Regulation of the neurovascular patterning by growth factors and cytokines during anterior ocular development
Ojeda Cardenas, Ana
Bennett, George N
Doctor of Philosophy
The cornea is a transparent, avascular, and one of the most innervated tissue of the body. Corneal diseases including injuries, neovascularization, congenital eye defects and degenerations, represent a major public health burden. Although, studies have been focused on understanding the basis of transparency, innervation, and neovascularization of the adult cornea, little is known about the molecular mechanisms that lead to this specialized structure results in a highly innervated but avascular tissue during embryogenesis. The purpose of this work was to identify molecular regulators of the neurovascular patterning during cornea development. First, Sema3A, a well-known chemorepulser of axons, was identified as a key modulator in the establishment of cornea avascularity in both, avian and murine models. Moreover, I demonstrated that chemokines, initially described for their function in controlling immune cell migration, also play an important role in axon guidance and vasculogenesis during ocular development. Examination of the expression of the chemokine CXCL14 by in situ hybridization and immunohistochemistry revealed novel patterns of localization in the corneal stroma, iris, lens epithelium, retina and trigeminal ganglion. Comparison in the expression of CXCL14 and CXCL12 shows that they are expressed in complementary patterns in most tissues during ocular development, suggesting an interactive regulation of these chemokines. Visual examination of Retrovirus-mediated Knockdown of CXCL14 embryos revealed relatively smaller eyes compared to controls, and immunohistochemical analysis of ocular nerves indicated exacerbated projection of sensory nerves into the corneal stroma, corneal epithelium and iris, which subsequently elevated nerve density in these tissues. In vitro analyses revealed that CXCL14 has an inhibitory effect on CXCL12-induced axon growth of trigeminal ganglion sensory neurons. Furthermore, Knockdown of CXCL14 in Tg(tie1: H2B:eYFP) transgenic Japanese quail embryos resulted in ectopic migration of YFP fluorescently labeled angioblasts into the cornea and exogenous CXCL14 inhibits VEGF- and CXCL12-induced angioblast migration into the cornea. This is the first time that CXCL14 has been shown to have a critical function during embryogenesis that may be mediated through inhibition of CXCL12 signaling. Collectively, these results demonstrate that neurovascular patterning of the anterior eye during development depends on an intricate process and fine balance of growth factors and cytokines. These findings will contribute to a better understanding of the molecular mechanisms involved in pathological conditions such as cornea neovascularization, anterior segment ocular dysgeneses and wound healing, where angiogenesis and nerve regeneration are critically compromised.
Cornea; neurovascular patterning; development