Male <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> flies exposed to hypergravity at young age are protected against a non-lethal heat shock at middle age but not against behavioral impairments due to this shock

Previous studies have shown that exposing flies to hypergravity (3 or 5g) for two weeks at young age slightly increases longevity of male flies and survival time at 37 °C of both sexes, and delays an age-linked behavioral change. The present experiments tested whether hypergravity could also protect flies from a non-lethal 37 °C heat shock applied at young, middle or old age (2, 4 or 6weeks of age). Various durations of exposure at 37 °C had similar deleterious effects on climbing activity, spontaneous locomotor activity and learning in flies that lived or not in hypergravity at young age. Therefore, hypergravity does not protect the behavior of flies from a deleterious non-lethal heat shock. Hypergravity increased longevity of virgin males and decreased that of mated ones; it also increased longevity of virgins at 25 °C, the usual rearing temperature, but not at 30 °C. Thus, the positive effect of hypergravity on longevity is observed only if flies are not subjected to living conditions decreasing longevity, like mating and high temperature. Finally, 4 weeks-old males that lived in hypergravity at young age lived slightly longer (+ 15%) after a non-lethal heat shock (60 or 90 min at 37 °C) than flies that always lived at 1 g, but this positive effect of hypergravity was not observed in females or in older males. Therefore, all these results show that hypergravity exposure can help male middle-aged flies recovering from a heat shock, but does not protect them from behavioral impairments linked to this shock: a mild stress occurring at young age can partially protect from a moderate stress at middle age.     

Hormetic effects of repeated exposures to cold at young age on longevity,aging and resistance to heat or cold shocks in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Exposing young flies to hypergravity has hormetic effects on aging, longevity and resistance to heat stress. The present experiments tested whether cold shocks at young age could also have hormetic effects. Flies were cold-shocked at 0°C daily for 60 min during two periods of 5 days separated by 2 days, starting at 5 days of age. This cold stress increased longevity, resistance to a lethal heat stress or to cold up to 6 weeks of age, resistance to a non-lethal heat stress at middle age, and delayed behavioral aging. Cold and hypergravity exposure at young age have thus similar effects, excepting on resistance to cold stress, which is not increased after exposure to hypergravity. Mild heat stress has also been shown to slightly increase longevity and resistance to a lethal heat stress, but not to delay behavioral aging. Since there are thus at least two mild stresses with large hormetic effects at old age in flies, i.e. cold and hypergravity, hormetic effects in flies are not stress-specific. Therefore, it could be hypothetized that hormetic effects of mild stress on aging and longevity are a general phenomenon and that they could also be observed in other species such as rodents.     

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.     

A cold stress applied at various ages can increase resistance to heat and fungal infection in aged <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> flies

A cold stress applied to young flies can have positive effects on longevity, behavioral aging, and resistance to heat and infection. However, the same mild stress, if applied at older ages, i.e. in frailer flies, could be a strong stress with negative effects. Cold stress was applied at various ages (weeks 1–2, 2–3, 3–4, and 4–5) and its effect on longevity and on resistance at 6 weeks of age to heat or fungal infection was observed. In males, the cold stress had positive effects on longevity and resistance to infection, except when applied at the oldest age. No positive effect on longevity or resistance to infection was detected in cold-stressed females, as already observed in previous experiments using a cold stress at young age only. By contrast, cold stress applied at various ages increased resistance to heat in both sexes. Therefore, a mild stress can have positive effects on longevity and resistance to strong stresses not only when used at a young age, but also at older ages.     

