Structural characterization of acyl-CoA oxidases reveals a direct link between pheromone biosynthesis and metabolic state in Caenorhabditis elegans

WWP2 Regulates Renal Fibrosis and the Metabolic Reprogramming of Profibrotic Myofibroblasts

Key Points

WWP2 expression is elevated in the tubulointerstitium of fibrotic kidneys and contributes to CKD pathogenesis and progression. WWP2 uncouples the profibrotic activation and cell proliferation in renal myofibroblasts. WWP2 controls mitochondrial respiration in renal myofibroblasts through the metabolic regulator peroxisome proliferator-activated receptor gamma coactivator 1-alpha.

Background

Renal fibrosis is a common pathologic end point in CKD that is challenging to reverse, and myofibroblasts are responsible for the accumulation of a fibrillar collagen–rich extracellular matrix. Recent studies have unveiled myofibroblasts' diversity in proliferative and fibrotic characteristics, which are linked to different metabolic states. We previously demonstrated the regulation of extracellular matrix genes and tissue fibrosis by WWP2, a multifunctional E3 ubiquitin–protein ligase. Here, we investigate WWP2 in renal fibrosis and in the metabolic reprograming of myofibroblasts in CKD.

Methods

We used kidney samples from patients with CKD and WWP2 -null kidney disease mice models and leveraged single-cell RNA sequencing analysis to detail the cell-specific regulation of WWP2 in fibrotic kidneys. Experiments in primary cultured myofibroblasts by bulk-RNA sequencing, chromatin immunoprecipitation sequencing, metabolomics, and cellular metabolism assays were used to study the metabolic regulation of WWP2 and its downstream signaling.

Results

The tubulointerstitial expression of WWP2 was associated with fibrotic progression in patients with CKD and in murine kidney disease models. WWP2 deficiency promoted myofibroblast proliferation and halted profibrotic activation, reducing the severity of renal fibrosis in vivo . In renal myofibroblasts, WWP2 deficiency increased fatty acid oxidation and activated the pentose phosphate pathway, boosting mitochondrial respiration at the expense of glycolysis. WWP2 suppressed the transcription of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a metabolic mediator of fibrotic response, and pharmacologic inhibition of PGC-1α partially abrogated the protective effects of WWP2 deficiency on myofibroblasts.

Conclusions

WWP2 regulates the metabolic reprogramming of profibrotic myofibroblasts by a WWP2-PGC-1α axis, and WWP2 deficiency protects against renal fibrosis in CKD.

PPARα Agonism Enhances Immune Response to Radiotherapy While Dietary Oleic Acid Results in Counteraction

PURPOSE

Head and neck cancer (HNC) improvements are stagnant, even with advances in immunotherapy. Our previous clinical trial data show that altered fatty acid (FA) metabolism correlates with outcome. We hypothesized that pharmacologic and dietary modulation of FA catabolism will affect therapeutic efficacy.

EXPERIMENTAL DESIGN

We performed in vivo and in vitro experiments using PPARα agonism with fenofibrate (FF) or high oleic acid diets (OAD) with radiotherapy, generating metabolomic, proteomic, stable isotope tracing, extracellular flux analysis, and flow-cytometric data to investigate these alterations.

RESULTS

FF improved antitumor efficacy of high dose per fraction radiotherapy in HNC murine models, whereas the OAD reversed this effect. FF-treated mice on the control diet had evidence of increased FA catabolism. Stable isotope tracing showed less glycolytic utilization by ex vivo CD8+ T cells. Improved efficacy correlated with intratumoral alterations in eicosanoid metabolism and downregulated mTOR and CD36.

CONCLUSIONS

Metabolic intervention with increased FA catabolism improves the efficacy of HNC therapy and enhances antitumoral immune response.

Pheromone-based communication influences the production of somatic extracellular vesicles in C. elegans

Extracellular vesicles (EVs) are integral to numerous biological processes, yet it is unclear how environmental factors or interactions among individuals within a population affect EV-regulated systems. In Caenorhabditis elegans, the evolutionarily conserved large EVs, known as exophers, are part of a maternal somatic tissue resource management system. Consequently, the offspring of individuals exhibiting active exopher biogenesis (exophergenesis) develop faster. Our research focuses on unraveling the complex inter-tissue and social dynamics that govern exophergenesis. We found that ascr#10, the primary male pheromone, enhances exopher production in hermaphrodites, mediated by the G-protein-coupled receptor STR-173 in ASK sensory neurons. In contrast, pheromone produced by other hermaphrodites, ascr#3, diminishes exophergenesis within the population. This process is regulated via the neuropeptides FLP-8 and FLP-21, which originate from the URX and AQR/PQR/URX neurons, respectively. Our results reveal a regulatory network that controls the production of somatic EV by the nervous system in response to social signals.

