Insights and challenges in using C. elegans for investigation of fat metabolism

Application of 3Rs in Caenorhabditis elegans Research for the Identification of Health-Promoting Natural Products

The average age of the population is increasing worldwide, which has a profound impact on our society. This leads to an increasing demand for medicines and requires the development of new strategies to promote health during the additional years. In the search for resources and therapeutics for improved health during an extended life span, attention has to be paid to environmental exposure and ecosystem burdens that inevitably emerge with the extended consumption of medicines and drug development, even in the preclinical stage. The hereby introduced sustainable strategy for drug discovery is built on 3Rs, "R: obustness, R: eliability, and saving R: esources", inspired by both the 3Rs used in animal experiments and environmental protection, and centers on the usefulness and the variety of the small model organism Caenorhabditis elegans for detecting health-promoting natural products. A workflow encompassing a multilevel screening approach is presented to maximize the amount of information on health-promoting samples, while considering the 3Rs. A detailed, methodology- and praxis-oriented compilation and discussion of proposed C. elegans health span assays and more disease-specific assays are presented to offer guidance for scientists intending to work with C. elegans, thus facilitating the initial steps towards the integration of C. elegans assays in their laboratories.

Using C. elegans as a model for neurodegenerative diseases: Methodology and evaluation

Caenorhabditis elegans is a nematode that has been used as an animal model for almost 50years. It has primitive and simple tissues and organs, making it an ideal model for studying neurological pathways involved in neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD). C. elegans has conserved neurological pathways and is able to mimic human diseases, providing valuable insights into the human disease phenotype. This methodological review presents current approaches to generate neurodegenerative-like models of AD and PD in C. elegans, and evaluates the experiments commonly used to validate the diseases. These experimental approaches include assessing survival, fertility, mobility, electropharyngeogram assays, confocal mitochondrial imaging, RNA extraction for qRT-PCR or RT-PCR, and rate of defecation. This review also summarizes the current knowledge acquired on AD and PD using the aforementioned experimental approaches. Additionally, gaps in knowledge and future directions for research are also discussed in the review.

Caenorhabditis elegans as a Screening Model for Probiotics with Properties against Metabolic Syndrome

There is a growing need to develop new approaches to prevent and treat diseases related to metabolic syndromes, including obesity or type 2 diabetes, that focus on the different factors involved in the pathogenesis of these diseases. Due to the role of gut microbiota in the regulation of glucose and insulin homeostasis, probiotics with beneficial properties have emerged as an alternative therapeutic tool to ameliorate metabolic diseases-related disturbances, including fat excess or inflammation. In the last few years, different strains of bacteria, mainly lactic acid bacteria (LAB) and species from the genus Bifidobacterium, have emerged as potential probiotics due to their anti-obesogenic and/or anti-diabetic properties. However, in vivo studies are needed to demonstrate the mechanisms involved in these probiotic features. In this context, Caenorhabditis elegans has emerged as a very powerful simple in vivo model to study the physiological and molecular effects of probiotics with potential applications regarding the different pathologies of metabolic syndrome. This review aims to summarize the main studies describing anti-obesogenic, anti-diabetic, or anti-inflammatory properties of probiotics using C. elegans as an in vivo research model, as well as providing a description of the molecular mechanisms involved in these activities.

Antidiabetic and anti-obesity properties of a polyphenol-rich flower extract from Tagetes erecta L. and its effects on Caenorhabditis elegans fat storages

Diabetes mellitus (DM) is a metabolic disease characterized by a high blood sugar level that can cause severe complications to the organism or even death when not treated. However, certain dietary habits and foods may have beneficial effects on this condition. A polyphenolic-rich extract (containing hyperoside, isoquercitrin, quercetin, ellagic acid, and vanillic acid) of Tageres erecta L. (T. erecta) was obtained from yellow and orange flowers using an ethanolic Soxhlet extraction. These extracts were screened for antidiabetic and anti-obesity properties using in vitro and in vivo procedures. The capacity to inhibit the enzymes lipase and α-glucosidase, as well as the inhibition of advance glycation end-products (AGEs) was tested in vitro. Caenorhabditis elegans (C. elegans) was used as an obesity in vivo model to assess extracts effects on fat accumulation using the wild-type strain N2 and a mutant with no N3 fatty acid desaturase activity BX24. Extracts from both cultivars (yellow and orange) T. erecta presented in vitro inhibitory activity against the enzymes lipase and α-glucosidase, showing lower IC₅₀ values than acarbose (control). They also showed important activity in preventing AGEs formation. The polyphenol-rich matrices reduced the fat content of obese worms in the wild-type strain (N2) down to levels of untreated C. elegans, with no significant differences found between negative control (100% reduction) and both tested samples (p < 0.05). Meanwhile, the fat reduction was considerably lower in the BX24 mutants (fat-1(wa-9)), suggesting that N3 fatty acid desaturase activity could be partially involved in the T. erecta flower effect. Our findings suggested that polyphenols from T. erecta can be considered candidate bioactive compounds in the prevention and improvement of metabolic chronic diseases such as obesity and diabetes.

