Food-derived sensory cues modulate longevity via distinct neuroendocrine insulin-like peptides

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.

Functional analysis of conserved C. elegans bHLH family members uncovers lifespan control by a peptidergic hub neuron

Throughout the animal kingdom, several members of the basic helix-loop-helix (bHLH) family act as proneural genes during early steps of nervous system development. Roles of bHLH genes in specifying terminal differentiation of postmitotic neurons have been less extensively studied. We analyze here the function of 5 Caenorhabditis elegans bHLH genes, falling into 3 phylogenetically conserved subfamilies, which are continuously expressed in a very small number of postmitotic neurons in the central nervous system. We show (a) that 2 orthologs of the vertebrate bHLHe22/e23 genes, called hlh-17 and hlh-32, function redundantly to specify the identity of a single head interneuron class (AUA), as well as an individual motor neuron (VB2); (b) that the PTF1a ortholog hlh-13 acts as a terminal selector to control terminal differentiation and function of the sole octopaminergic neuron class in C. elegans, RIC; and (c) that the NHLH1/2 ortholog hlh-15 controls terminal differentiation and function of the peptidergic AVK head interneuron class, a known neuropeptidergic signaling hub in the animal. Strikingly, through null mutant analysis and cell-specific rescue experiments, we find that loss of hlh-15/NHLH in the peptidergic AVK neurons and the resulting abrogation of neuropeptide secretion from these neurons causes a substantially extended lifespan of the animal, which we propose to be akin to hypothalamic control of lifespan in vertebrates. Our functional analysis reveals themes of bHLH gene function during terminal differentiation that are complementary to the earlier lineage specification roles of other bHLH family members. However, such late functions are much more sparsely employed by members of the bHLH transcription factor family, compared to the function of the much more broadly employed homeodomain transcription factor family.

The role of kinesin-1 in neuronal dense core vesicle transport, locomotion and lifespan regulation in C. elegans

Fast axonal transport is crucial for neuronal function and is driven by kinesins and cytoplasmic dynein. Here, we investigated the role of kinesin-1 in dense core vesicle (DCV) transport in C. elegans, using mutants in the kinesin light chains (klc-1 and klc-2) and the motor subunit (unc-116) expressing an ida-1::gfp transgene that labels DCVs. DCV transport in both directions was greatly impaired in an unc-116 mutant and had reduced velocity in a klc-2 mutant. In contrast, the speed of retrograde DCV transport was increased in a klc-1 mutant whereas anterograde transport was unaffected. We identified striking differences between the klc mutants in their effects on worm locomotion and responses to drugs affecting neuromuscular junction activity. We also determined lifespan, finding that unc-116 mutant was short-lived whereas the klc single mutant lifespan was wild type. The ida-1::gfp transgenic strain was also short-lived, but surprisingly, klc-1 and klc-2 extended the ida-1::gfp lifespan beyond that of wild type. Our findings suggest that kinesin-1 not only influences anterograde and retrograde DCV transport but is also involved in regulating lifespan and locomotion, with the two kinesin light chains playing distinct roles.

Functional analysis of conserved C. elegans bHLH family members uncovers lifespan control by a peptidergic hub neuron

Throughout the animal kingdom, several members of the basic helix-loop-helix (bHLH) family act as proneural genes during early steps of nervous system development. Roles of bHLH genes in specifying terminal differentiation of postmitotic neurons have been less extensively studied. We analyze here the function of five C. elegans bHLH genes, falling into three phylogenetically conserved subfamilies, which are continuously expressed in a very small number of postmitotic neurons in the central nervous system. We show (a) that two orthologs of the vertebrate bHLHb4/b5 genes, called hlh-17 and hlh-32, function redundantly to specify the identity of a single head interneuron (AUA), as well as an individual motor neuron (VB2), (b) that the PTF1a ortholog hlh-13 acts as a terminal selector to control terminal differentiation and function of the sole octopaminergic neuron class in C. elegans, RIC, and (c) that the NHLH1/2 ortholog hlh-15 controls terminal differentiation and function of the peptidergic AVK head interneuron class, a known neuropeptidergic signaling hub in the animal. Strikingly, through null mutant analysis and cell-specific rescue experiments, we find that loss of hlh-15/NHLH in the peptidergic AVK neurons and the resulting abrogation of neuropeptide secretion causes a substantially expanded lifespan of the animal, revealing an unanticipated impact of a central, peptidergic hub neuron in regulating lifespan, which we propose to be akin to hypothalamic control of lifespan in vertebrates. Taken together, our functional analysis reveals themes of bHLH gene function during terminal differentiation that are complementary to the earlier lineage specification roles of other bHLH family members. However, such late functions are much more sparsely employed by members of the bHLH transcription factor family, compared to the function of the much more broadly employed homeodomain transcription factor family.