Oxidoreductase enzymes: Characteristics, applications, and challenges as a biocatalyst

Oxidoreductases are enzymes with distinctive characteristics that favor their use in different areas, such as agriculture, environmental management, medicine, and analytical chemistry. Among these enzymes, oxidases, dehydrogenases, peroxidases, and oxygenases are very interesting. Because their substrate diversity, they can be used in different biocatalytic processes by homogeneous and heterogeneous catalysis. Immobilization of these enzymes has favored their use in the solution of different biotechnological problems, with a notable increase in the study and optimization of this technology in the last years. In this review, the main structural and catalytical features of oxidoreductases, their substrate specificity, immobilization, and usage in biocatalytic processes, such as bioconversion, bioremediation, and biosensors obtainment, are presented.

Acyl CoA oxidase: from its expression, structure, folding, and import to its role in human health and disease

β-oxidation of fatty acids is an important metabolic pathway and is a shared function between mitochondria and peroxisomes in mammalian cells. On the other hand, peroxisomes are the sole site for the degradation of fatty acids in yeast. The first reaction of this pathway is catalyzed by the enzyme acyl CoA oxidase housed in the matrix of peroxisomes. Studies in various model organisms have reported the conserved function of the protein in fatty acid oxidation. The importance of this enzyme is highlighted by the lethal conditions caused in humans due to its altered function. In this review, we discuss various aspects ranging from gene expression, structure, folding, and import of the protein in both yeast and human cells. Further, we highlight recent findings on the role of the protein in human health and aging, and discuss the identified mutations in the protein associated with debilitating conditions in patients.

Natural genetic variation in the pheromone production of C. elegans

From bacterial quorum sensing to human language, communication is essential for social interactions. Nematodes produce and sense pheromones to communicate among individuals and respond to environmental changes. These signals are encoded by different types and mixtures of ascarosides, whose modular structures further enhance the diversity of this nematode pheromone language. Interspecific and intraspecific differences in this ascaroside pheromone language have been described previously, but the genetic basis and molecular mechanisms underlying the variation remain largely unknown. Here, we analyzed natural variation in the production of 44 ascarosides across 95 wild Caenorhabditis elegans strains using high-performance liquid chromatography coupled to high-resolution mass spectrometry. We discovered wild strains defective in the production of specific subsets of ascarosides (e.g., the aggregation pheromone icas#9) or short- and medium-chain ascarosides, as well as inversely correlated patterns between the production of two major classes of ascarosides. We investigated genetic variants that are significantly associated with the natural differences in the composition of the pheromone bouquet, including rare genetic variants in key enzymes participating in ascaroside biosynthesis, such as the peroxisomal 3-ketoacyl-CoA thiolase, daf-22, and the carboxylesterase cest-3. Genome-wide association mappings revealed genomic loci harboring common variants that affect ascaroside profiles. Our study yields a valuable dataset for investigating the genetic mechanisms underlying the evolution of chemical communication.

Mitochondrial targets exploration of epigallocatechin gallate and theaflavin in regards to differences in stress protection under different temperatures

The study investigated the impacts of epigallocatechin gallate (EGCG) and theaflavin (TF1) on temperature tolerance of nematodes and explored targets on mitochondria. Survival rate, mitochondrial membrane potential (MMP) and ATP content of nematodes at different temperatures incubated with EGCG or TF1 were quantified. Thermogenesis and function of ex-vivo mitochondria were characterized. Targeted proteins of substances were explored via drug affinity responsive target stability (DARTS) and RT-qPCR. Results showed that EGCG and TF1 increased survival rates of nematodes under heat and cold stress, respectively. TF1 exhibited lower MMP of nematodes and more mitochondrial thermogenesis than EGCG for the cold-protection, and upregulated gpi-1, pgk-1, acox-1.2, acox-1.3 and acaa-2 to compensate the energy loss due to the uncoupling and downregulation of sdha-1 and atp-1. EGCG upregulated ctl-1, hsp-60 and enol-1 expression for the thermo-protection, as well as pgk-1, acox-1.3 and acaa-2 to compensate energy loss due to the downregulation of sdha-1.

