Regulation of the cellular heat shock response in Caenorhabditis elegans by thermosensory neurons

CaMK modulates sensory neural activity to control longevity and proteostasis

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

Reticulon-dependent ER-phagy mediates adaptation to heat stress in C. elegans

The selective degradation of endoplasmic reticulum (ER) by autophagy, named ER-phagy, promotes the recovery of ER homeostasis after stress. Depending on the ER stress, different types of ER-phagy involve various selective autophagy receptors. In this study, we report a macroER-phagy induced by the fragmentation of tubular ER in response to acute heat stress. We identified a novel ER-phagy receptor encoded by the reticulon long isoform RET-1d. RET-1d is mainly expressed in the nervous system and the epidermis and colocalizes with the ubiquitin-like autophagy protein LGG-1/GABARAP during heat-stress-induced autophagy. Two LC3-interacting region (LIR) motifs in the long intrinsically disordered region of RET-1d mediate its interaction with the LGG-1 protein. The specific depletion of the RET-1d isoform or the mutations of the LIRs resulted in a defective ER-phagy and a decrease in the capacity of animals to adapt to heat stress. Our data revealed a RET-1d- and LGG-1-dependent ER-phagy mechanism that takes place in neurons and epidermis and participates in the adaptation of C. elegans to heat stress.

Beyond genes and environment: mapping biological stochasticity in aging

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

Role of HSF1 in cell division, tumorigenesis and therapy: a literature review

Heat shock factor 1 (HSF1) is the master orchestrator of the heat shock response (HSR), a critical process for maintaining cellular health and protein homeostasis. These effects are achieved through rapid expression of molecular chaperones, the heat shock proteins (HSPs), which ensure correct protein folding, repair, degradation and stabilization of multiprotein complexes. In addition to its role in the HSR, HSF1 influences the cell cycle, including processes such as S phase progression and regulation of the p53 pathway, highlighting its importance in cellular protein synthesis and division. While HSF1 activity offers neuroprotective benefits in neurodegenerative diseases, its proteome-stabilizing function may also reinforce tumorigenic transformation. HSF1 overexpression in many types of cancer reportedly enhances cell growth enables survival, alters metabolism, weakens immune response and promotes angiogenesis or epithelial-mesenchymal transition (EMT) as these cells enter a form of "HSF1 addiction". Furthermore, the client proteins of HSF1-regulated chaperones, particularly Hsp90, include numerous key players in classical tumorigenic pathways. HSF1 thus presents a promising therapeutic target for cancer treatment, potentially in combination with HSP inhibitors to alleviate typical initiation of HSR upon their use.

Human Strongyloides stercoralis infection

Strongyloides stercoralis is an important soil-transmitted helminth occurring world-wide and affecting 30-100 million people. Because many cases are asymptomatic and sensitive diagnostic methods are lacking, S. stercoralis infection is frequently underdiagnosed. The increasing incidence of autoimmune and wasting diseases and increased use of immunosuppressive agents, as well as the increased use of immunosuppressants and cytotoxic drugs, have increased S. stercoralis infection and their mortality. This review provides information about S. stercoralis epidemiology, life cycle, aetiology, pathology, comorbidities, immunology, vaccines, diagnosis, treatment, prevention, control and makes some recommendations for future prevention and control of this important parasite.

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

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

Temperature Acclimation and Cold Tolerance in Caenorhabditis Elegans are Regulated by Multiorgan Coordination

To ensure survival and reproduction, organisms must continually adapt to environmental fluctuations, such as temperature, humidity, oxygen level, and salinity. Particularly, temperature profoundly influences biochemical reactions crucial for survival. Here, we present the mechanisms employed by the nematode Caenorhabditis elegans to anticipate and respond to cold temperatures. Our findings reveal that temperature is detected by specific neurons linked to various physiological processes in the gut, spermatheca, and muscles. Notably, the gut, a primary fat storage organ in C. elegans, regulates fat mobilization and accumulation in a temperature-dependent manner, thereby contributing to temperature adaptation. Furthermore, normal spermatogenetic mechanisms influence cold tolerance by modulating the responsiveness of thermosensory neurons to temperature changes. Considering our results together with recent reports, we suggest that a polyU-specific endoribonuclease expressed in muscle cells plays a role in cold tolerance through a non-cell-autonomous mechanism, possibly involving transportation intertissues. Thus, understanding cold tolerance and temperature acclimation in C. elegans can provide valuable insights on systemic physiological regulation in response to temperature fluctuations. Moreover, they could help elucidate the actions of thermosensory neurons and their downstream neuronal circuits or neuropeptides on the peripheral organs.

Assessment of developmental neurotoxicology-associated alterations in neuronal architecture and function using Caenorhabditis elegans

Few of the many chemicals that regulatory agencies are charged with assessing for risk have been carefully tested for developmental neurotoxicity (DNT). To speed up testing efforts, as well as to reduce the use of vertebrate animals, great effort is being devoted to alternate laboratory models for testing DNT. A major mechanism of DNT is altered neuronal architecture resulting from chemical exposure during neurodevelopment. Caenorhabditis elegans is a nematode that has been extensively studied by neurobiologists and developmental biologists, and to a lesser extent by neurotoxicologists. The developmental trajectory of the nervous system in C. elegans is easily visualized, normally entirely invariant, and fully mapped. Therefore, we hypothesized that C. elegans could be a powerful in vivo model to test chemicals for the potential to alter developmental patterning of neuronal architecture. To test whether this might be true, we developed a novel C. elegans DNT testing paradigm that includes exposure throughout development, examines all major neurotransmitter neuronal types for architectural alterations, and tests behaviors specific to dopaminergic, cholinergic, and glutamatergic functions. We used this paradigm to characterize the effects of early-life exposures to the developmental neurotoxicants lead, cadmium, and benzo(a)pyrene (BaP) on dopaminergic, cholinergic, and glutamatergic architecture. We also assessed whether exposures would alter neuronal specification as assessed by expression of reporter genes diagnostic of specific neurotransmitters. We identified no cases in which the apparent neurotransmitter type of the neurons we examined changed, but many in which neuronal morphology was altered. We also found that neuron-specific behaviors were altered during C. elegans mid-adulthood for populations with measured morphological neurodegeneration in earlier stages. The functional changes were consistent with the morphological changes we observed in terms of type of neuron affected. We identified changes consistent with those reported in the mammalian DNT literature, strengthening the case for C. elegans as a DNT model, and made novel observations that should be followed up in future studies.