The neuron-specific IIS/FOXO transcriptome in aged animals reveals regulatory mechanisms of cognitive aging

Cognitive decline is a significant health concern in our aging society. Here, we used the model organism C. elegans to investigate the impact of the IIS/FOXO pathway on age-related cognitive decline. The daf-2 Insulin/IGF-1 receptor mutant exhibits a significant extension of learning and memory span with age compared to wild-type worms, an effect that is dependent on the DAF-16 transcription factor. To identify possible mechanisms by which aging daf-2 mutants maintain learning and memory with age while wild-type worms lose neuronal function, we carried out neuron-specific transcriptomic analysis in aged animals. We observed downregulation of neuronal genes and upregulation of transcriptional regulation genes in aging wild-type neurons. By contrast, IIS/FOXO pathway mutants exhibit distinct neuronal transcriptomic alterations in response to cognitive aging, including upregulation of stress response genes and downregulation of specific insulin signaling genes. We tested the roles of significantly transcriptionally-changed genes in regulating cognitive functions, identifying novel regulators of learning and memory. In addition to other mechanistic insights, a comparison of the aged vs young daf-2 neuronal transcriptome revealed that a new set of potentially neuroprotective genes is upregulated; instead of simply mimicking a young state, daf-2 may enhance neuronal resilience to accumulation of harm and take a more active approach to combat aging. These findings suggest a potential mechanism for regulating cognitive function with age and offer insights into novel therapeutic targets for age-related cognitive decline.

Screening for cold tolerance genes in C. elegans, whose expressions are affected by anticancer drugs camptothecin and leptomycin B

Temperature is a vital environmental factor affecting organisms' survival as they determine the mechanisms to tolerate rapid temperature changes. We demonstrate an experimental system for screening chemicals that affect cold tolerance in Caenorhabditis elegans. The anticancer drugs leptomycin B and camptothecin were among the 4000 chemicals that were screened as those affecting cold tolerance. Genes whose expression was affected by leptomycin B or camptothecin under cold stimuli were investigated by transcriptome analysis. Abnormal cold tolerance was detected in several mutants possessing genes that were rendered defective and whose expression altered after exposure to either leptomycin B or camptothecin. The genetic epistasis analysis revealed that leptomycin B or camptothecin may increase cold tolerance by affecting a pathway upstream of the insulin receptor DAF-2 that regulates cold tolerance in the intestine. Our experimental system combining drug and cold tolerance could be used for a comprehensive screening of genes that control cold tolerance at a low cost and in a short time period.

The evolution of entomopathogeny in nematodes

Understanding how parasites evolved is crucial to understand the host and parasite interaction. The evolution of entomopathogenesis in rhabditid nematodes has traditionally been thought to have occurred twice within the phylum Nematoda: in Steinernematidae and Heterorhabditidae families, which are associated with the entomopathogenic bacteria Xenorhabdus and Photorhabdus, respectively. However, nematodes from other families that are associated with entomopathogenic bacteria have not been considered to meet the criteria for "entomopathogenic nematodes." The evolution of parasitism in nematodes suggests that ecological and evolutionary properties shared by families in the order Rhabditida favor the convergent evolution of the entomopathogenic trait in lineages with diverse lifestyles, such as saprotrophs, phoretic, and necromenic nematodes. For this reason, this paper proposes expanding the term "entomopathogenic nematode" considering the diverse modes of this attribute within Rhabditida. Despite studies are required to test the authenticity of the entomopathogenic trait in the reported species, they are valuable links that represent the early stages of specialized lineages to entomopathogenic lifestyle. An ecological and evolutionary exploration of these nematodes has the potential to deepen our comprehension of the evolution of entomopathogenesis as a convergent trait spanning across the Nematoda.

