Fatty acid desaturation and the regulation of adiposity in Caenorhabditis elegans

Withanolides-enriched leaf extract of Withania somnifera exert anti-obesity effects by inducing brown adipocyte-like phenotype via tuning MAP-kinase signaling axis

Present study investigated anti-obesity potential of Withania somnifera (L.) Dunal leaf extract (WSLE). Phytochemical characterization of WSLE was performed by UPLC/MS-QToF and HPLC-based analysis. WSLE was assessed for its effect on lipid metabolism and mitochondrial biogenesis in vitro using differentiated 3T3-L1 adipocytes. WSLE was found to contain 59 phytometabolites with a total of 10.601 μg withanolides per mg of extract. WSLE (30 μg/ml) treatment decreased basal levels of intracellular lipids and triglycerides to 13.85 % and 41.58 %, respectively. WSLE downregulated the expression of PPARγ, C/EBPα, C/EBPβ, and their target genes responsible for lipogenesis dose-dependently. An upregulation in expression of lipolytic (ATGL and HSL), thermogenic (PGC1α, UCP1, and PRDM16), and glucose transporter (GLUT4) genes was also observed. Furthermore, WSLE treatment increased glucose uptake by 1.5-fold. These beneficial effects of WSLE were abolished in presence of AMPK, p38MAPK, and ERK inhibitors. These observations were then validated in vivo using Caenorhabditis elegans as a model organism. Intriguingly, WSLE diminished fat accumulation in wild-type N2 worms as evident from reduced Oil-red-O staining and reduction in GFP expression of fat-5, 6, and 7 in transgenic strains. Overall, these results highlight anti-obesity potential of WSLE exerting its effects via alterations in AMPK/p38MAPK/ERK axis.

Caffeic acid: A game changer in pine wood nematode overwintering survival

Following the invasion by the pine wood nematode (PWN) into north-east China, a notable disparity in susceptibility was observed among Pinaceae species. Larix olgensis exhibited marked resilience and suffered minimal fatalities, while Pinus koraiensis experienced significant mortality due to PWN infection. Our research demonstrated that the PWNs in L. olgensis showed a 13.43% reduction in lipid content compared to P. koraiensis (p < 0.05), which was attributable to the accumulation of caffeic acid in L. olgensis. This reduction in lipid content was correlated with a decreased overwintering survival of PWNs. The diminished lipid reserves were associated with substantial stunting in PWNs, including reduced body length and maximum body width. The result suggests that lower lipid content is a major factor contributing to the lower overwintering survival rate of PWNs in L. olgensis induced by caffeic acid. Through verification tests, we concluded that the minimal fatalities observed in L. olgensis could be attributed to the reduced overwintering survival of PWNs, a consequence of caffeic acid-induced stunting. This study provides valuable insights into PWN-host interactions and suggests that targeting caffeic acid biosynthesis pathways could be a potential strategy for managing PWN in forest ecosystems.

Nutritional vitamin B12 regulates RAS/MAPK-mediated cell fate decisions through one-carbon metabolism

Vitamin B12 is an essential nutritional co-factor for the folate and methionine cycles, which together constitute one-carbon metabolism. Here, we show that dietary uptake of vitamin B12 modulates cell fate decisions controlled by the conserved RAS/MAPK signaling pathway in C. elegans. A bacterial diet rich in vitamin B12 increases vulval induction, germ cell apoptosis and oocyte differentiation. These effects are mediated by different one-carbon metabolites in a tissue-specific manner. Vitamin B12 enhances via the choline/phosphatidylcholine metabolism vulval induction by down-regulating fat biosynthesis genes and increasing H3K4 tri-methylation, which results in increased expression of RAS/MAPK target genes. Furthermore, the nucleoside metabolism and H3K4 tri-methylation positively regulate germ cell apoptosis and oocyte production. Using mammalian cells carrying different activated KRAS and BRAF alleles, we show that the effects of methionine on RAS/MAPK-regulated phenotype are conserved in mammals. Our findings suggest that the vitamin B12-dependent one-carbon metabolism is a limiting factor for diverse RAS/MAPK-induced cellular responses.

LET-767 determines lipid droplet protein targeting and lipid homeostasis

Lipid droplets (LDs) are composed of a core of neutral lipids wrapped by a phospholipid (PL) monolayer containing several hundred proteins that vary between different cells or organisms. How LD proteins target to LDs is still largely unknown. Here, we show that RNAi knockdown or gene mutation of let-767, encoding a member of hydroxysteroid dehydrogenase (HSD), displaced the LD localization of three well-known LD proteins: DHS-3 (dehydrogenase/reductase), PLIN-1 (perilipin), and DGAT-2 (diacylglycerol O-acyltransferase 2), and also prevented LD growth in Caenorhabditis elegans. LET-767 interacts with ARF-1 (ADP-ribosylation factor 1) to prevent ARF-1 LD translocation for appropriate LD protein targeting and lipid homeostasis. Deficiency of LET-767 leads to the release of ARF-1, which further recruits and promotes translocation of ATGL-1 (adipose triglyceride lipase) to LDs for lipolysis. The displacement of LD proteins caused by LET-767 deficiency could be reversed by inhibition of either ARF-1 or ATGL-1. Our work uncovers a unique LET-767 for determining LD protein targeting and maintaining lipid homeostasis.

Lactobacillus fermentum WC2020 increased the longevity of Caenorhabditis elegans via JNK-mediated antioxidant pathway

Lactobacillus fermentum can exert antiaging effects, but their roles are strain-specific, and little is known about the molecular mechanisms in some strains. This study investigated the antiaging effects of L. fermentum WC2020 (WC2020) isolated from Chinese fermented pickles and the underlying mechanism of the action in Caenorhabditis elegans. WC2020 enhanced the mean lifespan of L1-stage and L4-stage worms by 22.67% and 12.42%, respectively, compared with Escherichia coli OP50 (OP50), a standard food source for C. elegans. WC2020-induced longevity was accompanied by an increase in body length and mitochondrial transmembrane potential and a reduction in lipid accumulation and the production of reactive oxygen species and malondialdehyde. Moreover, WC2020 increased the production of glutathione, superoxide dismutases, and catalases and altered the transcripts of many phenotype-related genes. Furthermore, WC2020-fed jnk-1 rather than akt-2 or pmk-1 loss-of-function mutants showed similar lifespans to OP50-fed worms. Correspondingly, WC2020 significantly upregulated the expression of jnk-1 rather than genes involved in insulin-like, p38 MAPK, bate-catenin, or TGF-beta pathway. Moreover, the increase in body length, mitochondrial transmembrane potential, and antioxidant capability and the decrease in lipid accumulation induced by WC2020 were not observed in jnk-1 mutants. Additionally, WC2020 increased the expression of daf-16 and the proportion of daf-16::GFP in the nucleus, and increased lifespan disappeared in WC2020-fed daf-16 loss-of-function mutants. In conclusion, WC2020 activated the JNK/DAF-16 pathway to improve mitochondria function, reduce oxidative stress, and then extend the longevity of nematodes, suggesting WC2020 could be a potential probiotic targeting JNK-mediated antioxidant pathway for antiaging in food supplements and bioprocessing. PRACTICAL APPLICATION: Aging has a profound impact on the global economy and human health and could be delayed by specific diets and nutrient resources. This study demonstrated that Lactobacillus fermentum WC2020 could be a potential probiotic strain used in food to promote longevity and health via the JNK-mediated antioxidant pathway.

Purification of Phenolic Compounds from Camellia polyodonta Flower: Composition Analysis, Antioxidant Property, and Hypolipidemic Activity In Vitro and In Vivo

Camellia polyodonta flowers are rich sources of phenolics and less attention has been paid to their potential biological activity. This study aims to explore the crude extracts and resulting purified fractions (CPFP-I, II, III, and IV) through compositional analysis and antioxidant and hypolipidemic activities in vitro and in vivo. Among four fractions, CPFP-II contained the highest total phenolic content and flavonoid content, while CPFP-III exhibited the greatest total proanthocyanidin content. Among the 14 phenolic compounds, CPFP-II displayed the highest content of procyanidin B2, B4, and C1, whereas CPFP-III contained the highest amount of 1,2,3,6-tetragalloylglucose. The DPPH, ABTS, and FRAP assessments demonstrated a consistent trend: CPFP-II > CPFP-III > CPFP-I > CPFP-IV. In vivo experiments showed that that all four fractions significantly reduced lipid levels in hyperlipidemic C. elegans (p < 0.05), with CPFP-II exhibiting the most potent effect. Furthermore, CPFP-II effectively bound to bile acids and inhibited the enzymatic activity of pancreatic lipase in vitro. Consequently, CPFP-II should be prioritized as a promising fraction for further exploration and should provide substantial support for the feasibility of the C. polyodonta flower as a natural alternative.

