Mechanism of Induction of Choroidal Neovascularization in Sorsby Fundus Dystrophy

Abstract

Abstract: : Purpose: Sorsby fundus dystrophy (SFD) is a dominantly inherited condition characterized by the development of choroidal neovascularization, subretinal hemorrhages and changes consistent with disciform degeneration. Mutations in the Tissue Inhibitor of Metalloproteinases-3 (TIMP-3) gene, all of which introduce an extra cysteine residue into exon 5, cause Sorsby Fundus Dystrophy (SFD). TIMP-3, a regulator of matrix metalloproteinases (MMPs) is deposited by retinal pigment epithelial (RPE) cells into Bruch's membrane (BM) where it is a component of the extracellular matrix. In this study we set out to elucidate the mechanism by which TIMP-3 mutations induce the angiogenic phenotype. Methods: We have introduced TIMP-3 into porcine aortic endothelial cells expressing VEGFR-2 as well as human retinal pigment epithelial cells. In vitro, VEGF induced proliferation and migration of endothelial cells were analyzed by Coulter particle counting and modified Boyden chamber assays respectively. VEGF induced autophosphorylation of VEGFR-2 and activation of p44/p42 MAP kinase was evaluated by western blot analysis. Conditioned medium from RPE cells was tested for their ability to induce angiogenesis in an in vivo chick chorio-allantoic membrane (CAM) assay. Results: TIMP-3 over-expression in endothelial cells resulted in an inhibition of the proliferative and migratory response of these cells to VEGF. VEGF-induced autophosphorylation of VEGFR-2 and p44/p42 MAP kinase activation were also suppressed. These effects appear to be independent of its MMP inhibitory activity. Conditioned medium from RPE cells expressing SFD mutant TIMP-3 demonstrated increased MMP activity as well as increased angiogenic activity on CAM assay. Conclusions: Our data indicate that expression of SFD mutant TIMP-3 in RPE cells results in increased MMP activity and induction of angiogenesis.

Keywords: retinal degenerations: hereditary • neovascularization • retinal pigment epithelium