Variable pathogenicity determines individual lifespan in Caenorhabditis elegans

Beyond genes and environment: mapping biological stochasticity in aging

Aging is characterized by extensive variability in the onset of morbidity and mortality, even in genetically identical populations with carefully controlled environments. This points to the important role stochasticity plays in shaping the divergent aging process between individual organisms. Here, we survey how stochastic factors at the level of molecules, cells, tissues, and organisms manifest in and impact the aging process, with a focus on the nematode Caenorhabditis elegans. Findings of stochasticity in C. elegans give additional insights for aspects of aging in the more complex settings of mammals with parallels drawn between organisms when appropriate. The emerging understanding of the stochastic contributors to longevity will enhance research strategies and medical interventions for personalized medicine.

Similarities and differences in the gene expression signatures of physiological age versus future lifespan

Across all taxa of life, individuals within a species exhibit variable lifespans. Differences in genotype or environment are not sufficient to explain this variance, as even isogenic Caenorhabditis elegans nematodes reared under uniform conditions show significant variability in lifespan. To investigate this phenomenon, we used lifespan-predictive biomarkers to isolate, at mid-adulthood, prospectively long- and short-lived individuals from an otherwise identical population. We selected two biomarkers which correlated positively with lifespan, lin-4p::GFP and mir-243p::GFP, and two which correlated negatively, mir-240/786p::GFP and autofluorescence. The gene-expression signature of long versus short future lifespan was strikingly similar across all four biomarkers tested. Since these biomarkers are expressed in different tissues, these results suggest a shared connection to a global health state correlated with future lifespan. To further investigate this underlying state, we compared the transcriptional signature of long versus short future lifespan to that of chronologically young versus old individuals. By comparison to a high-resolution time series of the average aging transcriptome, we determined that subpopulations predicted to be long- or short-lived by biomarker expression had significantly different transcriptional ages despite their shared chronological age. We found that this difference in apparent transcriptional age accounted for the majority of differentially expressed genes associated with future lifespan. Interestingly, we also identified several genes whose expression consistently separated samples by biomarker expression independent of apparent transcriptional age. These results suggest that the commonalities in the long-lived versus short-lived state reported across different biomarkers of aging extends beyond simply transcriptionally young versus transcriptionally old.

Environmental Concentrations of Polystyrene Nanoplastics Induce Low-Dose Tamoxifen Toxicity Through Oxidative Stress in Caenorhabditis elegans

In recent years, significant focus has been placed on the negative impacts of nanoplastics on living organisms. However, nanoplastics at environmental concentrations may interact with drugs, leading to more severe side effects in organisms. This study used Caenorhabditis elegans (C. elegans) to investigate how environmental levels (μg/L) of polystyrene nanoparticles (PS-NPs) influence tamoxifen toxicity and its mechanisms. Combined exposure to tamoxifen and PS-NPs significantly impaired locomotion, pumping, brood size, growth, and induced oxidative stress in both parents and offspring compared to single exposures. DAF-2 mutations conferred resistance, while DAF-16 mutations increased susceptibility. The combined exposure promoted DAF-16::GFP nuclear translocation and decreased SOD-3::GFP and HSP-16.2::GFP fluorescence, indicating toxicity through the DAF-2/DAF-16 IIS pathway. Bacterial metabolism was also linked to the toxic effects, feeding C. elegans metabolically inactivated OP50 significantly reduced the toxicity associated with the combined exposure of PS-NPs and tamoxifen. Additionally, dietary N-acetyl-L-cysteine significantly improved resistance to combined PS-NP and tamoxifen exposure. In summary, this study highlights how long-term exposure to environmental nanoplastic levels can enhance drug side effects, providing new insights into nanoplastics' role in drug interactions.

Automated cell annotation in multi-cell images using an improved CRF_ID algorithm

Cell identification is an important yet difficult process in data analysis of biological images. Previously, we developed an automated cell identification method called CRF_ID and demonstrated its high performance in Caenorhabditis elegans whole-brain images (Chaudhary et al., 2021). However, because the method was optimized for whole-brain imaging, comparable performance could not be guaranteed for application in commonly used C. elegans multi-cell images that display a subpopulation of cells. Here, we present an advancement, CRF_ID 2.0, that expands the generalizability of the method to multi-cell imaging beyond whole-brain imaging. To illustrate the application of the advance, we show the characterization of CRF_ID 2.0 in multi-cell imaging and cell-specific gene expression analysis in C. elegans. This work demonstrates that high-accuracy automated cell annotation in multi-cell imaging can expedite cell identification and reduce its subjectivity in C. elegans and potentially other biological images of various origins.

ELO-6 expression predicts longevity in isogenic populations of Caenorhabditis elegans

Variations of individual lifespans within genetically identical populations in homogenous environments are remarkable, with the cause largely unknown. Here, we show the expression dynamic of the Caenorhabditis elegans fatty acid elongase ELO-6 during aging predicts individual longevity in isogenic populations. elo-6 expression is reduced with age. ELO-6 expression level exhibits obvious variation between individuals in mid-aged worms and is positively correlated with lifespan and health span. Interventions that prolong longevity enhance ELO-6 expression stability during aging, indicating ELO-6 is also a populational lifespan predictor. Differentially expressed genes between short-lived and long-lived isogenic worms regulate lifespan and are enriched for PQM-1 binding sites. pqm-1 in young to mid-aged adults causes individual ELO-6 expression heterogeneity and restricts health span and life span. Thus, our study identifies ELO-6 as a predictor of individual and populational lifespan and reveals the role of pqm-1 in causing individual health span variation in the mid-aged C. elegans.

Biomarkers for aging in Caenorhabditis elegans high throughput screening

Aging is characterized by a functional decline in organism fitness over time due to a complex combination of genetic and environmental factors [ 1-4]. With an increasing elderly population at risk of age-associated diseases, there is a pressing need for research dedicated to promoting health and longevity through anti-aging interventions. The roundworm Caenorhabditis elegans is an established model organism for aging studies due to its short life cycle, ease of culture, and conserved aging pathways. These benefits also make the worm well-suited for high-throughput screening (HTS) methods to study biomarkers of the molecular changes, cellular dysfunction, and physiological decline associated with aging. Within this review, we offer a summary of recent advances in HTS techniques to study biomarkers of aging in C. elegans.

Reduction in metabolic noise reveals rejuvenation following transient severe caloric restriction

Among land vertebrates, the laying hen stands out due to its great reproductive efficiency: producing an egg daily all year long. This production rate makes the laying hen a special model animal to study the general process of reproduction and aging. One unique aspect of hens is their ability to undergo reproductive plasticity and to rejuvenate their reproductive tract during molting, a standard industrial feed restriction protocol for transiently pausing reproduction, followed by improved laying efficiency almost to peak production. Here we use longitudinal metabolomics, immunology, and physiological assays to show that molting promotes reproduction, compresses morbidity, and restores youthfulness when applied to old hens. We identified circulating metabolic biomarkers that quantitatively predict the reproduction and age of individuals. Lastly, we introduce metabolic noise, a robust, unitless, and quantifiable measure for heterogeneity of the complete metabolome as a general marker that can indicate the rate of aging of a population. Indeed, metabolic noise increased with age in control hens, whereas molted hens exhibited reduced noise following molting, indicating systemic rejuvenation. Our results suggest that metabolic noise can be used as a quick and universal proxy for assessing successful aging treatments, accelerating the timeline for drug development.