Polyunsaturated fatty acids promote the rapid fusion of lipid droplets in Caenorhabditis elegans

Lipid droplets (LDs) are intracellular organelles that dynamically regulate lipids and energy homeostasis in the cell. LDs can grow through either local lipid synthesis or LD fusion. However, how lipids involving in LD fusion for LD growth is largely unknown. Here, we show that genetic mutation of acox-3 (acyl-CoA oxidase), maoc-1 (enoyl-CoA hydratase), dhs-28 (3-hydroxylacyl-CoA dehydrogenase), and daf-22 (3-ketoacyl-CoA thiolase), all involved in the peroxisomal β-oxidation pathway in Caenorhabditis elegans, led to rapid fusion of adjacent LDs to form giant LDs (gLDs). Mechanistically, we show that dysfunction of peroxisomal β-oxidation results in the accumulation of long-chain fatty acid-CoA and phosphocholine, which may activate the sterol-binding protein 1/sterol regulatory element–binding protein to promote gLD formation. Furthermore, we found that inactivation of either FAT-2 (delta-12 desaturase) or FAT-3 and FAT-1 (delta-15 desaturase and delta-6 desaturase, respectively) to block the biosynthesis of polyunsaturated fatty acids (PUFAs) with three or more double bonds (n≥3-PUFAs) fully repressed the formation of gLDs; in contrast, dietary supplementation of n≥3-PUFAs or phosphocholine bearing these PUFAs led to recovery of the formation of gLDs in peroxisomal β-oxidation–defective worms lacking PUFA biosynthesis. Thus, we conclude that n≥3-PUFAs, distinct from other well-known lipids and proteins, promote rapid LD fusion leading to LD growth.

Crystal structures of apo- and FAD-bound human peroxisomal acyl-CoA oxidase provide mechanistic basis explaining clinical observations

Peroxisomal acyl-CoA oxidase 1a (ACOX1a) catalyzes the first and rate-limiting step of fatty acid oxidation, the conversion of acyl-CoAs to 2-trans-enoyl-CoAs. The dysfunction of human ACOX1a (hACOX1a) leads to deterioration of the nervous system manifesting in myeloneuropathy, hypotonia and convulsions. Crystal structures of hACOX1a in apo- and cofactor (FAD)-bound forms were solved at 2.00 and 2.09 Å resolution, respectively. hACOX1a exists as a homo-dimer with solvation free energy gain (ΔG^o) of -44.7 kcal mol^-1. Two FAD molecules bind at the interface of protein monomers completing the active sites. The substrate binding cleft of hACOX1a is wider compared to mitochondrial very-long chain specific acyl-CoA dehydrogenase. Mutations (p.G178C, p.M278V and p.N237S) reported to cause dysfunctionality of hACOX1a are analyzed on its 3D-structure to understand structure-function related perturbations and explain the associated phenotypes.

CYP4V2 fatty acid omega hydroxylase, a druggable target for the treatment of metabolic associated fatty liver disease (MAFLD)

Fatty acids are essential in maintaining cellular homeostasis by providing lipids for energy production, cell membrane integrity, protein modification, and the structural demands of proliferating cells. Fatty acids and their derivatives are critical bioactive signaling molecules that influence many cellular processes, including metabolism, cell survival, proliferation, migration, angiogenesis, and cell barrier function. The CYP4 Omega hydroxylase gene family hydroxylate various short, medium, long, and very-long-chain saturated, unsaturated and polyunsaturated fatty acids. Selective members of the CYP4 family metabolize vitamins and biochemicals with long alkyl side chains and bioactive prostaglandins, leukotrienes, and arachidonic acids. It is uncertain of the physiological role of different members of the CYP4 omega hydroxylase gene family in the metabolic control of physiological and pathological processes in the liver. CYP4V2 is a unique member of the CYP4 family. CYP4V2 inactivation in retinal pigment epithelial cells leads to cholesterol accumulation and Bietti's Crystalline Dystrophy (BCD) pathogenesis. This commentary provides information on the role CYP4V2 has in metabolic syndrome and nonalcoholic fatty liver disease progression. This is accomplished by identifying its role in BCD, its control of cholesterol synthesis and lipid droplet formation in C. elegans, and the putative function in cardiovascular disease and gastrointestinal/hepatic pathologies.

