Systemic and cell intrinsic roles of Gqalpha signaling in the regulation of innate immunity, oxidative stress, and longevity in Caenorhabditis elegans

Ganoderma lucidum methyl ganoderate E extends lifespan and modulates aging-related indicators in Caenorhabditis elegans

Methyl Ganoderate E (MGE) is a triterpenoid derived from Ganoderma lucidum (Reishi), an edible mushroom, commonly processed into food forms such as soups, drinks, culinary dishes, and supplements. MGE has been shown to inhibit 3T3-L1 murine adipocyte differentiation when combined with other G. lucidum triterpenes. However, the specific effect of MGE on biological processes remains unknown. In this study, we present the first evidence of MGE's anti-aging effect in Caenorhabditis elegans. Through our screening process using the UPRER regulation ability, we evaluated a library of 74 pure compounds isolated from G. lucidum, and MGE exhibited the most promising results. Subsequent experiments demonstrated that MGE extended the lifespan by 26% at 10 μg ml-1 through daf-16, hsf-1, and skn-1-dependent pathways. MGE also enhanced resistance to various molecular stressors, improved healthspan, increased fertility, and reduced the aggregation of alpha-synuclein and amyloid-beta. Transcriptome data revealed that MGE promoted processes associated with proteolysis and neural activity, while not promoting cell death processes. Collectively, our findings suggest that G. lucidum MGE could be considered as a potential anti-aging intervention, adding to the growing list of such interventions.

Further Extension of Lifespan by Unc-43/CaMKII and Egl-8/PLCβ Mutations in Germline-Deficient Caenorhabditis elegans

Reduction of insulin/insulin-like growth factor 1 (IGF1) signaling (IIS) promotes longevity across species. In the nematode Caenorhabditis elegans, ablation of germline stem cells (GSCs) and activity changes of the conserved signaling mediators unc-43/CaMKII (calcium/calmodulin-dependent kinase type II) and egl-8/PLCβ (phospholipase Cβ) also increase lifespan. Like IIS, these pathways depend on the conserved transcription factor daf-16/FOXO for lifespan extension, but how they functionally interact is unknown. Here, we show that altered unc-43/egl-8 activity further increases the lifespan of long-lived GSC-deficient worms, but not of worms that are long-lived due to a strong reduction-of-function mutation in the insulin/IGF1-like receptor daf-2. Additionally, we provide evidence for unc-43 and, to a lesser extent, egl-8 modulating the expression of certain collagen genes, which were reported to be dispensable for longevity of these particular daf-2 mutant worms, but not for other forms of longevity. Together, these results provide new insights into the conditions and potential mechanisms by which CaMKII- and PLCβ-signals modulate C. elegans lifespan.

Decreased spliceosome fidelity and egl-8 intron retention inhibit mTORC1 signaling to promote longevity

Changes in splicing fidelity are associated with loss of homeostasis and aging, yet only a handful of splicing factors have been shown to be causally required to promote longevity, and the underlying mechanisms and downstream targets in these paradigms remain elusive. Surprisingly, we found a hypomorphic mutation within ribonucleoprotein RNP-6/poly(U)-binding factor 60 kDa (PUF60), a spliceosome component promoting weak 3′-splice site recognition, which causes aberrant splicing, elevates stress responses and enhances longevity in Caenorhabditis elegans. Through genetic suppressor screens, we identify a gain-of-function mutation within rbm-39, an RNP-6-interacting splicing factor, which increases nuclear speckle formation, alleviates splicing defects and curtails longevity caused by rnp-6 mutation. By leveraging the splicing changes induced by RNP-6/RBM-39 activities, we uncover intron retention in egl-8/phospholipase C β4 (PLCB4) as a key splicing target prolonging life. Genetic and biochemical evidence show that neuronal RNP-6/EGL-8 downregulates mammalian target of rapamycin complex 1 (mTORC1) signaling to control organismal lifespan. In mammalian cells, PUF60 downregulation also potently and specifically inhibits mTORC1 signaling. Altogether, our results reveal that splicing fidelity modulates lifespan through mTOR signaling.

Ag2Se quantum dots damage the nervous system of nematode Caenorhabditis elegans

Silver selenide quantum dots (Ag₂Se QDs), as a novel type of QDs, are valuable in the biomedical application due to their low-toxic and excellent optical property in near infrared region, but the biosafety assessment of Ag₂Se QDs is rare. In this study, the findings suggested that the accumulation of Ag₂Se QDs in the body of nematodes decreased the lifespan and damaged normal neurobehaviors of Caenorhabditis elegan (C. elegans). Furthermore, Ag₂Se QDs caused excessive reactive oxygen species (ROS) productions and altered expressions of several genes associated with redox equilibrium, which might contribute to neurotoxic outcomes in nematode C. elegans. According to this study, it is necessary and important for researchers to pay attention to the biosafety assessment of presumed low-toxic nanomaterials, like Ag₂Se QDs, especially on sensitively toxic targets, i.e. the nervous system.

