Wnt/β-catenin signaling modulates corneal epithelium stratification via inhibition of Bmp4 during mouse development

Abstract

The development of organs with an epithelial parenchyma relies on reciprocal mesenchymal-epithelial communication. Mouse corneal epithelium stratification is the consequence of a coordinated developmental process based on mesenchymal-epithelial interactions. The molecular mechanism underlying these interactions remains unclear. The Wnt/β-catenin signaling pathway is involved in fundamental aspects of development through the regulation of various growth factors. Here, we show that conditional ablation of either β-catenin (Ctnnb1 cKO ) or co-receptors Lrp5/6 (Lrp5/6 cKO ) in corneal stromal cells results in precocious stratification of the corneal epithelium. By contrast, ectopic expression of a murine Ctnnb1 gainof-function mutant (Ctnnb1 cGOF ) retards corneal epithelium stratification. We also discovered that Bmp4 is upregulated in the absence of β-catenin in keratocytes, which further triggers ERK1/2 (Mapk3/1) and Smad1/5 phosphorylation and enhances transcription factor p63 (Trp63) expression in mouse corneal basal epithelial cells and in a human corneal epithelial cell line (HTCE). Interestingly, mouse neonates given a subconjunctival BMP4 injection displayed a phenotype resembling that of Ctnnb1 cKO . Conditional ablation of Bmp4 eradicates the phenotype produced in Ctnnb1 cKO mice. Furthermore, ChIP and promoter-luciferase assays show that β-catenin binds to and suppresses Bmp4 promoter activity. These data support the concept that cross-talk between the Wnt/β-catenin/ Bmp4 axis (in the stromal mesenchyme) and Bmp4/p63 signaling (in the epithelium) plays a pivotal role in epithelial stratification during corneal morphogenesis.

Primary cilia maintain corneal epithelial homeostasis by regulation of the Notch signaling pathway

“…Moreover, reporter mouse lines indicated absence or low activity of these pathways during CE development and homeostasis (Fig. S2) in overall agreement with previous findings (Mukhopadhyay et al, 2006;Saika et al, 2004a;Zhang et al, 2015). By contrast, we found that ablation of Ift88 in the CE downregulated the expression of the Notch pathway target genes.…”

Accumulation of sequence variants in genes of Wnt signaling and focal adhesion pathways in human corneas further explains their involvement in keratoconus

“…The LRP6 gene encodes the low-density lipoprotein receptor-related protein, which is a component of a Wnt receptor complex. This complex is involved in Wnt ligands binding resulting in the nuclear translocation of β-catenin and regulation of the transcription of target genes (Zhang et al, 2015). Knock-out of β-catenin or its both co-receptors (Lrp5 and Lrp6) in mouse corneal stromal cells resulted in premature stratification of the corneal epithelium, suggesting these genes play a role in the regulation of corneal morphogenesis (Zhang et al, 2015).…”

“…This complex is involved in Wnt ligands binding resulting in the nuclear translocation of β-catenin and regulation of the transcription of target genes (Zhang et al, 2015). Knock-out of β-catenin or its both co-receptors (Lrp5 and Lrp6) in mouse corneal stromal cells resulted in premature stratification of the corneal epithelium, suggesting these genes play a role in the regulation of corneal morphogenesis (Zhang et al, 2015). In this study, the expression of LRP6 in the cornea of the carrier of variant c.4822C>T (KC17) was unchanged compared to the other four KTCN individuals.…”

The core planar cell polarity gene, Vangl2, maintains apical‐basal organisation of the corneal epithelium

“…The corneal epithelium originates as a monolayer during development and in mice stratification occurs neonatally concomitant with eye opening, controlled at least in part by Wnt/β‐catenin signalling inhibiting action of bone morphogenetic protein 4 (Zhang et al. ).…”