Single-worm quantitative proteomics reveals aging heterogeneity in isogenic Caenorhabditis elegans

The heterogeneity of aging has been investigated at cellular and organic levels in the mouse model and human, but the exploration of aging heterogeneity at whole-organism level is lacking. C. elegans is an ideal model organism for studying this question as they are self-fertilized and cultured in the same chamber. Despite the tremendous progress made in single-cell proteomic analysis, there is few single-worm proteomics studies about aging. Here, we apply single-worm quantitative mass spectrometry to quantify the heterogenous proteomic changes during aging across individuals, a total of 3524 proteins from 157 C. eleagns individuals were quantified. A reconstructed C. elegans aging trajectory and proteomic landscape of fast-aging individuals were used to analyze the heterogeneity of C. elegans aging. We characterized inter-individual proteomic variation during aging and revealed contributing factors that distinguish fast-aging individuals from their siblings.

Automated cell annotation in multi-cell images using an improved CRF_ID algorithm

Cell identification is an important yet difficult process in data analysis of biological images. Previously, we developed an automated cell identification method called CRF_ID and demonstrated its high performance in C. elegans whole-brain images (Chaudhary et al, 2021). However, because the method was optimized for whole-brain imaging, comparable performance could not be guaranteed for application in commonly used C. elegans multi-cell images that display a subpopulation of cells. Here, we present an advance CRF_ID 2.0 that expands the generalizability of the method to multi-cell imaging beyond whole-brain imaging. To illustrate the application of the advance, we show the characterization of CRF_ID 2.0 in multi-cell imaging and cell-specific gene expression analysis in C. elegans. This work demonstrates that high accuracy automated cell annotation in multi-cell imaging can expedite cell identification and reduce its subjectivity in C. elegans and potentially other biological images of various origins.

Butein Increases Resistance to Oxidative Stress and Lifespan with Positive Effects on the Risk of Age-Related Diseases in Caenorhabditis elegans

Butein is a flavonoid found in many plants, including dahlia, butea, and coreopsis, and has both antioxidant and sirtuin-activating activities. In light of the postulated role of free radicals in aging, we examined the effects of butein on aging and on genetic or nutritional models of age-related diseases in Caenorhabditis elegans. Butein showed radical scavenging activity and increased resistance to oxidative stress in Caenorhabditis elegans. The mean lifespan of Caenorhabditis elegans was significantly increased by butein, from 22.7 days in the untreated control to 25.0 days in the butein-treated group. However, the lifespan-extending effect of butein was accompanied by reduced production of progeny as a trade-off. Moreover, the age-related decline in motility was delayed by butein supplementation. Genetic analysis showed that the lifespan-extending effect of butein required the autophagic protein BEC-1 and the transcription factor DAF-16 to regulate stress response and aging. At the genetic level, expression of the DAF-16 downstream target genes hsp-16.2 and sod-3 was induced in butein-treated worms. Butein additionally exhibited a preventive effect in models of age-related diseases. In an Alzheimer's disease model, butein treatment significantly delayed the paralysis caused by accumulation of amyloid-beta in muscle, which requires SKN-1, not DAF-16. In a high-glucose-diet model of diabetes mellitus, butein markedly improved survival, requiring both SKN-1 and DAF-16. In a Parkinson's disease model, dopaminergic neurodegeneration was completely inhibited by butein supplementation and the accumulation of α-synuclein was significantly reduced. These findings suggest the use of butein as a novel nutraceutical compound for aging and age-related diseases.

Sniffer worm, C. elegans, as a toxicity evaluation model organism with sensing and locomotion abilities

Additive manufacturing, or 3D printing, has revolutionized the way we create objects. However, its layer-by-layer process may lead to an increased incidence of local defects compared to traditional casting-based methods. Factors such as light intensity, depth of light penetration, component inhomogeneity, and fluctuations in nozzle temperature all contribute to defect formations. These defective regions can become sources of toxic component leakage, but pinpointing their locations in 3D printed materials remains a challenge. Traditional toxicological assessments rely on the extraction and subsequent exposure of living organisms to these harmful agents, thus only offering a passive detection approach. Therefore, the development of an active system to both identify and locate sources of toxicity is essential in the realm of 3D printing technologies. Herein, we introduce the use of the nematode model organism, Caenorhabditis elegans (C. elegans), for toxicity evaluation. C. elegans exhibits distinctive 'sensing' and 'locomotion' capabilities that enable it to actively navigate toward safe zones while steering clear of hazardous areas. This active behavior sets C. elegans apart from other aquatic and animal models, making it an exceptional choice for immediate and precise identification and localization of toxicity sources in 3D printed materials.

A tandem segmentation-classification approach for the localization of morphological predictors of C. elegans lifespan and motility

C. elegans is an established model organism for studying genetic and drug effects on aging, many of which are conserved in humans. It is also an important model for basic research, and C. elegans pathologies is a new emerging field. Here we develop a proof-of-principal convolutional neural network-based platform to segment C. elegans and extract features that might be useful for lifespan prediction. We use a dataset of 734 worms tracked throughout their lifespan and classify worms into long-lived and short-lived. We designed WormNet - a convolutional neural network (CNN) to predict the worm lifespan class based on young adult images (day 1 - day 3 old adults) and showed that WormNet, as well as, InceptionV3 CNN can successfully classify lifespan. Based on U-Net architecture we develop HydraNet CNNs which allow segmenting worms accurately into anterior, mid-body and posterior parts. We combine HydraNet segmentation, WormNet prediction and the class activation map approach to determine the segments most important for lifespan classification. Such a tandem segmentation-classification approach shows the posterior part of the worm might be more important for classifying long-lived worms. Our approach can be useful for the acceleration of anti-aging drug discovery and for studying C. elegans pathologies.

Stochastic and Age-Dependent Proteostasis Decline Underlies Heterogeneity in Heat-Shock Response Dynamics

Significant non-genetic stochastic factors affect aging, causing lifespan differences among individuals, even those sharing the same genetic and environmental background. In Caenorhabditis elegans, differences in heat-shock response (HSR) are predictive of lifespan. However, factors contributing to the heterogeneity of HSR are still not fully elucidated. Here, the authors characterized HSR dynamics in isogenic C. elegans expressing GFP reporter for hsp-16.2 for identifying the key contributors of HSR heterogeneity. Specifically, microfluidic devices that enable cross-sectional and longitudinal measurements of HSR dynamics in C. elegans at different scales are developed: in populations, within individuals, and in embryos. The authors adapted a mathematical model of HSR to single C. elegans and identified model parameters associated with proteostasis-maintenance of protein homeostasis-more specifically, protein turnover, as the major drivers of heterogeneity in HSR dynamics. It is verified that individuals with enhanced proteostasis fidelity in early adulthood live longer. The model-based comparative analysis of protein turnover in day-1 and day-2 adult C. elegans revealed a stochastic-onset of age-related proteostasis decline that increases the heterogeneity of HSR capacity. Finally, the analysis of C. elegans embryos showed higher HSR and proteostasis capacity than young adults and established transgenerational contribution to HSR heterogeneity that depends on maternal age.

