Expression of VLDLR in the Retina and Evolution of Subretinal Neovascularization in the Knockout Mouse Model's Retinal Angiomatous Proliferation

Very-low-density lipoprotein receptor (VLDLR) in knockout mice (vldlr(-/-)) has been reported to induce subretinal neovascularization. Therefore, VLDLR expression in the wild-type mouse retina was investigated and the retinal angiogenic process in vldlr(-/-) mice was characterized. VLDLR expression in the retina and in purified retinal vascular endothelial cells (RECs) and retinal pigment epithelial (RPE) cells was determined by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. Angiogenic evolution in vldlr(-/-) mice was examined by fundus fluorescein angiography, histology, double-staining of FITC-dextran perfusion and elastin immunohistochemistry, isolectin staining, and confocal fluorescence microscopy. VLDLR mRNA was detected in the wild-type mouse retina and in purified RECs and RPE cells. The VLDLR protein was localized in the RPE layer, vessels in the ganglion cell layer, and around the outer limiting membrane of the retina. The retinal pathogenic process in vldlr(-/-) mice recapitulates key features of retinal angiomatous proliferation (RAP) in humans, a subtype of neovascular age-related macular degeneration (AMD). These include neovascular growth originating from retinal vessels and progressing to the subretinal space with intraretinal, subretinal, and choroidal angiogenic stages, RPE disruption and Bruch membrane exposure, retinal-choroidal anastomosis, subsequent photoreceptor degeneration, RPE hyperplasia, and subretinal fibrosis at the end stage. VLDLR is expressed in the wild-type mouse retina, especially in RECs and RPE cells. The vldlr(-/-) mouse exhibits histologic and angiographic characteristics of RAP and is a reproducible animal model facilitating studies of the molecular mechanisms of RAP.