Neuronal control of lipid metabolism by STR-2 G protein-coupled receptor promotes longevity in Caenorhabditis elegans

Anemarrhena asphodeloides Bunge total saponins lower lipid via modulating MAOA activity to enhance defense mechanisms in mice and C. elegans

ETHNOPHARMACOLOGICAL RELEVANCE

Within Anemarrhena asphodeloides Bunge (AAB), the pivotal bioactive constituents are identified as Anemarrhena asphodeloides Bunge total saponins (ABS). In traditional pharmacology, ABS has exhibited notable anti-inflammatory, hypoglycemic, and cardioprotective properties. Despite these observed effects, the specific protective mechanisms of ABS against metabolic diseases and improving the endocrine system remain largely uncharted.

AIM TO STUDY

This work intends to shed light on the effects and intrinsic mechanisms of ABS on metabolic diseases.

MATERIALS AND METHODS

The characterization of ABS components was achieved through High-Performance Liquid Chromatography/Mass Spectrometry (HPLC/MS). To evaluate ABS's anti-inflammatory efficacy, mouse macrophages underwent analysis using the Griess method. Induced differentiation of mouse fibroblasts was assessed through Oil Red O staining. In an obesity model with C57BL/6 N mice, ABS administration prompted measurements of glucose and insulin tolerance. Western blot analysis quantified lipolysis and anti-inflammatory protein expression. Nile red staining gauged body fat content in C. elegans post-ABS treatment. The mechanism of ABS action was elucidated through mRNA sequencing, further validated using RNA interference technology, and nematode mutants.

RESULTS

ABS showcased the ability to diminish Nitric Oxide (NO) production in inflammatory macrophages and shrink adipocyte lipid droplets. In mice experiments, ABS was effective in alleviating fat accumulation and affecting serum lipid metabolism in diabetic mice. It enhanced oral glucose tolerance and insulin tolerance while increasing lipolysis-associated protein expression. ABS notably reduced fat content in C. elegans. Mechanistically, ABS downregulated NOD-like receptor thermal protein domain associated protein 3 (NLRP3) and monoamine oxidase A (MAOA) expression while enhancing UGT, ilys-2, and ilys-3. Lipolysis emerged as a pivotal pathway for ABS in the therapeutic intervention of metabolic diseases.

CONCLUSIONS

Our investigation has revealed that ABS exert a role in combating metabolic diseases by enhancing the body's defense mechanisms. ABS activate the NLRP3-neurotransmitter-visceral adipose pathway in mice, thereby bolstering resistance and diminishing fat accumulation. In C. elegans, ABS downregulated the expression of MAOA, bolstered resistance, and augmented glucuronidase activity, consequently leading to a reduction in fat content.

ASI-RIM neuronal axis regulates systemic mitochondrial stress response via TGF-β signaling cascade

Morphogens play a critical role in coordinating stress adaptation and aging across tissues, yet their involvement in neuronal mitochondrial stress responses and systemic effects remains unclear. In this study, we reveal that the transforming growth factor beta (TGF-β) DAF-7 is pivotal in mediating the intestinal mitochondrial unfolded protein response (UPRmt) in Caenorhabditis elegans under neuronal mitochondrial stress. Two ASI sensory neurons produce DAF-7, which targets DAF-1/TGF-β receptors on RIM interneurons to orchestrate a systemic UPRmt response. Remarkably, inducing mitochondrial stress specifically in ASI neurons activates intestinal UPRmt, extends lifespan, enhances pathogen resistance, and reduces both brood size and body fat levels. Furthermore, dopamine positively regulates this UPRmt activation, while GABA acts as a systemic suppressor. This study uncovers the intricate mechanisms of systemic mitochondrial stress regulation, emphasizing the vital role of TGF-β in metabolic adaptations that are crucial for organismal fitness and aging during neuronal mitochondrial stress.