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.

Endocrine pheromones couple fat rationing to dauer diapause through HNF4α nuclear receptors

Developmental diapause is a widespread strategy for animals to survive seasonal starvation and environmental harshness. Diapaused animals often ration body fat to generate a basal level of energy for enduring survival. How diapause and fat rationing are coupled, however, is poorly understood. The nematode Caenorhabditis elegans excretes pheromones to the environment to induce a diapause form called dauer larva. Through saturated forward genetic screens and CRISPR knockout, we found that dauer pheromones feed back to repress the transcription of ACOX-3, MAOC-1, DHS-28, DAF-22 (peroxisomal β-oxidation enzymes dually involved in pheromone synthesis and fat burning), ALH-4 (aldehyde dehydrogenase for pheromone synthesis), PRX-10 and PRX-11 (peroxisome assembly and proliferation factors). Dysfunction of these pheromone enzymes and factors relieves the repression. Surprisingly, transcription is repressed not by pheromones excreted but by pheromones endogenous to each animal. The endogenous pheromones regulate the nuclear translocation of HNF4α family nuclear receptor NHR-79 and its co-receptor NHR-49, and, repress transcription through the two receptors. The feedback repression maintains pheromone homeostasis, increases fat storage, decreases fat burning, and prolongs dauer lifespan. Thus, the exocrine dauer pheromones possess an unexpected endocrine function to mediate a peroxisome-nucleus crosstalk, coupling dauer diapause to fat rationing.

Interaction of Symbiotic Rhizobia and Parasitic Root-Knot Nematodes in Legume Roots: From Molecular Regulation to Field Application

Legumes form two types of root organs in response to signals from microbes, namely, nodules and root galls. In the field, these interactions occur concurrently and often interact with each other. The outcomes of these interactions vary and can depend on natural variation in rhizobia and nematode populations in the soil as well as abiotic conditions. While rhizobia are symbionts that contribute fixed nitrogen to their hosts, parasitic root-knot nematodes (RKN) cause galls as feeding structures that consume plant resources without a contribution to the plant. Yet, the two interactions share similarities, including rhizosphere signaling, repression of host defense responses, activation of host cell division, and differentiation, nutrient exchange, and alteration of root architecture. Rhizobia activate changes in defense and development through Nod factor signaling, with additional functions of effector proteins and exopolysaccharides. RKN inject large numbers of protein effectors into plant cells that directly suppress immune signaling and manipulate developmental pathways. This review examines the molecular control of legume interactions with rhizobia and RKN to elucidate shared and distinct mechanisms of these root-microbe interactions. Many of the molecular pathways targeted by both organisms overlap, yet recent discoveries have singled out differences in the spatial control of expression of developmental regulators that may have enabled activation of cortical cell division during nodulation in legumes. The interaction of legumes with symbionts and parasites highlights the importance of a comprehensive view of root-microbe interactions for future crop management and breeding strategies.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Enterovirus 71 induces neural cell apoptosis and autophagy through promoting ACOX1 downregulation and ROS generation

Enterovirus 71 (EV71) infection causes hand, foot, and mouth disease (HFMD), and even fatal neurological complications. However, the mechanisms underlying EV71 neurological pathogeneses are largely unknown. This study reveals a distinct mechanism by which EV71 induces apoptosis and autophagy in neural cells. EV71 non-structure protein 3D (also known as RNA-dependent RNA polymerase, RdRp) interacts with the peroxisomal protein acyl-CoA oxidase 1 (ACOX1), and contributes to ACOX1 downregulation. Further studies demonstrate that EV71 reduces peroxisome numbers. Additionally, knockdown of ACOX1 or peroxin 19 (PEX19) induces apoptosis and autophagy in neural cells including human neuroblastoma (SK-N-SH) cells and human astrocytoma (U251) cells, and EV71 infection induces neural cell death through attenuating ACOX1 production. Moreover, EV71 infection and ACOX1 knockdown facilitate reactive oxygen species (ROS) production and attenuate the cytoprotective protein deglycase (DJ-1)/Nuclear factor erythroid 2-related factor 2 (NRF2)/Heme oxygenase 1 (HO-1) pathway (DJ-1/NRF2/HO-1), which collectively result in ROS accumulation in neural cells. In conclusion, EV71 downregulates ACOX1 protein expression, reduces peroxisome numbers, enhances ROS generation, and attenuates the DJ-1/NRF2/HO-1 pathway, thereby inducing apoptosis and autophagy in neural cells. These findings provide new insights into the mechanism underlying EV71-induced neural pathogenesis, and suggest potential treatments for EV71-associated diseases.

