Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Filters applied. Clear all
. 2016 Dec 6;7:216.
doi: 10.3389/fgene.2016.00216. eCollection 2016.

Empirical Validation of a Hypothesis of the Hormetic Selective Forces Driving the Evolution of Longevity Regulation Mechanisms

Affiliations
Free PMC article

Empirical Validation of a Hypothesis of the Hormetic Selective Forces Driving the Evolution of Longevity Regulation Mechanisms

Alejandra Gomez-Perez et al. Front Genet. .
Free PMC article

Abstract

Exogenously added lithocholic bile acid and some other bile acids slow down yeast chronological aging by eliciting a hormetic stress response and altering mitochondrial functionality. Unlike animals, yeast cells do not synthesize bile acids. We therefore hypothesized that bile acids released into an ecosystem by animals may act as interspecies chemical signals that generate selective pressure for the evolution of longevity regulation mechanisms in yeast within this ecosystem. To empirically verify our hypothesis, in this study we carried out a three-step process for the selection of long-lived yeast species by a long-term exposure to exogenous lithocholic bile acid. Such experimental evolution yielded 20 long-lived mutants, three of which were capable of sustaining their considerably prolonged chronological lifespans after numerous passages in medium without lithocholic acid. The extended longevity of each of the three long-lived yeast species was a dominant polygenic trait caused by mutations in more than two nuclear genes. Each of the three mutants displayed considerable alterations to the age-related chronology of mitochondrial respiration and showed enhanced resistance to chronic oxidative, thermal, and osmotic stresses. Our findings empirically validate the hypothesis suggesting that hormetic selective forces can drive the evolution of longevity regulation mechanisms within an ecosystem.

Keywords: aging; ecosystems; evolution; longevity; longevity regulation mechanisms; natural aging-delaying compounds; yeast.