MONITTR allows real-time imaging of transcription and endogenous proteins in C. elegans

Maximizing cell survival under stress requires rapid and transient adjustments of RNA and protein synthesis. However, capturing these dynamic changes at both single-cell level and across an organism has been challenging. Here, we developed a system named MONITTR (MS2-embedded mCherry-based monitoring of transcription) for real-time simultaneous measurement of nascent transcripts and endogenous protein levels in C. elegans. Utilizing this system, we monitored the transcriptional bursting of fasting-induced genes and found that the epidermis responds to fasting by modulating the proportion of actively transcribing nuclei and transcriptional kinetics of individual alleles. Additionally, our findings revealed the essential roles of the transcription factors NHR-49 and HLH-30 in governing the transcriptional kinetics of fasting-induced genes under fasting. Furthermore, we tracked transcriptional dynamics during heat-shock response and ER unfolded protein response and observed rapid changes in the level of nascent transcripts under stress conditions. Collectively, our study provides a foundation for quantitatively investigating how animals spatiotemporally modulate transcription in various physiological and pathological conditions.

The neurohormone tyramine stimulates the secretion of an insulin-like peptide from the Caenorhabditis elegans intestine to modulate the systemic stress response

The DAF-2/insulin/insulin-like growth factor signaling (IIS) pathway plays an evolutionarily conserved role in regulating reproductive development, life span, and stress resistance. In Caenorhabditis elegans, DAF-2/IIS signaling is modulated by an extensive array of insulin-like peptides (ILPs) with diverse spatial and temporal expression patterns. However, the release dynamics and specific functions of these ILPs in adapting to different environmental conditions remain poorly understood. Here, we show that the ILP, insulin-3 (INS-3), plays a crucial role in modulating the response to various environmental stressors in C. elegans. ins-3 mutants display increased resistance to heat, oxidative stress, and starvation; however, this advantage is countered by slower reproductive development under favorable conditions. We find that ins-3 expression is downregulated in response to environmental stressors, whereas, the neurohormone tyramine, which is released during the acute flight response, increases ins-3 expression. We show that tyramine induces intestinal calcium (Ca2+) transients through the activation of the TYRA-3 receptor. Our data support a model in which tyramine negatively impacts environmental stress resistance by stimulating the release of INS-3 from the intestine via the activation of a TYRA-3-Gαq-IP3 pathway. The release of INS-3 systemically activates the DAF-2 pathway, resulting in the inhibition of cytoprotective mechanisms mediated by DAF-16/FOXO. These studies offer mechanistic insights into a brain-gut communication pathway that weighs adaptive strategies to respond to acute and long-term stressors.

Temperature perception by ER UPR promotes preventive innate immunity and longevity

Microbial infectivity increases with rising environmental temperature, heightening the risk of infection to host organisms. The host's basal immunity is activated accordingly to mitigate upcoming pathogenic threats; still, how animals sense temperature elevation to adjust their preventive immune response remains elusive. This study reports that high temperature enhances innate immunity differently from pathogen infection. Unlike pathogen invasion requiring the mitochondrial unfolded protein response (UPR), high temperature engages the endoplasmic reticulum (ER) UPR to trigger the innate immune response. Furthermore, chronic activation of the XBP-1 UPR branch represses nucleolar ribosome biogenesis, a highly energy-consuming process, leading to lipid accumulation. The subsequent increase in oleic acid promotes the activation of the PMK-1 immune pathway. Additionally, ribosome biogenesis was identified as a regulator of longevity, wherein its impact is dependent on lipid metabolism and innate immunity. Collectively, our findings reveal the crucial role of ER-nucleolus crosstalk in shaping preventive immune responses and lifespan regulation.

Endogenous hydrogen peroxide positively regulates secretion of a gut-derived peptide in neuroendocrine potentiation of the oxidative stress response in Caenorhabditis elegans

The gut-brain axis mediates bidirectional signaling between the intestine and the nervous system and is critical for organism-wide homeostasis. Here, we report the identification of a peptidergic endocrine circuit in which bidirectional signaling between neurons and the intestine potentiates the activation of the antioxidant response in Caenorhabditis elegans in the intestine. We identify an FMRF-amide-like peptide, FLP-2, whose release from the intestine is necessary and sufficient to activate the intestinal oxidative stress response by promoting the release of the antioxidant FLP-1 neuropeptide from neurons. FLP-2 secretion from the intestine is positively regulated by endogenous hydrogen peroxide (H2O2) produced in the mitochondrial matrix by sod-3/superoxide dismutase, and is negatively regulated by prdx-2/peroxiredoxin, which depletes H2O2 in both the mitochondria and cytosol. H2O2 promotes FLP-2 secretion through the DAG and calcium-dependent protein kinase C family member pkc-2 and by the SNAP25 family member aex-4 in the intestine. Together, our data demonstrate a role for intestinal H2O2 in promoting inter-tissue antioxidant signaling through regulated neuropeptide-like protein exocytosis in a gut-brain axis to activate the oxidative stress response.

Resolving transitions between distinct phases of memory consolidation at high resolution in Caenorhabditis elegans

Memory consolidation following learning is a dynamic and complex process comprising several transitions between distinct memory phases. Although memory consolidation has been studied extensively, it remains difficult to draw an integral description that can delimit the transition points between specific memory phases at the behavioral, neuronal, and genetic levels. To this end, we have developed a rapid and robust aversive conditioning protocol for the nematode worm Caenorhabditis elegans, tracing memory consolidation within the first hour post conditioning and then up to 18 h post conditioning. This made it possible to uncover time-dependent involvement of primary sensory neurons, transcription and translation processes, and diverse gene populations in memory consolidation. The change in neuronal valence was strong enough to induce second order conditioning, and was amenable to considerable modulation in specific mutant strains. Together, our work lends memory consolidation to detailed temporal and spatial analysis, advancing system-wide understanding of learning and memory.

Bakuchiol modulates acetylcholine synthesis and alleviates Aβ proteotoxicity

The transmission of acetylcholine (ACh) is critically important for memory, learning, and behaviour. The most promising approaches for the treatment of cholinergic dysfunction involve the enhancement of ACh via nootropic phytomolecules. In the same line, the present study identifies the active molecule Bakuchiol derived from Psoralea corylifolia. Bakuchiol demonstrated significant elevation of ACh transmission, reduction of reactive oxygen species (ROS) levels, and extension of lifespan. Further investigation indicated that modulation of mRNA expression of genes encoding choline transporter, choline acetyltransferase, and acetylcholine transporter as possible effectors of amassed neural transmission. Moreover, Bakuchiol showed efficacy in reducing amyloid β and lipid levels, possibly through the upregulation of heat shock transcription factor 1 (hsf-1) and autophagy (lgg-1) genes. Overall, our findings establish the efficacy of Bakuchiol in modulating cholinergic dysfunction.