Evolutionarily related host and microbial pathways regulate fat desaturation in C. elegans

Fatty acid desaturation is central to metazoan lipid metabolism and provides building blocks of membrane lipids and precursors of diverse signaling molecules. Nutritional conditions and associated microbiota regulate desaturase expression, but the underlying mechanisms have remained unclear. Here, we show that endogenous and microbiota-dependent small molecule signals promote lipid desaturation via the nuclear receptor NHR-49/PPARα in C. elegans. Untargeted metabolomics of a β-oxidation mutant, acdh-11, in which expression of the stearoyl-CoA desaturase FAT-7/SCD1 is constitutively increased, revealed accumulation of a β-cyclopropyl fatty acid, becyp#1, that potently activates fat-7 expression via NHR-49. Biosynthesis of becyp#1 is strictly dependent on expression of cyclopropane synthase by associated bacteria, e.g., E. coli. Screening for structurally related endogenous metabolites revealed a β-methyl fatty acid, bemeth#1, which mimics the activity of microbiota-dependent becyp#1 but is derived from a methyltransferase, fcmt-1, that is conserved across Nematoda and likely originates from bacterial cyclopropane synthase via ancient horizontal gene transfer. Activation of fat-7 expression by these structurally similar metabolites is controlled by distinct mechanisms, as microbiota-dependent becyp#1 is metabolized by a dedicated β-oxidation pathway, while the endogenous bemeth#1 is metabolized via α-oxidation. Collectively, we demonstrate that evolutionarily related biosynthetic pathways in metazoan host and associated microbiota converge on NHR-49/PPARα to regulate fat desaturation.

Comparison of Lipid Composition between Quasipaa spinosa Oil and Rana catesbeiana Oil and Its Effect on Lipid Accumulation in Caenorhabditis elegans

Frog oil has been recognized for its nutritional and medicinal value. However, there is limited research on the role of frog oil in preventing obesity. In this study, we aimed to investigate the lipid composition of Quasipaa spinosa oil (QSO) and Rana catesbeiana oil (RCO) using lipidomics analysis. We compared the lipid accumulation effects of these two kinds of frog oils and soybean oil (SO) in Caenorhabditis elegans (C. elegans). Additionally, we determined the gene expression related to lipid metabolism and used the nhr-49 mutant (RB1716) and sir-2.1 mutant (VC199) for validation experiments. The results showed that the lipid composition of QSO and RCO was significantly different (p < 0.05), and QSO was rich in more polyunsaturated fatty acids (PUFAs). After feeding C. elegans, the lipid accumulation of the QSO group was the lowest among the three dietary oil groups. In addition, compared with RCO and SO, QSO significantly inhibited the production of malondialdehyde (MDA) and increased the activity of superoxide dismutase (SOD). The effects of three kinds of dietary oils on the fatty acid composition of C. elegans were significantly different. Compared with SO and RCO, QSO significantly up-regulated (p < 0.05) the expression of sir-2.1 and ech-1 genes. The results showed that QSO might reduce lipid accumulation through the SIRT1 and nuclear hormone signaling pathways. Such a situation was verified experimentally by the nhr-49 mutant (RB1716) and sir-2.1 mutant (VC199). This study proposed a new functional oil, laying the groundwork for developing functional foods from Quasipaa spinosa.

Lacticaseibacillus rhamnosus HA-114 and Bacillus subtilis R0179 Prolong Lifespan and Mitigate Amyloid-β Toxicity in C. elegans via Distinct Mechanisms

Background

Recent advances linking gut dysbiosis with neurocognitive disorders such as Alzheimer's disease (AD) suggest that the microbiota-gut-brain axis could be targeted for AD prevention, management, or treatment.

Objective

We sought to identify probiotics that can delay Aβ-induced paralysis.

Methods

Using C. elegans expressing human amyloid-β (Aβ)1-42 in body wall muscles (GMC101), we assessed the effects of several probiotic strains on paralysis.

Results

We found that Lacticaseibacillus rhamnosus HA-114 and Bacillus subtilis R0179, but not their supernatants or heat-treated forms, delayed paralysis and prolonged lifespan without affecting the levels of amyloid-β aggregates. To uncover the mechanism involved, we explored the role of two known pathways involved in neurogenerative diseases, namely mitophagy, via deletion of the mitophagy factor PINK-1, and fatty acid desaturation, via deletion of the Δ9 desaturase FAT-5. Pink-1 deletion in GMC101 worms did not modify the life-prolonging and anti-paralysis effects of HA-114 but reduced the protective effect of R0179 against paralysis without affecting its life-prolonging effect. Upon fat5 deletion in GMC101 worms, the monounsaturated C14:1 and C16:1 FAs conserved their beneficial effect while the saturated C14:0 and C16:0 FAs did not. The beneficial effects of R0179 on both lifespan and paralysis remained unaffected by fat-5 deletion, while the beneficial effect of HA-114 on paralysis and lifespan was significantly reduced.

Conclusions

Collectively with clinical and preclinical evidence in other models, our results suggest that HA-114 or R0179 could be studied as potential therapeutical adjuncts in neurodegenerative diseases such as AD.

Oleic Acid Metabolism in Response to Glucose in C. elegans

A key response to glucose stress is an increased production of unsaturated fatty acids to balance the increase in saturated fatty acids in the membrane. The C. elegans homolog of stearoyl-CoA desaturase, FAT-7, introduces the first double bond into saturated C18 fatty acids yielding oleic acid, and is a critical regulatory point for surviving cold and glucose stress. Here, we incorporated 13C stable isotopes into the diet of nematodes and quantified the 13C-labelled fatty acid using GC-MS and HPLC/MS-MS to track its metabolic response to various concentrations of glucose. Previous work has analyzed the membrane composition of C. elegans when responding to mild glucose stress and showed few alterations in the overall fatty acid composition in the membrane. Here, in nematodes exposed to higher concentrations of glucose, a specific reduction in oleic acid and linoleic acid was observed. Using time courses and stable isotope tracing, the response of fatty acid metabolism to increasing levels of glucose stress is characterized, revealing the funneling of monounsaturated fatty acids to preserve the abundance of polyunsaturated fatty acids. Taken together, higher levels of glucose unveil a specific reduction in oleic and linolenic acid in the metabolic rewiring required to survive glucose stress.

Eicosapentaenoic acid influences the pathogenesis of Candida albicans in Caenorhabditis elegans via inhibition of hyphal formation and stimulation of the host immune response

The intake of omega-3 polyunsaturated fatty acids, including eicosapentaenoic acid (EPA), is associated with health benefits due to its anti-inflammatory properties. This fatty acid also exhibits antifungal properties in vitro. In order to determine if this antifungal property is valid in vivo, we examined how EPA affects Candida albicans pathogenesis in the Caenorhabditis elegans infection model, an alternative to mammalian host models. The nematodes were supplemented with EPA prior to infection, and the influence of EPA on C. elegans lipid metabolism, survival and immune response was studied. In addition, the influence of EPA on hyphal formation in C. albicans was investigated. It was discovered that EPA supplementation changed the lipid composition, but not the unsaturation index of C. elegans by regulating genes involved in fatty acid and eicosanoid production. EPA supplementation also delayed killing of C. elegans by C. albicans due to the inhibition of hyphal formation in vivo, via the action of the eicosanoid metabolite of EPA, 17,18-epoxyeicosatetraenoic acid. Moreover, EPA supplementation also caused differential expression of biofilm-related gene expression in C. albicans and stimulated the immune response of C. elegans. This provides a link between EPA and host susceptibility to microbial infection in this model.

