Caenorhabditis elegans SKN-1 (ortholog of mammalian Nrf1/2/3) is critical for oxidative stress resistance and promotes longevity under reduced insulin/IGF-1-like signaling (IIS), dietary restriction ...(DR), and normal conditions. SKN-1 inducibly activates genes involved in detoxification, protein homeostasis, and other functions in response to stress. Here we used genome-scale RNA interference (RNAi) screening to identify mechanisms that prevent inappropriate SKN-1 target gene expression under non-stressed conditions. We identified 41 genes for which knockdown leads to activation of a SKN-1 target gene (gcs-1) through skn-1-dependent or other mechanisms. These genes correspond to multiple cellular processes, including mRNA translation. Inhibition of translation is known to increase longevity and stress resistance and may be important for DR-induced lifespan extension. One model postulates that these effects derive from reduced energy needs, but various observations suggest that specific longevity pathways are involved. Here we show that translation initiation factor RNAi robustly induces SKN-1 target gene transcription and confers skn-1-dependent oxidative stress resistance. The accompanying increases in longevity are mediated largely through the activities of SKN-1 and the transcription factor DAF-16 (FOXO), which is required for longevity that derives from reduced IIS. Our results indicate that the SKN-1 detoxification gene network monitors various metabolic and regulatory processes. Interference with one of these processes, translation initiation, leads to a transcriptional response whereby SKN-1 promotes stress resistance and functions together with DAF-16 to extend lifespan. This stress response may be beneficial for coping with situations that are associated with reduced protein synthesis.
Caloric restriction (CR) protects against aging and disease, but the mechanisms by which this affects mammalian life span are unclear. We show in mice that deletion of ribosomal S6 protein kinase 1 ...(S6K1), a component of the nutrient-responsive mTOR (mammalian target of rapamycin) signaling pathway, led to increased life span and resistance to age-related pathologies, such as bone, immune, and motor dysfunction and loss of insulin sensitivity. Deletion of S6K1 induced gene expression patterns similar to those seen in CR or with pharmacological activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), a conserved regulator of the metabolic response to CR. Our results demonstrate that S6K1 influences healthy mammalian life-span and suggest that therapeutic manipulation of S6K1 and AMPK might mimic CR and could provide broad protection against diseases of aging.
Summary
In C. elegans, the skn‐1 gene encodes a transcription factor that resembles mammalian Nrf2 and activates a detoxification response. skn‐1 promotes resistance to oxidative stress (Oxr) and ...also increases lifespan, and it has been suggested that the former causes the latter, consistent with the theory that oxidative damage causes aging. Here, we report that effects of SKN‐1 on Oxr and longevity can be dissociated. We also establish that skn‐1 expression can be activated by the DAF‐16/FoxO transcription factor, another central regulator of growth, metabolism, and aging. Notably, skn‐1 is required for Oxr but not increased lifespan resulting from over‐expression of DAF‐16; concomitantly, DAF‐16 over‐expression rescues the short lifespan of skn‐1 mutants but not their hypersensitivity to oxidative stress. These results suggest that SKN‐1 promotes longevity by a mechanism other than protection against oxidative damage.
In
C. elegans
, mutations in the conserved insulin/IGF-1 signaling (IIS) pathway lead to a robust extension in lifespan, improved late life health, and protection from age-related disease. These ...effects are mediated by the FoxO transcription factor DAF-16 which lies downstream of the IIS kinase cascade. Identifying and functionally testing DAF-16 target genes has been a focal point of ageing research for the last 10 years. Here, I review the recent advances in identifying and understanding IIS/DAF-16 targets. These studies continue to reveal the intricate nature of the IIS/DAF-16 gene regulation network and are helping us to understand the mechanisms that control lifespan. Ageing and age related disease is an area of intense public interest, and the biochemical characterization of the genes involved will be critical for identifying drugs to improve the health of our ageing population.
