PHAGOCYTOSIS AND H2O2 INDUCE CATALASE AND METALLOTHIONEIN GENE-EXPRESSION IN HUMAN RETINAL-PIGMENT EPITHELIAL-CELLS

Purpose. Reactive oxygen intermediates have been implicated in the agi ng process and degenerative diseases of the eye, including retinopathy of prematurity, cataractogenesis, and macular degeneration. The purpo se of this study was to investigate the effect of phagocytosis of phot oreceptor outer segments and the addition of exogenous H2O2 on catalas e and metallothionein expression in human retinal pigment epithelial c ells. Methods. Confluent RPE cells were treated with bovine photorecep tor outer segments or H2O2 for either 6 or 18 hours. Slot blot hybridi zation was used to assess catalase and metallothionein gene expression after 6 hours. Catalase enzyme activity and metallothionein content w ere measured after 18 hours. Results. Phagocytosis or the addition of H2O2 increased catalase enzyme activity and metallothionein twofold ab ove control levels. The addition of n-acetyl cysteine abrogated the in ductive effect caused by either stress. Catalase and metallothionein g ene expression, measured by slot blot hybridization, also were measura bly induced by either stress. Phagocytosis of photoreceptor outer segm ents increased extracellular H2O2 concentration nine times above contr ol. 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 phagocy tosis may act as an intracellular signal in retinal pigment epithelial cells that leads to increased levels of key antioxidant enzymes and o ther proteins important for protecting the cells from oxidative damage .