Expression and Modulation of RPE Cell Membrane Complement Regulatory Proteins

Abstract

PURPOSE: Complement, inflammation, and oxidant injury contribute to age-related macular degeneration (AMD). Membrane complement regulatory proteins (mCRPs) such as CD46, CD55, and CD59, protect host cells from complement attack. The factors that regulate RPE mCRP expression are not well understood. In this study, the authors sought to determine whether cytokines and hydroquinone (HQ) affect mCRP expression in cultured human RPE (hRPE) and cultured mouse RPE (mRPE) cells. METHODS: Cultured hRPE and mRPE cells were stimulated with cytokines for various times or with HQ for multiple 6-hour periods. mRNA and protein expression of mCRPs in cultured hRPE cells from 10 donors, native hRPE, and mouse eyecups and native mRPE cells were evaluated by real-time RT-PCR, Western blot analysis, and flow cytometry, respectively. RESULTS: Three mCRPs were expressed in cultured hRPE cells (CD59>CD46>CD55). CD46 and CD59 protein were detected in native hRPE cells. CD59 protein levels in cultured hRPE cells were higher than in native hRPE cells. CD46 protein polymorphisms were observed in cultured hRPE cells. Cultured hRPE cell mCRP expression was upregulated by TNF-alpha, IL-1beta, and a repetitive nonlethal dose of HQ. CD59a levels were higher in mouse eyecups than in nonocular tissues. Mouse mCRP mRNA and protein were detected in native mRPE cells. Responsiveness to cytokines in cultured mRPE cells differed from that in cultured hRPE cells. CONCLUSIONS: Human and mouse RPE cell mCRPs are upregulated by inflammatory cytokines and repetitive nonlethal oxidant exposure in a species-specific manner. Increased cell mCRPs may help to protect RPE cells from complement- and oxidant-mediated injury in diseases such as AMD.