Hormetic effects on longevity of hydrogen peroxide in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> flies living on a poorly nutritious medium

Subjecting flies to a mild stress at a young age may increase longevity and protect against strong stresses occurring at middle age. The purpose of this article is to test whether a mild stress could also increase survival time of flies living in stressful conditions. Flies were transferred at middle age in vials where they could only feed on a saccharose solution without any other nutrient. This poor medium is known to decrease longevity and it was hypothetized that adding hydrogen peroxide to it could minimize this negative effect. While high doses of hydrogen peroxide decreased further longevity, a low dose increased it in 4-week-old males and, only in some experiments, in females. This low dose had however not any positive effect on behavioral aging, resistance to heat and starvation. The positive effect of hydrogen peroxide appeared not to be due to a sanitary action upon the environment. Rather, it seems that hydrogen peroxide was a mild stress helping flies to cope with the negative effects of saccharose on longevity. Therefore, it is concluded that hydrogen peroxide, beyond the deleterious effects of high doses, could have positive effects in organisms when used at a low dose, particularly in stressful living conditions.     

A mild stress, hypergravity exposure, postpones behavioral aging in Drosophila melanogaster.

Flies were submitted to two weeks of hypergravity in a centrifuge (3 or 5 g), starting at the second day of imaginal life, and their behavior (spontaneous locomotor activity, patterns of movement, and climbing activity) was observed from removal of the centrifuge to an older age; the usual effects of age on these behaviors were generally observed. Hypergravity-kept flies had worse behavioral scores on removal of centrifuge than those always kept at 1 g. When they aged, they got either similar or better scores than 1 g flies, which indicates that their behavioral aging may be slower. These results show that a mild stress such as hypergravity, which has been previously shown to increase the longevity of males and resistance to heat shock in both sexes, is an environmental manipulation postponing aging in flies.     

Lack of hypergravity-associated longevity extension in Drosophila melanogaster flies overexpressing hsp70

Previous studies have shown that Drosophila melanogaster males live longer if exposed to hypergravity at young age. Similarly, thermotolerance and climbing activity in old age are enhanced and it has been hypothetized that the 70 kDa inducible heat-shock protein (hsp70) may play a role in some of these effects. In this article, longevity, thermotolerance and climbing activity were studied in transgenic flies (OE+strain) over expressing hsp70 and in control flies harboring the transfection vector at the same chromosomal location but no extra-copies of the hsp70 gene (OE−strain). No positive effect from exposure to hypergravity at a young age was observed for longevity and climbing activity. Thermotolerance was increased by hypergravity but to the same extent in OE+ and OE− strains. Since no positive effect from hypergravity exposure or similar effects were observed in the two strains, it may be concluded that over expression ofhsp70 does not provide an advantage to flies subjected to a mild stress and that it may not be of any help during aging. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Cold stress increases resistance to fungal infection throughout life in Drosophila melanogaster

Flies were subjected to one of three mild stresses known to have positive effects on longevity (heat, hypergravity, cold), prior to an infection with the entomopathogenic fungus Beauveria bassiana. Flies subjected to cold survived longer to infection, while the other mild stresses had no positive effect. These positive effects of a cold stress on resistance to infection were observed mainly in males and throughout life, i.e., a long time after the cold stress was applied. It was confirmed that cold and hypergravity stresses increased longevity of non-infected flies, but no positive effect of heat shocks were however observed.     

Locomotor activity as a function of age and life span in Drosophila melanogaster overexpressing hsp70

Heat shock protein induction might be responsible for the longevity increase conferred by exposure to non-lethal stresses. To test this hypothesis, we studied in transgenic Drosophila melanogaster overexpressing hsp70 and controls, two behavioral variables (spontaneous locomotor activity and climbing activity) to evaluate the rate of aging, and life span. The results showed that in flies kept in groups, life span was decreased in transgenic flies compared to the parental line, but the contrary was observed in individually kept flies. Hsp70 overexpression had no dramatic effect on life span. Furthermore, we did not detect any advantage of Drosophila overexpressing hsp70 on the two measurements of locomotor activity. These results indicate that the rate of aging in transgenic flies is not different than in non-transgenic lines and that they are not more able to cope with the effects of aging on locomotor activity.     

