Positive feedback between transcriptional and kinase suppression in nematodes with extraordinary longevity and stress resistance

Aspirin-Mediated Acetylation Protects Against Multiple Neurodegenerative Pathologies by Impeding Protein Aggregation

AIMS

Many progressive neurological disorders, including Alzheimer's disease (AD), Huntington's disease, and Parkinson's disease (PD), are characterized by accumulation of insoluble protein aggregates. In prospective trials, the cyclooxygenase inhibitor aspirin (acetylsalicylic acid) reduced the risk of AD and PD, as well as cardiovascular events and many late-onset cancers. Considering the role played by protein hyperphosphorylation in aggregation and neurodegenerative diseases, and aspirin's known ability to donate acetyl groups, we asked whether aspirin might reduce both phosphorylation and aggregation by acetylating protein targets.

RESULTS

Aspirin was substantially more effective than salicylate in reducing or delaying aggregation in human neuroblastoma cells grown in vitro, and in Caenorhabditis elegans models of human neurodegenerative diseases in vivo. Aspirin acetylates many proteins, while reducing phosphorylation, suggesting that acetylation may oppose phosphorylation. Surprisingly, acetylated proteins were largely excluded from compact aggregates. Molecular-dynamic simulations indicate that acetylation of amyloid peptide energetically disfavors its association into dimers and octamers, and oligomers that do form are less compact and stable than those comprising unacetylated peptides.

INNOVATION

Hyperphosphorylation predisposes certain proteins to aggregate (e.g., tau, α-synuclein, and transactive response DNA-binding protein 43 [TDP-43]), and it is a critical pathogenic marker in both cardiovascular and neurodegenerative diseases. We present novel evidence that acetylated proteins are underrepresented in protein aggregates, and that aggregation varies inversely with acetylation propensity after diverse genetic and pharmacologic interventions.

CONCLUSIONS

These results are consistent with the hypothesis that aspirin inhibits protein aggregation and the ensuing toxicity of aggregates through its acetyl-donating activity. This mechanism may contribute to the neuro-protective, cardio-protective, and life-prolonging effects of aspirin. Antioxid. Redox Signal. 27, 1383-1396.

Stability analysis of a model gene network links aging, stress resistance, and negligible senescence

Several animal species are considered to exhibit what is called negligible senescence, i.e. they do not show signs of functional decline or any increase of mortality with age. Recent studies in naked mole rat and long-lived sea urchins showed that these species do not alter their gene-expression profiles with age as much as other organisms do. This is consistent with exceptional endurance of naked mole rat tissues to various genotoxic stresses. We conjectured, therefore, that the lifelong transcriptional stability of an organism may be a key determinant of longevity. We analyzed the stability of a simple genetic-network model and found that under most common circumstances, such a gene network is inherently unstable. Over a time it undergoes an exponential accumulation of gene-regulation deviations leading to death. However, should the repair systems be sufficiently effective, the gene network can stabilize so that gene damage remains constrained along with mortality of the organism. We investigate the relationship between stress-resistance and aging and suggest that the unstable regime may provide a mathematical basis for the Gompertz "law" of aging in many species. At the same time, this model accounts for the apparently age-independent mortality observed in some exceptionally long-lived animals.

Rec-8 dimorphism affects longevity, stress resistance and X-chromosome nondisjunction in C. elegans, and replicative lifespan in S. cerevisiae

