A genetic program promotes C. elegans longevity at cold temperatures via a thermosensitive TRP channel

Regulation of Pain and Itch by TRP Channels

Nociception is an important physiological process that detects harmful signals and results in pain perception. In this review, we discuss important experimental evidence involving some TRP ion channels as molecular sensors of chemical, thermal, and mechanical noxious stimuli to evoke the pain and itch sensations. Among them are the TRPA1 channel, members of the vanilloid subfamily (TRPV1, TRPV3, and TRPV4), and finally members of the melastatin group (TRPM2, TRPM3, and TRPM8). Given that pain and itch are pro-survival, evolutionarily-honed protective mechanisms, care has to be exercised when developing inhibitory/modulatory compounds targeting specific pain/itch-TRPs so that physiological protective mechanisms are not disabled to a degree that stimulus-mediated injury can occur. Such events have impeded the development of safe and effective TRPV1-modulating compounds and have diverted substantial resources. A beneficial outcome can be readily accomplished via simple dosing strategies, and also by incorporating medicinal chemistry design features during compound design and synthesis. Beyond clinical use, where compounds that target more than one channel might have a place and possibly have advantageous features, highly specific and high-potency compounds will be helpful in mechanistic discovery at the structure-function level.

Movement decline across lifespan of Caenorhabditis elegans mutants in the insulin/insulin-like signaling pathway

Research in aging biology has identified several pathways that are molecularly conserved across species that extend lifespan when mutated. The insulin/insulin-like signaling (IIS) pathway is one of the most widely studied of these. It has been assumed that extending lifespan also extends healthspan (the period of life with minimal functional loss). However, data supporting this assumption conflict and recent evidence suggest that life extension may, in and of itself, extend the frail period. In this study, we use Caenorhabditis elegans to further probe the link between lifespan and healthspan. Using movement decline as a measure of health, we assessed healthspan across the entire lifespan in nine IIS pathway mutants. In one series of experiments, we studied healthspan in mass cultures, and in another series, we studied individuals longitudinally. We found that long-lived mutants display prolonged mid-life movement and do not prolong the frailty period. Lastly, we observed that early-adulthood movement was not predictive of late-life movement or survival, within identical phenotypes. Overall, these observations show that extending lifespan does not prolong the period of frailty. Both genotype and a stochastic component modulate aging, and movement late in life is more variable than early-life movement.

The extraordinary AFD thermosensor of C. elegans

The nematode C. elegans exhibits complex thermal experience-dependent navigation behaviors in response to environmental temperature changes of as little as 0.01°C over a > 10°C temperature range. The remarkable thermosensory abilities of this animal are mediated primarily via the single pair of AFD sensory neurons in its head. In this review, we describe the contributions of AFD to thermosensory behaviors and temperature-dependent regulation of organismal physiology. We also discuss the mechanisms that enable this neuron type to adapt to recent temperature experience and to exhibit extraordinary thermosensitivity over a wide dynamic range.

Reprogramming of energy metabolism as a driver of aging

Aging is characterized by progressive loss of cellular function and integrity. It has been thought to be driven by stochastic molecular damage. However, genetic and environmental maneuvers enhancing mitochondrial function or inhibiting glycolysis extend lifespan and promote healthy aging in many species. In post-fertile Caenorhabditis elegans, a progressive decline in phosphoenolpyruvate carboxykinase with age, and a reciprocal increase in pyruvate kinase shunt energy metabolism from oxidative metabolism to anaerobic glycolysis. This reduces the efficiency and total of energy generation. As a result, energy-dependent physical activity and other cellular functions decrease due to unmatched energy demand and supply. In return, decrease in physical activity accelerates this metabolic shift, forming a vicious cycle. This metabolic event is a determinant of aging, and is retarded by caloric restriction to counteract aging. In this review, we summarize these and other evidence supporting the idea that metabolic reprogramming is a driver of aging. We also suggest strategies to test this hypothesis

Genetic interaction with temperature is an important determinant of nematode longevity

As in other poikilotherms, longevity in C. elegans varies inversely with temperature; worms are longer-lived at lower temperatures. While this observation may seem intuitive based on thermodynamics, the molecular and genetic basis for this phenomenon is not well understood. Several recent reports have argued that lifespan changes across temperatures are genetically controlled by temperature-specific gene regulation. Here, we provide data that both corroborate those studies and suggest that temperature-specific longevity is more the rule than the exception. By measuring the lifespans of worms with single modifications reported to be important for longevity at 15, 20, or 25 °C, we find that the effect of each modification on lifespan is highly dependent on temperature. Our results suggest that genetics play a major role in temperature-associated longevity and are consistent with the hypothesis that while aging in C. elegans is slowed by decreasing temperature, the major cause(s) of death may also be modified, leading to different genes and pathways becoming more or less important at different temperatures. These differential mechanisms of age-related death are not unlike what is observed in humans, where environmental conditions lead to development of different diseases of aging.

Isoform-specific modulation of the chemical sensitivity of conserved TRPA1 channel in the major honeybee ectoparasitic mite, Tropilaelaps mercedesae

We identified and characterized the TRPA1 channel of Tropilaelaps mercedesae (TmTRPA1), one of two major species of honeybee ectoparasitic mite. Three TmTRPA1 isoforms with unique N-terminal sequences were activated by heat, and the isoform highly expressed in the mite's front legs, TmTRPA1b, was also activated by 27 plant-derived compounds including electrophiles. This suggests that the heat- and electrophile-dependent gating mechanisms as nocisensitive TRPA1 channel are well conserved between arthropod species. Intriguingly, one TmTRPA1 isoform, TmTRPA1a, was activated by only six compounds compared with two other isoforms, demonstrating that the N-terminal sequences are critical determinants for the chemical sensitivity. This is the first example of isoform-specific modulation of chemical sensitivity of TRPA1 channel in one species. α-terpineol showed repellent activity towards T. mercedesae in a laboratory assay and repressed T. mercedesae entry for reproduction into the brood cells with fifth instar larvae in hives. Thus, α-terpineol could be used as the potential compound to control two major honeybee ectoparasitic mites, T. mercedesae and Varroa destructor, in the apiculture industry.