Immunomodulatory and Antiaging Mechanisms of Resveratrol, Rapamycin, and Metformin: Focus on mTOR and AMPK Signaling Networks

Aging results from the progressive dysregulation of several molecular pathways and mTOR and AMPK signaling have been suggested to play a role in the complex changes in key biological networks involved in cellular senescence. Moreover, multiple factors, including poor nutritional balance, drive immunosenescence progression, one of the meaningful aspects of aging. Unsurprisingly, nutraceutical and pharmacological interventions could help maintain an optimal biological response by providing essential bioactive micronutrients required for the development, maintenance, and the expression of the immune response at all stages of life. In this regard, many studies have provided evidence of potential antiaging properties of resveratrol, as well as rapamycin and metformin. Indeed, in vitro and in vivo models have demonstrated for these molecules a number of positive effects associated with healthy aging. The current review focuses on the mechanisms of action of these three important compounds and their suggested use for the clinical treatment of immunosenescence and aging.

Regulation of Aging and Longevity by Ion Channels and Transporters

Despite significant advances in our understanding of the mechanisms that underlie age-related physiological decline, our ability to translate these insights into actionable strategies to extend human healthspan has been limited. One of the major reasons for the existence of this barrier is that with a few important exceptions, many of the proteins that mediate aging have proven to be undruggable. The argument put forth here is that the amenability of ion channels and transporters to pharmacological manipulation could be leveraged to develop novel therapeutic strategies to combat aging. This review delves into the established roles for ion channels and transporters in the regulation of aging and longevity via their influence on membrane excitability, Ca2+ homeostasis, mitochondrial and endolysosomal function, and the transduction of sensory stimuli. The goal is to provide the reader with an understanding of emergent themes, and prompt further investigation into how the activities of ion channels and transporters sculpt the trajectories of cellular and organismal aging.

Automated recognition and analysis of head thrashes behavior in C. elegans

Background

Locomotive behaviors are a rapid evaluation indicator reflecting whether the nervous system of worms is damaged, and has been proved to be sensitive to chemical toxicity. In many toxicological studies, C. elegans head thrashes is a key indicator of locomotive behaviors to measure the vitality of worms. In previous studies, the number of head thrashes was manually counted, which is time-consuming and labor-intensive.

Results

This paper presents an automatic recognition and counting method for head thrashes behavior of worms from experimental videos. First, the image processing algorithm is designed for worm morphology features calculation, mean gray values of head and tail are used to locate the head of worm accurately. Next, the worm skeleton is extracted and divided into equal parts. The angle formulas are used to calculate the bending angle of the head of worm. Finally, the number of head thrashes is counted according to the bending angle of the head in each frame. The robustness of the proposed algorithm is evaluated by comparing the counting results of the manual counting. It is proved that the proposed algorithm can recognize the occurrence of head thrashes of C. elegans of different strains. In addition, the difference of the head thrashes behavior of different worm strains is analyzed, it is proved that the relationship between worm head thrashes behavior and lifespan.

Conclusions

A new method is proposed to automatically count the number of head thrashes of worms. This algorithm makes it possible to count the number of head thrashes from the worm videos collected by the automatic tracking system. The proposed algorithm will play an important role in toxicological research and worm vitality research. The code is freely available at https://github.com/hthana/HTC.

Genetic signature of human longevity in PKC and NF-κB signaling

Gene variants associated with longevity are also associated with protection against cognitive decline, dementia and Alzheimer's disease, suggesting that common physiologic pathways act at the interface of longevity and cognitive function. To test the hypothesis that variants in genes implicated in cognitive function may promote exceptional longevity, we performed a comprehensive 3‐stage study to identify functional longevity‐associated variants in ~700 candidate genes in up to 450 centenarians and 500 controls by target capture sequencing analysis. We found an enrichment of longevity‐associated genes in the nPKC and NF‐κB signaling pathways by gene‐based association analyses. Functional analysis of the top three gene variants (NFKBIA, CLU, PRKCH) suggests that non‐coding variants modulate the expression of cognate genes, thereby reducing signaling through the nPKC and NF‐κB. This matches genetic studies in multiple model organisms, suggesting that the evolutionary conservation of reduced PKC and NF‐κB signaling pathways in exceptional longevity may include humans.

Metformin promotes innate immunity through a conserved PMK-1/p38 MAPK pathway

Metformin, as the first-line oral drug for type 2 diabetes, has proven benefits against aging, cancer and cardiovascular diseases. But the influence of metformin to the immune response and its molecular mechanisms remain obscure. Metformin increases resistance to not only the Gram-negative pathogens Pseudomonas aeruginosa and Salmonella enterica but also the Gram-positive pathogens Enterococcus faecalis and Staphylococcus aureus. Meanwhile, metformin protects the animals from the infection by enhancing the tolerance to the pathogen infection rather than by reducing the bacterial burden. Through the screening of classical immune pathways in C. elegans, we find metformin enhances innate immunity through p38 MAPK pathway. Furthermore, activated p38/PMK-1 by metformin acts on the intestine for innate immune response. In addition, metformin-treated mice have increased resistance to P. aeruginosa PA14 infection and significantly increased the levels of active PMK-1. Therefore, promoted p38/PMK-1-mediated innate immunity by metformin is conserved from worms to mammals. Our work provides a conserved mechanism by which metformin enhances immune response and boosts its therapeutic application in the treatment of pathogen infection.

