Targeting Type I IFN/STAT1 signaling inhibited and reversed corneal squamous metaplasia in Aire-deficient mouse

Corneal transparency and integrity are essential for obtaining good vision; nevertheless, squamous metaplasia (SQM) of ocular epithelium is a kind of serious blinding corneal diseases, without therapeutic medication in clinic. Here, we found that deficiency of the autoimmune regulator (AIRE) in corneas spontaneously developed corneal plaques. Using corneal abrasion model, we revealed that deletion of Aire not only resulted in delayed corneal re-epithelialization, but also promoted a cell-fate transition from transparent corneal epithelium to keratinized epithelium, histopathologically characterized with SQM based on the transcriptomic analysis. Mechanistically, Aire-deficient corneas led to the heightened Type I interferon (IFN-I)/STAT1 signaling after abrasion. Pharmacological blockade of IFN-I/JAK/STAT1 signaling in Aire-knockout (KO) corneas not only accelerated epithelial wound healing, but also alleviated corneal plaques and SQM. Collectively, our findings revealed critical roles of AIRE in governing corneal epithelial homeostasis and pathologic keratinization, and further identified IFN-I/STAT1 signaling as a potential target for treating ocular surface diseases with SQM, and even for treating pathological scenarios related to SQM in other tissues.

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.

Abnormal corneal epithelial maintenance in mice heterozygous for the micropinna microphthalmia mutation Mp

We investigated the corneal morphology of adult Mp/+ mice, which are heterozygous for the micropinna microphthalmia mutation, and identified several abnormalities, which implied that corneal epithelial maintenance was abnormal. The Mp/+ corneal epithelium was thin, loosely packed and contained goblet cells in older mice. Evidence also suggested that the barrier function was compromised. However, there was no major effect on corneal epithelial cell turnover and mosaic patterns of radial stripes indicated that radial cell movement was normal. Limbal blood vessels formed an abnormally wide limbal vasculature ring, K19-positive cells were distributed more widely than normal and K12 was weakly expressed in the peripheral cornea. This raises the possibilities that the limbal-corneal boundary was poorly defined or the limbus was wider than normal. BrdU label-retaining cell numbers and quantitative clonal analysis suggested that limbal epithelial stem cell numbers were not depleted and might be higher than normal. However, as corneal epithelial homeostasis was abnormal, it is possible that Mp/+ stem cell function was impaired. It has been shown recently that the Mp mutation involves a chromosome 18 inversion that disrupts the Fbn2 and Isoc1 genes and produces an abnormal, truncated fibrillin-2^MP protein. This abnormal protein accumulates in the endoplasmic reticulum (ER) of cells that normally express Fbn2 and causes ER stress. It was also shown that Fbn2 is expressed in the corneal stroma but not the corneal epithelium, suggesting that the presence of truncated fibrillin-2^MP protein in the corneal stroma disrupts corneal epithelial homeostasis in Mp/+ mice.

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Heterozygous mutant Mp/+ mice have small, abnormal eyes.

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The corneal epithelium is thin, loosely packed and has goblet cells.

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Corneal epithelial cell turnover and radial cell movement appear normal.

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The cornea-limbal border is poorly defined and the limbus appears wider than normal.

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Indirect tests suggest stem cells are not depleted and numbers might be increased.

Limbal stem cells: Central concepts of corneal epithelial homeostasis

A strong cohort of evidence exists that supports the localisation of corneal stem cells at the limbus. The distinguishing characteristics of limbal cells as stem cells include slow cycling properties, high proliferative potential when required, clonogenicity, absence of differentiation marker expression coupled with positive expression of progenitor markers, multipotency, centripetal migration, requirement for a distinct niche environment and the ability of transplanted limbal cells to regenerate the entire corneal epithelium. The existence of limbal stem cells supports the prevailing theory of corneal homeostasis, known as the XYZ hypothesis where X represents proliferation and stratification of limbal basal cells, Y centripetal migration of basal cells and Z desquamation of superficial cells. To maintain the mass of cornea, the sum of X and Y must equal Z and very elegant cell tracking experiments provide strong evidence in support of this theory. However, several recent studies have suggested the existence of oligopotent stem cells capable of corneal maintenance outside of the limbus. This review presents a summary of data which led to the current concepts of corneal epithelial homeostasis and discusses areas of controversy surrounding the existence of a secondary stem cell reservoir on the corneal surface