Low Temperature Extends the Lifespan of Bursaphelenchus xylophilus through the cGMP Pathway

The causal agent of pine wilt disease, pine wood nematode (PWN) (Bursaphelenchus xylophilus), revealed extended lifespan at low temperature. To discover the molecular mechanism of this phenomenon, we attempted to study the molecular characterization, transcript abundance, and functions of three genes of the cyclic guanosine monophosphate (cGMP) pathway from B. xylophilus. Three cGMP pathway genes were identified from B. xylophilus. Bioinformatic software was utilized to analyze the characteristics of the three putative proteins. Function of the three genes in cold tolerance was studied with RNA interference (RNAi). The results showed that the deduced protein of Bx-DAF-11 has an adenylate and guanylate cyclase catalytic domain, indicating an ability to bind to extracellular ligands and synthesizing cGMP. Both Bx-TAX-2 and Bx-TAX-4 have cyclic nucleotide-binding domains and ion transport protein domains, illustrating that they are cGMP-gated ion channels. The transcript level of Bx-daf-11, Bx-tax-2, and Bx-tax-4 increased at low temperature. The survival rates of three gene silenced B. xylophilus revealed a significant decrease at low temperature. This study illustrated that the cGMP pathway plays a key role in low-temperature-induced lifespan extension in B. xylophilus.

Membrane ion Channels and Receptors in Animal lifespan Modulation

Acting in the interfaces between environment and membrane compartments, membrane ion channels, and receptors transduce various physical and chemical cues into downstream signaling events. Not surprisingly, these membrane proteins play essential roles in a wide range of cellular processes such as sensory perception, synaptic transmission, cellular growth and development, fate determination, and apoptosis. However, except insulin and insulin-like growth factor receptors, the functions of membrane receptors in animal lifespan modulation have not been well appreciated. On the other hand, although ion channels are popular therapeutic targets for many age-related diseases, their potential roles in aging itself are largely neglected. In this review, we will discuss our current understanding of the conserved functions and mechanisms of membrane ion channels and receptors in the modulation of lifespan across multiple species including Caenorhabditis elegans, Drosophila, mouse, and human.

Dihydrocapsiate improved age-associated impairments in mice by increasing energy expenditure

Metabolic dysfunction is associated with aging and results in age-associated chronic diseases, including type 2 diabetes mellitus, cardiovascular disease, and stroke. Hence, there has been a focus on increasing energy expenditure in aged populations to protect them from age-associated diseases. Dihydrocapsiate (DCT) is a compound that belongs to the capsinoid family. Capsinoids are capsaicin analogs that are found in nonpungent peppers and increase whole body energy expenditure. However, their effect on energy expenditure has been reported only in young populations, and to date the effectiveness of DCT in increasing energy expenditure in aged populations has not been investigated. In this study, we investigated whether DCT supplementation in aged mice improves age-associated impairments. We obtained 5-wk-old and 1-yr-old male C57BL/6J mice and randomly assigned the aged mice to two groups, resulting in a total of three groups: 1) young mice, 2) old mice, and 3) old mice supplemented with 0.3% DCT. After 12 wk of supplementation, blood and tissue samples were collected and analyzed. DCT significantly suppressed age-associated fat accumulation, adipocyte hypertrophy, and liver steatosis. In addition, the DCT treatment dramatically suppressed age-associated increases in hepatic inflammation, immune cell infiltration, and oxidative stress. DCT exerted these suppression effects by increasing energy expenditure linked to upregulation of both the oxidative phosphorylation gene program and fatty acid oxidation in skeletal muscle. These results indicate that DCT efficiently improves age-associated impairments, including liver steatosis and inflammation, in part by increasing energy expenditure via activation of the fat oxidation pathway in skeletal muscle.

A Calcium- and Diacylglycerol-Stimulated Protein Kinase C (PKC), Caenorhabditis elegans PKC-2, Links Thermal Signals to Learned Behavior by Acting in Sensory Neurons and Intestinal Cells

Ca²⁺- and diacylglycerol (DAG)-activated protein kinase C (cPKC) promotes learning and behavioral plasticity. However, knowledge of in vivo regulation and exact functions of cPKCs that affect behavior is limited. We show that PKC-2, a Caenorhabditis elegans cPKC, is essential for a complex behavior, thermotaxis. C. elegans memorizes a nutrient-associated cultivation temperature (T_c ) and migrates along the T_c within a 17 to 25°C gradient. pkc-2 gene disruption abrogated thermotaxis; a PKC-2 transgene, driven by endogenous pkc-2 promoters, restored thermotaxis behavior in pkc-2^-/- animals. Cell-specific manipulation of PKC-2 activity revealed that thermotaxis is controlled by cooperative PKC-2-mediated signaling in both AFD sensory neurons and intestinal cells. Cold-directed migration (cryophilic drive) precedes T_c tracking during thermotaxis. Analysis of temperature-directed behaviors elicited by persistent PKC-2 activation or inhibition in AFD (or intestine) disclosed that PKC-2 regulates initiation and duration of cryophilic drive. In AFD neurons, PKC-2 is a Ca²⁺ sensor and signal amplifier that operates downstream from cyclic GMP-gated cation channels and distal guanylate cyclases. UNC-18, which regulates neurotransmitter and neuropeptide release from synaptic vesicles, is a critical PKC-2 effector in AFD. UNC-18 variants, created by mutating Ser³¹¹ or Ser³²², disrupt thermotaxis and suppress PKC-2-dependent cryophilic migration.

TRPA1 channels: molecular sentinels of cellular stress and tissue damage

TRPA1 is a non-selective cation channel expressed in mammalian peripheral pain receptors, with a major role in chemonociception. TRPA1 has also been implicated in noxious cold and mechanical pain sensation. TRPA1 has an ancient origin and plays important functions in lower organisms, including thermotaxis, mechanotransduction and modulation of lifespan. Here we highlight the role of TRPA1 as a multipurpose sensor of harmful signals, including toxic bacterial products and UV light, and as a sensor of stress and tissue damage. Sensing roles span beyond the peripheral nervous system to include major barrier tissues: gut, skin and lung. Tissue injury, environmental irritants and microbial pathogens are danger signals that can threaten the health of organisms. These signals lead to the coordinated activation of the nociceptive and the innate immune system to provide a homeostatic response trying to re-establish physiological conditions including tissue repair. Activation of TRPA1 participates in protective neuroimmune interactions at multiple levels, sensing ROS and bacterial products and triggering the release of neuropeptides. However, an exaggerated response to danger signals is maladaptive and can lead to the development of chronic inflammatory conditions.

