The Expression of Angiogenic Factors and Their Receptors During Retinal Neovascularization: Effects of VEGF Trap Administration

Abstract

Abstract: : Purpose: To evaluate the expression of vascular endothelial growth factor (VEGF), Angiopoietins, platelet derived growth factor (PDGF) and their receptors in a mouse model of proliferative retinopathy. Methods: An oxygen-induced retinopathy model (OIR) was employed to produce retinal neovascularization. Eyes from oxygen-exposed and control mice were collected on postnatal day 17 (PN17), sectioned and processed for localization of VEGFA, Angiopoietin-2, VEGFR2 and PDGFRß mRNAs by in situ hybridization. Retinal flat mounts were prepared for staining endothelial and peri-endothelial cells with Griffonia simplicifolia lectin B4 or an antibody against smooth muscle actin (αSMA), respectively. In a second experiment, the VEGF Trap (a VEGF antagonist, 25mg/kg, IP) or a control protein (hFc) was administrated on PN12.5 (6 hours after mice returned to room air) and PN15. The retinas were harvested on PN17 for analysis. A microarray analysis was conducted to further profile gene regulation during neovascularization. Results: OIR was associated with significant upregulation of VEGFA mRNA in the inner nuclear layer of the central retina. Angiopoietin-2, VEGFR2 and PDGFRß mRNAs also were upregulated in proliferating vessels at the retinal surface. OIR resulted in expression of αSMA in peri-endothelial cells throughout the retina, including those associated with veins and capillaries. Similar changes in gene expression were evident in microarrays: VEGF, PDGFB, and desmin were all significantly increased. As reported previously, administration of VEGF Trap almost completely inhibited the growth of pathological neovessels, without blocking the revascularization of the central retina. VEGF Trap suppressed the upregulation of VEGFA and VEGFR2 mRNAs as well the induction of αSMA immunoreactivity in peri-endothelial cells. Conclusions: OIR is associated with increased expression of numerous growth factors, receptors and peri-endothelial cell markers. VEGF appears to be the primary initiating factor in this response, as neutralization of endogenous VEGF not only inhibits the pathological angiogenesis but also the concommitant upregulation of pro-angiogenic growth factors and receptors.

Keywords: retinal neovascularization • neovascularization