The DAF-16/FoxO transcription factor controls growth, metabolism and aging in Caenorhabditis elegans. The large number of genes that it regulates has been an obstacle to understanding its function. ...However, recent analysis of transcript and chromatin profiling implies that DAF-16 regulates relatively few genes directly, and that many of these encode other regulatory proteins. We have investigated the regulation by DAF-16 of genes encoding the AMP-activated protein kinase (AMPK), which has α, β and γ subunits. C. elegans has 5 genes encoding putative AMP-binding regulatory γ subunits, aakg-1-5. aakg-4 and aakg-5 are closely related, atypical isoforms, with orthologs throughout the Chromadorea class of nematodes. We report that ∼75% of total γ subunit mRNA encodes these 2 divergent isoforms, which lack consensus AMP-binding residues, suggesting AMP-independent kinase activity. DAF-16 directly activates expression of aakg-4, reduction of which suppresses longevity in daf-2 insulin/IGF-1 receptor mutants. This implies that an increase in the activity of AMPK containing the AAKG-4 γ subunit caused by direct activation by DAF-16 slows aging in daf-2 mutants. Knock down of aakg-4 expression caused a transient decrease in activation of expression in multiple DAF-16 target genes. This, taken together with previous evidence that AMPK promotes DAF-16 activity, implies the action of these two metabolic regulators in a positive feedback loop that accelerates the induction of DAF-16 target gene expression. The AMPK β subunit, aakb-1, also proved to be up-regulated by DAF-16, but had no effect on lifespan. These findings reveal key features of the architecture of the gene-regulatory network centered on DAF-16, and raise the possibility that activation of AMP-independent AMPK in nutritionally replete daf-2 mutant adults slows aging in C. elegans. Evidence of activation of AMPK subunits in mammals suggests that such FoxO-AMPK interactions may be evolutionarily conserved.
Insulin/IGF-1-like signaling (IIS) is central to growth and metabolism and has a conserved role in aging. In
C. elegans, reductions in IIS increase stress resistance and longevity, effects that ...require the IIS-inhibited FOXO protein DAF-16. The
C. elegans transcription factor SKN-1 also defends against oxidative stress by mobilizing the conserved phase 2 detoxification response. Here we show that IIS not only opposes DAF-16 but also directly inhibits SKN-1 in parallel. The IIS kinases AKT-1, -2, and SGK-1 phosphorylate SKN-1, and reduced IIS leads to constitutive SKN-1 nuclear accumulation in the intestine and SKN-1 target gene activation. SKN-1 contributes to the increased stress tolerance and longevity resulting from reduced IIS and delays aging when expressed transgenically. Furthermore, SKN-1 that is constitutively active increases life span independently of DAF-16. Our findings indicate that the transcription network regulated by SKN-1 promotes longevity and is an important direct target of IIS.
Caenorhabditis elegans is an excellent model for high‐throughput experimental approaches but lacks an automated means to pinpoint time of death during survival assays over a short time frame, that ...is, easy to implement, highly scalable, robust, and versatile. Here, we describe an automated, label‐free, high‐throughput method using death‐associated fluorescence to monitor nematode population survival (dubbed LFASS for label‐free automated survival scoring), which we apply to severe stress and infection resistance assays. We demonstrate its use to define correlations between age, longevity, and severe stress resistance, and its applicability to parasitic nematodes. The use of LFASS to assess the effects of aging on susceptibility to severe stress revealed an unexpected increase in stress resistance with advancing age, which was largely autophagy‐dependent. Correlation analysis further revealed that while severe thermal stress resistance positively correlates with lifespan, severe oxidative stress resistance does not. This supports the view that temperature‐sensitive protein‐handling processes more than redox homeostasis underpin aging in C. elegans. That the ages of peak resistance to infection, severe oxidative stress, heat shock, and milder stressors differ markedly suggests that stress resistance and health span do not show a simple correspondence in C. elegans.