Identifying lipid particle sub-types in live Caenorhabditis elegans with two-photon fluorescence lifetime imaging

Fat metabolism is an important modifier of aging and longevity in Caenorhabditis elegans. Given the anatomy and hermaphroditic nature of C. elegans, a major challenge is to distinguish fats that serve the energetic needs of the parent from those that are allocated to the progeny. Broadband coherent anti-Stokes Raman scattering (BCARS) microscopy has revealed that the composition and dynamics of lipid particles are heterogeneous both within and between different tissues of this organism. Using BCARS, we have previously succeeded in distinguishing lipid-rich particles that serve as energetic reservoirs of the parent from those that are destined for the progeny. While BCARS microscopy produces high-resolution images with very high information content, it is not yet a widely available platform. Here we report a new approach combining the lipophilic vital dye Nile Red and two-photon fluorescence lifetime imaging microscopy (2p-FLIM) for the in vivo discrimination of lipid particle sub-types. While it is widely accepted that Nile Red staining yields unreliable results for detecting lipid structures in live C. elegans due to strong interference of autofluorescence and non-specific staining signals, our results show that simple FLIM phasor analysis can effectively separate those signals and is capable of differentiating the non-polar lipid-dominant (lipid-storage), polar lipid-dominant (yolk lipoprotein) particles, and the intermediates that have been observed using BCARS microscopy. An advantage of this approach is that images can be acquired using common, commercially available 2p-FLIM systems within about 10% of the time required to generate a BCARS image. Our work provides a novel, broadly accessible approach for analyzing lipid-containing structures in a complex, live whole organism context.

Bond-selective intensity diffraction tomography

Recovering molecular information remains a grand challenge in the widely used holographic and computational imaging technologies. To address this challenge, we developed a computational mid-infrared photothermal microscope, termed Bond-selective Intensity Diffraction Tomography (BS-IDT). Based on a low-cost brightfield microscope with an add-on pulsed light source, BS-IDT recovers both infrared spectra and bond-selective 3D refractive index maps from intensity-only measurements. High-fidelity infrared fingerprint spectra extraction is validated. Volumetric chemical imaging of biological cells is demonstrated at a speed of ~20 s per volume, with a lateral and axial resolution of ~350 nm and ~1.1 µm, respectively. BS-IDT's application potential is investigated by chemically quantifying lipids stored in cancer cells and volumetric chemical imaging on Caenorhabditis elegans with a large field of view (~100 µm x 100 µm).

Expanding the Biological Properties of Alkannins and Shikonins: Their Impact on Adipogenesis and Life Expectancy in Nematodes

Alkannin, shikonin (A/S) and their derivatives are naturally occurring hydroxynaphthoquinones biosynthesized in some species of the Boraginaceae family. These natural compounds have been extensively investigated for their biological properties over the last 40 years, demonstrating a plethora of activities, such as wound healing, regenerative, anti-inflammatory, antitumor, antimicrobial and antioxidant. This study aims to extend the current knowledge by investigating the effects of various A/S compounds on two model systems, namely on 3T3-L1 pre-adipocytes and the nematode Caenorhabditis elegans. The former constitutes an established in vitro model for investigating anti-obesity and insulin-mimetic properties, while the latter has been widely used as a model organism for studying fat accumulation, lifespan and the anthelmintic potential. A set of chemically well-defined A/S derivatives were screened for their effect on pre-adipocytes to assess cell toxicity, cell morphology, and cell differentiation. The differentiation of pre-adipocytes into mature adipocytes was examined upon treatment with A/S compounds in the presence/absence of insulin, aiming to establish a structure-activity relationship. The majority of A/S compounds induced cell proliferation at sub-micromolar concentrations. The ester derivatives exhibited higher IC₅₀ values, and thus, proved to be less toxic to 3T3-L1 cells. The parent molecules, A and S tested at 1 μM resulted in a truncated differentiation with a reduced number of forming lipids, whereas compounds lacking the side chain hydroxyl group projected higher populations of mature adipocytes. In C. elegans mutant strain SS104, A/S enriched extracts were not able to inhibit the fat accumulation but resulted in a drastic shortage of survival. Thus, the set of A/S compounds were tested at 15 and 60 μg/ml in the wild-type strain N2 for their nematocidal activity, which is of relevance for the discovery of anthelmintic drugs. The most pronounced nematocidal activity was observed for naphthazarin and β,β-dimethyl-acryl-shikonin, followed by isovaleryl-shikonin. The latter 2 A/S esters were identified as the most abundant constituents in the mixture of A/S derivatives isolated from Alkanna tinctoria (L.) Tausch. Taken together, the findings show that the structural variations in the moiety of A/S compounds significantly impact the modulation of their biological activities in both model systems investigated in this study.