Metabolomic Changes Are Predictive of Aging in Laying Hens

Aging in vertebrates is an extremely complex process that is still poorly understood. One confining factor to studying vertebrate aging is the lack of appropriate models. The laying hen is a good model to study vertebrate aging, as it can be maintained under standard housing conditions, its breeds are genetically well defined and it exhibits significant aging phenotypes at around 18 months of age. Furthermore, laying hens are maintained in a challenging realistic environment and possess a fully functional immune system. Here we used, for the first time, metabolomic profiling of laying hens' blood for identifying biomarkers of aging. Random forest classifier was used to quantify the quality of the markers and found that the markers can predict the correct age group of individuals with 90% accuracy. Animals under time-restricted feeding, a condition known to increase health span, appeared younger under the markers, indicating that the aging biomarkers can also predict the effectiveness of environmental treatments. Additionally, we found that noise, defined as the ratio between the standard deviation and the mean, is an exceptionally robust and universal biomarker of aging, as metabolomic noise increases significantly with age in laying hens, humans, and mice. Our study suggests the laying hen as a useful model to study aging in vertebrates and establishes metabolomic noise as a novel, universal biomarker of aging.

Global, cell non-autonomous gene regulation drives individual lifespan among isogenic C. elegans

Across species, lifespan is highly variable among individuals within a population. Even genetically identical Caenorhabditis elegans reared in homogeneous environments are as variable in lifespan as outbred human populations. We hypothesized that persistent inter-individual differences in expression of key regulatory genes drives this lifespan variability. As a test, we examined the relationship between future lifespan and the expression of 22 microRNA promoter::GFP constructs. Surprisingly, expression of nearly half of these reporters, well before death, could effectively predict lifespan. This indicates that prospectively long- vs. short-lived individuals have highly divergent patterns of transgene expression and transcriptional regulation. The gene-regulatory processes reported on by two of the most lifespan-predictive transgenes do not require DAF-16, the FOXO transcription factor that is a principal effector of insulin/insulin-like growth factor (IGF-1) signaling. Last, we demonstrate a hierarchy of redundancy in lifespan-predictive ability among three transgenes expressed in distinct tissues, suggesting that they collectively report on an organism-wide, cell non-autonomous process that acts to set each individual's lifespan.

DAF-16 and SMK-1 Contribute to Innate Immunity During Adulthood in Caenorhabditis elegans

Aging is accompanied by a progressive decline in immune function termed "immunosenescence". Deficient surveillance coupled with the impaired function of immune cells compromises host defense in older animals. The dynamic activity of regulatory modules that control immunity appears to underlie age-dependent modifications to the immune system. In the roundworm Caenorhabditis elegans levels of PMK-1 p38 MAP kinase diminish over time, reducing the expression of immune effectors that clear bacterial pathogens. Along with the PMK-1 pathway, innate immunity in C. elegans is regulated by the insulin signaling pathway. Here we asked whether DAF-16, a Forkhead box (FOXO) transcription factor whose activity is inhibited by insulin signaling, plays a role in host defense later in life. While in younger C. elegans DAF-16 is inactive unless stimulated by environmental insults, we found that even in the absence of acute stress the transcriptional activity of DAF-16 increases in an age-dependent manner. Beginning in the reproductive phase of adulthood, DAF-16 upregulates a subset of its transcriptional targets, including genes required to kill ingested microbes. Accordingly, DAF-16 has little to no role in larval immunity, but functions specifically during adulthood to confer resistance to bacterial pathogens. We found that DAF-16-mediated immunity in adults requires SMK-1, a regulatory subunit of the PP4 protein phosphatase complex. Our data suggest that as the function of one branch of the innate immune system of C. elegans (PMK-1) declines over time, DAF-16-mediated immunity ramps up to become the predominant means of protecting adults from infection, thus reconfiguring immunity later in life.

C. elegans to model autophagy-related human disorders

Autophagy is a highly conserved degradation process that clears damaged intracellular macromolecules and organelles in order to maintain cellular health. Dysfunctional autophagy is fundamentally linked to the development of various human disorders and pathologies. The use of the nematode Caenorhabditis elegans as a model system to study autophagy has improved our understanding of its regulation and function in organismal physiology. Here, we review the genetic, functional, and regulatory conservation of the autophagy pathway in C. elegans and we describe tools to quantify and study the autophagy process in this incredibly useful model organism. We further discuss how these nematodes have been modified to model autophagy-related human diseases and underscore the important insights obtained from such models. Altogether, we highlight the strengths of C. elegans as an exceptional tool to understand the genetic and molecular foundations underlying autophagy-related human diseases.

Mechanical properties measured by atomic force microscopy define health biomarkers in ageing C. elegans

Genetic and environmental factors are key drivers regulating organismal lifespan but how these impact healthspan is less well understood. Techniques capturing biomechanical properties of tissues on a nano-scale level are providing new insights into disease mechanisms. Here, we apply Atomic Force Microscopy (AFM) to quantitatively measure the change in biomechanical properties associated with ageing Caenorhabditis elegans in addition to capturing high-resolution topographical images of cuticle senescence. We show that distinct dietary restriction regimes and genetic pathways that increase lifespan lead to radically different healthspan outcomes. Hence, our data support the view that prolonged lifespan does not always coincide with extended healthspan. Importantly, we identify the insulin signalling pathway in C. elegans and interventions altering bacterial physiology as increasing both lifespan and healthspan. Overall, AFM provides a highly sensitive technique to measure organismal biomechanical fitness and delivers an approach to screen for health-improving conditions, an essential step towards healthy ageing.

Chaperone biomarkers of lifespan and penetrance track the dosages of many other proteins

Many traits vary among isogenic individuals in homogeneous environments. In microbes, plants and animals, variation in the protein chaperone system affects many such traits. In the animal model C. elegans, the expression level of hsp-16.2 chaperone biomarkers correlates with or predicts the penetrance of mutations and lifespan after heat shock. But the physiological mechanisms causing cells to express different amounts of the biomarker were unknown. Here, we used an in vivo microscopy approach to dissect different contributions to cell-to-cell variation in hsp-16.2 expression in the intestines of young adult animals, which generate the most lifespan predicting signal. While we detected both cell autonomous intrinsic noise and signaling noise, we found both contributions were relatively unimportant. The major contributor to cell-to-cell variation in biomarker expression was general differences in protein dosage. The hsp-16.2 biomarker reveals states of high or low effective dosage for many genes.

