Oxidative stress and longevity in Caenorhabditis elegans as mediated by SKN-1

Mutations in the Caenorhabditis elegans orthologs of human genes required for mitochondrial tRNA modification cause similar electron transport chain defects but different nuclear responses

Several oxidative phosphorylation (OXPHOS) diseases are caused by defects in the post-transcriptional modification of mitochondrial tRNAs (mt-tRNAs). Mutations in MTO1 or GTPBP3 impair the modification of the wobble uridine at position 5 of the pyrimidine ring and cause heart failure. Mutations in TRMU affect modification at position 2 and cause liver disease. Presently, the molecular basis of the diseases and why mutations in the different genes lead to such different clinical symptoms is poorly understood. Here we use Caenorhabditis elegans as a model organism to investigate how defects in the TRMU, GTPBP3 and MTO1 orthologues (designated as mttu-1, mtcu-1, and mtcu-2, respectively) exert their effects. We found that whereas the inactivation of each C. elegans gene is associated with a mild OXPHOS dysfunction, mutations in mtcu-1 or mtcu-2 cause changes in the expression of metabolic and mitochondrial stress response genes that are quite different from those caused by mttu-1 mutations. Our data suggest that retrograde signaling promotes defect-specific metabolic reprogramming, which is able to rescue the OXPHOS dysfunction in the single mutants by stimulating the oxidative tricarboxylic acid cycle flux through complex II. This adaptive response, however, appears to be associated with a biological cost since the single mutant worms exhibit thermosensitivity and decreased fertility and, in the case of mttu-1, longer reproductive cycle. Notably, mttu-1 worms also exhibit increased lifespan. We further show that mtcu-1; mttu-1 and mtcu-2; mttu-1 double mutants display severe growth defects and sterility. The animal models presented here support the idea that the pathological states in humans may initially develop not as a direct consequence of a bioenergetic defect, but from the cell’s maladaptive response to the hypomodification status of mt-tRNAs. Our work highlights the important association of the defect-specific metabolic rewiring with the pathological phenotype, which must be taken into consideration in exploring specific therapeutic interventions.

Post-transcriptional modification of tRNAs is a universal process, thought to be essential for optimizing the functions of tRNAs. In humans, defects in the modification at position 2 (performed by protein TRMU) and 5 (carried out by proteins GTPBP3 and MTO1) of the uridine located at the wobble position of mitochondrial tRNAs (mt-tRNAs) cause oxidative phosphorylation (OXPHOS) dysfunction, and lead to liver and heart failure, respectively. However, the underlying mechanisms leading to pathogenesis are not well-known, and hence there is no molecular explanation for the different clinical phenotypes. We use Caenorhabditis elegans to compare in the same animal model and genetic background the effects of inactivating the TRMU, GTPBP3 and MTO1 orthologues on the phenotype and gene expression pattern of nuclear and mitochondrial DNA. Our data show that C. elegans responds to mt-tRNA hypomodification by changing in a defect-specific manner the expression of nuclear and mitochondrial genes, which leads, in all single mutants, to a rescue of the OXPHOS dysfunction that is associated with a biological cost. Our work suggests that pathology may develop as a consequence of the cell’s maladaptive response to the hypomodification status of mt-tRNAs.

Lifespan extension by peroxidase and dual oxidase-mediated ROS signaling through pyrroloquinoline quinone in C. elegans

Reactive oxygen species (ROS), originally characterized based on their harmful effects on cells or organisms, are now recognized as important signal molecules regulating various biological processes. In particular, low levels of ROS released from mitochondria extend lifespan. Here, we identified a novel mechanism of generating appropriate levels of ROS at the plasma membrane through a peroxidase and dual oxidase (DUOX) system, which could extend lifespan in Caenorhabditis elegans A redox co-factor, pyrroloquinoline quinone (PQQ), activates the C. elegans DUOX protein BLI-3 to produce the ROS H₂O₂ at the plasma membrane, which is subsequently degraded by peroxidase (MLT-7), eventually ensuring adequate levels of ROS. These ROS signals are transduced mainly by the oxidative stress transcriptional factors SKN-1 (Nrf2 or NFE2L2 in mammals) and JUN-1, and partially by DAF-16 (a FOXO protein homolog). Cell biology experiments demonstrated a similarity between the mechanisms of PQQ-induced activation of human DUOX1 and DUOX2 and that of C. elegans BLI-3, suggesting that DUOXs are potential targets of intervention for lifespan extension. We propose that low levels of ROS, fine-tuned by the peroxidase and dual oxidase system at the plasma membrane, act as second messengers to extend lifespan by the effect of hormesis.

A Genetic Analysis of the Caenorhabditis elegans Detoxification Response

Oxidative damage contributes to human diseases of aging including diabetes, cancer, and cardiovascular disorders. Reactive oxygen species resulting from xenobiotic and endogenous metabolites are sensed by a poorly understood process, triggering a cascade of regulatory factors and leading to the activation of the transcription factor Nrf2 (Nuclear factor-erythroid-related factor 2, SKN-1 in Caenorhabditis elegans). Nrf2/SKN-1 activation promotes the induction of the phase II detoxification system that serves to limit oxidative stress. We have extended a previous C. elegans genetic approach to explore the mechanisms by which a phase II enzyme is induced by endogenous and exogenous oxidants. The xrep (xenobiotics response pathway) mutants were isolated as defective in their ability to properly regulate the induction of a glutathione S-transferase (GST) reporter. The xrep-1 gene was previously identified as wdr-23, which encodes a C. elegans homolog of the mammalian β-propeller repeat-containing protein WDR-23 Here, we identify and confirm the mutations in xrep-2, xrep-3, and xrep-4 The xrep-2 gene is alh-6, an ortholog of a human gene mutated in familial hyperprolinemia. The xrep-3 mutation is a gain-of-function allele of skn-1 The xrep-4 gene is F46F11.6, which encodes a F-box-containing protein. We demonstrate that xrep-4 alters the stability of WDR-23 (xrep-1), a key regulator of SKN-1 (xrep-3). Epistatic relationships among the xrep mutants and their interacting partners allow us to propose an ordered genetic pathway by which endogenous and exogenous stressors induce the phase II detoxification response.

Single swim sessions in C. elegans induce key features of mammalian exercise

BACKGROUND

Exercise exerts remarkably powerful effects on metabolism and health, with anti-disease and anti-aging outcomes. Pharmacological manipulation of exercise benefit circuits might improve the health of the sedentary and the aging populations. Still, how exercised muscle signals to induce system-wide health improvement remains poorly understood. With a long-term interest in interventions that promote animal-wide health improvement, we sought to define exercise options for Caenorhabditis elegans.

RESULTS

Here, we report on the impact of single swim sessions on C. elegans physiology. We used microcalorimetry to show that C. elegans swimming has a greater energy cost than crawling. Animals that swam continuously for 90 min specifically consumed muscle fat supplies and exhibited post-swim locomotory fatigue, with both muscle fat depletion and fatigue indicators recovering within 1 hour of exercise cessation. Quantitative polymerase chain reaction (qPCR) transcript analyses also suggested an increase in fat metabolism during the swim, followed by the downregulation of specific carbohydrate metabolism transcripts in the hours post-exercise. During a 90 min swim, muscle mitochondria matrix environments became more oxidized, as visualized by a localized mitochondrial reduction-oxidation-sensitive green fluorescent protein reporter. qPCR data supported specific transcriptional changes in oxidative stress defense genes during and immediately after a swim. Consistent with potential antioxidant defense induction, we found that a single swim session sufficed to confer protection against juglone-induced oxidative stress inflicted 4 hours post-exercise.