Pediococcus acidilactici CECT9879 (pA1c) Counteracts the Effect of a High-Glucose Exposure in C. elegans by Affecting the Insulin Signaling Pathway (IIS)

The increasing prevalence of metabolic syndrome-related diseases, including type-2 diabetes and obesity, makes it urgent to develop new alternative therapies, such as probiotics. In this study, we have used Caenorhabditis elegans under a high-glucose condition as a model to examine the potential probiotic activities of Pediococcusacidilactici CECT9879 (pA1c). The supplementation with pA1c reduced C. elegans fat accumulation in a nematode growth medium (NGM) and in a high-glucose (10 mM) NGM medium. Moreover, treatment with pA1c counteracted the effect of the high glucose by reducing reactive oxygen species by 20%, retarding the aging process and extending the nematode median survival (>2 days in comparison with untreated control worms). Gene expression analyses demonstrated that the probiotic metabolic syndrome-alleviating activities were mediated by modulation of the insulin/IGF-1 signaling pathway (IIS) through the reversion of the glucose-nuclear-localization of daf-16 and the overexpression of ins-6 and daf-16 mediators, increased expression of fatty acid (FA) peroxisomal β-oxidation genes, and downregulation of FA biosynthesis key genes. Taken together, our data suggest that pA1c could be considered a potential probiotic strain for the prevention of the metabolic syndrome-related disturbances and highlight the use of C. elegans as an appropriate in vivo model for the study of the mechanisms underlying these diseases.

Workflow for Segmentation of Caenorhabditis elegans from Fluorescence Images for the Quantitation of Lipids

The small and transparent nematode Caenorhabditis elegans is increasingly employed for phenotypic in vivo chemical screens. The influence of compounds on worm body fat stores can be assayed with Nile red staining and imaging. Segmentation of C. elegans from fluorescence images is hereby a primary task. In this paper, we present an image-processing workflow that includes machine-learning-based segmentation of C. elegans directly from fluorescence images and quantifies their Nile red lipid-derived fluorescence. The segmentation is based on a J48 classifier using pixel entropies and is refined by size-thresholding. The accuracy of segmentation was >90% in our external validation. Binarization with a global threshold set to the brightness of the vehicle control group worms of each experiment allows a robust and reproducible quantification of worm fluorescence. The workflow is available as a script written in the macro language of imageJ, allowing the user additional manual control of classification results and custom specification settings for binarization. Our approach can be easily adapted to the requirements of other fluorescence image-based experiments with C. elegans.

Grifola frondosa (Maitake) Extract Reduces Fat Accumulation and Improves Health Span in C. elegans through the DAF-16/FOXO and SKN-1/NRF2 Signalling Pathways

In recent years, food ingredients rich in bioactive compounds have emerged as candidates to prevent excess adiposity and other metabolic complications characteristic of obesity, such as low-grade inflammation and oxidative status. Among them, fungi have gained popularity for their high polysaccharide content and other bioactive components with beneficial activities. Here, we use the C. elegans model to investigate the potential activities of a Grifola frondosa extract (GE), together with the underlying mechanisms of action. Our study revealed that GE represents an important source of polysaccharides and phenolic compounds with in vitro antioxidant activity. Treatment with our GE extract, which was found to be nongenotoxic through a SOS/umu test, significantly reduced the fat content of C. elegans, decreased the production of intracellular ROS and aging–lipofuscin pigment, and increased the lifespan of nematodes. Gene expression and mutant analyses demonstrated that the in vivo anti-obesity and antioxidant activities of GE were mediated through the daf-2/daf-16 and skn-1/nrf-2 signalling pathways, respectively. Taken together, our results suggest that our GE extract could be considered a potential functional ingredient for the prevention of obesity-related disturbances.

The Mitochondrial Prohibitin (PHB) Complex in C. elegans Metabolism and Ageing Regulation

The mitochondrial prohibitin (PHB) complex, composed of PHB-1 and PHB-2, is an evolutionarily conserved context-dependent modulator of longevity. This extremely intriguing phenotype has been linked to alterations in mitochondrial function and lipid metabolism. The true biochemical function of the mitochondrial PHB complex remains elusive, but it has been shown to affect membrane lipid composition. Recent work, using large-scale biochemical approaches, has highlighted a broad effect of PHB on the C. elegans metabolic network. Collectively, the biochemical data support the notion that PHB modulates, at least partially, worm longevity through the moderation of fat utilisation and energy production via the mitochondrial respiratory chain. Herein, we review, in a systematic manner, recent biochemical insights into the impact of PHB on the C. elegans metabolome.