The discovery and consequences of the central role of the nervous system in the control of protein homeostasis

Organisms function despite wide fluctuations in their environment through the maintenance of homeostasis. At the cellular level, the maintenance of proteins as functional entities at target expression levels is called protein homeostasis (or proteostasis). Cells implement proteostasis through universal and conserved quality control mechanisms that surveil and monitor protein conformation. Recent studies that exploit the powerful ability to genetically manipulate specific neurons in C. elegans have shown that cells within this metazoan lose their autonomy over this fundamental survival mechanism. These studies have uncovered novel roles for the nervous system in controlling how and when cells activate their protein quality control mechanisms. Here we discuss the conceptual underpinnings, experimental evidence and the possible consequences of such a control mechanism. PRELUDE: Whether the detailed examination of parts of the nervous system and their selective perturbation is sufficient to reconstruct how the brain generates behavior, mental disease, music and religion remains an open question. Yet, Sydney Brenner's development of C. elegans as an experimental organism and his faith in the bold reductionist approach that 'the understanding of wild-type behavior comes best after the discovery and analysis of mutations that alter it', has led to discoveries of unexpected roles for neurons in the biology of organisms.

Sphingosine Kinase Regulates Neuropeptide Secretion During the Oxidative Stress-Response Through Intertissue Signaling

The Nrf2 antioxidant transcription factor promotes redox homeostasis in part through reciprocal signaling between neurons and neighboring cells, but the signals involved in intertissue signaling in response to Nrf2 activation are not well defined. In Caenorhabditis elegans, activation of SKN-1/Nrf2 in the intestine negatively regulates neuropeptide secretion from motor neurons. Here, we show that sphingosine kinase (SPHK-1) functions downstream of SKN-1/Nrf2 in the intestine to regulate neuropeptide secretion from motor neurons during the oxidative stress response in C. elegans hermaphrodites. SPHK-1 localizes to mitochondria in the intestine and SPHK-1 mitochondrial localization and kinase activity are essential for its function in regulating motor neuron function. SPHK-1 is recruited to mitochondria from cytosolic pools and its mitochondrial abundance is negatively regulated by acute or chronic SKN-1 activation. Finally, the regulation of motor function by SKN-1 requires the activation of the p38 MAPK cascade in the intestine and occurs through controlling the biogenesis or maturation of dense core vesicles in motor neurons. These findings show that the inhibition of SPHK-1 in the intestine by SKN-1 negatively regulates neuropeptide secretion from motor neurons, revealing a new mechanism by which SPHK-1 signaling mediates its effects on neuronal function in response to oxidative stress.SIGNIFICANCE STATEMENT Neurons are highly susceptible to damage by oxidative stress, yet have limited capacity to activate the SKN-1/Nrf2 oxidative stress response, relying instead on astrocytes to provide redox homeostasis. In Caenorhabditis elegans, intertissue signaling from the intestine plays a key role in regulating neuronal function during the oxidative stress response. Here, through a combination of genetic, behavioral, and fluorescent imaging approaches, we found that sphingosine kinase functions in the SKN-1/Nrf2 pathway in the intestine to regulate neuropeptide biogenesis and secretion in motor neurons. These results implicate sphingolipid signaling as a new component of the oxidative stress response and suggest that C. elegans may be a genetically tractable model to study non-cell-autonomous oxidative stress signaling to neurons.

Lipid and Carbohydrate Metabolism in Caenorhabditis elegans

Lipid and carbohydrate metabolism are highly conserved processes that affect nearly all aspects of organismal biology. Caenorhabditis elegans eat bacteria, which consist of lipids, carbohydrates, and proteins that are broken down during digestion into fatty acids, simple sugars, and amino acid precursors. With these nutrients, C. elegans synthesizes a wide range of metabolites that are required for development and behavior. In this review, we outline lipid and carbohydrate structures as well as biosynthesis and breakdown pathways that have been characterized in C. elegans We bring attention to functional studies using mutant strains that reveal physiological roles for specific lipids and carbohydrates during development, aging, and adaptation to changing environmental conditions.

PKA/KIN-1 mediates innate immune responses to bacterial pathogens in Caenorhabditis elegans

The genetically tractable organism Caenorhabditis elegans is a powerful model animal for the study of host innate immunity. Although the intestine and the epidermis of C. elegans that is in contact with pathogens are likely to function as sites for the immune function, recent studies indicate that the nervous system could control innate immunity in C. elegans. In this report, we demonstrated that protein kinase A (PKA)/KIN-1 in the neurons contributes to resistance against Salmonella enterica infection in C. elegans. Microarray analysis revealed that PKA/KIN-1 regulates the expression of a set of antimicrobial effectors in the non-neuron tissues, which are required for innate immune responses to S. enterica. Furthermore, PKA/KIN-1 regulated the expression of lysosomal genes during S. enterica infection. Our results suggest that the lysosomal signaling molecules are involved in autophagy by controlling autophagic flux, rather than formation of autophagosomes. As autophagy is crucial for host defense against S. enterica infection in a metazoan, the lysosomal pathway also acts as a downstream effector of the PKA/KIN-1 signaling for innate immunity. Our data indicate that the PKA pathway contributes to innate immunity in C. elegans by signaling from the nervous system to periphery tissues to protect the host against pathogens.