Saponin-rich extracts from Holothuria leucospilota mediate lifespan extension and stress resistance in Caenorhabditis elegans via daf-16

Saponins are secondary metabolite compounds that can be found in sea cucumbers (Holothuroidea spp.). However, little is known about how saponin-rich extracts from Holothuria leucospilota can delay and prolong the lifespan of the whole organism. In this study, anti-aging effects of H. leucospilota extracts were studied on Caenorhabditis elegans. NMR analysis revealed that body wall n-butanol-extract of H. leucospilota (BW-BU) is saponin-rich. BW-BU extracts exhibited antioxidant activities by 2,2'-diphenyl-2-picrylhydrazyl assay (EC₅₀  = 10.23 ± 0.12 mg/ml) and 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid assay (EC₅₀  = 3.91 ± 0.04 mg/ml). BW-BU extracts increased lifespan of L4 and L1 C. elegans (5.92% and 15.76%, respectively), which also increased worm growth, stress resistance, and reduced biomarkers for aging. BW-BU extracts activated DAF-16 nuclear localization and upregulated daf-16 and DAF-16 target genes expression. Taken together, this study revealed the evidences on anti-aging activities of saponin-rich extracts from H. leucospilota, which can extend lifespan of C. elegans via daf-16. PRACTICAL APPLICATIONS: In recent years, age-associated chronic diseases have had a significant impact on quality of life. Many natural compounds exhibit anti-aging activities, especially in sea cucumber, H. leucospilota. Our results indicated that H. leucospilota is good for health. Extracts from H. leucospilota contain a bioactive compound that can be potentially used to promote longevity and disease prevention in aging.

Phosphatidylcholine Extends Lifespan via DAF-16 and Reduces Amyloid-Beta-Induced Toxicity in Caenorhabditis elegans

Phosphatidylcholine is one of the major phospholipids comprising cellular membrane and is known to have several health-promoting activities, including the improvement of brain function and liver repair. In this paper, we examine the in vivo effect of dietary supplementation with phosphatidylcholine on the response to environmental stressors and aging in C. elegans. Treatment with phosphatidylcholine significantly increased the survival of worms under oxidative stress conditions. However, there was no significant difference in response to stresses caused by heat shock or ultraviolet irradiation. Oxidative stress is believed to be one of the major causal factors of aging. Then, we examined the effect of phosphatidylcholine on lifespan and age-related physiological changes. Phosphatidylcholine showed a lifespan-extending effect and a reduction in fertility, possibly as a tradeoff for long lifespan. Age-related decline of motility was also significantly delayed by supplementation with phosphatidylcholine. Interestingly, the expressions of well-known longevity-assuring genes, hsp-16.2 and sod-3, were significantly upregulated by dietary intervention with phosphatidylcholine. DAF-16, a transcription factor modulating stress response genes, was accumulated in the nucleus by phosphatidylcholine treatment. Increase of the ROS level with phosphatidylcholine suggests that the antioxidant and lifespan-extending effects are due to the hormetic effect of phosphatidylcholine. Phosphatidylcholine also showed a protective effect against amyloid beta-induced toxicity in Alzheimer's disease model animals. Experiments with long-lived mutants revealed that the lifespan-extending effect of phosphatidylcholine specifically overlapped with that of reduced insulin/IGF-1-like signaling and required DAF-16. These findings showed the antioxidant and antiaging activities of phosphatidylcholine for the first time in vivo. Further studies focusing on the identification of underlying cellular mechanisms involved in the antiaging effect will increase the possibility of using phosphatidylcholine for the development of antiaging therapeutics.

Using Bacterial Transcriptomics to Investigate Targets of Host-Bacterial Interactions in Caenorhabditis elegans

The interactions between a host and its resident microbes form complicated networks that can affect host physiology. Disentangling these host-microbe interactions can help us better understand mechanisms by which bacteria affect hosts, while also defining the integral commensal protection that host-associated microbiota offer to promote health. Here we utilize a tractable genetic model organism, Caenorhabditis elegans, to study the effects of host environments on bacterial gene expression and metabolic pathways. First, we compared the transcriptomic profiles of E. coli OP50 in vitro (on agar plates) versus in vivo (fed to C. elegans host). Our data revealed that 110 biosynthetic genes were enriched in host-associated E. coli. Several of these expressed genes code for the precursors and products needed for the synthesis of lipopolysaccharides (LPS), which are important for innate immune and stress responses, as well as pathogenicity. Secondly, we compared the transcriptomic profiles of E. coli fed to hosts with different genetic backgrounds, including the long-lived daf-2/insulin like growth factor (IGF) receptor and short lived daf-16/FOXO transcription factor mutants. We find that hosts genetics also alters bacterial metabolic pathways. Given that bacteria influence host health, this transcriptomics approach can elucidate genes mediating host aging.

Age-dependent changes and biomarkers of aging in Caenorhabditis elegans

Caenorhabditis elegans is an exceptionally valuable model for aging research because of many advantages, including its genetic tractability, short lifespan, and clear age‐dependent physiological changes. Aged C. elegans display a decline in their anatomical and functional features, including tissue integrity, motility, learning and memory, and immunity. Caenorhabditis elegans also exhibit many age‐associated changes in the expression of microRNAs and stress‐responsive genes and in RNA and protein quality control systems. Many of these age‐associated changes provide information on the health of the animals and serve as valuable biomarkers for aging research. Here, we review the age‐dependent changes in C. elegans and their utility as aging biomarkers indicative of the physiological status of aging.

Yeast lifespan variation correlates with cell growth and SIR2 expression

Isogenic wild type yeast cells raised in controlled environments display a significant range of lifespan variation. Recent microfluidic studies suggest that differential growth or gene expression patterns may explain some of the heterogeneity of aging assays. Herein, we sought to complement this work by similarly examining a large set of replicative lifespan data from traditional plate assays. In so doing, we reproduced the finding that short-lived cells tend to arrest at senescence with a budded morphology. Further, we found that wild type cells born unusually small did not have an extended lifespan. However, large birth size and/or high inter-generational growth rates significantly correlated with a reduced lifespan. Finally, we found that SIR2 expression levels correlated with lifespan and intergenerational growth. SIR2 expression was significantly reduced in large cells and increased in small wild type cells. A moderate increase in SIR2 expression correlated with reduced growth, decreased proliferation and increased lifespan in plate aging assays. We conclude that cellular growth rates and SIR2 expression levels may contribute to lifespan variation in individual cells.

Quinolinic acid and glutamatergic neurodegeneration in Caenorhabditis elegans

Quinolinic acid (QUIN) is an endogenous neurotoxin that acts as an N-methyl-D-aspartate receptor (NMDAR) agonist generating a toxic cascade, which can lead to neurodegeneration. The action of QUIN in Caenorhabditis elegans and the neurotoxins that allow the study of glutamatergic system disorders have not been carefully addressed. The effects of QUIN on toxicological and behavioral parameters in VM487 and VC2623 transgenic, as well as wild-type (WT) animals were performed to evaluate whether QUIN could be used as a neurotoxin in C. elegans. QUIN reduced survival of WT worms in a dose-dependent manner. A sublethal dose of QUIN (20 mM) increased reactive oxygen species (ROS) levels in an nmr-1/NMDAR-dependent manner, activated the DAF-16/FOXO transcription factor, and increased expression of the antioxidant enzymes, superoxide dismutase-3, glutathione S-transferase-4, and heat shock protein-16.2. QUIN did not change motor behavioral parameters, but altered the sensory behavior in N2 and VM487 worms. Notably, the effect of QUIN on the sensory behavioral parameters might occur, at least in part, secondary to increased ROS. However, the touch response behavior indicates a mechanism of action that is independent of ROS generation. In addition, non-lethal doses of QUIN triggered neurodegeneration in glutamatergic neurons. Our findings indicate that C. elegans might be useful as a model for studies of QUIN as a glutamatergic neurotoxin in rodent models.