The Mitochondrial PHB Complex Determines Lipid Composition and Interacts With the Endoplasmic Reticulum to Regulate Ageing

Metabolic disorders are frequently associated with physiological changes that occur during ageing. The mitochondrial prohibitin complex (PHB) is an evolutionary conserved context-dependent modulator of longevity, which has been linked to alterations in lipid metabolism but which biochemical function remains elusive. In this work we aimed at elucidating the molecular mechanism by which depletion of mitochondrial PHB shortens the lifespan of wild type animals while it extends that of insulin signaling receptor (daf-2) mutants. A liquid chromatography coupled with mass spectrometry approach was used to characterize the worm lipidome of wild type and insulin deficient animals upon PHB depletion. Toward a mechanistic interpretation of the insights coming from this analysis, we used a combination of biochemical, microscopic, and lifespan analyses. We show that PHB depletion perturbed glycerophospholipids and glycerolipids pools differently in short- versus long-lived animals. Interestingly, PHB depletion in otherwise wild type animals induced the endoplasmic reticulum (ER) unfolded protein response (UPR), which was mitigated in daf-2 mutants. Moreover, depletion of DNJ-21, which functionally interacts with PHB in mitochondria, mimicked the effect of PHB deficiency on the UPR^ER and on the lifespan of wild type and insulin signaling deficient mutants. Our work shows that PHB differentially modulates lipid metabolism depending on the worm’s metabolic status and provides evidences for a new link between PHB and ER homeostasis in ageing regulation.

Methylmercury Induces Metabolic Alterations in Caenorhabditis elegans: Role for C/EBP Transcription Factor

Methylmercury (MeHg) is a well-known neurotoxicant; however, its role in metabolic diseases has been gaining wider attention. We have previously shown that MeHg causes metabolic alterations in Caenorhabditis elegans, leading to decreased nicotinamide adenine dinucleotide cofactor, mitochondrial dysfunction, and oxidative stress. We were, therefore, interested in whether MeHg also affects nutrient metabolism, particularly lipid homeostasis, which may contribute to the development of metabolic conditions such as obesity or metabolic syndrome (MS). RNA from wild-type worms exposed to MeHg was collected immediately after treatment and used for gene expression analysis by DNA microarray. MeHg differentially regulated 215 genes, 17 genes involved in lipid homeostasis, and 12 genes involved in carbohydrate homeostasis. Of particular interest was cebp-1, the worm ortholog to human C/EBP, a pro-adipogenic transcription factor implicated in MS. MeHg increased the expression of cebp-1 as well as pro-adipogenic transcription factors sbp-1 and nhr-49, triglyceride synthesis enzyme acl-6, and lipid transport proteins vit-2 and vit-6. Concurrent with the altered gene expression, MeHg increased triglyceride levels, lipid storage, and feeding behaviors. Worms expressing mutant cebp-1 were protected from MeHg-induced alterations in lipid content, feeding behaviors, and gene expression, highlighting the importance of this transcription factor in the worm's response to MeHg. Taken together, our data demonstrate that MeHg induces biochemical, metabolic, and behavioral changes in C. elegans that can lead to metabolic dysfunction.

Alternative model organisms for toxicological fingerprinting of relevant parameters in food and nutrition

In the field of (food) toxicology, there is a strong trend of replacing animal trials with alternative methods for the assessment of adverse health effects in humans. The replacement of animal trials is not only driven by ethical concerns but also by the number of potential testing substances (food additives, packaging material, contaminants, and toxicants), which is steadily increasing. In vitro 2D cell culture applications in combination with in silico modeling might provide an applicable first response. However, those systems lack accurate predictions of metabolic actions. Thus, alternative in vivo models could fill the gap between cell culture and animal trials. In this review, we highlight relevant studies in the field and spotlight the applicability of alternative models, including C. elegans, D. rerio, Drosophila, HET-CAM and Lab-on-a-chip.

Azelaic Acid Promotes Caenorhabditis elegans Longevity at Low Temperature Via an Increase in Fatty Acid Desaturation

PURPOSE

Azelaic acid (AzA) is a dicarboxylic acid naturally occurring in various grains having anti-inflammatory and anti-oxidation properties. Recently, AzA is shown to reduce high-fat diet-induced adiposity in animals. However, its physiological role in lipid metabolism and aging in various environmental stresses is unknown.

METHODS AND RESULTS

Using C. elegans as an invertebrate animal model, we demonstrate that AzA suppresses fat accumulation with no effect on lifespan at normal temperatures. Moreover, AzA promotes lifespan at low temperatures by elevation of unsaturated long-chain fatty acids and expression of genes in fatty acid desaturation. We further find that genes encoding fatty acid desaturases such as fat-1, fat-5, fat-6, and fat-7 are crucial for the lifespan-extending effect of AzA at low temperature.