Insulin-like growth factor 1 receptor regulates hypothermia during calorie restriction

When food resources are scarce, endothermic animals can lower core body temperature (T_b). This phenomenon is believed to be part of an adaptive mechanism that may have evolved to conserve energy until more food becomes available. Here, we found in the mouse that the insulin-like growth factor 1 receptor (IGF-1R) controls this response in the central nervous system. Pharmacological or genetic inhibition of IGF-1R enhanced the reduction of temperature and of energy expenditure during calorie restriction. Full blockade of IGF-1R affected female and male mice similarly. In contrast, genetic IGF-1R dosage was effective only in females, where it also induced transient and estrus-specific hypothermia in animals fed ad libitum. These effects were regulated in the brain, as only central, not peripheral, pharmacological activation of IGF-1R prevented hypothermia during calorie restriction. Targeted IGF-1R knockout selectively in forebrain neurons revealed that IGF signaling also modulates calorie restriction-dependent T_b regulation in regions rostral of the canonical hypothalamic nuclei involved in controlling body temperature. In aggregate, these data identify central IGF-1R as a mediator of the integration of nutrient and temperature homeostasis. They also show that calorie restriction, IGF-1R signaling, and body temperature, three of the main regulators of metabolism, aging, and longevity, are components of the same pathway.

The 4E-BP growth pathway regulates the effect of ambient temperature on Drosophila metabolism and lifespan

Changes in body temperature can profoundly affect survival. The dramatic longevity-enhancing effect of cold has long been known in organisms ranging from invertebrates to mammals, yet the underlying mechanisms have only recently begun to be uncovered. In the nematode Caenorhabditis elegans, this process is regulated by a thermosensitive membrane TRP channel and the DAF-16/FOXO transcription factor, but in more complex organisms the underpinnings of cold-induced longevity remain largely mysterious. We report that, in Drosophila melanogaster, variation in ambient temperature triggers metabolic changes in protein translation, mitochondrial protein synthesis, and posttranslational regulation of the translation repressor, 4E-BP (eukaryotic translation initiation factor 4E-binding protein). We show that 4E-BP determines Drosophila lifespan in the context of temperature changes, revealing a genetic mechanism for cold-induced longevity in this model organism. Our results suggest that the 4E-BP pathway, chiefly thought of as a nutrient sensor, may represent a master metabolic switch responding to diverse environmental factors.

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.

Heat FLiPs a Hormonal Switch for Longevity

Temperature-sensing neurons in C. elegans reduce the life-shortening effects of high temperatures via steroid signaling. In this issue of Developmental Cell, Chen et al. (2016) elucidate the underlying mechanisms by which the transcription factor CREB induces the neuropeptide FLP-6 in the temperature-sensing neurons to counteract the life-shortening effects of high temperature.

The intestinal TORC2 signaling pathway contributes to associative learning in Caenorhabditis elegans

Several types of associative learning are dependent upon the presence or absence of food, and are crucial for the survival of most animals. Target of rapamycin (TOR), a kinase which exists as a component of two complexes, TOR complex 1 (TORC1) and TOR complex 2 (TORC2), is known to act as a nutrient sensor in numerous organisms. However, the in vivo roles of TOR signaling in the nervous system remain largely unclear, partly because its multifunctionality and requirement for survival make it difficult to investigate. Here, using pharmacological inhibitors and genetic analyses, we show that TORC1 and TORC2 contribute to associative learning between salt and food availability in the nematode Caenorhabditis elegans in a process called taste associative learning. Worms migrate to salt concentrations experienced previously during feeding, but they avoid salt concentrations experienced under starvation conditions. Administration of the TOR inhibitor rapamycin causes a behavioral defect after starvation conditioning. Worms lacking either RICT-1 or SINH-1, two TORC2 components, show defects in migration to high salt levels after learning under both fed and starved conditions. We also analyzed the behavioral phenotypes of mutants of the putative TORC1 substrate RSKS-1 (the C. elegans homolog of the mammalian S6 kinase S6K) and the putative TORC2 substrates SGK-1 and PKC-2 (homologs of the serum and glucocorticoid-induced kinase 1, SGK1, and protein kinase C-α, PKC-α, respectively) and found that neuronal RSKS-1 and PKC-2, as well as intestinal SGK-1, are involved in taste associative learning. Our findings shed light on the functions of TOR signaling in behavioral plasticity and provide insight into the mechanisms by which information sensed in the intestine affects the nervous system to modulate food-searching behaviors.

Octopamine enhances oxidative stress resistance through the fasting-responsive transcription factor DAF-16/FOXO in C. elegans

Dietary restriction regimens lead to enhanced stress resistance and extended life span in many species through the regulation of fasting and/or diet-responsive mechanisms. The fasting stimulus is perceived by sensory neurons and causes behavioral and metabolic adaptations. Octopamine (OA), one of the Caenorhabditis elegans neurotransmitters, is involved in behavioral adaptations, and its levels are increased under fasting conditions. However, it remains largely unknown how OA contributes to the fasting responses. In this study, we found that OA administration enhanced organismal resistance to oxidative stress. This enhanced resistance was suppressed by a mutation of the OA receptors, SER-3 and SER-6. Moreover, we found that OA administration promoted the nuclear translocation of DAF-16, the key transcription factor in fasting responses, and that the OA-induced enhancement of stress resistance required DAF-16. Altogether, our results suggest that OA signaling, which is triggered by the absence of food, shifts the organismal state to a more protective one to prepare for environmental stresses.

TRPA1 mediates sensation of the rate of temperature change in Drosophila larvae

Avoidance of noxious ambient heat is crucial for survival. A well-known phenomenon is that animals are sensitive to the rate of temperature change. However, the cellular and molecular underpinnings through which animals sense and respond much more vigorously to fast temperature changes are unknown. Using Drosophila larvae, we found that nociceptive rolling behavior was triggered at lower temperatures and at higher frequencies when the temperature increased rapidly. We identified neurons in the brain that were sensitive to the speed of the temperature increase rather than just to the absolute temperature. These cellular and behavioral responses depended on the TRPA1 channel, whose activity responded to the rate of temperature increase. We propose that larvae use low-threshold sensors in the brain to monitor rapid temperature increases as a protective alert signal to trigger rolling behaviors, allowing fast escape before the temperature of the brain rises to dangerous levels.

The C. elegans Taste Receptor Homolog LITE-1 Is a Photoreceptor

Many animal tissues/cells are photosensitive, yet only two types of photoreceptors (i.e., opsins and cryptochromes) have been discovered in metazoans. The question arises as to whether unknown types of photoreceptors exist in the animal kingdom. LITE-1, a seven-transmembrane gustatory receptor (GR) homolog, mediates UV-light-induced avoidance behavior in C. elegans. However, it is not known whether LITE-1 functions as a chemoreceptor or photoreceptor. Here, we show that LITE-1 directly absorbs both UVA and UVB light with an extinction coefficient 10-100 times that of opsins and cryptochromes, indicating that LITE-1 is highly efficient in capturing photons. Unlike typical photoreceptors employing a prosthetic chromophore to capture photons, LITE-1 strictly depends on its protein conformation for photon absorption. We have further identified two tryptophan residues critical for LITE-1 function. Interestingly, unlike GPCRs, LITE-1 adopts a reversed membrane topology. Thus, LITE-1, a taste receptor homolog, represents a distinct type of photoreceptor in the animal kingdom.

