The response of cultured human retinal pigment epithelium to hypoxia: A comparison to other cell types

Purpose. To characterize the response of cultured human retinal pigment epithelial (RPE) cells to lowered environmental oxygen. Methods. The response of cultured RPE cells to lowered oxygen environments was compared to that of cell types of presumed high (Madin-Darby canine kidney [MDCK] cells, an epithelial cell line) and low (CSF, corneal stromal fibroblasts) aerobic requirements. Cultures in a range of densities were exposed for 7 days to 3%, 8%, or 20% O₂ with measurements of adenosine triphosphate (ATP), cell number, and cytochrome oxidase (CO) activity (an enzyme marker of aerobic metabolism). Results. RPE cells had levels of CO activity and total cellular ATP intermediate between those of CSF (low) and MDCK (high) in all oxygen environments. Hypoxia led to modestly lowered ATP pools and CO activity for RPE cells over a wide range of culture densities. Hypoxia induced a greater cell loss in MDCK cells than in RPE cells, and the effects of hypoxia were greater in dense cultures of both epithelial cell types. Hypoxia had little effect on cell number for CSF. Conclusions. The data suggest that cultured RPE cells, though aerobically active, are not as dependent upon oxidative phosphorylation and are more resistant to hypoxia than MDCK cells, a cell type derived from another well-perfused tissue. The authors conclude that RPE cells are unlikely to suffer from hypoxic injury in situ because of a moderate aerobic demand and an abundant oxygen supply.