Regulation of the longevity response to temperature by thermosensory neurons in Caenorhabditis elegans

CaMK modulates sensory neural activity to control longevity and proteostasis

The impact of neural activity on aging and longevity remains poorly understood, with limited understanding of the specific neuron groups and molecular mechanisms that regulate lifespan. In this study, we uncover a correlation between human longevity and reduced CaMK4 expression in the frontal cortex. We further show that this link is conserved in Caenorhabditis elegans, where the loss of the homolog CMK-1 leads to increased longevity and enhanced proteostasis. These beneficial effects are primarily driven by suppressed excitation in the primary thermosensory AFD neurons, particularly at elevated temperatures that trigger hyperactivation. In the thermosensory neural circuit, suppression of AFD neuron activity promotes the release of INS-1/insulin from AIZ, which in turn activates DAF-16/FOXO in the intestine. Our findings reveal a causal mechanism through which sensory neural activity governs lifespan and organismal proteostasis, highlighting the significance of CaMK in shaping these processes through the regulation of neural activity.

The Caenorhabditis elegans neuronal GPCR OCTR-1 modulates longevity responses to both warm and cold temperatures

Many animal species live longer in cold climates than in warm climates, which was traditionally explained using the rate of living theory, i.e., higher temperatures increase chemical reaction rates, thus speeding up the aging process. However, recent studies have identified specific molecules and cells that are involved in longevity responses to temperature, indicating that such responses are not simply thermodynamic but are regulated processes. Here, we report that Caenorhabditis elegans lacking the neuronal G protein-coupled receptor OCTR-1 have extended lifespans at a warm temperature but shortened lifespans at a cold temperature, demonstrating that OCTR-1 modulates temperature-induced longevity responses. These responses are regulated by the OCTR-1-expressing, chemosensory ASH neurons. Furthermore, the OCTR-1 pathway controls such responses to warm and cold temperatures by regulating the expressions of immune response genes and the intestinal transcriptional factor ELT-2, respectively. Overall, our study provides cellular and molecular insights into the relationship between temperature and longevity.

The Proprotein Convertase BLI-4 Is Required for Axenic Dietary Restriction Mediated Longevity in Caenorhabditis elegans

Dietary restriction (DR) is a well-established method for extending lifespan across various species, including C. elegans. Among the different DR regimens, axenic dietary restriction (ADR), in which worms are grown in a nutrient-rich sterile liquid medium, yields the most powerful lifespan extension. However, the molecular mechanisms underlying this longevity phenotype remain largely unexplored. Through a pilot screen of candidate genes, we identified the proprotein convertase BLI-4 as a crucial factor in neurons for modulating lifespan under ADR conditions. BLI-4's role appears to be specific to ADR, as it does not significantly impact longevity under other DR regimens. We further explored the involvement of different bli-4 isoforms and found that isoforms b, f, i and j redundantly contribute to the ADR-mediated lifespan extension, while the bli-4d isoform is mainly involved in development. Proteomics analysis revealed that the loss of BLI-4 function under ADR conditions specifically downregulates GOLG-2, involved in Golgi complex organization. This gene also partially mediates the longevity effects of BLI-4 under ADR conditions. Our findings highlight the importance of neuronal BLI-4 and its downstream targets in regulating lifespan extension induced by ADR in C. elegans.

Stress-induced neurodegeneration and behavioral alterations in Caenorhabditis elegans: Insights into the evolutionary conservation of stress-related pathways and implications for human health

Stress is a significant determinant for a range of neurological and psychiatric illnesses, and comprehending its influence on the brain is vital for developing effective interventions. Caenorhabditis elegans (C. elegans), a tiny nematode, has become a potent model system for investigating the impact of stress on neuronal integrity, behavior, and lifespan. This chapter presents a comprehensive summary of the existing understanding of stress-induced neurodegeneration, behavioral abnormalities, and changes in lifespan in C. elegans. We explored the stress response pathways in C. elegans, specifically focusing on the heat shock response and insulin-like signaling (ILS) pathway, targeting how these pathways affect neural integrity and functions. Additionally, this chapter highlighted behavioral modifications such as changes in locomotion, feeding, pharyngeal pumping, defecation, and copulation behaviors that occur in C. elegans following exposure to stressors, and how these findings contribute to our comprehension of stress-related illnesses. Furthermore, the evolutionary preservation of stress responses in both C. elegans and humans, underscoring the significance of C. elegans studies for translational research were highlighted. In conclusion, the possible implications of C. elegans research on human well-being, with a specific emphasis on the discovery of targets for treatment and the creation of innovative approaches to address stress-related conditions are discussed in this chapter.

Temperature-dependent lifespan extension is achieved in miR-80-deleted Caenorhabditis elegans by NLP-45 to modulate endoplasmic reticulum unfolded protein responses

MicroRNA plays a crucial role in post-transcriptional gene regulation and has recently emerged as a factor linked to aging, but the underlying regulatory mechanisms remain incompletely understood. In this study, we observed lifespan-extending effects in miR-80-deficient Caenorhabditis elegans at 20°C but not 25°C. At 20°C, miR-80 deletion leads to NLP-45 upregulation, which positively correlates to increased abu transcripts and extended lifespan. Supportively, we identified miR-80 binding regions in the 5' and 3' UTR of nlp-45. As the temperature rises to 25°C, wildtype increases miR-80 levels, but removal of miR-80 is accompanied by decreased nlp-45 expression, suggesting intervention from other temperature-sensitive mechanisms. These findings support the concept that microRNAs and neuropeptide-like proteins can form molecular regulatory networks involving downstream molecules to regulate lifespan, and such regulatory effects vary on environmental conditions. This study unveils the role of an axis of miR-80/NLP-45/UPRER components in regulating longevity, offering new insights on strategies of aging attenuation and health span prolongation.

Thermosensory behaviors of the free-living life stages of Strongyloides species support parasitism in tropical environments

Soil-transmitted parasitic nematodes infect over 1 billion people worldwide and are a common source of neglected disease. Strongyloides stercoralis is a potentially fatal skin-penetrating human parasite that is endemic to tropical and subtropical regions around the world. The complex life cycle of Strongyloides species is unique among human-parasitic nematodes in that it includes a single free-living generation featuring soil-dwelling, bacterivorous adults whose progeny all develop into infective larvae. The sensory behaviors that enable free-living Strongyloides adults to navigate and survive soil environments are unknown. S. stercoralis infective larvae display parasite-specific sensory-driven behaviors, including robust attraction to mammalian body heat. In contrast, the free-living model nematode Caenorhabditis elegans displays thermosensory behaviors that guide adult worms to stay within a physiologically permissive range of environmental temperatures. Do S. stercoralis and C. elegans free-living adults, which experience similar environmental stressors, display common thermal preferences? Here, we characterize the thermosensory behaviors of the free-living adults of S. stercoralis as well as those of the closely related rat parasite, Strongyloides ratti. We find that Strongyloides free-living adults are exclusively attracted to near-tropical temperatures, despite their inability to infect mammalian hosts. We further show that lifespan is shorter at higher temperatures for free-living Strongyloides adults, similar to the effect of temperature on C. elegans lifespan. However, we also find that the reproductive potential of the free-living life stage is enhanced at warmer temperatures, particularly for S. stercoralis. Together, our results reveal a novel role for thermotaxis to maximize the infectious capacity of obligate parasites and provide insight into the biological adaptations that may contribute to their endemicity in tropical climates.