The role of insulin/IGF-1 signaling in the longevity of model invertebrates, C. elegans and D. melanogaster

Insulin/insulin-like growth factor (IGF)-1 signaling (IIS) pathway regulates aging in many organisms, ranging from simple invertebrates to mammals, including humans. Many seminal discoveries regarding the roles of IIS in aging and longevity have been made by using the roundworm Caenorhabditis elegans and the fruit fly Drosophila melanogaster. In this review, we describe the mechanisms by which various IIS components regulate aging in C. elegans and D. melanogaster. We also cover systemic and tissue-specific effects of the IIS components on the regulation of lifespan. We further discuss IIS-mediated physiological processes other than aging and their effects on human disease models focusing on C. elegans studies. As both C. elegans and D. melanogaster have been essential for key findings regarding the effects of IIS on organismal aging in general, these invertebrate models will continue to serve as workhorses to help our understanding of mammalian aging. [BMB Reports 2016; 49(2): 81-92]

A Caenorhabditis elegans Model Elucidates a Conserved Role for TRPA1-Nrf Signaling in Reactive α-Dicarbonyl Detoxification

Reactive α-dicarbonyls (α-DCs), like methylglyoxal (MGO), accumulate with age and have been implicated in aging and various age-associated pathologies, such as diabetic complications and neurodegenerative disorders like Alzheimer's and Parkinson's diseases. Evolutionarily conserved glyoxalases are responsible for α-DC detoxification; however, their core biochemical regulation has remained unclear. We have established a Caenorhabditis elegans model, based on an impaired glyoxalase (glod-4/GLO1), to broadly study α-DC-related stress. We show that, in comparison to wild-type (N2, Bristol), glod-4 animals rapidly exhibit several pathogenic phenotypes, including hyperesthesia, neuronal damage, reduced motility, and early mortality. We further demonstrate TRPA-1/TRPA1 as a sensor for α-DCs, conserved between worms and mammals. Moreover, TRPA-1 activates SKN-1/Nrf via calcium-modulated kinase signaling, ultimately regulating the glutathione-dependent (GLO1) and co-factor-independent (DJ1) glyoxalases to detoxify α-DCs. Interestingly, this pathway is in stark contrast to the TRPA-1 activation and the ensuing calcium flux implicated in cold sensation in C. elegans, whereby DAF-16/FOXO gets activated via complementary kinase signaling. Finally, a phenotypic drug screen using C. elegans identified podocarpic acid as a novel activator of TRPA1 that rescues α-DC-induced pathologies in C. elegans and mammalian cells. Our work thus identifies TRPA1 as a bona fide drug target for the amelioration of α-DC stress, which represents a viable option to address aging-related pathologies in diabetes and neurodegenerative diseases.

A C. elegans Thermosensory Circuit Regulates Longevity through crh-1/CREB-Dependent flp-6 Neuropeptide Signaling

Sensory perception, including thermosensation, shapes longevity in diverse organisms, but longevity-modulating signals from the sensory neurons are largely obscure. Here we show that CRH-1/CREB activation by CMK-1/CaMKI in the AFD thermosensory neuron is a key mechanism that maintains lifespan at warm temperatures in C. elegans. In response to temperature rise and crh-1 activation, the AFD neurons produce and secrete the FMRFamide neuropeptide FLP-6. Both CRH-1 and FLP-6 are necessary and sufficient for longevity at warm temperatures. Our data suggest that FLP-6 targets the AIY interneurons and engages DAF-9 sterol hormone signaling. Moreover, we show that FLP-6 signaling downregulates ins-7/insulin-like peptide and several insulin pathway genes, whose activity compromises lifespan. Our work illustrates how temperature experience is integrated by the thermosensory circuit to generate neuropeptide signals that remodel insulin and sterol hormone signaling and reveals a neuronal-endocrine circuit driven by thermosensation to promote temperature-specific longevity.

TRPA1 Channels in Drosophila and Honey Bee Ectoparasitic Mites Share Heat Sensitivity and Temperature-Related Physiological Functions

The transient receptor potential cation channel, subfamily A, member 1 (TRPA1) is conserved between many arthropods, and in some has been shown to function as a chemosensor for noxious compounds. Activation of arthropod TRPA1 channels by temperature fluctuations has been tested in only a few insect species, and all of them were shown to be activated by heat. The recent identification of chemosensitive TRPA1 channels from two honey bee ectoparasitic mite species (VdTRPA1 and TmTRPA1) have provided an opportunity to study the temperature-dependent activation and the temperature-associated physiological functions of TRPA1 channels in non-insect arthropods. We found that both mite TRPA1 channels are heat sensitive and capable of rescuing the temperature-related behavioral defects of a Drosophila melanogaster trpA1 mutant. These results suggest that heat-sensitivity of TRPA1 could be conserved between many arthropods despite its amino acid sequence diversity. Nevertheless, the ankyrin repeats (ARs) 6 and 7 are well-conserved between six heat-sensitive arthropod TRPA1 channels and have critical roles for the heat activation of VdTRPA1.

Natural variations of cold tolerance and temperature acclimation in Caenorhabditis elegans

Temperature is critical for the survival and proliferation of animals, which must be adapted to cope with environmental temperature changes. In this study, we demonstrated natural variations in the phenotypes of temperature tolerance and temperature acclimation of the nematode Caenorhabditis elegans, and we decoded whole genome sequence of six natural variations, which enabled us to map responsible gene polymorphisms onto specific chromosomal regions. The C. elegans laboratory strain, N2, survives at 2 °C after cultivation at 15 °C but is unable to survive at 2 °C after cultivation at 20 or 25 °C. This cultivation-temperature-dependent cold tolerance occurs within a few hours after the temperature shift and is termed cold acclimation. We measured the cold tolerance and cold acclimation phenotypes of many natural variants isolated from various areas. CB4854 showed weaker cold tolerance associated with gene polymorphisms on the sex chromosome decoded by whole genome sequencing. Variable cold acclimation phenotypes were exhibited in twelve natural isolates and the large difference was seen between CB4856 and AB1 strains. CB4856, isolated from Hawaii, acclimated slowly to a new temperature, whereas AB1, isolated from Australia, acclimated rapidly. By the whole genome sequencing analysis, two different polymorphisms responsible for the accelerated cold acclimation in AB1 were mapped to specific chromosomal regions.