Exposure to 6-PPD quinone enhances lipid accumulation through activating metabolic sensors of SBP-1 and MDT-15 in Caenorhabditis elegans

Although it has been shown that exposure to 6-PPDQ can cause toxicity on environmental organisms, its possible effects on metabolic state remain largely unclear. We here determined the effect of 6-PPDQ exposure on lipid accumulation in Caenorhabditis elegans. We observed increase in triglyceride content, enhancement in lipid accumulation, and increase in size of lipid droplets in 6-PPDQ (1-10 μg/L) exposed nematodes. This detected lipid accumulation was associated with both increase in fatty acid synthesis reflected by increased expressions of fasn-1 and pod-2 and inhibition in mitochondrial and peroxisomal fatty acid β-oxidation indicated by decreased expressions of acs-2, ech-2, acs-1, and ech-3. The observed lipid accumulation in 6-PPDQ (1-10 μg/L) exposed nematodes was also related to the increase in synthesis of monounsaturated fatty acylCoAs reflected by altered expressions of fat-5, fat-6, and fat-7. Exposure to 6-PPDQ (1-10 μg/L) further increased expressions of sbp-1 and mdt-15 encoding two metabolic sensors to initiate the lipid accumulation and to regulate the lipid metabolism. Moreover, the observed increase in triglyceride content, enhancement in lipid accumulation, and alterations in fasn-1, pod-2, acs-2, and fat-5 expressions in 6-PPDQ exposed nematodes were obviously inhibited by sbp-1 and mdt-15 RNAi. Our observations demonstrated the risk of 6-PPDQ at environmentally relevant concentration in affecting lipid metabolic state in organisms.

Evolutionarily related host and microbial pathways regulate fat desaturation

Fatty acid desaturation is central to metazoan lipid metabolism and provides building blocks of membrane lipids and precursors of diverse signaling molecules. Nutritional conditions and associated microbiota regulate desaturase expression1-4, but the underlying mechanisms have remained unclear. Here, we show that endogenous and microbiota-dependent small molecule signals promote lipid desaturation via the nuclear receptor NHR-49/PPARα in C. elegans. Untargeted metabolomics of a β-oxidation mutant, acdh-11, in which expression of the stearoyl-CoA desaturase FAT-7/SCD1 is constitutively increased, revealed accumulation of a β-cyclopropyl fatty acid, becyp#1, that potently activates fat-7 expression via NHR-49. Biosynthesis of becyp#1 is strictly dependent on expression of cyclopropane synthase by associated bacteria, e.g., E. coli. Screening for structurally related endogenous metabolites revealed a β-methyl fatty acid, bemeth#1, whose activity mimics that of microbiota-dependent becyp#1, but is derived from a methyltransferase, fcmt-1, that is conserved across Nematoda and likely originates from bacterial cyclopropane synthase via ancient horizontal gene transfer. Activation of fat-7 expression by these structurally similar metabolites is controlled by distinct mechanisms, as microbiota-dependent becyp#1 is metabolized by a dedicated β-oxidation pathway, while the endogenous bemeth#1 is metabolized via α-oxidation. Collectively, we demonstrate that evolutionarily related biosynthetic pathways in metazoan host and associated microbiota converge on NHR-49/PPARα to regulate fat desaturation.

Astaxanthin reduces fat storage in a fat-6/fat-7 dependent manner determined using high fat Caenorhabditis elegans

Although astaxanthin has been shown to have high potential for weight loss, the specific action site and signal pathway generally cannot be confirmed in other animal models. This prevents us from finding therapeutic targets. Hence, we further illuminated its efficacy and specific action sites by using Caenorhabditis elegans (C. elegans). In this study, 60 μM astaxanthin supplementation reduced overall fat deposition and triglyceride levels by 21.47% and 22.00% (p < 0.01). The content of large lipid droplets was reversed after astaxanthin treatment, and the ratio of oleic acid/stearic acid (C18:1Δ9/C18:0) decreased significantly, which were essential substrates for triglyceride biosynthesis. In addition, astaxanthin prevented obesity caused by excessive energy accumulation and insufficient energy consumption. Furthermore, the above effects were induced by sbp-1/mdt-15 and insulin/insulin-like growth factor pathways, and finally co-regulated the specific site-fat-6 and fat-7 down-regulation. These results provided insight into therapeutic targets for future astaxanthin as a nutritional health product to relieve obesity.

Nuclear hormone receptor NHR-49 is an essential regulator of stress resilience and healthy aging in Caenorhabditis elegans

The genome of Caenorhabditis elegans encodes 284 nuclear hormone receptor, which perform diverse functions in development and physiology. One of the best characterized of these is NHR-49, related in sequence and function to mammalian hepatocyte nuclear factor 4α and peroxisome proliferator-activated receptor α. Initially identified as regulator of lipid metabolism, including fatty acid catabolism and desaturation, additional important roles for NHR-49 have since emerged. It is an essential contributor to longevity in several genetic and environmental contexts, and also plays vital roles in the resistance to several stresses and innate immune response to infection with various bacterial pathogens. Here, we review how NHR-49 is integrated into pertinent signaling circuits and how it achieves its diverse functions. We also highlight areas for future investigation including identification of regulatory inputs that drive NHR-49 activity and identification of tissue-specific gene regulatory outputs. We anticipate that future work on this protein will provide information that could be useful for developing strategies to age-associated declines in health and age-related human diseases.

Lipid droplets and peroxisomes are co-regulated to drive lifespan extension in response to mono-unsaturated fatty acids

Dietary mono-unsaturated fatty acids (MUFAs) are linked to longevity in several species. But the mechanisms by which MUFAs extend lifespan remain unclear. Here we show that an organelle network involving lipid droplets and peroxisomes is critical for MUFA-induced longevity in Caenorhabditis elegans. MUFAs upregulate the number of lipid droplets in fat storage tissues. Increased lipid droplet number is necessary for MUFA-induced longevity and predicts remaining lifespan. Lipidomics datasets reveal that MUFAs also modify the ratio of membrane lipids and ether lipids-a signature associated with decreased lipid oxidation. In agreement with this, MUFAs decrease lipid oxidation in middle-aged individuals. Intriguingly, MUFAs upregulate not only lipid droplet number but also peroxisome number. A targeted screen identifies genes involved in the co-regulation of lipid droplets and peroxisomes, and reveals that induction of both organelles is optimal for longevity. Our study uncovers an organelle network involved in lipid homeostasis and lifespan regulation, opening new avenues for interventions to delay aging.

Characterization of betalain-loaded liposomes and its bioactive potential in vivo after ingestion

Betalains are plant pigments characterized by showing a wide range of beneficial properties for health. Its bioactive potential has been studied for the first time after its encapsulation in liposomes and subsequent administration to the animal model Caenorhabditis elegans. Phenylalanine-betaxanthin and indoline carboxylic acid-betacyanin encapsulated at concentrations of 25 and 500 μM managed to reduce lipid accumulation and oxidative stress in the nematodes. Highly antioxidant betalains dopaxanthin and betanidin were also included in the survival analyses. The results showed that phenylalanine-betaxanthin was the most effective betalain by increasing the lifespan of C. elegans by 21.8%. In addition, the administration of encapsulated natural betanidin increased the nematodes' survival rate by up to 13.8%. The preservation of the bioactive properties of betalains manifested in this study means that the stabilization of the plant pigments through encapsulation in liposomes can be postulated as a new way for administration in pharmacological and food applications.