CONCLUSIONS

Taken together, our results suggest that AzA promotes adaption to low temperature in C. elegans via shifting fatty acid profile to unsaturated long-chain fatty acids.

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.

Phenolic Compounds Reduce the Fat Content in Caenorhabditis elegans by Affecting Lipogenesis, Lipolysis, and Different Stress Responses

Supplementation with bioactive compounds capable of regulating energy homeostasis is a promising strategy to manage obesity. Here, we have screened the ability of different phenolic compounds (myricetin, kaempferol, naringin, hesperidin, apigenin, luteolin, resveratrol, curcumin, and epicatechin) and phenolic acids (p-coumaric, ellagic, ferulic, gallic, and vanillic acids) regulating C. elegans fat accumulation. Resveratrol exhibited the strongest lipid-reducing activity, which was accompanied by the improvement of lifespan, oxidative stress, and aging, without affecting worm development. Whole-genome expression microarrays demonstrated that resveratrol affected fat mobilization, fatty acid metabolism, and unfolded protein response of the endoplasmic reticulum (UPRER), mimicking the response to calorie restriction. Apigenin induced the oxidative stress response and lipid mobilization, while vanillic acid affected the unfolded-protein response in ER. In summary, our data demonstrates that phenolic compounds exert a lipid-reducing activity in C. elegans through different biological processes and signaling pathways, including those related with lipid mobilization and fatty acid metabolism, oxidative stress, aging, and UPR-ER response. These findings open the door to the possibility of combining them in order to achieve complementary activity against obesity-related disorders.

Modeling tissue-relevant Caenorhabditis elegans metabolism at network, pathway, reaction, and metabolite levels

Metabolism is a highly compartmentalized process that provides building blocks for biomass generation during development, homeostasis, and wound healing, and energy to support cellular and organismal processes. In metazoans, different cells and tissues specialize in different aspects of metabolism. However, studying the compartmentalization of metabolism in different cell types in a whole animal and for a particular stage of life is difficult. Here, we present MEtabolic models Reconciled with Gene Expression (MERGE), a computational pipeline that we used to predict tissue-relevant metabolic function at the network, pathway, reaction, and metabolite levels based on single-cell RNA-sequencing (scRNA-seq) data from the nematode Caenorhabditis elegans. Our analysis recapitulated known tissue functions in C. elegans, captured metabolic properties that are shared with similar tissues in human, and provided predictions for novel metabolic functions. MERGE is versatile and applicable to other systems. We envision this work as a starting point for the development of metabolic network models for individual cells as scRNA-seq continues to provide higher-resolution gene expression data.

Spectroscopic coherent Raman imaging of Caenorhabditis elegans reveals lipid particle diversity

Caenorhabditis elegans serves as a model for understanding adiposity and its connections to aging. Current methodologies do not distinguish between fats serving the energy needs of the parent, akin to mammalian adiposity, from those that are distributed to the progeny, making it difficult to accurately interpret the physiological implications of fat content changes induced by external perturbations. Using spectroscopic coherent Raman imaging, we determine the protein content, chemical profiles and dynamics of lipid particles in live animals. We find fat particles in the adult intestine to be diverse, with most destined for the developing progeny. In contrast, the skin-like epidermis contains fats that are the least heterogeneous, the least dynamic and have high triglyceride content. These attributes are most consistent with stored somatic energy reservoirs. These results challenge the prevailing practice of assessing C. elegans adiposity by measurements that are dominated by the intestinal fat content.

New Roles for the Heterochronic Transcription Factor LIN-29 in Cuticle Maintenance and Lipid Metabolism at the Larval-to-Adult Transition in Caenorhabditis elegans

Temporal regulation of gene expression is a crucial aspect of metazoan development. In the roundworm Caenorhabditis elegans, the heterochronic pathway controls multiple developmental events in a time-specific manner. The most downstream effector of this pathway, the zinc-finger transcription factor LIN-29, acts in the last larval stage (L4) to regulate elements of the larval-to-adult switch. Here, we explore new LIN-29 targets and their implications for this developmental transition. We used RNA-sequencing to identify genes differentially expressed between animals misexpressing LIN-29 at an early time point and control animals. Among 230 LIN-29-activated genes, we found that genes encoding cuticle collagens were overrepresented. Interestingly, expression of lin-29 and some of these collagens was increased in adults with cuticle damage, suggesting a previously unknown function for LIN-29 in adult cuticle maintenance. On the other hand, genes involved in fat metabolism were enriched among 350 LIN-29-downregulated targets. We used mass spectrometry to assay lipid content in animals overexpressing LIN-29 and observed reduced fatty acid levels. Many LIN-29-repressed genes are normally expressed in the intestine, suggesting cell-nonautonomous regulation. We identified several LIN-29 upregulated genes encoding signaling molecules that may act as mediators in the regulation of intestinally expressed genes encoding fat metabolic enzymes and vitellogenins. Overall, our results support the model of LIN-29 as a major regulator of adult cuticle synthesis and integrity, and as the trigger for metabolic changes that take place at the important transition from rapid growth during larval life to slower growth and offspring production during adulthood.

