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WNT7A and PAX6 define corneal epithelium homeostasis and pathogenesis.

ABSTRACT: The surface of the cornea consists of a unique type of non-keratinized epithelial cells arranged in an orderly fashion, and this is essential for vision by maintaining transparency for light transmission. Cornea epithelial cells (CECs) undergo continuous renewal from limbal stem or progenitor cells (LSCs), and deficiency in LSCs or corneal epithelium--which turns cornea into a non-transparent, keratinized skin-like epithelium--causes corneal surface disease that leads to blindness in millions of people worldwide. How LSCs are maintained and differentiated into corneal epithelium in healthy individuals and which key molecular events are defective in patients have been largely unknown. Here we report establishment of an in vitro feeder-cell-free LSC expansion and three-dimensional corneal differentiation protocol in which we found that the transcription factors p63 (tumour protein 63) and PAX6 (paired box protein PAX6) act together to specify LSCs, and WNT7A controls corneal epithelium differentiation through PAX6. Loss of WNT7A or PAX6 induces LSCs into skin-like epithelium, a critical defect tightly linked to common human corneal diseases. Notably, transduction of PAX6 in skin epithelial stem cells is sufficient to convert them to LSC-like cells, and upon transplantation onto eyes in a rabbit corneal injury model, these reprogrammed cells are able to replenish CECs and repair damaged corneal surface. These findings suggest a central role of the WNT7A-PAX6 axis in corneal epithelial cell fate determination, and point to a new strategy for treating corneal surface diseases.

SUBMITTER: Ouyang H

PROVIDER: S-EPMC4610745 | biostudies-literature | 2014 Jul

REPOSITORIES: biostudies-literature

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WNT7A and PAX6 define corneal epithelium homeostasis and pathogenesis.

Ouyang Hong H Xue Yuanchao Y Lin Ying Y Zhang Xiaohui X Xi Lei L Patel Sherrina S Cai Huimin H Luo Jing J Zhang Meixia M Zhang Ming M Yang Yang Y Li Gen G Li Hairi H Jiang Wei W Yeh Emily E Lin Jonathan J Pei Michelle M Zhu Jin J Cao Guiqun G Zhang Liangfang L Yu Benjamin B Chen Shaochen S Fu Xiang-Dong XD Liu Yizhi Y Zhang Kang K

Nature 20140702 7509

The surface of the cornea consists of a unique type of non-keratinized epithelial cells arranged in an orderly fashion, and this is essential for vision by maintaining transparency for light transmission. Cornea epithelial cells (CECs) undergo continuous renewal from limbal stem or progenitor cells (LSCs), and deficiency in LSCs or corneal epithelium--which turns cornea into a non-transparent, keratinized skin-like epithelium--causes corneal surface disease that leads to blindness in millions of ...[more]

PMID: 25030175

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Project description:BackgroundAltered dosage of the transcription factor PAX6 causes multiple human eye pathophysiologies. PAX6⁺/⁻ heterozygotes suffer from aniridia and aniridia-related keratopathy (ARK), a corneal deterioration that probably involves a limbal epithelial stem cell (LESC) deficiency. Heterozygous Pax6(+/Sey-Neu) (Pax6⁺/⁻) mice recapitulate the human disease and are a good model of ARK. Corneal pathologies also occur in other mouse Pax6 mutants and in PAX77(Tg/-) transgenics, which over-express Pax6 and model human PAX6 duplication.Methodology/principal findingsWe used electron microscopy to investigate ocular defects in Pax6⁺/⁻ heterozygotes (low Pax6 levels) and PAX77(Tg/-) transgenics (high Pax6 levels). As well as the well-documented epithelial defects, aberrant Pax6 dosage had profound effects on the corneal stroma and endothelium in both genotypes, including cellular vacuolation, similar to that reported for human macular corneal dystrophy. We used mosaic expression of an X-linked LacZ transgene in X-inactivation mosaic female (XLacZ(Tg/-)) mice to investigate corneal epithelial maintenance by LESC clones in Pax6⁺/⁻ and PAX77(Tg/-) mosaic mice. PAX77(Tg/-) mosaics, over-expressing Pax6, produced normal corneal epithelial radial striped patterns (despite other corneal defects), suggesting that centripetal cell movement was unaffected. Moderately disrupted patterns in Pax6⁺/⁻ mosaics were corrected by introducing the PAX77 transgene (in Pax6⁺/⁻, PAX77(Tg/-) mosaics). Pax6(Leca4/+), XLacZ(Tg/-) mosaic mice (heterozygous for the Pax6(Leca4) missense mutation) showed more severely disrupted mosaic patterns. Corrected corneal epithelial stripe numbers (an indirect estimate of active LESC clone numbers) declined with age (between 15 and 30 weeks) in wild-type XLacZ(Tg/-) mosaics. In contrast, corrected stripe numbers were already low at 15 weeks in Pax6⁺/⁻ and PAX77(Tg/-) mosaic corneas, suggesting Pax6 under- and over-expression both affect LESC clones.Conclusions/significancePax6⁺/⁻ and PAX77(Tg/-) genotypes have only relatively minor effects on LESC clone numbers but cause more severe corneal endothelial and stromal defects. This should prompt further investigations of the pathophysiology underlying human aniridia and ARK.

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WNT7A and PAX6 define corneal epithelium homeostasis and pathogenesis.

Publications

WNT7A and PAX6 define corneal epithelium homeostasis and pathogenesis.

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