Serotonin targets the DAF-16/FOXO signaling pathway to modulate stress responses

Neuroimmune Circuits in Allergic Diseases

Communication between the nervous and immune systems is evolutionarily conserved. From primitive eukaryotes to higher mammals, neuroimmune communication utilizes multiple complex and complementary mechanisms to trigger effective but balanced responses to environmental dangers such as allergens and tissue damage. These responses result from a tight integration of the nervous and immune systems, and accumulating evidence suggests that this bidirectional communication is crucial in modulating the initiation and development of allergic inflammation. In this review, we discuss the basic mechanisms of neuroimmune communication, with a focus on the recent advances underlying the importance of such communication in the allergic immune response. We examine neuronal sensing of allergens, how neuropeptides and neurotransmitters regulate allergic immune cell functions, and how inflammatory factors derived from immune cells coordinate complex peripheral and central nervous system responses. Furthermore, we highlight how fundamental aspects of host biology, from aging to circadian rhythm, might affect these pathways. Appreciating neuroimmune communications as an evolutionarily conserved and functionally integrated system that is fundamentally involved in type 2 immunity will provide new insights into allergic inflammation and reveal exciting opportunities for the management of acute and chronic allergic diseases.

Ovalbumin alters DAF-16 Class-II/I gene expressions via insulin/insulin-like growth factor-1 signaling to initiate the innate immune response of Caenorhabditis elegans

Innate immunity, as a significant defense system of the body, plays a key role in allergic reactions, but the mechanism of how food allergens trigger innate immune signaling is still unclear. Ovalbumin (OVA) is a model allergen in food allergy studies. Previous studies by our group have demonstrated that the innate immunity of Caenorhabditis elegans (C. elegans) elicited by OVA treatment was related to the insulin/insulin-like growth factor-1 signaling (IIS) pathway, but the details remain unknown. Therefore, in this study, the molecular mechanism of innate immune signaling transduction of C. elegans stimulated by OVA was determined using genetic mutations as well as RT-PCR, GFP fluorescence visualization monitoring, and slow-killing experiments. Results showed that the expression levels of DAF-16-class-I/II genes in the IIS pathway were significantly changed in C. elegans after OVA treatment, and the upstream gene daf-2 played an important role, which up-regulated the levels of DAF-16-class-II genes dod-22 and F55G11.8 by the daf-2-pqm-1 pathway, and down-regulated the level of DAF-16-class-I gene thn-2 by the daf-2-daf-16 pathway. Moreover, the upstream genes daf-2 and nhr-14, and the transcription factors DAF-16, PQM-1, and SKN-1 in the IIS pathway all participated in the up-regulations of DAF-16-class-II genes dod-17, dod-24, and F55G11.2. In conclusion, details of OVA activating innate immunity in C. elegans through the IIS pathway are reported here, and the results can be further extrapolated to mammals, which will contribute to a better understanding of the mechanism of the occurrence of food allergic reactions from the perspective of innate immunity.

L-Theanine Extends the Lifespan of Caenorhabditis elegans by Reducing the End Products of Advanced Glycosylation

L-theanine, a non-protein amino acid naturally occurring in tea leaves, is recognized for its antioxidant, anti-inflammatory, and neuroprotective properties. Despite its known benefits, the mechanisms by which L-theanine influences lifespan extension remain poorly understood. This study investigated the effects of L-theanine on the lifespan of Caenorhabditis elegans and explored the underlying mechanisms. Our findings indicate that L-theanine significantly diminishes the accumulation of advanced glycation end products (AGEs), which are biomarkers closely linked to aging and age-related diseases. Through an AGE-level analysis, we observed that L-theanine, when administered during early adulthood, notably extended the lifespan of Caenorhabditis elegans under both normal and high-glucose-induced stress conditions. L-theanine enhanced the lifespan under typical conditions and provided protective effects against high-glucose-induced stress. A further analysis demonstrated that L-theanine extends the lifespan of Caenorhabditis elegans by modulating the DAF-2/DAF-16 insulin-like signaling pathway and reducing the accumulation of advanced glycation end products (AGEs). In summary, this study identified L-theanine as a potential anti-aging intervention that extends the lifespan by reducing AGE accumulation and regulating insulin-like signaling pathways. These findings provide new insights for developing anti-aging strategies and lay the groundwork for further research on the potential benefits of L-theanine in mammals. Future studies could explore the molecular mechanisms, test L-theanine in mammalian models, and assess the long-term side effects.

Docosahexaenoic Acid (DHA) Supplementation in a Triglyceride Form Prevents from Polyglutamine-Induced Dysfunctions in Caenorhabditis elegans

A common hallmark of neurodegenerative diseases is the accumulation of polypeptide aggregates in neurons. Despite the primary cause of these diseases being inherently genetic, their development can be delayed with proper preventive treatments. Long-chain polyunsaturated fatty acids (ω-3 LCPUFA) are promising bioactive nutrients that are beneficial for brain health. In this study, the impact of an oil rich in a structured form of docosahexaenoic acid (DHA) triglyceride (TG) was assessed in a Caenorhabditis elegans model expressing long poly-glutamine (polyQ) chains, which mimics the symptomatology of polyQ-related neurodegenerative diseases such as Huntington's disease (HD), among others. The lifespan, the motility, the number of polyQ aggregates, the oxidative stress resistance, and the cognitive performance associated with sensitive stimuli was measured in mutant nematodes with polyQ aggregates. Overall, DHA-TG at 0.5 µM improved the lifespan, the motility, the oxidative stress resistance, and the cognitive performance of the nematodes, emphasizing the protection against serotonergic synapse dysfunction. Furthermore, the treatment reduced the polyQ aggregates in the nematodes. The data described herein shed light on the connection between DHA and the cognitive performance in neurodegenerative diseases and demonstrated the potential of DHA-TG as nutritional co-adjuvant to prevent the development of polyQ-associated dysfunctions.

Cornus officinalis Extract Enriched with Ursolic Acid Ameliorates UVB-Induced Photoaging in Caenorhabditis elegans

Ultraviolet B (UVB) exposure can contribute to photoaging of skin. Cornus officinalis is rich in ursolic acid (UA), which is beneficial to the prevention of photoaging. Because UA is hardly soluble in water, the Cornus officinalis extract (COE) was obtained using water as the antisolvent to separate the components containing UA from the crude extract of Cornus officinalis. The effect of COE on UVB damage was assessed using Caenorhabditis elegans. The results showed that COE could increase the lifespan and enhance the antioxidant enzyme activity of C. elegans exposed to UVB while decreasing the reactive oxygen species (ROS) level. At the same time, COE upregulated the expression of antioxidant-related genes and promoted the migration of SKN-1 to the nucleus. Moreover, COE inhibited the expression of the skn-1 downstream gene and the extension of the lifespan in skn-1 mutants exposed to UVB, indicating that SKN-1 was required for COE to function. Our findings indicate that COE mainly ameliorates the oxidative stress caused by UVB in C. elegans via the SKN-1/Nrf2 pathway.