Reducing Effect of Farnesylquinone on Lipid Mass in C. elegans by Modulating Lipid Metabolism

Bioassay-guided fractionation of marine-derived fungi revealed that the EtOAc fraction from the fermentation broth of a mutated fungal strain Streptomyces nitrosporeus YBH10-5 had lipid-lowering effects in HepG2 cells. Chromatographic separation of the EtOAc fraction resulted in the isolation of 11 PKS-based derivatives, including a structurally unique meroterpenoid namely nitrosporeunol H (1). The structure of compound 1 was determined by the analysis of spectroscopic data. Further bioassay resulted in farnesylquinone (2) and its analogues to exert in vivo fat-reducing effects in C.elegans worm model. The underlying mode of action of compound 2 in the context of live worms was investigated, uncovering that compound 2 enhanced the mitochondrial β-oxidation rate and changed the transcriptional level of energy metabolism genes. Additional experiments revealed that compound 2 exerted its effects in C. elegans partially through repressing FAT-5, an isoform of stearoyl-CoA desaturase (SCD) which catalyzes the conversion of saturated fatty acids to monounsaturated fatty acids, thereafter leading to the modification of the fatty acid profile. Thus, compound 2 was suggested to be a promising lead for further optimization to treat obesity.

Transcriptional alterations in Caenorhabditis elegans following exposure to an anthelmintic fraction of the plant Picria fel-terrae Lour

Background

Natural compounds from plants are known to provide a source of anthelmintic molecules. In previous studies, we have shown that plant extracts from the plant Picria fel-terrae Lour. and particular fractions thereof have activity against the free-living nematode Caenorhabditis elegans, causing quite pronounced stress responses in this nematode. We have also shown that a fraction, designated Pf-fraction 5, derived from this plant has a substantial adverse effect on this worm; however, nothing is known about the molecular processes affected in the worm. In the present study, we explored this aspect.

Results

Key biological processes linked to upregulated genes (n = 214) included ‘response to endoplasmic reticulum stress’ and ‘lipid metabolism’, and processes representing downregulated genes (n = 357) included ‘DNA-conformation change’ and ‘cellular lipid metabolism’.

Conclusions

Exposure of C. elegans to Pf-fraction 5 induces significant changes in the transcriptome. Gene ontology analysis suggests that Pf-fraction 5 induces endoplasmic reticulum and mitochondrial stress, and the changes in gene expression are either a direct or indirect consequence of this. Further work is required to assess specific responses to sub-fractions of Pf-fraction 5 in time-course experiments in C. elegans, to define the chemical(s) with potent anthelmintic properties, to attempt to unravel their mode(s) of action and to assess their selectivity against nematodes.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3429-4) contains supplementary material, which is available to authorized users.

Linking Lipid Metabolism to Chromatin Regulation in Aging

The lifespan of an organism is strongly influenced by environmental factors (including diet) and by internal factors (notably reproductive status). Lipid metabolism is critical for adaptation to external conditions or reproduction. Interestingly, specific lipid profiles are associated with longevity, and increased uptake of certain lipids extends longevity in Caenorhabditis elegans and ameliorates disease phenotypes in humans. How lipids impact longevity, and how lipid metabolism is regulated during aging, is just beginning to be unraveled. This review describes recent advances in the regulation and role of lipids in longevity, focusing on the interaction between lipid metabolism and chromatin states in aging and age-related diseases.

β-Cryptoxanthin Reduces Body Fat and Increases Oxidative Stress Response in Caenorhabditis elegans Model

β-Cryptoxanthin (BCX) is a major dietary pro-vitamin A carotenoid, found mainly in fruits and vegetables. Several studies showed the beneficial effects of BCX on different aspects of human health. In spite of the evidence, the molecular mechanisms of action of BCX need to be further investigated. The Caenorhabditis elegans model was used to analyze in vivo the activity of BCX on fat reduction and protection to oxidative stress. Dose-response assays provided evidence of the efficacy of BCX at very low dose (0.025 µg/mL) (p < 0.001) on these processes. Moreover, a comparative analysis with other carotenoids, such as lycopene and β-carotene, showed a stronger effect of BCX. Furthermore, a transcriptomic analysis of wild-type nematodes supplemented with BCX revealed upregulation of the energy metabolism, response to stress, and protein homeostasis as the main metabolic targets of this xanthophyll. Collectively, this study provides new in vivo evidence of the potential therapeutic use of BCX in the prevention of diseases related to metabolic syndrome and aging.