Exposure to an aversive odor alters Caenorhabditis elegans physiology

Perception of external cues is important for enhancing the fitness and survival of animals. However, the role of odor perception in regulation of longevity and health is incompletely defined. Here, we show that the exposure to an aversive odor 2-nonanone reduces life span, brood size, feeding rate, and increases lipid storage in worms. These effects are restored to normal levels in mutant worms lacking functional olfactory AWB neurons, suggesting a potential role of odor perception in the regulation of animal physiology and longevity.

Homeostatic control of stearoyl desaturase expression via patched-like receptor PTR-23 ensures the survival of C. elegans during heat stress

Organismal responses to temperature fluctuations include an evolutionarily conserved cytosolic chaperone machinery as well as adaptive alterations in lipid constituents of cellular membranes. Using C. elegans as a model system, we asked whether adaptable lipid homeostasis is required for survival during physiologically relevant heat stress. By systematic analyses of lipid composition in worms during and before heat stress, we found that unsaturated fatty acids are reduced in heat-stressed animals. This is accompanied by the transcriptional downregulation of fatty acid desaturase enzymes encoded by fat-1, fat-3, fat-4, fat-5, fat-6, and fat-7 genes. Conversely, overexpression of the Δ9 desaturase FAT-7, responsible for the synthesis of PUFA precursor oleic acid, and supplementation of oleic acid causes accelerated death of worms during heat stress. Interestingly, heat stress causes permeability defects in the worm's cuticle. We show that fat-7 expression is reduced in the permeability defective collagen (PDC) mutant, dpy-10, known to have enhanced heat stress resistance (HSR). Further, we show that the HSR of dpy-10 animals is dependent on the upregulation of PTR-23, a patched-like receptor in the epidermis, and that PTR-23 downregulates the expression of fat-7. Consequently, abrogation of ptr-23 in wild type animals affects its survival during heat stress. This study provides evidence for the negative regulation of fatty acid desaturase expression in the soma of C. elegans via the non-canonical role of a patched receptor signaling component. Taken together, this constitutes a skin-gut axis for the regulation of lipid desaturation to promote the survival of worms during heat stress.

Dioscin integrates regulation of monosaturated fatty acid metabolism to extend the life span through XBP-1/SBP-1 dependent manner

Delay aging, especially in healthy life extension, brought the most interest to the medical field. Searching for anti-aging drugs with relative safety profiles bring natural products in hotspot. In this study, we find that dioscin promotes the health span extension in wild-type Caenorhabditis elegans. Through the genetic screening in C. elegans, we further reveal that dioscin activates the transcription factor SBP-1/SREBP by the UPR^ER transcription factor XBP-1 to upregulate transcription of the Δ9 desaturase FAT-5 and FAT-7, resulting in increased monounsaturated fatty acid content which requires for healthy life span extension. Intriguingly, through tissue-specific knockdown, we find that dioscin modulates the health span by activating SBP-1 in the intestine. Unexpectedly, dietary supplementation of POA and OA rescues XBP-1, SBP-1 mutants-induced shortened life span phenotype. Considering the conservation of MUFAs metabolism, dioscin may promote health span in other species, including mammals. Our work suggests that dioscin might be a promising candidate for developing anti-aging agent.

Application of Caenorhabditis elegans in Lipid Metabolism Research

Over the last decade, the development and prevalence of obesity have posed a serious public health risk, which has prompted studies on the regulation of adiposity. With the ease of genetic manipulation, the diversity of the methods for characterizing body fat levels, and the observability of feeding behavior, Caenorhabditis elegans (C. elegans) is considered an excellent model for exploring energy homeostasis and the regulation of the cellular fat storage. In addition, the homology with mammals in the genes related to the lipid metabolism allows many aspects of lipid modulation by the regulators of the central nervous system to be conserved in this ideal model organism. In recent years, as the complex network of genes that maintain an energy balance has been gradually expanded and refined, the regulatory mechanisms of lipid storage have become clearer. Furthermore, the development of methods and devices to assess the lipid levels has become a powerful tool for studies in lipid droplet biology and the regulation of the nematode lipid metabolism. Herein, based on the rapid progress of C. elegans lipid metabolism-related studies, this review outlined the lipid metabolic processes, the major signaling pathways of fat storage regulation, and the primary experimental methods to assess the lipid content in nematodes. Therefore, this model system holds great promise for facilitating the understanding, management, and therapies of human obesity and other metabolism-related diseases.