Recent Progress in Regulation of Aging by Insulin/IGF-1 Signaling in Caenorhabditis elegans

Caenorhabditis elegans has been used as a major model organism to identify genetic factors that regulate organismal aging and longevity. Insulin/insulin-like growth factor 1 (IGF- 1) signaling (IIS) regulates aging in many species, ranging from nematodes to humans. C. elegans is a nonpathogenic genetic nematode model, which has been extensively utilized to identify molecular and cellular components that function in organismal aging and longevity. Here, we review the recent progress in the role of IIS in aging and longevity, which involves direct regulation of protein and RNA homeostasis, stress resistance, metabolism and the activities of the endocrine system. We also discuss recently identified genetic factors that interact with canonical IIS components to regulate aging and health span in C. elegans. We expect this review to provide valuable insights into understanding animal aging, which could eventually help develop anti-aging drugs for humans.

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.

The hypothalamus for whole-body physiology: from metabolism to aging

Obesity and aging are two important epidemic factors for metabolic syndrome and many other health issues, which contribute to devastating diseases such as cardiovascular diseases, stroke and cancers. The brain plays a central role in controlling metabolic physiology in that it integrates information from other metabolic organs, sends regulatory projections and orchestrates the whole-body function. Emerging studies suggest that brain dysfunction in sensing various internal cues or processing external cues may have profound effects on metabolic and other physiological functions. This review highlights brain dysfunction linked to genetic mutations, sex, brain inflammation, microbiota, stress as causes for whole-body pathophysiology, arguing brain dysfunction as a root cause for the epidemic of aging and obesity-related disorders. We also speculate key issues that need to be addressed on how to reveal relevant brain dysfunction that underlines the development of these disorders and diseases in order to develop new treatment strategies against these health problems.

A PTEN variant uncouples longevity from impaired fitness in Caenorhabditis elegans with reduced insulin/IGF-1 signaling

Insulin/IGF-1 signaling (IIS) regulates various physiological aspects in numerous species. In Caenorhabditis elegans, mutations in the daf-2/insulin/IGF-1 receptor dramatically increase lifespan and immunity, but generally impair motility, growth, and reproduction. Whether these pleiotropic effects can be dissociated at a specific step in insulin/IGF-1 signaling pathway remains unknown. Through performing a mutagenesis screen, we identified a missense mutation daf-18(yh1) that alters a cysteine to tyrosine in DAF-18/PTEN phosphatase, which maintained the long lifespan and enhanced immunity, while improving the reduced motility in adult daf-2 mutants. We showed that the daf-18(yh1) mutation decreased the lipid phosphatase activity of DAF-18/PTEN, while retaining a partial protein tyrosine phosphatase activity. We found that daf-18(yh1) maintained the partial activity of DAF-16/FOXO but restricted the detrimental upregulation of SKN-1/NRF2, contributing to beneficial physiological traits in daf-2 mutants. Our work provides important insights into how one evolutionarily conserved component, PTEN, can coordinate animal health and longevity.

Olfactory perception of food abundance regulates dietary restriction-mediated longevity via a brain-to-gut signal

The role of food nutrients in mediating the positive effect of dietary restriction (DR) on longevity has been extensively characterized, but how non-nutrient food components regulate lifespan is not well understood. Here, we show that food-associated odors shorten the lifespan of C. elegans under DR but not those fed ad libitum, revealing a specific effect of food odors on DR-mediated longevity. Food odors act on a neural circuit comprising the sensory neurons ADF and CEP, and the interneuron RIC. This olfactory circuit signals the gut to suppress DR-mediated longevity via octopamine, the invertebrate homolog of norepinephrine, by regulating the energy sensor AMPK through a Gq-PLCβ-CaMKK-dependent mechanism. In mouse primary cells, we find that norepinephrine signaling regulates AMPK through a similar mechanism. Our results identify a brain-gut axis that regulates DR-mediated longevity by relaying olfactory information about food abundance from the brain to the gut.

