12; up-regulation of β-catenin, survivin, and cyclin-D1; and a 2.5-fold increase in the number of proliferative Ki67⁺ cells. WT CE cells at the migrating edge and the HCLE cells undergoing TGF-β1–induced EMT displayed significant down-regulation of KLF4.

Conclusions

Collectively, these results reveal that KLF4 plays an essential role in CE homeostasis by promoting epithelial cell fate and suppressing EMT.