REACTIVE OXYGEN INTERMEDIATES INCREASE VASCULAR ENDOTHELIAL GROWTH-FACTOR EXPRESSION IN-VITRO AND IN-VIVO

Elevated vascular endothelial growth factor (VEGF) levels are required for ocular and tumor angiogenesis in animal models. Ischemic hypoxia is strongly correlated with increased VEGF expression in these systems and is considered a physiologically relevant stimulus. Because ischem ic hypoxia is often followed by reperfusion and reactive oxygen interm ediate (ROI) generation, we examined the potential role of ROI in the control of VEGF gene expression. Human retinal pigment epithelial cell s exposed to superoxide or hydrogen peroxide rapidly increased VEGF mR NA levels. Superoxide-associated mRNA increases were dose dependent, b locked by antioxidants, and associated with elevated VEGF protein leve ls in conditioned media. Increases in VEGF mRNA levels were also obser ved in cultured human melanoma and rat glioblastoma cells with superox ide or hydrogen peroxide. Cycloheximide prevented the ROI-associated i ncreases in VEGF mRNA. Transcriptional inhibition with actinomycin D r evealed an inducible increase in VEGF mRNA half-life, but nuclear run- on experiments showed no increase in VEGF transcriptional rate. Reoxyg enation of human retinal pigment epithelial cells in vitro and ocular reperfusion in vivo increased retinal VEGF mRNA levels. Antioxidants p revented the reperfusion-associated VEGF mRNA increases in retina. We conclude that ROIs increase VEGF gene expression in vitro and during t he reperfusion of ischemic retina in vivo. The ROI-associated increase s are mediated largely through increases in VEGF mRNA stability.