Diacetyl odor shortens longevity conferred by food deprivation in C. elegans via downregulation of DAF-16/FOXO

Dietary restriction extends lifespan in various organisms by reducing the levels of both nutrients and non‐nutritional food‐derived cues. However, the identity of specific food‐derived chemical cues that alter lifespan remains unclear. Here, we identified several volatile attractants that decreased the longevity on food deprivation, a dietary restriction regimen in Caenorhabditis elegans. In particular, we found that the odor of diacetyl decreased the activity of DAF‐16/FOXO, a life‐extending transcription factor acting downstream of insulin/IGF‐1 signaling. We then demonstrated that the odor of lactic acid bacteria, which produce diacetyl, reduced the nuclear accumulation of DAF‐16/FOXO. Unexpectedly, we showed that the odor of diacetyl decreased longevity independently of two established diacetyl receptors, ODR‐10 and SRI‐14, in sensory neurons. Thus, diacetyl, a food‐derived odorant, may shorten food deprivation‐induced longevity via decreasing the activity of DAF‐16/FOXO through binding to unidentified receptors.

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.

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.

mRNA decapping is an evolutionarily conserved modulator of neuroendocrine signaling that controls development and ageing

Eukaryotic 5'-3' mRNA decay plays important roles during development and in response to stress, regulating gene expression post-transcriptionally. In Caenorhabditis elegans, deficiency of DCAP-1/DCP1, the essential co-factor of the major cytoplasmic mRNA decapping enzyme, impacts normal development, stress survival and ageing. Here, we show that overexpression of dcap-1 in neurons of worms is sufficient to increase lifespan through the function of the insulin/IGF-like signaling and its effector DAF-16/FOXO transcription factor. Neuronal DCAP-1 affects basal levels of INS-7, an ageing-related insulin-like peptide, which acts in the intestine to determine lifespan. Short-lived dcap-1 mutants exhibit a neurosecretion-dependent upregulation of intestinal ins-7 transcription, and diminished nuclear localization of DAF-16/FOXO. Moreover, neuronal overexpression of DCP1 in Drosophila melanogaster confers longevity in adults, while neuronal DCP1 deficiency shortens lifespan and affects wing morphogenesis, cell non-autonomously. Our genetic analysis in two model-organisms suggests a critical and conserved function of DCAP-1/DCP1 in developmental events and lifespan modulation.

MALT-1 mediates IL-17 neural signaling to regulate C. elegans behavior, immunity and longevity

Besides pro-inflammatory roles, the ancient cytokine interleukin-17 (IL-17) modulates neural circuit function. We investigate IL-17 signaling in neurons, and the extent it can alter organismal phenotypes. We combine immunoprecipitation and mass spectrometry to biochemically characterize endogenous signaling complexes that function downstream of IL-17 receptors in C. elegans neurons. We identify the paracaspase MALT-1 as a critical output of the pathway. MALT1 mediates signaling from many immune receptors in mammals, but was not previously implicated in IL-17 signaling or nervous system function. C. elegans MALT-1 forms a complex with homologs of Act1 and IRAK and appears to function both as a scaffold and a protease. MALT-1 is expressed broadly in the C. elegans nervous system, and neuronal IL-17-MALT-1 signaling regulates multiple phenotypes, including escape behavior, associative learning, immunity and longevity. Our data suggest MALT1 has an ancient role modulating neural circuit function downstream of IL-17 to remodel physiology and behavior.

