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.     

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.     

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.     

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.     

Effect of shielding from environmental neutrons on the life span of Drosophila: Preliminary evidence

Shielding adult Drosophila melanogaster fruit flies from environmental neutrons with either paraffin wax or boric acid increased the median life span by between 4.6 and 9.7%. The increase in life span was significant only when the shielding began at 14–29 days of adult age. Shielding begun at 1 day of adult age did not result in a significant increase in life span. Shielding with boron during the reproductive, developmental and adult stages, however, resulted in a significant reduction of 11.9% in the median survival time. Environmental background neutrons, therefore, had surprisingly both a negative and positive influence on longevity depending upon the period of life when the exposure occurred.     

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.     

Neural-specific overexpression of Drosophila Plenty of SH3s (DPOSH) extends the longevity of adult flies

Extended longevity mutants are extremelyuseful to understand the molecular mechanism oflongevity determination. Here we reportidentification and characterization of the Drosophila Plenty of SH3s (DPOSH) gene,a candidate that might be associated with theextended longevity phenotype. DPOSHencodes a protein containing a RING fingerdomain and four SH3 domains. We showed thatneural-specific overexpression of DPOSHcould extend the mean longevity of adult fliesby 14% at 25 °C without affectingviability or morphology. In contrast, forcedexpression of DPOSH in developingimaginal discs produced various phenotypesincluding lethality and morphological defectssuch as loss of crossvein, notched wing, anddisordered hair polarity. Puckered, atarget gene of JNK/SAPK pathway, was activatedby overexpression of DPOSH and the forcedexpression phenotypes were suppressed byintroducing a mutation of Drosophila JNK(bsk) or JNKK (hep),suggesting that the JNK/SAPK signaling pathwayis one of the critical elements in thedetermination of longevity.     

Combined effects of two mild stresses (cold and hypergravity) on longevity, behavioral aging, and resistance to severe stresses in Drosophila melanogaster

Mild stresses may have positive effects on aging, longevity and resistance to severe stresses at various ages in Drosophila melanogaster. However, no study has combined two mild stresses to know whether more positive effects would be observed than with each stress alone. Cold and hypergravity (HG) have positive effects on some traits, but negative ones can also be observed, particularly in females. This study combined in the same flies cold and HG exposure. When cold and HG had each positive or negative effects their combination had additive effects but, when only one of the pretreatments had some effect, the effect of their combination usually reflected this effect. Therefore, combining two mild stresses with positive effects on aging and longevity can be more efficient than each stress alone. However, if one of these mild stresses had negative effects and the other one positive effects, the net result of their combination could be the suppression of the positive effect of the second stress. On the whole, if the net result of the combination of two mild stresses would be negative, it would be preferable not to combine them.     

Effects of mild heat shocks at young age on aging and longevity in Drosophila melanogaster

Young adult flies were submitted to heat shocks (37°C) ofvarious durations (5, 10, 20, 40 or 60 min daily) for 1, 2 or 3 weeks. Aslight longevity increase, in both sexes, was only observed with thelowest heat shock. Longer shocks had neutral or negative effects. Fliessubmitted to the procedure providing a longevity increase did not show adelayed behavioral aging but survived longer at 37°C thancontrol flies. This higher thermotolerance was not associated with anincreased hsp70 induction. The results are discussed in connection withhormesis and previous results showing that hypergravity, an other mildstress, increases longevity and delays behavioral aging: different mildstresses may have contrasting effects on aging and longevity.     

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.     

Resistance to Oxidative Stress Induced by Paraquat Correlates Well with Both Decreased and Increased Lifespan in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

There is increasing support for the notion that genetic variation for lifespan, both within and between species, is correlated with variation in the efficiency of the free radical scavenging system and the ability to withstand oxidative stress. In Drosophila, resistance to dietary paraquat, a free radical generator, is often used as a measure of resistance to oxidative stress and is reported to give firm positive correlations with longevity. Recently it has been suggested that an increase in antioxidative defences in Drosophila only has a beneficial effect in relatively short-lived stocks. This implies that mechanisms of lifespan determination can be different in lines with different genetic constitution. Here we test if variation in resistance to dietary paraquat co-segregates with variation in lifespan in two sets of Drosophila melanogaster lines that were selected for decreased and increased virgin lifespan respectively. Flies of the short-lived lines show decreased resistance to paraquat compared to the control lines, indicating low resistance against oxidative stress. On the other hand, both males and females of the long-lived lines show, despite increased feeding rates on paraquat-supplemented food, no decreased survival compared to control lines. This shows that flies of the long-lived lines have increased paraquat resistance, but that this is masked by increased feeding rate, resulting in increased exposure to paraquat. This suggests that resistance to paraquat is a correlated response to selection on virgin lifespan over the entire genetic range.     

Effects of X-irradiation in early ontogenesis on the longevity and amount of the S1 nuclease-sensitive DNA sites in adult Drosophila melanogaster

The long-term consequences of the X-irradiationof Drosophila melanogaster fruit flyone-hour eggs with doses of 0.25, 0.50, 0.75,1, 2 and 4 Gy were investigated. Longevityhormesis was observed in males exposed to 0.5Gy and 0.75 Gy, but no longevity increase wasobserved in females. The electrophoreticanalysis has shown that the amount of the DNAsegments resulting from cleavage in S1nuclease-sensitive sites (<3 kb) reached39.2% of the total DNA from control males. DNAfrom the irradiated males had a smaller amountof such fragments (10–30% in differentexperimental groups). These findings indicatethat the longevity hormesis may be associatedwith irradiation-induced long-term structuraland/or functional DNA modifications.     