Temperature-controlled molecular switches in mammalian cells

Temperature is an omnipresent factor impacting on many aspects of life. In bacteria and ectothermic eukaryotes, various thermosensors and temperature-controlled switches have been described, ranging from RNA thermometers controlling the heat shock response in prokaryotes to temperature-dependent sex determination in reptiles, likely controlled through protein phosphorylation. However, the impact of subtle changes of human core body temperature are only beginning to be acknowledged. In this review, we will discuss thermosensing mechanisms and their functional implications with a focus on mammalian cells, also in the context of disease conditions. We will point out open questions and possible future directions for this emerging research field, which, in addition to molecular-mechanistic insights, holds the potential for the development of new therapeutic approaches.

Age-dependent heat shock hormesis to HSF-1 deficiency suggests a compensatory mechanism mediated by the unfolded protein response and innate immunity in young Caenorhabditis elegans

The transcription factor HSF-1 (heat shock factor 1) acts as a master regulator of heat shock response in eukaryotic cells to maintain cellular proteostasis. The protein has a protective role in preventing cells from undergoing ageing, and neurodegeneration, and also mediates tumorigenesis. Thus, modulating HSF-1 activity in humans has a promising therapeutic potential for treating these pathologies. Loss of HSF-1 function is usually associated with impaired stress tolerance. Contrary to this conventional knowledge, we show here that inactivation of HSF-1 in the nematode Caenorhabditis elegans results in increased thermotolerance at young adult stages, whereas HSF-1 deficiency in animals passing early adult stages indeed leads to decreased thermotolerance, as compared to wild-type. Furthermore, a gene expression analysis supports that in young adults, distinct cellular stress response and immunity-related signaling pathways become induced upon HSF-1 deficiency. We also demonstrate that increased tolerance to proteotoxic stress in HSF-1-depleted young worms requires the activity of the unfolded protein response of the endoplasmic reticulum and the SKN-1/Nrf2-mediated oxidative stress response pathway, as well as an innate immunity-related pathway, suggesting a mutual compensatory interaction between HSF-1 and these conserved stress response systems. A similar compensatory molecular network is likely to also operate in higher animal taxa, raising the possibility of an unexpected outcome when HSF-1 activity is manipulated in humans.

Endogenous hydrogen peroxide positively regulates secretion of a gut-derived peptide in neuroendocrine potentiation of the oxidative stress response in C. elegans

The gut-brain axis mediates bidirectional signaling between the intestine and the nervous system and is critical for organism-wide homeostasis. Here we report the identification of a peptidergic endocrine circuit in which bidirectional signaling between neurons and the intestine potentiates the activation of the antioxidant response in C. elegans in the intestine. We identify a FMRF-amide-like peptide, FLP-2, whose release from the intestine is necessary and sufficient to activate the intestinal oxidative stress response by promoting the release of the antioxidant FLP-1 neuropeptide from neurons. FLP-2 secretion from the intestine is positively regulated by endogenous hydrogen peroxide (H2O2) produced in the mitochondrial matrix by sod-3/superoxide dismutase, and is negatively regulated by prdx-2/peroxiredoxin, which depletes H2O2 in both the mitochondria and cytosol. H2O2 promotes FLP-2 secretion through the DAG and calciumdependent protein kinase C family member pkc-2 and by the SNAP25 family member aex-4 in the intestine. Together, our data demonstrate a role for intestinal H2O2 in promoting inter-tissue antioxidant signaling through regulated neuropeptide-like protein exocytosis in a gut-brain axis to activate the oxidative stress response.

Neuronal CBP-1 is Required for Enhanced Body Muscle Proteostasis in Response to Reduced Translation Downstream of mTOR

BACKGROUND

The ability to maintain muscle function decreases with age and loss of proteostatic function. Diet, drugs, and genetic interventions that restrict nutrients or nutrient signaling help preserve long-term muscle function and slow age-related decline. Previously, it was shown that attenuating protein synthesis downstream of the mechanistic target of rapamycin (mTOR) gradually increases expression of heat shock response (HSR) genes in a manner that correlates with increased resilience to protein unfolding stress. Here, we investigate the role of specific tissues in mediating the cytoprotective effects of low translation.

METHODS

This study uses genetic tools (transgenic Caenorhabditis elegans (C. elegans), RNA interference and gene expression analysis) as well as physiological assays (survival and paralysis assays) in order to better understand how specific tissues contribute to adaptive changes involving cellular cross-talk that enhance proteostasis under low translation conditions.

RESULTS

We use the C. elegans system to show that lowering translation in neurons or the germline increases heat shock gene expression and survival under conditions of heat stress. In addition, we find that low translation in these tissues protects motility in a body muscle-specific model of proteotoxicity that results in paralysis. Low translation in neurons or germline also results in increased expression of certain muscle regulatory and structural genes, reversing reduced expression normally observed with aging in C. elegans. Enhanced resilience to protein unfolding stress requires neuronal expression of cbp-1.

CONCLUSIONS

Low translation in either neurons or the germline orchestrate protective adaptation in other tissues, including body muscle.

Protein folding, cellular stress and cancer

Proteins are acknowledged as the phenotypical manifestation of the genotype, because protein-coding genes carry the information for the strings of amino acids that constitute the proteins. It is widely accepted that protein function depends on the corresponding "native" structure or folding achieved within the cell, and that native protein folding corresponds to the lowest free energy minimum for a given protein. However, protein folding within the cell is a non-deterministic dissipative process that from the same input may produce different outcomes, thus conformational heterogeneity of folded proteins is the rule and not the exception. Local changes in the intracellular environment promote variation in protein folding. Hence protein folding requires "supervision" by a host of chaperones and co-chaperones that help their client proteins to achieve the folding that is most stable according to the local environment. Such environmental influence on protein folding is continuously transduced with the help of the cellular stress responses (CSRs) and this may lead to changes in the rules of engagement between proteins, so that the corresponding protein interactome could be modified by the environment leading to an alternative cellular phenotype. This allows for a phenotypic plasticity useful for adapting to sudden and/or transient environmental changes at the cellular level. Starting from this perspective, hereunder we develop the argument that the presence of sustained cellular stress coupled to efficient CSRs may lead to the selection of an aberrant phenotype as the resulting adaptation of the cellular proteome (and the corresponding interactome) to such stressful conditions, and this can be a common epigenetic pathway to cancer.

