The mechanisms through which dietary restriction enhances health and longevity in diverse species are unclear. The transsulfuration pathway (TSP) is a highly conserved mechanism for metabolizing the sulfur-containing amino acids, methionine and cysteine. Here we show that Drosophila cystathionine β-synthase (dCBS), which catalyzes the rate-determining step in the TSP, is a positive regulator of lifespan in Drosophila and that the pathway is required for the effects of diet restriction on animal physiology and lifespan. dCBS activity was up-regulated in flies exposed to reduced nutrient conditions, and ubiquitous or neuron-specific transgenic overexpression of dCBS enhanced longevity in fully fed animals. Inhibition of the TSP abrogated the changes in lifespan, adiposity, and protein content that normally accompany diet restriction. RNAi-mediated knockdown of dCBS also limited lifespan extension by diet. Diet restriction reduced levels of protein translation in Drosophila, and we show that this is largely caused by increased metabolic commitment of methionine cycle intermediates to transsulfuration. However, dietary supplementation of methionine restored normal levels of protein synthesis to restricted animals without affecting lifespan, indicating that global reductions in translation alone are not required for diet-restriction longevity. Our results indicate a mechanism by which dietary restriction influences physiology and aging.hydrogen sulfide | essential amino acids | metabolism | healthspan F or a broad range of taxonomically diverse organisms, the quality of their diet acts as a powerful modulator of health and longevity through molecular mechanisms that are largely unknown. Lifespan is extended, for example, when food is restricted to an extent that falls short of inducing starvation. In mammals, this manipulation, which is often called dietary restriction (DR), not only increases lifespan but also imparts a broad-spectrum improvement in health during aging. In humans, for example, DR reduces risk factors for diabetes, cardiovascular disease, and cancer (1).Transsulfuration is an evolutionarily ancient metabolic process that involves a network of enzymes responsible for the metabolism of sulfur-containing amino acids. The transsulfuration pathway (TSP) has been studied extensively in mammals, in which it has been shown to direct the conversion of homocysteine to cysteine following the breakdown of methionine, an essential amino acid. Flux through the TSP is known to affect overall cellular metabolism by directly influencing cysteine and methionine levels. Methionine availability affects protein synthesis and methylation, and it has been implicated in murine aging (2). Cysteine availability controls the synthesis of glutathione (GSH), which is the chief regulator of cellular redox homeostasis and an important agent in xenobiotic detoxification (Fig. 1A). Patients with genetic defects in the TSP are characterized by high levels of homocysteine, low levels of GSH, and increased incidence of age-related path...

Biotin deficiency is associated with fetal malformations and activation of cell survival pathways in mammals. In this study we determined whether biotin status affects life span, stress resistance, and fertility in the fruit fly Drosophila melanogaster. Male and female flies of the Canton-S strain had free access to diets containing 6.0 (control), 4.8, 2.5, or 0 pmol biotin/100 mg. Biotin concentrations in diets correlated with activities of biotin-dependent propionyl-CoA carboxylase and biotin concentrations in fly homogenates, but not with biotinylation of histones (DNA-binding proteins). Propionyl-CoA carboxylase activities and biotin concentrations were lower in males than in females fed diets low in biotin. The life span of biotin-deficient males and females was up to 30% shorter compared to biotinsufficient controls. Exposure to oxidative stress reversed the effects of biotin status on survival in male flies: survival times increased by 40% in biotin-deficient males compared to biotin-sufficient controls. Biotin status did not affect survival of females exposed to oxidative stress. Exposure of flies to cold, heat, and oxidative stress was associated with mobilization of biotin from yet unknown sources. Biotin deficiency decreased fertility of flies. When biotin-deficient males and females were mated, the hatching rate (larvae hatched per egg) decreased by about 28% compared to biotin-2 sufficient controls. These findings are consistent with the hypothesis that biotin affects life span, stress resistance, and fertility in fruit flies.

