Tissue Inhibitors of Metalloproteinase-3 (TIMP3) is a regulator of matrix metalloproteinase (MMPs) and a potent angiogenesis inhibitor. Sorsby fundus dystrophy (SFD), a rare, dominantly inherited, early onset macular degenerative disease that is caused by mutations in the TIMP3 gene has marked similarities to age- related macular degeneration (ARMD) disease phenotype including an increased accumulation of TIMP3 in Bruch's membrane (BM) and the development of choroidal neovasculaization (CNV), a major cause of severe vision loss in patients. Our studies using in vitro and in vivo SFD models indicate that SFD-related S156C- TIMP3 promotes CNV via vascular endothelial growth factor receptor-2 (VEGFR-2)- and retinal pigment epithelial (RPE) cell-dependent angiogenic pathways. We also found that increased mutant protein glycosylation is a characteristic of vascular endothelial and RPE cells. Furthermore, we have evidence of increased mutant TIMP3 protein glycosylation with a concomitant increase in mutant TIMP3 levels in RPE- choroid tissue of S156C-TIMP3 knock-in mice. We hypothesize that that S156C-TIMP3 mutation induces N- glycosylation at position184, the only potential N-glycosylation site of TIMP3, resulting in increased accumulation in BM and/or CNV development via VEGFR-2-and/or RPE cell-dependent angiogenic pathways. Using in vitro and in vivo SFD models coupled with pharmacological, mutagenesis, protein over-expression and biochemical characterization approaches our hypothesis will be tested with the following Specific Aims: 1. To determine if inhibition of TIMP-3 glycosylation prevents the increased accumulation of mutant protein in BM and CNV development in S156C-Timp3 knock-in mice. 2. To determine if mutation of Asn184 in S156C-TIMP3 inhibits VEGFR-2- and RPE cell-mediated angiogenesis. The long-term objectives of the proposed research is to identify and dissect the consequences of SFD mutations on TIMP3 structure and functions with particular emphasis on TIMP3 glycosylation as a potential molecular event mediating its accumulation in BM and the subsequent angiogenic or CNV phenotype. Undoubtedly, this would provide novel insights into the pathogenesis of SFD and ARMD that share similar disease phenotype, and thereby establish a potential therapeutic target for these ocular diseases.
Sorsby fundus dystrophy is a rare disease with striking similarities to age-related macular degeneration. Choroidal neovascularization (CNV) occurs in almost all patients with SFD and in about 20% of patients with AMD but accounts for the majority of vision loss in the disease. Thus analyzing CNV in SFD is a useful model to examine the pathophysiology of this phenotype. The molecular and pathological mechanism(s) contributing to CNV are unknown. It is likely that these studies will contribute to our understanding of fundamental principles of neovascularization, as well as provijde insight into the development of new therapeutic approaches for SFD as well as AMD , diabetic retinopathy and other diseases in which angiogenesis play a critical role.