Regulation of Drosophila life-span: Effect of genetic background,sex, mating and social status

During the past decade, model organisms such as Drosophila have made it possible to identify individual genes and pathways that regulate organismal life-span. However, despite the progress made in Drosophila aging research, many longevity studies have often yielded controversial results that can be attributed to differences both in genetic background and in experimental design. Here, we describe the results of a systematic analysis of life-span comparisons in two laboratory wild-type strains. The main goal of these studies is to clarify the effects of social status, mating and sex on life-span with the aim of defining the optimal experimental design whereby the influence of these factors would be minimized. We find that differences in environmental factors and genetic background can be minimized by measuring the life-span of flies that are maintained as mixed-sex groups that allow for regular sexual and social contacts and seems to be more physiologically relevant for estimation of population’s life-span. Taken together, these results may be especially important for screens designed to search for genes that may be involved in longevity as well as for comparative analysis of strains in which the genetic background is unknown or in those cases where it is very difficult to equilibrate.     

Food presentation modifies longevity and the beneficial action of dietary restriction in Drosophila

Recent studies have indicated that flies respond to dilute food solutions by compensatory feeding. The existence of compensation mechanisms calls for a reconsideration of the relationships between diet, feeding behaviour and longevity. This study shows that flies fed on liquid diets, sense sucrose and yeast nutrients and adapt to changes in the quantity and presentation of the two nutrients. They have a marked preference for sucrose and regulate their sucrose intake more tightly than their yeast intake. These preferences are not modified as fly age from 1 to 30 days. Compensatory feeding suppresses the beneficial action of dietary restriction on longevity when flies are fed on liquid diets supplemented with yeast extracts. Flies which are given the choice to feed on separate yeast and sucrose food sources were longer lived than flies fed on nutrient mixtures. We conclude that flies sense and respond to specific nutrients and that food presentation is a major factor which determines the sensitivity of flies to dietary restriction.     

Contrasted effects of suppressing live yeast from food on longevity,aging and resistance to several stresses in Drosophila melanogaster

It is often accepted that dietary restriction (DR) increases longevity in Drosophila melanogaster, but this is still a controversial issue. In the present study, adult flies were fed on a rich nutritious medium to which live yeast, a source of proteins, was added or not. Suppressing live yeast did not always increased longevity of virgin flies, but increased it in mated flies. It also decreased fecundity, delayed behavioral aging and increased resistance to heat of young females only. However, flies without live yeast suffered from a reduced resistance to cold, starvation and infection. This study thus reports some positive effects of suppressing live yeast on longevity, contrarily to previous studies of the same laboratory using other DR methods, but also shows that the absence of live yeast increases frailty. The effects of live yeast in flies are thus contrasted, and it is probable that flies without a high amount of proteins in the diet would not survive for a long time in the wild, due to their inability to resist stress and their low fecundity.     

Drosophila foxo acts in males to cause sexual-dimorphism in tissue-specific p53 life span effects

Sex-specific selective pressures are hypothesized to lead to sexually antagonistic gene functions that contribute to phenotypes such as aging and cancer. However, relatively little is known about the identity of such genes and possible mechanisms. Here we report that nervous system-specific over-expression of wild-type p53 in Drosophila caused decreased life span in males and increased life span in females. In contrast, tissue-general over-expression produced the opposite pattern: increased life span in males and decreased life span in females. In a foxo null background, p53 life span effects in males were reversed, becoming similar to the effects in females. In contrast, a Sir2 null background tended to reduce the magnitude of p53 effects. The data demonstrate that wild-type p53 over-expression can regulate life span independent of foxo, and suggest that foxo acts in males to produce sexually antagonistic life span effects of p53.     