Lifespan-regulating genes in C. elegans

The molecular mechanisms underlying the aging process have garnered much attention in recent decades because aging is the most significant risk factor for many chronic diseases such as type 2 diabetes and cancer. Until recently, the aging process was not considered to be an actively regulated process; therefore, discovering that the insulin/insulin-like growth factor-1 signaling pathway is a lifespan-regulating genetic pathway in Caenorhabditis elegans was a major breakthrough that changed our understanding of the aging process. Currently, it is thought that animal lifespans are influenced by genetic and environmental factors. The genes involved in lifespan regulation are often associated with major signaling pathways that link the rate of aging to environmental factors. Although many of the major mechanisms governing the aging process have been identified from studies in short-lived model organisms such as yeasts, worms and flies, the same mechanisms are frequently observed in mammals, indicating that the genes and signaling pathways that regulate lifespan are highly conserved among different species. This review summarizes the lifespan-regulating genes, with a specific focus on studies in C. elegans.

Moderately lower temperatures greatly extend the lifespan of Brachionus manjavacas (Rotifera): Thermodynamics or gene regulation?

Environmental temperature greatly affects lifespan in a wide variety of animals, but the exact mechanisms underlying this effect are still largely unknown. A moderate temperature decrease from 22°C to 16°C extends the lifespan of the monogonont rotifer Brachionus manjavacas by up to 163%. Thermodynamic effects on metabolism contribute to this increase in longevity, but are not the only cause. When rotifers are exposed to 16°C for four days and then transfered to 22°C, they survive until day 13 at nearly identical rates as rotifers maintained at 16°C continuously. This persistence of the higher survival for nine days after transfer to 22°C suggests that low temperature exposure alters the expression of genes that affect the rate of aging. The relative persistence of the gene regulation effect suggests that it may play an even larger role in slowing aging than the thermodynamic effects. The life extending effects of these short-term low temperature treatments are largest when the exposure happens early in the life cycle, demonstrating the importance of early development. There is no advantage to lowering the temperature below 16°C to 11° or 5°C. Rotifers exposed to 16°C also displayed increased resistance to heat, starvation, oxidative and osmotic stress. Reproductive rates at 16°C were lower than those at 22°C, but because they reproduce longer, there is no significant change in the lifetime fecundity of females. To investigate which genes contribute to these effects, the expression of specific temperature sensing genes was knocked down using RNAi. Of 12 genes tested, RNAi knockdown of four eliminated the survival enhancing effects of the four-day cold treatment: TRP7, forkhead box C, Y-box factor, and ribosomal protein S6. This demonstrates that active gene regulation is an important factor in temperature mediated life extension, and that these particular genes play an integral role in these pathways. As a thermoresponsive sensor, TRP7 may be responsible for triggering the signaling cascade contributing to temperature mediated life extension. The TRP genes may also provide especially promising candidates for targeted gene manipulations or pharmacological interventions capable of mimicking the effects of low temperature exposure. These results support recent theories of aging that claim rate of aging is determined by an actively regulated genetic mechanism rather than an accumulation of molecular damage.

Differential Effects of TRPA and TRPV Channels on Behaviors of Caenorhabditis elegans

TRPA and TRPV ion channels are members of the transient receptor potential (TRP) cation channel superfamily, which mediates various sensory transductions. In Caenorhabditis elegans, the TRPV channels are known to affect chemosensation, while the TRPA-1 channel is associated with thermosensation and mechanosensation. We examined thermosensation, chemosensation, and osmosensation in strains lacking TRPA-1 or TRPV channels. We found that TRPV channel knockout worms exhibited similar behavioral deficits associated with thermotaxis as the TRPA-1 channel knockout, suggesting a dual role for TRPV channels. In contrast, chemosensation responses, assessed by both avoidance reversal behavior and NaCl osmosensation, were dependent on TRPV channels but seemed independent of TRPA-1 channel. Our findings suggest that, in addition to TRPA-1 channel, TRPV channels are necessary for thermotaxis and may activate, or modulate, the function of TRPA-1 channels. In contrast, TRPA-1 channels do not have a dual responsibility, as they have no functional role in odorant avoidance or osmosensation.

Angiotensin Converting Enzyme (ACE) Inhibitor Extends Caenorhabditis elegans Life Span

Animal aging is characterized by progressive, degenerative changes in many organ systems. Because age-related degeneration is a major contributor to disability and death in humans, treatments that delay age-related degeneration are desirable. However, no drugs that delay normal human aging are currently available. To identify drugs that delay age-related degeneration, we used the powerful Caenorhabditis elegans model system to screen for FDA-approved drugs that can extend the adult lifespan of worms. Here we show that captopril extended mean lifespan. Captopril is an angiotensin-converting enzyme (ACE) inhibitor used to treat high blood pressure in humans. To explore the mechanism of captopril, we analyzed the acn-1 gene that encodes the C. elegans homolog of ACE. Reducing the activity of acn-1 extended the mean life span. Furthermore, reducing the activity of acn-1 delayed age-related degenerative changes and increased stress resistance, indicating that acn-1 influences aging. Captopril could not further extend the lifespan of animals with reduced acn-1, suggesting they function in the same pathway; we propose that captopril inhibits acn-1 to extend lifespan. To define the relationship with previously characterized longevity pathways, we analyzed mutant animals. The lifespan extension caused by reducing the activity of acn-1 was additive with caloric restriction and mitochondrial insufficiency, and did not require sir-2.1, hsf-1 or rict-1, suggesting that acn-1 functions by a distinct mechanism. The interactions with the insulin/IGF-1 pathway were complex, since the lifespan extensions caused by captopril and reducing acn-1 activity were additive with daf-2 and age-1 but required daf-16. Captopril treatment and reducing acn-1 activity caused similar effects in a wide range of genetic backgrounds, consistent with the model that they act by the same mechanism. These results identify a new drug and a new gene that can extend the lifespan of worms and suggest new therapeutic strategies for addressing age-related degenerative changes.