Social and sexual behaviors in C. elegans: the first fifty years

For the first 25 years after the landmark 1974 paper that launched the field, most C. elegans biologists were content to think of their subjects as solitary creatures. C. elegans presented no shortage of fascinating biological problems, but some of the features that led Brenner to settle on this species-in particular, its free-living, self-fertilizing lifestyle-also seemed to reduce its potential for interesting social behavior. That perspective soon changed, with the last two decades bringing remarkable progress in identifying and understanding the complex interactions between worms. The growing appreciation that C. elegans behavior can only be meaningfully understood in the context of its ecology and evolution ensures that the coming years will see similarly exciting progress.

Modular metabolite assembly in Caenorhabditis elegans depends on carboxylesterases and formation of lysosome-related organelles

Signaling molecules derived from attachment of diverse metabolic building blocks to ascarosides play a central role in the life history of C. elegans and other nematodes; however, many aspects of their biogenesis remain unclear. Using comparative metabolomics, we show that a pathway mediating formation of intestinal lysosome-related organelles (LROs) is required for biosynthesis of most modular ascarosides as well as previously undescribed modular glucosides. Similar to modular ascarosides, the modular glucosides are derived from highly selective assembly of moieties from nucleoside, amino acid, neurotransmitter, and lipid metabolism, suggesting that modular glucosides, like the ascarosides, may serve signaling functions. We further show that carboxylesterases that localize to intestinal organelles are required for the assembly of both modular ascarosides and glucosides via ester and amide linkages. Further exploration of LRO function and carboxylesterase homologs in C. elegans and other animals may reveal additional new compound families and signaling paradigms.

Loss- or Gain-of-Function Mutations in ACOX1 Cause Axonal Loss via Different Mechanisms

ACOX1 (acyl-CoA oxidase 1) encodes the first and rate-limiting enzyme of the very-long-chain fatty acid (VLCFA) β-oxidation pathway in peroxisomes and leads to H2O2 production. Unexpectedly, Drosophila (d) ACOX1 is mostly expressed and required in glia, and loss of ACOX1 leads to developmental delay, pupal death, reduced lifespan, impaired synaptic transmission, and glial and axonal loss. Patients who carry a previously unidentified, de novo, dominant variant in ACOX1 (p.N237S) also exhibit glial loss. However, this mutation causes increased levels of ACOX1 protein and function resulting in elevated levels of reactive oxygen species in glia in flies and murine Schwann cells. ACOX1 (p.N237S) patients exhibit a severe loss of Schwann cells and neurons. However, treatment of flies and primary Schwann cells with an antioxidant suppressed the p.N237S-induced neurodegeneration. In summary, both loss and gain of ACOX1 lead to glial and neuronal loss, but different mechanisms are at play and require different treatments.

Convergent evolution of small molecule pheromones in Pristionchus nematodes

The small molecules that mediate chemical communication between nematodes-so-called 'nematode-derived-modular-metabolites' (NDMMs)-are of major interest because of their ability to regulate development, behavior, and life-history. Pristionchus pacificus nematodes produce an impressive diversity of structurally complex NDMMs, some of which act as primer pheromones that are capable of triggering irreversible developmental switches. Many of these NDMMs have only ever been found in P. pacificus but no attempts have been made to study their evolution by profiling closely related species. This study brings a comparative perspective to the biochemical study of NDMMs through the systematic MS/MS- and NMR-based analysis of exo-metabolomes from over 30 Pristionchus species. We identified 36 novel compounds and found evidence for the convergent evolution of complex NDMMs in separate branches of the Pristionchus phylogeny. Our results demonstrate that biochemical innovation is a recurrent process in Pristionchus nematodes, a pattern that is probably typical across the animal kingdom.

