Novel mechanism for age-related macular degeneration: An equilibrium shiftbetween the angiogenesis factors VEGF and PEDF

We investigated gene expression profiles of vascular endothelial growth fac tor (VEGF) and pigment epithelium-derived factor (PEDF) in differentiated a nd nondifferentiated retinal pigment-epithelial (RPE) cells during oxidativ e stress. Human RPE cells were grown in culture on laminin-coated flasks to obtain differentiated features. Cells cultured on plastic were used as non -differentiated controls. After confluence, hydrogen peroxide (H2O2) was ad ded for 48 h, then, total RNA was extracted and used for RT-PCR and Norther n blot analysis. Medium conditioned by RPE was used for ELISA, Western blot ting, and in vitro angiogenesis assay. As a result, differentiated RPE cell s expressed significantly higher levels of VEGF protein, as compared to the ir non-differentiated counterparts. The expression pattern remained consist ent even after cellular exposure to H2O2. Conversely, while elevated levels of PEDF transcript and protein were seen in differentiated RPE cells, comp ared to non-differentiated cells, a marked decrease at both PEDF mRNA and p rotein levels was seen after treatment with H2O2. Moreover, this decrease i n PEDF expression was dosage dependent. In in vitro angiogenesis assay, con ditioned medium from differentiated human RPE cells after exposure to H2O2 showed a dramatic increase in tubular formation and migratory activity of m icrovascular endothelial cells. These data suggest that, in physiological c onditions, a critical balance between PEDF and VEGF exists, and PEDF may co unteract the angiogenic potential of VEGF. Under oxidative stress, PEDF dec reases disrupting this balance. This equilibrium shift may be significant i n promoting a pathological condition of RPE cells and contributing to choro idal neovascularization in age-related macular degeneration. (C) 2001 Wiley -Liss, Inc.