Extended Longevity Phenotype Research Articles

Signatures of Extreme Longevity: A Perspective from Bivalve Molecular Evolution.

Among Metazoa, bivalves have the highest lifespan disparity, ranging from 1 to 500+ years, making them an exceptional testing ground to understand mechanisms underlying aging and the evolution of extended longevity. Nevertheless, comparative molecular evolution has been an overlooked approach in this instance. Here, we leveraged transcriptomic resources spanning 30 bivalve species to unravel the signatures of convergent molecular evolution in four long-lived species: Margaritifera margaritifera, Elliptio complanata, Lampsilis siliquoidea, and Arctica islandica (the latter represents the longest-lived noncolonial metazoan known so far). We applied a comprehensive approach-which included inference of convergent dN/dS, convergent positive selection, and convergent amino acid substitution-with a strong focus on the reduction of false positives. Genes with convergent evolution in long-lived bivalves show more physical and functional interactions to each other than expected, suggesting that they are biologically connected; this interaction network is enriched in genes for which a role in longevity has been experimentally supported in other species. This suggests that genes in the network are involved in extended longevity in bivalves and, consequently, that the mechanisms underlying extended longevity are-at least partially-shared across Metazoa. Although we believe that an integration of different genes and pathways is required for the extended longevity phenotype, we highlight the potential central roles of genes involved in cell proliferation control, translational machinery, and response to hypoxia, in lifespan extension.

Genetic perturbation of mitochondrial function reveals functional role for specific mitonuclear genes, metabolites, and pathways that regulate lifespan

Altered mitochondrial function is tightly linked to lifespan regulation, but underlying mechanisms remain unclear. Here, we report the chronological and replicative lifespan variation across 167 yeast knock-out strains, each lacking a single nuclear-coded mitochondrial gene, including 144 genes with human homologs, many associated with diseases. We dissected the signatures of observed lifespan differences by analyzing profiles of each strain’s proteome, lipidome, and metabolome under fermentative and respiratory culture conditions, which correspond to the metabolic states of replicative and chronologically aging cells, respectively. Examination of the relationships among extended longevity phenotypes, protein, and metabolite levels revealed that although many of these nuclear-encoded mitochondrial genes carry out different functions, their inhibition attenuates a common mechanism that controls cytosolic ribosomal protein abundance, actin dynamics, and proteasome function to regulate lifespan. The principles of lifespan control learned through this work may be applicable to the regulation of lifespan in more complex organisms, since many aspects of mitochondrial function are highly conserved among eukaryotes.

Oxidative stress resistance as a factor in aging: evidence from an extended longevity phenotype of Drosophila melanogaster.

Longevity of a species is a multifactorial quantitative trait influenced by genetic background, sex, age and environment of the organism. Extended longevity phenotypes (ELP) from experimental evolution in the laboratory can be used as model systems to investigate the mechanisms underlying aging and senescence. ELPs of Drosophila are correlated with various life history attributes such as resistance to environmental stressors (starvation, desiccation, cold and paraquat), developmental time, biochemical defenses, etc. The association between oxidative stress resistance and longevity is not clear and ELPs offer an opportunity to examine the role of oxidative stress resistance in longevity. Here, we have investigated the hypothesis that enhanced oxidative stress resistance and elevated antioxidant defense system play a positive role in longevity using an ELP of Drosophila melanogaster. An ELP of D. melanogaster isolated and characterized in our laboratory through artificial selection (inbred laboratory strain of Oregon K) is employed in this study. Our ELP, named as long lifespan (LLS) flies, shows marked extension in lifespan when compared to the progenitor population (normal lifespan, NLS) and makes a suitable model to study the role of mitochondrial genome in longevity because of its least heterogeneity. In this study, sensitivity to ethanol with age was employed as a measure of resistance to oxidative stress in NLS and LLS flies. Effect of age and oxidative stress on longevity was examined by employing NLS and LLS flies of different age groups against ethanol-induced oxidative stress. Results show that the lower mortality against ethanol was associated with enhanced oxidative stress resistance, higher antioxidant defenses, lower reactive oxygen species (ROS) levels, enhanced alcohol dehydrogenase activity and better locomotor ability attributes of LLS flies. In addition, age-related changes like locomotor impairments, decreased antioxidant defenses, higher ROS levels and sensitivity to oxidative stress were delayed in LLS flies when compared to NLS. Our study supports the hypothesis that higher oxidative stress resistance and enhanced antioxidant defenses are significant factors in extending longevity.