The lipidomes of C. elegans with mutations in asm-3/acid sphingomyelinase and hyl-2/ceramide synthase show distinct lipid profiles during aging

Lipid metabolism affects cell and physiological functions that mediate animal healthspan and lifespan. Lipidomics approaches in model organisms have allowed us to better understand changes in lipid composition related to age and lifespan. Here, using the model C. elegans, we examine the lipidomes of mutants lacking enzymes critical for sphingolipid metabolism; specifically, we examine acid sphingomyelinase (asm-3), which breaks down sphingomyelin to ceramide, and ceramide synthase (hyl-2), which synthesizes ceramide from sphingosine. Worm asm-3 and hyl-2 mutants have been previously found to be long- and short-lived, respectively. We analyzed longitudinal lipid changes in wild type animals compared to mutants at 1-, 5-, and 10-days of age. We detected over 700 different lipids in several lipid classes. Results indicate that wildtype animals exhibit increased triacylglycerols (TAG) at 10-days compared to 1-day, and decreased lysophoshatidylcholines (LPC). We find that 10-day hyl-2 mutants have elevated total polyunsaturated fatty acids (PUFA) and increased LPCs compared to 10-day wildtype animals. These changes mirror another short-lived model, the daf-16/FOXO transcription factor that is downstream of the insulin-like signaling pathway. In addition, we find that hyl-2 mutants have poor oxidative stress response, supporting a model where mutants with elevated PUFAs may accumulate more oxidative damage. On the other hand, 10-day asm-3 mutants have fewer TAGs. Intriguingly, asm-3 mutants have a similar lipid composition as the long-lived, caloric restriction model eat-2/mAChR mutant. Together, these analyses highlight the utility of lipidomic analyses to characterize metabolic changes during aging in C. elegans.

A new AMPK isoform mediates glucose-restriction induced longevity non-cell autonomously by promoting membrane fluidity

Dietary restriction (DR) delays aging and the onset of age-associated diseases. However, it is yet to be determined whether and how restriction of specific nutrients promote longevity. Previous genome-wide screens isolated several Escherichia coli mutants that extended lifespan of Caenorhabditis elegans. Here, using ¹H-NMR metabolite analyses and inter-species genetics, we demonstrate that E. coli mutants depleted of intracellular glucose extend C. elegans lifespans, serving as bona fide glucose-restricted (GR) diets. Unlike general DR, GR diets don't reduce the fecundity of animals, while still improving stress resistance and ameliorating neuro-degenerative pathologies of Aβ₄₂. Interestingly, AAK-2a, a new AMPK isoform, is necessary and sufficient for GR-induced longevity. AAK-2a functions exclusively in neurons to modulate GR-mediated longevity via neuropeptide signaling. Last, we find that GR/AAK-2a prolongs longevity through PAQR-2/NHR-49/Δ9 desaturases by promoting membrane fluidity in peripheral tissues. Together, our studies identify the molecular mechanisms underlying prolonged longevity by glucose specific restriction in the context of whole animals.

Lactobacillus pentosus MJM60383 Inhibits Lipid Accumulation in Caenorhabditis elegans Induced by Enterobacter cloacae and Glucose

Gut microbiota are known to play an important role in obesity. Enterobacter cloacae, a Gram-negative bacterium, has been considered a pathogenic bacterium related to obesity in the gut. In this study, we established an obesity model of C. elegans by feeding E. cloacae combined with a high glucose diet (HGD), which significantly induced lipid accumulation. An anti-lipid mechanism study revealed that the fatty acid composition and the expression level of fat metabolism-related genes were altered by feeding E. cloacae to C. elegans under HGD conditions. Lactic acid bacteria that showed antagonistic activity against E. cloacae were used to screen anti-obesity candidates in this model. Among them, L. pentosus MJM60383 (MJM60383) showed good antagonistic activity. C. eleans fed with MJM60383 significantly reduced lipid accumulation and triglyceride content. The ratio of C18:1Δ9/C18:0 was also changed in C. elegans by feeding MJM60383. In addition, the expression level of genes related to fatty acid synthesis was significantly decreased and the genes related to fatty acid β-oxidation were up-regulated by feeding MJM60383. Moreover, MJM60383 also exhibited a high adhesive ability to Caco-2 cells and colonized the gut of C. elegans. Thus, L. pentosus MJM60383 can be a promising candidate for anti-obesity probiotics. To the best of our knowledge, this is the first report that uses E. cloacae combined with a high-glucose diet to study the interactions between individual pathogens and probiotics in C. elegans.

Astaxanthin Induces Transcriptomic Responses Associated with Lifespan Extension in Caenorhabditis elegans

Astaxanthin is a marine xanthophyll carotenoid which effectively prevents intracellular oxidative stress and has beneficial effects against various human diseases. It has been shown that astaxanthin protects Caenorhabditis elegans (C. elegans) from oxidative damages and extends the lifespan of C. elegans possibly by modulating genes involved in insulin/insulin-like growth factor (IGF) signaling (IIS) and the oxidoreductase system, although the exact mechanisms remain elusive. In this study, RNA sequencing analyses were employed to identify the differentially expressed genes in C. elegans in response to astaxanthin treatment. A total of 190 mRNAs and 6 microRNAs (miRNAs) were significantly changed by astaxanthin treatment in C. elegans. Gene ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses indicated that the mRNAs and miRNAs significantly altered by astaxanthin mainly function in innate immunity, lipid metabolism and stress responses, a significant portion of which are related to lifespan regulation in C. elegans. The study revealed novel mRNA and miRNA targets of astaxanthin, providing new insights for understanding the anti-aging mechanisms and the biological function of astaxanthin.

Integrating Transcriptomics and Free Fatty Acid Profiling Analysis Reveal Cu Induces Shortened Lifespan and Increased Fat Accumulation and Oxidative Damage in C. elegans

Nowadays, human beings are exposed to Cu in varieties of environmental mediums, resulting in health risks needing urgent attention. Our research found that Cu shortened lifespan and induced aging-related phenotypes of Caenorhabditis elegans (C. elegans). Transcriptomics data showed differential expression genes induced by Cu were mainly involved in regulation of metabolism and longevity, especially in fatty acid metabolism. Quantitative detection of free fatty acid by GC/MS further found that Cu upregulated free fatty acids of C. elegans. A mechanism study confirmed that Cu promoted the fat accumulation in nematodes, which was owing to disorder of fatty acid desaturase and CoA synthetase, endoplasmic reticulum unfolded protein response (UPRER), mitochondrial membrane potential, and unfolded protein response (UPRmt). In addition, Cu activated oxidative stress and prevented DAF-16 translocating into nuclear with a concomitant reduction in the expression of environmental stress-related genes. Taken together, the research suggested that Cu promoted aging and induced fat deposition and oxidative damage.

Chronic exposure to environmentally relevant levels of di(2-ethylhexyl) phthalate (DEHP) disrupts lipid metabolism associated with SBP-1/SREBP and ER stress in C. elegans

DEHP is commonly found in the environment, biota, food, and humans, raising significant health concerns. Whether developmental stage and exposure duration modify the obesogenic effects of DEHP is unclear, especially the underlying mechanisms by which chronic exposure to DEHP as well as its metabolites remain largely unknown. This study investigated the obesogenic effects of chronic DEHP exposure, with levels below environmentally-relevant amounts and provide the mechanism in Caenorhabditis elegans. We show that early-life DEHP exposure resulted in an increased lipid and triglyceride (TG) accumulation mainly attributed to DEHP itself, not its metabolite mono-2-ethylhexyl phthalate (MEHP). In addition, developmental stage and exposure timing influence DEHP-induced TG accumulation and chronic DEHP exposure resulted in the most significant effect. Analysis of fatty acid composition shows that chronic DEHP exposure altered fatty acid composition and TG, resulting in an increased ω-6/ω-3 ratio. The increased TG content by chronic DEHP exposure required lipogenic genes fat-6, fat-7, pod-2, fasn-1, and sbp-1. Moreover, chronic DEHP exposure induced XBP-1-mediated endoplasmic reticulum (ER) stress which might lead to up-regulation of sbp-1. This study suggests the possible involvement of ER stress and SBP-1/SREBP-mediated lipogenesis in chronic DEHP-induced obesogenic effects. Results from this study implies that chronic exposure to DEHP disrupts lipid metabolism, which is likely conserved across species due to evolutionary conservation of molecular mechanisms, raising concerns in ecological and human health.