CUL-6/cullin ubiquitin ligase-mediated degradation of HSP-90 by intestinal lysosomes promotes thermotolerance

Heat shock can be a lethal stressor. Previously, we described a CUL-6/cullin-ring ubiquitin ligase complex in the nematode Caenorhabditis elegans that is induced by intracellular intestinal infection and proteotoxic stress and that promotes improved survival upon heat shock (thermotolerance). Here, we show that CUL-6 promotes thermotolerance by targeting the heat shock protein HSP-90 for degradation. We show that CUL-6-mediated lowering of HSP-90 protein levels, specifically in the intestine, improves thermotolerance. Furthermore, we show that lysosomal function is required for CUL-6-mediated promotion of thermotolerance and that CUL-6 directs HSP-90 to lysosome-related organelles upon heat shock. Altogether, these results indicate that a CUL-6 ubiquitin ligase promotes organismal survival upon heat shock by promoting HSP-90 degradation in intestinal lysosomes. Thus, HSP-90, a protein commonly associated with protection against heat shock and promoting degradation of other proteins, is itself degraded to protect against heat shock.

Degrees of freedom: temperature's influence on developmental rate

Temperature exerts a fundamental influence across scales of biology, from the biophysical nature of molecules, to the sensitivity of cells, and the coordinated progression of development in embryos. Species-specific developmental rates and temperature-induced acceleration of development indicate that these sensing mechanisms are harnessed to influence developmental dynamics. Tracing how temperature sensitivity propagates through biological scales to influence the pace of development can therefore reveal how embryogenesis remains robust to environmental influences. Cellular protein homeostasis (proteostasis), and cellular metabolic rate are linked to both temperature-induced and species-specific developmental tempos in specific cell types, hinting toward generalized mechanisms of timing control. New methods to extract timing information from single-cell profiling experiments are driving further progress in understanding how mechanisms of temperature sensitivity can direct cell-autonomous responses, coordination across cell types, and evolutionary modifications of developmental timing.

Neuronal CBP-1 is required for enhanced body muscle proteostasis in response to reduced translation downstream of mTOR

Background

The ability to maintain muscle function decreases with age and loss of proteostatic function. Diet, drugs, and genetic interventions that restrict nutrients or nutrient signaling help preserve long-term muscle function and slow age-related decline. Previously, it was shown that attenuating protein synthesis downstream of the mechanistic target of rapamycin (mTOR) gradually increases expression of heat shock response (HSR) genes in a manner that correlates with increased resilience to protein unfolding stress. Here, we investigate the role of specific tissues in mediating the cytoprotective effects of low translation.

Methods

This study uses genetic tools (transgenic C. elegans , RNA interference and gene expression analysis) as well as physiological assays (survival and paralysis assays) in order to better understand how specific tissues contribute to adaptive changes involving cellular cross-talk that enhance proteostasis under low translation conditions.

Results

We use the C. elegans system to show that lowering translation in neurons or the germline increases heat shock gene expression and survival under conditions of heat stress. In addition, we find that low translation in these tissues protects motility in a body muscle-specific model of proteotoxicity that results in paralysis. Low translation in neurons or germline also results in increased expression of certain muscle regulatory and structural genes, reversing reduced expression normally observed with aging in C. elegans . Enhanced resilience to protein unfolding stress requires neuronal expression of cbp-1 .

Conclusion

Low translation in either neurons or the germline orchestrate protective adaptation in other tissues, including body muscle.

Heat shock and thermotolerance in Caenorhabditis elegans: An overview of laboratory techniques

The soil nematode worm Caenorhabditis elegans is a simple and well-established model for the study of many biological processes. Heat shock and thermotolerance assays have been developed for this nematode, and have been used to decipher the molecular relationships between thermal stress and aging, among others. Nevertheless, a systematic and methodological comparison of the different approaches and tools utilized is lacking in the literature. Here, we aim to provide a comprehensive summary of the most commonly used strategies for carrying out heat shock and thermotolerance assays that have been reported, highlighting specific readouts and scientific questions that can be addressed. Furthermore, we offer examples of thermotolerance assays performed with wild type nematodes, that can serve as a gauge of the animal survival under diverse conditions of stress.

Dendrobium Nobile Alcohol Extract Extends the Lifespan of Caenorhabditis elegans via hsf-1 and daf-16

Dendrobium nobile is a traditional Chinese herb with anti-inflammatory, antioxidant, and neuroprotective properties. However, its antiaging effects are unclear. Herein, we studied the aging-related functions and the mechanism of action of the alcohol extract of Dendrobium nobile (DnAE) in the model organism Caenorhabditis elegans. The results indicated that 1 mg/mL DnAE slowed lipofuscin accumulation, decreased the levels of reactive oxygen species, elevated superoxide dismutase activity, enhanced oxidative and heat stress resistance, extended the lifespan of nematodes, protected their dopamine neurons from 6-hydroxydopamine-induced neurodegeneration, and reduced Aβ-induced neurotoxicity. DnAE upregulated the mRNA expression of the transcription factors DAF-16 and HSF-1, promoted the nuclear localization of DAF-16, and enhanced the fluorescence intensity of HSP-16.2. However, it had no effect on the lifespan of DAF-16 mutants. Thus, DnAE can significantly extend lifespan, enhance heat stress tolerance, and delay age-related diseases through a DAF-16-dependent pathway.

Mitochondrial recovery by the UPRmt: Insights from C. elegans

Mitochondria are multifaceted organelles, with such functions as the production of cellular energy to the regulation of cell death. However, mitochondria incur various sources of damage from the accumulation of reactive oxygen species and DNA mutations that can impact the protein folding environment and impair their function. Since mitochondrial dysfunction is often associated with reductions in organismal fitness and possibly disease, cells must have safeguards in place to protect mitochondrial function and promote recovery during times of stress. The mitochondrial unfolded protein response (UPRmt) is a transcriptional adaptation that promotes mitochondrial repair to aid in cell survival during stress. While the earlier discoveries into the regulation of the UPRmt stemmed from studies using mammalian cell culture, much of our understanding about this stress response has been bestowed to us by the model organism Caenorhabditis elegans. Indeed, the facile but powerful genetics of this relatively simple nematode has uncovered multiple regulators of the UPRmt, as well as several physiological roles of this stress response. In this review, we will summarize these major advancements originating from studies using C. elegans.

