Expression of Angiogeneis-related Factors in Retinal Pigment Epithelial Cells under Hypoxia

ABSTRACT

PURPOSE: To elucidate the mechanism of neoangiogenesis of human retinal pigment epithelium (HRPE) under hypoxia. METHODS: HRPE cells were cultured for 2 and 24 hours in a hypoxic chamber. Expression and production of the angiogenic factor, vascular endothelial growth factor (VEGF) and the anti-angiogenic factor, pigment epithelium-derived factor (PEDF) were analyzed by RT-PCR and Western blot, respectively. Neoangiogenesis was induced by adding culture supernatant harvested from cells exposed to hypoxic conditions. Neoangeogenesis was measured with a tube formation assay that uses ECV 304 cells and with a migration assay that uses human dermal microvascular endothelial cells. RESULTS: Competitive RT-PCR showed that the expression of the PEDF gene in HRPE cells under hypoxic state decreased compared to normoxic state (p<0.01) but the expression of the VEGF gene increased (p<0.01) when exposed to hypoxic conditions. These results corresponded to those of the Western blot analysis which revealed a significant increase of VEGF production (p<0.01) and a decrease of PEDF production (p<0.01). Moreover, the tube formation and migration assays demonstrated that angiogenesis was increased by exposure to hypoxic stress. Taken together, HRPE cells under hypoxic stress produce more VEGF and less PEDF, which lead to neoangiogenesis. CONCLUSIONS: These results suggest that the subretinal neovascularization that occurs under hypoxic stress might be caused by an imbalance of angiogenesis-related factors in HRPE cells.