A quantitative trait locus (QTL) in the nematode C. elegans, “lsq4,” was recently implicated by mapping longevity genes. QTLs for lifespan and three stress-resistance traits coincided within a span of <300 kbp, later narrowed to <200 kbp. A single gene in this interval is now shown to modulate all lsq4-associated traits. Full-genome analysis of transcript levels indicates that lsq4 contains a dimorphic gene governing the expression of many sperm-specific genes, suggesting an effect on spermatogenesis. Quantitative analysis of allele-specific transcripts encoded within the lsq4 interval revealed significant, 2- to 15-fold expression differences for 10 of 33 genes. Fourteen “dual-candidate” genes, implicated by both position and expression, were tested for RNA-interference effects on QTL-linked traits. In a strain carrying the shorter-lived allele, knockdown of rec-8 (encoding a meiotic cohesin) reduced its transcripts 4-fold, to a level similar to the longer-lived strain, while extending lifespan 25–26%, whether begun before fertilization or at maturity. The short-lived lsq4 allele also conferred sensitivity to oxidative and thermal stresses, and lower male frequency (reflecting X-chromosome non-disjunction), traits reversed uniquely by rec-8 knockdown. A strain bearing the longer-lived lsq4 allele, differing from the short-lived strain at <0.3% of its genome, derived no lifespan or stress-survival benefit from rec-8 knockdown. We consider two possible explanations: high rec-8 expression may include increased “leaky” expression in mitotic cells, leading to deleterious destabilization of somatic genomes; or REC-8 may act entirely in germ-line meiotic cells to reduce aberrations such as non-disjunction, thereby blunting a stress-resistance response mediated by innate immunity. Replicative lifespan was extended 20% in haploid S. cerevisiae (BY4741) by deletion of REC8, orthologous to nematode rec-8, implying that REC8 disruption of mitotic-cell survival is widespread, exemplifying antagonistic pleiotropy (opposing effects on lifespan vs. reproduction), and/or balancing selection wherein genomic disruption increases genetic variation under harsh conditions.

Comparison of the mammalian insulin signalling pathway to invertebrates in the context of FOXO-mediated ageing

MOTIVATION

A large number of experimental studies on ageing focus on the effects of genetic perturbations of the insulin/insulin-like growth factor signalling pathway (IIS) on lifespan. Short-lived invertebrate laboratory model organisms are extensively used to quickly identify ageing-related genes and pathways. It is important to extrapolate this knowledge to longer lived mammalian organisms, such as mouse and eventually human, where such analyses are difficult or impossible to perform. Computational tools are needed to integrate and manipulate pathway knowledge in different species.

RESULTS

We performed a literature review and curation of the IIS and target of rapamycin signalling pathways in Mus Musculus. We compare this pathway model to the equivalent models in Drosophila melanogaster and Caenorhabtitis elegans. Although generally well-conserved, they exhibit important differences. In general, the worm and mouse pathways include a larger number of feedback loops and interactions than the fly. We identify 'functional orthologues' that share similar molecular interactions, but have moderate sequence similarity. Finally, we incorporate the mouse model into the web-service NetEffects and perform in silico gene perturbations of IIS components and analyses of experimental results. We identify sub-paths that, given a mutation in an IIS component, could potentially antagonize the primary effects on ageing via FOXO in mouse and via SKN-1 in worm. Finally, we explore the effects of FOXO knockouts in three different mouse tissues.

AVAILABILITY AND IMPLEMENTATION

http://www.ebi.ac.uk/thornton-srv/software/NetEffects.

A recent global selective sweep on the age-1 phosphatidylinositol 3-OH kinase regulator of the insulin-like signaling pathway within Caenorhabditis remanei

The discovery that genetic pathways can be manipulated to extend lifespan has revolutionized our understanding of aging, yet their function within natural populations remains poorly characterized. In particular, evolutionary theories of aging predict tradeoffs in resource investment toward somatic maintenance vs. reproductive output that should impose strong natural selection on genetic components that influence this balance. To explore such selective pressure at the molecular level, we examine population genetic variation in the insulin-like signaling pathway of the nematode Caenorhabditis remanei. We document a recent global selective sweep on the phosphoinositide-3-kinase pathway regulator, age-1, the first life-extension gene to have been identified. In particular, we find that age-1 has 5−20 times less genetic variation than any other insulin-like signaling pathway components and that evolutionary signatures of selection center on the age-1 locus within its genomic environment. These results demonstrate that critical components of aging-related pathways can be subject to shifting patterns of strong selection, as predicted by theory. This highly polymorphic outcrossing species offers high-resolution, population-level analyses of molecular variation as a complement to functional genetic studies within the self-reproducing C. elegans model system.