Heating stress patterns in Caenorhabditis elegans longevity and survivorship

Survival data from Caenorhabditis elegans strain TJ1060 (spe-9; fer-15) following brief exposure to 35 °C have been investigated. Three experiments with 3-day-old worms were conducted with heat duration ranging between 0 and 12 hours. A statistically significant increase in life expectancy was observed in the groups heated for less than 2 hours, as compared to the unheated control groups. In different experiments P-values for the observed life spans under the hypothesis that heating has no influence on longevity were P < 0.004 after 0.5 hour heat, P < 0.012 after 1 hour heat and P < 0.055 after 2 hours of heating. A biphasic survival model with Gamma distributed frailty has been constructed to describe the survival of worms after heating. The increase in the remaining life expectancy is determined by more effective protection by heat-induced substances in the ages yanger than 27 days. The unheated control group demonstrated acquired heterogeneity of frailty with chronological age while the heat-induced substances defend the worms in a universal way and protect against the development of frailty.     

Messenger RNA levels of lung extracellular matrix proteins during ozone exposure

Continuous exposure of rats to ozone has been shown to result in lung epithelial damage, inflammation, and subsequent increases in collagen content. The main goal of this study was to identify the earliest time point of altered extracellular matrix protein gene expression by utilizing Northern blot analyses of rat lungs continuously exposed to 1.0 ppm ozone for 14 days. An early increase of steady-state fibronectin mRNA levels was observed at 2 days of exposure, prior to the time point of increased type I collagen mRNA, which was seen at 4 days. This increased level of type I collagen mRNA preceded measurable changes in total lung collagen content, observed at 7 days. In addition, peak levels of the growth-related proto-oncogene c-myc mRNA could be correlated with maximal increases of lung DNA content, although the initial increase in c-myc mRNA preceded measurable changes of total lung DNA. The use of specific cDNA probes for measuring altered gene expression can be useful for defining the early cellular and molecular events in ozone-induced lung injury. Offprint requests to: D. J. P. Bassett     

A review of the effects of microgravity and of hypergravity on aging and longevity.

This article reviews the literature dealing with the effects of acute or chronic exposure to microgravity (spacecrafts) or hypergravity (centrifuge) on longevity and the aging process. Even if space flights are now common, the effects of these two kinds of environment on aging are still poorly documented, particularly in mammals. However, there is a growing interest for the use of the fruit fly Drosophila melanogaster, and this species may be now considered as a model organism in gravitational biology studies dealing with aging.     

Hypergravity and ageing in Drosophila melanogaster. 2. Longevity

Longevity of Drosophila melanogaster flies was observed at various gravity levels in three different breeding conditions of decreasing quality. A slight longevity decrease was observed in the 1-4 g range of the two best conditions. In the third one, a large decrease was observed in all hypergravity groups. Longevity decreased at 5 g in the first two groups (no data collected for the third one). Results are discussed in relation with Pearl's rate-of-living theory.     

Longevity and aging: beneficial effects ofexposure to mild stress

Every organism has to deal with exposure to stresses.Animals have developed various strategies to cope with stress. It appears that the developed resistanceto stress is often related to longevity. Somescientists have advanced the hypothesis that thestress response may also counteract the negativeeffects of aging, and that exposing organisms to amild, sublethal stress, inducing a stress response,may help them to live longer. Several mild stresseshave been reported to increase longevity (irradiation,heat and cold shock, hypergravity, exercise, etc.), andone of them, hypergravity, to decrease the rate ofbehavioral aging. The mechanisms whereby thesestresses increase longevity have not yet been elucidated.However, the studies conducted so far show that theymay involve metabolic regulation and stress protein(hsps) induction.     

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.     

Guinea pig lung inflammatory cell changes following acute ozone exposure

The time course of inflammatory cell infiltration into guinea pig lungs following a single 4 h exposure to 2 ppm O₃ was established by measuring the changing cell populations recovered by both bronchoalveolar lavage (BAL) and collagenase tissue digestion. Analysis of BAL-recovered albumin was used as an indicator of permeability damage and demonstrated an increase immediately following ozone exposure, reaching a maximum within 24 h, but returning to air-control levels by 7 days post-ozone exposure. A twofold enhancement in macrophages was observed in the lavage-recovered cell population after 2 days, returning to air-control numbers by 7 days. Collagenase digest-recovered monocytes and macrophages, identified by nonspecific esterase staining, were found to be elevated between 2 and 14 days following O₃ exposure. Immediately following O₃ exposure, a 4.5-fold increase in collagenase digest-recovered neutrophils was observed, with a subsequent decline to air-exposed lung levels during the next 12 h. In contrast, BAL-recovered neutrophils were observed to be increased immediately following O₃ exposure at a level that was sustained for up to 3 days. The tissue accumulation of neutrophils was not associated with their subsequent appearance in the lavageable spaces. Although significant increases in collagenase digest-recovered eosinophils could not be detected, lavage-recovered eosinophil numbers were transiently increased by threefold after 3 days. By employing both BAL and collagenase digestion to evaluate this model of reversible lung injury, this study demonstrated that the use of BAL-recovered cell measurements alone does not adequately reflect the early inflammatory cell changes taking place within oxidant-exposed lungs. Offprint requests to: D. J. P. Bassett