Sertraline Promotes Health and Longevity in Caenorhabditis elegans

INTRODUCTION

While several antidepressants have been identified as potential geroprotectors, the effect and mechanism of sertraline on healthspan remain to be elucidated. Here, we explored the role of sertraline in the lifespan and healthspan of Caenorhabditis elegans.

METHODS

The optimal effect concentration of sertraline was first screened in wild-type N2 worms under heat stress conditions. Then, we examined the effects of sertraline on lifespan, reproduction, lipofuscin accumulation, mobility, and stress resistance. Finally, the expression of serotonin signaling and aging-related genes was investigated to explore the underlying mechanism, and the lifespan assays were performed in ser-7 RNAi strain, daf-2, daf-16, and aak-2 mutants.

RESULTS

Sertraline extended the lifespan in C. elegans with concomitant extension of healthspan as indicated by increasing mobility and reducing fertility and lipofuscin accumulation, as well as enhanced resistance to different abiotic stresses. Mechanistically, ser-7 orchestrated sertraline-induced longevity via the regulation of insulin and AMPK pathways, and sertraline-induced lifespan extension in nematodes was abolished in ser-7 RNAi strain, daf-2, daf-16, and aak-2 mutants.

CONCLUSION

Sertraline promotes health and longevity in C. elegans through ser-7-insulin/AMPK pathways.

Amphid sensory neurons of Caenorhabditis elegans orchestrate its survival from infection with broad classes of pathogens

The survival of a host during infection relies on its ability to rapidly sense the invading pathogen and mount an appropriate response. The bacterivorous nematode Caenorhabditis elegans lacks most of the traditional pattern recognition mechanisms. In this study, we hypothesized that the 12 pairs of amphid sensory neurons in the heads of worms provide sensing capability and thus affect survival during infection. We tested animals lacking amphid neurons to three major classes of pathogens, namely-a Gram-negative bacterium Pseudomonas aeruginosa, a Gram-positive bacterium Enterococcus faecalis, and a pathogenic yeast Cryptococcus neoformans By using individual neuronal ablation lines or mutants lacking specific neurons, we demonstrate that some neurons broadly suppress the survival of the host and colonization of all pathogens, whereas other amphid neurons differentially regulate host survival during infection. We also show that the roles of some of these neurons are pathogen-specific, as seen with the AWB odor sensory neurons that promote survival only during infections with P aeruginosa Overall, our study reveals broad and specific roles for amphid neurons during infections.

GABAergic signaling between enteric neurons and intestinal smooth muscle promotes innate immunity and gut defense in Caenorhabditis elegans

The nervous system is critical for intestinal homeostasis and function, but questions remain regarding its impact on gut immune defense. By screening the major neurotransmitters of C. elegans, we found that γ-aminobutyric acid (GABA) deficiency enhanced susceptibility to pathogenic Pseudomonas aeruginosa PA14 infection. GABAergic signaling between enteric neurons and intestinal smooth muscle promoted gut defense in a PMK-1/p38-dependent, but IIS/DAF-16- and DBL-1/TGF-β-independent, pathway. Transcriptomic profiling revealed that the neuropeptide, FLP-6, acted downstream of enteric GABAergic signaling. Further data determined that FLP-6 was expressed and secreted by intestinal smooth muscle cells and functioned as a paracrine molecule on the intestinal epithelium. FLP-6 suppressed the transcription factors ZIP-10 and KLF-1 that worked in parallel and converged to the PMK-1/p38 pathway in the intestinal epithelia for innate immunity and gut defense. Collectively, these findings uncover an enteric neuron-muscle-epithelium axis that may be evolutionarily conserved in higher organisms.

Ring neurons in the Drosophila central complex act as a rheostat for sensory modulation of aging

Sensory perception modulates aging, yet we know little about how. An understanding of the neuronal mechanisms through which animals orchestrate biological responses to relevant sensory inputs would provide insight into the control systems that may be important for modulating lifespan. Here, we provide new awareness into how the perception of dead conspecifics, or death perception, which elicits behavioral and physiological effects in many different species, affects lifespan in the fruit fly, Drosophila melanogaster. Previous work demonstrated that cohousing Drosophila with dead conspecifics decreases fat stores, reduces starvation resistance, and accelerates aging in a manner that requires both sight and the serotonin receptor 5-HT2A. In this manuscript, we demonstrate that a discrete, 5-HT2A-expressing neural population in the ellipsoid body (EB) of the Drosophila central complex, identified as R2/R4 neurons, acts as a rheostat and plays an important role in transducing sensory information about the presence of dead individuals to modulate lifespan. Expression of the insulin-responsive transcription factor foxo in R2/R4 neurons and insulin-like peptides dilp3 and dilp5, but not dilp2, are required, with the latter likely altered in median neurosecretory cells (MNCs) after R2/R4 neuronal activation. These data generate new insights into the neural underpinnings of how perceptive events may impact aging and physiology across taxa.

7,10,13,16-Docosatetraenoic acid impairs neurobehavioral development by increasing reactive oxidative species production in Caenorhabditis elegans

AIMS

To investigate human breast milk (HBM) lipids that may adversely affect infant neurodevelopment.

MAIN METHODS

We performed multivariate analyses that combined lipidomics and psychologic Bayley-III scales to identify which HBM lipids are involved in regulating infant neurodevelopment. We observed a significant moderate negative correlation between 7,10,13,16-docosatetraenoic acid (omega-6, C₂₂H₃₆O₂, the common name adrenic acid, AdA) and adaptive behavioral development. We further studied the effects of AdA on neurodevelopment by using Caenorhabditis elegans (C. elegans) as a model. Worms from larval stages L1 to L4 were supplemented with AdA at 5 nominal concentrations (0 μM [control], 0.1 μM, 1 μM, 10 μM, and 100 μM) and subjected to behavioral and mechanistic analyses.

KEY FINDINGS

Supplementation with AdA from larval stages L1 to L4 impaired neurobehavioral development, such as locomotive behaviors, foraging ability, chemotaxis behavior, and aggregation behavior. Furthermore, AdA upregulated the production of intracellular reactive oxygen species. AdA-induced oxidative stress blocked serotonin synthesis and serotoninergic neuron activity and inhibited expression of daf-16 and the daf-16-regulated genes mtl-1, mtl-2, sod-1, and sod-3, resulting in attenuation of the lifespan in C. elegans.

SIGNIFICANCE

Our study reveals that AdA is a harmful HBM lipid that may have adverse effects on infant adaptive behavioral development. We believe this information may be critical for AdA administration guidance in children's health care.