LC-MS proteomics analysis of the insulin/IGF-1-deficient Caenorhabditis elegans daf-2(e1370) mutant reveals extensive restructuring of intermediary metabolism

The insulin/IGF-1 receptor is a major known determinant of dauer formation, stress resistance, longevity, and metabolism in Caenorhabditis elegans. In the past, whole-genome transcript profiling was used extensively to study differential gene expression in response to reduced insulin/IGF-1 signaling, including the expression levels of metabolism-associated genes. Taking advantage of the recent developments in quantitative liquid chromatography mass spectrometry (LC-MS)-based proteomics, we profiled the proteomic changes that occur in response to activation of the DAF-16 transcription factor in the germline-less glp-4(bn2);daf-2(e1370) receptor mutant. Strikingly, the daf-2 profile suggests extensive reorganization of intermediary metabolism, characterized by the upregulation of many core intermediary metabolic pathways. These include glycolysis/gluconeogenesis, glycogenesis, pentose phosphate cycle, citric acid cycle, glyoxylate shunt, fatty acid β-oxidation, one-carbon metabolism, propionate and tyrosine catabolism, and complexes I, II, III, and V of the electron transport chain. Interestingly, we found simultaneous activation of reciprocally regulated metabolic pathways, which is indicative of spatiotemporal coordination of energy metabolism and/or extensive post-translational regulation of these enzymes. This restructuring of daf-2 metabolism is reminiscent to that of hypometabolic dauers, allowing the efficient and economical utilization of internal nutrient reserves and possibly also shunting metabolites through alternative energy-generating pathways to sustain longevity.

Genetics and epigenetics of aging and longevity

Evolutionary theories of aging predict the existence of certain genes that provide selective advantage early in life with adverse effect on lifespan later in life (antagonistic pleiotropy theory) or longevity insurance genes (disposable soma theory). Indeed, the study of human and animal genetics is gradually identifying new genes that increase lifespan when overexpressed or mutated: gerontogenes. Furthermore, genetic and epigenetic mechanisms are being identified that have a positive effect on longevity. The gerontogenes are classified as lifespan regulators, mediators, effectors, housekeeping genes, genes involved in mitochondrial function, and genes regulating cellular senescence and apoptosis. In this review we demonstrate that the majority of the genes as well as genetic and epigenetic mechanisms that are involved in regulation of longevity are highly interconnected and related to stress response.

Neuronal inputs and outputs of aging and longevity

An animal’s survival strongly depends on its ability to maintain homeostasis in response to the changing quality of its external and internal environment. This is achieved through intracellular and intercellular communication within and among different tissues. One of the organ systems that plays a major role in this communication and the maintenance of homeostasis is the nervous system. Here we highlight different aspects of the neuronal inputs and outputs of pathways that affect aging and longevity. Accordingly, we discuss how sensory inputs influence homeostasis and lifespan through the modulation of different types of neuronal signals, which reflects the complexity of the environmental cues that affect physiology. We also describe feedback, compensatory, and feed-forward mechanisms in these longevity-modulating pathways that are necessary for homeostasis. Finally, we consider the temporal requirements for these neuronal processes and the potential role of natural genetic variation in shaping the neurobiology of aging.