Effect of Olive Fruit Volatiles on Landing, Egg Production, and Longevity of Bactrocera oleae Females under Different Temperatures

Females of the olive fruit fly Bactrocera oleae use various contact and volatile plant stimuli to find olive fruits and lay their eggs on them. We detected certain volatile organic compounds (VOCs) emitted from the olive fruit and studied their effect on female landings on olive fruits, egg production, and longevity under a series of different temperatures from 15 °C to 35 °C. When female flies were maintained at temperatures from 17 °C to 30 °C and exposed to different fruit VOCs either increased or decreased, depending on the substance tested, their landings on olives, egg production, and longevity. Temperature significantly affected the females' responses to fruit VOCs. The highest responses of the flies to fruit VOCs were observed at 30 °C, except for longevity. By contrast, at 15 °C or 35 °C, the flies did not show any response to VOCs. Our results may contribute to a better understanding of the olive fly positive or negative responses to fruit VOCs and the improvement of its control.

Thermosensory behaviors of the free-living life stages of Strongyloides species support parasitism in tropical environments

Soil-transmitted parasitic nematodes infect over 1 billion people worldwide and are a common source of neglected disease. Strongyloides stercoralis is a potentially fatal skin-penetrating human parasite that is endemic to tropical and subtropical regions around the world. The complex life cycle of Strongyloides species is unique among human-parasitic nematodes in that it includes a single free-living generation featuring soil-dwelling, bacterivorous adults whose progeny all develop into infective larvae. The sensory behaviors that enable free-living Strongyloides adults to navigate and survive soil environments are unknown. S. stercoralis infective larvae display parasite-specific sensory-driven behaviors, including robust attraction to mammalian body heat. In contrast, the free-living model nematode Caenorhabditis elegans displays thermosensory behaviors that guide adult worms to stay within a physiologically permissive range of environmental temperatures. Do S. stercoralis and C. elegans free-living adults, which experience similar environmental stressors, display common thermal preferences? Here, we characterize the thermosensory behaviors of the free-living adults of S. stercoralis as well as those of the closely related rat parasite, Strongyloides ratti. We find that Strongyloides free-living adults are exclusively attracted to near-tropical temperatures, despite their inability to infect mammalian hosts. We further show that lifespan is shorter at higher temperatures for free-living Strongyloides adults, similar to the effect of temperature on C. elegans lifespan. However, we also find that the reproductive potential of the free-living life stage is enhanced at warmer temperatures, particularly for S. stercoralis. Together, our results reveal a novel role for thermotaxis to maximize the infectious capacity of obligate parasites and provide insight into the biological adaptations that may contribute to their endemicity in tropical climates.

The intron binding protein EMB-4 is an opposite regulator of cold and high temperature tolerance in Caenorhabditis elegans

Adaptation and tolerance to changes in heat and cold temperature are essential for survival and proliferation in plants and animals. However, there is no clear information regarding the common molecules between animals and plants. In this study, we found that heat, and cold tolerance of the nematode Caenorhabditis elegans is oppositely regulated by the RNA-binding protein EMB-4, whose plant homolog contains polymorphism causing heat tolerance diversity. Caenorhabditis elegans alters its cold and heat tolerance depending on the previous cultivation temperature, wherein EMB-4 respectively acts as a positive and negative controller of heat and cold tolerance by altering gene expression. Among the genes whose expression is regulated by EMB-4, a phospholipid scramblase, and an acid sphingomyelinase, which are involved in membrane lipid metabolism, were found to play essential roles in the negative regulation of heat tolerance.

Regulatory mechanism of cold-inducible diapause in Caenorhabditis elegans

Temperature is a critical environmental cue that controls the development and lifespan of many animal species; however, mechanisms underlying low-temperature adaptation are poorly understood. Here, we describe cold-inducible diapause (CID), another type of diapause induced by low temperatures in Caenorhabditis elegans. A premature stop codon in heat shock factor 1 (hsf-1) triggers entry into CID at 9 °C, whereas wild-type animals enter CID at 4 °C. Furthermore, both wild-type and hsf-1(sy441) mutant animals undergoing CID can survive for weeks, and resume growth at 20 °C. Using epistasis analysis, we demonstrate that neural signalling pathways, namely tyraminergic and neuromedin U signalling, regulate entry into CID of the hsf-1 mutant. Overexpression of anti-ageing genes, such as hsf-1, XBP1/xbp-1, FOXO/daf-16, Nrf2/skn-1, and TFEB/hlh-30, also inhibits CID entry of the hsf-1 mutant. Based on these findings, we hypothesise that regulators of the hsf-1 mutant CID may impact longevity, and successfully isolate 16 long-lived mutants among 49 non-CID mutants via genetic screening. Furthermore, we demonstrate that the nonsense mutation of MED23/sur-2 prevents CID entry of the hsf-1(sy441) mutant and extends lifespan. Thus, CID is a powerful model to investigate neural networks involving cold acclimation and to explore new ageing mechanisms.

A cGAL-UAS bipartite expression toolkit for Caenorhabditis elegans sensory neurons

Animals integrate sensory information from the environment and display various behaviors in response to external stimuli. In Caenorhabditis elegans hermaphrodites, 33 types of sensory neurons are responsible for chemosensation, olfaction, and mechanosensation. However, the functional roles of all sensory neurons have not been systematically studied due to the lack of facile genetic accessibility. A bipartite cGAL-UAS system has been previously developed to study tissue- or cell-specific functions in C. elegans. Here, we report a toolkit of new cGAL drivers that can facilitate the analysis of a vast majority of the 60 sensory neurons in C. elegans hermaphrodites. We generated 37 sensory neuronal cGAL drivers that drive cGAL expression by cell-specific regulatory sequences or intersection of two distinct regulatory regions with overlapping expression (split cGAL). Most cGAL-drivers exhibit expression in single types of cells. We also constructed 28 UAS effectors that allow expression of proteins to perturb or interrogate sensory neurons of choice. This cGAL-UAS sensory neuron toolkit provides a genetic platform to systematically study the functions of C. elegans sensory neurons.

