Intraretinal and Subretinal Neovascularization Associated with a Mutation in the Gene for the Very Low Density Lipoprotein Receptor

Abstract

Abstract: : Purpose: To characterize the natural course of retinal neovascularization in mice with a mutation in the gene for the very low density lipoprotein receptor (VLDLR). Methods: C57 mice with a mutation in the VLDLR gene were sacrificed at postnatal day 8 (P8), P13, P16, P23, P33, P42, P56, and P70. Retinal flatmounts and frozen sections were analyzed using fluorescent dextran perfusion to assess vascular permeability and immunohistochemistry to characterize vascular endothelial cells (isolectin, Collagen IV) and astrocytes (glial fibrillary acidic protein, GFAP). The B6;129-Vldlrtm1Her mouse was developed in the laboratory of Dr. Joachim Herz at The University of Texas, Southwestern Medical Center at Dallas. Results: In both control and mutant mice, a trilaminar intraretinal vascular system is established in the first two weeks of life, with blood vessels in the nerve fiber layer and at the inner and outer edges of the inner nuclear layer. By P13, all VLDLR mutant mice have sprouts in the deep vascular plexus that grow into the normally avascular outer retina. Over the next week, these sprouts form perfused angiomatous structures in the photoreceptor layer. GFAP+ Mueller cell processes accompany the new vessels to the retina-RPE border and by P14-16 altered vascular permeability is evidenced by accumulation of rhodamine-dextran in the extravascular space. Expanding angiomatous lesions in the subretinal space extend along the retinal pigment epithelium (RPE) to form placoid neovascular membranes. By day 42, RPE cells surround these lesions and the neovascularization begins to regress; this coincides with a decrease in permeability. By P70, neovascular structures are seen only rarely. Conclusions: Extensive and spontaneous intraretinal neovascularization, reactive gliosis and altered retinal vascular permeability are associated with a mutation in the VLDLR gene. This mutant strain will be useful in the study of mechanisms that direct developing vessels to specific retinal laminae, as a model for vascular permeability, and to evaluate antiangiogenic therapy. VLDLR interacts with a number of extracellular matrix ligands (including reelin) that regulate neuronal guidance during development of brain laminae. The use of similar guidance cues to specify development of retinal vascular architecture will be discussed.

Keywords: retinal development • retinal neovascularization • retina