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

ABSTRACT: 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.

SUBMITTER: Douvaras P

PROVIDER: S-EPMC4974241 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature

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

Douvaras Panagiotis P Dorà Natalie J NJ Mort Richard L RL Lodge Emily J EJ Hill Robert E RE West John D JD

Experimental eye research 20160526

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 i ...[more]

PMID: 27235794

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Project description:Aldehyde dehydrogenase 1A1 (ALDH1A1) and ALDH3A1 are corneal crystallins. They protect inner ocular tissues from ultraviolet radiation (UVR)-induced oxidative damage through catalytic and non-catalytic mechanisms. Additionally, ALDH3A1 has been postulated to play a regulatory role in the corneal epithelium based on several studies that report an inverse association between ALDH3A1 expression and corneal cell proliferation. The underlying molecular mechanisms and the physiological significance of such association remain poorly understood. In the current study, we established Tet-On human corneal epithelial cell (hTCEpi) lines, which express tetracycline-inducible wild-type (wt) or catalytically-inactive (mu) ALDH3A1. Utilizing this cellular model system, we confirmed that human ALDH3A1 decreases corneal cell proliferation; importantly, this effect appears to be partially mediated by its enzymatic activity. Mechanistically, wt-ALDH3A1, but not mu-ALDH3A1, promotes sequestering of tumor suppressor p53 in the nucleus. In the mouse cornea, however, augmented cell proliferation is noted only in Aldh1a1(-/-)/3a1(-/-) double knockout (DKO) mice, indicating in vivo the anti-proliferation effect of ALDH3A1 can be rescued by the presence of ALDH1A1. Interestingly, the hyper-proliferative epithelium of the DKO corneas display nearly complete loss of p53 expression, implying that p53 may be involved in ALDH3A1/1A1-mediated effect. In hTCEpi cells grown in high calcium concentration, mRNA levels of a panel of corneal differentiation markers were altered by ALDH3A1 expression and modulated by its enzyme activity. In conclusion, we show for the first time that: (i) ALDH3A1 decreases corneal epithelial proliferation through both non-enzymatic and enzymatic properties; (ii) ALDH1A1 contributes to the regulation of corneal cellular proliferation in vivo; and (iii) ALDH3A1 modulates corneal epithelial differentiation. Collectively, our studies indicate a functional role of ALDH3A1 in the maintenance of corneal epithelial homeostasis by simultaneously modulating proliferation and differentiation through both enzymatic and non-enzymatic mechanisms.

Project description:BACKGROUND:The molecular basis of Meesmann's epithelial corneal dystrophy (MECD) has recently been attributed to mutations in the cornea specific keratin genes KRT3 and KRT12. The mechanisms by which these mutations cause the Meesmann's phenotype are not clear. This study presents new data, examines clinical, histological, ultrastructural, and molecular aspects of MECD, and compares the features seen in this condition with those observed in other well studied keratin diseases such as epidermolysis bullosa simplex. METHODS:A two generation family with typical features of Meesmann's epithelial corneal dystrophy (MECD) was studied. All family members were examined under a slit lamp. Biopsy material from elective keratoplasty was studied by histopathological and ultrastructural analysis using standard techniques. Direct automated sequencing of genomic DNA was used for mutation detection, mutations were confirmed by restriction digest analysis. RESULTS:The abnormal corneal epithelium was acanthotic and contained numerous dyskeratotic cells and intraepithelial vesicles. By electron microscopy abnormally aggregated and clumped keratin filament bundles were detected in basal and suprabasal keratinocytes from the centre of the cornea. Direct sequencing of the patients' genomic DNA revealed a novel missense mutation (423T>G) in exon 1 of the cornea specific keratin 12 (KRT12) gene. This mutation predicts the amino acid change N133K within the helix initiation motif of the K12 polypeptide. Comparative studies with well established keratin disorders of other human epithelia underscore the pathogenic relevance of K3 and K12 gene mutations in Meesmann's epithelial corneal dystrophy. The morphological data presented here illustrate the disruptive effects of keratin gene mutations on the integrity of corneal keratinocytes. CONCLUSIONS:A clinical, histopathological, and ultrastructural study of a previously unreported family with MECD is presented. In this family the disease is ascribed to a novel mutation in KRT12. A molecular mechanism is proposed for MECD based on the comparison with other well characterised keratin diseases.

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

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

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