The C. elegans Myc-family of transcription factors coordinate a dynamic adaptive response to dietary restriction

Dietary restriction (DR), the process of decreasing overall food consumption over an extended period of time, has been shown to increase longevity across evolutionarily diverse species and delay the onset of age-associated diseases in humans. In Caenorhabditis elegans, the Myc-family transcription factors (TFs) MXL-2 (Mlx) and MML-1 (MondoA/ChREBP), which function as obligate heterodimers, and PHA-4 (orthologous to forkhead box transcription factor A) are both necessary for the full physiological benefits of DR. However, the adaptive transcriptional response to DR and the role of MML-1::MXL-2 and PHA-4 remains elusive. We identified the transcriptional signature of C. elegans DR, using the eat-2 genetic model, and demonstrate broad changes in metabolic gene expression in eat-2 DR animals, which requires both mxl-2 and pha-4. While the requirement for these factors in DR gene expression overlaps, we found many of the DR genes exhibit an opposing change in relative gene expression in eat-2;mxl-2 animals compared to wild-type, which was not observed in eat-2 animals with pha-4 loss. We further show functional deficiencies of the mxl-2 loss in DR outside of lifespan, as eat-2;mxl-2 animals exhibit substantially smaller brood sizes and lay a proportion of dead eggs, indicating that MML-1::MXL-2 has a role in maintaining the balance between resource allocation to the soma and to reproduction under conditions of chronic food scarcity. While eat-2 animals do not show a significantly different metabolic rate compared to wild-type, we also find that loss of mxl-2 in DR does not affect the rate of oxygen consumption in young animals. The gene expression signature of eat-2 mutant animals is consistent with optimization of energy utilization and resource allocation, rather than induction of canonical gene expression changes associated with acute metabolic stress -such as induction of autophagy after TORC1 inhibition. Consistently, eat-2 animals are not substantially resistant to stress, providing further support to the idea that chronic DR may benefit healthspan and lifespan through efficient use of limited resources rather than broad upregulation of stress responses, and also indicates that MML-1::MXL-2 and PHA-4 may have different roles in promotion of benefits in response to different pro-longevity stimuli.

Olfactory chemosensation extends lifespan through TGF-β signaling and UPR activation

Animals rely on chemosensory cues to survive in pathogen-rich environments. In Caenorhabditis elegans, pathogenic bacteria trigger aversive behaviors through neuronal perception and activate molecular defenses throughout the animal. This suggests that neurons can coordinate the activation of organism-wide defensive responses upon pathogen perception. In this study, we found that exposure to volatile pathogen-associated compounds induces activation of the endoplasmic reticulum unfolded protein response (UPRER) in peripheral tissues after xbp-1 splicing in neurons. This odorant-induced UPRER activation is dependent upon DAF-7/transforming growth factor beta (TGF-β) signaling and leads to extended lifespan and enhanced clearance of toxic proteins. Notably, rescue of the DAF-1 TGF-β receptor in RIM/RIC interneurons is sufficient to significantly recover UPRER activation upon 1-undecene exposure. Our data suggest that the cell non-autonomous UPRER rewires organismal proteostasis in response to pathogen detection, pre-empting proteotoxic stress. Thus, chemosensation of particular odors may be a route to manipulation of stress responses and longevity.

The longevity response to warm temperature is neurally controlled via the regulation of collagen genes

Studies in diverse species have associated higher temperatures with shorter lifespan and lower temperatures with longer lifespan. These inverse effects of temperature on longevity are traditionally explained using the rate of living theory, which posits that higher temperatures increase chemical reaction rates, thus speeding up the aging process. Recent studies have identified specific molecules and cells that affect the longevity response to temperature, indicating that this response is regulated, not simply thermodynamic. Here, we demonstrate that in Caenorhabditis elegans, functional loss of NPR-8, a G protein-coupled receptor related to mammalian neuropeptide Y receptors, increases worm lifespan at 25°C but not at 20°C or 15°C, and that the lifespan extension at 25°C is regulated by the NPR-8-expressing AWB and AWC chemosensory neurons as well as AFD thermosensory neurons. Integrative transcriptomic analyses revealed that both warm temperature and old age profoundly alter gene expression and that genes involved in the metabolic and biosynthetic processes increase expression at 25°C relative to 20°C, indicating elevated metabolism at warm temperature. These data demonstrate that the temperature-induced longevity response is neurally regulated and also provide a partial molecular basis for the rate of living theory, suggesting that these two views are not mutually exclusive. Genetic manipulation and functional assays further uncovered that the NPR-8-dependent longevity response to warm temperature is achieved by regulating the expression of a subset of collagen genes. As increased collagen expression is a common feature of many lifespan-extending interventions and enhanced stress resistance, collagen expression could be critical for healthy aging.

Photo-and thermo-regulation by photonic crystals for extended longevity of C. elegans

Methods allowing light energy to be modulated in a controllable fashion are potentially important for finding the correlation between light-related environmental factors and aging-related lifespan. Here, we report photo- and thermo-regulation based on photonic crystals (PCs) for extended longevity of C. elegans. We show that PCs can function as a regulator of visible spectrum to tune photonic energy received by C.elegans. We provide direct evidence that lifespan depends on photonic energy, and the use of PCs reflecting blue light (440-537nm) gives 8.3% increasement in lifespan. We demonstrate that the exposure to modulated light alleviates photo-oxidative stress and unfolded-protein response. We realize reflective passive cooling temperature using PCs, and favorable low temperature could be created for worms to extend lifespan. This work offers a new path based on PCs to resist negative effects light and temperature for longevity, provides an available platform for studying the role of light in aging.

Temperature acclimation: Temperature shift induces system conversion to cold tolerance in C. elegans

Acclimation to temperature is one of the survival strategies used by organisms to adapt to changing environmental temperatures. Caenorhabditis elegans' cold tolerance is altered by previous cultivation temperature, and similarly, past low-temperature induces a longer lifespan. Temperature is thought to cause a large shift in homeostasis, lipid metabolism, and reproduction in the organism because it is a direct physiological factor during chemical events. This paper will share and discuss what we know so far about the neural and molecular mechanisms that control cold tolerance and lifespan by altering lipid metabolism and physiological characteristics. We hope that this will contribute to a better understanding of how organisms respond to temperature changes.

Cold temperature extends longevity and prevents disease-related protein aggregation through PA28γ-induced proteasomes

Aging is a primary risk factor for neurodegenerative disorders that involve protein aggregation. Because lowering body temperature is one of the most effective mechanisms to extend longevity in both poikilotherms and homeotherms, a better understanding of cold-induced changes can lead to converging modifiers of pathological protein aggregation. Here, we find that cold temperature (15 °C) selectively induces the trypsin-like activity of the proteasome in Caenorhabditis elegans through PSME-3, the worm orthologue of human PA28γ/PSME3. This proteasome activator is required for cold-induced longevity and ameliorates age-related deficits in protein degradation. Moreover, cold-induced PA28γ/PSME-3 diminishes protein aggregation in C. elegans models of age-related diseases such as Huntington's and amyotrophic lateral sclerosis. Notably, exposure of human cells to moderate cold temperature (36 °C) also activates trypsin-like activity through PA28γ/PSME3, reducing disease-related protein aggregation and neurodegeneration. Together, our findings reveal a beneficial role of cold temperature that crosses evolutionary boundaries with potential implications for multi-disease prevention.