Curcumin is an early-acting stage-specific inducer of extended functional longevity in Drosophila

Larval feeding with curcumin induces an extended health span with significantly increased median and maximum longevities in the adult fly. This phenotype is diet insensitive and shows no additive effect on longevity when combined with an adult dietary restriction (DR) diet, suggesting that curcumin and DR operate via the same or overlapping pathways for this trait. This treatment significantly slows the aging rate so that it is comparable with that of genetically selected long lived animals. The larval treatment also enhances the adult animal's geotactic activity in an additive manner with DR, suggesting that curcumin and DR may use different pathways for different traits. Feeding the drug to adults during only the health span also results in a significantly extended health span with increased median and maximum life span. This extended longevity phenotype is induced only during these stage-specific periods. Feeding adults with the drug over their whole life results in a weakly negative effect on median longevity with no increase in maximum life span. There are no negative effects on reproduction, although larval curcumin feeding increases development time, and also apparently accelerates the normal late-life neuromuscular degeneration seen in the legs. Gene expression data from curcumin-fed larvae shows that the TOR pathway is inhibited in the larvae and the young to midlife adults, although several other genes involved in longevity extension are also affected. These data support the hypothesis that curcumin acts as if it is a DR mimetic nutraceutical. These data also suggest that the search for DR mimetics may be enhanced by the use of stage-specific screening of candidate molecules.     

Ageing in Drosophila: The role of the insulin/Igf and TOR signalling network

A remarkable discovery of recent years is that, despite the complexity of ageing, simple genetic interventions can increase lifespan and improve health during ageing in laboratory animals. The pathways involved have often proved to sense nutrients and to match costly activities of organisms, such as growth, metabolism and reproduction, to nutrient status. For instance, the insulin/insulin-like growth factor and Target of Rapamycin signalling network has proved to play a function in ageing, from yeast to mammals, seemingly including humans. In the fruit fly Drosophila, altered activity of several components of this network can increase lifespan and improve locomotor and cardiac function during ageing. The fly brain, fat body (equivalent of mammalian liver and white adipose tissue) and the germ line are important in determination of lifespan, with considerable communication between different tissues. Cellular detoxification pathways, increased autophagy and altered protein synthesis have all been implicated in increased lifespan from reduced IIS/TOR activity, with the role of defence against oxidative stress unresolved. Reduced IIS/TOR signalling can alter or block the response of lifespan to dietary restriction. Reduced IIS can act acutely to lower death rate, implying that it may ameliorate the effects of ageing-related damage, rather than preventing it.     

Predicting death in female Drosophila

We have previously described a phenomenon called the death spiral that is characterized by a rapid decline in female fecundity 6–15 days prior to death in Drosophila. To carry out destructive physiological analyses of females in the death spiral would require a method to reliably classify individual females via the prediction of their age at death. Using cohorts of Drosophila we describe how to use the observed mortality prior to some target day and a female’s fecundity 3 days prior to the target day to determine if the female is in the death spiral. The method works at all ages and although the method does not result in perfect classification, with sufficient sample sizes any physiological trait whose means differ between the groups can be detected.     

Drosophila as a model for age-related impairment in locomotor and other behaviors

Aging is a multifaceted phenomenon that occurs in most species including humans and the fruit fly, Drosophila melanogaster. One of the most fundamental features of aging is the progressive decline in functional capacity that occurs with age (i.e. functional senescence). Age-related declines in function undermine many aspects of normal youthful physiology including behavior. Age-related behavioral declines are quite telling because they presumably reflect primary functional defects in the nervous system or musculature. Consequently, a more detailed understanding of behavioral declines that occur with age, including mechanisms that impinge on them, could ultimately lead to improved treatment or diagnosis of age-related defects in physiological processes that depend on normal function of the nervous system or musculature. Such advances in diagnosis or treatment would translate into tremendous gains in quality of life for elderly populations. In this article, we review progress using Drosophila to better understand age-related behavioral declines with a focus on age-related locomotor impairment.     

The Role of Mitochondria in Drosophila Aging

Understanding how alterations in mitochondrial function in different cells and tissues impacts the aging process remains one of the greatest challenges facing biogerontologists. Here, we discuss the recent upsurge in research in this area using the fruit fly Drosophila melanogaster as a model system. Topics that are discussed include age-related changes in mitochondrial function, mitochondrial oxidative stress and lifespan, life extension mediated by moderate knock-down of genes important for mitochondrial electron transport chain (ETC) function, and the relationship between dietary restriction and ETC activity. Finally, we review recent approaches to supplement the endogenous fly ETC with a single-subunit mitochondrial respiratory enzyme from yeast.     