Extreme Depletion of PIP3 Accompanies the Increased Life Span and Stress Tolerance of PI3K-null C. elegans Mutants

The regulation of animal longevity shows remarkable plasticity, in that a variety of genetic lesions are able to extend lifespan by as much as 10-fold. Such studies have implicated several key signaling pathways that must normally limit longevity, since their disruption prolongs life. Little is known, however, about the proximal effectors of aging on which these pathways are presumed to converge, and to date, no pharmacologic agents even approach the life-extending effects of genetic mutation. In the present study, we have sought to define the downstream consequences of age-1 nonsense mutations, which confer 10-fold life extension to the nematode Caenorhabditis elegans – the largest effect documented for any single mutation. Such mutations insert a premature stop codon upstream of the catalytic domain of the AGE-1/p110α subunit of class-I PI3K. As expected, we do not detect class-I PI3K (and based on our sensitivity, it constitutes <14% of wild-type levels), nor do we find any PI3K activity as judged by immunodetection of phosphorylated AKT, which strongly requires PIP₃ for activation by upstream kinases, or immunodetection of its product, PIP₃. In the latter case, the upper 95%-confidence limit for PIP₃ is 1.4% of the wild-type level. We tested a variety of commercially available PI3K inhibitors, as well as three phosphatidylinositol analogs (PIAs) that are most active in inhibiting AKT activation, for effects on longevity and survival of oxidative stress. Of these, GDC-0941, PIA6, and PIA24 (each at 1 or 10 μM) extended lifespan by 7–14%, while PIAs 6, 12, and 24 (at 1 or 10 μM) increased survival time in 5 mM peroxide by 12–52%. These effects may have been conferred by insulinlike signaling, since a reporter regulated by the DAF-16/FOXO transcription factor, SOD-3::GFP, was stimulated by these PIAs in the same rank order (PIA24 > PIA6 > PIA12) as lifespan. A second reporter, PEPCK::GFP, was equally activated (∼40%) by all three.

Seed Fatty Acid Reducer acts downstream of gibberellin signalling pathway to lower seed fatty acid storage in Arabidopsis

Previous studies based on microarray analysis have found that DELLAs down-regulate several GDSL genes in unopened flowers and/or imbibed seeds. This suggests the role of DELLAs in seed fatty acid (FA) metabolism. In the present study, enhancement of gibberellin (GA) signalling through DELLA mutation or exogenous gibberellin acid A3 (GA(3) ) resulted in the up-regulated expression of transcription factors for embryogenesis and seed development, genes involved in the FA biosynthesis pathway, and five GDSL-type Seed Fatty Acid Reducer (SFAR) genes. SFAR overexpression reduced the total seed FA content and led to a particular pattern of seed FA composition. This 'SFAR footprint' can also be found in plants with enhanced GA(3) signalling. By contrast, the loss of SFAR function dramatically increases the seed FA content. The transgenic lines that overexpress SFAR were less sensitive to stressful environments, reflected by a higher germination rate and better seedling establishment compared with the wild type (WT) plants. The GDSL-type hydrolyzer is a family of proteins largely uncharacterized in Arabidopsis. Their biological function remains poorly understood. SFAR reduces seed FA storage and acts downstream of the GA signalling pathway. We provide the first evidence that some GDSL proteins are somehow involved in FA degradation in Arabidopsis seeds.

Dissecting the gene network of dietary restriction to identify evolutionarily conserved pathways and new functional genes