Intestinal peroxisomal fatty acid β-oxidation regulates neural serotonin signaling through a feedback mechanism

The ability to coordinate behavioral responses with metabolic status is fundamental to the maintenance of energy homeostasis. In numerous species including Caenorhabditis elegans and mammals, neural serotonin signaling regulates a range of food-related behaviors. However, the mechanisms that integrate metabolic information with serotonergic circuits are poorly characterized. Here, we identify metabolic, molecular, and cellular components of a circuit that links peripheral metabolic state to serotonin-regulated behaviors in C. elegans. We find that blocking the entry of fatty acyl coenzyme As (CoAs) into peroxisomal β-oxidation in the intestine blunts the effects of neural serotonin signaling on feeding and egg-laying behaviors. Comparative genomics and metabolomics revealed that interfering with intestinal peroxisomal β-oxidation results in a modest global transcriptional change but significant changes to the metabolome, including a large number of changes in ascaroside and phospholipid species, some of which affect feeding behavior. We also identify body cavity neurons and an ether-a-go-go (EAG)-related potassium channel that functions in these neurons as key cellular components of the circuitry linking peripheral metabolic signals to regulation of neural serotonin signaling. These data raise the possibility that the effects of serotonin on satiety may have their origins in feedback, homeostatic metabolic responses from the periphery.

Ascaroside Pheromones: Chemical Biology and Pleiotropic Neuronal Functions

Pheromones are neuronal signals that stimulate conspecific individuals to react to environmental stressors or stimuli. Research on the ascaroside (ascr) pheromones in Caenorhabditis elegans and other nematodes has made great progress since ascr#1 was first isolated and biochemically defined in 2005. In this review, we highlight the current research on the structural diversity, biosynthesis, and pleiotropic neuronal functions of ascr pheromones and their implications in animal physiology. Experimental evidence suggests that ascr biosynthesis starts with conjugation of ascarylose to very long-chain fatty acids that are then processed via peroxisomal β-oxidation to yield diverse ascr pheromones. We also discuss the concentration and stage-dependent pleiotropic neuronal functions of ascr pheromones. These functions include dauer induction, lifespan extension, repulsion, aggregation, mating, foraging and detoxification, among others. These roles are carried out in coordination with three G protein-coupled receptors that function as putative pheromone receptors: SRBC-64/66, SRG-36/37, and DAF-37/38. Pheromone sensing is transmitted in sensory neurons via DAF-16-regulated glutamatergic neurotransmitters. Neuronal peroxisomal fatty acid β-oxidation has important cell-autonomous functions in the regulation of neuroendocrine signaling, including neuroprotection. In the future, translation of our knowledge of nematode ascr pheromones to higher animals might be beneficial, as ascr#1 has some anti-inflammatory effects in mice. To this end, we propose the establishment of pheromics (pheromone omics) as a new subset of integrated disciplinary research area within chemical ecology for system-wide investigation of animal pheromones.

Biosynthetic tailoring of existing ascaroside pheromones alters their biological function in C. elegans

Caenorhabditis elegans produces ascaroside pheromones to control its development and behavior. Even minor structural differences in the ascarosides have dramatic consequences for their biological activities. Here, we identify a mechanism that enables C. elegans to dynamically tailor the fatty-acid side chains of the indole-3-carbonyl (IC)-modified ascarosides it has produced. In response to starvation, C. elegans uses the peroxisomal acyl-CoA synthetase ACS-7 to activate the side chains of medium-chain IC-ascarosides for β-oxidation involving the acyl-CoA oxidases ACOX-1.1 and ACOX-3. This pathway rapidly converts a favorable ascaroside pheromone that induces aggregation to an unfavorable one that induces the stress-resistant dauer larval stage. Thus, the pathway allows the worm to respond to changing environmental conditions and alter its chemical message without having to synthesize new ascarosides de novo. We establish a new model for biosynthesis of the IC-ascarosides in which side-chain β-oxidation is critical for controlling the type of IC-ascarosides produced.

Small roundworms such as Caenorhabditis elegans release chemical signals called ascarosides in order to communicate with other worms of the same species. Using the ascarosides, the worm can tell its friends, for example, how crowded the neighborhood is and whether there is enough food. The ascarosides thus help the worms in the population decide whether the neighborhood is good – meaning they should hang around, eat, and make babies – or whether the neighborhood is bad. If so, the worms should develop into a larval stage specialized for dispersal that will allow them to find a better neighborhood.