CONCLUSIONS

In addition to showing that even a single swim exercise bout confers physiological changes that increase robustness, our data reveal that acute swimming-induced changes share common features with some acute exercise responses reported in humans. Overall, our data validate an easily implemented swim experience as C. elegans exercise, setting the foundation for exploiting the experimental advantages of this model to genetically or pharmacologically identify the exercise-associated molecules and signaling pathways that confer system-wide health benefits.

Local neuropeptide signaling modulates serotonergic transmission to shape the temporal organization of C. elegans egg-laying behavior

Animal behaviors are often composed of distinct alternating behavioral states. Neuromodulatory signals are thought to be critical for establishing stable behavioral states and for orchestrating transitions between them. However, we have only a limited understanding of how neuromodulatory systems act in vivo to alter circuit performance and shape behavior. To address these questions, we have investigated neuromodulatory signaling in the context of Caenorhabditis elegans egg-laying. Egg-laying activity cycles between discrete states-short bursts of egg deposition (active phases) that alternate with prolonged quiescent periods (inactive phases). Here using genetic, pharmacological and optogenetic approaches for cell-specific activation and inhibition, we show that a group of neurosecretory cells (uv1) located in close spatial proximity to the egg-laying neuromusculature direct the temporal organization of egg-laying by prolonging the duration of inactive phases. We demonstrate that the modulatory effects of the uv1 cells are mediated by peptides encoded by the nlp-7 and flp-11 genes that act locally to inhibit circuit activity, primarily by inhibiting vesicular release of serotonin from HSN motor neurons. This peptidergic inhibition is achieved, at least in part, by reducing synaptic vesicle abundance in the HSN motor neurons. By linking the in vivo actions of specific neuropeptide signaling systems with the generation of stable behavioral outcomes, our study reveals how cycles of neuromodulation emanating from non-neuronal cells can fundamentally shape the organization of a behavioral program.

Plant-parasitic nematodes: towards understanding molecular players in stress responses

BACKGROUND

Plant-parasitic nematode interactions occur within a vast molecular plant immunity network. Following initial contact with the host plant roots, plant-parasitic nematodes (PPNs) activate basal immune responses. Defence priming involves the release in the apoplast of toxic molecules derived from reactive species or secondary metabolism. In turn, PPNs must overcome the poisonous and stressful environment at the plant-nematode interface. The ability of PPNs to escape this first line of plant immunity is crucial and will determine its virulence.

SCOPE

Nematodes trigger crucial regulatory cytoprotective mechanisms, including antioxidant and detoxification pathways. Knowledge of the upstream regulatory components that contribute to both of these pathways in PPNs remains elusive. In this review, we discuss how PPNs probably orchestrate cytoprotection to resist plant immune responses, postulating that it may be derived from ancient molecular mechanisms. The review focuses on two transcription factors, DAF-16 and SKN-1 , which are conserved in the animal kingdom and are central regulators of cell homeostasis and immune function. Both regulate the unfolding protein response and the antioxidant and detoxification pathways. DAF-16 and SKN-1 target a broad spectrum of Caenorhabditis elegans genes coding for numerous protein families present in the secretome of PPNs. Moreover, some regulatory elements of DAF-16 and SKN-1 from C. elegans have already been identified as important genes for PPN infection.

CONCLUSION

DAF-16 and SKN-1 genes may play a pivotal role in PPNs during parasitism. In the context of their hub status and mode of regulation, we suggest alternative strategies for control of PPNs through RNAi approaches.

Beneficial effects of antioxidative lactic acid bacteria

Oxidative stress is caused by exposure to reactive oxygen intermediates. The oxidative damage of cell components such as proteins, lipids, and nucleic acids one of the important factors associated with diabetes mellitus, cancers and cardiovascular diseases. This occurs as a result of imbalance between the generations of oxygen derived radicals and the organism's antioxidant potential. The amount of oxidative damage increases as an organism ages and is postulated to be a major causal factor of senescence. To date, many studies have focused on food sources, nutrients, and components that exert antioxidant activity in worms, flies, mice, and humans. Probiotics, live microorganisms that when administered in adequate amounts provide many beneficial effects on the human health, have been attracting growing interest for their health-promoting effects, and have often been administered in fermented milk products. In particular, lactic acid bacteria (LAB) are known to conferre physiologic benefits. Many studies have indicated the antioxidative activity of LAB. Here we review that the effects of lactic acid bacteria to respond to oxidative stress, is connected to oxidative-stress related disease and aging.

Non-linear impact of glutathione depletion on C. elegans life span and stress resistance

The redox environment in cells and organisms is set by low-molecular mass and protein-bound thiols, with glutathione (GSH) representing a major intracellular redox buffer. Subtle thiol oxidation elicits signal transduction processes and adaptive responses to cope with stressors, whereas highly oxidizing conditions may provoke cell death. We here tested how thiol depletion affects life span, stress resistance and stress signaling in the model organism Caenorhabditis elegans. Diethyl maleate (DEM), an α,β-unsaturated carbonyl compound that conjugates to GSH and other thiols, decreased C. elegans life span at a concentration of 1mM. In contrast, low and moderate doses of DEM (10-100µM) increased mean and maximum life span and improved resistance against oxidative stress. DEM-induced life span extension was not detectable in worms deficient in either the FoxO orthologue, DAF-16, or the Nrf2 orthologue, SKN-1, pointing to a collaborative role of the two transcription factors in life span extension induced by thiol depletion. Cytoprotective target genes of DAF-16 and SKN-1 were upregulated after at least 3 days of exposure to 100µM DEM, but not 1mM DEM, whereas only 1mM DEM caused upregulation of egl-1, a gene controlled by a p53-orthologue, CEP-1. In order to test whether depletion of GSH may elicit effects similar to DEM, we suppressed GSH biosynthesis in worms by attenuating γ-glutamylcysteine synthetase (gcs-1) expression through RNAi. The decline in GSH levels elicited by gcs-1 knockdown starting at young adult stage did not impair viability, but increased both stress resistance and life expectancy of the worms. In contrast, gcs-1 knockdown commencing right after hatching impaired nematode stress resistance and rendered young adult worms prone to vulval ruptures during egg-laying. Thus, modest decrease in GSH levels in young adult worms may promote stress resistance and life span, whereas depletion of GSH is detrimental to freshly hatched and developing worms.

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

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

The Skp1 Homologs SKR-1/2 Are Required for the Caenorhabditis elegans SKN-1 Antioxidant/Detoxification Response Independently of p38 MAPK

SKN-1/Nrf are the primary antioxidant/detoxification response transcription factors in animals and they promote health and longevity in many contexts. SKN-1/Nrf are activated by a remarkably broad-range of natural and synthetic compounds and physiological conditions. Defining the signaling mechanisms that regulate SKN-1/Nrf activation provides insights into how cells coordinate responses to stress. Nrf2 in mammals is regulated in part by the redox sensor repressor protein named Keap1. In C. elegans, the p38 MAPK cascade in the intestine activates SKN-1 during oxidative stress by promoting its nuclear accumulation. Interestingly, we find variation in the kinetics of p38 MAPK activation and tissues with SKN-1 nuclear accumulation among different pro-oxidants that all trigger strong induction of SKN-1 target genes. Using genome-wide RNAi screening, we identify new genes that are required for activation of the core SKN-1 target gene gst-4 during exposure to the natural pro-oxidant juglone. Among 10 putative activators identified in this screen was skr-1/2, highly conserved homologs of yeast and mammalian Skp1, which function to assemble protein complexes. Silencing of skr-1/2 inhibits induction of SKN-1 dependent detoxification genes and reduces resistance to pro-oxidants without decreasing p38 MAPK activation. Global transcriptomics revealed strong correlation between genes that are regulated by SKR-1/2 and SKN-1 indicating a high degree of specificity. We also show that SKR-1/2 functions upstream of the WD40 repeat protein WDR-23, which binds to and inhibits SKN-1. Together, these results identify a novel p38 MAPK independent signaling mechanism that activates SKN-1 via SKR-1/2 and involves WDR-23.