Complement pathway amplifies caspase-11-dependent cell death and endotoxin-induced sepsis severity

Cell death and release of proinflammatory mediators contribute to mortality during sepsis. Specifically, caspase-11-dependent cell death contributes to pathology and decreases in survival time in sepsis models. Priming of the host cell, through TLR4 and interferon receptors, induces caspase-11 expression, and cytosolic LPS directly stimulates caspase-11 activation, promoting the release of proinflammatory cytokines through pyroptosis and caspase-1 activation. Using a CRISPR-Cas9-mediated genome-wide screen, we identified novel mediators of caspase-11-dependent cell death. We found a complement-related peptidase, carboxypeptidase B1 (Cpb1), to be required for caspase-11 gene expression and subsequent caspase-11-dependent cell death. Cpb1 modifies a cleavage product of C3, which binds to and activates C3aR, and then modulates innate immune signaling. We find the Cpb1-C3-C3aR pathway induces caspase-11 expression through amplification of MAPK activity downstream of TLR4 and Ifnar activation, and mediates severity of LPS-induced sepsis (endotoxemia) and disease outcome in mice. We show C3aR is required for up-regulation of caspase-11 orthologues, caspase-4 and -5, in primary human macrophages during inflammation and that c3aR1 and caspase-5 transcripts are highly expressed in patients with severe sepsis; thus, suggesting that these pathways are important in human sepsis. Our results highlight a novel role for complement and the Cpb1-C3-C3aR pathway in proinflammatory signaling, caspase-11 cell death, and sepsis severity.

An Evolutionarily Conserved PLC-PKD-TFEB Pathway for Host Defense

The mechanisms that tightly control the transcription of host defense genes have not been fully elucidated. We previously identified TFEB as a transcription factor important for host defense, but the mechanisms that regulate TFEB during infection remained unknown. Here, we used C. elegans to discover a pathway that activates TFEB during infection. Gene dkf-1, which encodes a homolog of protein kinase D (PKD), was required for TFEB activation in nematodes infected with Staphylococcus aureus. Conversely, pharmacological activation of PKD was sufficient to activate TFEB. Furthermore, phospholipase C (PLC) gene plc-1 was also required for TFEB activation, downstream of Gαq homolog egl-30 and upstream of dkf-1. Using reverse and chemical genetics, we discovered a similar PLC-PKD-TFEB axis in Salmonella-infected mouse macrophages. In addition, PKCα was required in macrophages. These observations reveal a previously unknown host defense signaling pathway, which has been conserved across one billion years of evolution.

The Developmental Intestinal Regulator ELT-2 Controls p38-Dependent Immune Responses in Adult C. elegans

GATA transcription factors play critical roles in cellular differentiation and development. However, their roles in mature tissues are less understood. In C. elegans larvae, the transcription factor ELT-2 regulates terminal differentiation of the intestine. It is also expressed in the adult intestine, where it was suggested to maintain intestinal structure and function, and where it was additionally shown to contribute to infection resistance. To study the function of elt-2 in adults we characterized elt-2-dependent gene expression following its knock-down specifically in adults. Microarray analysis identified two ELT-2-regulated gene subsets: one, enriched for hydrolytic enzymes, pointed at regulation of constitutive digestive functions as a dominant role of adult elt-2; the second was enriched for immune genes that are induced in response to Pseudomonas aeruginosa infection. Focusing on the latter, we used genetic analyses coupled to survival assays and quantitative RT-PCR to interrogate the mechanism(s) through which elt-2 contributes to immunity. We show that elt-2 controls p38-dependent gene induction, cooperating with two p38-activated transcription factors, ATF-7 and SKN-1. This demonstrates a mechanism through which the constitutively nuclear elt-2 can impact induced responses, and play a dominant role in C. elegans immunity.

Molecular mechanisms of nematode-nematophagous microbe interactions: basis for biological control of plant-parasitic nematodes

Plant-parasitic nematodes cause significant damage to a broad range of vegetables and agricultural crops throughout the world. As the natural enemies of nematodes, nematophagous microorganisms offer a promising approach to control the nematode pests. Some of these microorganisms produce traps to capture and kill the worms from the outside. Others act as internal parasites to produce toxins and virulence factors to kill the nematodes from within. Understanding the molecular basis of microbe-nematode interactions provides crucial insights for developing effective biological control agents against plant-parasitic nematodes. Here, we review recent advances in our understanding of the interactions between nematodes and nematophagous microorganisms, with a focus on the molecular mechanisms by which nematophagous microorganisms infect nematodes and on the nematode defense against pathogenic attacks. We conclude by discussing several key areas for future research and development, including potential approaches to apply our recent understandings to develop effective biocontrol strategies.