Dietary restriction (DR), limiting nutrient intake from diet without causing malnutrition, delays the aging process and extends lifespan in multiple organisms. The conserved life-extending effect of DR suggests the involvement of fundamental mechanisms, although these remain a subject of debate. To help decipher the life-extending mechanisms of DR, we first compiled a list of genes that if genetically altered disrupt or prevent the life-extending effects of DR. We called these DR–essential genes and identified more than 100 in model organisms such as yeast, worms, flies, and mice. In order for other researchers to benefit from this first curated list of genes essential for DR, we established an online database called GenDR (http://genomics.senescence.info/diet/). To dissect the interactions of DR–essential genes and discover the underlying lifespan-extending mechanisms, we then used a variety of network and systems biology approaches to analyze the gene network of DR. We show that DR–essential genes are more conserved at the molecular level and have more molecular interactions than expected by chance. Furthermore, we employed a guilt-by-association method to predict novel DR–essential genes. In budding yeast, we predicted nine genes related to vacuolar functions; we show experimentally that mutations deleting eight of those genes prevent the life-extending effects of DR. Three of these mutants (OPT2, FRE6, and RCR2) had extended lifespan under ad libitum, indicating that the lack of further longevity under DR is not caused by a general compromise of fitness. These results demonstrate how network analyses of DR using GenDR can be used to make phenotypically relevant predictions. Moreover, gene-regulatory circuits reveal that the DR–induced transcriptional signature in yeast involves nutrient-sensing, stress responses and meiotic transcription factors. Finally, comparing the influence of gene expression changes during DR on the interactomes of multiple organisms led us to suggest that DR commonly suppresses translation, while stimulating an ancient reproduction-related process.

Dietary restriction has been shown to extend lifespan in diverse, evolutionarily distant species, yet its underlying mechanisms remain unknown. We first constructed a database of genes essential for the life-extending effects of dietary restriction in various model organisms and then studied their interactions using a variety of network and systems biology approaches. This enabled us to predict novel genes related to dietary restriction, which we validated experimentally in yeast. By comparing large-scale data compilations (interactomes and transcriptomes) from multiple organisms, we were able to condense this -omics information to the most conserved essential elements, eliminating species-specific adaptive responses. These results lead us to the rather surprising conclusion that lifespan extension by a restricted diet commonly may exploit an ancient rejuvenation process derived from gametogenesis.

Gene categories differentially expressed in C. elegans age-1 mutants of extraordinary longevity: new insights from novel data-mining procedures

Two nonsense mutants of age-1, the Caenorhabditis elegans gene encoding phosphoinositide 3-kinase, live nearly 10-fold longer than wild-type controls and are exceptionally resistant to several stresses. Genome-wide expression analyses implicated downregulation of many more genes than were upregulated in second-generation age-1 homozygotes. Functional-annotation analysis, based on Gene Ontology terms, suggested that novel mechanisms may mediate the stronger phenotypes observed for these worms than with milder age-1 disruption. For the current study, the same microarray data were reanalyzed using novel meta-analytic procedures that we developed recently. First, gene p values were corrected for systematic biases based on the observed distribution for nonexpressed genes; these values were then combined to derive an aggregate p value for each functional-annotation term while adjusting for intergene covariance. This resulted in much better coverage of relevant gene categories, including many that were independently supported by other data. The number of nonredundant GO categories significantly distinguishing age-1 alleles of exceptional longevity increased from sevenfold to greater than ninefold, improving both sensitivity and specificity of selection for altered pathways and implicating previously unsuspected longevity mechanisms. Of 150 genes whose differential expression underlay significant GO terms in both comparisons, over half were up- or down-regulated in accord with longevity, whereas one third showed altered expression uniquely in the longest-lived age-1-null strains, consistent with the activation or suppression of pathways peculiar to strong age-1 mutants.

Relationship of electrophilic stress to aging

This review begins with the premise that an organism's life span is determined by the balance between two countervailing forces: (i) the sum of destabilizing effects and (ii) the sum of protective longevity-assurance processes. Against this backdrop, the role of electrophiles is discussed, both as destabilizing factors and as signals that induce protective responses. Because most biological macromolecules contain nucleophilic centers, electrophiles are particularly reactive and toxic in a biological context. The majority of cellular electrophiles are generated from polyunsaturated fatty acids by a peroxidation chain reaction that is readily triggered by oxygen-centered radicals, but propagates without further input of reactive oxygen species (ROS). Thus, the formation of lipid-derived electrophiles such as 4-hydroxynon-2-enal (4-HNE) is proposed to be relatively insensitive to the level of initiating ROS, but to depend mainly on the availability of peroxidation-susceptible fatty acids. This is consistent with numerous observations that life span is inversely correlated to membrane peroxidizability, and with the hypothesis that 4-HNE may constitute the mechanistic link between high susceptibility of membrane lipids to peroxidation and shortened life span. Experimental interventions that directly alter membrane composition (and thus their peroxidizability) or modulate 4-HNE levels have the expected effects on life span, establishing that the connection is not only correlative but causal. Specific molecular mechanisms are considered, by which 4-HNE could (i) destabilize biological systems via nontargeted reactions with cellular macromolecules and (ii) modulate signaling pathways that control longevity-assurance mechanisms.

