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)1,2, 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 worldwide3. 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.

Transcription Factor PAX6 (Paired Box 6) Controls Limbal Stem Cell Lineage in Development and Disease

“…These two processes must be highly organized to maintain the integrity and homeostasis of the corneal epithelium. Pathological changes in LSCs can lead to a loss of transparency in the cornea and cause partial or complete blindness (2,15). In this study, we found that PAX6 is essential for the maintenance of LSC characteristics and their further commitment to the CEC lineage.…”

“…DKK2, an antagonist of canonical Wnt signaling, is required for accurate development of the ocular surface epithelium in mice by regulation of Wnt/␤-catenin activity (14). In addition, our previous work suggested a central role of the Wnt7A-PAX6 axis in CEC fate determination, in which SESCs could be converted to LSC-like cells by overexpression of PAX6 (15). In the present study, we have provided further evidence for the importance of the Wnt and Notch signaling pathways by comparison of gene expression profiles between LSCs and SESCs.…”

“…Microarray Data Analysis-Total RNA was isolated from LSCs and SESCs as in our previous study (15). Raw data were deposited in the Gene Expression Omnibus database under accession number GSE32145.…”

Horizontal Basal Cell-Specific Deletion ofPax6Impedes Recovery of the Olfactory Neuroepithelium Following Severe Injury

“…A recent study found that Pax6 + /Sox2 + / Nestin + multipotent retinal stem cells (RSCs) in the adult mouse retina are capable of producing functional photoreceptor cells [51]. Moreover, in humans, PAX6 and p63 are coexpressed in K5-positive limbal stem/progenitor cells (LSCs), which can differentiate into corneal epithelial cells, and WNT7A acts as an upstream regulator of PAX6, regulating corneal epithelium differentiation [52]. Finally, transfecting PAX6 into cultured skin epithelial stem cells differentiates the cells into corneal epithelial-like cells; conversely, deleting PAX6/WNT7A in LSCs causes abnormal skin epidermis-like differentiation [52].…”

“…Moreover, in humans, PAX6 and p63 are coexpressed in K5-positive limbal stem/progenitor cells (LSCs), which can differentiate into corneal epithelial cells, and WNT7A acts as an upstream regulator of PAX6, regulating corneal epithelium differentiation [52]. Finally, transfecting PAX6 into cultured skin epithelial stem cells differentiates the cells into corneal epithelial-like cells; conversely, deleting PAX6/WNT7A in LSCs causes abnormal skin epidermis-like differentiation [52]. These results obtained from research in the ocular system have several features in common with our findings.…”