A biphasic model of lifespan in nematode Caenorhabditis elegans worm

Ageing research focuses on identifying lifespan modifiers and understanding and appropriately interpreting their effects. One of the most relevant quantities being studied is the shape of the survival curve that can reveal crucial information on the mechanism of action. Here, we introduce a bilogistic model to describe the shape of the lifespan curves of Caenorhabditis elegans populations. Using the corrected Akaike information criterion and the RMSE as goodness-of-fit tests, we show that the bilogistic model provides a better fit to the experimental data from nematode worms than other mathematical models and can identify and confirm biphasic lifespan data. Our parametric model offers a method to interpret replicate experiments data in terms of the shape parameters of the lifespan curve and enables robust statistical analysis of intra- and inter-group variance. We apply the model to novel lifespan data from C. elegans and Drosophila melanogaster and provide a rational statistical analysis of lifespan modifiers such as temperature and daf-16/FOXO mutation.

Analyzing the postulated inhibitory effect of Manumycin A on farnesyltransferase

Manumycin A is postulated to be a specific inhibitor against the farnesyltransferase (FTase) since this effect has been shown in 1993 for yeast FTase. Since then, plenty of studies investigated Manumycin A in human cells as well as in model organisms like Caenorhabditis elegans. Some studies pointed to additional targets and pathways involved in Manumycin A effects like apoptosis. Therefore, these studies created doubt whether the main mechanism of action of Manumycin A is FTase inhibition. For some of these alternative targets half maximal inhibitory concentrations (IC₅₀) of Manumycin A are available, but not for human and C. elegans FTase. So, we aimed to 1) characterize missing C. elegans FTase kinetics, 2) elucidate the IC₅₀ and K_i values of Manumycin A on purified human and C. elegans FTase 3) investigate Manumycin A dependent expression of FTase and apoptosis genes in C. elegans. C. elegans FTase has its temperature optimum at 40°C with K_M of 1.3 µM (farnesylpyrophosphate) and 1.7 µM (protein derivate). Whilst other targets are inhibitable by Manumycin A at the nanomolar level, we found that Manumycin A inhibits cell-free FTase in micromolar concentrations (K_{i human} 4.15 μM; K_{i C. elegans} 3.16 μM). Furthermore, our gene expression results correlate with other studies indicating that thioredoxin reductase 1 is the main target of Manumycin A. According to our results, the ability of Manumycin A to inhibit the FTase at the micromolar level is rather neglectable for its cellular effects, so we postulate that the classification as a specific FTase inhibitor is no longer valid.

Variable rate of ageing within species: insights from Darwin’s frogs

Actuarial senescence, the increase in adult mortality risk with increasing age, is a widespread phenomenon across the animal kingdom. Although between-species variation in the rate of increase in mortality as organisms age (i.e. ageing rate) is now well documented, the occurrence of variation in ageing rate within a given species remains much more debatable. We evaluated the level of within-species variation in ageing rate in four populations of the southern Darwin’s frog (Rhinoderma darwinii) from Chile. Our results revealed strong among-population variation in ageing rates, and these were correlated with the population-specific generation time. A higher ageing rate occurred in populations where individuals exhibited a faster pace of life. Our results, along with recent studies in evolutionarily distant amphibian species, indicate that there can be substantial within-species variation in the rate of ageing, highlighting amphibians as emerging models to study the patterns and mechanisms of intraspecific variation in ageing rate.

The Thermal Stress Coping Network of the Nematode Caenorhabditis elegans

Response to hyperthermia, highly conserved from bacteria to humans, involves transcriptional upregulation of genes involved in battling the cytotoxicity caused by misfolded and denatured proteins, with the aim of proteostasis restoration. C. elegans senses and responds to changes in growth temperature or noxious thermal stress by well-defined signaling pathways. Under adverse conditions, regulation of the heat shock response (HSR) in C. elegans is controlled by a single transcription factor, heat-shock factor 1 (HSF-1). HSR and HSF-1 in particular are proven to be central to survival under proteotoxic stress, with additional roles in normal physiological processes. For years, it was a common belief that upregulation of heat shock proteins (HSPs) by HSF-1 was the main and most important step toward thermotolerance. However, an ever-growing number of studies have shown that targets of HSF-1 involved in cytoskeletal and exoskeletal integrity preservation as well as other HSF-1 dependent and independent pathways are equally important. In this review, we follow the thermal stimulus from reception by the nematode nerve endings till the activation of cellular response programs. We analyze the different HSF-1 functions in HSR as well as all the recently discovered mechanisms that add to the knowledge of the heat stress coping network of C. elegans.

Neuronal temperature perception induces specific defenses that enable C. elegans to cope with the enhanced reactivity of hydrogen peroxide at high temperature

Hydrogen peroxide is the most common reactive chemical that organisms face on the microbial battlefield. The rate with which hydrogen peroxide damages biomolecules required for life increases with temperature, yet little is known about how organisms cope with this temperature-dependent threat. Here, we show that Caenorhabditis elegans nematodes use temperature information perceived by sensory neurons to cope with the temperature-dependent threat of hydrogen peroxide produced by the pathogenic bacterium Enterococcus faecium. These nematodes preemptively induce the expression of specific hydrogen peroxide defenses in response to perception of high temperature by a pair of sensory neurons. These neurons communicate temperature information to target tissues expressing those defenses via an insulin/IGF1 hormone. This is the first example of a multicellular organism inducing their defenses to a chemical when they sense an inherent enhancer of the reactivity of that chemical.

Thermosensation in Caenorhabditis elegans is linked to ubiquitin-dependent protein turnover via insulin and calcineurin signalling

Organismal physiology and survival are influenced by environmental conditions and linked to protein quality control. Proteome integrity is achieved by maintaining an intricate balance between protein folding and degradation. In Caenorhabditis elegans, acute heat stress determines cell non-autonomous regulation of chaperone levels. However, how the perception of environmental changes, including physiological temperature, affects protein degradation remains largely unexplored. Here, we show that loss-of-function of dyf-1 in Caenorhabditis elegans associated with dysfunctional sensory neurons leads to defects in both temperature perception and thermal adaptation of the ubiquitin/proteasome system centered on thermosensory AFD neurons. Impaired perception of moderate temperature changes worsens ubiquitin-dependent proteolysis in intestinal cells. Brain-gut communication regulating protein turnover is mediated by upregulation of the insulin-like peptide INS-5 and inhibition of the calcineurin-regulated forkhead-box transcription factor DAF-16/FOXO. Our data indicate that perception of ambient temperature and its neuronal integration is important for the control of proteome integrity in complex organisms.

Exposome, Molecular Pathways and One Health: The Invertebrate Caenorhabditis elegans

Due to its preferred habitats in the environment, the free-living nematode Caenorhabditis elegans has become a realistic target organism for pollutants, including manufactured nanoparticles. In the laboratory, the invertebrate animal model represents a cost-effective tool to investigate the molecular mechanisms of the biological response to nanomaterials. With an estimated number of 22,000 coding genes and short life span of 2-3 weeks, the small worm is a giant when it comes to characterization of molecular pathways, long-term low dose pollutant effects and vulnerable age-groups. Here, we review (i) flows of manufactured nanomaterials and exposition of C. elegans in the environment, (ii) the track record of C. elegans in biomedical research, and (iii) its potential to contribute to the investigation of the exposome and bridge nanotoxicology between higher organisms, including humans. The role of C. elegans in the one health concept is taken one step further by proposing methods to sample wild nematodes and their molecular characterization by single worm proteomics.