Is Longevity a Heritable Trait? Evidence for Non-genomic Influence from an Extended Longevity Phenotype of Drosophila melanogaster.

Although genetic variations are heritable, some quantitative traits like longevity may have non-genomic influence on heritability. Laboratory-selected inbred strains of extended longevity phenotype of Drosophila offer an opportunity to study the inheritance of longevity. The aim of the study was to examine the heritability of longevity in an extended longevity phenotype of Drosophila melanogaster using reciprocal cross effects in F1 and F2 generations. Lifespan variations of virgin and mated flies in parent, F1 and F2 generations were investigated using reciprocal crosses between normal and long lifespan lines of inbred population of D. melanogaster. Heterosis, narrow-sense heritability, recombination loss, maternal effect and overdominance with respect to survivorship in virgin and mated flies were analyzed. Virgin flies lived longer than mated flies. There was no significant effect of mid-parent heterosis, recombination loss and overdominance on variations in longevity, whereas, significant maternal effect and narrow-sense heritability were observed in mated and virgin flies, respectively. Absence of heterosis in our study population of Drosophila phenotypes could be due to the lack of genetic heterogeneity. The heritability of the longevity trait in an inbred extended longevity phenotype depends on the variations in genetic and environmental factors.

Life History Traits of an Extended Longevity Phenotype of Drosophila melanogaster.

Aging or senescence is a complex biological phenomenon. Artificially selected Drosophila for extended longevity is one of the experimental models used to understand the mechanisms involved in aging and to test various theories. To examine the life history traits and biochemical defenses in relation to aging in an extended longevity phenotype of Drosophila melanogaster. Life history traits viz., survivability, fecundity, development time, dry weight, wing size, lipid content, starvation, desiccation and cold resistances, locomotory ability, antioxidant enzyme activities and reactive oxygen species level between control and selected lines of D. melanogaster were investigated. In our model of Drosophila, extended longevity is associated with no trade-off in fecundity and shows variable resistance to environmental stress such as starvation, cold and desiccation. Enhanced biochemical defense involving the antioxidant enzymes was positively correlated with longevity. Extended longevity phenotypes of Drosophila represent genomic plasticity associated with variable life history traits attributed to the genetic background of the progenitor population and the environment of selection. Oxidative stress resistance seems to be a significant factor in longevity.

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.

Different age-specific demographic profiles are generated in the same normal-lived Drosophila strain by different longevity stimuli.

We review the empirical data obtained with our normal-lived Ra control strain of Drosophila and show that this one genome is capable of invoking at least three different responses to external stimuli that induce the animal to express one of three different extended longevity phenotypes, each of which arises from one of three different antagonistic molecular mechanisms of stress resistance. The phenotypes are distinguished by different age-specific mortality patterns. Depending on the selected mechanism, the genome may respond by expressing a delayed onset of senescence (type 1), an increased early survival (type 2), or an increased late survival (type 3) phenotype, suggesting their different demographic effects. We suggest that the different demographic effects stem in part from the differential ability of each selection regime to reallocate the organism's energy from reproduction to somatic maintenance. These data document the complexity of the aging process and argue for a relationship between molecular mechanisms and longevity phenotypes.

Longevity determination genes in Drosophila melanogaster

Identification of longevity mutants is crucial for genetic approach to dissect the molecular mechanism of aging and longevity determination. In Drosophila melanogaster, several mutations have been shown to extend the longevity: methuselah encoding a putative G-protein coupled receptor, Indy encoding a sodium dicarboxylate cotransporter, chico encoding insulin receptor substrate, and InR encoding the insulin-like receptor. Extended longevity phenotypes were also observed in transgenic flies overexpressing antioxidant enzymes, Cu/Zn superoxide dismutase and Catalase, Cu/Zn SOD only, or a molecular chaperone, hsp70. Pleiotropism of mutations is a limitation associated with conventional mutagenesis for efficient detection of longevity determination genes. Using a conditional misexpression system, we identified Drosophila POSH ( DPOSH), a scaffold protein containing RING finger and four SH3 domains, whose ubiquitous overexpression in adult stage extends the longevity. Neural-specific overexpression of DPOSH is sufficient to extend the longevity, whereas overexpression in non-neural tissues during development induces apoptosis through activation of JNK/SAPK pathway.

