Hyperoxia Exposure Induced Hormesis Decreases Mitochondrial Superoxide Radical Levels via Ins/IGF-1 Signaling Pathway in a Long-lived age-1 Mutant of Caenorhabditis elegans

The hormetic effect, which extends the lifespan by various stressors, has been confirmed in Caenorhabditis elegans (C. elegans). We have previously reported that oxidative stress resistance in a long-lived mutant age-1 is associated with the hormesis. In the age-1 allele, which activates an insulin/insulin-like growth factor-1 (Ins/IGF-1) signaling pathway, the superoxide dismutase (SOD) and catalase activities increased during normal aging. We now demonstrate changes in the mitochondrial superoxide radical (*O(2)(-)) levels of the hormetic conditioned age-related strains. The *O(2)(-) levels in age-1 strain significantly decreased after intermittent hyperoxia exposure. On the other hand, this phenomenon was not observed in a daf-16 null mutant. This hormesis-dependent reduction of the *O(2)(-) levels was observed even if the mitochondrial Mn-SOD was experimentally reduced. Therefore, it is indicated that the hormesis is mediated by events that suppress the mitochondrial *O(2)(-) production. Moreover, some SOD gene expressions in the hormetic conditioned age-1 mutant were induced over steady state mRNA levels. These data suggest that oxidative stress-inducible hormesis is associated with a reduction of the mitochondrial *O(2)(-) production by activation of the antioxidant system via the Ins/IGF-1 signaling pathway.