IMPACT is a GCN2 inhibitor that limits lifespan in Caenorhabditis elegans

BACKGROUND

The General Control Nonderepressible 2 (GCN2) kinase is a conserved member of the integrated stress response (ISR) pathway that represses protein translation and helps cells to adapt to conditions of nutrient shortage. As such, GCN2 is required for longevity and stress resistance induced by dietary restriction (DR). IMPACT is an ancient protein that inhibits GCN2.

RESULTS

Here, we tested whether IMPACT down-regulation mimics the effects of DR in C. elegans. Knockdown of the C. elegans IMPACT homolog impt-1 activated the ISR pathway and increased lifespan and stress resistance of worms in a gcn-2-dependent manner. Impt-1 knockdown exacerbated DR-induced longevity and required several DR-activated transcription factors to extend lifespan, among them SKN-1 and DAF-16, which were induced during larval development and adulthood, respectively, in response to impt-1 RNAi.

CONCLUSIONS

IMPACT inhibits the ISR pathway, thus limiting the activation of stress response factors that are beneficial during aging and required under DR.

C. elegans screening strategies to identify pro-longevity interventions

Drugs screenings in search of enhancers or suppressors of selected readout(s) are nowadays mainly carried out in single cells systems. These approaches are however limited when searching for compounds with effects at the organismal level. To overcome this drawback the use of different model organisms to carry out modifier screenings has exponentially grown in the past decade. Unique characteristics such as easy manageability, low cost, fast reproductive cycle, short lifespan, simple anatomy and genetic amenability, make the nematode Caenorhabditis elegans especially suitable for this purpose. Here we briefly review the different high-throughput and high-content screenings which exploited the nematode to identify new compounds extending healthy lifespan. In this context, we describe our recently developed screening strategy to search for pro-longevity interventions taking advantage of the very reproducible phenotypes observed in C. elegans upon different degrees of mitochondrial stress. Indeed, in Mitochondrial mutants, the processes induced to cope with mild mitochondrial alterations during development, and ultimately extending animal lifespan, lead to reduced size and induction of specific stress responses. Instead, upon strong mitochondrial dysfunction, worms arrest their development. Exploiting these automatically quantifiable phenotypic readouts, we developed a new screening approach using the Cellomics ArrayScanVTI-HCS Reader and identified a new pro-longevity drug.

Polymorphism in ion channel genes of Dirofilaria immitis: Relevant knowledge for future anthelmintic drug design

Dirofilaria immitis, a filarial parasite, causes cardiopulmonary dirofilariasis in dogs, cats and wild canids. The macrocyclic lactone (ML) class of drugs has been used to prevent heartworm infection. There is confirmed ML resistance in D. immitis and thus there is an urgent need to find new anthelmintics that could prevent and/or control the disease. Targeting ion channels of D. immitis for drug design has obvious advantages. These channels, present in the nematode nervous system, control movement, feeding, mating and respond to environmental cues which are necessary for survival of the parasite. Any new drug that targets these ion channels is likely to have a motility phenotype and should act to clear the worms from the host. Many of the successful anthelmintics in the past have targeted these ion channels and receptors. Knowledge about genetic variability of the ion channel and receptor genes should be useful information for drug design as receptor polymorphism may affect responses to a drug. Such information may also be useful for anticipation of possible resistance development. A total of 224 ion channel genes/subunits have been identified in the genome of D. immitis. Whole genome sequencing data of parasites from eight different geographical locations, four from ML-susceptible populations and the other four from ML-loss of efficacy (LOE) populations, were used for polymorphism analysis. We identified 1762 single nucleotide polymorphic (SNP) sites (1508 intronic and 126 exonic) in these 224 ion channel genes/subunits with an overall polymorphic rate of 0.18%. Of the SNPs found in the exon regions, 129 of them caused a non-synonymous type of polymorphism. Fourteen of the exonic SNPs caused a change in predicted secondary structure. A few of the SNPs identified may have an effect on gene expression, function of the protein and resistance selection processes.

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In the Dirofilaria immitis genome, 126 ion channel genes were identified.

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Within 126 ion channel genes, 1762 polymorphic loci were identified.

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Fourteen exonic SNPs caused a change in predicted secondary structure.

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SNPs may effect gene expression, protein function or resistance selection.

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D. immitis populations have low genetic variability among ion channel genes.

Dopamine signaling promotes the xenobiotic stress response and protein homeostasis

Multicellular organisms encounter environmental conditions that adversely affect protein homeostasis (proteostasis), including extreme temperatures, toxins, and pathogens. It is unclear how they use sensory signaling to detect adverse conditions and then activate stress response pathways so as to offset potential damage. Here, we show that dopaminergic mechanosensory neurons in C. elegans release the neurohormone dopamine to promote proteostasis in epithelia. Signaling through the DA receptor DOP-1 activates the expression of xenobiotic stress response genes involved in pathogenic resistance and toxin removal, and these genes are required for the removal of unstable proteins in epithelia. Exposure to a bacterial pathogen (Pseudomonas aeruginosa) results in elevated removal of unstable proteins in epithelia, and this enhancement requires DA signaling. In the absence of DA signaling, nematodes show increased sensitivity to pathogenic bacteria and heat-shock stress. Our results suggest that dopaminergic sensory neurons, in addition to slowing down locomotion upon sensing a potential bacterial feeding source, also signal to frontline epithelia to activate the xenobiotic stress response so as to maintain proteostasis and prepare for possible infection.

Contrasting invertebrate immune defense behaviors caused by a single gene, the Caenorhabditis elegans neuropeptide receptor gene npr-1

Background

The invertebrate immune system comprises physiological mechanisms, physical barriers and also behavioral responses. It is generally related to the vertebrate innate immune system and widely believed to provide nonspecific defense against pathogens, whereby the response to different pathogen types is usually mediated by distinct signalling cascades. Recent work suggests that invertebrate immune defense can be more specific at least at the phenotypic level. The underlying genetic mechanisms are as yet poorly understood.

Results

We demonstrate in the model invertebrate Caenorhabditis elegans that a single gene, a homolog of the mammalian neuropeptide Y receptor gene, npr-1, mediates contrasting defense phenotypes towards two distinct pathogens, the Gram-positive Bacillus thuringiensis and the Gram-negative Pseudomonas aeruginosa. Our findings are based on combining quantitative trait loci (QTLs) analysis with functional genetic analysis and RNAseq-based transcriptomics. The QTL analysis focused on behavioral immune defense against B. thuringiensis, using recombinant inbred lines (RILs) and introgression lines (ILs). It revealed several defense QTLs, including one on chromosome X comprising the npr-1 gene. The wildtype N2 allele for the latter QTL was associated with reduced defense against B. thuringiensis and thus produced an opposite phenotype to that previously reported for the N2 npr-1 allele against P. aeruginosa. Analysis of npr-1 mutants confirmed these contrasting immune phenotypes for both avoidance behavior and nematode survival. Subsequent transcriptional profiling of C. elegans wildtype and npr-1 mutant suggested that npr-1 mediates defense against both pathogens through p38 MAPK signaling, insulin-like signaling, and C-type lectins. Importantly, increased defense towards P. aeruginosa seems to be additionally influenced through the induction of oxidative stress genes and activation of GATA transcription factors, while the repression of oxidative stress genes combined with activation of Ebox transcription factors appears to enhance susceptibility to B. thuringiensis.