Cabin1 domain-containing gene picd-1 interacts with pry-1/Axin to regulate multiple processes in Caenorhabditis elegans

The Axin family of scaffolding proteins control diverse processes, such as facilitating the interactions between cellular components and providing specificity to signaling pathways. While several Axin family members have been discovered in metazoans and shown to play crucial roles, their mechanism of action are not well understood. The Caenorhabditis elegans Axin homolog, pry-1, is a powerful tool for identifying interacting genes and downstream effectors that function in a conserved manner to regulate Axin-mediated signaling. Our lab and others have established pry-1's essential role in developmental processes that affect the reproductive system, seam cells, and a posterior P lineage cell, P11.p. Additionally, pry-1 is crucial for lipid metabolism, stress responses, and aging. In this study, we expanded on our previous work on pry-1 by reporting a novel interacting gene named picd-1 (pry-1-interacting and Cabin1 domain-containing). PICD-1 protein shares sequence conservation with CABIN1, a component of the HUCA complex. Our findings have revealed that PICD-1 is involved in several pry-1-mediated processes, including stress response and lifespan maintenance. picd-1's expression overlapped with that of pry-1 in multiple tissues throughout the lifespan. Furthermore, PRY-1 and PICD-1 inhibited CREB-regulated transcriptional coactivator homolog CRTC-1, which promotes longevity in a calcineurin-dependent manner. Overall, our study has demonstrated that picd-1 is necessary for mediating pry-1 function and provides the basis to investigate whether Cabin-1 domain-containing protein plays a similar role in Axin signaling in other systems.

CEST-2.2 overexpression alters lipid metabolism and extends longevity of mitochondrial mutants

Mitochondrial dysfunction can either extend or decrease Caenorhabditis elegans lifespan, depending on whether transcriptionally regulated responses can elicit durable stress adaptation to otherwise detrimental lesions. Here, we test the hypothesis that enhanced metabolic flexibility is sufficient to circumvent bioenergetic abnormalities associated with the phenotypic threshold effect, thereby transforming short‐lived mitochondrial mutants into long‐lived ones. We find that CEST‐2.2, a carboxylesterase mainly localizes in the intestine, may stimulate the survival of mitochondrial deficient animals. We report that genetic manipulation of cest‐2.2 expression has a minor lifespan impact on wild‐type nematodes, whereas its overexpression markedly extends the lifespan of complex I‐deficient gas‐1(fc21) mutants. We profile the transcriptome and lipidome of cest‐2.2 overexpressing animals and show that CEST‐2.2 stimulates lipid metabolism and fatty acid beta‐oxidation, thereby enhancing mitochondrial respiratory capacity through complex II and LET‐721/ETFDH, despite the inherited genetic lesion of complex I. Together, our findings unveil a metabolic pathway that, through the tissue‐specific mobilization of lipid deposits, may influence the longevity of mitochondrial mutant C. elegans.

Transcriptome Analysis of the Nematodes Caenorhabditis elegans and Litoditis marina in Different Food Environments

Diets regulate animal development, reproduction, and lifespan. However, the underlying molecular mechanisms remain elusive. We previously showed that a chemically defined CeMM diet attenuates the development and promotes the longevity of C. elegans, but whether it impacts other nematodes is unknown. Here, we studied the effects of the CeMM diet on the development and longevity of the marine nematode Litoditis marina, which belongs to the same family as C. elegans. We further investigated genome-wide transcriptional responses to the CeMM and OP50 diets for both nematodes, respectively. We observed that the CeMM diet attenuated L. marina development but did not extend its lifespan. Through KEEG enrichment analysis, we found that many of the FOXO DAF-16 signaling and lysosome and xenobiotic metabolism related genes were significantly increased in C. elegans on the CeMM diet, which might contribute to the lifespan extension of C. elegans. Notably, we found that the expression of lysosome and xenobiotic metabolism pathway genes was significantly down-regulated in L. marina on CeMM, which might explain why the CeMM diet could not promote the lifespan of L. marina compared to bacterial feeding. Additionally, the down-regulation of several RNA transcription and protein generation and related processes genes in C. elegans on CeMM might not only be involved in extending longevity, but also contribute to attenuating the development of C. elegans on the CeMM diet, while the down-regulation of unsaturated fatty acids synthesis genes in L. marina might contribute to slow down its growth while on CeMM. This study provided important insights into how different diets regulate development and lifespan, and further genetic analysis of the candidate gene(s) of development and longevity will facilitate exploring the molecular mechanisms underlying how diets regulate animal physiology and health in the context of variable nutritional environments.

Stearoyl-CoA desaturases sustain cholinergic excitation and copulatory robustness in metabolically aging C. elegansmales

Regulated metabolism is required for behaviors as adults age. To understand how lipid usage affects motor coordination, we studied male Caenorhabditis elegans copulation as a model of energy-intensive behavior. Copulation performance drops after 48 h of adulthood. We found that 12–24 h before behavioral decline, males prioritize exploring and copulation behavior over feeding, suggesting that catabolizing stored metabolites, such as lipids, occurs during this period. Because fat-6/7-encoded stearoyl-CoA desaturases are essential for converting the ingested fatty acids to lipid storage, we examined the copulation behavior and neural calcium transients of fat-6(lf); fat-7(lf) mutants. In wild-type males, intestinal and epithelial fat-6/7 expression increases during the first 48 h of adulthood. The fat-6(lf); fat-7(lf) behavioral and metabolic defects indicate that in aging wild-type males, the increased expression of stearoyl-CoA desaturases in the epidermis may indirectly modulate the levels of EAG-family K⁺ channels in the reproductive cholinergic neurons and muscles.

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Tissue distribution of fat-6-encoded stearoyl-CoA desaturase changes in adulthood

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Markov modeling shows reduced feeding linked with more exploring in day 2 males

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fat-6(lf); fat-7(lf) disrupted behavior can be rescued by epidermal FAT-6

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fat-6(lf); fat-7(lf) alters neural and muscular ERG and EAG K+ channel expression

Partial fads2 Gene Knockout Diverts LC-PUFA Biosynthesis via an Alternative Δ8 Pathway with an Impact on the Reproduction of Female Zebrafish (Danio rerio)

The zebrafish (Danio rerio) genome contains a single gene fads2 encoding a desaturase (FADS2) with both Δ6 and Δ5 activities, the key player in the endogenous biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs), which serve essential functions as membrane components, sources of energy and signaling molecules. LC-PUFAs include the precursors of eicosanoids and are thus predicted to be indispensable molecules for reproductive health in virtually all vertebrates. In mice, an amniotic vertebrate, fads2 deletion mutants, both males and females, have been confirmed to be sterile. In anamniotic vertebrates, such as fish, there is still no information available on the reproductive (in)ability of fads2 mutants, although zebrafish have become an increasingly important model of lipid metabolism, including some aspects of the generation of germ cells and early embryonic development. In the present study, we apply the CRISPR/Cas9 genome editing system to induce mutations in the zebrafish genome and create crispants displaying a degree of fads2 gene editing within the range of 50–80%. Focusing on adult G₀ crispant females, we investigated the LC-PUFA profiles of eggs. Our data suggest an impaired pathway of the LC-PUFA biosynthesis of the ω6 and ω3 series in the first-rate limiting steps of the conversion of linoleic acid (LA) into γ-linolenic acid (GLA), and α-linolenic acid (ALA) into stearidonic acid (SDA), respectively, finally resulting in bad-quality eggs. Our data suggest the existence of an alternative Δ8 pathway, which bypasses the first endogenous LC-PUFA biosynthetic step in zebrafish in vivo, and suggest that the zebrafish bifunctional FADS2 enzyme is actually a trifunctional Δ6/Δ5/Δ8 desaturase.

Dietary S. maltophilia induces supersized lipid droplets by enhancing lipogenesis and ER-LD contacts in C. elegans

Dietary and symbiotic bacteria can exert powerful influence on metazoan lipid metabolism. Recent studies have emerged that microbiota have a role in animal obesity and related health disorders, but the mechanisms by which bacteria influence lipid storage in their host are unknown. To reduce the complexity of the relationship between gut microbiota and the host, Caenorhabditis elegans (C. elegans) has been chosen as a model organism to study interspecies interaction. Here, we demonstrate that feeding C. elegans with an opportunistic pathogenic bacterium Stenotrophomonas maltophilia (S. maltophilia) retards growth and promotes excessive neutral lipid storage. Gene expression analysis reveals that dietary S. maltophilia induces a lipogenic transcriptional response that includes the SREBP ortholog SBP-1, and fatty acid desaturases FAT-6 and FAT-7. Live imaging and ultrastructural analysis suggest that excess neutral lipid is stored in greatly expanded lipid droplets (LDs), as a result of enhanced endoplasmic reticulum (ER)-LD interaction. We also report that loss of function mutations in dpy-9 in C. elegans confers resistance to S. maltophilia. Dietary S. maltophilia induces supersized LDs by enhancing lipogenesis and ER-LD contacts in C. elegans. This work delineates a new model for understanding microbial regulation of metazoan physiology.

