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F. Lamoke, M. Labazi, F. Scarinci, G. Ripandelli, D. M. Marcus, G. Buccafusco, G. Liou, M. Bartoli; Implication of the Small-G Protein Rac-1 in Amyloid Beta-Induced Oxidative Stress and Retinal Cells Toxicity. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3503.
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Deposition of amyloid beta peptides (A-beta) in retinal drusen has been implicated in the pathogenesis of age-related macular degeneration (ARMD). We have previously shown that retinal overexpression of A-beta provokes time-dependent and progressive retinal tissue damage and this effect correlated with induction of oxidative stress. The small G protein Rac-1 is upstream a number of cellular responses to stress conditions including generation of reactive oxygen species (ROS) and induction of pro-inflammatory factors. In this study we determined Abeta effects in promoting activation of Rac-1 in retinal tissue as well as in retinal pigmented epithelial cells (RPE) exposed to Abeta.
Transgenic mice overexpressing amyloid precursor protein (APP) as well as pre-senilin 1 (PS1) were used as model of Abeta-mediated retinal tissue injury. Cultures of ARPE19 exposed to oligomers of Abeta 1-42, or the reverse peptide Abeta 42-1, were used as in vitro model of retinal cell toxicity. Rac-1 activity was assessed by measuring, by immunoprecipitation analysis, ratio of Rac-1/ GTP binding and by determining Rac-1 translocation to the plasma membrane by cell fractionation and Western analysis. Rac-1 inhibition was achieved by adenovirus-mediated cell transduction of the inactive mutant Rac-1N17. ROS production was determined by fluorimetric assay using the fluorescent probe dichlorofluorescein (DCF).
Exposure of ARPE19 cells to Abeta 1-42 oligomers stimulated Rac-1 binding to GTP as well as its translocation to the plasma membrane. Overexpression of Rac-1N17 prevented Abeta-induced production of ROS as measured by DCF-based fluorimetric assay. Finally, immunoprecipitation studies revealed that ratio of Rac-1/GTP (active Rac-1) was increased in the retinal tissue of mice overexpressing Abeta and this correlated with enhanced production of ROS, thus confirming the in vitro data.
Activation of the small G protein Rac-1 in the retinas of mice overexpressing Abeta as well as in cultured RPE exposed to Abeta 1-42 oligomers may represent a critical initial step in Abeta induction of pro-oxidant and pro-inflammatory effects at both retinal cells and tissue levels.
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