Effect of overexpression of wild‐type and mutant Cu/Zn‐superoxide dismutases on oxidative stress and cell death induced by hydrogen peroxide, 4‐hydroxynonenal or serum deprivation: potentiation of injury by ALS‐related mutant superoxide dismutases and protection by Bcl‐2

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Abstract
Mutations in Cu/Zn‐superoxide dismutase (SOD1) are associated with some cases of familial amyotrophic lateral sclerosis (ALS). We overexpressed Bcl‐2, wild‐type SOD1 or mutant SOD1s (G37R and G85R) in NT‐2 and SK‐N‐MC cells. Overexpression of Bcl‐2 rendered cells more resistant to apoptosis induced by serum withdrawal, H2O2 or 4‐hydroxy‐2‐trans‐nonenal (HNE). Overexpression of Bcl‐2 had little effect on levels of protein carbonyls, lipid peroxidation, 8‐hydroxyguanine (8‐OHG) or 3‐nitrotyrosine. Serum withdrawal or H2O2 raised levels of protein carbonyls, lipid peroxidation, 8‐OHG and 3‐nitrotyrosine, changes that were attenuated in cells overexpressing Bcl‐2. Overexpression of either SOD1 mutant tended to increase levels of lipid peroxidation, protein carbonyls, and 3‐nitrotyrosine and accelerated viability loss induced by serum withdrawal, H2O2 or HNE, accompanied by greater rises in oxidative damage parameters. The effects of mutant SOD1s were attenuated by Bcl‐2. By contrast, expression of wild‐type SOD1 rendered cells more resistant to loss of viability induced by serum deprivation, HNE or H2O2. The levels of lipid peroxidation in wild‐type SOD1 transfectants were elevated. Overexpression of mutant SOD1s makes cells more predisposed to undergo apoptosis in response to several insults. Our cellular systems appear to mimic events in patients with ALS or transgenic mice overexpressing mutant SOD1.