Hypoxia Restrains Lipid Utilization via Protein Kinase A and Adipose Triglyceride Lipase Downregulation through Hypoxia-Inducible Factor

Oxygen is a key molecule for efficient energy production in living organisms. Although aerobic organisms have adaptive processes to survive in low-oxygen environments, it is poorly understood how lipolysis, the first step of energy production from stored lipid metabolites, would be modulated during hypoxia. Here, we demonstrate that fasting-induced lipolysis is downregulated by hypoxia through the hypoxia-inducible factor (HIF) signaling pathway. In Caenorhabditis elegans and mammalian adipocytes, hypoxia suppressed protein kinase A (PKA)-stimulated lipolysis, which is evolutionarily well conserved. During hypoxia, the levels of PKA activity and adipose triglyceride lipase (ATGL) protein were downregulated, resulting in attenuated fasting-induced lipolysis. In worms, HIF stabilization was sufficient to moderate the suppressive effect of hypoxia on lipolysis through ATGL and PKA inhibition. These data suggest that HIF activation under hypoxia plays key roles in the suppression of lipolysis, which might preserve energy resources in both C. elegans and mammalian adipocytes.

Multi-generational effects of lindane on nematode lipid metabolism with disturbances on insulin-like signal pathway

Influences on lipid metabolism and multi-generational obesogenic effects raised new concerns on lipophilic pollutants (e.g., lindane). Yet, the mechanisms remained unanswered. The present study exposed Caenorhabditis elegans to lindane for 4 consecutive generations (F0 to F3) at 1.0 ng/L, and measured effects in the directly exposed generations (F0 to F3), indirectly exposed ones (T1 and T1') and un-exposed ones (T3 and T3'). Lindane stimulated fat storages in all generations. At the biochemical level, lindane stimulated both acetyl-CoA carboxylase (ACC) and carnitine palmitoyl-transferases (CPT) in F0, T1 and T2, while inhibited them in F3, T1' and T3', demonstrating the balance between fatty acid synthesis and its depletion toward fat accumulation over generations. Moreover, lindane caused different effects on insulin among generations. It inhibited insulin in F0 and F3 and exhibited consistent effects on the expression changes of daf-2, sgk-1 and daf-16 genes in insulin-like signal pathway. Lindane also inhibited insulin in T1 and T3 but exhibited consistent effects on the expression changes of daf-2, akt-1 and daf-16. Different roles of sgk-1 and akt-1 indicated the response strategies from tolerance (F0 and F3) to avoidance (T1 and T3). Lindane stimulated insulin in T1' and T3' and exhibited consistent effects on expression changes of daf-2, sgk-1 and daf-16 genes that were similar in F0 and F3.

Use of Caenorhabditis elegans To Study the Potential Bioactivity of Natural Compounds

There is growing need and interest in finding specific compounds in natural products that have health benefits. Despite ongoing efforts to discover such compounds, the scientific evidence lags behind the vision, and it is important to find an effective paradigm for discovering such compounds. The model organism Caenorhabditis elegans offers a promising solution for studying the potential bioactivity and molecular mechanisms of natural compounds in vivo. This perspective discusses its use to study potential human health benefits, with focus on antioxidative, anti-aging, antimetabolic disorders (diabetes and obesity), and antineurodegenerative activities (Alzheimer's disease and Parkinson's disease), with practical examples. Finally, future directions in using a C. elegans-based model for discovering bioactive compounds for health promotion are discussed.

Time to move the fat

This outlook discusses Dowen et al.'s finding of a novel microRNA-mediated intertissue signaling pathway in the C. elegans epidermis that regulates vitellogenesis, the reallocation of intestinal fat to the germline to support reproduction.

In this issue of Genes & Development, Dowen and colleagues (pp. 1515–1528) elegantly unify two previously unconnected aspects of physiology. The investigators provide significant genetic evidence to support a critical link between developmental timing decisions and the regulation of lipid mobilization at the transition to adulthood in Caenorhabditis elegans. This novel connection involves cross-tissue signaling from the hypodermis (epidermis) to the intestine to promote reproductive success in the germline.