Heat shock response during the resolution of inflammation and its progressive suppression in chronic-degenerative inflammatory diseases

The heat shock response (HSR) is a crucial biochemical pathway that orchestrates the resolution of inflammation, primarily under proteotoxic stress conditions. This process hinges on the upregulation of heat shock proteins (HSPs) and other chaperones, notably the 70 kDa family of heat shock proteins, under the command of the heat shock transcription factor-1. However, in the context of chronic degenerative disorders characterized by persistent low-grade inflammation (such as insulin resistance, obesity, type 2 diabetes, nonalcoholic fatty liver disease, and cardiovascular diseases) a gradual suppression of the HSR does occur. This work delves into the mechanisms behind this phenomenon. It explores how the Western diet and sedentary lifestyle, culminating in the endoplasmic reticulum stress within adipose tissue cells, trigger a cascade of events. This cascade includes the unfolded protein response and activation of the NOD-like receptor pyrin domain-containing protein-3 inflammasome, leading to the emergence of the senescence-associated secretory phenotype and the propagation of inflammation throughout the body. Notably, the activation of the NOD-like receptor pyrin domain-containing protein-3 inflammasome not only fuels inflammation but also sabotages the HSR by degrading human antigen R, a crucial mRNA-binding protein responsible for maintaining heat shock transcription factor-1 mRNA expression and stability on heat shock gene promoters. This paper underscores the imperative need to comprehend how chronic inflammation stifles the HSR and the clinical significance of evaluating the HSR using cost-effective and accessible tools. Such understanding is pivotal in the development of innovative strategies aimed at the prevention and treatment of these chronic inflammatory ailments, which continue to take a heavy toll on global health and well-being.

Stress biology: Complexity and multifariousness in health and disease

Preserving and regulating cellular homeostasis in the light of changing environmental conditions or developmental processes is of pivotal importance for single cellular and multicellular organisms alike. To counteract an imbalance in cellular homeostasis transcriptional programs evolved, called the heat shock response, unfolded protein response, and integrated stress response, that act cell-autonomously in most cells but in multicellular organisms are subjected to cell-nonautonomous regulation. These transcriptional programs downregulate the expression of most genes but increase the expression of heat shock genes, including genes encoding molecular chaperones and proteases, proteins involved in the repair of stress-induced damage to macromolecules and cellular structures. Sixty-one years after the discovery of the heat shock response by Ferruccio Ritossa, many aspects of stress biology are still enigmatic. Recent progress in the understanding of stress responses and molecular chaperones was reported at the 12th International Symposium on Heat Shock Proteins in Biology, Medicine and the Environment in the Old Town Alexandria, VA, USA from 28th to 31st of October 2023.

Early-life stress triggers long-lasting organismal resilience and longevity via tetraspanin

Early-life stress experiences can produce lasting impacts on organismal adaptation and fitness. How transient stress elicits memory-like physiological effects is largely unknown. Here, we show that early-life thermal stress strongly up-regulates tsp-1, a gene encoding the conserved transmembrane tetraspanin in C. elegans. TSP-1 forms prominent multimers and stable web-like structures critical for membrane barrier functions in adults and during aging. Increased TSP-1 abundance persists even after transient early-life heat stress. Such regulation requires CBP-1, a histone acetyltransferase that facilitates initial tsp-1 transcription. Tetraspanin webs form regular membrane structures and mediate resilience-promoting effects of early-life thermal stress. Gain-of-function TSP-1 confers marked C. elegans longevity extension and thermal resilience in human cells. Together, our results reveal a cellular mechanism by which early-life thermal stress produces long-lasting memory-like impact on organismal resilience and longevity.

Early-life stress triggers long-lasting organismal resilience and longevity via tetraspanin

Early-life stress experiences can produce lasting impacts on organismal adaptation and fitness. How transient stress elicits memory-like physiological effects is largely unknown. Here we show that early-life thermal stress strongly up-regulates tsp-1, a gene encoding the conserved transmembrane tetraspanin in C. elegans. TSP-1 forms prominent multimers and stable web-like structures critical for membrane barrier functions in adults and during aging. The up-regulation of TSP-1 persists even after transient early-life stress. Such regulation requires CBP-1, a histone acetyl-transferase that facilitates initial tsp-1 transcription. Tetraspanin webs form regular membrane structures and mediate resilience-promoting effects of early-life thermal stress. Gain-of-function TSP-1 confers marked C. elegans longevity extension and thermal resilience in human cells. Together, our results reveal a cellular mechanism by which early-life thermal stress produces long-lasting memory-like impact on organismal resilience and longevity.

Proteostasis governs differential temperature sensitivity across embryonic cell types

Embryonic development is remarkably robust, but temperature stress can degrade its ability to generate animals with invariant anatomy. Phenotypes associated with environmental stress suggest that some cell types are more sensitive to stress than others, but the basis of this sensitivity is unknown. Here, we characterize hundreds of individual zebrafish embryos under temperature stress using whole-animal single-cell RNA sequencing (RNA-seq) to identify cell types and molecular programs driving phenotypic variability. We find that temperature perturbs the normal proportions and gene expression programs of numerous cell types and also introduces asynchrony in developmental timing. The notochord is particularly sensitive to temperature, which we map to a specialized cell type: sheath cells. These cells accumulate misfolded protein at elevated temperature, leading to a cascading structural failure of the notochord and anatomic defects. Our study demonstrates that whole-animal single-cell RNA-seq can identify mechanisms for developmental robustness and pinpoint cell types that constitute key failure points.

Near-Infrared Photothermal Manipulates Cellular Excitability and Animal Behavior in Caenorhabditis elegans

Near-infrared (NIR) photothermal manipulation has emerged as a promising and noninvasive technology for neuroscience research and disease therapy for its deep tissue penetration. NIR stimulated techniques have been used to modulate neural activity. However, due to the lack of suitable in vivo control systems, most studies are limited to the cellular level. Here, a NIR photothermal technique is developed to modulate cellular excitability and animal behaviors in Caenorhabditis elegans in vivo via the thermosensitive transient receptor potential vanilloid 1 (TRPV1) channel with an FDA-approved photothermal agent indocyanine green (ICG). Upon NIR stimuli, exogenous expression of TRPV1 in AFD sensory neurons causes Ca2+ influx, leading to increased neural excitability and reversal behaviors, in the presence of ICG. The GABAergic D-class motor neurons can also be activated by NIR irradiation, resulting in slower thrashing behaviors. Moreover, the photothermal manipulation is successfully applied in different types of muscle cells (striated muscles and nonstriated muscles), enhancing muscular excitability, causing muscle contractions and behavior changes in vivo. Altogether, this study demonstrates a noninvasive method to precisely regulate the excitability of different types of cells and related behaviors in vivo by NIR photothermal manipulation, which may be applied in mammals and clinical therapy.