Metabolic alterations and shifts in energy allocations are corequisites for the expression of extended longevity genes in Drosophila.

Evolutionary theories suggest that the expression of extended longevity depends on the organism's ability to shift energy from reproduction to somatic maintenance. New data led us to reexamine our older data and integrate the two into a larger picture of the genetic and metabolic alterations required if the animal is to live long. Our Ra normal-lived control strain can express any one of three different extended longevity phenotypes, only one of which involves significant and proportional increases in both mean and maximum longevity and thus a delayed onset of senescence. This phenotype is dependent on the up-regulation of the antioxidant defense system (ADS) genes and enzymes. Animals that express this phenotype typically have a pattern of altered specific activities in metabolically important enzymes, suggesting they are necessary to support the NAD+/NADP+ reducing system required for the continued high ADS enzyme activities. Fecundity data suggests that the energy required for this higher level of somatic maintenance initially came from a reduced egg production. This was only transient, however, for the females significantly increased their fecundity in later generations while still maintaining their longevity. The energy required for this enhanced fecundity was probably obtained from an increased metabolic efficiency, for the mitochondria of the La long-lived strain are metabolically more efficient and have a lower leakage of reactive oxygen species (ROS) to the cytosol. Selection pressures that do not lead to these shifts in energy allocations result in extended longevity phenotypes characterized by increased early survival or increased late survival but not by a delayed onset of senescence.

Metabolic alterations in genetically selected Drosophila strains with different longevities.

Sometime ago we obtained biomarker data suggesting that the earliest determining event in the expression of the extended longevity phenotype in our selected strains of Drosophila took place early in adult life at about 5-7 days of age. In a later series of experiments we documented that our La and Lb long lived strains underwent a specific up-regulation of the antioxidant defense system (ADS) genes and enzymes. This led to a reduction in oxidative damage and an extended longevity. In the current work, we assayed the activity of 17 metabolically important enzymes in 5-7 day old flies of 13 strains variously selected for different longevities. We conclude that the two sets of replicated long-lived strains have an altered metabolic pattern (relative to normal-lived animals) which is consistent with an increased flux through the pentose shunt and an enhanced NADP+ reducing system to support the increased activity of the ADS enzymes. This result can be interpreted as a shift of energy expenditure from reproduction to somatic maintenance. We conclude that theories based on differential energy allocations appear to empirically explain, at least in part, the mechanisms underlying the transformation of a normal longevity phenotype to an extended longevity phenotype.

Neural-specific overexpression of drosophila plenty of SH3s (DPOSH) extends the longevity of adult flies.

Extended longevity mutants are extremely useful to understand the molecular mechanism of longevity determination. Here we report identification and characterization of the Drosophila Plenty of SH3s (DPOSH) gene, a candidate that might be associated with the extended longevity phenotype. DPOSH encodes a protein containing a RING finger domain and four SH3 domains. We showed that neural-specific overexpression of DPOSH could extend the mean longevity of adult flies by 14% at 25 degrees C without affecting viability or morphology. In contrast, forced expression of DPOSH in developing imaginal discs produced various phenotypes including lethality and morphological defects such as loss of crossvein, notched wing, and disordered hair polarity. Puckered, a target gene of JNK/SAPK pathway, was activated by overexpression of DPOSH and the forced expression phenotypes were suppressed by introducing a mutation of Drosophila JNK (bsk) or JNKK (hep), suggesting that the JNK/SAPK signaling pathway is one of the critical elements in the determination of longevity.

Factors contributing to the plasticity of the extended longevity phenotypes of Drosophila.