Age-Related Changes in Central Nervous System 5-Hydroxytryptamine Signalling and Its Potential Effects on the Regulation of Lifespan

Serotonin or 5-hydroxytryptamine (5-HT) is an important neurotransmitter in the central nervous system and the periphery. Most 5-HT (~99%) is found in the periphery where it regulates the function of the gastrointestinal (GI) tract and is an important regulator of platelet aggregation. However, the remaining 1% that is found in the central nervous system (CNS) can regulate a range of physiological processes such as learning and memory formation, mood, food intake, sleep, temperature and pain perception. More recent work on the CNS of invertebrate model systems has shown that 5-HT can directly regulate lifespan.This chapter will focus on detailing how CNS 5-HT signalling is altered with increasing age and the potential consequences this has on its ability to regulate lifespan.

Elucidation of the nematicidal mode of action of grammicin on Caenorhabditis elegans

Grammicin (Gra) is derived from the endophytic fungus Xylaria grammica EL000614 and shows nematicidal activity against the devastating root-knot nematode Meloidogyne incognita in-vitro, in planta, and in-field experiments. However, the mechanism of the nematicidal action of Gra remains unclear. In this study, Gra exposure to the model genetic organism Caenorhabditis elegans affected its L1, L2/3, L4, and young adult stages. In addition, Gra treatment increased the intracellular reactive oxygen species (ROS) levels of C. elegans and M. incognita. Molecular docking interaction analysis indicated that Gra could bind and interact with GCS-1, GST-4, and DAF-16a in order of low binding energy, followed by SOD-3, SKN-1, and DAF-16b. This implies that the anthelmintic action of Gra is related to the oxidative stress response. To validate this mechanism, we examined the expression of the genes involved in the oxidative stress responses following treatment with Gra using transgenic C. elegans strains such as the TJ356 strain zIs356 [daf-16p::daf-16a/b::GFP + rol-6 (su1006)], LD1 ldIs7 [skn-1p::skn-1b/c::GFP + rol-6 (su1006)], LD1171 ldIs3 [gcs-1p::GFP + rol-6 (su1006)], CL2166 dvIs19 [(pAF15) gst-4p::GFP::NLS], and CF1553 strain muIs84 [(pAD76) sod-3p::GFP + rol-6 (su1006)]. Gra treatment caused nuclear translocation of DAF-16/FoxO and enhanced gst-4::GFP expression, but it had no change in sod-3::GFP expression. These results indicate that Gra induces oxidative stress response via phase II detoxification without reduced cellular redox machinery. Gra treatment also inhibited the nuclear localization of SKN-1::GFP in the intestine, which may lead to a condition in which oxidative stress tolerance is insufficient to protect C. elegans by the inactivation of SKN-1, thus inducing nematode lethality. Furthermore, Gra caused the mortality of two mutant strains of C. elegans, CB113 and DA1316, which are resistant to aldicarb and ivermectin, respectively. This indicates that the mode of action of Gra is different from the traditional nematicides currently in use, suggesting that it could help develop novel approaches to control plant-parasitic nematodes.

Modulation of sensory perception by hydrogen peroxide enables Caenorhabditis elegans to find a niche that provides both food and protection from hydrogen peroxide

Hydrogen peroxide (H2O2) is the most common chemical threat that organisms face. Here, we show that H2O2 alters the bacterial food preference of Caenorhabditis elegans, enabling the nematodes to find a safe environment with food. H2O2 induces the nematodes to leave food patches of laboratory and microbiome bacteria when those bacterial communities have insufficient H2O2-degrading capacity. The nematode's behavior is directed by H2O2-sensing neurons that promote escape from H2O2 and by bacteria-sensing neurons that promote attraction to bacteria. However, the input for H2O2-sensing neurons is removed by bacterial H2O2-degrading enzymes and the bacteria-sensing neurons' perception of bacteria is prevented by H2O2. The resulting cross-attenuation provides a general mechanism that ensures the nematode's behavior is faithful to the lethal threat of hydrogen peroxide, increasing the nematode's chances of finding a niche that provides both food and protection from hydrogen peroxide.

Depression and Antidepressants During Pregnancy: Craniofacial Defects Due to Stem/Progenitor Cell Deregulation Mediated by Serotonin

Depression is a common and debilitating mood disorder that increases in prevalence during pregnancy. Worldwide, 7 to 12% of pregnant women experience depression, in which the associated risk factors include socio-demographic, psychological, and socioeconomic variables. Maternal depression could have psychological, anatomical, and physiological consequences in the newborn. Depression has been related to a downregulation in serotonin levels in the brain. Accordingly, the most commonly prescribed pharmacotherapy is based on selective serotonin reuptake inhibitors (SSRIs), which increase local serotonin concentration. Even though the use of SSRIs has few adverse effects compared with other antidepressants, altering serotonin levels has been associated with the advent of anatomical and physiological changes in utero, leading to defects in craniofacial development, including craniosynostosis, cleft palate, and dental defects. Migration and proliferation of neural crest cells, which contribute to the formation of bone, cartilage, palate, teeth, and salivary glands in the craniofacial region, are regulated by serotonin. Specifically, craniofacial progenitor cells are affected by serotonin levels, producing a misbalance between their proliferation and differentiation. Thus, it is possible to hypothesize that craniofacial development will be affected by the changes in serotonin levels, happening during maternal depression or after the use of SSRIs, which cross the placental barrier, increasing the risk of craniofacial defects. In this review, we provide a synthesis of the current research on depression and the use of SSRI during pregnancy, and how this could be related to craniofacial defects using an interdisciplinary perspective integrating psychological, clinical, and developmental biology perspectives. We discuss the mechanisms by which serotonin could influence craniofacial development and stem/progenitor cells, proposing some transcription factors as mediators of serotonin signaling, and craniofacial stem/progenitor cell biology. We finally highlight the importance of non-pharmacological therapies for depression on fertile and pregnant women, and provide an individual analysis of the risk-benefit balance for the use of antidepressants during pregnancy.

Elucidating the Possible Role of FoxO in Depression

Forkhead box-O (FoxO) transcriptional factors perform essential functions in several physiological and biological processes. Recent studies have shown that FoxO is implicated in the pathophysiology of depression. Changes in the upstream mediators of FoxOs including brain-derived neurotrophic factor (BDNF) and protein kinase B have been associated with depressive disorder and the antidepressant agents are known to alter the phosphorylation of FoxOs. Moreover, FoxOs might be regulated by serotonin or noradrenaline signaling and the hypothalamic-pituitary-adrenal (HPA)-axis,both of them are associated with the development of the depressive disorder. FoxO also regulates neural morphology, synaptogenesis, and neurogenesis in the hippocampus, which accounts for the pathogenesis of the depressive disorder. The current article underlined the potential functions of FoxOs in the etiology of depressive disorder and formulate few essential proposals for further investigation. The review also proposes that FoxO and its signal pathway might establish possible therapeutic mediators for the management of depressive disorder.