Glial-derived mitochondrial signals affect neuronal proteostasis and aging

The nervous system plays a critical role in maintaining whole-organism homeostasis; neurons experiencing mitochondrial stress can coordinate the induction of protective cellular pathways, such as the mitochondrial unfolded protein response (UPRMT), between tissues. However, these studies largely ignored nonneuronal cells of the nervous system. Here, we found that UPRMT activation in four astrocyte-like glial cells in the nematode, Caenorhabditis elegans, can promote protein homeostasis by alleviating protein aggregation in neurons. Unexpectedly, we find that glial cells use small clear vesicles (SCVs) to signal to neurons, which then relay the signal to the periphery using dense-core vesicles (DCVs). This work underlines the importance of glia in establishing and regulating protein homeostasis within the nervous system, which can then affect neuron-mediated effects in organismal homeostasis and longevity.

Neuron-specific proteasome activation exerts cell non-autonomous protection against amyloid-beta (Aβ) proteotoxicity in Caenorhabditis elegans

Proteostasis reinforcement is a promising approach in the design of therapeutic interventions against proteinopathies, including Alzheimer's disease. Understanding how and which parts of the proteostasis network should be enhanced is crucial in developing efficient therapeutic strategies. The ability of specific tissues to induce proteostatic responses in distal ones (cell non-autonomous regulation of proteostasis) is attracting interest. Although the proteasome is a major protein degradation node, nothing is known on its cell non-autonomous regulation. We show that proteasome activation in the nervous system can enhance the proteasome activity in the muscle of Caenorhabditis elegans. Mechanistically, this communication depends on Small Clear Vesicles, with glutamate as one of the neurotransmitters required for the distal regulation. More importantly, we demonstrate that this cell non-autonomous proteasome activation is translated into efficient prevention of amyloid-beta (Αβ)-mediated proteotoxic effects in the muscle of C. elegans but notably not to resistance against oxidative stress. Our in vivo data establish a mechanistic link between neuronal proteasome reinforcement and decreased Aβ proteotoxicity in the muscle. The identified distal communication may have serious implications in the design of therapeutic strategies based on tissue-specific proteasome manipulation.

The RIDD activity of C. elegans IRE1 modifies neuroendocrine signaling in anticipation of environment stress to ensure survival

Xbp1 splicing and regulated IRE1-dependent RNA decay (RIDD) are two RNase activities of the ER stress sensor IRE1. While Xbp1 splicing has important roles in stress responses and animal physiology, the physiological role(s) of RIDD remain enigmatic. Genetic evidence in C. elegans connects XBP1-independent IRE1 activity to organismal stress adaptation, but whether this is via RIDD, and what are the targets is yet unknown. We show that cytosolic kinase/RNase domain of C. elegans IRE1 is indeed capable of RIDD in human cells, and that sensory neurons use RIDD to signal environmental stress, by degrading mRNA of TGFβ-like growth factor DAF-7. daf-7 was degraded in human cells by both human and worm IRE1 RNAse activity with same efficiency and specificity as Blos1, confirming daf-7 as RIDD substrate. Surprisingly, daf-7 degradation in vivo was triggered by concentrations of ER stressor tunicamycin too low for xbp-1 splicing. Decrease in DAF-7 normally signals food limitation and harsh environment, triggering adaptive changes to promote population survival. Because C. elegans is a bacteriovore, and tunicamycin, like other common ER stressors, is an antibiotic secreted by Streptomyces spp., we asked whether daf-7 degradation by RIDD could signal pending food deprivation. Indeed, pre-emptive tunicamycin exposure increased survival of C. elegans populations under food limiting/high temperature stress, and this protection was abrogated by overexpression of DAF-7. Thus, C. elegans uses stress-inducing metabolites in its environment as danger signals, and employs IRE1's RIDD activity to modulate the neuroendocrine signaling for survival of upcoming environmental challenge.

Glial-derived mitochondrial signals impact neuronal proteostasis and aging

The nervous system plays a critical role in maintaining whole-organism homeostasis; neurons experiencing mitochondrial stress can coordinate the induction of protective cellular pathways, such as the mitochondrial unfolded protein response (UPRMT), between tissues. However, these studies largely ignored non-neuronal cells of the nervous system. Here, we found that UPRMT activation in four, astrocyte-like glial cells in the nematode, C. elegans, can promote protein homeostasis by alleviating protein aggregation in neurons. Surprisingly, we find that glial cells utilize small clear vesicles (SCVs) to signal to neurons, which then relay the signal to the periphery using dense-core vesicles (DCVs). This work underlines the importance of glia in establishing and regulating protein homeostasis within the nervous system, which can then impact neuron-mediated effects in organismal homeostasis and longevity.

Amphid sensory neurons of Caenorhabditis elegans orchestrate its survival from infection with broad classes of pathogens

The survival of a host during infection relies on its ability to rapidly sense the invading pathogen and mount an appropriate response. The bacterivorous nematode Caenorhabditis elegans lacks most of the traditional pattern recognition mechanisms. In this study, we hypothesized that the 12 pairs of amphid sensory neurons in the heads of worms provide sensing capability and thus affect survival during infection. We tested animals lacking amphid neurons to three major classes of pathogens, namely-a Gram-negative bacterium Pseudomonas aeruginosa, a Gram-positive bacterium Enterococcus faecalis, and a pathogenic yeast Cryptococcus neoformans By using individual neuronal ablation lines or mutants lacking specific neurons, we demonstrate that some neurons broadly suppress the survival of the host and colonization of all pathogens, whereas other amphid neurons differentially regulate host survival during infection. We also show that the roles of some of these neurons are pathogen-specific, as seen with the AWB odor sensory neurons that promote survival only during infections with P aeruginosa Overall, our study reveals broad and specific roles for amphid neurons during infections.

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

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

A proton-inhibited DEG/ENaC ion channel maintains neuronal ionstasis and promotes neuronal survival under stress

The nervous system participates in the initiation and modulation of systemic stress. Ionstasis is of utmost importance for neuronal function. Imbalance in neuronal sodium homeostasis is associated with pathologies of the nervous system. However, the effects of stress on neuronal Na⁺ homeostasis, excitability, and survival remain unclear. We report that the DEG/ENaC family member DEL-4 assembles into a proton-inactivated sodium channel. DEL-4 operates at the neuronal membrane and synapse to modulate Caenorhabditis elegans locomotion. Heat stress and starvation alter DEL-4 expression, which in turn alters the expression and activity of key stress-response transcription factors and triggers appropriate motor adaptations. Similar to heat stress and starvation, DEL-4 deficiency causes hyperpolarization of dopaminergic neurons and affects neurotransmission. Using humanized models of neurodegenerative diseases in C. elegans, we showed that DEL-4 promotes neuronal survival. Our findings provide insights into the molecular mechanisms by which sodium channels promote neuronal function and adaptation under stress.