Roundworms make the ascarosides by attaching a long chemical ‘side chain’ to an ascarylose sugar. Further chemical modifications allow the worms to produce different signals. In general, to signal a good neighborhood, worms attach a structure called an indole group to the ascarosides. To signal a bad neighborhood, worms make the side chain very short. But how does a worm control which ascarosides it makes?

Zhou, Wang et al. now show that C. elegans can change the meaning of its chemical message by modifying the ascarosides that it has already produced instead of making new ones from scratch. Specifically, as their neighborhood runs out of food, C. elegans can use an enzyme called ACS-7 to initiate the shortening of the side chains of indole-ascarosides. The worm can thus change a favorable ascaroside signal that causes the worms to group together into an unfavorable ascaroside signal that causes the worms to enter their dispersal stage.

Although Zhou, Wang et al. have focused on chemical communication in C. elegans, the findings could easily apply to the many other species of roundworm that produce ascarosides. Knowing how worms communicate will help us to understand how worms respond to their environment. This knowledge could potentially be used to interfere with the lifecycles and survival of parasitic worm species that harm health and crops.

Acyl-CoA Oxidases Fine-Tune the Production of Ascaroside Pheromones with Specific Side Chain Lengths

Caenorhabditis elegans produces a complex mixture of ascaroside pheromones to control its development and behavior. Acyl-CoA oxidases, which participate in β-oxidation cycles that shorten the side chains of the ascarosides, regulate the mixture of pheromones produced. Here, we use CRISPR-Cas9 to make specific nonsense and missense mutations in acox genes and determine the effect of these mutations on ascaroside production in vivo. Ascaroside production in acox-1.1 deletion and nonsense strains, as well as a strain with a missense mutation in a catalytic residue, confirms the central importance of ACOX-1.1 in ascaroside biosynthesis and suggests that ACOX-1.1 functions in part by facilitating the activity of other acyl-CoA oxidases. Ascaroside production in an acox-1.1 strain with a missense mutation in an ATP-binding site at the ACOX-1.1 dimer interface suggests that ATP binding is important for the enzyme to function in ascaroside biosynthesis in vivo. Ascaroside production in strains with deletion, nonsense, and missense mutations in other acox genes demonstrates that ACOX-1.1 works with ACOX-1.3 in processing ascarosides with 7-carbon side chains, ACOX-1.4 in processing ascarosides with 9- and 11-carbon side chains, and ACOX-3 in processing ascarosides with 13- and 15-carbon side chains. It also shows that ACOX-1.2, but not ACOX-1.1, processes ascarosides with 5-carbon ω-side chains. By modeling the ACOX structures, we uncover characteristics of the enzyme active sites that govern substrate preferences. Our work demonstrates the role of specific acyl-CoA oxidases in controlling the length of ascaroside side chains and thus in determining the mixture of pheromones produced by C. elegans.

A Single-Neuron Chemosensory Switch Determines the Valence of a Sexually Dimorphic Sensory Behavior

Biological sex, a fundamental dimension of internal state, can modulate neural circuits to generate behavioral variation. Understanding how and why circuits are tuned by sex can provide important insights into neural and behavioral plasticity. Here we find that sexually dimorphic behavioral responses to C. elegans ascaroside sex pheromones are implemented by the functional modulation of shared chemosensory circuitry. In particular, the sexual state of a single sensory neuron pair, ADF, determines the nature of an animal's behavioral response regardless of the sex of the rest of the body. Genetic feminization of ADF causes males to be repelled by, rather than attracted to, ascarosides, whereas masculinization of ADF has the opposite effect in hermaphrodites. When ADF is ablated, both sexes are weakly repelled by ascarosides. Genetic sex modulates ADF function by tuning chemosensation: although ADF is functional in both sexes, it detects the ascaroside ascr#3 only in males, a consequence of cell-autonomous action of the master sexual regulator tra-1. This occurs in part through the conserved DM-domain gene mab-3, which promotes the male state of ADF. The sexual modulation of ADF has a key role in reproductive fitness, as feminization or ablation of ADF renders males unable to use ascarosides to locate mates. Our results reveal an economical mechanism in which sex-specific behavioral valence arises through the cell-autonomous regulation of a chemosensory switch by genetic sex, allowing a social cue with salience for both sexes to elicit navigational responses commensurate with the differing needs of each.