Autophagy protects C. elegans against necrosis during Pseudomonas aeruginosa infection

Autophagy, a conserved pathway that delivers intracellular materials into lysosomes for degradation, is involved in development, aging, and a variety of diseases. Accumulating evidence demonstrates that autophagy plays a protective role against infectious diseases by diminishing intracellular pathogens, including bacteria, viruses, and parasites. However, the mechanism by which autophagy regulates innate immunity remains largely unknown. Here, we show that autophagy is involved in host defense against a pathogenic bacterium Pseudomonas aeruginosa in the metazoan Caenorhabditis elegans. P. aeruginosa infection induces autophagy via a conserved extracellular signal-regulated kinase (ERK). Intriguingly, impairment of autophagy does not influence the intestinal accumulation of P. aeruginosa, but instead induces intestinal necrosis. Inhibition of necrosis results in the survival of autophagy-deficient worms after P. aeruginosa infection. These findings reveal a previously unidentified role for autophagy in protection against necrosis triggered by pathogenic bacteria in C. elegans and implicate that such a function of autophagy may be conserved through the inflammatory response in diverse organisms.

QuantWorm: a comprehensive software package for Caenorhabditis elegans phenotypic assays

Phenotypic assays are crucial in genetics; however, traditional methods that rely on human observation are unsuitable for quantitative, large-scale experiments. Furthermore, there is an increasing need for comprehensive analyses of multiple phenotypes to provide multidimensional information. Here we developed an automated, high-throughput computer imaging system for quantifying multiple Caenorhabditis elegans phenotypes. Our imaging system is composed of a microscope equipped with a digital camera and a motorized stage connected to a computer running the QuantWorm software package. Currently, the software package contains one data acquisition module and four image analysis programs: WormLifespan, WormLocomotion, WormLength, and WormEgg. The data acquisition module collects images and videos. The WormLifespan software counts the number of moving worms by using two time-lapse images; the WormLocomotion software computes the velocity of moving worms; the WormLength software measures worm body size; and the WormEgg software counts the number of eggs. To evaluate the performance of our software, we compared the results of our software with manual measurements. We then demonstrated the application of the QuantWorm software in a drug assay and a genetic assay. Overall, the QuantWorm software provided accurate measurements at a high speed. Software source code, executable programs, and sample images are available at www.quantworm.org. Our software package has several advantages over current imaging systems for C. elegans. It is an all-in-one package for quantifying multiple phenotypes. The QuantWorm software is written in Java and its source code is freely available, so it does not require use of commercial software or libraries. It can be run on multiple platforms and easily customized to cope with new methods and requirements.

Identifying evolutionarily conserved genes in the dietary restriction response using bioinformatics and subsequent testing in Caenorhabditis elegans

Dietary restriction (DR) increases life span, health span and resistance to stress in a wide range of organisms. Work from a large number of laboratories has revealed evolutionarily conserved mechanisms that mediate the DR response. Here, we analyzed the genome-wide gene expression profiles of Caenorhabditis elegans under DR versus ad libitum conditions. Using the Ortho2ExpressMatrix tool, we searched for C. elegans orthologs of mouse genes that have been shown to be differentially expressed under DR conditions in nearly 600 experiments. Based on our bioinformatic approaches, we obtained 189 DR-responsive genes, and 45 of these are highly conserved from worm to man. Subsequent testing of sixteen genes that are up-regulated under DR identified eight genes that abolish the DR-induced resistance to heat stress in C. elegans. Further analyses revealed that fkb-4, dod-22 and ikb-1 genes also abolish increased life span in response to DR. The identified genes that are necessary for the DR response are sensitive to certain stress signals such as metabolic perturbances (dod-22, fkb-4 and nhr-85), DNA damage (ikb-1), heat shock (hsp-12.6) and cancer-like overgrowth (prk-2 and tsp-15). We propose that most of the DR-responsive genes identified are components of the recently discovered cellular surveillance-activated detoxification and defenses pathway, which is, among others, important for the survival of organisms in times of food deprivation.

The DAF-16/FOXO transcription factor functions as a regulator of epidermal innate immunity

The Caenorhabditis elegans DAF-16 transcription factor is critical for diverse biological processes, particularly longevity and stress resistance. Disruption of the DAF-2 signaling cascade promotes DAF-16 activation, and confers resistance to killing by pathogenic bacteria, such as Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis. However, daf-16 mutants exhibit similar sensitivity to these bacteria as wild-type animals, suggesting that DAF-16 is not normally activated by these bacterial pathogens. In this report, we demonstrate that DAF-16 can be directly activated by fungal infection and wounding in wild-type animals, which is independent of the DAF-2 pathway. Fungal infection and wounding initiate the Gαq signaling cascade, leading to Ca(2+) release. Ca(2+) mediates the activation of BLI-3, a dual-oxidase, resulting in the production of reactive oxygen species (ROS). ROS then activate DAF-16 through a Ste20-like kinase-1/CST-1. Our results indicate that DAF-16 in the epidermis is required for survival after fungal infection and wounding. Thus, the EGL-30-Ca(2+)-BLI-3-CST-1-DAF-16 signaling represents a previously unknown pathway to regulate epidermal damage response.