Hsp90: From Cellular to Organismal Proteostasis

Assuring a healthy proteome is indispensable for survival and organismal health. Proteome disbalance and the loss of the proteostasis buffer are hallmarks of various diseases. The essential molecular chaperone Hsp90 is a regulator of the heat shock response via HSF1 and a stabilizer of a plethora of signaling proteins. In this review, we summarize the role of Hsp90 in the cellular and organismal regulation of proteome maintenance.

How to keep up with the analysis of classic and emerging neurotoxins: Age-resolved fitness tests in the animal model Caenorhabditis elegans - a step-by-step protocol

The global chemical inventory includes neurotoxins that are mostly interrogated concerning the biological response in developing organisms. Effects of pollutants on adults receive less attention, although vulnerabilities can be expected throughout the entire life span in young, middle-aged and old individuals. We use the animal model Caenorhabditis elegans to systematically quantify neurological outcomes by application of an age-resolved method. Adult hermaphrodite worms were exposed to pollutants or non-chemical stressors such as temperature in liquid culture on microtiter plates and locomotion fitness was analyzed in a whole-life approach. Cultivation at 15, 20 or 25 °C showed that worms held at 15 °C displayed an enhanced level of fitness concerning swimming movements until middle age (11-days-old) and then a decline. In contrast, C. elegans cultivated at ≥ 20 °C continually reduced their swimming movements with increasing age. Here, we provide a step-by-step protocol to investigate the health span of adult C. elegans that may serve as a platform for automation and data collection. Consistent with this, more neurotoxins can be investigated with respect to vulnerable age-groups as well as contributing non-chemical environmental factors such as temperature.

Temperature-Dependent Regulation of Proteostasis and Longevity

Temperature is an important environmental condition that determines the physiology and behavior of all organisms. Animals use different response strategies to adapt and survive fluctuations in ambient temperature. The hermaphrodite Caenorhabditis elegans has a well-studied neuronal network consisting of 302 neurons. The bilateral AFD neurons are the primary thermosensory neurons in the nematode. In addition to regulating thermosensitivity, AFD neurons also coordinate cellular stress responses through systemic mechanisms involving neuroendocrine signaling. Recent studies have examined the effects of temperature on altering various signaling pathways through specific gene expression programs that promote stress resistance and longevity. These studies challenge the proposed theories of temperature-dependent regulation of aging as a passive thermodynamic process. Instead, they provide evidence that aging is a well-defined genetic program. Loss of protein homeostasis (proteostasis) is one of the key hallmarks of aging. Indeed, proteostasis pathways, such as the heat shock response and aggregation of metastable proteins, are also controlled by thermosensory neurons in C. elegans. Prolonged heat stress is thought to play a critical role in the development of neurodegenerative protein misfolding diseases in humans. This review presents the latest evidence on how temperature coordinates proteostasis and aging. It also discusses how studies of poikilothermic organisms can be applied to vertebrates and provides new therapeutic strategies for human disease.

Cytochromes P450 of Caenorhabditis elegans: Implication in Biological Functions and Metabolism of Xenobiotics

Caenorhabditis elegans is an important model used for many aspects of biological research. Its genome contains 76 genes coding for cytochromes P450 (P450s), and few data about the biochemical properties of those P450s have been published so far. However, an increasing number of articles have appeared on their involvement in the metabolism of xenobiotics and endobiotics such as fatty acid derivatives and steroids. Moreover, the implication of some P450s in various biological functions of C. elegans, such as survival, dauer formation, life span, fat content, or lipid metabolism, without mention of the precise reaction catalyzed by those P450s, has been reported in several articles. This review presents the state of our knowledge about C. elegans P450s.

Thermal conditions predict intraspecific variation in senescence rate in frogs and toads

Variation in temperature is known to influence mortality patterns in ectotherms. Even though a few experimental studies on model organisms have reported a positive relationship between temperature and actuarial senescence (i.e., the increase in mortality risk with age), how variation in climate influences the senescence rate across the range of a species is still poorly understood in free-ranging animals. We filled this knowledge gap by investigating the relationships linking senescence rate, adult lifespan, and climatic conditions using long-term capture-recapture data from multiple amphibian populations. We considered two pairs of related anuran species from the Ranidae (Rana luteiventris and Rana temporaria) and Bufonidae (Anaxyrus boreas and Bufo bufo) families, which diverged more than 100 Mya and are broadly distributed in North America and Europe. Senescence rates were positively associated with mean annual temperature in all species. In addition, lifespan was negatively correlated with mean annual temperature in all species except A. boreas In both R. luteiventris and A. boreas, mean annual precipitation and human environmental footprint both had negligible effects on senescence rates or lifespans. Overall, our findings demonstrate the critical influence of thermal conditions on mortality patterns across anuran species from temperate regions. In the current context of further global temperature increases predicted by Intergovernmental Panel on Climate Change scenarios, a widespread acceleration of aging in amphibians is expected to occur in the decades to come, which might threaten even more seriously the viability of populations and exacerbate global decline.

Neuronal HSF-1 coordinates the propagation of fat desaturation across tissues to enable adaptation to high temperatures in C. elegans

To survive elevated temperatures, ectotherms adjust the fluidity of membranes by fine-tuning lipid desaturation levels in a process previously described to be cell autonomous. We have discovered that, in Caenorhabditis elegans, neuronal heat shock factor 1 (HSF-1), the conserved master regulator of the heat shock response (HSR), causes extensive fat remodeling in peripheral tissues. These changes include a decrease in fat desaturase and acid lipase expression in the intestine and a global shift in the saturation levels of plasma membrane's phospholipids. The observed remodeling of plasma membrane is in line with ectothermic adaptive responses and gives worms a cumulative advantage to warm temperatures. We have determined that at least 6 TAX-2/TAX-4 cyclic guanosine monophosphate (cGMP) gated channel expressing sensory neurons, and transforming growth factor ß (TGF-β)/bone morphogenetic protein (BMP) are required for signaling across tissues to modulate fat desaturation. We also find neuronal hsf-1 is not only sufficient but also partially necessary to control the fat remodeling response and for survival at warm temperatures. This is the first study to show that a thermostat-based mechanism can cell nonautonomously coordinate membrane saturation and composition across tissues in a multicellular animal.