Integrated -omics approach reveals persistent DNA damage rewires lipid metabolism and histone hyperacetylation via MYS-1/Tip60

Although DNA damage is intricately linked to metabolism, the metabolic alterations that occur in response to DNA damage are not well understood. We use a DNA repair-deficient model of ERCC1-XPF in Caenorhabditis elegans to gain insights on how genotoxic stress drives aging. Using multi-omic approach, we discover that nuclear DNA damage promotes mitochondrial β-oxidation and drives a global loss of fat depots. This metabolic shift to β-oxidation generates acetyl-coenzyme A to promote histone hyperacetylation and an associated change in expression of immune-effector and cytochrome genes. We identify the histone acetyltransferase MYS-1, as a critical regulator of this metabolic-epigenetic axis. We show that in response to DNA damage, polyunsaturated fatty acids, especially arachidonic acid (AA) and AA-related lipid mediators, are elevated and this is dependent on mys-1. Together, these findings reveal that DNA damage alters the metabolic-epigenetic axis to drive an immune-like response that can promote age-associated decline.

Upregulated galectin-1 in Angiostrongylus cantonensis L5 reduces body fat and increases oxidative stress tolerance

Background

Angiostrongylus cantonensis L5, parasitizing human cerebrospinal fluid, causes eosinophilic meningitis, which is attributed to tissue inflammatory responses caused primarily by the high percentage of eosinophils. Eosinophils are also involved in killing helminths, using the peroxidative oxidation and hydrogen peroxide (H₂O₂) generated by dismutation of superoxide produced during respiratory burst. In contrast, helminthic worms have evolved to attenuate eosinophil-mediated tissue inflammatory responses for their survival. In previous study, we demonstrated the extracellular function of Acan-Gal-1 in inducing the apoptosis of macrophages. Here, the intracellular functions of Acan-Gal-1 were investigated, aiming to further reveal the mechanism involved in A. cantonensis L5 worms surviving inflammatory responses in the human central nervous system.

Methods

In this study, a model organism, Caenorhabditis elegans, was used as a surrogate to investigate the intracellular functions of Acan-Gal-1 in protecting the worm from its host’s immune attacks. First, structural characterization of Acan-Gal-1 was analyzed using bioinformatics; second, qRT-PCR was used to monitor the stage specificity of Acan-gal-1 expression in A. cantonensis. Microinjections were performed to detect the tissue specificity of lec-1 expression, the homolog of Acan-gal-1 in C. elegans. Third, microinjection was performed to develop Acan-gal-1::rfp transgenic worms. Then, oxidative stress assay and Oil Red O fat staining were used to determine the functions of Acan-Gal-1 in C. elegans.

Results

The results of detecting the stage specificity of Acan-gal-1 expression showed that Acan-Gal-1 was upregulated in both L5 and adult worms. Detection of the tissue specificity showed that the homolog of Acan-gal-1 in C. elegans, lec-1 was expressed ubiquitously and mainly localized in cuticle. Investigating the intracellular functions of Acan-Gal-1 in the surrogate C. elegans showed that N2 worms expressing pCe-lec-1::Acan-gal-1::rfp, with lipid deposition reduced, were significantly resistant to oxidative stress; lec-1 mutant worms, where lipid deposition increased, showed susceptible to oxidative stress, and this phenotype could be rescued by expressing pCe-lec-1::Acan-gal-1::rfp. Expressing pCe-lec-1::Acan-gal-1::rfp or lec-1 RNAi in fat-6;fat-7 double-mutant worms, where fat stores were reduced, had no significant effect on the oxidative stress tolerance.

Conclusion

In C. elegans worms, upregulated Acan-Gal-1 plays a defensive role against damage due to oxidative stress for worm survival by reducing fat deposition. This might indicate the mechanism by which A. cantonensis L5 worms, with upregulated Acan-Gal-1, survive the immune attack of eosinophils in the human central nervous system.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05171-4.

A Potential Probiotic Lactobacillus plantarum JBC5 Improves Longevity and Healthy Aging by Modulating Antioxidative, Innate Immunity and Serotonin-Signaling Pathways in Caenorhabditis elegans

Since the hypothesis of Dr. Elie Metchnikoff on lactobacilli-mediated healthy aging, several microbes have been reported to extend the lifespan with different features of healthy aging. However, a microbe affecting diverse features of healthy aging is of choice for broader acceptance and marketability as a next-generation probiotic. We employed Caenorhabditis elegans as a model to understand the potential of Lactobacillus plantarum JBC5 (LPJBC5), isolated from fermented food sample on longevity and healthy aging as well as their underlying mechanisms. Firstly, LPJBC5 enhanced the mean lifespan of C. elegans by 27.81% compared with control (untreated). LPBC5-induced longevity was accompanied with better aging-associated biomarkers, such as physical functions, fat, and lipofuscin accumulation. Lifespan assay on mutant worms and gene expression studies indicated that LPJBC5-mediated longevity was due to upregulation of the skinhead-1 (skn-1) gene activated through p38 MAPK signaling cascade. Secondly, the activated transcription factor SKN-1 upregulated the expression of antioxidative, thermo-tolerant, and anti-pathogenic genes. In support, LPJBC5 conferred resistance against abiotic and biotic stresses such as oxidative, heat, and pathogen. LPJBC5 upregulated the expression of intestinal tight junction protein ZOO-1 and improved gut integrity. Thirdly, LPJBC5 improved the learning and memory of worms trained on LPJBC5 compared with naive worms. The results showed upregulation of genes involved in serotonin signaling (ser-1, mod-1, and tph-1) in LPJBC5-fed worms compared with control, suggesting that serotonin-signaling was essential for LPJBC5-mediated improved cognitive function. Fourthly, LPJBC5 decreased the fat accumulation in worms by reducing the expression of genes encoding key substrates and enzymes of fat metabolism (i.e., fat-5 and fat-7). Lastly, LPJBC5 reduced the production of reactive oxygen species and improved mitochondrial function, thereby reducing apoptosis in worms. The capability of a single bacterium on pro-longevity and the features of healthy aging, including enhancement of gut integrity and cognitive functions, makes it an ideal candidate for promotion as a next-generation probiotic.

Regulation and functions of membrane lipids: Insights from Caenorhabditis elegans

The Caenorhabditis elegans plasma membrane is composed of glycerophospholipids and sphingolipids with a small cholesterol. The C. elegans obtain the majority of the membrane lipids by modifying fatty acids present in the bacterial diet. The metabolic pathways of membrane lipid biosynthesis are well conserved across the animal kingdom. In C. elegans CDP-DAG and Kennedy pathway produce glycerophospholipids. Meanwhile, the sphingolipids are synthesized through a different pathway. They have evolved remarkably diverse mechanisms to maintain membrane lipid homeostasis. For instance, the lipid bilayer stress operates to accomplish homeostasis during any perturbance in the lipid composition. Meanwhile, the PAQR-2/IGLR-2 complex works with FLD-1 to balance unsaturated to saturated fatty acids to maintain membrane fluidity. The loss of membrane lipid homeostasis is observed in many human genetic and metabolic disorders. Since C. elegans conserved such genes and pathways, it can be used as a model organism.