Speculations on the activation of ROS generation in C. elegans innate immune signaling

We recently published work demonstrating that ROS (reactive oxygen species) generated by the dual oxidase, Ce-Duox1/BLI-3, in response to infection in Caenorhabditis elegans activates the transcription factor SKN-1, initiating a protective response. Moreover, we showed that the crucial innate immune pathway, p38 MAPK signaling, was responsible for relaying the activating signal. In this commentary, we speculate on the signaling pathway upstream of Ce-Duox1/BLI-3 that triggers its activity. Specifically, we hypothesize that a G-protein signaling pathway comprising Gαq - PLCβ - TPA-1 - DKF-2 activates Ce-Duox1/BLI-3. Our rationale is based on work showing that these components are connected to p38 MAPK signaling and innate immunity in the worm, and investigations in other organisms demonstrating that some of these components are involved in dual oxidase activation.

A neuronal signaling pathway of CaMKII and Gqα regulates experience-dependent transcription of tph-1

Dynamic serotonin biosynthesis is important for serotonin function; however, the mechanisms that underlie experience-dependent transcriptional regulation of the rate-limiting serotonin biosynthetic enzyme tryptophan hydroxylase (TPH) are poorly understood. Here, we characterize the molecular and cellular mechanisms that regulate increased transcription of Caenorhabditis elegans tph-1 in a pair of serotonergic neurons ADF during an aversive experience with pathogenic bacteria, a common environmental peril for worms. Training with pathogenic bacteria induces a learned aversion to the smell of the pathogen, a behavioral plasticity that depends on the serotonin signal from ADF neurons. We demonstrate that pathogen training increases ADF neuronal activity. While activating ADF increases tph-1 transcription, inhibiting ADF activity abolishes the training effect on tph-1, demonstrating the dependence of tph-1 transcriptional regulation on ADF neural activity. At the molecular level, the C. elegans homolog of CaMKII, UNC-43, functions cell-autonomously in ADF neurons to generate training-dependent enhancement in neuronal activity and tph-1 transcription, and this cell-autonomous function of UNC-43 is required for learning. Furthermore, selective expression of an activated form of UNC-43 in ADF neurons is sufficient to increase ADF activity and tph-1 transcription, mimicking the training effect. Upstream of ADF, the Gqα protein EGL-30 facilitates training-dependent induction of tph-1 by functional regulation of olfactory sensory neurons, which underscores the importance of sensory experience. Together, our work elucidates the molecular and cellular mechanisms whereby experience modulates tph-1 transcription.

Neuronal Goα and CAPS regulate behavioral and immune responses to bacterial pore-forming toxins

Pore-forming toxins (PFTs) are abundant bacterial virulence factors that attack host cell plasma membranes. Host defense mechanisms against PFTs described to date all function in the host tissue that is directly attacked by the PFT. Here we characterize a rapid and fully penetrant cessation of feeding of Caenorhabditis elegans in response to PFT attack. We demonstrate via analyses of C. elegans mutants that inhibition of feeding by PFT requires the neuronal G protein Goα subunit goa-1, and that maintenance of this response requires neuronally expressed calcium activator for protein secretion (CAPS) homolog unc-31. Independently from their role in feeding cessation, we find that goa-1 and unc-31 are additionally required for immune protection against PFTs. We thus demonstrate that the behavioral and immune responses to bacterial PFT attack involve the cross-talk between the nervous system and the cells directly under attack.

G-proteins: Fighting infection on two fronts

Animals have evolved multiple strategies for coping with the presence of pathogenic microbes. The best characterized is the immune response where animals activate their physical and cellular defenses to respond to invading microorganisms. However, behavioral changes can also be triggered by exposure to microbes and play an important role in defending many species, including humans, from pathogen attack. In our recent study we demonstrate that, following infection, C. elegans uses the same G-protein signaling pathway in neurons and epithelial cells to coordinate avoidance behaviors and immune responses. Coordination of these responses allows animals to mount an immune response to the immediate threat while simultaneously taking action to remove the pathogen, however, the complicated nature of the mammalian brain and immune system has made it difficult to identify the molecular mechanisms mediating these interactions. With its simple, well described, nervous system and a rapidly growing understanding of its immune system, C. elegans has emerged as an excellent model to study the mechanisms by which animals recognize pathogens and coordinate behavioral and immune responses to infection.

Studies on Shigella boydii infection in Caenorhabditis elegans and bioinformatics analysis of immune regulatory protein interactions