Reciprocal Changes in Phosphoenolpyruvate Carboxykinase and Pyruvate Kinase with Age Are a Determinant of Aging in Caenorhabditis elegans

Aging involves progressive loss of cellular function and integrity, presumably caused by accumulated stochastic damage to cells. Alterations in energy metabolism contribute to aging, but how energy metabolism changes with age, how these changes affect aging, and whether they can be modified to modulate aging remain unclear. In locomotory muscle of post-fertile Caenorhabditis elegans, we identified a progressive decrease in cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C), a longevity-associated metabolic enzyme, and a reciprocal increase in glycolytic pyruvate kinase (PK) that were necessary and sufficient to limit lifespan. Decline in PEPCK-C with age also led to loss of cellular function and integrity including muscle activity, and cellular senescence. Genetic and pharmacologic interventions of PEPCK-C, muscle activity, and AMPK signaling demonstrate that declines in PEPCK-C and muscle function with age interacted to limit reproductive life and lifespan via disrupted energy homeostasis. Quantifications of metabolic flux show that reciprocal changes in PEPCK-C and PK with age shunted energy metabolism toward glycolysis, reducing mitochondrial bioenergetics. Last, calorie restriction countered changes in PEPCK-C and PK with age to elicit anti-aging effects via TOR inhibition. Thus, a programmed metabolic event involving PEPCK-C and PK is a determinant of aging that can be modified to modulate aging.

Long-term recovery from acute cold shock in Caenorhabditis elegans

Background

Animals are exposed to a wide range of environmental stresses that can cause potentially fatal cellular damage. The ability to survive the period of stress as well as to repair any damage incurred is essential for fitness. Exposure to 2 °C for 24 h or longer is rapidly fatal to the nematode Caenorhabditis elegans, but the process of recovery from a shorter, initially non-lethal, cold shock is poorly understood.

Results

We report that cold shock of less than 12-hour duration does not initially kill C. elegans, but these worms experience a progression of devastating phenotypes over the next 96 h that correlate with their eventual fate: successful recovery from the cold shock and survival, or failure to recover and death. Cold-shocked worms experience a marked loss of pigmentation, decrease in the size of their intestine and gonads, and disruption to the vulva. Those worms who will successfully recover from the cold shock regain their pigmentation and much of the integrity of their intestine and gonads. Those who will die do so with a distinct phenotype from worms dying during or immediately following cold shock, suggesting independent mechanisms. Worms lacking the G-protein coupled receptor FSHR-1 are resistant to acute death from longer cold shocks, and are more successful in their recovery from shorter sub-lethal cold shocks.

Conclusions

We have defined two distinct phases of death associated with cold shock and described a progression of phenotypes that accompanies the course of recovery from that cold shock. The G-protein coupled receptor FSHR-1 antagonizes these novel processes of damage and recovery.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-015-0079-z) contains supplementary material, which is available to authorized users.

Experience Modulates the Reproductive Response to Heat Stress in C. elegans via Multiple Physiological Processes

Natural environments are considerably more variable than laboratory settings and often involve transient exposure to stressful conditions. To fully understand how organisms have evolved to respond to any given stress, prior experience must therefore be considered. We investigated the effects of individual and ancestral experience on C. elegans reproduction. We documented ways in which cultivation at 15°C or 25°C affects developmental time, lifetime fecundity, and reproductive performance after severe heat stress that exceeds the fertile range of the organism but is compatible with survival and future fecundity. We found that experience modulates multiple aspects of reproductive physiology, including the male and female germ lines and the interaction between them. These responses vary in their environmental sensitivity, suggesting the existence of complex mechanisms for coping with unpredictable and stressful environments.

Freeze-thaw Caenorhabditis elegans freeze-thaw stress response is regulated by the insulin/IGF-1 receptor daf-2

BACKGROUND

Adaption to cold temperatures, especially those below freezing, is essential for animal survival in cold environments. Freezing is also used for many medical, scientific, and industrial purposes. Natural freezing survival in animals has been extensively studied. However, the underlying mechanisms remain unclear. Previous studies demonstrated that animals survive in extremely cold weather by avoiding freezing or controlling the rate of ice-crystal formation in their bodies, which indicates that freezing survival is a passive thermodynamic process.

RESULTS

Here, we showed that genetic programming actively promotes freezing survival in Caenorhabditis elegans. We found that daf-2, an insulin/IGF-1 receptor homologue, and loss-of-function enhanced survival during freeze-thaw stress, which required the transcription factor daf-16/FOXO and age-independent target genes. In particular, the freeze-thaw resistance of daf-2(rf) is highly allele-specific and has no correlation with lifespan, dauer formation, or hypoxia stress resistance.

CONCLUSIONS

Our results reveal a new function for daf-2 signaling, and, most importantly, demonstrate that genetic programming contributes to freezing survival.

Metabotropic GABA signalling modulates longevity in C. elegans

The nervous system plays an important but poorly understood role in modulating longevity. GABA, a prominent inhibitory neurotransmitter, is best known to regulate nervous system function and behaviour in diverse organisms. Whether GABA signalling affects aging, however, has not been explored. Here we examined mutants lacking each of the major neurotransmitters in C. elegans, and find that deficiency in GABA signalling extends lifespan. This pro-longevity effect is mediated by the metabotropic GABA_B receptor GBB-1, but not ionotropic GABA_A receptors. GBB-1 regulates lifespan through G protein-PLCβ signalling, which transmits longevity signals to the transcription factor DAF-16/FOXO, a key regulator of lifespan. Mammalian GABA_B receptors can functionally substitute for GBB-1 in lifespan control in C. elegans. Our results uncover a new role of GABA signalling in lifespan regulation in C. elegans, raising the possibility that a similar process may occur in other organisms.

The C. elegans nervous system influences organismal lifespan but mechanistic details are poorly understood. Here, Chun et al. show that the neurotransmitter GABA regulates worm lifespan by acting on GABA_B receptors in motor neurons, which activate the transcription factor DAF-16 in the intestine.

SKN-1/Nrf, stress responses, and aging in Caenorhabditis elegans

The mammalian Nrf/CNC proteins (Nrf1, Nrf2, Nrf3, p45 NF-E2) perform a wide range of cellular protective and maintenance functions. The most thoroughly described of these proteins, Nrf2, is best known as a regulator of antioxidant and xenobiotic defense, but more recently has been implicated in additional functions that include proteostasis and metabolic regulation. In the nematode Caenorhabditis elegans, which offers many advantages for genetic analyses, the Nrf/CNC proteins are represented by their ortholog SKN-1. Although SKN-1 has diverged in aspects of how it binds DNA, it exhibits remarkable functional conservation with Nrf/CNC proteins in other species and regulates many of the same target gene families. C. elegans may therefore have considerable predictive value as a discovery model for understanding how mammalian Nrf/CNC proteins function and are regulated in vivo. Work in C. elegans indicates that SKN-1 regulation is surprisingly complex and is influenced by numerous growth, nutrient, and metabolic signals. SKN-1 is also involved in a wide range of homeostatic functions that extend well beyond the canonical Nrf2 function in responses to acute stress. Importantly, SKN-1 plays a central role in diverse genetic and pharmacologic interventions that promote C. elegans longevity, suggesting that mechanisms regulated by SKN-1 may be of conserved importance in aging. These C. elegans studies predict that mammalian Nrf/CNC protein functions and regulation may be similarly complex and that the proteins and processes that they regulate are likely to have a major influence on mammalian life- and healthspan.