Modulation of lipid biosynthesis contributes to stress resistance and longevity of C. elegans mutants

Many lifespan-modulating genes are involved in either generation of oxidative substrates and end-products, or their detoxification and removal. Among such metabolites, only lipoperoxides have the ability to produce free-radical chain reactions. For this study, fatty-acid profiles were compared across a panel of C. elegans mutants that span a tenfold range of longevities in a uniform genetic background. Two lipid structural properties correlated extremely well with lifespan in these worms: fatty-acid chain length and susceptibility to oxidation both decreased sharply in the longest-lived mutants (affecting the insulinlike-signaling pathway). This suggested a functional model in which longevity benefits from a reduction in lipid peroxidation substrates, offset by a coordinate decline in fatty-acid chain length to maintain membrane fluidity. This model was tested by disrupting the underlying steps in lipid biosynthesis, using RNAi knockdown to deplete transcripts of genes involved in fatty-acid metabolism. These interventions produced effects on longevity that were fully consistent with the functions and abundances of their products. Most knockdowns also produced concordant effects on survival of hydrogen peroxide stress, which can trigger lipoperoxide chain reactions.

Polyunsaturated fatty acids are involved in regulatory mechanism of fatty acid homeostasis via daf-2/insulin signaling in Caenorhabditis elegans

The development of the dauer form of Caenorhabditis elegans daf-2(e1370) enhances the expression of genes such as fatty acid desaturase fat-6 and fat-7 and fatty acid elongase elo-2, and increases the level of triglyceride (TAG). RNA interference (RNAi) of the fat-6, fat-7, and elo-2 genes lowers fat accumulation in the nematode. We recently clarified the fact that RNAi of fat-related genes, especially fat-2, reduced fat accumulation and activated DAF-16. FAT-2 regulates the first step of polyunsaturated fatty acid (PUFA) synthesis. RNAi of fat-2 induced nuclear translocation of DAF-16 and increased the level of TAG that could be detected by Oil Red-O, but suppressed the accumulation of lipid dyed by Nile red. TAG levels are also increased in the adult daf-2(e1370), whereas Nile red staining showed fat reduction. Introduction of RNAi of fat-2, fat-6, fat-7, and elo-2 genes into the daf-16 deficient worm recovered Nile red-stained lipid storage. These results suggest that Nile red stained the lipids except TAG, and that the levels of these lipids are regulated by daf-16. In fat-2, fat-6, fat-7, and elo-2-RNAi worms, the Nile red-stained fat level was restored through addition of fatty acids, especially PUFA. This suggests that reduction of Nile red-dyed lipid reflects the disorder of fatty acid metabolism. Furthermore, treatment of the fat-2-RNAi worm with PUFA--using the fatty acids from linoleic acid through eicosapentaenoic acid--suppressed nuclear localization of DAF-16. These results suggest that PUFA acts as a mediator of daf-2/insulin signaling and that daf-16 might be involved in fatty acid homeostasis under the control of PUFA.

