Expression of pigment epithelium–derived factor (PEDF) in human aged choroid and age–related macular degeneration

Abstract

Abstract: : Purpose: Pigment epithelium–derived factor (PEDF) is a secretable protein with neuroprotective, neurotrophic, and antiangiogenic properties. It has been suggested that PEDF plays a potential role in controlling ocular blood vessel growth in health and disease. The purpose of this study was to determine the localization and relative level of PEDF in human choroid and evaluate the changes in PEDF and vascular endothelial growth factor (VEGF) localization and their relationship in the age–related macular degeneration (AMD). Methods: Postmortem ocular tissues were obtained from 5 aged control donors (mean age 81 yrs) without evidence or history of chorioretinal disease and 5 donors with AMD (mean age 88 yrs). Tissues were cryopreserved, and streptavidin alkaline phosphatase immunohistochemistry was performed with a rabbit polyclonal antibody against recombinant human PEDF. Binding of the antibody was blocked by preincubation of the antibody with excess human recombinant PEDF. Blood vessels were identified in adjacent sections with anti–CD 34 antibody. Pigment in retinal pigment epithelium (RPE) and choroidal melanocytes was bleached. Three independent observers scored the immunohistochemical reaction product. Results: The most prominent site of PEDF and VEGF localization in aged control choroid was RPE–Bruchs membrane–choriocapillaris complex including RPE basal lamina, intercapillary septa, and choroidal stroma. Circulating leukocytes had the most intense VEGF immunoreactivity. AMD choroid had a similar pattern and intensity of PEDF and VEGF immunostaining as observed in aged controls. However, PEDF immunoreactivity was significantly lower in RPE cells (p= 0.001) and Bruchs membrane (p=0.0024) of AMD choroids. Intense immunoreactivity for PEDF was observed in disciform scars. Drusen were positive for VEGF. Conclusion: In aged control subjects, VEGF and PEDF immunostaining was most intense in RPE–Bruchs membrane–choriocapillaris complex. In AMD, PEDF was lower in RPE cells and Bruchs membrane. These data suggest that a critical balance between PEDF and VEGF exists, and PEDF may counteract the angiogenic potential of VEGF. Under pathological condition, PEDF decreases disrupting this balance. This equilibrium shift may be significant in permitting pathological processes involving RPE cells and Bruchs membrane to occur and also contribute to choroidal neovascularization in age–related macular degeneration.

Keywords: age–related macular degeneration • choroid: neovascularization • retinal pigment epithelium