FLP Recombinase-Mediated Induction of Cu/Zn-Superoxide Dismutase Transgene Expression Can Extend the Life Span of Adult Drosophila melanogaster Flies

Yeast FLP recombinase was used in a binary transgenic system (“FLP-OUT”) to allow induced overexpression of catalase and/or Cu/Zn-superoxide dismutase (Cu/ZnSOD) in adult Drosophila melanogaster. Expression of FLP recombinase was driven by the heat-inducible hsp70 promoter. Once expressed, FLP catalyzed the rearrangement and activation of a target construct in which expression of catalase or Cu/ZnSOD cDNAs was driven by the constitutive actin5C promoter. In this way a brief heat pulse (120 or 180 min, total) of young adult flies activated transgene expression for the rest of the life span. FLP-OUT allows the effects of induced transgene expression to be analyzed in control (no heat pulse) and experimental (heat pulse) populations with identical genetic backgrounds. Under the conditions used, the heat pulse itself always had neutral or slightly negative effects on the life span. Catalase overexpression significantly increased resistance to hydrogen peroxide but had neutral or slightly negative effects on the mean life span. Cu/ZnSOD overexpression extended the mean life span up to 48%. Simultaneous overexpression of catalase with Cu/ZnSOD had no added benefit, presumably due to a preexisting excess of catalase. The data suggest that oxidative damage is one rate-limiting factor for the life span of adult Drosophila. Finally, experimental manipulation of the genetic background demonstrated that the life span is affected by epistatic interactions between the transgene and allele(s) at other loci. An increasing number of data suggest that oxidative damage contributes to the aging process in Drosophila melanogaster and other organisms. The oxygen radical superoxide is produced primarily as a by-product of normal oxidative respiration in mitochondria. Superoxide can be converted by multiple pathways in vivo to the highly reactive hydroxyl radical. Hydroxyl radical and other oxygen radicals cause significant damage to cellular macromolecules including protein, DNA, and lipids (1, 48, 61). The enzymes catalase and Cu/Zn-superoxide dismutase (Cu/ZnSOD) are primary cellular defenses against oxygen radicals, and their functions are conserved from Escherichia coli to humans. Cu/ZnSOD converts superoxide to H2O2, and catalase converts H2O2 to H2O and O2. These cellular defenses against oxidative damage are not completely efficient, since oxidatively damaged macromolecules have been found to accumulate in virtually all aging organisms examined. In humans, mutations in Cu/ZnSOD which increase oxidative stress cause the neurodegenerative disease familial amyotrophic lateral sclerosis (10, 14, 42). Oxidative damage has also been implicated in several other neurodegenerative diseases, including Alzheimer’s disease and Parkinson’s disease (52). Increased wild-type Cu/ZnSOD activity can also have negative effects. Constitutive overexpression of Cu/ZnSOD in transgenic mice by using the homologous promoter causes cell-typespecific developmental and functional abnormalities generally attributed to disruption of normal oxidative stress defenses (3, 5).