Shigella boydii causes bacillary dysentery or shigellosis and generates a significant burden in the developing nations. S. boydii-mediated infection assays were performed at both physiological and molecular levels using Caenorhabditis elegans as a host. Continuous exposure of worms to S. boydii showed a reduced life span indicating the pathogenicity of Shigella. Quantitative Real-Time PCR analysis was performed to analyze the expression and regulation of host specific candidate-antimicrobial genes (clec-60, clec-87, lys-7), which were expressed significantly during early infection, but weakened during the latter hours. Increased mortality of mutant RB1285 by S. boydii and Shigella flexneri indicated the role of lys-7 during Shigella infection. Protein-protein interactions (PPIs) database was used to analyze the interaction of immune proteins in both C. elegans and humans. In addition, the expression and regulation were revealed about immune genes (clec-61, clec-62, clec-63, F54D5.3 and ZK1320.2), which encode several intermediate immune protein partners (CLEC-61, CLEC-62, CLEC-63, F54D5.3, ZK1320.2, W03D2.6 and THN-2) that interact with LYS-7 and CLEC-60 and were found to play a role in C. elegans immune defense against S. boydii infections. Similarly, the immune genes that are specific to the human defense system, which encode IGHV4-39, A2M, LTF, and CD79A, were predicted to be expressed with LYZ and MBL2, thus indicating their regulation during Shigella infections. Our results using the lowest eukaryotic model system and human database indicated that the major players involved in immunity-related processes appear to be common in cases of Shigella sp. mediated immune responses. This article is part of a Special Issue entitled: Computational Methods for Protein Interaction and Structural Prediction.

Activation of the Caenorhabditis elegans FOXO family transcription factor DAF-16 by pathogenic Bacillus thuringiensis

The FOXO family of transcription factors have recently been implicated in innate immunity, especially in case of DAF-16 from the nematode Caenorhabditis elegans. However, previous studies with this nematode proposed that DAF-16 is not directly activated by pathogens. Rather, DAF-16 mediates resistance if activated by some other cue as part of a general stress response. We specifically tested this notion by analysis of DAF-16 nuclear translocation and thus regulatory activity upon exposure to pathogenic Bacillus thuringiensis. Our results demonstrate that DAF-16 nuclear translocation is indeed particularly induced in response to bacterial pathogenicity, whereas infection load alone has little effect. Translocation is strongest at an early time point, suggesting a role during the immediate immune response. The increased DAF-16 availability is associated with higher resistance and a reduction in feeding behaviour. Taken together, our data highlight that a FOXO transcription factor directly responds to pathogens and thus contributes to immune defence.

Control of intestinal bacterial proliferation in regulation of lifespan in Caenorhabditis elegans

Background

A powerful approach to understanding complex processes such as aging is to use model organisms amenable to genetic manipulation, and to seek relevant phenotypes to measure. Caenorhabditis elegans is particularly suited to studies of aging, since numerous single-gene mutations have been identified that affect its lifespan; it possesses an innate immune system employing evolutionarily conserved signaling pathways affecting longevity. As worms age, bacteria accumulate in the intestinal tract. However, quantitative relationships between worm genotype, lifespan, and intestinal lumen bacterial load have not been examined. We hypothesized that gut immunity is less efficient in older animals, leading to enhanced bacterial accumulation, reducing longevity. To address this question, we evaluated the ability of worms to control bacterial accumulation as a functional marker of intestinal immunity.

Results

We show that as adult worms age, several C. elegans genotypes show diminished capacity to control intestinal bacterial accumulation. We provide evidence that intestinal bacterial load, regulated by gut immunity, is an important causative factor of lifespan determination; the effects are specified by bacterial strain, worm genotype, and biologic age, all acting in concert.

Conclusions

In total, these studies focus attention on the worm intestine as a locus that influences longevity in the presence of an accumulating bacterial population. Further studies defining the interplay between bacterial species and host immunity in C. elegans may provide insights into the general mechanisms of aging and age-related diseases.

Immune defense mechanisms in the Caenorhabditis elegans intestinal epithelium

Intestinal epithelial cells provide an essential line of defense for Caernohabditis elegans against ingested pathogens. Because nematodes consume microorganisms as their food source, there has presumably been selection pressure to evolve and maintain immune defense mechanisms within the intestinal epithelium. Here we review recent advances that further define the immune signaling network within these cells and suggest mechanisms used by the nematode to monitor for infection. In reviewing studies of pathogenesis that use this simple model system, we hope to illustrate some of the basic principles of epithelial immunity that may also be of relevance in higher order hosts.

Ce-Duox1/BLI-3 generated reactive oxygen species trigger protective SKN-1 activity via p38 MAPK signaling during infection in C. elegans

Infected animals will produce reactive oxygen species (ROS) and other inflammatory molecules that help fight pathogens, but can inadvertently damage host tissue. Therefore specific responses, which protect and repair against the collateral damage caused by the immune response, are critical for successfully surviving pathogen attack. We previously demonstrated that ROS are generated during infection in the model host Caenorhabditis elegans by the dual oxidase Ce-Duox1/BLI-3. Herein, an important connection between ROS generation by Ce-Duox1/BLI-3 and upregulation of a protective transcriptional response by SKN-1 is established in the context of infection. SKN-1 is an ortholog of the mammalian Nrf transcription factors and has previously been documented to promote survival, following oxidative stress, by upregulating genes involved in the detoxification of ROS and other reactive compounds. Using qRT-PCR, transcriptional reporter fusions, and a translational fusion, SKN-1 is shown to become highly active in the C. elegans intestine upon exposure to the human bacterial pathogens, Enterococcus faecalis and Pseudomonas aeruginosa. Activation is dependent on the overall pathogenicity of the bacterium, demonstrated by a weakened response observed in attenuated mutants of these pathogens. Previous work demonstrated a role for p38 MAPK signaling both in pathogen resistance and in activating SKN-1 upon exposure to chemically induced oxidative stress. We show that NSY-1, SEK-1 and PMK-1 are also required for SKN-1 activity during infection. Evidence is also presented that the ROS produced by Ce-Duox1/BLI-3 is the source of SKN-1 activation via p38 MAPK signaling during infection. Finally, for the first time, SKN-1 activity is shown to be protective during infection; loss of skn-1 decreases resistance, whereas increasing SKN-1 activity augments resistance to pathogen. Overall, a model is presented in which ROS generation by Ce-Duox1/BLI-3 activates a protective SKN-1 response via p38 MAPK signaling.