Caenorhabditis elegans death fluorescence affords automated label‐free tracking of population survival in stress and infection assays. Resistance to severe stress increases in C. elegans early aging, and then falls at different times depending on stress paradigm. Resistance to severe thermal stress rises and falls within the first week in an autophagy‐dependent manner, and strongly correlates with longevity. Resistance to severe oxidative stress increases during the first week of adulthood, is modulated by autophagy, but does not correlate with longevity.
The feeling of hunger or satiety results from integration of the sensory nervous system with other physiological and metabolic cues. This regulates food intake, maintains homeostasis and prevents ...disease. In C. elegans, chemosensory neurons sense food and relay information to the rest of the animal via hormones to control food-related behaviour and physiology. Here we identify a new component of this system, SKN-1B which acts as a central food-responsive node, ultimately controlling satiety and metabolic homeostasis. SKN-1B, an ortholog of mammalian NF-E2 related transcription factors (Nrfs), has previously been implicated with metabolism, respiration and the increased lifespan incurred by dietary restriction. Here we show that SKN-1B acts in two hypothalamus-like ASI neurons to sense food, communicate nutritional status to the organism, and control satiety and exploratory behaviours. This is achieved by SKN-1B modulating endocrine signalling pathways (IIS and TGF-β), and by promoting a robust mitochondrial network. Our data suggest a food-sensing and satiety role for mammalian Nrf proteins.
Reduced provision of protein translation machinery promotes healthy aging in a number of animal models. In humans, however, inborn impairments in translation machinery are a known cause of several ...developmental disorders, collectively termed ribosomopathies. Here, we use casual inference approaches in genetic epidemiology to investigate whether adult, tissue-specific biogenesis of translation machinery drives human aging. We assess naturally occurring variation in the expression of genes encoding subunits specific to the two RNA polymerases (Pols) that transcribe ribosomal and transfer RNAs, namely Pol I and III, and the variation in expression of ribosomal protein (RP) genes, using Mendelian randomization. We find each causally associated with human longevity (β = -0.15 ± 0.047,
= 9.6 × 10
,
= 0.015; β = -0.13 ± 0.040,
= 1.4 × 10
,
= 0.023; β = -0.048 ± 0.016,
= 3.5 × 10
,
= 0.056, respectively), and this does not appear to be mediated by altered susceptibility to a single disease. We find that reduced expression of Pol III, RPs, or Pol I promotes longevity from different organs, namely visceral adipose, liver, and skeletal muscle, echoing the tissue specificity of ribosomopathies. Our study shows the utility of leveraging genetic variation in expression to elucidate how essential cellular processes impact human aging. The findings extend the evolutionary conservation of protein synthesis as a critical process that drives animal aging to include humans.
The genetic pathways that modulate ageing in multicellular organisms are typically highly conserved across wide evolutionary distances. Recently RNA polymerase III (Pol III) was shown to promote ...ageing in yeast, C. elegans and D. melanogaster. In this study we investigated the role of Pol III in mammalian ageing using C57BL/6N mice heterozygous for Pol III (Polr3b+/−). We identified sexually dimorphic, organ‐specific beneficial as well as detrimental effects of the Polr3b+/− mutation on health. Female Polr3b+/− mice displayed improved bone health during ageing, but their ability to maintain an effective gut barrier function was compromised and they were susceptible to idiopathic dermatitis (ID). In contrast, male Polr3b+/− mice were lighter than wild‐type (WT) males and had a significantly improved gut barrier function in old age. Several metabolic parameters were affected by both age and sex, but no genotype differences were detected. Neither male nor female Polr3b+/− mice were long‐lived compared to WT controls. Overall, we find no evidence that a reduced Pol III activity extends mouse lifespan but we do find some potential organ‐ and sex‐specific benefits for old‐age health.
RNA polymerase III (Pol III) promotes ageing in yeast, C. elegans and D. melanogaster. We investigated the role of Pol III in mammalian ageing using male and female C57BL/6N mice heterozygous for the Pol III catalytic subunit Polr3b (Polr3b+/−). Polr3b+/− mice were not long‐lived but we did observe some organ‐ and sex‐specific benefits on age‐related health.
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