Conclusions

Our findings highlight the role of a single gene, npr-1, in fine-tuning nematode immune defense, showing the ability of the invertebrate immune system to produce highly specialized and potentially opposing immune responses via single regulatory genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2603-8) contains supplementary material, which is available to authorized users.

Effects and mechanisms of prolongevity induced by Lactobacillus gasseri SBT2055 in Caenorhabditis elegans

Lactic-acid bacteria are widely recognized beneficial host associated groups of the microbiota of humans and animals. Some lactic-acid bacteria have the ability to extend the lifespan of the model animals. The mechanisms behind the probiotic effects of bacteria are not entirely understood. Recently, we reported the benefit effects of Lactobacillus gasseriSBT2055 (LG2055) on animal and human health, such as preventing influenza A virus, and augmentation of IgA production. Therefore, it was preconceived that LG2055 has the beneficial effects on longevity and/or aging. We examined the effects of LG2055 on lifespan and aging of Caenorhabditis elegans and analyzed the mechanism of prolongevity. Our results demonstrated that LG2055 has the beneficial effects on longevity and anti-aging of C. elegans. Feeding with LG2055 upregulated the expression of the skn-1 gene and the target genes of SKN-1, encoding the antioxidant proteins enhancing antioxidant defense responses. We found that feeding with LG2055 directly activated SKN-1 activity via p38 MAPK pathway signaling. The oxidative stress response is elicited by mitochondrial dysfunction in aging, and we examined the influence of LG2055 feeding on the membrane potential of mitochondria. Here, the amounts of mitochondria were significantly increased by LG2055 feeding in comparison with the control. Our result suggests that feeding with LG2055 is effective to the extend lifespan in C. elegans by a strengthening of the resistance to oxidative stress and by stimulating the innate immune response signaling including p38MAPK signaling pathway and others.

TRX-1 Regulates SKN-1 Nuclear Localization Cell Non-autonomously in Caenorhabditis elegans

The Caenorhabditis elegans oxidative stress response transcription factor, SKN-1, is essential for the maintenance of redox homeostasis and is a functional ortholog of the Nrf family of transcription factors. The numerous levels of regulation that govern these transcription factors underscore their importance. Here, we add a thioredoxin, encoded by trx-1, to the expansive list of SKN-1 regulators. We report that loss of trx-1 promotes nuclear localization of intestinal SKN-1 in a redox-independent, cell non-autonomous fashion from the ASJ neurons. Furthermore, this regulation is not general to the thioredoxin family, as two other C. elegans thioredoxins, TRX-2 and TRX-3, do not play a role in this process. Moreover, TRX-1-dependent regulation requires signaling from the p38 MAPK-signaling pathway. However, while TRX-1 regulates SKN-1 nuclear localization, classical SKN-1 transcriptional activity associated with stress response remains largely unaffected. Interestingly, RNA-Seq analysis revealed that loss of trx-1 elicits a general, organism-wide down-regulation of several classes of genes; those encoding for collagens and lipid transport being most prevalent. Together, these results uncover a novel role for a thioredoxin in regulating intestinal SKN-1 nuclear localization in a cell non-autonomous manner, thereby contributing to the understanding of the processes involved in maintaining redox homeostasis throughout an organism.

Central nervous system promotes thermotolerance via FoxO/DAF-16 activation through octopamine and acetylcholine signaling in Caenorhabditis elegans

The autonomic nervous system (ANS) responds to many kinds of stressors to maintain homeostasis. Although the ANS is believed to regulate stress tolerance, the exact mechanism underlying this is not well understood. To understand this, we focused on longevity genes, which have functions such as lifespan extension and promotion of stress tolerance. To understand the relationship between ANS and longevity genes, we analyzed stress tolerance of Caenorhabditis elegans treated with octopamine, which has an affinity to noradrenaline in insects, and acetylcholine. Octopamine and acetylcholine did not show resistance against H2O2, but the neurotransmitters promoted thermotolerance via DAF-16. However, chronic treatment with octopamine and acetylcholine did not extend the lifespan, although DAF-16 plays an important role in longevity. In conclusion, our results show that octopamine and acetylcholine activate DAF-16 in response to stress, but chronic induction of octopamine and acetylcholine is not beneficial for increasing longevity.

Graded Proteasome Dysfunction in Caenorhabditis elegans Activates an Adaptive Response Involving the Conserved SKN-1 and ELT-2 Transcription Factors and the Autophagy-Lysosome Pathway

The maintenance of cellular proteins in a biologically active and structurally stable state is a vital endeavor involving multiple cellular pathways. One such pathway is the ubiquitin-proteasome system that represents a major route for protein degradation, and reductions in this pathway usually have adverse effects on the health of cells and tissues. Here, we demonstrate that loss-of-function mutants of the Caenorhabditis elegans proteasome subunit, RPN-10, exhibit moderate proteasome dysfunction and unexpectedly develop both increased longevity and enhanced resistance to multiple threats to the proteome, including heat, oxidative stress, and the presence of aggregation prone proteins. The rpn-10 mutant animals survive through the activation of compensatory mechanisms regulated by the conserved SKN-1/Nrf2 and ELT-2/GATA transcription factors that mediate the increased expression of genes encoding proteasome subunits as well as those mediating oxidative- and heat-stress responses. Additionally, we find that the rpn-10 mutant also shows enhanced activity of the autophagy-lysosome pathway as evidenced by increased expression of the multiple autophagy genes including atg-16.2, lgg-1, and bec-1, and also by an increase in GFP::LGG-1 puncta. Consistent with a critical role for this pathway, the enhanced resistance of the rpn-10 mutant to aggregation prone proteins depends on autophagy genes atg-13, atg-16.2, and prmt-1. Furthermore, the rpn-10 mutant is particularly sensitive to the inhibition of lysosome activity via either RNAi or chemical means. We also find that the rpn-10 mutant shows a reduction in the numbers of intestinal lysosomes, and that the elt-2 gene also plays a novel and vital role in controlling the production of functional lysosomes by the intestine. Overall, these experiments suggest that moderate proteasome dysfunction could be leveraged to improve protein homeostasis and organismal health and longevity, and that the rpn-10 mutant provides a unique platform to explore these possibilities.

Inhibition of the oxidative stress response by heat stress in Caenorhabditis elegans

It has long been recognized that simultaneous exposure to heat stress and oxidative stress shows a synergistic interaction that reduces organismal fitness, but relatively little is known about the mechanisms underlying this interaction. We investigated the role of molecular stress responses in driving this synergistic interaction using the nematode Caenorhabditis elegans. To induce oxidative stress, we used the pro-oxidant compounds acrylamide, paraquat, and juglone. As expected, we found that heat stress and oxidative stress interact synergistically to reduce survival. Compared to exposure to each stressor alone, during simultaneous, sub-lethal exposure to heat stress and oxidative stress the normal induction of key oxidative stress response (OxSR) genes was generally inhibited while the induction of key heat shock response (HSR) genes was not. Genetically activating the SKN-1 dependent OxSR increased a marker for protein aggregation and decreased whole-worm survival during heat stress alone, with the latter being independent of HSF-1. In contrast, inactivating the HSR by HSF-1 knockdown, which would be expected to decrease basal heat shock protein expression, increased survival during oxidative stress alone compared to wild- type worms. Taken together, these data suggest that in C. elegans the HSR and OxSR cannot be simultaneously activated to the same extent that each can be activated during a single stressor exposure. We conclude that the observed synergistic reduction in survival during combined exposure to heat stress and oxidative stress is due, at least in part, to inhibition of the OxSR during activation of the HSR.