Enhancing mask activity in dopaminergic neurons extends lifespan in flies

Dopaminergic neurons (DANs) are essential modulators for brain functions involving memory formation, reward processing, and decision‐making. Here I demonstrate a novel and important function of the DANs in regulating aging and longevity. Overexpressing the putative scaffolding protein Mask in two small groups of DANs in flies can significantly extend the lifespan in flies and sustain adult locomotor and fecundity at old ages. This Mask‐induced beneficial effect requires dopaminergic transmission but cannot be recapitulated by elevating dopamine production alone in the DANs. Independent activation of Gα_s in the same two groups of DANs via the drug‐inducible DREADD system also extends fly lifespan, further indicating the connection of specific DANs to aging control. The Mask‐induced lifespan extension appears to depend on the function of Mask to regulate microtubule (MT) stability. A structure–function analysis demonstrated that the ankyrin repeats domain in the Mask protein is both necessary for regulating MT stability (when expressed in muscles and motor neurons) and sufficient to prolong longevity (when expressed in the two groups of DANs). Furthermore, DAN‐specific overexpression of Unc‐104 or knockdown of p150^Glued, two independent interventions previously shown to impact MT dynamics, also extends lifespan in flies. Together, these data demonstrated a novel DANs‐dependent mechanism that, upon the tuning of their MT dynamics, modulates systemic aging and longevity in flies.

Fatty acid desaturation is essential for C. elegans longevity at high temperature

Metabolic reprogramming is crucial for the adaptation to environmental temperature stress. It is generally accepted that fatty acid (FA) desaturation is suppressed at high temperature, which decreases the ratio of unsaturated FAs to saturated FAs (UFAs/SFAs) to maintain the fluidity of cell membranes and favor cellular survival. Here by working in C. elegans, we found that FA desaturation is essential for longevity in response to temperature upshift at the organismal level, opposite to its role in cellular survival. High temperature unexpectedly increases the contents of total fat and multiple UFA species. Specifically, monounsaturated oleic acid (OA) is required for animal survival at high temperature. Mechanistic study showed that OA acts through HSF-1, which in turn promotes histone acetylation as well as the expression of defense genes that are crucial for longevity at high temperature. Together, our findings reveal an unprecedented role for FA desaturation in organismal fitness to temperature upshift, and implicate divergent metabolic requirements between cellular and organismal survival upon temperature stress.

Sensory perception of environmental cues as a modulator of aging and neurodegeneration: Insights from Caenorhabditis elegans

Environmental stimuli such as temperature, food, and smell significantly influence the physiology and behavior of animals. Animals are differentially adapted to maintain their internal body functions in response to varied environmental conditions. These external cues are sensed by specialized neurons which are a part of the chemosensory and thermosensory systems. The inability to respond correctly to varied environmental conditions may result in compromised bodily functions and reduced longevity. For example, the ability to sense food is derived from the integrated action of olfactory and gustatory systems. The damage to the olfactory system will affect our decision of palatable food items which in turn can affect the response of the gustatory system, ultimately causing abnormal feeding habits. Recent studies have provided evidence that aging is regulated by sensory perception of environment. Aging is one of the most common causes of various neurodegenerative diseases and the perception of environmental cues is also found to regulate the development of neurodegenerative phenotype in several animal models. However, specific molecular signaling pathways involved in the process are not completely understood. The research conducted on one of the best-studied animal models of aging, Caenorhabditis elegans, has demonstrated multiple examples of gene-environment interaction at the neuronal level which affects life span. The findings may be useful to identify the key neuronal regulators of aging and age-related diseases in humans owing to conserved core metabolic and aging pathways from worms to humans.

Stress increases in exopher-mediated neuronal extrusion require lipid biosynthesis, FGF, and EGF RAS/MAPK signaling

In human neurodegenerative diseases, neurons can transfer toxic protein aggregates to surrounding cells, promoting pathology via poorly understood mechanisms. In Caenorhabditis elegans, proteostressed neurons can expel neurotoxic proteins in large, membrane-bound vesicles called exophers. We investigated how specific stresses impact neuronal trash expulsion to show that neuronal exopher production can be markedly elevated by oxidative and osmotic stress. Unexpectedly, we also found that fasting dramatically increases exophergenesis. Mechanistic dissection focused on identifying nonautonomous factors that sense and activate the fasting-induced exopher response revealed that DAF16/FOXO-dependent and -independent processes are engaged. Fasting-induced exopher elevation requires the intestinal peptide transporter PEPT-1, lipid synthesis transcription factors Mediator complex MDT-15 and SBP-1/SREPB1, and fatty acid synthase FASN-1, implicating remotely initiated lipid signaling in neuronal trash elimination. A conserved fibroblast growth factor (FGF)/RAS/MAPK signaling pathway that acts downstream of, or in parallel to, lipid signaling also promotes fasting-induced neuronal exopher elevation. A germline-based epidermal growth factor (EGF) signal that acts through neurons is also required for exopher production. Our data define a nonautonomous network that links food availability changes to remote, and extreme, neuronal homeostasis responses relevant to aggregate transfer biology.

A Multicellular Network Mechanism for Temperature-Robust Food Sensing

Responsiveness to external cues is a hallmark of biological systems. In complex environments, it is crucial for organisms to remain responsive to specific inputs even as other internal or external factors fluctuate. Here, we show how the nematode Caenorhabditis elegans can discriminate between different food levels to modulate its lifespan despite temperature perturbations. This end-to-end robustness from environment to physiology is mediated by food-sensing neurons that communicate via transforming growth factor β (TGF-β) and serotonin signals to form a multicellular gene network. Specific regulations in this network change sign with temperature to maintain similar food responsiveness in the lifespan output. In contrast to robustness of stereotyped outputs, our findings uncover a more complex robustness process involving the higher order function of discrimination in food responsiveness. This process involves rewiring a multicellular network to compensate for temperature and provides a basis for understanding gene-environment interactions. Together, our findings unveil sensory computations that integrate environmental cues to govern physiology.

•

C. elegans’ ability to modulate lifespan in response to food is robust to temperature

•

Robustness requires TGF-β and serotonin signaling in a neuronal network

•

Specific regulations in the neuronal network change sign with temperature

•

Temperature-dependent regulations compensate for temperature

Cell non-autonomous regulation of health and longevity

As the demographics of the modern world skew older, understanding and mitigating the effects of aging is increasingly important within biomedical research. Recent studies in model organisms demonstrate that the aging process is frequently modified by an organism’s ability to perceive and respond to changes in its environment. Many well-studied pathways that influence aging involve sensory cells, frequently neurons, that signal to peripheral tissues and promote survival during the presence of stress. Importantly, this activation of stress response pathways is often sufficient to improve health and longevity even in the absence of stress. Here, we review the current landscape of research highlighting the importance of cell non-autonomous signaling in modulating aging from C. elegans to mammals. We also discuss emerging concepts including retrograde signaling, approaches to mapping these networks, and development of potential therapeutics.

Thermotolerance of tax-2 Is Uncoupled From Life Span Extension and Influenced by Temperature During Development in C. elegans

Thermotolerance of an organism is a complex trait that is influenced by a multitude of genetic and environmental factors. Many factors controlling thermotolerance in Caenorhabditis elegans are known to extend life. To understand the regulation of thermotolerance, we performed a genetic screen for mutants with better survival at warm temperature. Here we identified by dauer survival a tax-2 mutation and several mutations disrupting an insulin signaling pathway including the daf-2 gene. While the tax-2 mutant has improved thermotolerance and long life span, the newly identified daf-2 and other insulin signaling mutants, unlike the canonical daf-2(e1370), do not show improved thermotolerance despite being long-lived. Examination of tax-2 mutations and their mutant phenotypes suggest that the control of thermotolerance is not coupled with the control of life span or dauer survival. With genetic interaction studies, we concluded that tax-2 has complex roles in life span and dauer survival and that tax-2 is a negative regulator of thermotolerance independent of other known thermotolerance genes including those in the insulin signaling pathway. Moreover, cold growth temperature during development weakens the improved thermotolerance associated with tax-2 and other thermotolerance-inducing mutations. Together, this study reveals previously unknown genetic and environmental factors controlling thermotolerance and their complex relationship with life span regulation.