Exploiting inter-tissue stress signaling mechanisms to preserve organismal proteostasis during aging

Aging results in a decline of cellular proteostasis capacity which culminates in the accumulation of phototoxic material, causing the onset of age-related maladies and ultimately cell death. Mechanisms that regulate proteostasis such as cellular stress response pathways sense disturbances in the proteome. They are activated to increase the expression of protein quality control components that counteract cellular damage. Utilizing invertebrate model organisms such as Caenorhabditis elegans, it has become increasingly evident that the regulation of proteostasis and the activation of cellular stress responses is not a cell autonomous process. In animals, stress responses are orchestrated by signals coming from other tissues, including the nervous system, the intestine and the germline that have a profound impact on determining the aging process. Genetic pathways discovered in C. elegans that facilitate cell nonautonomous regulation of stress responses are providing an exciting feeding ground for new interventions. In this review I will discuss cell nonautonomous proteostasis mechanisms and their impact on aging as well as ongoing research and clinical trials that can increase organismal proteostasis to lengthen health- and lifespan.

Biological resilience and aging: Activation of stress response pathways contributes to lifespan extension

While aging was traditionally viewed as a stochastic process of damage accumulation, it is now clear that aging is strongly influenced by genetics. The identification and characterization of long-lived genetic mutants in model organisms has provided insights into the genetic pathways and molecular mechanisms involved in extending longevity. Long-lived genetic mutants exhibit activation of multiple stress response pathways leading to enhanced resistance to exogenous stressors. As a result, lifespan exhibits a significant, positive correlation with resistance to stress. Disruption of stress response pathways inhibits lifespan extension in multiple long-lived mutants representing different pathways of lifespan extension and can also reduce the lifespan of wild-type animals. Combined, this suggests that activation of stress response pathways is a key mechanism by which long-lived mutants achieve their extended longevity and that many of these pathways are also required for normal lifespan. These results highlight an important role for stress response pathways in determining the lifespan of an organism.

Neuronal HLH-30/TFEB modulates peripheral mitochondrial fragmentation to improve thermoresistance in Caenorhabditis elegans

Transcription factor EB (TFEB) is a conserved master transcriptional activator of autophagy and lysosomal genes that modulates organismal lifespan regulation and stress resistance. As neurons can coordinate organism-wide processes, we investigated the role of neuronal TFEB in stress resistance and longevity. To this end, the Caenorhabditis elegans TFEB ortholog, hlh-30, was rescued panneuronally in hlh-30 loss of function mutants. While important in the long lifespan of daf-2 animals, neuronal HLH-30/TFEB was not sufficient to restore normal lifespan in short-lived hlh-30 mutants. However, neuronal HLH-30/TFEB rescue mediated robust improvements in the heat stress resistance of wildtype but not daf-2 animals. Notably, these mechanisms can be uncoupled, as neuronal HLH-30/TFEB requires DAF-16/FOXO to regulate longevity but not thermoresistance. Through further transcriptomics profiling and functional analysis, we discovered that neuronal HLH-30/TFEB modulates neurotransmission through the hitherto uncharacterized protein W06A11.1 by inducing peripheral mitochondrial fragmentation and organismal heat stress resistance in a non-cell autonomous manner. Taken together, this study uncovers a novel mechanism of heat stress protection mediated by neuronal HLH-30/TFEB.

Investigation into the communication between unheated and heat-stressed Caenorhabditis elegans via volatile stress signals

Our research group has recently found that radiation-induced airborne stress signals can be used for communication among Caenorhabditis elegans (C. elegans). This paper addresses the question of whether heat stress can also induce the emission of airborne stress signals to alert neighboring C. elegans and elicit their subsequent stress response. Here, we report that heat-stressed C. elegans produces volatile stress signals that trigger an increase in radiation resistance in neighboring unheated C. elegans. When several loss-of-function mutations affecting thermosensory neuron (AFD), heat shock factor-1, HSP-4, and small heat-shock proteins were used to test heat-stressed C. elegans, we found that the production of volatile stress signals was blocked, demonstrating that the heat shock response and ER pathway are involved in controlling the production of volatile stress signals. Our data further indicated that mutations affecting the DNA damage response (DDR) also inhibited the increase in radiation resistance in neighboring unheated C. elegans that might have received volatile stress signals, indicating that the DDR might contribute to radioadaptive responses induction by volatile stress signals. In addition, the regulatory pattern of signal production and action was preliminarily clarified. Together, the results of this study demonstrated that heat-stressed nematodes communicate with unheated nematodes via volatile stress signals.

Nanoparticulate air pollution disrupts proteostasis in Caenorhabditis elegans

The proteostasis network comprises the biochemical pathways that together maintain and regulate proper protein synthesis, transport, folding, and degradation. Many progressive neurodegenerative diseases, such as Huntington's disease (HD) and Alzheimer's disease (AD), are characterized by an age-dependent failure of the proteostasis network to sustain the health of the proteome, resulting in protein misfolding, aggregation, and, often, neurotoxicity. Although important advances have been made in recent years to identify genetic risk factors for neurodegenerative diseases, we still know relatively little about environmental risk factors such as air pollution. Exposure to nano-sized particulate air pollution, referred to herein as nanoparticulate matter (nPM), has been shown to trigger the accumulation of misfolded and oligomerized amyloid beta (Aβ) in mice. Likewise, air pollution is known to exacerbate symptoms of AD in people. We asked whether nPM contributes to the misfolded protein load, thereby overwhelming the proteostasis network and triggering proteostasis decline. To address this, we utilized C. elegans that express reporter proteins that are sensitive to changes in the protein folding environment and respond by misfolding and displaying readily scorable phenotypes, such as localized YFP fluorescence or paralysis. We found that nPM exacerbated protein aggregation in body wall muscle cells, increasing the number of large visible protein aggregates, the amount of high molecular weight protein species, and proteotoxicity. Taken together, the data point to nPM negatively impacting proteostasis. Therefore, it seems plausible that nPM exposure may exacerbate symptoms of AD and age-related dementia in a manner that is at least partially dependent on proteostasis decline.