UPS Activation in the Battle Against Aging and Aggregation-Related Diseases: An Extended Review

Aging is a biological process accompanied by gradual increase of damage in all cellular macromolecules, i.e., nucleic acids, lipids, and proteins. When the proteostasis network (chaperones and proteolytic systems) cannot reverse the damage load due to its excess as compared to cellular repair/regeneration capacity, failure of homeostasis is established. This failure is a major hallmark of aging and/or aggregation-related diseases. Dysfunction of the major cellular proteolytic machineries, namely the proteasome and the lysosome, has been reported during the progression of aging and aggregation-prone diseases. Therefore, activation of these pathways is considered as a possible preventive or therapeutic approach against the progression of these processes. This chapter focuses on UPS activation studies in cellular and organismal models and the effects of such activation on aging, longevity and disease prevention or reversal.

Folic acid supplementation at lower doses increases oxidative stress resistance and longevity in Caenorhabditis elegans

Folic acid (FA) is an essential nutrient that the human body needs but cannot be synthesized on its own. Fortified foods and plant food sources such as green leafy vegetables, beans, fruits, and juices are good sources of FA to meet the daily requirements of the body. The aim was to evaluate the effect of dietary FA levels on the longevity of well-known experimental aging model Caenorhabditis elegans. Here, we show for first time that FA extends organism life span and causes a delay in aging. We observed that FA inhibits mechanistic target of rapamycin (mTOR) and insulin/insulin growth factor 1 (IGF-1) signaling pathways to control both oxidative stress levels and life span. The expression levels of stress- and life span-relevant gerontogenes, viz. daf-16, skn-1, and sir. 2.1, and oxidative enzymes, such as glutathione S-transferase 4 (GST-4) and superoxide dismutase 3 (SOD-3), were also found to be highly enhanced to attenuate the intracellular reactive oxygen species (ROS) damage and to delay the aging process. Our study promotes the use of FA to mitigate abiotic stresses and other aging-related ailments.

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

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

Lipid-mediated regulation of SKN-1/Nrf in response to germ cell absence

In Caenorhabditis elegans, ablation of germline stem cells (GSCs) extends lifespan, but also increases fat accumulation and alters lipid metabolism, raising the intriguing question of how these effects might be related. Here, we show that a lack of GSCs results in a broad transcriptional reprogramming in which the conserved detoxification regulator SKN-1/Nrf increases stress resistance, proteasome activity, and longevity. SKN-1 also activates diverse lipid metabolism genes and reduces fat storage, thereby alleviating the increased fat accumulation caused by GSC absence. Surprisingly, SKN-1 is activated by signals from this fat, which appears to derive from unconsumed yolk that was produced for reproduction. We conclude that SKN-1 plays a direct role in maintaining lipid homeostasis in which it is activated by lipids. This SKN-1 function may explain the importance of mammalian Nrf proteins in fatty liver disease and suggest that particular endogenous or dietary lipids might promote health through SKN-1/Nrf.

Discovery of ML358, a Selective Small Molecule Inhibitor of the SKN-1 Pathway Involved in Drug Detoxification and Resistance in Nematodes

Nematodes parasitize ∼1/3 of humans worldwide, and effective treatment via administration of anthelmintics is threatened by growing resistance to current therapies. The nematode transcription factor SKN-1 is essential for development of embryos and upregulates the expression of genes that result in modification, conjugation, and export of xenobiotics, which can promote resistance. Distinct differences in regulation and DNA binding relative to mammalian Nrf2 make SKN-1 a promising and selective target for the development of anthelmintics with a novel mode of action that targets stress resistance and drug detoxification. We report 17 (ML358), a first in class small molecule inhibitor of the SKN-1 pathway. Compound 17 resulted from a vanillamine-derived hit identified by high throughput screening that was advanced through analog synthesis and structure-activity studies. Compound 17 is a potent (IC50 = 0.24 μM, Emax = 100%) and selective inhibitor of the SKN-1 pathway and sensitizes the model nematode C. elegans to oxidants and anthelmintics. Compound 17 is inactive against Nrf2, the homologous mammalian detoxification pathway, and is not toxic to C. elegans (LC50 > 64 μM) and Fa2N-4 immortalized human hepatocytes (LC50 > 5.0 μM). In addition, 17 exhibits good solubility, permeability, and chemical and metabolic stability in human and mouse liver microsomes. Therefore, 17 is a valuable probe to study regulation and function of SKN-1 in vivo. By selective targeting of the SKN-1 pathway, 17 could potentially lead to drug candidates that may be used as adjuvants to increase the efficacy and useful life of current anthelmintics.

Polyamine-independent Expression of Caenorhabditis elegans Antizyme

Degradation of ornithine decarboxylase, the rate-limiting enzyme of polyamine biosynthesis, is promoted by the protein antizyme. Expression of antizyme is positively regulated by rising polyamine concentrations that induce a +1 translational frameshift required for production of the full-length protein. Antizyme itself is negatively regulated by the antizyme inhibitor. In our study, the regulation of Caenorhabditis elegans antizyme was investigated, and the antizyme inhibitor was identified. By applying a novel GFP-based method to monitor antizyme frameshifting in vivo, we show that the induction of translational frameshifting also occurs under stressful conditions. Interestingly, during starvation, the initiation of frameshifting was independent of polyamine concentrations. Because frameshifting was also prevalent in a polyamine auxotroph double mutant, a polyamine-independent regulation of antizyme frameshifting is suggested. Polyamine-independent induction of antizyme expression was found to be negatively regulated by the peptide transporter PEPT-1, as well as the target of rapamycin, but not by the daf-2 insulin signaling pathway. Stress-dependent expression of C. elegans antizyme occurred morely slowly than expression in response to increased polyamine levels, pointing to a more general reaction to unfavorable conditions and a diversion away from proliferation and reproduction toward conservation of energy. Interestingly, antizyme expression was found to drastically increase in aging individuals in a postreproductive manner. Although knockdown of antizyme did not affect the lifespan of C. elegans, knockdown of the antizyme inhibitor led to a significant reduction in lifespan. This is most likely caused by an increase in antizyme-mediated degradation of ornithine decarboxylase-1 and a resulting reduction in cellular polyamine levels.

mTORC1 signaling activates NRF1 to increase cellular proteasome levels

Defects in the maintenance of protein homeostasis, or proteostasis, has emerged as an underlying feature of a variety of human pathologies, including aging-related diseases. Proteostasis is achieved through the coordinated action of cellular systems overseeing amino acid availability, mRNA translation, protein folding, secretion, and degradation. The regulation of these distinct systems must be integrated at various points to attain a proper balance. In a recent study, we found that the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) pathway, well known to enhance the protein synthesis capacity of cells while concordantly inhibiting autophagy, promotes the production of more proteasomes. Activation of mTORC1 genetically, through loss of the tuberous sclerosis complex (TSC) tumor suppressors, or physiologically, through growth factors or feeding, stimulates a transcriptional program involving the sterol-regulatory element binding protein 1 (SREBP1) and nuclear factor erythroid-derived 2-related factor 1 (NRF1; also known as NFE2L1) transcription factors leading to an increase in cellular proteasome content. As discussed here, our findings suggest that this increase in proteasome levels facilitates both the maintenance of proteostasis and the recovery of amino acids in the face of an increased protein load consequent to mTORC1 activation. We also consider the physiological and pathological implications of this unexpected new downstream branch of mTORC1 signaling.

