Immunocytochemical and Ultrastructural Comparison of Postnatal Eyes from VEGF, PDGF-A, and PDGF-B Transgenic Mice

Abstract

Abstract: : Purpose:To determine the effects of growth factors on blood vessel development and stability, we performed an immunocytochemical and ultrastructural comparison between postnatal eyes from transgenic mice that overexpress VEGF, PDGF-A, or PDGF-B in the lens. Methods:Eyes from transgenic mice and PCR(-) controls were fixed at time points ranging from postnatal day 3 through adult. Vibratome sections were stained for Griffonia simplicifolia isolectin-B4 (GSA) to label endothelial cells, glial fibrillary acidic protein (GFAP) to label glia, VEGF, or albumin to localize sites of blood-retinal barrier breakdown, and examined by electron microscopy. Results:Overexpression of VEGF, PDGF-A, or PDGF-B in the lens results in neovascularization (NV), but the pathology is different. With VEGF, there are numerous perilenticular vessels and vessels on the surface of the retina, but beneath the inner limiting membrane. Perilenticular vessels are fenestrated, whereas retinal vessels are not. The abluminal surface of retinal vascular endothelial cells, perilenticular vessels, and the endothelial basement membrane are conspicuously labelled for VEGF, which is not seen if the source of VEGF is the photoreceptors. These vessels are leaky and occasionally occluded. With PDGF-A or B, a proliferating cell mass with a significant glial component forms between the lens and the retina. This cell mass is most substantial in PDGF-A transgenic mice and contains numerous vessel-like structures. Some inner retinal vascular leakage is evident in PDGF-A transgenic mice. The retinal vessels, rather than merely being enveloped by astrocytic processes as in control mice, have a thick covering of astrocytes. Astrocytes also surround clusters of endothelial cells that have not formed vessels. In PDGF-B transgenic mice with lens expression, as with photoreceptor expression, the formation of the deep capillary bed is inhibited. Conclusions:The principal result of VEGF overexpression in the lens is NV and increased vascular permeability fostered by a perivascular accumulation of VEGF. PDGF-A or B overexpression in the lens causes increased proliferation of astrocytes and pericytes respectively, which associate themselves with proliferating endothelial cells. These cellular changes result in NV.

Keywords: growth factors/growth factor receptors • retinal neovascularization • microscopy: electron microscopy