Superoxide dismutases: Dual roles in controlling ROS damage and regulating ROS signaling

Wang et al. review the dual role of superoxide dismutases in controlling reactive oxygen species (ROS) damage and regulating ROS signaling across model systems as well as their involvement in human diseases.

Superoxide dismutases (SODs) are universal enzymes of organisms that live in the presence of oxygen. They catalyze the conversion of superoxide into oxygen and hydrogen peroxide. Superoxide anions are the intended product of dedicated signaling enzymes as well as the byproduct of several metabolic processes including mitochondrial respiration. Through their activity, SOD enzymes control the levels of a variety of reactive oxygen species (ROS) and reactive nitrogen species, thus both limiting the potential toxicity of these molecules and controlling broad aspects of cellular life that are regulated by their signaling functions. All aerobic organisms have multiple SOD proteins targeted to different cellular and subcellular locations, reflecting the slow diffusion and multiple sources of their substrate superoxide. This compartmentalization also points to the need for fine local control of ROS signaling and to the possibility for ROS to signal between compartments. In this review, we discuss studies in model organisms and humans, which reveal the dual roles of SOD enzymes in controlling damage and regulating signaling.

Interacting effects of unobserved heterogeneity and individual stochasticity in the life history of the southern fulmar

Individuals are heterogeneous in many ways. Some of these differences are incorporated as individual states (e.g. age, size, breeding status) in population models. However, substantial amounts of heterogeneity may remain unaccounted for, due to unmeasurable genetic, maternal or environmental factors. Such unobserved heterogeneity (UH) affects the behaviour of heterogeneous cohorts via intra-cohort selection and contributes to inter-individual variance in demographic outcomes such as longevity and lifetime reproduction. Variance is also produced by individual stochasticity, due to random events in the life cycle of wild organisms, yet no study thus far has attempted to decompose the variance in demographic outcomes into contributions from UH and individual stochasticity for an animal population in the wild. We developed a stage-classified matrix population model for the southern fulmar breeding on Ile des Pétrels, Antarctica. We applied multievent, multistate mark-recapture methods to estimate a finite mixture model accounting for UH in all vital rates and Markov chain methods to calculate demographic outcomes. Finally, we partitioned the variance in demographic outcomes into contributions from UH and individual stochasticity. We identify three UH groups, differing substantially in longevity, lifetime reproductive output, age at first reproduction and in the proportion of the life spent in each reproductive state. -14% of individuals at fledging have a delayed but high probability of recruitment and extended reproductive life span. -67% of individuals are less likely to reach adulthood, recruit late and skip breeding often but have the highest adult survival rate. -19% of individuals recruit early and attempt to breed often. They are likely to raise their offspring successfully, but experience a relatively short life span. Unobserved heterogeneity only explains a small fraction of the variances in longevity (5.9%), age at first reproduction (3.7%) and lifetime reproduction (22%). UH can affect the entire life cycle, including survival, development and reproductive rates, with consequences over the lifetime of individuals and impacts on cohort dynamics. The respective role of UH vs. individual stochasticity varies greatly among demographic outcomes. We discuss the implication of our finding for the gradient of life-history strategies observed among species and argue that individual differences should be accounted for in demographic studies of wild populations.

Role of gut microbiota in aging-related health decline: insights from invertebrate models

Studies in mammals, including humans, have reported age-related changes in microbiota dynamics. A major challenge, however, is to dissect the cause and effect relationships involved. Invertebrate model organisms such as the fruit fly Drosophila and the nematode Caenorhabditis elegans have been invaluable in studies of the biological mechanisms of aging. Indeed, studies in flies and worms have resulted in the identification of a number of interventions that can slow aging and prolong life span. In this review, we discuss recent work using invertebrate models to provide insight into the interplay between microbiota dynamics, intestinal homeostasis during aging and life span determination. An emerging theme from these studies is that the microbiota contributes to cellular and physiological changes in the aging intestine and, in some cases, age-related shifts in microbiota dynamics can drive health decline in aged animals.

Effect of the diet type and temperature on the C. elegans transcriptome

The transcriptomes of model organisms have been defined under specific laboratory growth conditions. The standard protocol for Caenorhabditis elegans growth and maintenance is 20°C on an Escherichia coli diet. Temperatures ranging from 15°C to 25°C or feeding with other species of bacteria are considered physiological conditions, but the effect of these conditions on the worm transcriptome has not been well characterized. Here, we compare the global gene expression profile for the reference Caenorhabditis elegans strain (N2) grown at 15°C, 20°C, and 25°C on two different diets, Escherichia coli and Bacillus subtilis. When C. elegans were fed E. coli and the growth temperature was increased, we observed an enhancement of defense response pathways and down-regulation of genes associated with metabolic functions. However, when C. elegans were fed B. subtilis and the growth temperature was increased, the nematodes exhibited a decrease in defense response pathways and an enhancement of expression of genes associated with metabolic functions. Our results show that C. elegans undergo significant metabolic and defense response changes when the maintenance temperature fluctuates within the physiological range and that the degree of pathogenicity of the bacterial diet can further alter the worm transcriptome.

The addition of a developmental factor, unc-62, to already long-lived worms increases lifespan and healthspan

Aging is a complex trait that is affected by multiple genetic pathways. A relatively unexplored approach is to manipulate multiple independent aging pathways simultaneously in order to observe their cumulative effect on lifespan. Here, we report the phenotypic characterization of a strain with changes in five aging pathways: (1) mitochondrial reactive oxygen species (ROS) production, (2) innate immunity, (3) stress response, (4) metabolic control and (5) developmental regulation in old age. The quintuply modified strain has a lifespan that is 160% longer than the transgenic control strain. Additionally, the quintuply modified strain maintains several physiological markers of aging for a longer time than the transgenic control. Our results support a modular approach as a general scheme to study how multiple pathways interact to achieve extreme longevity.

Summary: This work uses a modular approach to combine five genes together to build worms that are long lived and much healthier than control animals, without a significant reduction in fertility. This article has an associated First Person interview with the first author of the paper as part of the supplementary information.

