Neuronal expression of p53 dominant-negative proteins in adult Drosophila melanogaster extends life span

Hyperactivation of p53 leads to a reduction in tumor formation and an unexpected shortening of life span in two different model systems . The decreased life span occurs with signs of accelerated aging, such as osteoporosis, reduction in body weight, atrophy of organs, decreased stress resistance, and depletion of hematopoietic stem cells. These observations suggest a role for p53 in the determination of life span and the speculation that decreasing p53 activity may result in positive effects on some aging phenotypes . In this report, we show that expression of dominant-negative versions of Drosophila melanogaster p53 in adult neurons extends life span and increases genotoxic stress resistance in the fly. Consistent with this, a naturally occurring allele with decreased p53 activity has been associated with extended survival in humans . Expression of the dominant-negative Drosophila melanogaster p53 constructs does not further increase the extended life span of flies that are calorie restricted, suggesting that a decrease in p53 activity may mediate a component of the calorie-restriction life span-extending pathway in flies.     

Overexpression of glutamate-cysteine ligase extends life span in Drosophila melanogaster

The hypothesis that overexpression of glutamate-cysteine ligase (GCL), which catalyzes the rate-limiting reaction in de novo glutathione biosynthesis, could extend life span was tested in the fruit fly, Drosophila melanogaster. The GAL4-UAS binary transgenic system was used to generate flies overexpressing either the catalytic (GCLc) or modulatory (GCLm) subunit of this enzyme, in a global or neuronally targeted pattern. The GCL protein content of the central nervous system was elevated dramatically in the presence of either global or neuronal drivers. GCL activity was increased in the whole body or in heads, respectively, of GCLc transgenic flies containing global or neuronal drivers. The glutathione content of fly homogenates was increased by overexpression of GCLc or GCLm, particularly in flies overexpressing either subunit globally, or in the heads of GCLc flies possessing neuronal drivers. Neuronal overexpression of GCLc in a long-lived background extended mean and maximum life spans up to 50%, without affecting the rate of oxygen consumption by the flies. In contrast, global overexpression of GCLm extended the mean life span only up to 24%. These results demonstrate that enhancement of the glutathione biosynthetic capability, particularly in neuronal tissues, can extend the life span of flies, and thus support the oxidative stress hypothesis of aging.     

Overexpression of glucose-6-phosphate dehydrogenase extends the life span of Drosophila melanogaster

The redox state of tissues tends to become progressively more prooxidizing during the aging process. The hypothesis tested in this study was that enhancement of reductive capacity by overexpression of glucose-6-phosphate dehydrogenase (G6PD), a key enzyme for NADPH biosynthesis, could protect against oxidative stress and extend the life span of transgenic Drosophila melanogaster. Overexpression of G6PD was achieved by combining a UAS-G6PD responder transgene at one of four independent loci with either a broad expression (armadillo-GAL4, Tubulin-GAL4, C23-GAL4, and da-GAL4) or a neuronal driver (D42-GAL4 and Appl-GAL4). The mean life spans of G6PD overexpressor flies were extended, in comparison with driver and responder controls, as follows: armadillo-GAL4 (up to 38%), Tubulin-GAL4 (up to 29%), C23-GAL4 (up to 27%), da-GAL4 (up to 24%), D42-GAL4 (up to 18%), and Appl-GAL4 (up to 16%). The G6PD enzymatic activity was increased, as were the levels of NADPH, NADH, and the GSH/GSSG ratio. Resistance to experimental oxidative stress was enhanced. Furthermore, metabolic rates and fertility were essentially the same in G6PD overexpressors and control flies. Collectively, the results demonstrate that enhancement of the NADPH biosynthetic capability can extend the life span of a relatively long-lived strain of flies, which supports the oxidative stress hypothesis of aging.     

Alternative mitochondrial fuel extends life span

In this issue of Cell Metabolism, Ristow and colleagues (Zarse et?al., 2012) elucidate a conserved mechanism through which reduced insulin-IGF1 signaling activates an AMP-kinase-driven metabolic shift toward oxidative proline metabolism. This, in turn, produces an adaptive mitochondrial ROS signal that extends worm life span. These findings further bolster the concept of mitohormesis as a critical component of conserved aging and longevity pathways.     