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Selenoproteins are essential in vertebrates because of their crucial role in cellular redox homeostasis, but some invertebrates that lack selenoproteins have recently been identified. Genetic disruption of selenoprotein biosynthesis had no effect on lifespan and oxidative stress resistance of Drosophila melanogaster. In the current study, fruit flies with knock-out of the selenocysteine-specific elongation factor were metabolically labeled with 75 Se; they did not incorporate selenium into proteins and had the same lifespan on a chemically defined diet with or without selenium supplementation. These flies were, however, more susceptible to starvation than controls, and this effect could be ascribed to the function of selenoprotein K. We further expressed mouse methionine sulfoxide reductase B1 (MsrB1), a selenoenzyme that catalyzes the reduction of oxidized methionine residues and has protein repair function, in the whole body or the nervous system of fruit flies. This exogenous selenoprotein could only be expressed when the Drosophila selenocysteine insertion sequence element was used, whereas the corresponding mouse element did not support selenoprotein synthesis. Ectopic expression of MsrB1 in the nervous system led to an increase in the resistance against oxidative stress and starvation, but did not affect lifespan and reproduction, whereas ubiquitous MsrB1 expression had no effect. Dietary selenium did not influence lifespan of MsrB1-expressing flies. Thus, in contrast to vertebrates, fruit flies preserve only three selenoproteins, which are not essential and play a role only under certain stress conditions, thereby limiting the use of the micronutrient selenium by these organisms. Selenium is an important dietary micronutrient in mammals.The major biological form of selenium is the non-canonical amino acid, selenocysteine (Sec).2 The majority of selenoproteins with known type of catalytic activity act as oxidoreductases that use Sec directly for catalysis and maintenance of cellular redox homeostasis. The number of selenoproteins in eukaryotic organisms varies significantly. Higher plants and fungi lack selenoprotein genes, whereas there are many such genes in algae and vertebrates, e.g. 10 -57 in algae, 30 -37 in fish, and 23-25 in mammals (1). At least five mammalian selenoproteins are essential (2-4). Remarkably, insects possess cysteinecontaining homologs or lack all essential mammalian selenoproteins, e.g. thioredoxin reductases and glutathione peroxidases. Moreover, recent studies identified five species of selenoproteinless insects, including the red flour beetle Tribolium castaneum (5), the silkworm Bombyx mori (5), the fly Drosophila willistoni (6), the honey bee Apis mellifera (6), and the wasp Nasonia vitripennis (6). This evolutionary reduction in the use of selenoproteins could be associated with considerable changes in antioxidant defense systems of insects (7-9).The Sec incorporation machinery is conserved across eukaryotes. Sec is encoded by the UGA codon that usually serves as a terminatio...

Superoxide dismutase (SOD) activities were determined for dietary dilution conditions that extend the life span of Drosophila melanogaster. The hypothesis motivating this research was that elevated SOD activity is associated with increased life span resulting from flies being held on a restricted diet. SOD activities were also measured for chico 1 which is a mutation in the insulin receptor substrate protein gene associated with life span extension. This allowed us to confirm the results of (Clancy et al. 2001) and extend the results by measuring CuZn SOD and Mn SOD activities in addition to the previously determined overall SOD activity. If the same form of SOD activity (CuZn SOD or Mn SOD) was elevated on the dilute diet that extends life span and in the long lived chico 1 homozygotes, then it would suggest that life span extension by dietary restriction and by insulin signaling mutations has a similar underlying mechanism. However, overall SOD activity, and CuZn SOD or Mn SOD activities did not differ among the diets tested. As observed previously (Clancy et al. 2001), overall SOD activity was elevated in chico 1 homozygotes compared to the heterozygote or wild type.Results from the present study indicate that elevated CuZn SOD activity, not Mn SOD, is the basis for the relatively high level of SOD activity in the chico 1 homozygotes.

We examine how aging is impacted by various chemical challenges that organisms face and by the molecular mechanisms that have evolved to regulate lifespan in response to them. For example, environmental information, which is detected and processed through sensory systems, can modulate lifespan by providing information about the presence and quality of food as well as presence and density of conspecifics and predators. In addition, the diverse forms of molecular damage that result from constant exposure to damaging chemicals that are generated from the environment and from metabolism pose an informatic and energetic challenge for detoxification systems, which are important in ensuring longevity. Finally, systems of innate immunity are vital for recognizing and combating pathogens but are also seen as of increasing importance in causing the aging process. Integrating ideas of molecular mechanism with context derived from evolutionary considerations will lead to exciting new insights into the evolution of aging.