Lipid Extraction and Analysis

Lipids are major components of cellular membranes and energy stores. Lipids contribute vital structural, energetic, and signaling functions. We have optimized methods to extract and analyze lipids from the nematode Caenorhabditis elegans based on standard methods. Here we describe a method to extract total lipids from C. elegans larvae, adults, or embryos. We describe a thin-layer chromatography method to separate major lipid classes and a gas chromatography method to analyze fatty acid composition from lipid extracts, lipid fractions, or directly from nematode larvae, adults, or embryos.

mmBCFA C17iso ensures endoplasmic reticulum integrity for lipid droplet growth

In eukaryote cells, lipid droplets (LDs) are key intracellular organelles that dynamically regulate cellular energy homeostasis. LDs originate from the ER and continuously contact the ER during their growth. How the ER affects LD growth is largely unknown. Here, we show that RNAi knockdown of acs-1, encoding an acyl-CoA synthetase required for the biosynthesis of monomethyl branched-chain fatty acids C15iso and C17iso, remarkably prevented LD growth in Caenorhabditis elegans. Dietary C17iso, or complex lipids with C17iso including phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol, could fully restore the LD growth in the acs-1RNAi worms. Mechanistically, C17iso may incorporate into phospholipids to ensure the membrane integrity of the ER so as to maintain the function of ER-resident enzymes such as SCD/stearoyl-CoA desaturase and DGAT2/diacylglycerol acyltransferase for appropriate lipid synthesis and LD growth. Collectively, our work uncovers a unique fatty acid, C17iso, as the side chain of phospholipids for determining the ER homeostasis for LD growth in an intact organism, C. elegans.

Fatty acid desaturation is essential for C. elegans longevity at high temperature

Metabolic reprogramming is crucial for the adaptation to environmental temperature stress. It is generally accepted that fatty acid (FA) desaturation is suppressed at high temperature, which decreases the ratio of unsaturated FAs to saturated FAs (UFAs/SFAs) to maintain the fluidity of cell membranes and favor cellular survival. Here by working in C. elegans, we found that FA desaturation is essential for longevity in response to temperature upshift at the organismal level, opposite to its role in cellular survival. High temperature unexpectedly increases the contents of total fat and multiple UFA species. Specifically, monounsaturated oleic acid (OA) is required for animal survival at high temperature. Mechanistic study showed that OA acts through HSF-1, which in turn promotes histone acetylation as well as the expression of defense genes that are crucial for longevity at high temperature. Together, our findings reveal an unprecedented role for FA desaturation in organismal fitness to temperature upshift, and implicate divergent metabolic requirements between cellular and organismal survival upon temperature stress.

Multi- and trans-generational disturbances of perfluorobutane sulfonate and perfluorohexane sulfonate on lipid metabolism in Caenorhabditis elegans

Short-chained perfluorobutane sulfonate (PFBS, four-carbon) and perfluorohexane sulfonate (PFHxS, six-carbon) are widely employed to substitute long-chained per- and poly-fluoroalkyl substances (PFASs). Recent studies showed the potential persistence of PFBS and PFHxS, and also reported their correlation with obesity. However, the long-term outcome and underlying mechanisms remained poorly understood. Presently, the effects of PFBS and PFHxS were studied on C. elegans with multi- and trans-generational experiments. The multi-generational effects were measured in continuous four generational exposure (i.e., F1 to F4). Results showed that PFBS did not stimulate the fat content in F1 but in F4 with continuous but different disturbances on the lipid metabolism and the insulin and insulin-like (IIS) pathway. PFHxS stimulated the fat content in F1 and F4 with similar disturbances on the lipid metabolism and IIS pathway. The trans-generational results showed that the effects of PFBS and PFHxS on the lipid metabolism and IIS pathway were not totally recovered in the offspring of F1 (i.e., T1-T3) and F4 (i.e., T1'-T3') which were not continuously exposed. PFHxS showed a common pattern to up-regulate daf-7 in both multi- and trans-generational effects. The long-term consequences of the short-chained PFASs substitutes should be concerned and epigenetic regulations should be considered in future mechanism studies.

Effect of fluensulfone on different functional genes of root-knot nematode Meloidogyne incognita

Meloidogyne incognita is an obligate plant-parasitic nematode causing serious damage to agricultural crops. Major constraints in nematode management arose due to the limited availability of non-fumigant nematicides in conjunction with the considerable ill effects of fumigants on human and non-target organisms. Recently, fluensulfone has been reported to be an effective non-fumigant nematicide against plant-parasitic nematodes and the model nematode Caenorhabditis elegans. The nematicidal efficacy varies according to its concentration at the time of application, exposure timing, nematode species variability, and even across subpopulations within the same species. It interferes with the key physiological processes of nematodes, like motility, behavior, chemosensation, stylet thrusting, infectivity, metabolism, lipid consumption, tissue integrity, oviposition, egg hatching, and survival. However, the molecular basis of these multivariate physiological anomalies is still largely unknown. Quantitative real-time PCR was carried out to understand the acute transcriptional perturbation of 30 functional genes associated with key physiological and life processes in a M. incognita population, following exposure of 10, 50, and 100 ppm of fluensulfone for 5 and 10 hr. The chemical treatment resulted in significant downregulation of all the neuropeptidergic genes, with concomitant repression of majority of genes related to chemosensation, esophageal gland secretion, parasitism, fatty acid metabolism, and G-protein coupled receptors. Collectively, the parasitism genes were found to be perturbed at highest magnitude, followed by the GPCRs and neuropeptidergic genes. These results establish the wide ranging effect of fluensulfone on various metabolic and physiological pathways of nematode.

Differentiated 4,4-dimethylsterols from vegetable oils reduce fat deposition depending on the NHR-49/SCD pathway in Caenorhabditis elegans

Consumption of 4-desmethylsterols has been claimed to have many beneficial effects, but the benefits of 4,4-dimethylsterols are less appreciated. We utilized a nematode model, Caenorhabditis elegans (C. elegans), to explore the anti-obesity effects of different classes of 4,4-dimethylsterols purified from rice bran oil (RST) and shea nut butter (SST). Both SST and RST significantly reduced fat deposition in C. elegans with smaller sizes and numbers of lipid droplets. But the food intake was not significantly affected. Metabolomics analysis indicated a significantly altered pathway after treatment with 4,4-dimethylsterols. Finally, it was found that 4,4-dimethylsterols targeted stearoyl-CoA desaturases (SCD) and nuclear hormone receptor-49 (NHR-49), resulting in a reduced desaturation index as proved by a lower ratio of oleic acid (C18:1n-9) to stearic acid (C18:0). Overall, 4,4-dimethylsterols can inhibit fat deposition via regulating the NHR-49/SCD pathway in C. elegans.

Oleic Acid Protects Caenorhabditis Mothers From Mating-Induced Death and the Cost of Reproduction

Reproduction comes at a cost, including accelerated death. Previous studies of the interconnections between reproduction, lifespan, and fat metabolism in C. elegans were predominantly performed in low-reproduction conditions. To understand how increased reproduction affects lifespan and fat metabolism, we examined mated worms; we find that a Δ9 desaturase, FAT-7, is significantly up-regulated. Dietary supplementation of oleic acid (OA), the immediate downstream product of FAT-7 activity, restores fat storage and completely rescues mating-induced death, while other fatty acids cannot. OA-mediated lifespan restoration is also observed in C. elegans mutants suffering increased death from short-term mating, and in mated C. remanei females, indicating a conserved role of oleic acid in post-mating lifespan regulation. Our results suggest that increased reproduction can be uncoupled from the costs of reproduction from somatic longevity regulation if provided with the limiting lipid, oleic acid.

Evaluation of changes in C. elegans immune response during bacterial infection: A single nematode approach

Routinely, studies were performed using age-synchronized group of C. elegans as host which suggested a collective response by the host system. Here, we report the modulation of immune response in a single nematode against Staphylococcus aureus and Proteus mirabilis. Initially, the survival of wild-type N2 was tested and was found that S. aureus killed single nematode at 42 h while P. mirabilis failed to provoke infection but colonized the nematode's intestine. With this milieu, the pathogenicity of the bacteria was assessed by Fourier Transform Infra-Red (FTIR) spectroscopy and Cyclic Voltammetry (CV) and was found that S. aureus in the presence of host elicited its virulence while P. mirabilis and Escherichia coli OP50 did not show any alteration. Vertical transmission of infection was also deduced by colony forming unit assay using Cyanine dyes. The MALDI-TOF/TOF analysis was also performed to identify the proteome changes in the single nematode that showcased different proteins related to various immune pathways. This study suggested the importance of understanding the infection pathology and traits of individual nematode which could help our understanding on otherwise the disordered processes during host and microbe interactions.