Lipid peroxidation and the life span of Drosophila melanogaster

Studies have been made on the relationship between incubation temperature (20-30 degrees C) of D. melanogaster and the life span as well as the content of various products of lipid peroxidation. It was shown that the increase in the environmental temperature results in the decrease in the life span, the content of unsaturated fatty acids and conjugated hydroxyperoxids; ketodienic content increases. Strong correlation was observed between the life span and the content of peroxidation products. As it is indicated by coefficients of bifactorial linear regression with interaction, conjugated hydroperoxids and ketodiens exert negative influence on the life span. Their combined effect on the life span is less significant than the sum of their separate effects, which indicates the existence of common "canals" of their influences on the life span.     

Phenotypic consequences of copper-zinc superoxide dismutase overexpression in Drosophila melanogaster

We report here the isolation of a tandem duplication of a small region of the third chromosome of Drosophila melanogaster containing the Cu-Zn superoxide dismutase (cSOD) gene. This duplication is associated with a dosage-dependent increase in cSOD activity. The biological consequences of hypermorphic levels of cSOD in genotypes carrying this duplication have been investigated under diverse conditions of oxygen stress imposed by acute exposure to ionizing radiation, chronic exposure to paraquat, and the normoxia of standard laboratory culture. We find that a 50% increase in cSOD activity above the normal diploid level confers increased resistance to ionizing radiation and, in contrast, confers decreased resistance to the superoxide-generating agent paraquat. The duplication is associated with a minor increase in adult life-span under conditions of normoxia. These results reveal important features of the biological function of cSOD within the context of the overall oxygen defense system of Drosophila.     

Partial ablation of adult Drosophila insulin-producing neurons modulates glucose homeostasis and extends life span without insulin resistance

In Drosophila melanogaster (D. melanogaster), neurosecretory insulin-like peptide-producing cells (IPCs), analogous to mammalian pancreatic β cells are involved in glucose homeostasis. Extending those findings, we have developed in the adult fly an oral glucose tolerance test and demonstrated that IPCs indeed are responsible for executing an acute glucose clearance response. To further develop D. melanogaster as a relevant system for studying age-associated metabolic disorders, we set out to determine the impact of adult-specific partial ablation of IPCs (IPC knockdown) on insulin-like peptide (ILP) action, metabolic outcomes and longevity. Interestingly, while IPC knockdown flies are hyperglycemic and glucose intolerant, these flies remain insulin sensitive as measured by peripheral glucose disposal upon insulin injection and serine phosphorylation of a key insulin-signaling molecule, Akt. Significant increases in stored glycogen and triglyceride levels as well as an elevated level of circulating lipid measured in adult IPC knockdown flies suggest profound modulation in energy metabolism. Additional physiological outcomes measured in those flies include increased resistance to starvation and impaired female fecundity. Finally, increased life span and decreased mortality rates measured in IPC knockdown flies demonstrate that it is possible to modulate ILP action in adult flies to achieve life span extension without insulin resistance. Taken together, we have established and validated an invertebrate genetic system to further investigate insulin action, metabolic homeostasis and regulation of aging regulated by adult IPCs.Key words: Drosophila melanogaster, insulin-producing cells (IPCs), drosophila insulin-like peptides (DILPs), type 2 diabetes, oral glucose tolerance test (OGTT), insulin sensitivity, energy metabolism, life span     

Radioinduced change in life span of laboratory strains of Drosophila melanogaster

Chronic irradiation (accumulated dose 0.6-0.8 Gy) was shown to change the life span in male Drosophila melanogaster. Death was retarded in wild-type strains and accelerated in mutant strains defective in DNA repair and displaying a higher sensitivity to induction of apoptosis.     

Absence of mitochondrial translation control proteins extends life span by activating sirtuin-dependent silencing

Altered mitochondrial functionality can extend organism life span, but the underlying mechanisms are obscure. Here we report that inactivating SOV1, a member of the yeast mitochondrial translation control (MTC) module, causes a robust Sir2-dependent extension of replicative life span in the absence of respiration and without affecting oxidative damage. We found that SOV1 interacts genetically with the cAMP-PKA pathway and the chromatin remodeling apparatus. Consistently, Sov1p-deficient cells displayed reduced cAMP-PKA signaling and an elevated, Sir2p-dependent, genomic silencing. Both increased silencing and life span extension in sov1Δ cells require the PKA/Msn2/4p target Pnc1p, which scavenges nicotinamide, a Sir2p inhibitor. Inactivating other members of the MTC module also resulted in Sir2p-dependent life span extension. The data demonstrate that the nuclear silencing apparatus senses and responds to the absence of MTC proteins and that this response converges with a pathway for life span extension elicited by reducing TOR signaling.     