Caenorhabditis elegans PI3K mutants reveal novel genes underlying exceptional stress resistance and lifespan

Two age-1 nonsense mutants, truncating the class-I phosphatidylinositol 3-kinase catalytic subunit (PI3K(CS)) before its kinase domain, confer extraordinary longevity and stress-resistance to Caenorhabditis elegans. These traits, unique to second-generation homozygotes, are blunted at the first generation and are largely reversed by additional mutations to DAF-16/FOXO, a transcription factor downstream of AGE-1 in insulin-like signaling. The strong age-1 alleles (mg44, m333) were compared with the weaker hx546 allele on expression microarrays, testing four independent cohorts of each allele. Among 276 genes with significantly differential expression, 92% showed fewer transcripts in adults carrying strong age-1 alleles rather than hx546. This proportion is significantly greater than the slight bias observed when contrasting age-1 alleles to wild-type worms. Thus, transcriptional changes peculiar to nonsense alleles primarily involve either gene silencing or failure of transcriptional activation. A subset of genes responding preferentially to age-1-nonsense alleles was reassessed by real-time polymerase chain reaction, in worms bearing strong or weak age-1 alleles; nearly all of these were significantly more responsive to the age-1(mg44) allele than to age-1(hx546). Additional mutation of daf-16 reverted the majority of altered mg44-F2 expression levels to approximately wild-type values, although a substantial number of genes remained significantly distinct from wild-type, implying that age-1(mg44) modulates transcription through both DAF-16/FOXO-dependent and -independent channels. When age-1-inhibited genes were targeted by RNA interference (RNAi) in wild-type or age-1(hx546) adults, most conferred significant oxidative-stress protection. RNAi constructs targeting two of those genes were shown previously to extend life, and RNAi's targeting five novel genes were found here to increase lifespan. PI3K-null mutants may thus implicate novel mechanisms of life extension.

Disruption of the mGsta4 gene increases life span of C57BL mice

The lipid peroxidation product 4-hydroxynonenal (4-HNE) forms as a consequence of oxidative stress. By electrophilic attack on biological macromolecules, 4-HNE mediates signaling or may cause toxicity. A major route of 4-HNE disposal is via glutathione conjugation, in the mouse catalyzed primarily by glutathione transferase mGSTA4-4. Unexpectedly, mGsta4-null mice, in which 4-HNE detoxification is impaired, have an extended life span. This finding could be explained by the observed activation of the transcription factor Nrf2 in the knockout mice, which in turn leads to an induction of antioxidant and antielectrophilic defenses. Especially, the latter could provide a detoxification mechanism that contributes to enhanced longevity. We propose that disruption of 4-HNE conjugation elicits a hormetic response in which an initially increased supply of 4-HNE is translated into activation of Nrf2, leading to a new steady state in which the rise of 4-HNE concentrations is dampened, but life-extending detoxification mechanisms are concomitantly induced.

Extreme-longevity mutations orchestrate silencing of multiple signaling pathways

Long-lived mutants provide unique insights into the genetic factors that limit lifespan in wild-type animals. Most mutants and RNA interference targets found to extend life, typically by 1.5- to 2.5-fold, were discovered in C. elegans. Several longevity-assurance pathways are conserved across widely divergent taxa, indicating that mechanisms of lifespan regulation evolved several hundred million years ago. Strong mutations to the C. elegans gene encoding AGE-1/PI3KCS achieve unprecedented longevity by orchestrating the modulation (predominantly silencing) of multiple signaling pathways. This is evident in a profound attenuation of total kinase activity, leading to reduced phosphoprotein content. Mutations to the gene encoding the catalytic subunit of PI3K (phosphatidylinositol 3-kinase) have the potential to modulate all enzymes that depend on its product, PIP3, for membrane tethering or activation by other kinases. Remarkably, strong mutants inactivating PI3K also silence multiple signaling pathways at the transcript level, partially but not entirely mediated by the DAF-16/FOXO transcription factor. Mammals have a relatively large proportion of somatic cells, and survival depends on their replication, whereas somatic cell divisions in nematodes are limited to development and reproductive tissues. Thus, translation of longevity gains from nematodes to mammals requires disentangling the downstream consequences of signaling mutations, to avoid their deleterious consequences.