Catalpol Modulates Lifespan via DAF-16/FOXO and SKN-1/Nrf2 Activation in Caenorhabditis elegans

Catalpol is an effective component of rehmannia root and known to possess various pharmacological properties. The present study was aimed at investigating the potential effects of catalpol on the lifespan and stress tolerance using C. elegans model system. Herein, catalpol showed potent lifespan extension of wild-type nematode under normal culture condition. In addition, survival rate of catalpol-fed nematodes was significantly elevated compared to untreated control under heat and oxidative stress but not under hyperosmolality conditions. We also found that elevated antioxidant enzyme activities and expressions of stress resistance proteins were attributed to catalpol-mediated increased stress tolerance of nematode. We further investigated whether catalpol's longevity effect is related to aging-related factors including reproduction, food intake, and growth. Interestingly, catalpol exposure could attenuate pharyngeal pumping rate, indicating that catalpol may induce dietary restriction of nematode. Moreover, locomotory ability of aged nematode was significantly improved by catalpol treatment, while lipofuscin levels were attenuated, suggesting that catalpol may affect age-associated changes of nematode. Our mechanistic studies revealed that mek-1, daf-2, age-1, daf-16, and skn-1 are involved in catalpol-mediated longevity. These results indicate that catalpol extends lifespan and increases stress tolerance of C. elegans via DAF-16/FOXO and SKN-1/Nrf activation dependent on insulin/IGF signaling and JNK signaling.

Neuronal protein with tau-like repeats (PTL-1) regulates intestinal SKN-1 nuclear accumulation in response to oxidative stress

Oxidative stress is a central pathomechanism in Alzheimer's disease (AD) and other diseases with tau pathology. The Nrf2 transcription factor induces detoxification enzymes and improves tau pathology and cognition. Its homologue in C. elegans is SKN-1. We previously showed that the worm tau homologue, PTL-1, regulates neuronal aging and lifespan. Here, we tested PTL-1's involvement in the stress response. ptl-1 mutant animals are hypersensitive to oxidative stress and are defective in stress-mediated nuclear accumulation of SKN-1. This defect can be rescued by PTL-1 re-expression under the control of the ptl-1 promoter. Given the close relationship between aging and stress tolerance, we tested lifespan and found that PTL-1 and SKN-1 regulate longevity via similar processes. Our data also suggest that PTL-1 functions via neurons to modulate SKN-1, clarifying the role of this protein in the stress response and longevity.

Age- and manganese-dependent modulation of dopaminergic phenotypes in a C. elegans DJ-1 genetic model of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, yet its etiology and pathogenesis are poorly understood. PD is characterized by selective dopaminergic (DAergic) degeneration and progressive hypokinetic motor impairment. Mutations in dj-1 cause autosomal recessive early-onset PD. DJ-1 is thought to protect DAergic neurons via an antioxidant mechanism, but the precise basis of this protection has not yet been resolved. Aging and manganese (Mn) exposure are significant non-genetic risk factors for PD. Caenorhabditis elegans (C. elegans) is an optimal model for PD and aging studies because of its simple nervous system, conserved DAergic machinery, and short 20-day lifespan. Here we tested the hypothesis that C. elegans DJ-1 homologues were protective against Mn-induced DAergic toxicity in an age-dependent manner. We showed that the deletion of C. elegans DJ-1 related (djr) genes, djr-1.2, decreased survival after Mn exposure. djr-1.2, the DJ-1 homologue was expressed in DAergic neurons and its deletion decreased lifespan and dopamine (DA)-dependent dauer movement behavior after Mn exposure. We also tested the role of DAF-16 as a regulator of dj-1.2 interaction with Mn toxicity. Lifespan defects resulting from djr-1.2 deletion could be restored to normal by overexpression of either DJR-1.2 or DAF-16. Furthermore, dauer movement alterations after djr-1.2 deletion were abolished by constitutive activation of DAF-16 through mutation of its inhibitor, DAF-2 insulin receptor. Taken together, our results reveal PD-relevant interactions between aging, the PD environmental risk factor manganese, and homologues of the established PD genetic risk factor DJ-1. Our data demonstrate a novel role for the DJ-1 homologue, djr-1.2, in mitigating Mn-dependent lifespan reduction and DA signaling alterations, involving DAF-2/DAF-16 signaling.

Lifespan regulation under axenic dietary restriction: a close look at the usual suspects

In Caenorhabditis elegans, there are several ways to impose dietary restriction (DR) all of which extend lifespan to a different degree. Until recently, the molecular mechanisms underlying the DR-mediated lifespan extension were completely unknown but extensive efforts led to the identification of several key players in this process. Culture in sterile axenic medium is a method of DR (ADR), leading to an impressive doubling of lifespan. Earlier, we established that ADR-mediated longevity is independent of Ins/IGF signaling and eat-2. The only gene reported to be indispensable for the ADR lifespan effect is cbp-1 (Zhang et al., 2009) which was confirmed in this study. In an attempt to identify more genes involved in ADR-mediated longevity, we tested several candidate genes known to regulate lifespan extension in other DR regimens. We found that cup-4 is equally important as cbp-1 in ADR-mediated longevity and we identified some genes that may contribute to ADR-induced longevity, but are not required for the full lifespan effect.

Worming our way to novel drug discovery with the Caenorhabditis elegans proteostasis network, stress response and insulin-signaling pathways

INTRODUCTION

Many human diseases result from a failure of a single protein to achieve the correct folding and tertiary conformation. These so-called 'conformational diseases' involve diverse proteins and distinctive cellular pathologies. They all engage the proteostasis network (PN), to varying degrees in an attempt to mange cellular stress and restore protein homeostasis. The insulin/insulin-like growth factor signaling (IIS) pathway is a master regulator of cellular stress response, which is implicated in regulating components of the PN.

AREAS COVERED

This review focuses on novel approaches to target conformational diseases. The authors discuss the evidence supporting the involvement of the IIS pathway in modulating the PN and regulating proteostasis in Caenorhabditis elegans. Furthermore, they review previous PN and IIS drug screens and explore the possibility of using C. elegans for whole organism-based drug discovery for modulators of IIS-proteostasis pathways.

EXPERT OPINION

An alternative approach to develop individualized therapy for each conformational disease is to modulate the global PN. The involvement of the IIS pathway in regulating longevity and response to a variety of stresses is well documented. Increasing data now provide evidence for the close association between the IIS and the PN pathways. The authors believe that high-throughput screening campaigns, which target the C. elegans IIS pathway, may identify drugs that are efficacious in treating numerous conformational diseases.

Caloric restriction confers persistent anti-oxidative, pro-angiogenic, and anti-inflammatory effects and promotes anti-aging miRNA expression profile in cerebromicrovascular endothelial cells of aged rats

In rodents, moderate caloric restriction (CR) without malnutrition exerts significant cerebrovascular protective effects, improving cortical microvascular density and endothelium-dependent vasodilation, but the underlying cellular mechanisms remain elusive. To elucidate the persisting effects of CR on cerebromicrovascular endothelial cells (CMVECs), primary CMVECs were isolated from young (3 mo old) and aged (24 mo old) ad libitum-fed and aged CR F344xBN rats. We found an age-related increase in cellular and mitochondrial oxidative stress, which is prevented by CR. Expression and transcriptional activity of Nrf2 are both significantly reduced in aged CMVECs, whereas CR prevents age-related Nrf2 dysfunction. Expression of miR-144 was upregulated in aged CMVECs, and overexpression of miR-144 significantly decreased expression of Nrf2 in cells derived from both young animals and aged CR rats. Overexpression of a miR-144 antagomir in aged CMVECs significantly decreases expression of miR-144 and upregulates Nrf2. We found that CR prevents age-related impairment of angiogenic processes, including cell proliferation, adhesion to collagen, and formation of capillary-like structures and inhibits apoptosis in CMVECs. CR also exerts significant anti-inflammatory effects, preventing age-related increases in the transcriptional activity of NF-κB and age-associated pro-inflammatory shift in the endothelial secretome. Characterization of CR-induced changes in miRNA expression suggests that they likely affect several critical functions in endothelial cell homeostasis. The predicted regulatory effects of CR-related differentially expressed miRNAs in aged CMVECs are consistent with the anti-aging endothelial effects of CR observed in vivo. Collectively, we find that CR confers persisting anti-oxidative, pro-angiogenic, and anti-inflammatory cellular effects, preserving a youthful phenotype in rat cerebromicrovascular endothelial cells, suggesting that through these effects CR may improve cerebrovascular function and prevent vascular cognitive impairment.