Detection of Pathogens and Regulation of Immunity by the Caenorhabditis elegans Nervous System

Although Caenorhabditis elegans has been used as a model host for studying host-pathogen interactions for more than 20 years, the mechanisms by which it identifies pathogens are not well understood. This is largely due to its lack of most known pattern recognition receptors (PRRs) that recognize pathogen-derived molecules. Recent behavioral research in C. elegans indicates that its nervous system plays a major role in microbe sensing. With the increasing integration of neurobiology in immunological research, future studies may find that neuronal detection of pathogens is an integral part of C. elegans-pathogen interactions. Similar to that of mammals, the C. elegans nervous system regulates its immune system to maintain immunological homeostasis. Studies in the nematode have revealed unprecedented details regarding the molecules, cells, and signaling pathways involved in neural regulation of immunity. Notably, some of the studies indicate that some neuroimmune regulatory circuits need not be "activated" by pathogen infection because they are tonically active and that there could be a predetermined set point for internal immunity, around which the nervous system adjusts immune responses to internal or external environmental changes. Here, we review recent progress on the roles of the C. elegans nervous system in pathogen detection and immune regulation. Because of its advantageous characteristics, we expect that the C. elegans model will be critical for deciphering complex neuroimmune signaling mechanisms that integrate and process multiple sensory cues.

Induction of Protective Response Associated with Expressional Alterations in Neuronal G Protein-Coupled Receptors in Polystyrene Nanoparticle Exposed Caenorhabditis elegans

In this study, the association of expressional alterations in neuronal G protein-coupled receptors (GPCRs) with induction of protective response to polystyrene nanoparticles (PS-NPs) was investigated in Caenorhabditis elegans. On the basis of both phenotypic analysis and expression levels, the alterations in expressions of NPR-1, NPR-4, NPR-8, NPR-9, NPR-12, DCAR-1, GTR-1, DOP-2, SER-4, and DAF-37 in neuronal cells mediated the protective response to PS-NPs exposure. In neuronal cells, NPR-9, NPR-12, DCAR-1, and GTR-1 controlled the PS-NPs toxicity by activating or inhibiting JNK-1/JNK MAPK signaling. Neuronal NPR-8, NPR-9, DCAR-1, DOP-2, and DAF-37 controlled the PS-NPs toxicity by activating or inhibiting MPK-1/ERK MAPK signaling. Neuronal NPR-4, NPR-8, NPR-9, NPR-12, GTR-1, DOP-2, and DAF-37 controlled the PS-NPs toxicity by activating or inhibiting DBL-1/TGF-β signaling. Neuronal NPR-1, NPR-4, NPR-12, and GTR-1 controlled the PS-NPs toxicity by activating or inhibiting DAF-7/TGF-β signaling. Our data provides an important neuronal basis for induction of protective response to PS-NPs in C. elegans.

FoxO3a suppresses neuropeptide W expression in neuronal cells and in rat hypothalamus and its implication in hypothalamic-pituitary-adrenal (HPA) axis

FoxO3a, a forkhead family member of transcription factors, is involved in the regulation of cell metabolism, proliferation, differentiation and apoptosis. However, whether FoxO3a participates in the regulation of glucocorticoids induced-hypothalamic-pituitary-adrenal (HPA) dysfunction is still unknown. Our present results indicate that dexamethasone(DEX) increased FoxO3a expression in PC12 and hypothalamic neuronal cultures in correlation to reduced expression of NPW, a process that could be blocked by GR2 antagonist. DEX restrained the phosphorylation of Akt and FoxO3a, but not ERK1/2 phosphorylation, resulting with FoxO3a nuclear localization. Overexpression of FoxO3a inhibited NPW expression, while FoxO3a knockdown by siRNA had the opposite effect. The regulatory region of NPW promoter contains multiple FoxO3a binding sites, and FoxO3a bonding to these sites inhibited its transcriptional activity. In a rat model, chronic administration of corticosterone reduced animals' body weight and sucrose consumption and caused stress- depression like behavior. Corticosterone treatment induced a marked increase in FoxO3a levels, while decreased the expression of NPW protein in the hypothalamus. Immunofluorescent double labeling demonstrated that FoxO3a and NPW were collocated in the hypothalamus. Taken together, these data indicate that NPW is a new direct downstream target gene of FoxO3a. FoxO3a suppressed the transcription of NPW and modulated glucocorticoids-induced HPA dysfunction by directly regulating the expression of NPW. Thus, present findings suggest that FoxO3a and NPW may be potential therapeutic targets for endocrine and psychiatric disorders.

A neurotransmitter produced by gut bacteria modulates host sensory behaviour

Animals coexist in commensal, pathogenic or mutualistic relationships with complex communities of diverse organisms, including microorganisms1. Some bacteria produce bioactive neurotransmitters that have previously been proposed to modulate nervous system activity and behaviours of their hosts2,3. However, the mechanistic basis of this microbiota-brain signalling and its physiological relevance are largely unknown. Here we show that in Caenorhabditis elegans, the neuromodulator tyramine produced by commensal Providencia bacteria, which colonize the gut, bypasses the requirement for host tyramine biosynthesis and manipulates a host sensory decision. Bacterially produced tyramine is probably converted to octopamine by the host tyramine β-hydroxylase enzyme. Octopamine, in turn, targets the OCTR-1 octopamine receptor on ASH nociceptive neurons to modulate an aversive olfactory response. We identify the genes that are required for tyramine biosynthesis in Providencia, and show that these genes are necessary for the modulation of host behaviour. We further find that C. elegans colonized by Providencia preferentially select these bacteria in food choice assays, and that this selection bias requires bacterially produced tyramine and host octopamine signalling. Our results demonstrate that a neurotransmitter produced by gut bacteria mimics the functions of the cognate host molecule to override host control of a sensory decision, and thereby promotes fitness of both the host and the microorganism.

DAF-16 and SMK-1 Contribute to Innate Immunity During Adulthood in Caenorhabditis elegans

Aging is accompanied by a progressive decline in immune function termed "immunosenescence". Deficient surveillance coupled with the impaired function of immune cells compromises host defense in older animals. The dynamic activity of regulatory modules that control immunity appears to underlie age-dependent modifications to the immune system. In the roundworm Caenorhabditis elegans levels of PMK-1 p38 MAP kinase diminish over time, reducing the expression of immune effectors that clear bacterial pathogens. Along with the PMK-1 pathway, innate immunity in C. elegans is regulated by the insulin signaling pathway. Here we asked whether DAF-16, a Forkhead box (FOXO) transcription factor whose activity is inhibited by insulin signaling, plays a role in host defense later in life. While in younger C. elegans DAF-16 is inactive unless stimulated by environmental insults, we found that even in the absence of acute stress the transcriptional activity of DAF-16 increases in an age-dependent manner. Beginning in the reproductive phase of adulthood, DAF-16 upregulates a subset of its transcriptional targets, including genes required to kill ingested microbes. Accordingly, DAF-16 has little to no role in larval immunity, but functions specifically during adulthood to confer resistance to bacterial pathogens. We found that DAF-16-mediated immunity in adults requires SMK-1, a regulatory subunit of the PP4 protein phosphatase complex. Our data suggest that as the function of one branch of the innate immune system of C. elegans (PMK-1) declines over time, DAF-16-mediated immunity ramps up to become the predominant means of protecting adults from infection, thus reconfiguring immunity later in life.