Autofluorescence as a measure of senescence in C. elegans: look to red, not blue or green

In C. elegans, intestinal autofluorescence (sometimes referred to as lipofuscin or “age pigment”) accumulates with age and is often used as a marker of health or the rate of aging. We show that this autofluorescent material is spectrally heterogeneous, and that materials that fluoresce under different excitation wavelengths have distinct biological properties. Red autofluorescence (visible with a TRITC filterset) correlates well with an individual's remaining days of life, and is therefore a candidate marker of health. In contrast, blue autofluorescence (via a DAPI filterset) is chiefly an indicator of an individual's incipient or recent demise. Thus, population averages of blue fluorescence essentially measure the fraction of dead or near-dead individuals. This is related to but distinct from the health of the living population. Green autofluorescence (via a FITC or GFP filterset) combines both properties, and is therefore ill suited as a marker of either death or health. Moreover, our results show that care must be taken to distinguish GFP expression near the time of death from full-body green autofluorescence. Finally, none of this autofluorescence increases after oxidative stress, suggesting that the material, or its biology in C. elegans, is distinct from lipofuscin as reported in the mammalian literature.

Aging causes decreased resistance to multiple stresses and a failure to activate specific stress response pathways

In this work, we examine the relationship between stress resistance and aging. We find that resistance to multiple types of stress peaks during early adulthood and then declines with age. To dissect the underlying mechanisms, we use C. elegans transcriptional reporter strains that measure the activation of different stress responses including: the heat shock response, mitochondrial unfolded protein response, endoplasmic reticulum unfolded protein response, hypoxia response, SKN-1-mediated oxidative stress response, and the DAF-16-mediated stress response. We find that the decline in stress resistance with age is at least partially due to a decreased ability to activate protective mechanisms in response to stress. In contrast, we find that any baseline increase in stress caused by the advancing age is too mild to detectably upregulate any of the stress response pathways. Further exploration of how worms respond to stress with increasing age revealed that the ability to mount a hormetic response to heat stress is also lost with increasing age. Overall, this work demonstrates that resistance to all types of stress declines with age. Based on our data, we speculate that the decrease in stress resistance with advancing age results from a genetically-programmed inactivation of stress response pathways, not accumulation of damage.

Coherent Raman Imaging of Live Muscle Sarcomeres Assisted by SFG Microscopy

In this study, we used spectrally focused coherent anti-Stokes Raman scattering (spCARS) microscopy assisted by sum-frequency generation (SFG) to monitor the variations in the structural morphology and molecular vibrations of a live muscle of Caenorhabditis elegans. The subunits of the muscle sarcomeres, such as the M-line, myosin, dense body, and α-actinin, were alternatively observed using spCARS microscopy for different sample orientations, with the guidance of a myosin positional marker captured by SFG microscopy. Interestingly enough, the beam polarization dependence of the spCARS contrasts for two parallel subunits (dense body and myosin) showed a ~90° phase difference. The chemically sensitive spCARS spectra induced by the time-varying overlap of two pulses allowed (after a robust subtraction of the non-resonant background using a modified Kramers–Krönig transformation method) high-fidelity detection of various genetically modified muscle sarcomeres tuned to the C-H vibration (2800–3100 cm⁻¹). Conversely, SFG image mapping assisted by phase-retrieved spCARS spectra also facilitated label-free monitoring of the changes in the muscle content of C. elegans that are associated with aging, based on the hypothesis that the C-H vibrational modes could serve as qualitative chemical markers sensitive to the amount and/or structural modulation of the muscle.

Environmental Canalization of Life Span and Gene Expression in Caenorhabditis elegans

Animals, particularly poikilotherms, exhibit distinct physiologies at different environmental temperatures. Here, we hypothesized that temperature-based differences in physiology could affect the amount of variation in complex quantitative traits. Specifically, we examined, in Caenorhabditis elegans, how different temperatures (15°C, 20°C, and 25°C) affected the amount of interindividual variation in life span and also expression of three reporter genes-transcriptional reporters for vit-2, gpd-2, and hsp-16.2 (a life-span biomarker). We found the expected inverse relationship between temperature and average life span. Surprisingly, we found that at the highest temperature, there were fewer differences between individuals in life span and less interindividual variation in expression of all three reporters. We suggest that growth at 25°C might canalize (reduce interindividual differences in) life span and expression of some genes by eliciting a small constitutive heat shock response. Growth at 25°C requires wild-type hsf-1, which encodes the main heat shock response transcriptional activator. We speculate that increased chaperone activity at 25°C may reduce interindividual variation in gene expression by increasing protein folding efficiency. We hypothesize that reduced variation in gene expression may ultimately cause reduced variation in life span.

Glycogen controls Caenorhabditis elegans lifespan and resistance to oxidative stress

A high-sugar diet has been associated with reduced lifespan in organisms ranging from worms to mammals. However, the mechanisms underlying the harmful effects of glucose are poorly understood. Here we establish a causative relationship between endogenous glucose storage in the form of glycogen, resistance to oxidative stress and organismal aging in Caenorhabditis elegans. We find that glycogen accumulated on high dietary glucose limits C. elegans longevity. Glucose released from glycogen and used for NADPH/glutathione reduction renders nematodes and human hepatocytes more resistant against oxidative stress. Exposure to low levels of oxidants or genetic inhibition of glycogen synthase depletes glycogen stores and extends the lifespan of animals fed a high glucose diet in an AMPK-dependent manner. Moreover, glycogen interferes with low insulin signalling and accelerates aging of long-lived daf-2 worms fed a high glucose diet. Considering its extensive evolutionary conservation, our results suggest that glycogen metabolism might also have a role in mammalian aging.

Glycogen is a storage form of glucose in cells. Here, Gusarov et al. show that glycogen-derived glucose can be used to quickly regenerate the antioxidant glutathione and that inhibiting glycogen synthesis extends C. elegans lifespan, whereas glycogen accumulation drives organismal ageing in worms.

Two forms of death in ageing Caenorhabditis elegans

Ageing generates senescent pathologies, some of which cause death. Interventions that delay or prevent lethal pathologies will extend lifespan. Here we identify life-limiting pathologies in Caenorhabditis elegans with a necropsy analysis of worms that have died of old age. Our results imply the presence of multiple causes of death. Specifically, we identify two classes of corpse: early deaths with a swollen pharynx (which we call 'P deaths'), and later deaths with an atrophied pharynx (termed 'p deaths'). The effects of interventions on lifespan can be broken down into changes in the frequency and/or timing of either form of death. For example, glp-1 mutation only delays p death, while eat-2 mutation reduces P death. Combining pathology and mortality analysis allows mortality profiles to be deconvolved, providing biological meaning to complex survival and mortality profiles.

How a Mutation that Slows Aging Can Also Disproportionately Extend End-of-Life Decrepitude

The goal of aging research is to extend healthy, active life. For decades, C. elegans daf-2 insulin/insulin-like growth factor 1 (IGF-1) receptor mutants have served as a model for extended lifespan and youthfulness. However, a recent report suggested that their longevity is associated with an undesirable phenotype: a disproportionately long period of decrepitude at the end of life. In the human population, such an outcome would be a burden to society, bringing into question the relevance of daf-2 mutants as a model for life extension. However, here we report that, following an extended period of movement, daf-2 mutants survive longer in a decrepit state because of a beneficial trait: they are resistant to colonization of the digestive tract by dietary bacteria, a condition that leads to premature death in the wild-type and prevents their manifestation of decrepitude. If bacterial colonization is prevented, then daf-2 mutants lead both chronologically and proportionately healthier lives relative to the wild-type.

