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Kyle Carver, Dongli Yang; Oxidative stress induces microparticle release from retinal pigment epithelial cells. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2375.
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© ARVO (1962-2015); The Authors (2016-present)
Oxidative stress is one of major factors involved in the retinal pigment epithelium (RPE) dysfunction and death that underlie age-related macular degeneration (AMD). Drusen and subretinal deposits are extracellular lipid- and protein-containing deposits that are found in early AMD and are strongly associated with the development of late AMD. Microparticles (MPs) are small membrane-bound vesicles that have been demonstrated to be released from cells under both normal and pathologic conditions. The purpose of this study was to determine if oxidative stress drives MP release from RPE cells and to assess whether these MPs may carry membrane complement regulatory proteins that are present in drusen or subretinal deposits.
Primary RPE cells isolated from human donor eyes were cultured and treated with 50-2000 µM hydrogen peroxide for 2-24 hours to induce oxidative stress. MPs were isolated with differential centrifugation and stained for component analysis by flow cytometry and confocal microscopy or fixed for electron microscopy.
Transmission electron microscopy showed that the size of MPs, released from both hydrogen peroxide- and vehicle-treated RPE cells, ranged from 100 to 1000 nm. Hydrogen peroxide treatment led to time- and dose-dependent elevations in MPs with exposed phosphatidylserine and phosphatidylethanolamine, known markers of MPs. These increases were strongly correlated (Pearson correlation coefficient = 0.756 and 0.9173, respectively) to RPE cell apoptosis, as measured by annexin V and propidium iodide labelling. In addition, oxidative stress significantly increased the presence of membrane complement regulatory proteins CD46 (10-fold increase, p < 0.0001), CD55 (6-fold, p = 0.0015), and CD59 (6-fold, p < 0.0001) on released MPs.
This is the first evidence that oxidative stress induces primary cultured human RPE cells to release MPs, strongly correlated with RPE cell apoptosis, which contain CD46, CD55, and CD59. Together with previous detection of CD46 in drusen and CD59 in subretinal deposits in early AMD, as well as oxidative stress-induced loss of CD46, CD55, and CD59 from the RPE surface, we suggest that oxidative stress may render RPE cells more sensitive to complement activation by inducing loss of the complement inhibitors and could trigger drusen or subretinal deposit formation by releasing MPs from the RPE.
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