Effect of temperature on replicative aging of the budding yeast Saccharomyces cerevisiae

The use of the budding yeast Saccharomyces cerevisiae in gerontological studies was based on the assumption that the reproduction limit of a single cell (replicative aging) is a consequence of accumulation of a hypothetical universal "senescence factor" within the mother cell. However, some evidence suggests that molecules or structures proposed as the "aging factor", such as rDNA circles, oxidatively damaged proteins (with carbonyl groups) or mitochondria, have little effect on replicative lifespan of yeast cells. Our results also suggest that protein aggregates associated with Hsp104, treated as a marker of yeast aging, do not seem to affect the numeric value of replicative lifespan of yeast. What these results indicate, however, is the need for finding a different way of expressing age and longevity of yeast cells instead of the commonly used number of daughters produced over units of time, as in the case of other organisms. In this paper, we show that the temperature has a stronger influence on the time of life (the total lifespan) than on the reproductive potential of yeast cells.

Metabolome and proteome changes with aging in Caenorhabditis elegans

To expand the understanding of aging in the model organism Caenorhabditis elegans, global quantification of metabolite and protein levels in young and aged nematodes was performed using mass spectrometry. With age, there was a decreased abundance of proteins functioning in transcription termination, mRNA degradation, mRNA stability, protein synthesis, and proteasomal function. Furthermore, there was altered S-adenosyl methionine metabolism as well as a decreased abundance of the S-adenosyl methionine synthetase (SAMS-1) protein. Other aging-related changes included alterations in free fatty acid levels and composition, decreased levels of ribosomal proteins, decreased levels of NADP-dependent isocitrate dehydrogenase (IDH1), a shift in the cellular redox state, an increase in sorbitol content, alterations in free amino acid levels, and indications of altered muscle function and sarcoplasmic reticulum Ca(2+) homeostasis. There were also decreases in pyrimidine and purine metabolite levels, most markedly nitrogenous bases. Supplementing the culture medium with cytidine (a pyrimidine nucleoside) or hypoxanthine (a purine base) increased lifespan slightly, suggesting that aging-induced alterations in ribonucleotide metabolism affect lifespan. An age-related increase in body size, lipotoxicity from ectopic yolk lipoprotein accumulation, a decline in NAD(+) levels, and mitochondrial electron transport chain dysfunction may explain many of these changes. In addition, dietary restriction in aged worms resulting from sarcopenia of the pharyngeal pump likely decreases the abundance of SAMS-1, possibly leading to decreased phosphatidylcholine levels, larger lipid droplets, and ER and mitochondrial stress. The complementary use of proteomics and metabolomics yielded unique insights into the molecular processes altered with age in C. elegans.

Spatio-temporal distribution of human lifespan in China

Based on the data of latest three Chinese population censuses (1990–2010), four lifespan indicators were calculated: centenarians per one hundred thousand inhabitants (CH); longevity index (LI); the percentage of the population aged at least 80 years (ultra-octogenarian index, UOI) and life expectancy at birth (LEB). The spatio-temporal distributions of data at Chinese county level show that high-longevity areas (high values of CH and LI) and low-longevity areas (low CH and LI values) both exhibit clear non-uniformity of spatial distribution and relative immobility through time. Contrarily, the distribution of UOI and LEB shows a decline from the east to the west. The spatial autocorrelation analyses indicate less spatial dependency and several discontinuous clusters regions of high-CH and LI areas. The factors of temperature, topography and wet/dry climate lack of significant influence on CH and LI. It can be inferred that, in addition to genetic factor and living custom, some unique and long-term environmental effects may be related with high or low values of CH and LI.

Being cool: how body temperature influences ageing and longevity

Temperature is a basic and essential property of any physical system, including living systems. Even modest variations in temperature can have profound effects on organisms, and it has long been thought that as metabolism increases at higher temperatures so should rates of ageing. Here, we review the literature on how temperature affects longevity, ageing and life history traits. From poikilotherms to homeotherms, there is a clear trend for lower temperature being associated with longer lifespans both in wild populations and in laboratory conditions. Many life-extending manipulations in rodents, such as caloric restriction, also decrease core body temperature. Nonetheless, an inverse relationship between temperature and lifespan can be obscured or reversed, especially when the range of body temperatures is small as in homeotherms. An example is observed in humans: women appear to have a slightly higher body temperature and yet live longer than men. The mechanisms involved in the relationship between temperature and longevity also appear to be less direct than once thought with neuroendocrine processes possibly mediating complex physiological responses to temperature changes. Lastly, we discuss species differences in longevity in mammals and how this relates to body temperature and argue that the low temperature of the long-lived naked mole-rat possibly contributes to its exceptional longevity.

Serum- and Glucocorticoid-Inducible Kinase-1 (SGK-1) Plays a Role in Membrane Trafficking in Caenorhabditis elegans

The mammalian serum- and glucocorticoid-inducible kinase SGK1 regulates the endocytosis of ion channels. Here we report that in C. elegans sgk-1 null mutants, GFP-tagged MIG-14/Wntless, the sorting receptor of Wnt, failed to localize to the basolateral membrane of intestinal cells; instead, it was mis-sorted to lysosomes. This effect can be explained in part by altered sphingolipid levels, because reducing glucosylceramide biosynthesis restored the localization of MIG-14::GFP. Membrane traffic was not perturbed in general, as no obvious morphological defects were detected for early endosomes, the Golgi apparatus, and the endoplasmic reticulum (ER) in sgk-1 null animals. The recycling of MIG-14/Wntless through the Golgi might be partially responsible for the observed phenotype because the subcellular distribution of two plasma membrane cargoes that do not recycle through the trans-Golgi network (TGN) was affected to a lesser degree. Consistently, knockdown of the ArfGEF gbf-1 altered the distribution of SGK-1 at the basolateral membrane of intestinal cells. In addition, we found that sgk-1(RNAi) induced unfolded protein response in the ER, suggesting at least an indirect role of SGK-1 early in the secretory pathway. We propose that SGK-1 function is required for lipid homeostasis and that it acts at different intracellular trafficking steps.