Neuronal Mechanisms that Drive Organismal Aging Through the Lens of Perception

Sensory neurons provide organisms with data about the world in which they live, for the purpose of successfully exploiting their environment. The consequences of sensory perception are not simply limited to decision-making behaviors; evidence suggests that sensory perception directly influences physiology and aging, a phenomenon that has been observed in animals across taxa. Therefore, understanding the neural mechanisms by which sensory input influences aging may uncover novel therapeutic targets for aging-related physiologies. In this review, we examine different perceptive experiences that have been most clearly linked to aging or age-related disease: food perception, social perception, time perception, and threat perception. For each, the sensory cues, receptors, and/or pathways that influence aging as well as the individual or groups of neurons involved, if known, are discussed. We conclude with general thoughts about the potential impact of this line of research on human health and aging.

Neuronal TORC1 modulates longevity via AMPK and cell nonautonomous regulation of mitochondrial dynamics in C. elegans

Target of rapamycin complex 1 (TORC1) and AMP-activated protein kinase (AMPK) antagonistically modulate metabolism and aging. However, how they coordinate to determine longevity and if they act via separable mechanisms is unclear. Here, we show that neuronal AMPK is essential for lifespan extension from TORC1 inhibition, and that TORC1 suppression increases lifespan cell non autonomously via distinct mechanisms from global AMPK activation. Lifespan extension by null mutations in genes encoding raga-1 (RagA) or rsks-1 (S6K) is fully suppressed by neuronal-specific rescues. Loss of RAGA-1 increases lifespan via maintaining mitochondrial fusion. Neuronal RAGA-1 abrogation of raga-1 mutant longevity requires UNC-64/syntaxin, and promotes mitochondrial fission cell nonautonomously. Finally, deleting the mitochondrial fission factor DRP-1 renders the animal refractory to the pro-aging effects of neuronal RAGA-1. Our results highlight a new role for neuronal TORC1 in cell nonautonomous regulation of longevity, and suggest TORC1 in the central nervous system might be targeted to promote healthy aging.

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.

Ascaroside Pheromones: Chemical Biology and Pleiotropic Neuronal Functions

Pheromones are neuronal signals that stimulate conspecific individuals to react to environmental stressors or stimuli. Research on the ascaroside (ascr) pheromones in Caenorhabditis elegans and other nematodes has made great progress since ascr#1 was first isolated and biochemically defined in 2005. In this review, we highlight the current research on the structural diversity, biosynthesis, and pleiotropic neuronal functions of ascr pheromones and their implications in animal physiology. Experimental evidence suggests that ascr biosynthesis starts with conjugation of ascarylose to very long-chain fatty acids that are then processed via peroxisomal β-oxidation to yield diverse ascr pheromones. We also discuss the concentration and stage-dependent pleiotropic neuronal functions of ascr pheromones. These functions include dauer induction, lifespan extension, repulsion, aggregation, mating, foraging and detoxification, among others. These roles are carried out in coordination with three G protein-coupled receptors that function as putative pheromone receptors: SRBC-64/66, SRG-36/37, and DAF-37/38. Pheromone sensing is transmitted in sensory neurons via DAF-16-regulated glutamatergic neurotransmitters. Neuronal peroxisomal fatty acid β-oxidation has important cell-autonomous functions in the regulation of neuroendocrine signaling, including neuroprotection. In the future, translation of our knowledge of nematode ascr pheromones to higher animals might be beneficial, as ascr#1 has some anti-inflammatory effects in mice. To this end, we propose the establishment of pheromics (pheromone omics) as a new subset of integrated disciplinary research area within chemical ecology for system-wide investigation of animal pheromones.

KIN-4/MAST kinase promotes PTEN-mediated longevity of Caenorhabditis elegans via binding through a PDZ domain

PDZ domain‐containing proteins (PDZ proteins) act as scaffolds for protein–protein interactions and are crucial for a variety of signal transduction processes. However, the role of PDZ proteins in organismal lifespan and aging remains poorly understood. Here, we demonstrate that KIN‐4, a PDZ domain‐containing microtubule‐associated serine‐threonine (MAST) protein kinase, is a key longevity factor acting through binding PTEN phosphatase in Caenorhabditis elegans. Through a targeted genetic screen for PDZ proteins, we find that kin‐4 is required for the long lifespan of daf‐2/insulin/IGF‐1 receptor mutants. We then show that neurons are crucial tissues for the longevity‐promoting role of kin‐4. We find that the PDZ domain of KIN‐4 binds PTEN, a key factor for the longevity of daf‐2 mutants. Moreover, the interaction between KIN‐4 and PTEN is essential for the extended lifespan of daf‐2 mutants. As many aspects of lifespan regulation in C. elegans are evolutionarily conserved, MAST family kinases may regulate aging and/or age‐related diseases in mammals through their interaction with PTEN.