To fight infection, an animal's immune response produces a variety of toxic compounds that are directed at the invading pathogen. However, these toxic compounds can also damage the host's tissue. Therefore an important job of the immune response is to prevent and repair damage caused by “friendly fire.” In this study, we explore this damage control function of the immune response in a small worm called C. elegans, which can be infected by feeding on human pathogens and serves as a model of human infection. Upon exposure of C. elegans to reactive compounds, a factor called SKN-1 was shown to induce the production of protective, detoxifying enzymes. Here, we demonstrate that SKN-1 also becomes active in infected animals. The cause of SKN-1 activation is reactive compounds produced by the animal's immune system, i.e. a source of “friendly fire.” We additionally show that a highly conserved signaling pathway, called the p38 MAPK pathway, controls SKN-1 activity during infection. Finally, we demonstrate that SKN-1 activity is beneficial to the worm during infection, enhancing survival. Because humans share many of the components of the interaction we describe, this study provides broad insights into the principals of damage control during immune response.

A Gαq-Ca²⁺ signaling pathway promotes actin-mediated epidermal wound closure in C. elegans

BACKGROUND

Repair of skin wounds is essential for animals to survive in a harsh environment, yet the signaling pathways initiating wound repair in vivo remain little understood. In Caenorhabditis elegans, a p38 mitogen-activated protein kinase (MAPK) cascade promotes innate immune responses to wounding but is not required for other aspects of wound healing. We therefore set out to identify additional wound response pathways in C. elegans epidermis.

RESULTS

We show here that wounding the adult C. elegans skin triggers a rapid and sustained rise in epidermal Ca(2+) that is critical for survival after wounding. The wound-triggered rise in Ca(2+) requires the epidermal transient receptor potential channel, melastatin family (TRPM) channel GTL-2 and IP(3)R-stimulated release from internal stores. We identify an epidermal signal transduction pathway that includes the Gα(q) EGL-30 and its effector PLCβ EGL-8. Loss of function in this pathway impairs survival after wounding. The Gα(q)-Ca(2+) pathway is not required for known innate immune responses to wounding but instead promotes actin-dependent wound closure. Wound closure requires the Cdc42 small GTPase and Arp2/3-dependent actin polymerization and is negatively regulated by Rho and nonmuscle myosin. Finally, we show that the death-associated protein kinase DAPK-1 acts as a negative regulator of wound closure.

CONCLUSIONS

Skin wounding in C. elegans triggers a Ca(2+)-dependent signaling cascade that promotes wound closure, in parallel to the innate immune response to damage. Wound closure requires actin polymerization and is negatively regulated by nonmuscle myosin.

The interplay between protein L-isoaspartyl methyltransferase activity and insulin-like signaling to extend lifespan in Caenorhabditis elegans

The protein L-isoaspartyl-O-methyltransferase functions to initiate the repair of isomerized aspartyl and asparaginyl residues that spontaneously accumulate with age in a variety of organisms. Caenorhabditis elegans nematodes lacking the pcm-1 gene encoding this enzyme display a normal lifespan and phenotype under standard laboratory growth conditions. However, significant defects in development, egg laying, dauer survival, and autophagy have been observed in pcm-1 mutant nematodes when deprived of food and when exposed to oxidative stress. Interestingly, overexpression of this repair enzyme in both Drosophila and C. elegans extends adult lifespan under thermal stress. In this work, we show the involvement of the insulin/insulin-like growth factor-1 signaling (IIS) pathway in PCM-1-dependent lifespan extension in C. elegans. We demonstrate that reducing the levels of the DAF-16 downstream transcriptional effector of the IIS pathway by RNA interference reduces the lifespan extension resulting from PCM-1 overexpression. Using quantitative real-time PCR analysis, we show the up-regulation of DAF-16-dependent stress response genes in the PCM-1 overexpressor animals compared to wild-type and pcm-1 mutant nematodes under mild thermal stress conditions. Additionally, similar to other long-lived C. elegans mutants in the IIS pathway, including daf-2 and age-1 mutants, PCM-1 overexpressor adult animals display increased resistance to severe thermal stress, whereas pcm-1 mutant animals survive less long under these conditions. Although we observe a higher accumulation of damaged proteins in pcm-1 mutant nematodes, the basal level of isoaspartyl residues detected in wild-type animals was not reduced by PCM-1 overexpression. Our results support a signaling role for the protein L-isoaspartyl methyltransferase in lifespan extension that involves the IIS pathway, but that may be independent of its function in overall protein repair.