Global Transcriptome Changes That Accompany Alterations in Serotonin Levels in Caenorhabditis elegans

Serotonin (5-hydroxytryptamine, 5-HT), is a phylogenetically ancient molecule best characterized as a neurotransmitter that modulates multiple aspects of mood and social cognition. The roles that 5-HT plays in normal and abnormal behavior are not fully understood but have been posited to be due to its common function as a 'defense signal'. However, 5-HT levels also systemically impact cell physiology, modulating cell division, migration, apoptosis, mitochondrial biogenesis, cellular metabolism and differentiation. Whether these diverse cellular effects of 5-HT also share a common basis is unclear. C. elegans provides an ideal system to interrogate the systemic effects of 5-HT, since lacking a blood-brain barrier, 5-HT synthesized and released by neurons permeates the organism to modulate neuronal as well as non-neuronal cells throughout the body. Here we used RNA-Seq to characterize the systemic changes in gene expression that occur in C. elegans upon altering 5-HT levels, and compared the transcriptomes to published datasets. We find that an acute increase in 5-HT is accompanied by a global decrease in gene expression levels, upregulation of genes involved in stress pathways, changes that significantly correlate with the published transcriptomes of animals that have activated defense and immune responses, and an increase in levels of phosphorylated eukaryotic initiation factor, eIF2α. In 5-HT deficient animals lacking tryptophan hydroxylase (tph-1(mg280)II) there is a net increase in gene expression, with an overrepresentation of genes related to development and chromatin. Surprisingly, the transcriptomes of animals with acute increases in 5-HT levels, and 5-HT deficiency do not overlap with transcriptomes of mutants with whom they share striking physiological resemblance. These studies are the first to catalog systemic transcriptome changes that occur upon alterations in 5-HT levels. They further show that in C. elegans changes in gene expression upon altering 5-HT levels, and changes in physiology, are not directly correlated.

Peripheral cathepsin L inhibition induces fat loss in C. elegans and mice through promoting central serotonin synthesis

BACKGROUND

Cathepsin L and some other cathepsins have been implicated in the development of obesity in humans and mice. The functional inactivation of the proteases reduces fat accumulation during mammalian adipocyte differentiation. However, beyond degrading extracellular matrix protein fibronectin, the molecular mechanisms by which cathepsins control fat accumulation remain unclear. We now provide evidence from Caenorhabditis elegans and mouse models to suggest a conserved regulatory circuit in which peripheral cathepsin L inhibition lowers fat accumulation through promoting central serotonin synthesis.

RESULTS

We established a C. elegans model of fat accumulation using dietary supplementation with glucose and palmitic acid. We found that nutrient supplementation elevated fat storage in C. elegans, and along with worm fat accumulation, an increase in the expression of cpl-1 was detected using real-time PCR and western blot. The functional inactivation of cpl-1 reduced fat storage in C. elegans through activating serotonin signaling. Further, knockdown of cpl-1 in the intestine and hypodermis promoted serotonin synthesis in worm ADF neurons and induced body fat loss in C. elegans via central serotonin signaling. We found a similar regulatory circuit in high-fat diet-fed mice. Cathepsin L knockout promoted fat loss and central serotonin synthesis. Intraperitoneal injection of the cathepsin L inhibitor CLIK195 similarly reduced body weight gain and white adipose tissue (WAT) adipogenesis, while elevating brain serotonin level and WAT lipolysis and fatty acid β-oxidation. These effects of inhibiting cathepsin L were abolished by intracranial injection of p-chlorophenylalanine, inhibitor of a rate-limiting enzyme for serotonin synthesis.

CONCLUSION

This study reveals a previously undescribed molecular mechanism by which peripheral CPL-1/cathepsin L inhibition induces fat loss in C. elegans and mice through promoting central serotonin signaling.

Investigation of the underling mechanism of ketamine for antidepressant effects in treatment-refractory affective disorders via molecular profile analysis

Ketamine elicits a rapid antidepressant effect in treatment-refractory affective disorders. The aim of the present study was to elucidate the underlying mechanism of this effect and to identify potential targets of ketamine for antidepressant effects. GSE73798 and GSE73799 datasets were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were identified in hippocampus or striatum samples treated with ketamine, phencyclidyne or memantine compared with a saline or normal group at 1, 2, 4 and 8 h. The overlapping DEGs were the DEGs in both hippocampus and striatum samples. Kyoto Encyclopedia of Genes and Genomes and BioCyc databases were used to perform functional annotation and pathway analyses. Protein-protein interactions (PPIs) were predicted using Search Tool for the Retrieval of Interacting Genes/Proteins version 9.1 for the DEGs in the striatum samples treated with ketamine, phencyclidine or memantine compared with normal samples. Reverse transcription-quantitative polymerase chain reaction was performed to determine mRNA levels. Perilipin 4 (Plin4), serum/glucocorticoid regulated kinase 1 (Sgk1), kruppel like factor 2 (Klf2) and DDB1 and CUL4 associated factor 12 like 1 (Dcaf12l1) were the overlapping DEGs in the striatum samples treated with the three drugs at different time points. The mRNA expression levels of Plin4, Sgk1 and Klf2 were significantly higher (P<0.05), and the mRNA expression level of Dcaf12l1 was significantly lower in the striatum samples of the ketamine-treated group compared with the control group in an in vivo experiment. Both Sgk1 and Klf2 were enriched in the ‘forkhead box O (FoxO) signaling pathway’, and Sgk1 was additionally enriched in the ‘mechanistic target of rapamycin kinase (mTOR) signaling pathway’. PPI networks of DEGs in the striatum samples treated with ketamine, phencyclidine and memantine compared with normal samples were constructed, and Klf2 was involved in more pairs and was therefore a gene hub in the three networks. The four genes, Plin4, Sgk1, Klf2 and Dcaf12l1, were differentially expressed in all of the groups that treated with the three drugs and their expression levels were verified in in vivo experiments. The FoxO and mTOR signaling pathways may be involved in the underlying mechanism of the antidepressant effects of ketamine, and Plin4, Sgk1, Klf2 and Dcaf12l1 may be potential biomarkers for depression in N-methyl-D-aspartic acid receptor antagonist treatment.

Role of Forkhead Box O Transcription Factors in Oxidative Stress-Induced Chondrocyte Dysfunction: Possible Therapeutic Target for Osteoarthritis?

Chondrocyte dysfunction occurs during the development of osteoarthritis (OA), typically resulting from a deleterious increase in oxidative stress. Accordingly, strategies for arresting oxidative stress-induced chondrocyte dysfunction may lead to new potential therapeutic targets for OA treatment. Forkhead box O (FoxO) transcription factors have recently been shown to play a protective role in chondrocyte dysfunction through the regulation of inflammation, autophagy, aging, and oxidative stress. They also regulate growth, maturation, and matrix synthesis in chondrocytes. In this review, we discuss the recent progress made in the field of oxidative stress-induced chondrocyte dysfunction. We also discuss the protective role of FoxO transcription factors as potential molecular targets for the treatment of OA. Understanding the function of FoxO transcription factors in the OA pathology may provide new insights that will facilitate the development of next-generation therapies to prevent OA development and to slow OA progression.