Figures

FIGURE 1
FIGURE 1
A three-step process for selection of long-lived yeast species by a lasting exposure to LCA under laboratory conditions. For each of the 5 weeks-long selection steps, the number of cell generations and enrichment factor for surviving cells were calculated as shown. The genomes of some of the cells surviving a selection step may contain mutations that extend yeast chronological lifespan (CLS). The genomes of other cells surviving a selection step may not undergo any changes affecting their CLS; the survival of these cells may have been caused only by the ability of LCA to extend yeast CLS. LCA concentrations used during each selection step are indicated. See text for details. LCA, lithocholic acid; ST, stationary growth phase; YP, medium containing 1% yeast extract and 2% peptone.
FIGURE 2
FIGURE 2
Changes in the percentage of long-lived mutants within a population of yeast during three consecutive steps of the LCA-driven evolution of yeast species that live longer. The percentage of such long-lived mutants in a population of yeast exposed to LCA is increased by the end of each selection step. Each next selection step yields the higher percentage of such mutants than the previous one. See text for details. LCA, lithocholic acid; ST, stationary growth phase; WT, wild-type.
FIGURE 3
FIGURE 3
Spot-assays of cell survival for each of the three consecutive steps of the LCA-driven selection of long-lived yeast species under laboratory conditions. The selection steps were carried out as outlined in Figures 1 and 2. (A) No long-lived mutant yeast species were found at the end of the first selection step. (B) Four long-lived mutant yeast species were recovered at the end of the second selection step. (C) Sixteen long-lived mutant yeast species were recovered at the end of the third selection step.
FIGURE 4
FIGURE 4
The selected long-lived yeast species 3, 5, and 12 maintain their ability to live much longer than WT following five successive passages in medium lacking LCA. Long-lived mutants 3, 5, and 12 underwent five consecutive passages in liquid medium without LCA. Each of them was then inoculated into liquid YP medium lacking LCA and initially containing 0.2% glucose. (A) Survival curves of chronologically aging WT and long-lived mutant strains cultured in this medium are shown. Data are presented as means ± SEM (n = 3). (B) p Values for pairs of survival curves of the WT and mutant strains. Survival curves shown in (A) were compared. The survival curve for the WT strain was considered statistically different from the survival curve for the mutant strain if the p value was less than 0.05. The p values for comparing pairs of survival curves using the log-rank test were calculated as described in Section “Materials and Methods.” (C) Survival curves shown in (A) were used to calculate the mean and maximum chronological lifespans for WT and mutant strains. Data are presented as means ± SEM (n = 3; p < 0.05; ∗∗p < 0.01).
FIGURE 5
FIGURE 5
The extended longevity of each of the three long-lived yeast mutants evolved under laboratory conditions is a dominant genetic trait. The parental haploid WT strain BY4742, the WT × WT diploid strain formed by mating between the haploid WT strains BY4741 and BY4742, the long-lived mutant strains 3, 5, and 12 (each in the BY4742 genetic background), and the WT × 3, WT × 5, and WT × 12 diploid strains were cultured in YP medium without LCA initially containing 0.2% glucose. Survival curves of chronologically aging cells are shown. Data are presented as means ± SEM (n = 4). The p values for comparing pairs of survival curves using the log-rank test were calculated as described in Section “Materials and Methods.” The survival curve for the WT × 3, WT × 5, or WT × 12 diploid strain was considered statistically different from the survival curve for the parental haploid mutant strain, parental haploid WT strain, or WT × WT diploid strain if the p value was less than 0.05. ns, not significant.
FIGURE 6
FIGURE 6
The extended longevity of each of the three long-lived yeast mutants evolved under laboratory conditions is a dominant genetic trait. The parental haploid WT strain BY4742, the WT × WT diploid strain formed by mating between the haploid WT strains BY4741 and BY4742, the long-lived mutant strains 3, 5, and 12 (each in the BY4742 genetic background), and the WT × 3, WT × 5, and WT × 12 diploid strains were cultured in YP medium without LCA initially containing 0.2% glucose. Survival curves shown in Figure 7 were used to calculate the mean and maximum chronological lifespans for WT and mutant strains. Data are presented as means ± SEM (n = 4; p < 0.05; ∗∗p < 0.01; ∗∗∗p < 0.001).
FIGURE 7
FIGURE 7
Each of the three selected long-lived yeast mutants exhibits altered age-related chronology of mitochondrial respiration. The parental haploid WT strain and the long-lived mutant strains 3, 5, and 12 were cultured in YP medium without LCA initially containing 0.2% glucose. The dynamics of age-dependent changes in the rate of oxygen consumption by chronologically aging yeast is shown. Data are presented as means ± SEM (n = 3). D, diauxic growth phase; L, logarithmic growth phase; PD, post-diauxic growth phase; ST, stationary growth phase.
FIGURE 8
FIGURE 8
Each of the three selected long-lived yeast mutants displays enhanced resistance to chronic oxidative, thermal, and osmotic stresses. The parental haploid WT strain and the long-lived mutant strains 3, 5, and 12 were cultured in YP medium without LCA initially containing 0.2% glucose. Cell aliquots were recovered from various growth phases. The resistance of yeast to chronic oxidative, thermal, and osmotic stresses was monitored as described in Section “Materials and Methods.” D, diauxic growth phase; L, logarithmic growth phase; PD, post-diauxic growth phase; ST, stationary growth phase.

Similar articles

See all similar articles

Cited by 5 articles

References

    1. Amador-Noguez D., Dean A., Huang W., Setchell K., Moore D., Darlington G. (2007). Alterations in xenobiotic metabolism in the long-lived little mice. Aging Cell 6 453–470. 10.1111/j.1474-9726.2007.00300.x - DOI - PMC - PubMed
    1. Amador-Noguez D., Yagi K., Venable S., Darlington G. (2004). Gene expression profile of long-lived Ames dwarf mice and little mice. Aging Cell 3 423–441. 10.1111/j.1474-9728.2004.00125.x - DOI - PubMed
    1. Amaral J. D., Viana R. J., Ramalho R. M., Steer C. J., Rodrigues C. M. (2009). Bile acids: regulation of apoptosis by ursodeoxycholic acid. J. Lipid Res. 50 1721–1734. 10.1194/jlr.R900011-JLR200 - DOI - PMC - PubMed
    1. Amberg D. C., Burke D. J., Strathern J. N. (2005). Methods in Yeast Genetics 2005. Laurel Hollow, NY: Cold Spring Harbor Laboratory.
    1. Arlia-Ciommo A., Leonov A., Piano A., Svistkova V., Titorenko V. I. (2014a). Cell-autonomous mechanisms of chronological aging in the yeast Saccharomyces cerevisiae. Microbial Cell 1 164–178. 10.15698/mic2014.06.152 - DOI - PMC - PubMed

LinkOut - more resources

Feedback