Prefoldin 6 mediates longevity response from heat shock factor 1 to FOXO in C. elegans

Heat shock factor 1 (HSF-1) and forkhead box O (FOXO) are key transcription factors that protect cells from various stresses. In Caenorhabditis elegans, HSF-1 and FOXO together promote a long life span when insulin/IGF-1 signaling (IIS) is reduced. However, it remains poorly understood how HSF-1 and FOXO cooperate to confer IIS-mediated longevity. Here, we show that prefoldin 6 (PFD-6), a component of the molecular chaperone prefoldin-like complex, relays longevity response from HSF-1 to FOXO under reduced IIS. We found that PFD-6 was specifically required for reduced IIS-mediated longevity by acting in the intestine and hypodermis. We showed that HSF-1 increased the levels of PFD-6 proteins, which in turn directly bound FOXO and enhanced its transcriptional activity. Our work suggests that the prefoldin-like chaperone complex mediates longevity response from HSF-1 to FOXO to increase the life span in animals with reduced IIS.

Emerging topics in C. elegans aging research: Transcriptional regulation, stress response and epigenetics

Key discoveries in aging research have been made possible with the use of model organisms. Caenorhabditis elegans is a short-lived nematode that has become a well-established system to study aging. The practicality and powerful genetic manipulations associated with this metazoan have revolutionized our ability to understand how organisms age. 25 years after the publication of the discovery of the daf-2 gene as a genetic modifier of lifespan, C. elegans remains as relevant as ever in the quest to understand the process of aging. Nematode aging research has proven useful in identifying transcriptional regulators, small molecule signals, cellular mechanisms, epigenetic modifications associated with stress resistance and longevity, and lifespan-extending compounds. Here, we review recent discoveries and selected topics that have emerged in aging research using this incredible little worm.

Brain-gut communications via distinct neuroendocrine signals bidirectionally regulate longevity in C. elegans

Zhang et al. identified two distinct neuroendocrine signaling circuits by which the worm nervous system senses cool and warm environmental temperatures through cool- and warm-sensitive neurons and then signals the gut to extend and shorten life span, respectively.

Tissue–tissue communications are integral to organismal aging, orchestrating a body-wide aging process. The brain plays a key role in this process by detecting and processing signals from the environment and then communicating them to distal tissues such as the gut to regulate longevity. How this is achieved, however, is poorly understood. Here, using Caenorhabditis elegans as a model, we identified two distinct neuroendocrine signaling circuits by which the worm nervous system senses cool and warm environmental temperatures through cool- and warm-sensitive neurons and then signals the gut to extend and shorten life span, respectively. The prolongevity “cool” circuit uses the small neurotransmitters glutamate and serotonin, whereas the anti-longevity “warm” circuit is mediated by insulin-like neuropeptides. Both types of neuroendocrine signals converge on the gut through their cognate receptors to differentially regulate the transcription factor DAF-16/FOXO, leading to opposing outcomes in longevity. Our study illustrates how the brain detects and processes environmental signals to bidirectionally regulate longevity by signaling the gut.

