Abstract
Purpose :
Impaired development and maintenance of the Schlemm’s Canal (SC) vasculature, characterized by both venous and lymphatic identity, is associated with impaired aqueous humor outflow regulation and the progression of glaucoma and loss of vision. Several key molecular regulators, such as Angpt/TEK, VEGFC/VEGFR3, and PROX1, were demonstrated to regulate SC development and maintenance, but mechanisms of paracrine signaling from neighboring tissues and cells contributing to SC development are poorly understood. Human forkhead box (FOX) FOXC2 variants were identified as modifier factors in congenital glaucoma (Medina-Trillo et al. PLoS One 2019) and our laboratory demonstrated that neural crest (NC)-derived periocular mesenchymal cells require expression of Foxc2 for development of the anterior segment (Seo et al. IOVS 2017). However, the role of Foxc2 in contribution to the development of the SC has yet to be investigated.
Methods :
Using Foxc2-CreERT2; mTmG reporter mice, we identified positive FOXC2 expression in both NC-derived trabecular meshwork and SC endothelium. Foxc2 was deleted from NC-derived cells by crossing Foxc2F mice with Wnt1-Cre mice. Eyes of NC-Foxc2-KO and control mice were imaged in vivo using a visible light optical coherence tomography (Vis-OCT) system as previously described (Zhang et al., IOVS 2020). Inducible deletion of Foxc2 from endothelial cells (EC) was achieved by administering tamoxifen postnatally to Cdh5-CreERT2; Foxc2F mice. Immunohistochemistry for characterization of SC morphology was performed on flatmounted eyes where the lens and retina were removed.
Results :
Vis-OCT image volumes showed different levels of narrowed and discontinuous SC morphology in NC-Foxc2-KO mice while OCT angiography showed various levels of corneal neovascularization . Immunostaining of CD31 identified abnormal SC morphology, or the absence of SC, in NC-Foxc2-KO compared to Cre-negative mice, which was accompanied by reduced PROX1, VEGFR-3, and TEK expression. Additionally, deletion of Foxc2 in the endothelium resulted in impaired SC morphogenesis at postnatal day 7, which was accompanied by reduced TEK expression compared to littermate controls.
Conclusions :
Both Foxc2 expression in the NC lineage and ECs is required for morphogenesis of the SC vasculature. NC-derived Foxc2 expression is key for maintenance of SC identity and EC-derived Foxc2 expression regulates SC TEK expression.
This is a 2021 ARVO Annual Meeting abstract.