Vascular endothelial growth factor and its receptors expression in the rat eye

Vascular endothelial growth factor (VEGF) plays a pivotal role in the angiogenesis of embryonic development and tumorigenesis. Recent extensive studies show that VEGF also affects non-vascular cells. In the present study, we performed an immunohistochemical examination of cellular distribution of VEGF and its receptors, Flt-1 and Flk-1, in the retina in vivo and in vitro. Moreover, we addressed their expression in the cornea, iris and ciliary body. In the retina, both Flt-1 and Flk-1 were localized to the axon of retinal ganglion cells (RGCs) and to the retinal pigment epithelium. In vitro experiments showed that both VEGF receptors seemed to be expressed in the cytoplasm of RGCs and Muller cells. In the extra-ocular tissues, ciliary body epithelium showed VEGF, Flt-1 and Flk-1 expression, while iris epithelium showed VEGF and Flk-1 but not Flt-1. Corneal endothelium only showed Flk-1. These data support the hypothesis that VEGF plays a role in many ocular tissues via Flt-1, Flk-1 or both.