HYPOXIC REGULATION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR IN RETINAL CELLS

Background: Vascular endothelial growth factor (VEGF) is an angiogenic protein and vasopermeability factor whose intraocular concentrations are closely correlated with active neovascularization in patients with diabetes mellitus, central retinal vein occlusion, retinopathy of pre maturity, and rubeosis iridis. Objective: To determine whether hypoxia could induce expression of VEGF in retinal cells, which then promotes retinal endothelial cell proliferation. Methods: Retinal pigment epit helial cells, pericytes, and microvascular endothelial cells were expo sed to hypoxic conditions in vitro, and RNA expression of VEGF was eva luated by Northern blot analysis. The VEGF-specific proliferative pote ntial of the medium was measured by means of retinal endothelial cell growth assays and VEGF-neutralizing VEGF receptor IgG chimeric protein . Results: The VEGF RNA levels increased within 4 hours and reached el evations of threefold to 30-fold after 18 hours of hypoxia (0% to 5% o xygen, 5% carbon dioxide, 90% to 95% nitrogen) in all cell types (.01 < P < .03). Stimulation was dependent on oxygen concentration. The VEG F RNA levels were normalized by reinstitution of normoxia for 24 hours (P < .004). Medium conditioned by hypoxic retinal pericytes and retin al pigment epithelial cells stimulated retinal endothelial cell growth by 20% (P = .04), and this stimulation was entirely inhibited by VEGF -neutralizing receptor chimeric protein (P = .02). Conclusion: Hypoxia increases VEGF expression in retinal cells, which promotes retinal en dothelial cell proliferation, suggesting that VEGF plays a major role in mediating intraocular neovascularization resulting from ischemic re tinal diseases.