Metabolic adaptation to calorie restriction

Calorie restriction (CR) enhances health span (the length of time that an organism remains healthy) and increases longevity across species. In mice, these beneficial effects are partly mediated by the lowering of core body temperature that occurs during CR. Conversely, the favorable effects of CR on health span are mitigated by elevating ambient temperature to thermoneutrality (30°C), a condition in which hypothermia is blunted. In this study, we compared the global metabolic response to CR of mice housed at 22°C (the standard housing temperature) or at 30°C and found that thermoneutrality reverted 39 and 78% of total systemic or hypothalamic metabolic variations caused by CR, respectively. Systemic changes included pathways that control fuel use and energy expenditure during CR. Cognitive computing-assisted analysis of these metabolomics results helped to prioritize potential active metabolites that modulated the hypothermic response to CR. Last, we demonstrated with pharmacological approaches that nitric oxide (NO) produced through the citrulline-NO pathway promotes CR-triggered hypothermia and that leucine enkephalin directly controls core body temperature when exogenously injected into the hypothalamus. Because thermoneutrality counteracts CR-enhanced health span, the multiple metabolites and pathways altered by thermoneutrality may represent targets for mimicking CR-associated effects.

Short-Term Mild Temperature-Stress-Induced Alterations in the C. elegans Phosphoproteome

Exposure to mild early-life stresses can slow down aging, and protein phosphorylation might be an essential regulator in this process. However, the mechanisms of phosphorylation-based signaling networks during mild early-life stress remain elusive. Herein, we systematically analyzed the phosphoproteomes of Caenorhabditis elegans, which were treated with three mild temperatures (15 °C, 20 °C, and 25 °C) in two different short-term groups (10 min and 60 min). By utilizing an iTRAQ-based quantitative phosphoproteomic approach, 18,187 phosphosites from 3330 phosphoproteins were detected in this study. Volcano plots illustrated that the phosphorylation abundance of 374 proteins and 347 proteins, were significantly changed at 15 °C and 25 °C, respectively. Gene ontology, KEGG pathway and protein-protein interaction network analyses revealed that these phosphoproteins were primarily associated with metabolism, translation, development, and lifespan determination. A motif analysis of kinase substrates suggested that MAPK, CK, and CAMK were most likely involved in the adaption processes. Moreover, 16 and 14 aging-regulated proteins were found to undergo phosphorylation modifications under the mild stresses of 15 °C and 25 °C, respectively, indicating that these proteins might be important for maintaining long-term health. Further lifespan experiments confirmed that the candidate phosphoproteins, e.g., EGL-27 and XNP-1 modulated longevity at 15 °C, 20 °C, and 25 °C, and they showed increased tolerance to thermal and oxidative stresses. In conclusion, our findings offered data that supports understanding of the phosphorylation mechanisms involved in mild early-life stresses in C. elegans. Data are available via ProteomeXchange with identifier PXD021081.

Transcriptome Profile Changes Associated With Heat Shock Reaction in the Entomopathogenic Nematode, Steinernema carpocapsae

The entomopathogenic nematode Steinernema carpocapsae has been used for control of soil insects. However, S. carpocapse is sensitive to environmental factors, particularly temperature. We studied an S. carpocapse group that was shocked with high temperature. We also studied the transcriptome-level responses associated with temperature stress using a BGIseq sequencing platform. We de novo assembled the reads from the treatment and control groups into one transcriptome consisting of 43.9 and 42.9 million clean reads, respectively. Based on the genome database, we aligned the clean reads to the Nr, Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases and analyzed the differentially expressed genes (DEGs). Compared with the control, the heat-shocked group had significant differential expression of the heat shock protein (HSP) family, antioxidase [glutathione S-transferases (GSTs) and superoxide dismutase (SOD)], monooxygenase (P450), and transcription factor genes (DAF-16 and DAF-2). These DEGs were demonstrated to be part of the Longevity pathway and insulin/insulin-like signaling pathway. The results revealed the potential mechanisms, at the transcriptional level, of S. carpocapsae under thermal stress.

Regulatory systems that mediate the effects of temperature on the lifespan of Caenorhabditis elegans

Temperature affects animal physiology, including aging and lifespan. How temperature and biological systems interact to influence aging and lifespan has been investigated using model organisms, including the nematode Caenorhabditis elegans. In this review, we discuss mechanisms by which diverse cellular factors modulate the effects of ambient temperatures on aging and lifespan in C. elegans. C. elegans thermosensory neurons alleviate lifespan-shortening effects of high temperatures via sterol endocrine signaling and probably through systemic regulation of cytosolic proteostasis. At low temperatures, C. elegans displays a long lifespan by upregulating the cold-sensing TRPA channel, lipid homeostasis, germline-mediated prostaglandin signaling, and autophagy. In addition, co-chaperone p23 amplifies lifespan changes affected by high and low temperatures. Our review summarizes how external temperatures modulate C. elegans lifespan and provides information regarding responses of biological processes to temperature changes, which may affect health and aging at an organism level.

Neuronal control of lipid metabolism by STR-2 G protein-coupled receptor promotes longevity in Caenorhabditis elegans

The G protein-coupled receptor (GPCR) encoding family of genes constitutes more than 6% of genes in Caenorhabditis elegans genome. GPCRs control behavior, innate immunity, chemotaxis, and food search behavior. Here, we show that C. elegans longevity is regulated by a chemosensory GPCR STR-2, expressed in AWC and ASI amphid sensory neurons. STR-2 function is required at temperatures of 20°C and higher on standard Escherichia coli OP50 diet. Under these conditions, this neuronal receptor also controls health span parameters and lipid droplet (LD) homeostasis in the intestine. We show that STR-2 regulates expression of delta-9 desaturases, fat-5, fat-6 and fat-7, and of diacylglycerol acyltransferase dgat-2. Rescue of the STR-2 function in either AWC and ASI, or ASI sensory neurons alone, restores expression of fat-5, dgat-2 and restores LD stores and longevity. Rescue of stored fat levels of GPCR mutant animals to wild-type levels, with low concentration of glucose, rescues its lifespan phenotype. In all, we show that neuronal STR-2 GPCR facilitates control of neutral lipid levels and longevity in C. elegans.