Role of Forkhead Box O Transcription Factors in Oxidative Stress-Induced Chondrocyte Dysfunction: Possible Therapeutic Target for Osteoarthritis?

Chondrocyte dysfunction occurs during the development of osteoarthritis (OA), typically resulting from a deleterious increase in oxidative stress. Accordingly, strategies for arresting oxidative stress-induced chondrocyte dysfunction may lead to new potential therapeutic targets for OA treatment. Forkhead box O (FoxO) transcription factors have recently been shown to play a protective role in chondrocyte dysfunction through the regulation of inflammation, autophagy, aging, and oxidative stress. They also regulate growth, maturation, and matrix synthesis in chondrocytes. In this review, we discuss the recent progress made in the field of oxidative stress-induced chondrocyte dysfunction. We also discuss the protective role of FoxO transcription factors as potential molecular targets for the treatment of OA. Understanding the function of FoxO transcription factors in the OA pathology may provide new insights that will facilitate the development of next-generation therapies to prevent OA development and to slow OA progression.

Past experience shapes sexually dimorphic neuronal wiring through monoaminergic signalling

Differences between female and male brains exist across the animal kingdom and extend from molecular to anatomical features. Here we show that sexually dimorphic anatomy, gene expression and function in the nervous system can be modulated by past experiences. In the nematode Caenorhabditis elegans, sexual differentiation entails the sex-specific pruning of synaptic connections between neurons that are shared by both sexes, giving rise to sexually dimorphic circuits in adult animals1. We discovered that starvation during juvenile stages is memorized in males to suppress the emergence of sexually dimorphic synaptic connectivity. These circuit changes result in increased chemosensory responsiveness in adult males following juvenile starvation. We find that an octopamine-mediated starvation signal dampens the production of serotonin (5-HT) to convey the memory of starvation. Serotonin production is monitored by a 5-HT1A serotonin receptor homologue that acts cell-autonomously to promote the pruning of sexually dimorphic synaptic connectivity under well-fed conditions. Our studies demonstrate how life history shapes neurotransmitter production, synaptic connectivity and behavioural output in a sexually dimorphic circuit.

An Elongin-Cullin-SOCS Box Complex Regulates Stress-Induced Serotonergic Neuromodulation

Neuromodulatory cells transduce environmental information into long-lasting behavioral responses. However, the mechanisms governing how neuronal cells influence behavioral plasticity are difficult to characterize. Here, we adapted the translating ribosome affinity purification (TRAP) approach in C. elegans to profile ribosome-associated mRNAs from three major tissues and the neuromodulatory dopaminergic and serotonergic cells. We identified elc-2, an Elongin C ortholog, specifically expressed in stress-sensing amphid neuron dual ciliated sensory ending (ADF) serotonergic sensory neurons, and we found that it plays a role in mediating a long-lasting change in serotonin-dependent feeding behavior induced by heat stress. We demonstrate that ELC-2 and the von Hippel-Lindau protein VHL-1, components of an Elongin-Cullin-SOCS box (ECS) E3 ubiquitin ligase, modulate this behavior after experiencing stress. Also, heat stress induces a transient redistribution of ELC-2, becoming more nuclearly enriched. Together, our results demonstrate dynamic regulation of an E3 ligase and a role for an ECS complex in neuromodulation and control of lasting behavioral states.

A Proteomic Analysis Provides Novel Insights into the Stress Responses of Caenorhabditis elegans towards Nematicidal Cry6A Toxin from Bacillus thuringiensis

Cry6A represents a novel family of nematicidal crystal proteins from Bacillus thuringiensis. It has distinctive architecture as well as mechanism of action from Cry5B, a highly focused family of nematicidal crystal proteins, and even from other insecticidal crystal proteins containing the conserved three-domain. However, how nematode defends against Cry6A toxin remains obscure. In this study, the global defense pattern of Caenorhabditis elegans against Cry6Aa2 toxin was investigated by proteomic analysis. In response to Cry6Aa2, 12 proteins with significantly altered abundances were observed from worms, participating in innate immune defense, insulin-like receptor (ILR) signaling pathway, energy metabolism, and muscle assembly. The differentially expressed proteins (DEPs) functioning in diverse biological processes suggest that a variety of defense responses participate in the stress responses of C. elegans to Cry6Aa2. The functional verifications of DEPs suggest that ILR signaling pathway, DIM-1, galectin LEC-6 all are the factors of defense responses to Cry6Aa2. Moreover, Cry6Aa2 also involves in accelerating the metabolic energy production which fulfills the energy demand for the immune responses. In brief, our findings illustrate the global pattern of defense responses of nematode against Cry6A for the first time, and provide a novel insight into the mechanism through which worms respond to Cry6A.

Progressive metabolic impairment underlies the novel nematicidal action of fluensulfone on the potato cyst nematode Globodera pallida

BACKGROUND

Fluensulfone is a new nematicide with an excellent profile of selective toxicity against plant parasitic nematodes. Here, its effects on the physiology and biochemistry of the potato cyst nematode Globodera pallida have been investigated and comparisons made with its effect on the life-span of the free-living nematode Caenorhabditis elegans to provide insight into its mode of action and its selective toxicity.

RESULTS

Fluensulfone exerts acute effects (≤1h; ≥100μM) on stylet thrusting and motility of hatched second stage G. pallida juveniles (J2s). Chronic exposure to lower concentrations of fluensulfone (≥3days; ≤30μM), reveals a slowly developing metabolic insult in which G. pallida J2s sequentially exhibit a reduction in motility, loss of a metabolic marker for cell viability, high lipid content and tissue degeneration prior to death. These effects are absent in adults and dauers of the model genetic nematode Caenorhabditis elegans.

CONCLUSION

The nematicidal action of fluensulfone follows a time-course which progresses from an early impact on motility through to an accumulating metabolic impairment, an inability to access lipid stores and death.