Proteasome activation delays aging in vitro and in vivo

Aging is a natural biological process that is characterized by a progressive accumulation of macromolecular damage. In the proteome, aging is accompanied by decreased protein homeostasis and function of the major cellular proteolytic systems, leading to the accumulation of unfolded, misfolded, or aggregated proteins. In particular, the proteasome is responsible for the removal of normal as well as damaged or misfolded proteins. Extensive work during the past several years has clearly demonstrated that proteasome activation by either genetic means or use of compounds significantly retards aging. Importantly, this represents a common feature across evolution, thereby suggesting proteasome activation to be an evolutionarily conserved mechanism of aging and longevity regulation. This review article reports on the means of function of these proteasome activators and how they regulate aging in various species.

Caenorhabditis elegans: A useful model for studying metabolic disorders in which oxidative stress is a contributing factor

Caenorhabditis elegans is a powerful model organism that is invaluable for experimental research because it can be used to recapitulate most human diseases at either the metabolic or genomic level in vivo. This organism contains many key components related to metabolic and oxidative stress networks that could conceivably allow us to increase and integrate information to understand the causes and mechanisms of complex diseases. Oxidative stress is an etiological factor that influences numerous human diseases, including diabetes. C. elegans displays remarkably similar molecular bases and cellular pathways to those of mammals. Defects in the insulin/insulin-like growth factor-1 signaling pathway or increased ROS levels induce the conserved phase II detoxification response via the SKN-1 pathway to fight against oxidative stress. However, it is noteworthy that, aside from the detrimental effects of ROS, they have been proposed as second messengers that trigger the mitohormetic response to attenuate the adverse effects of oxidative stress. Herein, we briefly describe the importance of C. elegans as an experimental model system for studying metabolic disorders related to oxidative stress and the molecular mechanisms that underlie their pathophysiology.

Beta-caryophyllene modulates expression of stress response genes and mediates longevity in Caenorhabditis elegans

Beta-caryophyllene (BCP) is a natural bicyclic sesquiterpene and is a FDA approved food additive, found as an active ingredient in essential oils of numerous edible plants. It possesses a wide range of biological activities including anti-oxidant, anti-inflammatory, anti-cancerous and local anesthetic actions. We used the well established Caenorhabditis elegans model system to elucidate the stress modulatory and lifespan prolonging action of BCP. The present study for the first time reports the lifespan extension and stress modulation potential of BCP in C. elegans. Upon evaluation, it was found that 50μM dose of BCP increased the lifespan of C. elegans by over 22% (P≤0.0001) and significantly reduced intracellular free radical levels, maintaining cellular redox homeostasis. Moreover, the results suggest that BCP modulates feeding behavior, pharyngeal pumping and body size effectively. Further, this compound also exhibited significant reduction in intestinal lipofuscin levels. In the present investigation, we have predicted possible biological molecular targets for BCP using molecular docking approaches and BCP was found to have interaction with SIR-2.1, SKN-1 and DAF-16. The prediction was further validated in vivo using mutants and transgenic strains unraveling underlying genetic mechanism. It was observed that BCP increased lifespan of mev-1 and daf-16 but failed to augment lifespan in eat-2, sir-2.1 and skn-1 mutants. Relative quantification of mRNA demonstrated that several genes regulating oxidative stress, xenobiotic detoxification and longevity were modulated by BCP treatment. The study unravels the involvement of multiple signaling pathways in BCP mediated lifespan extension.

The conserved Mediator subunit MDT-15 is required for oxidative stress responses in Caenorhabditis elegans

Reactive oxygen species (ROS) play important signaling roles in metazoans, but also cause significant molecular damage. Animals tightly control ROS levels using sophisticated defense mechanisms, yet the transcriptional pathways that induce ROS defense remain incompletely understood. In the nematode Caenorhabditis elegans, the transcription factor SKN-1 is considered a master regulator for detoxification and oxidative stress responses. Here, we show that MDT-15, a subunit of the conserved Mediator complex, is also required for oxidative stress responses in nematodes. Specifically, mdt-15 is required to express SKN-1 targets upon chemical and genetic increase in SKN-1 activity. mdt-15 is also required to express genes in SKN-1-dependent and SKN-1-independent fashions downstream of insulin/IGF-1 signaling and for the longevity of daf-2/insulin receptor mutants. At the molecular level, MDT-15 binds SKN-1 through a region distinct from the classical transcription-factor-binding KIX-domain. Moreover, mdt-15 is essential for the transcriptional response to and survival on the organic peroxide tert-butyl-hydroperoxide (tBOOH), a largely SKN-1-independent response. The MDT-15 interacting nuclear hormone receptor, NHR-64, is specifically required for tBOOH but not arsenite resistance, but NHR-64 is dispensable for the transcriptional response to tBOOH. Hence, NHR-64 and MDT-15’s mode of action remain elusive. Lastly, the role of MDT-15 in oxidative stress defense is functionally separable from its function in fatty acid metabolism, as exogenous polyunsaturated fatty acid complementation rescues developmental, but not stress sensitivity phenotypes of mdt-15 worms. Our findings reveal novel conserved players in the oxidative stress response and suggest a broad cytoprotective role for MDT-15.

The ubiquitin proteasome system in Caenorhabditis elegans and its regulation

Protein degradation constitutes a major cellular function that is responsible for maintenance of the normal cellular physiology either through the degradation of normal proteins or through the elimination of damaged proteins. The Ubiquitin–Proteasome System (UPS)¹ is one of the main proteolytic systems that orchestrate protein degradation. Given that up- and down- regulation of the UPS system has been shown to occur in various normal (such as ageing) and pathological (such as neurodegenerative diseases) processes, the exogenous modulation of the UPS function and activity holds promise of (a) developing new therapeutic interventions against various diseases and (b) establishing strategies to maintain cellular homeostasis. Since the proteasome genes are evolutionarily conserved, their role can be dissected in simple model organisms, such as the nematode, Caenorhabditis elegans. In this review, we survey findings on the redox regulation of the UPS in C. elegans showing that the nematode is an instrumental tool in the identification of major players in the UPS pathway. Moreover, we specifically discuss UPS-related genes that have been modulated in the nematode and in human cells and have resulted in similar effects thus further exhibiting the value of this model in the study of the UPS.

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UPS is one of the main proteolytic systems that orchestrate protein degradation.

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Proteasome function can be dissected in Caenorhabditis elegans.

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Nematodes can be used in the identification of major players in the UPS pathway.

Regulation of synaptic nlg-1/neuroligin abundance by the skn-1/Nrf stress response pathway protects against oxidative stress

The Nrf family of transcription factors mediates adaptive responses to stress and longevity, but the identities of the crucial Nrf targets, and the tissues in which they function in multicellular organisms to promote survival, are not known. Here, we use whole transcriptome RNA sequencing to identify 810 genes whose expression is controlled by the SKN-1/Nrf2 negative regulator WDR-23 in the nervous system of Caenorhabditis elegans. Among the genes identified is the synaptic cell adhesion molecule nlg-1/neuroligin. We find that the synaptic abundance of NLG-1 protein increases following pharmacological treatments that generate oxidative stress or by the genetic activation of skn-1. Increasing nlg-1 dosage correlates with increased survival in response to oxidative stress, whereas genetic inactivation of nlg-1 reduces survival and impairs skn-1-mediated stress resistance. We identify a canonical SKN-1 binding site in the nlg-1 promoter that binds to SKN-1 in vitro and is necessary for SKN-1 and toxin-mediated increases in nlg-1 expression in vivo. Together, our results suggest that SKN-1 activation in the nervous system can confer protection to organisms in response to stress by directly regulating nlg-1/neuroligin expression.