A number of laboratories have constructed independently derived long-lived strains of Drosophila, each of which have similar but not identical patterns of variability in their adult longevity. Given the observed plasticity of longevity within each of these strains, it would be useful to review the operational and environmental factors that give rise to this phenotypic plasticity and ascertain whether they are common or strain specific. Our review of the more extensively analyzed strains suggests that the allelic composition of the initial genomes and the selection/transgene strategy employed yield extended longevity strains with superficially similar phenotypes but which are probably each the result of different proximal genetic mechanisms. This then offers a plausible explanation for the differential effects of various environmental factors on each strain's particular pattern of phenotypic plasticity. It also illustrates that the species has the potential to employ any one of a number of different proximal mechanisms, each of which give rise to a similar longevity phenotype.

A coordinate upregulation of antioxidant gene activities is associated with the delayed onset of senescence in a long-lived strain of Drosophila.

The extended longevity phenotype (ELP) characteristic of our selected long-lived strain of Drosophila is brought about by a delayed onset of senescence which occurs in the young (5-7 day) adult. Genetically competent animals will not express the resistance to exogenous paraquat characteristic of the ELP as adults unless they develop in a particular larval environment. This induction leads to a series of coordinated increases in their antioxidant defense system mRNA levels and in their enzyme activities. Not all genes show such changes. These increases in antioxidant gene product levels appear to be functional, as witnessed by the fact that the long-lived animals show an increase in their resistance to exogenous paraquat at that same time. Aminotriazole-induced destruction of catalase activity in the long-lived animals results in the loss of their increased resistance to paraquat. The non-induced control animals do not show such elevations in antioxidant defense system elevations, and shortly thereafter show a significant decline in their paraquat resistance followed by the subsequent loss of certain behavioral traits diagnostic of senescence.

Comparative biochemical and stress analysis of genetically selected drosophila strains with different longevities

We have performed a comparative analysis of the effects of age of reproduction on the biochemical (protein, lipid, and glycogen content) and stress resistance (ability to survive starvation, desiccation, and exogenous paraquat) parameters on 10 sister lines of five different Drosophila strains. Four pairs of these sister lines were selected under different regimens for either early or delayed reproduction; the fifth pair was maintained in a nonselected state and served as the baseline strain to which all others were compared. It is generally accepted that the early regimens give rise to short-lived phenotypes, whereas the delayed regimens give rise to long-lived phenotypes. Our results suggest that a mechanism involving lipid and starvation resistance is not operative in our long-lived strains. In addition, a mechanism involving glycogen content and desiccation resistance is only weakly supported. Finally, there is strong support for a mechanism that gives rise to enhanced paraquat resistance and therefore may involve regulatory changes in the pattern of ADS gene expression. In addition, the 15-day early age of reproduction regimen (M type) shows qualitatively similar responses to that of the late age at reproduction regimen (L type). These results suggest that correlations between biochemical traits and longevity must be interpreted with caution. We discuss possible reasons for these results, including the possibility of multiple mechanisms, each leading to a different extended longevity phenotype.

The expression of the EF1α genes of Drosophila is not associated with the extended longevity phenotype in a selected long-lived strain

A quantitative dot blot analysis was performed to determine whether the expression of the EF-1α genes of Drosophila melanogaster are associated with the extended longevity phenotype characteristic of our genetically selected long-lived strain. These data were compared to that obtained from two normal-lived strains and from two iso-chromosomal strains with an intermediate life span. The relative mRNA levels of both EF-1α genes (EF-1α and EF-1α F2) for all five strains were measured through the larval, pupal, and early adult stages, and statistically analyzed. Our findings from these studies indicate that the F2 mRNA tracks with the extended longevity; however, the F1 mRNA is the major component and, thus, the relative total expression of these genes at the mRNA level is approximately equivalent for all five strains. These conclusions suggest that the expression of the EF-1α genes is not associated with the extended longevity phenotype.