Microbiota-derived metabolites in regulating the development and physiology of Caenorhabditis elegans

Microbiota consist of microorganisms that provide essential health benefits and contribute to the animal's physiological homeostasis. Microbiota-derived metabolites are crucial mediators in regulating host development, system homeostasis, and overall fitness. In this review, by focusing on the animal model Caenorhabditis elegans, we summarize key microbial metabolites and their molecular mechanisms that affect animal development. We also provide, from a bacterial perspective, an overview of host-microbiota interaction networks used for maintaining host physiological homeostasis. Moreover, we discuss applicable methodologies for profiling new bacterial metabolites that modulate host developmental signaling pathways. Microbiota-derived metabolites have the potential to be diagnostic biomarkers for diseases, as well as promising targets for engineering therapeutic interventions against animal developmental or health-related defects.

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.

Thermosensation in Caenorhabditis elegans is linked to ubiquitin-dependent protein turnover via insulin and calcineurin signalling

Organismal physiology and survival are influenced by environmental conditions and linked to protein quality control. Proteome integrity is achieved by maintaining an intricate balance between protein folding and degradation. In Caenorhabditis elegans, acute heat stress determines cell non-autonomous regulation of chaperone levels. However, how the perception of environmental changes, including physiological temperature, affects protein degradation remains largely unexplored. Here, we show that loss-of-function of dyf-1 in Caenorhabditis elegans associated with dysfunctional sensory neurons leads to defects in both temperature perception and thermal adaptation of the ubiquitin/proteasome system centered on thermosensory AFD neurons. Impaired perception of moderate temperature changes worsens ubiquitin-dependent proteolysis in intestinal cells. Brain-gut communication regulating protein turnover is mediated by upregulation of the insulin-like peptide INS-5 and inhibition of the calcineurin-regulated forkhead-box transcription factor DAF-16/FOXO. Our data indicate that perception of ambient temperature and its neuronal integration is important for the control of proteome integrity in complex organisms.

Lipid metabolism and ageing in Caenorhabditis elegans: a complex interplay

Life expectancy in Western countries is increasing, with concomitant rise in ageing-related pathologies, including Parkinson's and Alzheimer's disease, as well as other neurodegenerative diseases. Consequently, the medical, psychological and economic burden to society is increasing. Thus, understanding the cellular and molecular mechanisms underlying the association of ageing with elevated vulnerability to disease is crucial towards promoting quality of life in old age. Caenorhabditis elegans has emerged as a versatile model to study ageing, due to its simplicity, fast life cycle, and the availability of a wide range of biological tools to target specific genes and cells. Indeed, recent studies in C. elegans have revealed that lipid metabolism plays a key role in controlling longevity by impinging on a plethora of molecular pathways and cell types. Here, we summarise findings relevant to the interplay between lipid metabolism and ageing in C. elegans, and discuss the implications for the pathogenesis of age-related disorders in humans.

Crosstalk between neurons and glia through G-protein coupled receptors: Insights from Caenorhabditis elegans

The past decades have witnessed a dogmatic shift from glia as supporting cells in the nervous system to their active roles in neurocentric functions. Neurons and glia communicate and show bidirectional responses through tripartite synapses. Studies across species indicate that neurotransmitters released by neurons are perceived by glial receptors, which allow for gliotransmitter release. These gliotransmitters can result in activation of neurons via neuronal GPCR receptors. However, studies of these molecular interactions are in their infancy. Caenorhabditis elegans has a conserved neuron-glia architectural repertoire with molecular and functional resemblance to mammals. Further, glia in C. elegans can be manipulated through ablation and mutations allowing for deciphering of glial dependent processes in vivo at single glial resolutions. Here, we will review recent findings from vertebrate and invertebrate organisms with a focus on how C. elegans can be used to advance our understanding of neuron-glia interactions through GPCRs.