Antagonistic Serotonergic and Octopaminergic Neural Circuits Mediate Food-Dependent Locomotory Behavior in Caenorhabditis elegans

Biogenic amines are conserved signaling molecules that link food cues to behavior and metabolism in a wide variety of organisms. In the nematode Caenorhabditis elegans, the biogenic amines serotonin (5-HT) and octopamine regulate a number of food-related behaviors. Using a novel method for long-term quantitative behavioral imaging, we show that 5-HT and octopamine jointly influence locomotor activity and quiescence in feeding and fasting hermaphrodites, and we define the neural circuits through which this modulation occurs. We show that 5-HT produced by the ADF neurons acts via the SER-5 receptor in muscles and neurons to suppress quiescent behavior and promote roaming in fasting worms, whereas 5-HT produced by the NSM neurons acts on the MOD-1 receptor in AIY neurons to promote low-amplitude locomotor behavior characteristic of well fed animals. Octopamine, produced by the RIC neurons, acts via SER-3 and SER-6 receptors in SIA neurons to promote roaming behaviors characteristic of fasting animals. We find that 5-HT signaling is required for animals to assume food-appropriate behavior, whereas octopamine signaling is required for animals to assume fasting-appropriate behavior. The requirement for both neurotransmitters in both the feeding and fasting states enables increased behavioral adaptability. Our results define the molecular and neural pathways through which parallel biogenic amine signaling tunes behavior appropriately to nutrient conditions.SIGNIFICANCE STATEMENT Animals adjust behavior in response to environmental changes, such as fluctuations in food abundance, to maximize survival and reproduction. Biogenic amines, such as like serotonin, are conserved neurotransmitters that regulate behavior and metabolism in relation to energy status. Disruptions of biogenic amine signaling contribute to human neurological diseases of mood, appetite, and movement. In this study, we investigated the roles of the biogenic amines serotonin and octopamine in regulating locomotion behaviors associated with feeding and fasting in the roundworm Caenorhabditis elegans We identified neural circuits through which these signals work to govern behavior. Understanding the molecular pathways through which biogenic amines function in model organisms may improve our understanding of dysfunctions of appetite and behavior found in mammals, including humans.

Heat-Induced Calcium Leakage Causes Mitochondrial Damage in Caenorhabditis elegans Body-Wall Muscles

Acute onset of organ failure in heatstroke is triggered by rhabdomyolysis of skeletal muscle. Here, we showed that elevated temperature increases free cytosolic Ca²⁺ [Ca²⁺]f from RYR (ryanodine receptor)/UNC-68in vivo in the muscles of an experimental model animal, the nematode Caenorhabditis elegans. This subsequently leads to mitochondrial fragmentation and dysfunction, and breakdown of myofilaments similar to rhabdomyolysis. In addition, treatment with an inhibitor of RYR (dantrolene) or activation of FoxO (Forkhead box O)/DAF-16 is effective against heat-induced muscle damage. Acute onset of organ failure in heatstroke is triggered by rhabdomyolysis of skeletal muscle. To gain insight into heat-induced muscle breakdown, we investigated alterations of Ca²⁺ homeostasis and mitochondrial morphology in vivo in body-wall muscles of C. elegans exposed to elevated temperature. Heat stress for 3 hr at 35° increased the concentration of [Ca²⁺]f, and led to mitochondrial fragmentation and subsequent dysfunction in the muscle cells. A similar mitochondrial fragmentation phenotype is induced in the absence of heat stress by treatment with a calcium ionophore, ionomycin. Mutation of the unc-68 gene, which encodes the ryanodine receptor that is linked to Ca²⁺ release from the sarcoplasmic reticulum, could suppress the mitochondrial dysfunction, muscle degeneration, and reduced mobility and life span induced by heat stress. In addition, in a daf-2 mutant, in which the DAF-16/FoxO transcription factor is activated, resistance to calcium overload, mitochondrial fragmentation, and dysfunction was observed. These findings reveal that heat-induced Ca²⁺ accumulation causes mitochondrial damage and consequently induces muscle breakdown.

Food responsiveness regulates episodic behavioral states in Caenorhabditis elegans

Animals optimize survival and reproduction in part through control of behavioral states, which depend on an organism's internal and external environments. In the nematode Caenorhabditis elegans a variety of behavioral states have been described, including roaming, dwelling, quiescence, and episodic swimming. These states have been considered in isolation under varied experimental conditions, making it difficult to establish a unified picture of how they are regulated. Using long-term imaging, we examined C. elegans episodic behavioral states under varied mechanical and nutritional environments. We found that animals alternate between high-activity (active) and low-activity (sedentary) episodes in any mechanical environment, while the incidence of episodes and their behavioral composition depend on food levels. During active episodes, worms primarily roam, as characterized by continuous whole body movement. During sedentary episodes, animals exhibit dwelling (slower movements confined to the anterior half of the body) and quiescence (a complete lack of movement). Roaming, dwelling, and quiescent states are manifest not only through locomotory characteristics but also in pharyngeal pumping (feeding) and in egg-laying behaviors. Next, we analyzed the genetic basis of behavioral states. We found that modulation of behavioral states depends on neuropeptides and insulin-like signaling in the nervous system. Sensory neurons and the Foraging homolog EGL-4 regulate behavior through control of active/sedentary episodes. Optogenetic stimulation of dopaminergic and serotonergic neurons induced dwelling, implicating dopamine as a dwell-promoting neurotransmitter. Our findings provide a more unified description of behavioral states and suggest that perception of nutrition is a conserved mechanism for regulating animal behavior.NEW & NOTEWORTHY One strategy by which animals adapt to their internal states and external environments is by adopting behavioral states. The roundworm Caenorhabditis elegans is an attractive model for investigating how behavioral states are genetically and neuronally controlled. Here we describe the hierarchical organization of behavioral states characterized by locomotory activity, feeding, and egg-laying. We show that decisions to engage in these behaviors are controlled by the nervous system through insulin-like signaling and the perception of food.

Depressing Antidepressant: Fluoxetine Affects Serotonin Neurons Causing Adverse Reproductive Responses in Daphnia magna

Selective serotonin reuptake inhibitors (SSRIs) are widely used antidepressants. As endocrine disruptive contaminants in the environment, SSRIs affect reproduction in aquatic organisms. In the water flea Daphnia magna, SSRIs increase offspring production in a food ration-dependent manner. At limiting food conditions, females exposed to SSRIs produce more but smaller offspring, which is a maladaptive life-history strategy. We asked whether increased serotonin levels in newly identified serotonin-neurons in the Daphnia brain mediate these effects. We provide strong evidence that exogenous SSRI fluoxetine selectively increases serotonin-immunoreactivity in identified brain neurons under limiting food conditions thereby leading to maladaptive offspring production. Fluoxetine increases serotonin-immunoreactivity at low food conditions to similar maximal levels as observed under high food conditions and concomitantly enhances offspring production. Sublethal amounts of the neurotoxin 5,7-dihydroxytryptamine known to specifically ablate serotonin-neurons markedly decrease serotonin-immunoreactivity and offspring production, strongly supporting the effect to be serotonin-specific by reversing the reproductive phenotype attained under fluoxetine. Thus, SSRIs impair serotonin-regulation of reproductive investment in a planktonic key organism causing inappropriately increased reproduction with potentially severe ecological impact.

