Nearly all multicellular organisms show changes in redox balance with aging leading to oxidative damage of macromolecules. This study investigated the role of the [NADP+]/[NADPH] redox couple in aging. This redox couple plays an important role in maintaining tissue redox balance and becomes slightly more oxidized in aged tissues. NADPH is a major source of reducing equivalents for enzymes that detoxify hydrogen peroxide. However, catalase detoxifies hydrogen peroxide independently of NADPH. But catalase is absent from mitochondria, a major source of hydrogen peroxide, where instead glutathione plays the major role in hydrogen peroxide detoxification in an NADPH-dependent manner. Three major cytoplasmic and three major mitochondrial NADPH generating enzymes were knocked down by the RNAi feeding technique in C. elegans, but little to no significant effects on lifespan were observed. The C. elegans genome contains two predicted, yet uncharacterized, NAD kinase (NADK) genes nadk-1 and nadk-2 to synthesize NADP+. Data suggest that NADK-1 is cytoplasmic, while NADK-2 is mitochondrial. NADK activity assays strongly suggested that both NADK-1 and NADK-2 possess NADK activity. Knockdown of NADKs did not affect the rate of body bending in young nematodes. However, knockdown of nadk-2 in nadk-1 mutant worms slightly decreased lifespan. Deficiency of NADKs increased the [NADP+]/[NADPH] and decreased the [NAD+]/[NADH], similar to redox changes that occur with aging. Unexpectedly, nadk-1 or nadk-2 knockdown resulted in decreased reactive oxygen species (ROS) levels and increased survival in young adult nematodes in the presence of juglone, a superoxide generator. The antioxidant response generated upon NADK knockdown required the transcription factors DAF-16/FOXO, SKN-1/Nrf2, and HSF-1 in nadk-2 knockdown nematodes, but only required HSF-1 in nadk-1 knockdown nematodes. NADK-1 or NADK-2 deficiency led to increased catalase activity and a strong trend for increased cytoplasmic catalase-1 (ctl-1) gene expression. Peroxisomal catalase-2 (ctl-2) mutant worms showed increased SOD activity when either NADK gene was knocked down, while ctl-1 mutant worms showed increased glutathione peroxidase or glutathione reductase activities following NADK knockdown. In summary, NADK knockdown oxidizes the [NADP+]/[NADPH] to compromise the antioxidant system, but young nematodes are able to mount a compensatory broad antioxidant response leading to decreased ROS levels.

Bien que les statines forment la classe d'hypolipidémiants la plus utilisée, une toxicité musculaire a été reportée, pouvant ainsi provoquer l’apparition d’une myopathie. Dans la première partie, nous avons montré chez l’Homme et l’animal que les statines inhibent directement la chaine respiratoire mitochondriale, et induisent la production de radicaux libres dérivés de l’oxygène (RLO), qui active les voies apoptotiques dans les muscles glycolytiques, alors que les muscles oxydatifs ne sont pas atteints. Nous avons ensuite montré in vitro que le stress réducteur peut engendrer une oxydation mitochondriale, pouvant conduire à une activation de la voie de biogenèse mitochondriale. De plus l’augmentation du contenu mitochondrial induite a permis de protéger les cellules contre l’apoptose induite par les statines. Enfin, nous avons montré in vivo que l’induction des voies de biogenèse mitochondriale est nécessaire à la tolérance des statines dans les muscles oxydatifs. En conclusion, le phénotype mitochondrial, tant au niveau quantitatif que qualitatif, semble être un facteur clé dans l’apparition de la myopathie aux statines. / Although statins are the most prescribed class of lipid-lowering agents, adverse muscular toxicity has been reported, which can lead to the appearance of a myopathy. In the first part, we showed in Humans and animals that statins inhibit directly the mitochondrial respiratory chain, and induce the production of reactive oxygen species (ROS), that trigger apoptotic pathways in glycolytic skeletal muscles, whereas oxidative muscles are not impaired. We then showed in vitro that reductive stress can provoke mitochondrial oxidation, that could lead to an activation of mitochondrial biogenesis pathways. Moreover, the consequent increase in mitochondrial content enabled to protect cells against statin-induced apoptosis. Finally, we showed in vivo that the induction of mitochondrial biogenesis is necessary for statin tolerance in oxidative skeletal muscles. In conclusion, mitochondrial phenotype, both quantitatively and qualitatively, seems to be a key factor in the appearance of statin myopathy.