Phagocytosis and H2O2 induce catalase and metallothionein gene expression in human retinal pigment epithelial cells.

PURPOSE Reactive oxygen intermediates have been implicated in the aging process and degenerative diseases of the eye, including retinopathy of prematurity, cataractogenesis, and macular degeneration. The purpose of this study was to investigate the effect of phagocytosis of photoreceptor outer segments and the addition of exogenous H2O2 on catalase and metallothionein expression in human retinal pigment epithelial cells. METHODS Confluent RPE cells were treated with bovine photoreceptor outer segments or H2O2 for either 6 or 18 hours. Slot blot hybridization was used to assess catalase and metallothionein gene expression after 6 hours. Catalase enzyme activity and metallothionein content were measured after 18 hours. RESULTS Phagocytosis or the addition of H2O2 increased catalase enzyme activity and metallothionein twofold above control levels. The addition of n-acetyl cysteine abrogated the inductive effect caused by either stress. Catalase and metallothionein gene expression, measured by slot blot hybridization, also were measurably induced by either stress. Phagocytosis of photoreceptor outer segments increased extracellular H2O2 concentration nine times above control. CONCLUSIONS The response of the retinal pigment epithelial cells to phagocytosis was indistinguishable from the response observed after the addition of exogenous H2O2. The generation of H2O2 during phagocytosis may act as an intracellular signal in retinal pigment epithelial cells that leads to increased levels of key antioxidant enzymes and other proteins important for protecting the cells from oxidative damage.