Choroidal neovascularization (CNV) is the major cause of severe vision loss in patients with age-related macular degeneration (AMD). The neovascularization originates from the choriocapillaris and grows through Bruch's membrane, into the sub-retinal pigment epithelial (RPE) space. Sorsby's Fundus Dystrophy (SFD), a rare, dominantly inherited, early onset macular degenerative disease is of considerable interest as it is the only genetic disorder in which choroidal neovascularization occurs in the majority of affected patients. Mutations in the Tissue Inhibitor of Metalloproteinases-3 (TIMP-3) gene cause SFD. TIMP-3, an inhibitor of matrix metalloproteinases (MMPs) is deposited by RPE cells into Bruch's membrane (BM) where it is a component of the extracellular matrix (ECM). We have demonstrated that TIMP-3 is a potent inhibitor of angiogenesis and functions independent of its MMP inhibition in this respect. We have also shown that expression of SFD mutant TIMP-3 in RPE cells reduces MMP inhibition and promotes angiogenesis. Since CNV is a prominent feature of SFD, we propose to study the mechanisms by which wild type and mutant TIMP-3 regulate neovascularization. The following model is proposed: Under physiological conditions, wild type (wt) TIMP-3 deposited by RPE cells into Bruch's membrane efficiently inhibits neovascular invasion from the choriocapillaris by preventing the binding of VEGF to its receptor KDR. During pathological choroidal neovascularization as seen in SFD, mutant TIMP-3 is compromised in its angiostatic ability and results in increased neovascularization. The long term goal of this proposal is to gain an understanding of the mechanism(s) by which TIMP-3 and its mutations regulate choroidal neovascularization. Using both in vitro and in vivo studies our hypothesis will be tested with the following Specific Aims. 1. To determine the molecular mechanism by which TIMP-3 inhibits angiogenesis. a) Does binding to proteoglycan play a role in the ability of TIMP-3 to inhibit angiogenesis? b) Do TIMP-3 null mice demonstrate abnormal development of retinal and/or choroidal vasculature? c) Are TIMP-3 null mice more susceptible to VEGF induced CNV? 2. To determine the mechanism by which TIMP-3 mutations cause CNV in SFD. a) Do mice expressing S156C TIMP-3 show increased angiogenic responses to VEGF? b) What are the molecular mechanisms by which S156C TIMP-3 accentuates VEGF mediated angiogenesis?
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