Counting calories in Drosophila diet restriction

The extension of life span by diet restriction in Drosophila has been argued to occur without limiting calories. Here we directly measure the calories assimilated by flies when maintained on full- and restricted-diets. We find that caloric intake is reduced on all diets that extend life span. Flies on low-yeast diet are long-lived and consume about half the calories of flies on high-yeast diets, regardless of the energetic content of the diet itself. Since caloric intake correlates with yeast concentration and thus with the intake of every metabolite in this dietary component, it is premature to conclude for Drosophila that calories do not explain extension of life span.     

Investigation of the endocrine system in extended longevity lines of Drosophila melanogaster

There is a complete absence of information about the endocrinology of Drosophila melanogaster in relation to genetic-based differential longevity in this model species. In the present study, aspects of the endocrine system of D. melanogaster were investigated in selected and control lines characterized by relative differences in life span. By using extracts from whole bodies, steroid hormone (ecdysteroid) titers were determined by radioimmunoassay in all replicate selected and control lines on the first and fourth day of adult life. The results suggest that ecdysteroid titers were relatively reduced on the first day post-eclosion in females from the long-lived lines, but this difference was not present on the fourth day posteclosion. The reduction in early-age ecdysteroid titers in long-lived females might be related to the decrease in early-age fecundity in the selected lines. There was no difference between line types in male ecdysteroid titers on either day post-eclosion. Two classes of enzymes that act on juvenile hormone were also investigated in the present study. Esterase and epoxide hydrolase activity on juvenile hormone was assessed in females in all replicate selected and control lines at approximately 12 h or 4 days post-eclosion. There was no difference between selected and control lines in the specific activity of either class of enzymes that metabolize juvenile hormone.     

Using Drosophila melanogaster to study the positive effects of mild stress on aging

Several studies in the fly Drosophila melanogaster have shown that a mild stress can increase longevity, resistance to strong stresses (e.g., heat, fungal infection, cold) and delay behavioral aging. However, not all mild stresses have similar effects on the various studied traits. For instance, exposure to cold increases resistance to a fungal infection, but hypergravity and heat shocks do not. In addition to studies in flies and other invertebrates, it is necessary to perform experiments in mammals, to know whether mild stress could be used in therapy more thoroughly than today.     

New insights about cross-reactive epitopes of six trypanosomatid genera revealed that Crithidia and Leptomonas have antigenic similarity to L. (L.) chagasi

We investigated whether ELISA using crude antigens from insect and plant trypanosomatids, which are non-pathogenic and easily cultivated in large scale, has the same positivity data as Leishmania (Leishmania) chagasi, the etiological agent of human visceral leishmaniasis (VL) or canine leishmaniasis (CanL), or as Trypanosoma cruzi, the etiological agent of Chagas disease (CD). The antigens from Crithidia fasciculata, Crithidia luciliae, and Leptomonas seymouri showed 100% cross-reactivity with VL and CanL samples, with no statistically titers differences from L. (L.) chagasi, however, 34% (17/50) of VL samples revealed higher titers using the insect trypanosomatids than the homologous antigen. On the other hand, antigens from Strigomonas culicis, Angomonas deanei, and Phytomonas serpens showed low cross-reactivity with VL and CanL samples. The sera from patients with American tegumentary leishmaniasis showed low levels of cross-reactivity with all trypanosomatids investigated, even with L. (L) chagasi, without titers dissimilarity among them. These parasites were also worthless as antigen source for detection of CD cases, which required homologous antigens to reach 100% positivity. This study showed, by ELISA, that crude extract of Crithidia and Leptomonas have epitopes similar to L. (L.) chagasi, which supports the idea of using them as antigens source for the serodiagnosis of visceral leishmaniasis.     

A mild stress due to hypergravity exposure at youngage increases longevity in Drosophila melanogaster males

Drosophila melanogaster flies were exposed to hypergravity starting at two days of age, the range of gravity levels used being 2.58–7.38 g. No longevity change was observed for exposures of less than 14 days. The longevity of males increased if they were submitted to hypergravity for durations ranging from 14 to 24 days. This increase in longevity was never observed in females. The positive effect of exposure to hypergravity has been replicated in two laboratories using two wild-type strains and different rearing conditions. A short hypergravity exposure seems to be a mild stress, yielding positive effects on longevity. This is in accordance with two previous studies showing a slight longevity increase after heat shock in the nematode Caenorhabditis elegans and in Drosophila melanogaster.