Combined effects of suppressing live yeast and of a cold pretreatment on longevity,aging and resistance to several stresses in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

A cold pretreatment has various positive effects on aging, longevity, and resistance to some stresses in Drosophila melanogaster flies. Removing live yeast from food has either favorable or deleterious effects on these traits. This study combined a cold pretreatment and removal of live yeast in the same flies, in order to know whether higher favorable effects would be observed with this combination than with each treatment alone. Each treatment had positive effects on climbing activity and their combination had additive effects, thus giving the highest climbing scores in flies subjected to the two treatments and the lowest ones in flies with live yeast and no cold pretreatment. Therefore, combining the two treatments had favorable effects if each of them had favorable effects. When removing live yeast had very deleterious effects, as on resistance to cold, a cold pretreatment was unable to reverse these effects, which was not unexpected. Finally, when removal had no effect or not a tragic negative effect, as on resistance to infection or to heat, a cold pretreatment was neutral or slightly compensated the negative effects of live yeast removal. These results lead to the conclusion that next studies using a combination of two mild stresses having beneficial effects on aging and longevity could bring more positive effects than each mild stress alone.     

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.     

Enhancement of stress resistances and downregulation of Imd pathway by lower developmental temperature in Drosophila melanogaster

Ambient temperature affects the lifespan of cold-blooded organisms such as Drosophila melanogaster. To better understand what influences the lifespan of an adult fruit fly, we tested whether developmental temperature could affect stress responses used as surrogate markers for the aging process. When 2-day-old adult flies developed at two representative temperatures (18 °C and 25 °C) were challenged with three stresses (starvation, oxidation, and heat), both male and female flies developed at 18 °C exhibited stronger resistance to all three stresses compared to those developed at 25 °C. Nutrient composition analyses showed that fat, protein, and glycogen levels increased when male flies were developed at 18 °C. These differences in stress resistance by developmental temperature were sustained even between 30-day-old male flies of two groups aged at the same temperature. We also showed that development at a lower temperature represented by 18 °C significantly downregulates anti-microbial peptide genes, AttA and DptB, of Imd pathway.     

Quantitative trait loci for longevity in heat-stressed Drosophila melanogaster

Longevity is a typical quantitative trait which is influenced by multiple genes. Here we explore the genetic variation in longevity of Drosophila melanogaster in both mildly heat-stressed and control flies. Quantitative trait loci (QTL) analysis for longevity was performed in a single-sex environment at 25 °C with and without a mild heat-stress pre-treatment, using a previously reported set of recombinant inbred lines (RIL). QTL regions for longevity in heat-stressed flies overlapped with QTL for longevity in control flies. All longevity QTL co-localized with QTL for longevity identified in previous studies using very different sets of RIL in mixed sex environments, though the genome is nearly saturated with QTL for longevity when considering all previous studies. Heat stress decreased the number of significant QTL for longevity if compared to the control environment. Our mild heat-stress pre-treatment had a beneficial effect (hormesis) more often in shorter-lived than in longer-lived RIL.     

Protein synthesis elongation factor EF-1 alpha expression and longevity in Drosophila melanogaster.

It has been proposed that the decline in protein synthesis observed in aging organisms may result from a decrease in elongation factor EF-1 alpha. Transgenic Drosophila melanogaster flies carrying an additional copy of the EF-1 alpha gene under control of a heat-inducible promoter have an extended lifespan, further indicating that the EF-1 alpha gene may play an important role in determining longevity. To test this hypothesis, we have quantitated EF-1 alpha mRNA, EF-1 alpha protein, and the EF-1 alpha complex-formation activity in these transgenic flies. Furthermore, we have tested whether the transgene construct is functional--i.e., whether transgenic mRNA is induced when flies are grown at higher temperature. The results show that although there is a clear difference in mean lifespan between the EF-1 alpha transgenic (E) flies and the control transgenic (C) flies, E flies do not express more EF-1 alpha protein or mRNA than C flies kept at the same experimental conditions. Although the transgene can be induced when E flies are heat-shocked at 37 degrees C, transgenic mRNA is not detectable in E flies aged at 29 degrees C. In both lines, the loss in catalytic activity with age is the same. We conclude that the E flies examined here do not live longer because of overexpressing the EF-1 alpha gene.     