Extension of Drosophila melanogaster life span with a GPCR peptide inhibitor

G protein-coupled receptors (GPCRs) mediate signaling from extracellular ligands to intracellular signal transduction proteins. Methuselah (Mth) is a class B (secretin-like) GPCR, a family typified by their large, ligand-binding, N-terminal extracellular domains. Downregulation of mth increases the life span of Drosophila melanogaster; inhibitors of Mth signaling should therefore enhance longevity. We used mRNA display selection to identify high-affinity (K(d) = 15 to 30 nM) peptide ligands that bind to the N-terminal ectodomain of Mth. The selected peptides are potent antagonists of Mth signaling, and structural studies suggest that they perturb the interface between the Mth ecto- and transmembrane domains. Flies constitutively expressing a Mth antagonist peptide have a robust life span extension, which suggests that the peptides inhibit Mth signaling in vivo. Our work thus provides new life span-extending ligands for a metazoan and a general approach for the design of modulators of this important class of GPCRs.     

The effects of catalase gene overexpression on life span and resistance to oxidative stress in transgenic Drosophila melanogaster.

Oxygen free radicals and hydroperoxides have been postulated to play a causal role in the aging process, implying that antioxidant enzymes may act as longevity determinants. Catalase (H2O2:H2O2 oxidoreductase; EC1.11.1.6) is the sole enzyme involved in the elimination of H2O2 in Drosophila melanogaster; glutathione peroxidase being absent. A genomic fragment containing the Drosophila catalase gene was used to construct transgenic Drosophila lines by means of P element-mediated transformation. Enhanced levels of catalase (up to 80%) did not prolong the life span of flies, nor did they provide improved protection against oxidative stress induced by hyperoxia or paraquat treatment. However, enhanced resistance to hydrogen peroxide was observed in the overexpressors.     

Survival analysis of life span quantitative trait loci in Drosophila melanogaster

We used quantitative trait loci (QTL) mapping to evaluate the age specificity of naturally segregating alleles affecting life span. Estimates of age-specific mortality rates were obtained from observing 51,778 mated males and females from a panel of 144 recombinant inbred lines (RILs). Twenty-five QTL were found, having 80 significant effects on life span and weekly mortality rates. Generation of RILs from heterozygous parents enabled us to contrast effects of QTL alleles with the means of RIL populations. Most of the low-frequency alleles increased mortality, especially at younger ages. Two QTL had negatively correlated effects on mortality at different ages, while the remainder were positively correlated. Chromosomal positions of QTL were roughly concordant with estimates from other mapping populations. Our findings are broadly consistent with a mix of transient deleterious mutations and a few polymorphisms maintained by balancing selection, which together contribute to standing genetic variation in life span.     

Extension of life span of Drosophila melanogaster by the inhibitors of tryptophan-kynurenine metabolism

Upregulation of kynurenine (KYN) formation from tryptophan (TRY) was associated with aging in animal and human studies. TRY-KYN metabolism is affected by the activities of TRY 2,3-dioxygenase 2 (TDO) and AT P-binding cassette (ABC) transporter regulating TRY access to intracellular TDO. We studied the effects of TDO inhibitor, alpha-methyl tryptophan (aMT) and ABC transported inhibitor, 5-methyl tryptophan (5MT), on the life span of wild strain female Drosophila flies (Oregon-R). aMT and 5MT prolonged mean and maximum life span (by 27% and 43%, and 21% and 23%, resp.). The present results are the first observation of the extension of life span of Drosophila melanogaster by inhibitors of TRY-KYN metabolism, and in line with literature and previous studies on prolonged life span of TDO- and ABC-deficient female Drosophila mutants. Inhibition of TDO and ABC transporter activity might offer the new target for anti-aging interventions.     

