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C. Nischler, M. Zareba, M. M. Henry, C. M. Skumatz, T. Sarna, J. M. Burke; Human RPE Cells Aged in vitro Differ From Young Cells in Sensitivity to Oxidative Stress - But the Aging Effect is not Simple and the Type of Stress Matters. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5074.
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A lifetime of oxidative stress to the RPE is believed to cause tissue dysfunction, contributing to diseases like age-related macula degeneration. Here we asked whether young and aged RPE cells differ in susceptibility to oxidative stress induced chemically or photically.
Human RPE cells from 6 donors were aged in vitro by replicative senescence. Young (<12 passages) and aged (>20 passages) cultures were treated with a range of concentrations of H2O2 or illuminated with blue or full spectrum visible light followed by analysis of cytotoxicity by measures of mitochondrial function (MTT) and cell-substrate reattachment, and by live cell imaging to quantify time of apoptotic blebbing. Markers of antioxidant status were also compared in young and aged cultures.
As compared to young cells, aged cells were more resistant to chemical stress, but more sensitive to photic stress. The differences could not be attributed to the following, which when normalized to cellular protein did not differ with cellular aging: amount of catalase, glutathione peroxidase (GPx), superoxide dismutase 1, hemeoxigenase 1; activities of catalase and GPx; content of glutathione, ATP and mitochondria. However, with aging cells showed a larger surface area (increasing cell-substrate contact, which may confer adhesion-related cytoprotection), and higher levels of the anti-apoptotic protein Bcl-2, which together may decrease the sensitivity of aged cells to chemical oxidant stress. On the other hand, aged cells also have slightly higher oxygen consumption and greater cytoplasmic autofluorescence, which may increase their sensitivity to photic stress.
Overall, RPE cells aged in vitro, and theoretically also aged cells in vivo, may not be universally more susceptible to oxidative stress than young cells. The type of stress also matters. (NIH grants EY13722 and P30 EY01931; RPB)
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