Pinewood nematode-associated bacteria contribute to oxidative stress resistance of Bursaphelenchus xylophilus

Background

Pine wilt disease (PWD) caused by the pinewood nematode Bursaphelenchus xylophilus is one of the most serious forest diseases in the world. The role of B. xylophilus-associated bacteria in PWD and their interaction with the nematode, have recently been under substantial investigation. Several studies report a potential contribution of the bacteria for the PWD development, either as a helper to enhance the pathogenicity of the nematode or as a pathogenic agent expressing interesting traits related to lifestyle host-adaptation.

Results

We investigated the nematode-bacteria interaction under a severe oxidative stress (OS) condition using a pro-oxidant hydrogen peroxide and explored the adhesion ability of these bacteria to the cuticle surface of the nematodes. Our results clearly demonstrated a beneficial effect of the Serratia spp. (isolates LCN-4, LCN-16 and PWN-146) to B. xylophilus under the OS condition. Serratia spp. was found to be extremely OS-resistant, and promote survival of B. xylophilus and down-regulate two B. xylophilus catalase genes (Bxy-ctl-1 and Bxy-ctl-2). In addition, we show that the virulent isolate (Ka4) of B. xylophilus survives better than the avirulent (C14-5) isolate under the OS condition. The bacterial effect was transverse for both B. xylophilus isolates. We could not observe a strong and specific adhesion of these bacteria on the B. xylophilus cuticle surface.

Conclusions

We report, for the first time, that B. xylophilus associated bacteria may assist the nematode opportunistically in the disease, and that a virulent B. xylophilus isolate displayed a higher tolerance towards the OS conditions than an avirulent isolate.

Constitutive activation of the Nrf2/Keap1 pathway in insecticide-resistant strains of Drosophila

Pesticide resistance poses a major challenge for the control of vector-borne human diseases and agricultural crop protection. Although a number of studies have defined how mutations in specific target proteins can lead to insecticide resistance, much less is known about the mechanisms by which constitutive overexpression of detoxifying enzymes contributes to metabolic pesticide resistance. Here we show that the Nrf2/Keap1 pathway is constitutively active in two laboratory-selected DDT-resistant strains of Drosophila, 91R and RDDTR, leading to the overexpression of multiple detoxifying genes. Disruption of the Drosophila Nrf2 ortholog, CncC, or overexpression of Keap1, is sufficient to block this transcriptional response. In addition, a CncC-responsive reporter is highly active in both DDT-resistant strains and this response is dependent on the presence of an intact CncC binding site in the promoter. Microarray analysis revealed that ∼20% of the genes differentially expressed in the 91R strain are known CncC target genes. Finally, we show that CncC is partially active in these strains, consistent with the fitness cost associated with constitutive activation of the pathway. This study demonstrates that the Nrf2/Keap1 pathway contributes to the widespread overexpression of detoxification genes in insecticide-resistant strains and raises the possibility that inhibitors of this pathway could provide effective synergists for insect population control.

Constitutive activation of the Nrf2/Keap1 pathway in insecticide-resistant strains of Drosophila

Pesticide resistance poses a major challenge for the control of vector-borne human diseases and agricultural crop protection. Although a number of studies have defined how mutations in specific target proteins can lead to insecticide resistance, much less is known about the mechanisms by which constitutive overexpression of detoxifying enzymes contributes to metabolic pesticide resistance. Here we show that the Nrf2/Keap1 pathway is constitutively active in two laboratory-selected DDT-resistant strains of Drosophila, 91R and RDDTR, leading to the overexpression of multiple detoxifying genes. Disruption of the Drosophila Nrf2 ortholog, CncC, or overexpression of Keap1, is sufficient to block this transcriptional response. In addition, a CncC-responsive reporter is highly active in both DDT-resistant strains and this response is dependent on the presence of an intact CncC binding site in the promoter. Microarray analysis revealed that ∼20% of the genes differentially expressed in the 91R strain are known CncC target genes. Finally, we show that CncC is partially active in these strains, consistent with the fitness cost associated with constitutive activation of the pathway. This study demonstrates that the Nrf2/Keap1 pathway contributes to the widespread overexpression of detoxification genes in insecticide-resistant strains and raises the possibility that inhibitors of this pathway could provide effective synergists for insect population control.

Oxidative stress mechanisms underlying Parkinson's disease-associated neurodegeneration in C. elegans

Oxidative stress is thought to play a significant role in the development and progression of neurodegenerative diseases. Although it is currently considered a hallmark of such processes, the interweaving of a multitude of signaling cascades hinders complete understanding of the direct role of oxidative stress in neurodegeneration. In addition to its extensive use as an aging model, some researchers have turned to the invertebrate model Caenorhabditis elegans (C. elegans) in order to further investigate molecular mediators that either exacerbate or protect against reactive oxygen species (ROS)-mediated neurodegeneration. Due to their fully characterized genome and short life cycle, rapid generation of C. elegans genetic models can be useful to study upstream markers of oxidative stress within interconnected signaling pathways. This report will focus on the roles of C. elegans homologs for the oxidative stress-associated transcription factor Nrf2, as well as the autosomal recessive, early-onset Parkinson’s disease (PD)-associated proteins Parkin, DJ-1, and PINK1, in neurodegenerative processes.

Advance in research of microRNA in Caenorhabditis elegans

microRNA (miRNA) is a family of small, non-coding RNA first discovered as an important regulator of development in Caenorhabditis elegans (C. elegans). Numerous miRNAs have been found in C. elegans, and some of them are well conserved in many organisms. Though, the biologic function of miRNAs in C. elegans was largely unknown, more and more studies support the idea that miRNA is an important molecular for C. elegans. In this review, we revisit the research progress of miRNAs in C. elegans related with development, aging, cancer, and neurodegenerative diseases and compared the function of miRNAs between C. elegans and human.

Adaptive and specialised transcriptional responses to xenobiotic stress in Caenorhabditis elegans are regulated by nuclear hormone receptors

Characterisation of the pathways by which xenobiotics are metabolised and excreted in both target and non-target organisms is crucial for the rational design of effective and specific novel bioactive molecules. Consequently, we have investigated the induced responses of the model nematode Caenorhabditis elegans to a variety of xenobiotics which represent a range of putative modes of action. The majority of genes that were specifically induced in preliminary microarray analyses encoded enzymes from Phase I and II metabolism, including cytochrome P450s, short chain dehydrogenases, UDP-glucuronosyl transferases and glutathione transferases. Changes in gene expression were confirmed by quantitative PCR and GFP induction in reporter strains driven by promoters for transcription of twelve induced enzymes was investigated. The particular complement of metabolic genes induced was found to be highly contingent on the xenobiotic applied. The known regulators of responses to applied chemicals ahr-1, hif-1, mdt-15 and nhr-8 were not required for any of these inducible responses and skn-1 regulated GFP expression from only two of the promoters. Reporter strains were used in conjunction with systematic RNAi screens to identify transcription factors which drive expression of these genes under xenobiotic exposure. These transcription factors appeared to regulate specific xenobiotic responses and have no reported phenotypes under standard conditions. Focussing on nhr-176 we demonstrate the role of this transcription factor in mediating the resistance to thiabendazole.