Lens VEGF-A Contributes to the Formation of the Fetal Vasculature, but Is Not Necessary for Lens Development

Abstract

Abstract: : Purpose:Vascular endothelial growth factor (VEGF-A) is a potent angiogenic factor that is expressed in the lens throughout pre- and postnatal life. VEGF receptor 2 is present and phosphorylated in the lens, suggesting a possible role for VEGF signaling during lens development (Shui, et al., submitted). VEGF-A levels in the lens increase as the capillaries of the fetal vasculature (FV), the tunica vasculosa lentis (TVL) and the anterior pupillary membrane (APM), regress postnatally. We determined the role of VEGF-A during lens development and in the formation and regression of the TVL and APM by selectively deleting the VEGF-A gene in the lens early in embryonic development using the Cre-LoxP system. Methods:Mice that express Cre recombinase in the entire lens from embryonic day 10.5 onward were mated to mice that had the VEGF-A gene flanked by loxP sequences (VEGF-A^flox). Progeny were genotyped using PCR and mice heterozygous for Cre and the targeted VEGF-A gene were mated to obtain wild type, heterozygous and VEGF-A^flox/flox offspring. Eyes from adult and postnatal day 1 (P1) animals were prepared for histological examination. Results:Mice not expressing Cre recombinase had histologically normal lenses at all stages studied and the FV formed and regressed normally. P1 pups lacking the VEGF-A gene (Cre+, VEGF-A^flox/flox) had lenses of normal morphology. In these animals TVL capillaries were absent at the posterior of the lens, but were present at its periphery, where the lens was close to the peripheral retina. VEGF-A null P1 pups had an APM, but this structure lacked capillaries with red blood cells present in their lumens. Adult mice lacking the VEGF-A gene had lenses of normal morphology. Whatever components of the FV that were present regressed normally in Cre+ animals of all genotypes. Conclusions:Lens VEGF-A is required for the formation of the capillaries of the TVL and APM. VEGF-A from the lens and a normal fetal vasculature are not necessary for normal morphological development of the lens.

Keywords: vascular cells • growth factors/growth factor receptors