A Year at the Forefront of Proteostasis and Aging

During aging, animals experience a decline in proteostasis activity, including loss of stress-response activation, culminating in the accumulation of misfolded proteins and toxic aggregates, which are causal in the onset of some chronic diseases. Finding genetic and pharmaceutical treatments that can increase organismal proteostasis and lengthen life is an ongoing goal of current research. The regulation of stress responses by cell non-autonomous mechanisms appears to be a potent way to impact organismal healthspan. In this Review, we cover recent findings in the intersection of proteostasis and aging, with a special focus on articles and preprints published between November 2021 and October 2022. A significant number of papers published during this time increased our understanding of how cells communicate with each other during proteotoxic stress. Finally, we also draw attention to emerging datasets that can be explored to generate new hypotheses that explain age-related proteostasis collapse.

Transcellular chaperone signaling is an intercellular stress-response distinct from the HSF-1-mediated heat shock response

Organismal proteostasis is maintained by intercellular signaling processes including cell nonautonomous stress responses such as transcellular chaperone signaling (TCS). When TCS is activated upon tissue-specific knockdown of hsp-90 in the Caenorhabditis elegans intestine, heat-inducible hsp-70 is induced in muscle cells at the permissive temperature resulting in increased heat stress resistance and lifespan extension. However, our understanding of the molecular mechanism and signaling factors mediating transcellular activation of hsp-70 expression from one tissue to another is still in its infancy. Here, we conducted a combinatorial approach using transcriptome RNA-Seq profiling and a forward genetic mutagenesis screen to elucidate how stress signaling from the intestine to the muscle is regulated. We find that the TCS-mediated "gut-to-muscle" induction of hsp-70 expression is suppressed by HSF-1 and instead relies on transcellular-X-cross-tissue (txt) genes. We identify a key role for the PDZ-domain guanylate cyclase txt-1 and the homeobox transcription factor ceh-58 as signaling hubs in the stress receiving muscle cells to initiate hsp-70 expression and facilitate TCS-mediated heat stress resistance and lifespan extension. Our results provide a new view on cell-nonautonomous regulation of "inter-tissue" stress responses in an organism that highlight a key role for the gut. Our data suggest that the HSF-1-mediated heat shock response is switched off upon TCS activation, in favor of an intercellular stress-signaling route to safeguard survival.

Organismal Roles of Hsp90

Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone that assists in the maturation of many client proteins involved in cellular signal transduction. As a regulator of cellular signaling processes, it is vital for the maintenance of cellular proteostasis and adaptation to environmental stresses. Emerging research shows that Hsp90 function in an organism goes well beyond intracellular proteostasis. In metazoans, Hsp90, as an environmentally responsive chaperone, is involved in inter-tissue stress signaling responses that coordinate and safeguard cell nonautonomous proteostasis and organismal health. In this way, Hsp90 has the capacity to influence evolution and aging, and effect behavioral responses to facilitate tissue-defense systems that ensure organismal survival. In this review, I summarize the literature on the organismal roles of Hsp90 uncovered in multicellular organisms, from plants to invertebrates and mammals.

Homeodomain-interacting protein kinase maintains neuronal homeostasis during normal Caenorhabditis elegans aging and systemically regulates longevity from serotonergic and GABAergic neurons

Aging and the age-associated decline of the proteome is determined in part through neuronal control of evolutionarily conserved transcriptional effectors, which safeguard homeostasis under fluctuating metabolic and stress conditions by regulating an expansive proteostatic network. We have discovered the Caenorhabditis elegans h omeodomain-interacting p rotein k inase (HPK-1) acts as a key transcriptional effector to preserve neuronal integrity, function, and proteostasis during aging. Loss of hpk-1 results in drastic dysregulation in expression of neuronal genes, including genes associated with neuronal aging. During normal aging hpk-1 expression increases throughout the nervous system more broadly than any other kinase. Within the aging nervous system, hpk-1 is co-expressed with key longevity transcription factors, including daf-16 (FOXO), hlh-30 (TFEB), skn-1 (Nrf2), and hif-1 , which suggests hpk-1 expression mitigates natural age-associated physiological decline. Consistently, pan-neuronal overexpression of hpk-1 extends longevity, preserves proteostasis both within and outside of the nervous system, and improves stress resistance. Neuronal HPK-1 improves proteostasis through kinase activity. HPK-1 functions cell non-autonomously within serotonergic and GABAergic neurons to improve proteostasis in distal tissues by specifically regulating distinct components of the proteostatic network. Increased serotonergic HPK-1 enhances the heat shock response and survival to acute stress. In contrast, GABAergic HPK-1 induces basal autophagy and extends longevity. Our work establishes hpk-1 as a key neuronal transcriptional regulator critical for preservation of neuronal function during aging. Further, these data provide novel insight as to how the nervous system partitions acute and chronic adaptive response pathways to delay aging by maintaining organismal homeostasis.

Glia of C. elegans coordinate a protective organismal heat shock response independent of the neuronal thermosensory circuit

Aging organisms lose the ability to induce stress responses, becoming vulnerable to protein toxicity and tissue damage. Neurons can signal to peripheral tissues to induce protective organelle-specific stress responses. Recent work shows that glia can independently induce such responses. Here, we show that overexpression of heat shock factor 1 (hsf-1) in the four astrocyte-like cephalic sheath cells of Caenorhabditis elegans induces a non-cell-autonomous cytosolic unfolded protein response, also known as the heat shock response (HSR). These animals have increased lifespan and heat stress resistance and decreased protein aggregation. Glial HSR regulation is independent of canonical thermosensory circuitry and known neurotransmitters but requires the small clear vesicle release protein UNC-13. HSF-1 and the FOXO transcription factor DAF-16 are partially required in peripheral tissues for non-cell-autonomous HSR, longevity, and thermotolerance. Cephalic sheath glial hsf-1 overexpression also leads to pathogen resistance, suggesting a role for this signaling pathway in immune function.

Neuronal IRE-1 coordinates an organism-wide cold stress response by regulating fat metabolism

Cold affects many aspects of biology, medicine, agriculture, and industry. Here, we identify a conserved endoplasmic reticulum (ER) stress response, distinct from the canonical unfolded protein response, that maintains lipid homeostasis during extreme cold. We establish that the ER stress sensor IRE-1 is critical for resistance to extreme cold and activated by cold temperature. Specifically, neuronal IRE-1 signals through JNK-1 and neuropeptide signaling to regulate lipid composition within the animal. This cold-response pathway can be bypassed by dietary supplementation with unsaturated fatty acids. Altogether, our findings define an ER-centric conserved organism-wide cold stress response, consisting of molecular neuronal sensors, effectors, and signaling moieties, which control adaptation to cold conditions in the organism. Better understanding of the molecular basis of this stress response is crucial for the optimal use of cold conditions on live organisms and manipulation of lipid saturation homeostasis, which is perturbed in human pathologies.

The Thermal Stress Coping Network of the Nematode Caenorhabditis elegans

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