Supplementation with Triptolide Increases Resistance to Environmental Stressors and Lifespan in C. elegans

Triptolide is a major active compound found in Tripterygium wilfordii., also known as Thunder God Vine. Triptolide has been shown to have anti-inflammatory and anticancer activities. In this study, we examined the effect of dietary supplementation with triptolide on response to environmental stressors and lifespan in vivo using Caenorhabditis elegans as a model system. Treatment with 50 mg/L of triptolide in the growth media increased resistance to oxidative stress and reduced the generation of intracellular reactive oxygen species. We also observed a lifespan-extending activity for triptolide. Both mean and maximum lifespans were significantly increased by supplementation with triptolide. Response to other environmental stressors was modulated by triptolide. The survival after heat shock or UV irradiation was markedly increased in worms treated with triptolide. Unlike many lifespan-extending genetic or nutritional interventions, the longevity phenotype conferred by triptolide did not have the trade-off of a reduction in fertility or a delay in the gravid period. The expressions of hsp-16.2 and sod-3, known to positively correlate with a long lifespan, were significantly upregulated by supplementation with triptolide. These findings suggest that triptolide can exhibit antistress and lifespan-extending effects in vivo, possibly through its antioxidant activity and support the free radical theory of aging, which emphasizes the causative role of oxidative stress in aging.

Extended Twilight among Isogenic C. elegans Causes a Disproportionate Scaling between Lifespan and Health

Although many genetic factors and lifestyle interventions are known to affect the mean lifespan of animal populations, the physiological variation displayed by individuals across their lifespans remains largely uncharacterized. Here, we use a custom culture apparatus to continuously monitor five aspects of aging physiology across hundreds of isolated Caenorhabditis elegans individuals kept in a constant environment from hatching until death. Aggregating these measurements into an overall estimate of senescence, we find two chief differences between longer- and shorter-lived individuals. First, though long- and short-lived individuals are physiologically equivalent in early adulthood, longer-lived individuals experience a lower rate of physiological decline throughout life. Second, and counter-intuitively, long-lived individuals have a disproportionately extended "twilight" period of low physiological function. While longer-lived individuals experience more overall days of good health, their proportion of good to bad health, and thus their average quality of life, is systematically lower than that of shorter-lived individuals. We conclude that, within a homogeneous population reared under constant conditions, the period of early-life good health is comparatively uniform, and the most plastic period in the aging process is end-of-life senescence.

Tenebrio molitor Extracts Modulate the Response to Environmental Stressors and Extend Lifespan in Caenorhabditis elegans

Tenebrio molitor are large insects and their larvae are consumed as food in many countries. The nutritional composition of T. molitor has been studied and contains high amounts of proteins, unsaturated fatty acids, and valuable minerals. However, the bioactivity of T. molitor has not been fully understood. We examined the effects of T. molitor extracts on resistance to oxidative stress and organism's lifespan using Caenorhabditis elegans as a model system. The response to heat shock and ultraviolet (UV) irradiation was monitored in vivo. The extracts from T. molitor showed significant effects on resistance to oxidative stress and UV irradiation and extend both mean and maximum lifespan of C. elegans. The number of progeny produced significantly increased in animals supplemented with T. molitor extracts. In addition, the expression of hsp-16.2 and sod-3 was markedly upregulated by supplementation with T. molitor extracts. These findings suggest that T. molitor extracts can increase response to stressors and extend lifespan by the induction of longevity assurance genes in C. elegans.

The Invertebrate Lysozyme Effector ILYS-3 Is Systemically Activated in Response to Danger Signals and Confers Antimicrobial Protection in C. elegans

Little is known about the relative contributions and importance of antibacterial effectors in the nematode C. elegans, despite extensive work on the innate immune responses in this organism. We report an investigation of the expression, function and regulation of the six ilys (invertebrate-type lysozyme) genes of C. elegans. These genes exhibited a surprising variety of tissue-specific expression patterns and responses to starvation or bacterial infection. The most strongly expressed, ilys-3, was investigated in detail. ILYS-3 protein was expressed constitutively in the pharynx and coelomocytes, and dynamically in the intestine. Analysis of mutants showed that ILYS-3 was required for pharyngeal grinding (disruption of bacterial cells) during normal growth and consequently it contributes to longevity, as well as being protective against bacterial pathogens. Both starvation and challenge with Gram-positive pathogens resulted in ERK-MAPK-dependent up-regulation of ilys-3 in the intestine. The intestinal induction by pathogens, but not starvation, was found to be dependent on MPK-1 activity in the pharynx rather than in the intestine, demonstrating unexpected communication between these two tissues. The coelomocyte expression appeared to contribute little to normal growth or immunity. Recombinant ILYS-3 protein was found to exhibit appropriate lytic activity against Gram-positive cell wall material.

Innate immune defenses against bacterial pathogenesis depend on the activation of antibacterial factors. We examined the expression and relative importance of a gene family encoding six invertebrate-type lysozymes in the much-studied nematode C. elegans. The ilys genes exhibit distinct patterns of tissue-specific expression and response to pathogenic challenge and/or starvation. The most abundantly expressed, ilys-3, exhibits constitutive pharyngeal expression, which we show is essential for efficient disruption of bacteria under non-pathogenic growth conditions, and consequently it contributes to normal longevity. ilys-3 is also strongly up-regulated in intestinal cells after starvation or exposure to Gram-positive pathogens such as Microbacterium nematophilum and acts as a ‘slow-effector’ in limiting pathogenic damage from intestinal infections. We show that this induction by pathogens depends on the action of an ERK-MAPK cascade, which acts in pharyngeal rather than intestinal cells; this implies communication between pharynx and intestine. Tagged ILYS-3 protein was detected mainly in recycling endosomes of intestinal cells and in the intestinal lumen after starvation. ILYS-3 was also expressed in coelomocytes (scavenger cells) but we found that these cells make little or no contribution to defense. We examined the enzymatic properties of recombinant ILYS-3 protein, finding that it has lytic activity against M. nematophilum cell-walls.

Cell size and fat content of dietary-restricted Caenorhabditis elegans are regulated by ATX-2, an mTOR repressor

Dietary restriction (DR) is a metabolic intervention that extends the lifespan of multiple species, including yeast, flies, nematodes, rodents, and, arguably, rhesus monkeys and humans. Hallmarks of lifelong DR are reductions in body size, fecundity, and fat accumulation, as well as slower development. We have identified atx-2, the Caenorhabditis elegans homolog of the human ATXN2L and ATXN2 genes, as the regulator of these multiple DR phenotypes. Down-regulation of atx-2 increases the body size, cell size, and fat content of dietary-restricted animals and speeds animal development, whereas overexpression of atx-2 is sufficient to reduce the body size and brood size of wild-type animals. atx-2 regulates the mechanistic target of rapamycin (mTOR) pathway, downstream of AMP-activated protein kinase (AMPK) and upstream of ribosomal protein S6 kinase and mTOR complex 1 (TORC1), by its direct association with Rab GDP dissociation inhibitor β, which likely regulates RHEB shuttling between GDP-bound and GTP-bound forms. Taken together, this work identifies a previously unknown mechanism regulating multiple aspects of DR, as well as unknown regulators of the mTOR pathway. They also extend our understanding of diet-dependent growth retardation, and offers a potential mechanism to treat obesity.