Larval regulation of adult longevity in a genetically-selected long-lived strain of Drosophila

Our previous work has shown that the major genes involved in the expression of the extended-longevity phenotype are located on the third chromosome. Furthermore, their expression is negatively and positively influenced by chromosomes 2 and 1, respectively. In this report we show that the expression of the extended-longevity phenotype is dependent on the larval environment. A controlled chromosome substitution experiment was carried out using a strain selected for long life (L) and its parent (R) strain. Twenty different combinations of the three major chromosomes were conducted and their longevities were determined under both high (HD) and low (LD) larval density conditions. The extended-longevity phenotype was only expressed under HD conditions. The chromosome interactions were not apparent under LD conditions. Density-shift experiments delineate a critical period for expression of the extended-longevity phenotype, extending from 60 h after egg laying (AEL) to 96 h AEL, during which the developing animal must be exposed to HD conditions if the extended-longevity phenotype is to be expressed. The change from HD to LD conditions is accompanied by statistically significant increases in body weight. The possible role of a dietary restriction phenomenon is examined and the implications of these findings discussed. It is now apparent, however, that the extended-longevity phenotype in Drosophila is a developmental genetic process.

Chromosomal localization and regulation of the longevity determinant genes in a selected strain of Drosophila melanogaster

A controlled chromosome substitution experiment was performed on a strain (NDC-L) selected for long life to determine if the genes responsible for the extended-longevity phenotype could be localized to any particular chromosome(s). All 27 different possible combinations of the three major chromosomes of Drosophila melanogaster were constructed and longevities were determined on 3875 individual animals of both sexes and analysed. The results are statistically significant and demonstrate that mean longevity is specified primarily by recessive genes on the third chromosome (c3). The extended longevity phenotype (ELP) is only expressed in those lines which are homozygous for the NDC-L type c3. Loci on the first (c1) and second (c2) chromosomes interact, both positively (c1) and negatively (c2), respectively, such that c1 represses c2 which in turn represses c3. The ELP is fully expressed in the mutual presence and mutual absence of c1 and c2. The significance of these results is discussed in the context of broader categories of molecular genetic mechanisms suggested previously to be involved in the modulation of longevity in Drosophila.

Genetic and environmental factors regulating the expression of an extended longevity phenotype in a long lived strain of Drosophila.

We have demonstrated that the expression of the ELP in our strains is the outcome of a genetically determined, environmentally modulated, event dependent, developmental process. Given the appropriate genetic and environmental conditions, we observe an early acting temporal progression of alterations in specific gene activity patterns which appear to give rise to functional phenotypic changes. The observed patterns are consistent with the interpretations drawn from our chromosome substitution and biomarker experiments. The interaction of specific environmental and genetic factors is sufficient to explain the observed plasticity of longevity in our L strain. Independently derived long lived strains may have altered different combinations of physiological mechanisms so as to give rise to a statistically equivalent ELP. Theoretically based conclusions obtained from only one set of sister strains may be difficult to extrapolate to other strains. Future work will involve the experimental verification of the genetic-environmental circuitry discussed here, using novel molecular genetic techniques to define, characterize, and isolate the genes involved in the expression of the ELP.

Elevated paraquat resistance can be used as a bioassay for longevity in a genetically based long‐lived strain of Drosophila

A long-lived (L) strain of Drosophila melanogaster, derived from a normal-lived (R) strain by artificial selection, has a significantly different adult longevity. Previous work has shown that 1) the two strains age in the same manner, 2) the major genes responsible for much of the L strain's extended longevity are located on the 3rd chromosome, and 3) the extended longevity phenotype is significantly modulated by the larval environment. In this report, we investigate the resistance of the L and R strains to the lethal effects of dietary paraquat. We show that, within the limitations of our described chromosomal and environmental manipulations, the extended longevity phenotype always accompanies the phenotype of elevated paraquat resistance. In addition, reversed selection applied to the L strain results in the simultaneous decrease of both life span and paraquat resistance. Thus, the presence or absence of the latter phenotype may be used as a bioassay for the presence or absence of the extended longevity phenotype, without any necessary implication of causality. Use of this bioassay should greatly speed up the genetic analysis of this system by allowing us to identify long-lived animals at a young age. Finally, we show that the age-related loss of elevated paraquat resistance in both strains precedes all the other age-related functional decrements which we have previously noted in this system.