Temperature-Dependent Regulation of Proteostasis and Longevity

Temperature is an important environmental condition that determines the physiology and behavior of all organisms. Animals use different response strategies to adapt and survive fluctuations in ambient temperature. The hermaphrodite Caenorhabditis elegans has a well-studied neuronal network consisting of 302 neurons. The bilateral AFD neurons are the primary thermosensory neurons in the nematode. In addition to regulating thermosensitivity, AFD neurons also coordinate cellular stress responses through systemic mechanisms involving neuroendocrine signaling. Recent studies have examined the effects of temperature on altering various signaling pathways through specific gene expression programs that promote stress resistance and longevity. These studies challenge the proposed theories of temperature-dependent regulation of aging as a passive thermodynamic process. Instead, they provide evidence that aging is a well-defined genetic program. Loss of protein homeostasis (proteostasis) is one of the key hallmarks of aging. Indeed, proteostasis pathways, such as the heat shock response and aggregation of metastable proteins, are also controlled by thermosensory neurons in C. elegans. Prolonged heat stress is thought to play a critical role in the development of neurodegenerative protein misfolding diseases in humans. This review presents the latest evidence on how temperature coordinates proteostasis and aging. It also discusses how studies of poikilothermic organisms can be applied to vertebrates and provides new therapeutic strategies for human disease.

G protein-coupled receptors that influence lifespan of human and animal models

Humanity has always sought to live longer and for this, multiple strategies have been tried with varying results. In this sense, G protein-coupled receptors (GPCRs) may be a good option to try to prolong our life while maintaining good health since they have a substantial participation in a wide variety of processes of human pathophysiology and are one of the main therapeutic targets. In this way, we present the analysis of a series of GPCRs whose activity has been shown to affect the lifespan of animal and human models, and in which we put a special interest in describing the molecular mechanisms involved. Our compilation of data revealed that the mechanisms most involved in the role of GPCRs in lifespan are those that mimic dietary restriction, those related to insulin signaling and the AMPK and TOR pathways, and those that alter oxidative homeostasis and severe and/or chronic inflammation. We also discuss the possibility of using agonist or antagonist drugs, depending on the beneficial or harmful effects of each GPCR, in order to prolong people's lifespan and healthspan.

Sensory perception of environmental cues as a modulator of aging and neurodegeneration: Insights from Caenorhabditis elegans

Environmental stimuli such as temperature, food, and smell significantly influence the physiology and behavior of animals. Animals are differentially adapted to maintain their internal body functions in response to varied environmental conditions. These external cues are sensed by specialized neurons which are a part of the chemosensory and thermosensory systems. The inability to respond correctly to varied environmental conditions may result in compromised bodily functions and reduced longevity. For example, the ability to sense food is derived from the integrated action of olfactory and gustatory systems. The damage to the olfactory system will affect our decision of palatable food items which in turn can affect the response of the gustatory system, ultimately causing abnormal feeding habits. Recent studies have provided evidence that aging is regulated by sensory perception of environment. Aging is one of the most common causes of various neurodegenerative diseases and the perception of environmental cues is also found to regulate the development of neurodegenerative phenotype in several animal models. However, specific molecular signaling pathways involved in the process are not completely understood. The research conducted on one of the best-studied animal models of aging, Caenorhabditis elegans, has demonstrated multiple examples of gene-environment interaction at the neuronal level which affects life span. The findings may be useful to identify the key neuronal regulators of aging and age-related diseases in humans owing to conserved core metabolic and aging pathways from worms to humans.