The Role of Cation Diffusion Facilitator CDF-1 in Lipid Metabolism in Caenorhabditis elegans

Zinc is one of the most important trace elements as it plays a vital role in many biological processes. As well, aberrant zinc metabolism has been implicated in lipid-related metabolic diseases. Previously, we showed that zinc antagonizes iron to regulate sterol regulatory element-binding proteins and the stearoyl-CoA desaturase (SREBP-SCD) pathway in lipid metabolism in the model organism Caenorhabditis elegans. In this study, we present the identification of another cation diffusion facilitator, CDF-1, which regulates lipid metabolism along with SUR-7 in response to zinc. Inactivation of SBP-1, the only homolog of SREBPs, leads to an increased zinc level but decreased lipid accumulation. However, either the cdf-1(n2527) or sur-7(tm6523) mutation could successfully restore the altered fatty acid profile, fat content, and zinc level of the sbp-1(ep79) mutant. Furthermore, we found that CDF-1/SUR-7 may functionally bypass SBP-1 to directly affect the conversion activity of SCD in the biosynthesis of unsaturated fatty acids and lipid accumulation. Collectively, these results consistently support the link between zinc homeostasis and lipid metabolism via the SREBP-SCD axis by the cation diffusion facilitators CDF-1 and SUR-7.

The C. elegans PAQR-2 and IGLR-2 membrane homeostasis proteins are uniquely essential for tolerating dietary saturated fats

How cells maintain vital membrane lipid homeostasis while obtaining most of their constituent fatty acids from a varied diet remains largely unknown. Here, we report the first whole-organism (Caenorhabditis elegans) forward genetic screen to identify genes essential for tolerance to dietary saturated fatty acids (SFAs). We found that only the PAQR-2/IGLR-2 pathway, homologous to the human adiponectin receptor 2 (AdipoR2) pathway, is uniquely essential to prevent SFA-mediated toxicity. When provided a SFA-rich diet, worms lacking either protein accumulate an excess of SFAs in their membrane phospholipids, which is accompanied by membrane rigidification. Additionally, we used fluorescence resonance energy transfer (FRET) to show that the interaction between PAQR-2 and IGLR-2 is regulated by membrane fluidity, suggesting a mechanism by which this protein complex senses membrane properties. We also created versions of PAQR-2 that lacked parts of the cytoplasmic N-terminal domain and showed that these were still functional, though still dependent on the interaction with IGLR-2. We conclude that membrane homeostasis via the PAQR-2/IGLR-2 fluidity sensor is the only pathway specifically essential for the non-toxic uptake of dietary SFAs in C. elegans.

DNA damage promotes ER stress resistance through elevation of unsaturated phosphatidylcholine in Caenorhabditis elegans

DNA damage triggers the cellular adaptive response to arrest proliferation and repair DNA damage; when damage is too severe to be repaired, apoptosis is initiated to prevent the spread of genomic insults. However, how cells endure DNA damage to maintain cell function remains largely unexplored. By using Caenorhabditis elegans as a model, we report that DNA damage elicits cell maintenance programs, including the unfolded protein response of the endoplasmic reticulum (UPRER). Mechanistically, sublethal DNA damage unexpectedly suppresses apoptotic genes in C. elegans, which in turn increases the activity of the inositol-requiring enzyme 1/X-box binding protein 1 (IRE-1/XBP-1) branch of the UPRER by elevating unsaturated phosphatidylcholine. In addition, UPRER activation requires silencing of the lipid regulator skinhead-1 (SKN-1). DNA damage suppresses SKN-1 activity to increase unsaturated phosphatidylcholine and activate UPRER. These findings reveal the UPRER activation as an organismal adaptive response that is important to maintain cell function during DNA damage.

Identification of a Novel Link between the Intermediate Filament Organizer IFO-1 and Cholesterol Metabolism in the Caenorhabditis elegans Intestine

The intestine is an organ essential to organismal nutrient absorption, metabolic control, barrier function and immunoprotection. The Caenorhabditis elegans intestine consists of 20 cells harboring a dense intermediate filament network positioned below the apical plasma membrane that forms a junction-anchored sheath around the intestinal lumen. This evolutionarily conserved arrangement provides mechanical and overall stress-protection, and it serves as an important model for deciphering the role of intestinal architecture in metazoan biology. We recently reported that the loss-of-function mutation of the intestinal intermediate filament organizer IFO-1 perturbs this architecture, leading to reduced body size and reproduction. Here, we demonstrate that the IFO-1 mutation dramatically affects cholesterol metabolism. Mutants showed an increased sensitivity to cholesterol depletion, reduced cholesterol uptake, and cholesterol transfer to the gonads, which is also observed in worms completely lacking an intermediate filament network. Accordingly, we found striking similarities to transcriptome and lipidome profiles of a nuclear hormone receptor (NHR)-8 mutant. NHR-8 is homologous to mammalian LXR (liver X receptor) that serves as a sterol sensor and transcriptional regulator of lipid metabolism. Remarkably, increasing exogenous cholesterol partially rescues the developmental retardation in IFO-1 mutants. Our results uncover a novel link of the intestinal intermediate filament cytoskeleton to cholesterol metabolism that contributes to compromised growth and reproduction.

Effects of Phosphoethanolamine Supplementation on Mitochondrial Activity and Lipogenesis in a Caffeine Ingestion Caenorhabditis elegans Model

Caffeine intake is strongly linked to lipid metabolism. We previously reported the age-dependent physiological effects of caffeine intake in a Caenorhabditis elegans model. Since nutritional status can actively influence metabolism and overall health, in this study, we evaluated the effect of caffeine intake on lipid metabolism in adult-stage C. elegans. We found that, in C. elegans, fat storage and the level of phosphoethanolamine (PE) were significantly reduced with caffeine intake. In addition, mitochondrial activity decreased and mitochondrial morphology was disrupted, and the expression of oxidative stress response genes, hsp-6, gst-4, and daf-16, was induced by caffeine intake. Furthermore, the level of an energy metabolism sensor, phospho-AMP-activated protein kinase, was increased, whereas the expression of the sterol regulatory element binding protein gene and its target stearoyl-CoA desaturase genes, fat-5, -6, and -7, was decreased with caffeine intake. These findings suggest that caffeine intake causes mitochondrial dysfunction and reduces lipogenesis. Interestingly, these changes induced by caffeine intake were partially alleviated by PE supplementation, suggesting that the reduction in mitochondrial activity and lipogenesis is in part because of the low PE level, and proper dietary supplementation can improve organelle integrity.

Behavioral States

Caenorhabditis elegans' behavioral states, like those of other animals, are shaped by its immediate environment, its past experiences, and by internal factors. We here review the literature on C. elegans behavioral states and their regulation. We discuss dwelling and roaming, local and global search, mate finding, sleep, and the interaction between internal metabolic states and behavior.

Polyunsaturated fatty acids and p38-MAPK link metabolic reprogramming to cytoprotective gene expression during dietary restriction

The metabolic state of an organism instructs gene expression modalities, leading to changes in complex life history traits, such as longevity. Dietary restriction (DR), which positively affects health and life span across species, leads to metabolic reprogramming that enhances utilisation of fatty acids for energy generation. One direct consequence of this metabolic shift is the upregulation of cytoprotective (CyTP) genes categorized in the Gene Ontology (GO) term of "Xenobiotic Detoxification Program" (XDP). How an organism senses metabolic changes during nutritional stress to alter gene expression programs is less known. Here, using a genetic model of DR, we show that the levels of polyunsaturated fatty acids (PUFAs), especially linoleic acid (LA) and eicosapentaenoic acid (EPA), are increased following DR and these PUFAs are able to activate the CyTP genes. This activation of CyTP genes is mediated by the conserved p38 mitogen-activated protein kinase (p38-MAPK) pathway. Consequently, genes of the PUFA biosynthesis and p38-MAPK pathway are required for multiple paradigms of DR-mediated longevity, suggesting conservation of mechanism. Thus, our study shows that PUFAs and p38-MAPK pathway function downstream of DR to help communicate the metabolic state of an organism to regulate expression of CyTP genes, ensuring extended life span.