Automation of C. elegans lifespan measurement

Aging is a fundamental biological process that is still not fully understood. As many of the most significant human diseases have aging as their greatest risk factor, a better understanding of aging potentially has enormous practical implications in treating these diseases. The nematode C. elegans is an exceptionally useful genetic model organism that had been used with great success to shed light on many genes and pathways that are involved in aging. Many of these pathways and mechanisms have been shown to be conserved through mammals. The standard methods for assaying survival in C. elegans to measure changes in lifespan are tedious and time consuming. This limits the throughput and productivity of C. elegans aging researchers. In recent years, many inroads have been made into automating various facets of the collection and analysis of C. elegans lifespan experimental data. The advances described in this review all work to ameliorate some of the hurdles that come with manual worm lifespan scoring, by automating or eliminating some of the most time consuming aspects of the assay. By greatly increasing the throughput of lifespan assays, these methods will enable types of experiments (e.g., drug library screens) whose scale is currently impractical. These methods have already proved exceptionally useful, and some of them are likely to be the predecessors of even more refined methods that could lead to breakthroughs in the ability to study lifespan in C. elegans. This could in turn potentially revolutionize our understanding of the basic biology of aging, and one day lead to treatments that could offset or delay age-related diseases in humans.

How Caenorhabditis elegans Senses Mechanical Stress, Temperature, and Other Physical Stimuli

Caenorhabditis elegans lives in a complex habitat in which they routinely experience large fluctuations in temperature, and encounter physical obstacles that vary in size and composition. Their habitat is shared by other nematodes, by beneficial and harmful bacteria, and nematode-trapping fungi. Not surprisingly, these nematodes can detect and discriminate among diverse environmental cues, and exhibit sensory-evoked behaviors that are readily quantifiable in the laboratory at high resolution. Their ability to perform these behaviors depends on <100 sensory neurons, and this compact sensory nervous system together with powerful molecular genetic tools has allowed individual neuron types to be linked to specific sensory responses. Here, we describe the sensory neurons and molecules that enable C. elegans to sense and respond to physical stimuli. We focus primarily on the pathways that allow sensation of mechanical and thermal stimuli, and briefly consider this animal’s ability to sense magnetic and electrical fields, light, and relative humidity. As the study of sensory transduction is critically dependent upon the techniques for stimulus delivery, we also include a section on appropriate laboratory methods for such studies. This chapter summarizes current knowledge about the sensitivity and response dynamics of individual classes of C. elegans mechano- and thermosensory neurons from in vivo calcium imaging and whole-cell patch-clamp electrophysiology studies. We also describe the roles of conserved molecules and signaling pathways in mediating the remarkably sensitive responses of these nematodes to mechanical and thermal cues. These studies have shown that the protein partners that form mechanotransduction channels are drawn from multiple superfamilies of ion channel proteins, and that signal transduction pathways responsible for temperature sensing in C. elegans share many features with those responsible for phototransduction in vertebrates.

GABA receptors differentially regulate life span and health span in C. elegans through distinct downstream mechanisms

GABA, a prominent inhibitory neurotransmitter, is best known to regulate neuronal functions in the nervous system. However, much less is known about the role of GABA signaling in other physiological processes. Interestingly, recent work showed that GABA signaling can regulate life span via a metabotropic GABA_B receptor in Caenorhabditis elegans. However, the role of other types of GABA receptors in life span has not been clearly defined. It is also unclear whether GABA signaling regulates health span. Here, using C. elegans as a model, we systematically interrogated the role of various GABA receptors in both life span and health span. We find that mutations in four different GABA receptors extend health span by promoting resistance to stress and pathogen infection and that two such receptor mutants also show extended life span. Different GABA receptors engage distinct transcriptional factors to regulate life span and health span, and even the same receptor regulates life span and health span via different transcription factors. Our results uncover a novel, profound role of GABA signaling in aging in C. elegans, which is mediated by different GABA receptors coupled to distinct downstream effectors.

MDT-15/MED15 permits longevity at low temperature via enhancing lipidostasis and proteostasis

Low temperatures delay aging and promote longevity in many organisms. However, the metabolic and homeostatic aspects of low-temperature–induced longevity remain poorly understood. Here, we show that lipid homeostasis regulated by Caenorhabditis elegans Mediator 15 (MDT-15 or MED15), a transcriptional coregulator, is essential for low-temperature–induced longevity and proteostasis. We find that inhibition of mdt-15 prevents animals from living long at low temperatures. We show that MDT-15 up-regulates fat-7, a fatty acid desaturase that converts saturated fatty acids (SFAs) to unsaturated fatty acids (UFAs), at low temperatures. We then demonstrate that maintaining a high UFA/SFA ratio is essential for proteostasis at low temperatures. We show that dietary supplementation with a monounsaturated fatty acid, oleic acid (OA), substantially mitigates the short life span and proteotoxicity in mdt-15(-) animals at low temperatures. Thus, lipidostasis regulated by MDT-15 appears to be a limiting factor for proteostasis and longevity at low temperatures. Our findings highlight the crucial roles of lipid regulation in maintaining normal organismal physiology under different environmental conditions.

Low temperatures delay aging and promote longevity in many organisms. This study shows that at low ambient temperatures, Mediator 15, a transcriptional coregulator, allows the nematode Caenorhabditis elegans to live longer by increasing the levels of unsaturated lipids, helping to maintain protein homeostasis.

Prostaglandin signals from adult germ stem cells delay somatic aging of Caenorhabditis elegans

A moderate reduction of body temperature can induce a remarkable lifespan extension. Here we examine the link between cold temperature, germ line fitness and organismal longevity. We show that low temperature reduces age-associated exhaustion of germ stem cells (GSCs) in Caenorhabditis elegans, a process modulated by thermosensory neurons. Notably, robust self-renewal of adult GSCs delays reproductive aging and is required for extended lifespan at cold temperatures. These cells release prostaglandin E2 (PGE2) to induce cbs-1 expression in the intestine, increasing somatic production of hydrogen sulfide (H₂S), a gaseous signaling molecule that prolongs lifespan. Whereas loss of adult GSCs reduces intestinal cbs-1 expression and cold-induced longevity, application of exogenous PGE2 rescues these phenotypes. Importantly, tissue-specific intestinal overexpression of cbs-1 mimics cold-temperature conditions and extends longevity even at warm temperatures. Thus, our results indicate that GSCs communicate with somatic tissues to coordinate extended reproductive capacity with longevity.

CBP-1 Acts in GABAergic Neurons to Double Life Span in Axenically Cultured Caenorhabditis elegans

When cultured in axenic medium, Caenorhabditis elegans shows the largest life-span extension compared with other dietary restriction regimens. However, the underlying molecular mechanism still remains elusive. The gene cbp-1, encoding the worm ortholog of p300/CBP (CREB-binding protein), is one of the very few key genes known to be essential for life span doubling under axenic dietary restriction (ADR). By using tissue-specific RNAi, we found that cbp-1 expression in the germline is essential for fertility, whereas this gene functions specifically in the GABAergic neurons to support the full life span-doubling effect of ADR. Surprisingly, GABA itself is not required for ADR-induced longevity, suggesting a role of neuropeptide signaling. In addition, chemotaxis assays illustrate that neuronal inactivation of CBP-1 affects the animals' food sensing behavior. Together, our results show that the strong life-span extension in axenic medium is under strict control of GABAergic neurons and may be linked to food sensing.