Changes in Superoxide Dismutase and Catalase in Aging Heat-ShockedDrosophila

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Abstract
We have examined the age-dependent expression of CuZn superoxide dismutase (SOD) and catalase (CAT) in Drosophila melanogaster following heat shock. Quantitative northern blot analysis was performed after heat shock on 2-, 23- and 49-day-old flies, using a 0.48 kb Sall EcoRl fragment of the Drosophila SOD cDNA and a 1.4 kb fragment of the human catalase cDNA. Heat shock induction was monitored with a 5.4 kb DNA fragment of the Drosophila hsp70 gene. After exposure to 37°C for 30 min and 60 min, the level of SOD RNA in young flies was elevated above that of nonstressed conditions. Changes in the transcription of SOD gene with age paralleled the expression of hsp70 RNA. The SOD RNA was elevated in heat-shocked middle aged (23-25 days old) flies compared to young Drosophila (2 days old), then it decreased in 49-50-day-old flies. The relative expression of CAT RNA did not change with age or after heat shock. Enzymatic activities of these two antioxidant enzymes were evaluated in nondenaturing polyacrylamide electrophoresis gels. SOD migrates on this gel as three different electromorphs. These were designated as fast, intermediate and slow migrating bands. The most intense activity was associated with the fast band in these flies. In the absence of heat shock, there was an age-dependent decrease in the intermediate, but not in the slow or fast bands. Heat shock does not affect the intensity of the fast band in young or old flies, however; in middle aged flies, there is a shift in this band toward the slow position. No change was detected in the activity of catalase with age or heat shock, although flies of all ages exhibited a shift toward a faster-migrating electromorph with increasing time of heat shock. This effect was also observed in flies fed H2O2 and is more pronounced in insects fed higher concentrations. These results are discussed in relation to the role of these antioxidant enzymes in protecting against age-induced oxidative stresses.