Tissue- and Time-Specific Expression of Otherwise Identical tRNA Genes

Codon usage bias affects protein translation because tRNAs that recognize synonymous codons differ in their abundance. Although the current dogma states that tRNA expression is exclusively regulated by intrinsic control elements (A- and B-box sequences), we revealed, using a reporter that monitors the levels of individual tRNA genes in Caenorhabditis elegans, that eight tryptophan tRNA genes, 100% identical in sequence, are expressed in different tissues and change their expression dynamically. Furthermore, the expression levels of the sup-7 tRNA gene at day 6 were found to predict the animal's lifespan. We discovered that the expression of tRNAs that reside within introns of protein-coding genes is affected by the host gene's promoter. Pairing between specific Pol II genes and the tRNAs that are contained in their introns is most likely adaptive, since a genome-wide analysis revealed that the presence of specific intronic tRNAs within specific orthologous genes is conserved across Caenorhabditis species.

Dietary and microbiome factors determine longevity in Caenorhabditis elegans

Diet composition affects organismal health. Nutrient uptake depends on the microbiome. Caenorhabditis elegans fed a Bacillus subtilis diet live longer than those fed the standard Escherichia coli diet. Here we report that this longevity difference is primarily caused by dietary coQ, an antioxidant synthesized by E. coli but not by B. subtilis. CoQ-supplemented E. coli fed worms have a lower oxidation state yet live shorter than coQ-less B. subtilis fed worms. We showed that mutations affecting longevity for E. coli fed worms do not always lead to similar effects when worms are fed B. subtilis. We propose that coQ supplementation by the E. coli diet alters the worm cellular REDOX homeostasis, thus decreasing longevity. Our results highlight the importance of microbiome factors in longevity, argue that antioxidant supplementation can be detrimental, and suggest that the C. elegans standard E. coli diet can alter the effect of signaling pathways on longevity.

Constant mortality and fertility over age in Hydra

Senescence, the increase in mortality and decline in fertility with age after maturity, was thought to be inevitable for all multicellular species capable of repeated breeding. Recent theoretical advances and compilations of data suggest that mortality and fertility trajectories can go up or down, or remain constant with age, but the data are scanty and problematic. Here, we present compelling evidence for constant age-specific death and reproduction rates in Hydra, a basal metazoan, in a set of experiments comprising more than 3.9 million days of observations of individual Hydra. Our data show that 2,256 Hydra from two closely related species in two laboratories in 12 cohorts, with cohort age ranging from 0 to more than 41 y, have extremely low, constant rates of mortality. Fertility rates for Hydra did not systematically decline with advancing age. This falsifies the universality of the theories of the evolution of aging that posit that all species deteriorate with age after maturity. The nonsenescent life history of Hydra implies levels of maintenance and repair that are sufficient to prevent the accumulation of damage for at least decades after maturity, far longer than the short life expectancy of Hydra in the wild. A high proportion of stem cells, constant and rapid cell turnover, few cell types, a simple body plan, and the fact that the germ line is not segregated from the soma are characteristics of Hydra that may make nonsenescence feasible. Nonsenescence may be optimal because lifetime reproduction may be enhanced more by extending adult life spans than by increasing daily fertility.

Bacillus licheniformis Isolated from Traditional Korean Food Resources Enhances the Longevity of Caenorhabditis elegans through Serotonin Signaling

In this study, we investigated potentially probiotic Bacillus licheniformis strains isolated from traditional Korean food sources for ability to enhance longevity using the nematode Caenorhabditis elegans as a simple in vivo animal model. We first investigated whether B. licheniformis strains were capable of modulating the lifespan of C. elegans. Among the tested strains, preconditioning with four B. licheniformis strains significantly enhanced the longevity of C. elegans. Unexpectedly, plate counting and transmission electron microscopy (TEM) results indicated that B. licheniformis strains were not more highly attached to the C. elegans intestine compared with Escherichia coli OP50 or Lactobacillus rhamnosus GG controls. In addition, qRT-PCR and an aging assay with mutant worms showed that the conditioning of B. licheniformis strain 141 directly influenced genes associated with serotonin signaling in nematodes, including tph-1 (tryptophan hydroxylase), bas-1 (serotonin- and dopamine-synthetic aromatic amino acid decarboxylase), mod-1 (serotonin-gated chloride channel), ser-1, and ser-7 (serotonin receptors) during C. elegans aging. Our findings suggest that B. licheniformis strain 141, which is isolated from traditional Korean foods, is a probiotic generally recognized as safe (GRAS) strain that enhances the lifespan of C. elegans via host serotonin signaling.

C. elegans maximum velocity correlates with healthspan and is maintained in worms with an insulin receptor mutation

Ageing is marked by physical decline. Caenorhabditis elegans is a valuable model for identifying genetic regulatory mechanisms of ageing and longevity. Here we report a simple method to assess C. elegans' maximum physical ability based on the worms' maximum movement velocity. We show maximum velocity declines with age, correlates well with longevity, accurately reports movement ability and, if measured in mid-adulthood, is predictive of maximal lifespan. Contrary to recent findings, we observe that maximum velocity of worm with mutations in daf-2(e1370) insulin/IGF-1 signalling scales with lifespan. Because of increased odorant receptor expression, daf-2(e1370) mutants prefer food over exploration, causing previous on-food motility assays to underestimate movement ability and, thus, worm health. Finally, a disease-burden analysis of published data reveals that the daf-2(e1370) mutation improves quality of life, and therefore combines lifespan extension with various signs of an increased healthspan.

Increases in lifespan do not necessarily translate into prolonged healthspan. Here, the authors devise a simple metric, maximum velocity, to study ageing in C. elegans and, using this metric, show that reduced insulin signalling improves physical healthspan as well as worm lifespan.

Heterotypic Signals from Neural HSF-1 Separate Thermotolerance from Longevity

Integrating stress responses across tissues is essential for the survival of multicellular organisms. The metazoan nervous system can sense protein-misfolding stress arising in different subcellular compartments and initiate cytoprotective transcriptional responses in the periphery. Several subcellular compartments possess a homotypic signal whereby the respective compartment relies on a single signaling mechanism to convey information within the affected cell to the same stress-responsive pathway in peripheral tissues. In contrast, we find that the heat shock transcription factor, HSF-1, specifies its mode of transcellular protection via two distinct signaling pathways. Upon thermal stress, neural HSF-1 primes peripheral tissues through the thermosensory neural circuit to mount a heat shock response. Independent of this thermosensory circuit, neural HSF-1 activates the FOXO transcription factor, DAF-16, in the periphery and prolongs lifespan. Thus a single transcription factor can coordinate different stress response pathways to specify its mode of protection against changing environmental conditions.