C. elegans Locomotion: Finding Balance in Imbalance

The excitation-inhibition (E-I) imbalance in neural circuits represents a hallmark of several neuropsychiatric disorders. The tiny nematode Caenorhabditis elegans has emerged as an excellent system to study the molecular mechanisms underlying this imbalance in neuronal circuits. The C. elegans body wall muscles receive inputs from both excitatory cholinergic and inhibitory GABAergic motor neurons at neuromuscular junctions (NMJ), making it an excellent model for studying the genetic and molecular mechanisms required for maintaining E-I balance at the NMJ. The cholinergic neurons form dyadic synapses wherein they synapse onto ipsilateral body wall muscles allowing for muscle contraction as well as onto GABAergic motor neurons that in turn synapse on the contralateral body wall muscles causing muscle relaxation. An alternating wave of contraction and relaxation mediated by excitatory and inhibitory signals maintains locomotion in C. elegans. This locomotory behavior requires an intricate balance between the excitatory cholinergic signaling and the inhibitory GABAergic signaling mechanisms.Studies on the C. elegans NMJ have provided insights into several molecular mechanisms that could regulate this balance in neural circuits. This review provides a discussion on multiple genetic factors including neuropeptides and their receptors, cell adhesion molecules, and other molecular pathways that have been associated with maintaining E-I balance in C. elegans motor circuits. Further, it also discusses the implications of these studies that could help us in understanding the role of E-I balance in mammalian neural circuits and how changes in this balance could give rise to brain disorders.

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.

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.

RNA surveillance via nonsense-mediated mRNA decay is crucial for longevity in daf-2/insulin/IGF-1 mutant C. elegans

Long-lived organisms often feature more stringent protein and DNA quality control. However, whether RNA quality control mechanisms, such as nonsense-mediated mRNA decay (NMD), which degrades both abnormal as well as some normal transcripts, have a role in organismal aging remains unexplored. Here we show that NMD mediates longevity in C. elegans strains with mutations in daf-2/insulin/insulin-like growth factor 1 receptor. We find that daf-2 mutants display enhanced NMD activity and reduced levels of potentially aberrant transcripts. NMD components, including smg-2/UPF1, are required to achieve the longevity of several long-lived mutants, including daf-2 mutant worms. NMD in the nervous system of the animals is particularly important for RNA quality control to promote longevity. Furthermore, we find that downregulation of yars-2/tyrosyl-tRNA synthetase, an NMD target transcript, by daf-2 mutations contributes to longevity. We propose that NMD-mediated RNA surveillance is a crucial quality control process that contributes to longevity conferred by daf-2 mutations.

Age-Dependent Neuroendocrine Signaling from Sensory Neurons Modulates the Effect of Dietary Restriction on Longevity of Caenorhabditis elegans

Dietary restriction extends lifespan in evolutionarily diverse animals. A role for the sensory nervous system in dietary restriction has been established in Drosophila and Caenorhabditis elegans, but little is known about how neuroendocrine signals influence the effects of dietary restriction on longevity. Here, we show that DAF-7/TGFβ, which is secreted from the C. elegans amphid, promotes lifespan extension in response to dietary restriction in C. elegans. DAF-7 produced by the ASI pair of sensory neurons acts on DAF-1/TGFβ receptors expressed on interneurons to inhibit the co-SMAD DAF-3. We find that increased activity of DAF-3 in the presence of diminished or deleted DAF-7 activity abrogates lifespan extension conferred by dietary restriction. We also observe that DAF-7 expression is dynamic during the lifespan of C. elegans, with a marked decrease in DAF-7 levels as animals age during adulthood. We show that this age-dependent diminished expression contributes to the reduced sensitivity of aging animals to the effects of dietary restriction. DAF-7 signaling is a pivotal regulator of metabolism and food-dependent behavior, and our studies establish a molecular link between the neuroendocrine physiology of C. elegans and the process by which dietary restriction can extend lifespan.

Reductions in food intake have long been observed to improve longevity, extending lifespan in many evolutionarily divergent organisms. While great progress has been made in identifying the mechanisms by which nutritional interventions act to delay the aging process, much remains unclear. Particularly, while work in multiple species has found evidence that the sensation of food availability by the nervous system contributes to lifespan extension in response to reduced food levels, little is known about how these contributions are executed. Here, we have characterized how a specific neuroendocrine peptide, expressed in a set of sensory neurons, responds to changes in food conditions to modulate lifespan effects of dietary restriction at the organismal level. We further find that age-related changes in expression of this neuroendocrine signal contribute to the declining efficacy of nutritional interventions as animals get older. This work highlights the importance of neuroendocrine regulation in both the aging process and in treatments aimed at increasing longevity.