Investigating Connections between Metabolism, Longevity, and Behavior in Caenorhabditis elegans

An overview of Caenorhabditis elegans as an experimental organism for studying energy balance is presented. Some of the unresolved questions that complicate the interpretation of lipid measurements from C. elegans are highlighted. We review studies that show that both lipid synthesis and lipid breakdown pathways are activated and needed for the longevity of hermaphrodites that lack their germlines. These findings illustrate the heterogeneity of triglyceride-rich lipid particles in C. elegans and reveal specific lipid signals that promote longevity. Finally, we provide a brief overview of feeding behavioral responses of C. elegans to varying nutritional conditions and highlight an unanticipated metabolic pathway that allows the incorporation of experience in feeding behavior.

Neural Regulatory Pathways of Feeding and Fat in Caenorhabditis elegans

The compact nervous system of Caenorhabditis elegans and its genetic tractability are features that make this organism highly suitable for investigating energy balance in an animal system. Here, we focus on molecular components and organizational principles emerging from the investigation of pathways that largely originate in the nervous system and regulate feeding behavior but also peripheral fat regulation through neuroendocrine signaling. We provide an overview of studies aimed at understanding how C. elegans integrate internal and external cues in feeding behavior. We highlight some of the similarities and differences in energy balance between C. elegans and mammals. We also provide our perspective on unresolved issues, both conceptual and technical, that we believe have hampered critical evaluation of findings relevant to fat regulation in C. elegans.

The double mutation of cytochrome P450's and fatty acid desaturases affect lipid regulation and longevity in C. elegans

An imbalance between energy uptake and energy expenditure can lead to obesity and increase the risk of coronary heart disease, high blood pressure, stroke, type II diabetes and some cancers. Given that key elements of the energy pathway are evolutionary conserved, invertebrate research is an attractive alternative that overcomes the many legislative, financial and experimental hurdles typical of research with higher metazoan animals. Recent studies have suggested that some members of the cytochrome P450 superfamily are involved in lipid metabolism in addition to the traditional xenobiotic activity. To investigate this notion in more detail, the present study aimed to pinpoint phenotypic, genetic and genomic-level responses of Caenorhabditis elegans using selected deletion mutants including fat-5 (a member of the Δ9 desaturases) and cyp-35A2 (a member of the cytochrome P450 family). The creation of a fat-5(tm420);cyp-35A2(gk317) mutant uncovered that the deletion of both genes resulted in a strain which is marked by an extended lifespan. Furthermore, it diminished the overall level of Nile Red positive compartments, which is indicative of a change in lipid metabolism. Comprehensive transcriptomics revealed that several genes involved in aging and lipid transport/homeostasis were modulated following the double deletion of fat-5 and cyp-35A2. Taken together, the results suggest the presence of a putative correlation between longevity and lipid regulation and given that both genes have human homologs, this finding may offer a new lead to investigate in higher organisms.

Analysis of the effect of the mitochondrial prohibitin complex, a context-dependent modulator of longevity, on the C. elegans metabolome

The mitochondrial prohibitin complex, composed of two proteins, PHB-1 and PHB-2, is a context-dependent modulator of longevity. Specifically, prohibitin deficiency shortens the lifespan of otherwise wild type worms, while it dramatically extends the lifespan under compromised metabolic conditions. This extremely intriguingly phenotype has been linked to alterations in mitochondrial function and in fat metabolism. However, the true function of the mitochondrial prohibitin complex remains elusive. Here, we used gas chromatography coupled to a flame ionization detector (GC/FID) and ¹H NMR spectroscopy to gain molecular insights into the effect of prohibitin depletion on the Caenorhabditis elegans metabolome. We analysed the effect of prohibitin deficiency in two different developmental stages and under two different conditions, which result in opposing longevity phenotypes, namely wild type worms and daf-2(e1370) insulin signalling deficient mutants. Prohibitin depletion was shown to alter the fatty acid (GC/FID) and ¹H NMR metabolic profiles of wild type animals both at the fourth larval stage of development (L4) and at the young adult (YA) stage, while being more pronounced at the later stage. Furthermore, wild type and the diapause mutant daf-2(e1370), either expressing or not prohibitin, were clearly distinguishable based on their metabolic profiles, revealing changes in fatty acid composition, as well as in carbohydrate and amino acid metabolism. Moreover, the metabolic data indicate that daf-2(e1370) mutants are more robust than the wild type animals to changes induced by prohibitin depletion. The impact of prohibitin depletion on the C. elegans metabolome will be discussed herein in the scope of its effect on longevity. This article is part of a Special Issue entitled: Mitochondrial Dysfunction in Aging. Guest Editor: Aleksandra Trifunovic

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Impact of the mitochondrial prohibitin (PHB) complex on the C. elegans metabolome

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Depletion of individual PHB subunits results in similar metabolic profiles.

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PHB affects fatty acid composition, amino acid and carbohydrate metabolism.

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daf-2 mutants are more robust than wild type worms to the effect of PHB depletion.

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Modulation of fermentation may contribute to the longevity of PHB-depleted worms.