Thermosensation and longevity

Temperature has profound effects on behavior and aging in both poikilotherms and homeotherms. To thrive under the ever fluctuating environmental temperatures, animals have evolved sophisticated mechanisms to sense and adapt to temperature changes. Animals sense temperature through various molecular thermosensors, such as thermosensitive transient receptor potential (TRP) channels expressed in neurons, keratinocytes, and intestine. These evolutionarily conserved thermosensitive TRP channels feature distinct activation thresholds, thereby covering a wide spectrum of ambient temperature. Temperature changes trigger complex thermosensory behaviors. Due to the simplicity of the nervous system in model organisms such as Caenorhabditis elegans and Drosophila, the mechanisms of thermosensory behaviors in these species have been extensively studied at the circuit and molecular levels. While much is known about temperature regulation of behavior, it remains largely unclear how temperature affects aging. Recent studies in C. elegans demonstrate that temperature modulation of longevity is not simply a passive thermodynamic phenomenon as suggested by the rate-of-living theory, but rather a process that is actively regulated by genes, including those encoding thermosensitive TRP channels. In this review, we discuss our current understanding of thermosensation and its role in aging.

Environmental Temperature Differentially Modulates C. elegans Longevity through a Thermosensitive TRP Channel

Temperature profoundly affects aging in both poikilotherms and homeotherms. A general belief is that lower temperatures extend lifespan, whereas higher temperatures shorten it. Although this "temperature law" is widely accepted, it has not been extensively tested. Here, we systematically evaluated the role of temperature in lifespan regulation in C. elegans. We found that, although exposure to low temperatures at the adult stage prolongs lifespan, low-temperature treatment at the larval stage surprisingly reduces lifespan. Interestingly, this differential effect of temperature on longevity in larvae and adults is mediated by the same thermosensitive TRP channel TRPA-1 that signals to the transcription factor DAF-16/FOXO. DAF-16/FOXO and TRPA-1 act in larva to shorten lifespan but extend lifespan in adulthood. DAF-16/FOXO differentially regulates gene expression in larva and adult in a temperature-dependent manner. Our results uncover complexity underlying temperature modulation of longevity, demonstrating that temperature differentially regulates lifespan at different stages of life.

RNAi Interrogation of Dietary Modulation of Development, Metabolism, Behavior, and Aging in C. elegans

Diet affects nearly every aspect of animal life such as development, metabolism, behavior, and aging, both directly by supplying nutrients and indirectly through gut microbiota. C. elegans feeds on bacteria, and like other animals, different bacterial diets induce distinct dietary responses in the worm. However, the lack of certain critical tools hampers the use of worms as a model for dietary signaling. Here, we genetically engineered the bacterial strain OP50, the standard laboratory diet for C. elegans, making it compatible for dsRNA production and delivery. Using this RNAi-compatible OP50 strain and the other bacterial strain HT115, we feed worms different diets while delivering RNAi to interrogate the genetic basis underlying diet-dependent differential modulation of development, metabolism, behavior, and aging. We show by RNAi that neuroendocrine and mTOR pathways are involved in mediating differential dietary responses. This genetic tool greatly facilitates the use of C. elegans as a model for dietary signaling.

Ambient temperature reduction extends lifespan via activating cellular degradation activity in an annual fish (Nothobranchius rachovii)

Ambient temperature reduction (ATR) can extend the lifespan of organisms, but the underlying mechanism is poorly understood. In this study, cellular degradation activity was evaluated in the muscle of an annual fish (Nothobranchius rachovii) reared under high (30 °C), moderate (25 °C), and low (20 °C) ambient temperatures. The results showed the following: (i) the activity of the 20S proteasome and the expression of polyubiquitin aggregates increased with ATR, whereas 20S proteasome expression did not change; (ii) the expression of microtubule-associated protein 1 light chain 3-II (LC3-II) increased with ATR; (iii) the expression of lysosome-associated membrane protein type 2a (Lamp 2a) increased with ATR, whereas the expression of the 70-kD heat shock cognate protein (Hsc 70) decreased with ATR; (iv) lysosome activity increased with ATR, whereas the expression of lysosome-associated membrane protein type 1 (Lamp 1) did not change with ATR; and (v) the expression of molecular target of rapamycin (mTOR) and phosphorylated mTOR (p-mTOR) as well as the p-mTOR/mTOR ratio did not change with ATR. These findings indicate that ATR activates cellular degradation activity, constituting part of the mechanism underlying the longevity-promoting effects of ATR in N. rachovii.

Co-chaperone p23 regulates C. elegans Lifespan in Response to Temperature

Temperature potently modulates various physiologic processes including organismal motility, growth rate, reproduction, and ageing. In ectotherms, longevity varies inversely with temperature, with animals living shorter at higher temperatures. Thermal effects on lifespan and other processes are ascribed to passive changes in metabolic rate, but recent evidence also suggests a regulated process. Here, we demonstrate that in response to temperature, daf-41/ZC395.10, the C. elegans homolog of p23 co-chaperone/prostaglandin E synthase-3, governs entry into the long-lived dauer diapause and regulates adult lifespan. daf-41 deletion triggers constitutive entry into the dauer diapause at elevated temperature dependent on neurosensory machinery (daf-10/IFT122), insulin/IGF-1 signaling (daf-16/FOXO), and steroidal signaling (daf-12/FXR). Surprisingly, daf-41 mutation alters the longevity response to temperature, living longer than wild-type at 25°C but shorter than wild-type at 15°C. Longevity phenotypes at 25°C work through daf-16/FOXO and heat shock factor hsf-1, while short lived phenotypes converge on daf-16/FOXO and depend on the daf-12/FXR steroid receptor. Correlatively daf-41 affected expression of DAF-16 and HSF-1 target genes at high temperature, and nuclear extracts from daf-41 animals showed increased occupancy of the heat shock response element. Our studies suggest that daf-41/p23 modulates key transcriptional changes in longevity pathways in response to temperature.

Molecular biology of thermosensory transduction in C. elegans

As the environmental temperature prominently influences diverse biological aspects of the animals, thermosensation and the subsequent information processing in the nervous system has attracted much attention in biology. Thermotaxis in the nematode Caenorhabditis elegans is an ideal behavioral paradigm by which to address the molecular mechanism underlying thermosensory transduction. Molecular genetic analysis in combination with other physiological and behavioral studies revealed that sensation of ambient temperature is mediated mainly by cyclic guanosine monophosphate (cGMP) signaling in thermosensory neurons. The information of the previously perceived temperature is also stored within the thermosensory neurons, and the consequence of the comparison between the past and the present temperature is conveyed to the downstream interneurons to further regulate the motor-circuits that encode the locomotion.