Biomarkers of aging in Drosophila - PubMed (original) (raw)

Biomarkers of aging in Drosophila

Jake Jacobson et al. Aging Cell. 2010 Aug.

Abstract

Low environmental temperature and dietary restriction (DR) extend lifespan in diverse organisms. In the fruit fly Drosophila, switching flies between temperatures alters the rate at which mortality subsequently increases with age but does not reverse mortality rate. In contrast, DR acts acutely to lower mortality risk; flies switched between control feeding and DR show a rapid reversal of mortality rate. Dietary restriction thus does not slow accumulation of aging-related damage. Molecular species that track the effects of temperatures on mortality but are unaltered with switches in diet are therefore potential biomarkers of aging-related damage. However, molecular species that switch upon instigation or withdrawal of DR are thus potential biomarkers of mechanisms underlying risk of mortality, but not of aging-related damage. Using this approach, we assessed several commonly used biomarkers of aging-related damage. Accumulation of fluorescent advanced glycation end products (AGEs) correlated strongly with mortality rate of flies at different temperatures but was independent of diet. Hence, fluorescent AGEs are biomarkers of aging-related damage in flies. In contrast, five oxidized and glycated protein adducts accumulated with age, but were reversible with both temperature and diet, and are therefore not markers either of acute risk of dying or of aging-related damage. Our approach provides a powerful method for identification of biomarkers of aging.

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Figures

Figure 1

Figure 1. Effects of temperature and DR on Drosophila mortality

A: Mortality rates of flies housed at different temperatures. Age-specific mortality analysis of lifespan data from once-mated female flies was performed (n = 5146 at 27°C, n = 3843 at 18°C, n = 1540 switched from 27°C to 18°C and n = for the reciprocal switch). The initial rate of mortality (a) was statistically indistinguishable for flies chronically housed at either temperature but the rate of mortality increased with age (b, the slope of the mortality trajectory, was significantly different between the two groups (see text, Table S1). Switching flies between temperatures altered the mortality trajectory slopes but the age-specific mortality rates of the switched groups always remained distinct from those of the chronic groups. B: Mortality rates of fully-fed flies or flies undergoing DR. Male flies were maintained on full feed (n = 1184) or DR (n = 1171) or switched between the regimes (n = 464 switched from control to DR, n = 515 for the reciprocal switch). Age-specific mortality analysis of lifespan data was performed and a Gompertz model was fitted to the linear portion of the mortality curves. The initial rate of mortality (a, the intercept with the ordinate) was significantly different in flies subjected to DR (see text, Table S2). Switched flies rapidly adopted the age-specific mortalities of flies on chronic feeding regimens.

Figure 2

Figure 2. Fluorescent AGE accumulation reflects temperature-dependent mortality but is independent of diet

A: Fluorescent AGE products accumulated with chronological age in flies housed at different temperatures (20 flies per sample, n = 3 samples for each condition). At all time points flies chronically housed at 27°C had higher AGE levels than those at 18°C. Switching flies to 18°C induced an immediate slowing in AGE accumulation to a rate indistinguishable from flies chronically maintained at 18°C but AGE accrual was irreversible in the time scale of this experiment. The reverse switch (18°C to 27°C) induced an immediate rise in AGE accumulation rate to that of flies kept chronically at 27°C but total AGE content never reached that of flies chronically maintained at 27°C. ***, P < 0.001. B: There was no significant difference in either slope or intercept in regression lines fitted to plots of μx (Figure 1B) against AGE content (from panel C) for either chronic or switched cohorts. The data is best described by a single mathematical relationship. C: Fluorescent AGE products accumulated with chronological age in fully-fed and DR flies, and in flies where diet was switched, but there was no difference in AGE levels between treatments (20 flies per sample, n = 3 samples for each condition). D: Plotting mortality rate (μx, Figure 1A) against AGE content (from panel A) revealed that there was a significantly lower (P<0.0001) intercept in the regression line fitted to the DR group as compared with that of the control group indicating that the accumulation of AGEs in DR was delayed as compared with control flies. Once begun, the rate of AGE accumulation in the two groups was identical. Flies switched between DR and fully fed regimes adopted the mortality rate/AGE content relationship of the fully fed controls.

Figure 3A

Figure 3A. Effect of temperature on the accumulation of protein adducts

Whole-fly GSA, AASA, CEL, CML and MDAL concentration rose with age in both 18°C and 27°C groups (comparison of first and final day levels by one-way analysis of variance, n = 3 in all cases. See text). With the exception of CML (all time points) and the CEL level at day 34, all adduct levels were significantly higher at all time points in the 27°C group as compared with the 18°C group. Switching flies between 27°C and 18°C at Day 21 induced a complete decrease in the amounts of all measured adducts. The reversal was so emphatic that in all cases the measured amounts of adduct undershot the amounts measured in the chronic 18°C temperature group. The reciprocal switch induced a rise in all protein adducts in the switched group resulting in no difference between the switched flies and those maintained chronically at 27°C (P > 0.05 in all cases). Error bars represent standard error of the mean (n = 3). *, P < 0.05; **, P < 0.01; ***, P < 0.001.

Figure 3B

Figure 3B. Mathematical relationship between protein adduct accumulation at different temperatures and mortality rate

Plotting protein adduct accrual against mortality rate revealed a different mathematical relationship for each adduct measured (see Table S3).

Figure 4A

Figure 4A. Effect of diet on the accumulation of protein adducts

Whole fly GSA, AASA, CEL, CML and MDAL concentrations rose with age in both fully fed and DR flies (comparison of first and final day levels by one-way analysis of variance, P < 0.001**,** n = 5 in all cases. See Table S3). There was no difference in adduct levels between fully fed and DR flies at Day 8 but AASA and MDAL were significantly higher in the fully fed group at Day 21 and by Day 26 all adducts were significantly higher in the fully fed controls as compared with DR flies. Switching fully fed flies to a DR regime induced an immediate and rapid fall in all adduct levels such that levels at Day 26 were indistinguishable from those of the chronic DR flies (P > 0.05 in all cases). The converse switch, where DR flies were switched to the control diet, induced an immediate rise in all adducts. In all cases the adduct level of the switched flies was statistically indistinguishable from the chronic DR group by Day 26 (P > 0.05 for each assay). Error bars represent standard error of the mean (n = 5). *, P < 0.05; ***, P < 0.001.

Figure 4B

Figure 4B. Mathematical relationship between protein adduct accumulation and mortality rate in fully fed and DR diets

Neither slope nor intercept were different between fully fed and DR groups when protein adduct accrual was plotted against mortality. Switching from DR to fully fed reduced the slope but this only reached statistical significance for MDAL (see text). There was a further reduction in slope when flies were switched from fully fed to DR but this did not quite reach statistical significance.

Figure 5

Figure 5

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