Extension of life span of Drosophila melanogaster by the inhibitors of tryptophan-kynurenine metabolism

Upregulation of kynurenine (KYN) formation from tryptophan (TRY) was associated with aging in animal and human studies. TRY - KYN metabolism is affected by the activities of TRY 2,3-dioxygenase 2 (TDO) and ATP-binding cassette (ABC) transporter regulating TRY access to intracellular TDO. We studied the effects of TDO inhibitor, alpha-methyl tryptophan (aMT), and ABC transported inhibitor, 5-methyl tryptophan (5MT), on the life span of wild strain female Drosophila flies (Oregon-R). aMT and 5MT prolonged mean and maximum life span (by 27% and 43%, and 21% and 23%, resp.). The present results are the first observation of the extension of life span of Drosophila melanogaster by inhibitors of TRY - KYN metabolism, and in line with literature and previous studies on prolonged life span of TDO- and ABC-deficient female Drosophila mutants. Inhibition of TDO and ABC transporter activity might offer the new target for anti-aging and anti-AAMPD interventions.     

The effect of developmental nutrition on life span and fecundity depends on the adult reproductive environment in Drosophila melanogaster

Both developmental nutrition and adult nutrition affect life‐history traits; however, little is known about whether the effect of developmental nutrition depends on the adult environment experienced. We used the fruit fly to determine whether life‐history traits, particularly life span and fecundity, are affected by developmental nutrition, and whether this depends on the extent to which the adult environment allows females to realize their full reproductive potential. We raised flies on three different developmental food levels containing increasing amounts of yeast and sugar: poor, control, and rich. We found that development on poor or rich larval food resulted in several life‐history phenotypes indicative of suboptimal conditions, including increased developmental time, and, for poor food, decreased adult weight. However, development on poor larval food actually increased adult virgin life span. In addition, we manipulated the reproductive potential of the adult environment by adding yeast or yeast and a male. This manipulation interacted with larval food to determine adult fecundity. Specifically, under two adult conditions, flies raised on poor larval food had higher reproduction at certain ages – when singly mated this occurred early in life and when continuously mated with yeast this occurred during midlife. We show that poor larval food is not necessarily detrimental to key adult life‐history traits, but does exert an adult environment‐dependent effect, especially by affecting virgin life span and altering adult patterns of reproductive investment. Our findings are relevant because (1) they may explain differences between published studies on nutritional effects on life‐history traits; (2) they indicate that optimal nutritional conditions are likely to be different for larvae and adults, potentially reflecting evolutionary history; and (3) they urge for the incorporation of developmental nutritional conditions into the central life‐history concept of resource acquisition and allocation.     

Genotype-environment interaction for quantitative trait loci affecting life span in Drosophila melanogaster

The nature of genetic variation for Drosophila longevity in a population of recombinant inbred lines was investigated by estimating quantitative genetic parameters and mapping quantitative trait loci (QTL) for adult life span in five environments: standard culture conditions, high and low temperature, and heat-shock and starvation stress. There was highly significant genetic variation for life span within each sex and environment. In the analysis of variance of life span pooled over sexes and environments, however, the significant genetic variation appeared in the genotype x sex and genotype x environment interaction terms. The genetic correlation of longevity across the sexes and environments was not significantly different from zero in these lines. We estimated map positions and effects of QTL affecting life span by linkage to highly polymorphic roo transposable element markers, using a multiple-trait composite interval mapping procedure. A minimum of 17 QTL were detected; all were sex and/or environment-specific. Ten of the QTL had sexually antagonistic or antagonistic pleiotropic effects in different environments. These data provide support for the pleiotropy theory of senescence and the hypothesis that variation for longevity might be maintained by opposing selection pressures in males and females and variable environments. Further work is necessary to assess the generality of these results, using different strains, to determine heterozygous effects and to map the life span QTL to the level of genetic loci.     

Expression of multiple copies of mitochondrially targeted catalase or genomic Mn superoxide dismutase transgenes does not extend the life span of Drosophila melanogaster

The simultaneous overexpression of multiple copies of Mn superoxide dismutase (SOD) and ectopic catalase (mtCat) transgenes in the mitochondria of the fruit fly, Drosophila melanogaster, was shown previously to diminish the life span. The hypothesis tested in this study was that this effect was due primarily to the presence of one or the other transgene. An alternative hypothesis was that both transgenes have additive, negative effects. Crosses were performed between five pairs of transgenic lines containing single-copy insertions of mtCat, Mn SOD, or P element vector control transgenes at unique loci, and the life spans of progeny containing two mtCat, Mn SOD, or vector insertions were determined. Increasing amounts of mitochondrial catalase activity tended to be associated with decreases in mean life span. Overexpression of two copies of the genomic Mn SOD transgene had no effect on life span. The results do not support the hypothesis that enhanced mitochondrial SOD or catalase activity promotes longevity in flies.