Korean mistletoe (Viscum album coloratum) extract extends the lifespan of nematodes and fruit flies

Viscum album coloratum (Korean mistletoe) is a semi-parasitic plant that grows on various trees and has a variety of biological functions such as immunomodulation, apoptosis, and anti-tumor activity. In this study, we investigated the effects of Korean mistletoe extract (KME) on lifespan in experimental models using Caenorhabditis elegans and Drosophila melanogaster. Supplementation of KME at 50 μg/ml extended the mean survival time by 9.61 and 19.86 % in worms and flies, respectively. The longevity benefit of KME was not due to reduced feeding, reproduction, and/or locomotion in flies and worms. The supplementation of KME also did not increase resistance to various stresses including heat shock, oxidative, or starvation stresses. Furthermore, KME did not further extend the lifespan of flies fed a dietary restricted diet but did increase the expression of Sir2, one of the target genes of dietary restriction, suggesting that KME may function as a putative dietary restriction mimetic. These results also suggest that the longevity promoting effects of KME may be an example of mild stress-induced hormesis.     

Is Lifespan Extension Accompanied by Improved Antioxidant Defences? A Study of Superoxide Dismutase and Catalase in Drosophila Melanogaster Flies that Lived in Hypergravity at a Young Age

It has been previously shown that exposing Drosophila melanogaster flies to hypergravity (3g or 5g) at a young age for 2 weeks increases male longevity, resistance to heat in both sexes, and delays behavioural ageing, but the causes of these effects are unknown. We hypothesised that these flies could be well protected against free radical attacks and, if this protection persists after removal from hypergravity, can better resist free radicals and finally live longer than flies that have always lived at 1g. If so, the activity of enzymes detoxifying free radicals superoxide dismutase and catalase should be increased in flies that have lived in hypergravity. Results showed that no effect of hypergravity on the activity of these enzymes was observed at 2, 4 or 6 weeks of age. The greater longevity of male flies that have lived in hypergravity at a young age thus cannot be explained by the activity changes of these major antioxidant enzymes.     

Effects of dietary composition on life span of Drosophila buzzatii and its short-lived sibling species D. koepferae

Two sibling Drosophila species dramatically divergent in longevity, Drosophila buzzatii and D. koepferae, were examined for possible effects of both developmental culture medium and dietary composition (DC) on longevity. Longevity was greatly increased in the longer lived D. buzzatii when flies were reared and fed on a rich-in-nutrient and cactus-based culture (R-CBC) as compared to longevity in a poor nutrient culture (PNC). In D. buzzatii, life span was further increased by exposing flies to short periods of a poor-in-nutrient and cactus-based culture (P-CBC). In contrast, variation in the here used nutrient composition did not change life span in the shorter lived D. koepferae, as longevity in this species did not differ among R-CBC, P-CBC and PNC cultures. Hormesis is a plausible explanation for the beneficial biological effects against aging arising from brief exposure to a lowed calorie food source in D. buzzatii. This study shows that genetic variation between closely related species is substantial for dietary effects on longevity.     

Ascorbic acid in Drosophila and changes during aging.

The ascorbic acid content of Drosophila melanogaster was found to be high in the absence of a dietary source. The amount of ascorbic acid per fly declined with aging in both the Oregon R and Swedish C strains. The median life span at 25 degrees C was 45 days for Swedish C and 59 days for Oregon R. The amount of ascorbic acid in Swedish C flies (0.078 micrograms/fly) was higher than that for Oregon R (0.058 micrograms/fly) for newly emerged flies but the rate of decline with aging was greater for Swedish C than Oregon R. The decline in ascorbic acid content with aging was 70.4% for Swedish C versus 19.9% for Oregon R. A brief cold shock was found to significantly increase the amount of ascorbic acid in Oregon R flies. Feeding the precursor of ascorbic acid synthesis, L-gulonolactone, did not improve the life span. Life-time feeding of ascorbic acid did not improve the life span of either Swedish C or Oregon R flies.