SIRT5 inhibits peroxisomal ACOX1 to prevent oxidative damage and is downregulated in liver cancer

Peroxisomes account for ~35% of total H₂O₂ generation in mammalian tissues. Peroxisomal ACOX1 (acyl-CoA oxidase 1) is the first and rate-limiting enzyme in fatty acid β-oxidation and a major producer of H₂O₂ ACOX1 dysfunction is linked to peroxisomal disorders and hepatocarcinogenesis. Here, we show that the deacetylase sirtuin 5 (SIRT5) is present in peroxisomes and that ACOX1 is a physiological substrate of SIRT5. Mechanistically, SIRT5-mediated desuccinylation inhibits ACOX1 activity by suppressing its active dimer formation in both cultured cells and mouse livers. Deletion of SIRT5 increases H₂O₂ production and oxidative DNA damage, which can be alleviated by ACOX1 knockdown. We show that SIRT5 downregulation is associated with increased succinylation and activity of ACOX1 and oxidative DNA damage response in hepatocellular carcinoma (HCC). Our study reveals a novel role of SIRT5 in inhibiting peroxisome-induced oxidative stress, in liver protection, and in suppressing HCC development.

Structural insight into the substrate specificity of acyl-CoA oxidase1 from Yarrowia lipolytica for short-chain dicarboxylyl-CoAs

Acyl-CoA oxidase (ACOX) plays an important role in fatty acid degradation. The enzyme catalyzes the first reaction in peroxisomal fatty acid β-oxidation by reducing acyl-CoA to 2-trans-enoyl-CoA. The yeast Yarrowia lipolytica is able to utilize fatty acids, fats, and oil as carbon sources to produce valuable bioproducts. We determined the crystal structure of ACOX1 from Y. lipolytica (YlACOX1) at a resolution of 2.5 Å. YlACOX1 forms a homodimer, and the monomeric structure is composed of four domains, the Nα, Nβ, Cα1, and Cα2. The FAD cofactor is bound at the dimerization interface between the Nβ- and Cα1-domains. The substrate-binding tunnel formed by the interface between the Nα-, Nβ-, and Cα1-domains is located proximal to FAD. Amino acid and structural comparisons of YlACOX1 with other ACOXs show that the substrate-binding pocket of YlACOX1 is much smaller than that of the medium- or long-chain ACOXs but is rather similar to that of the short-chain ACOXs. Moreover, the hydrophilicity of residues constituting the end region of the substrate-binding pocket in YlACOX1 is quite similar to those in the short-chain ACOXs but different from those of the medium- or long-chain ACOXs. These observations provide structural insights how YlACOX1 prefers short-chain dicarboxylyl-CoAs as a substrate.

Small-molecule pheromones and hormones controlling nematode development

The existence of small-molecule signals that influence development in Caenorhabditis elegans has been known for several decades, but only in recent years have the chemical structures of several of these signals been established. The identification of these signals has enabled connections to be made between these small molecules and fundamental signaling pathways in C. elegans that influence not only development but also metabolism, fertility, and lifespan. Spurred by these important discoveries and aided by recent advances in comparative metabolomics and NMR spectroscopy, the field of nematode chemistry has the potential to expand dramatically in the coming years. This Perspective will focus on small-molecule pheromones and hormones that influence developmental events in the nematode life cycle (ascarosides, dafachronic acids, and nemamides), will cover more recent work regarding the biosynthesis of these signals, and will explore how the discovery of these signals is transforming our understanding of nematode development and physiology.

Decoding chemical communication in nematodes

The nematode Caenorhabditis elegans produces tens, if not hundreds, of different ascarosides as pheromones to communicate with other members of its species. Overlapping mixtures of these pheromones affect the development of the worm and a variety of different behaviors. The ascarosides represent a unique tool for dissecting the neural circuitry that controls behavior and that connects to important signaling pathways, such as the insulin and TGFβ pathways, that lie at the nexus of development, metabolism, and lifespan in C. elegans. However, the exact physiological roles of many of the ascarosides are unclear, especially since many of these pheromones likely have multiple functions depending on their concentrations, the presence of other pheromones, and a variety of other factors. Determining these physiological roles will be facilitated by top-down approaches to characterize the pheromone receptors and their function, as well as bottom-up approaches to characterize the pheromone biosynthetic enzymes and their regulation.