Dauer Formation in C. elegans Is Modulated through AWC and ASI-Dependent Chemosensation

The perception of our surrounding environment is an amalgamation of stimuli detected by sensory neurons. In Caenorhabditis elegans, olfaction is an essential behavior that determines various behavioral functions such as locomotion, feeding and development. Sensory olfactory cues also initiate downstream neuroendocrine signaling that controls aging, learning, development and reproduction. Innate sensory preferences toward odors (food, pathogens) and reproductive pheromones are modulated by 11 pairs of amphid chemosensory neurons in the head region of C. elegans. Amongst these sensory neurons, the ASI neuron has neuroendocrine functions and secretes neuropeptides, insulin-like peptide (DAF-28) and the TGF-β protein, DAF-7. Its expression levels are modulated by the presence of food (increased levels) and population density (decreased levels). A recent study has shown that EXP-1, an excitatory GABA receptor regulates DAF-7/TGF-β levels and participates in DAF-7/TGF-β-mediated behaviors such as aggregation and bordering. Here, we show that exp-1 mutants show defective responses toward AWC-sensed attractive odors in a non-autonomous manner through ASI neurons. Our dauer experiments reveal that in daf-7 mutants, ASI expressed EXP-1 and STR-2 (a G-protein-coupled receptor; GPCR) that partially maintained reproductive growth of animals. Further, studies suggest that neuronal connections between ASI and AWC neurons are allowed at least partially through ASI secreted DAF-7 or through alternate TGF- β pathway/s regulated by EXP-1 and STR-2. Together, our behavioral, genetic and imaging experiments propose that EXP-1 and STR-2 integrate food cues and allow the animals to display DAF-7/TGF-β neuroendocrine dependent or independent behavioral responses contributing to chemosensensory and developmental plasticity.

Worms, Fat, and Death: Caenorhabditis elegans Lipid Metabolites Regulate Cell Death

Caenorhabditis elegans is well-known as the model organism used to elucidate the genetic pathways underlying the first described form of regulated cell death, apoptosis. Since then, C. elegans investigations have contributed to the further understanding of lipids in apoptosis, especially the roles of phosphatidylserines and phosphatidylinositols. More recently, studies in C. elegans have shown that dietary polyunsaturated fatty acids can induce the non-apoptotic, iron-dependent form of cell death, ferroptosis. In this review, we examine the roles of various lipids in specific aspects of regulated cell death, emphasizing recent work in C. elegans.

Total Triglyceride Quantification in Caenorhabditis elegans

Several studies suggest an important role of lipid metabolism in regulating longevity of Caenorhabditis elegans. Therefore, assays to quantify lipids have enormous value in understanding aging and pathologies associated with it. Approximately 70% of lipid metabolism genes in the nematode have orthologs in humans. Amenability of C. elegans to genetic manipulations has allowed investigations into the role of specific genetic factors in lipid metabolism. Here, we describe a protocol to quantify total triglycerides in C. elegans, which can be extended to studies of the effects of altered environmental and genetic factors on stored fats. This protocol quantifies the picomoles of the triglycerides, in whole worm lysate. Due to the sensitivity of the assay, it could help in identifying subtle changes in the total stored fat which are not discernible with microscopy techniques.

Neuronal control of lipid metabolism by STR-2 G protein-coupled receptor promotes longevity in Caenorhabditis elegans

The G protein-coupled receptor (GPCR) encoding family of genes constitutes more than 6% of genes in Caenorhabditis elegans genome. GPCRs control behavior, innate immunity, chemotaxis, and food search behavior. Here, we show that C. elegans longevity is regulated by a chemosensory GPCR STR-2, expressed in AWC and ASI amphid sensory neurons. STR-2 function is required at temperatures of 20°C and higher on standard Escherichia coli OP50 diet. Under these conditions, this neuronal receptor also controls health span parameters and lipid droplet (LD) homeostasis in the intestine. We show that STR-2 regulates expression of delta-9 desaturases, fat-5, fat-6 and fat-7, and of diacylglycerol acyltransferase dgat-2. Rescue of the STR-2 function in either AWC and ASI, or ASI sensory neurons alone, restores expression of fat-5, dgat-2 and restores LD stores and longevity. Rescue of stored fat levels of GPCR mutant animals to wild-type levels, with low concentration of glucose, rescues its lifespan phenotype. In all, we show that neuronal STR-2 GPCR facilitates control of neutral lipid levels and longevity in C. elegans.