NPR-9 regulates the innate immune response in Caenorhabditis elegans by antagonizing the activity of AIB interneurons

npr-9 encodes a homologue of the gastrin-releasing peptide receptor (GRPR) and is expressed in AIB interneurons. In this study, we investigated the role of NPR-9 in the neuronal control of innate immunity using the model system Caenorhabditis elegans. After exposure to Pseudomonas aeruginosa PA14, npr-9(tm1652) mutants showed resistance to infection, decreased PA14 colonization and increased expression of immunity-related genes. Nematodes overexpressing NPR-9 exhibited increased susceptibility to infection, increased PA14 colonization and reduced expression of immunity-related genes. In nematodes, ChR2-mediated AIB interneuron activation strengthened the innate immune response and decreased PA14 colonization. Overexpression of NPR-9 suppressed the innate immune response and increased PA14 colonization in nematodes with the activation of AIB interneurons mediated by ChR2 or by expressing pkc-1(gf) in AIB interneurons. We, therefore, hypothesize that NPR-9 regulates the innate immune response by antagonizing the activity of AIB interneurons. Furthermore, expression of GRPR, the human homologue of NPR-9, could largely mimic NPR-9 function by regulating innate immunity in nematodes. Our results provide insight into the pivotal role of interneurons in controlling innate immunity and the complex biological functions of GRPRs.

Axotomy-induced HIF-serotonin signalling axis promotes axon regeneration in C. elegans

The molecular mechanisms underlying the ability of axons to regenerate after injury remain poorly understood. Here we show that in Caenorhabditis elegans, axotomy induces ectopic expression of serotonin (5-HT) in axotomized non-serotonergic neurons via HIF-1, a hypoxia-inducible transcription factor, and that 5-HT subsequently promotes axon regeneration by autocrine signalling through the SER-7 5-HT receptor. Furthermore, we identify the rhgf-1 and rga-5 genes, encoding homologues of RhoGEF and RhoGAP, respectively, as regulators of axon regeneration. We demonstrate that one pathway initiated by SER-7 acts upstream of the C. elegans RhoA homolog RHO-1 in neuron regeneration, which functions via G12α and RHGF-1. In this pathway, RHO-1 inhibits diacylglycerol kinase, resulting in an increase in diacylglycerol. SER-7 also promotes axon regeneration by activating the cyclic AMP (cAMP) signalling pathway. Thus, HIF-1-mediated activation of 5-HT signalling promotes axon regeneration by activating both the RhoA and cAMP pathways.

Functional Selectivity and Antidepressant Activity of Serotonin 1A Receptor Ligands

Serotonin (5-HT) is a monoamine neurotransmitter that plays an important role in physiological functions. 5-HT has been implicated in sleep, feeding, sexual behavior, temperature regulation, pain, and cognition as well as in pathological states including disorders connected to mood, anxiety, psychosis and pain. 5-HT1A receptors have for a long time been considered as an interesting target for the action of antidepressant drugs. It was postulated that postsynaptic 5-HT1A agonists could form a new class of antidepressant drugs, and mixed 5-HT1A receptor ligands/serotonin transporter (SERT) inhibitors seem to possess an interesting pharmacological profile. It should, however, be noted that 5-HT1A receptors can activate several different biochemical pathways and signal through both G protein-dependent and G protein-independent pathways. The variables that affect the multiplicity of 5-HT1A receptor signaling pathways would thus result from the summation of effects specific to the host cell milieu. Moreover, receptor trafficking appears different at pre- and postsynaptic sites. It should also be noted that the 5-HT1A receptor cooperates with other signal transduction systems (like the 5-HT1B or 5-HT2A/2B/2C receptors, the GABAergic and the glutaminergic systems), which also contribute to its antidepressant and/or anxiolytic activity. Thus identifying brain specific molecular targets for 5-HT1A receptor ligands may result in a better targeting, raising a hope for more effective medicines for various pathologies.

A gene-expression-based neural code for food abundance that modulates lifespan

How the nervous system internally represents environmental food availability is poorly understood. Here, we show that quantitative information about food abundance is encoded by combinatorial neuron-specific gene-expression of conserved TGFβ and serotonin pathway components in Caenorhabditis elegans. Crosstalk and auto-regulation between these pathways alters the shape, dynamic range, and population variance of the gene-expression responses of daf-7 (TGFβ) and tph-1 (tryptophan hydroxylase) to food availability. These intricate regulatory features provide distinct mechanisms for TGFβ and serotonin signaling to tune the accuracy of this multi-neuron code: daf-7 primarily regulates gene-expression variability, while tph-1 primarily regulates the dynamic range of gene-expression responses. This code is functional because daf-7 and tph-1 mutations bidirectionally attenuate food level-dependent changes in lifespan. Our results reveal a neural code for food abundance and demonstrate that gene expression serves as an additional layer of information processing in the nervous system to control long-term physiology.

DOI:http://dx.doi.org/10.7554/eLife.06259.001

To maximize their chances of survival, animals need to be able to sense changes in the abundance of food in their environment and respond in an appropriate manner. The nervous system is able to sense cues from the environment and coordinate responses in the whole organism, but it is not clear how this leads to long-term changes in the organism's biology.

In nematode worms, two genes called daf-7 and tph-1 appear to be involved in connecting the sensing of food availability with changes in the biology of the organism. The daf-7 gene encodes a hormone, while tph-1 encodes an enzyme that makes a neurochemical called serotonin.

Here, Entchev, Patel, Zhan et al. found that daf-7 and tph-1 genes are active in three pairs of neurons in nematode worms. The experiments show that these neurons collectively form a circuit that carries information about the abundance of food, which leads to changes in how long the worms live. When this circuit was disrupted by removing these genes, the worms' ability to adjust their lifespan in response to changes in the availability of food was weakened, likely because they were unable to sense food. The experiments also show that the circuit regulates itself, largely because daf-7 and tph-1 are able to control each-other's activity.

Together, these results suggest that changing the activity of certain genes in neurons enables nematode worms to alter their biology in response to changes in the availability of food. Neurons in the brain use electrical activity to communicate and process information and Entchev, Patel, Zhan et al.'s findings imply that gene activity can also perform a similar role.

DOI:http://dx.doi.org/10.7554/eLife.06259.002

Kynurenic acid is a nutritional cue that enables behavioral plasticity

The kynurenine pathway of tryptophan metabolism is involved in the pathogenesis of several brain diseases, but its physiological functions remain unclear. We report that kynurenic acid, a metabolite in this pathway, functions as a regulator of food-dependent behavioral plasticity in C. elegans. The experience of fasting in C. elegans alters a variety of behaviors, including feeding rate, when food is encountered post-fast. Levels of neurally produced kynurenic acid are depleted by fasting, leading to activation of NMDA-receptor-expressing interneurons and initiation of a neuropeptide-y-like signaling axis that promotes elevated feeding through enhanced serotonin release when animals re-encounter food. Upon refeeding, kynurenic acid levels are eventually replenished, ending the elevated feeding period. Because tryptophan is an essential amino acid, these findings suggest that a physiological role of kynurenic acid is in directly linking metabolism to activity of NMDA and serotonergic circuits, which regulate a broad range of behaviors and physiologies.

Loss of a neural AMP-activated kinase mimics the effects of elevated serotonin on fat, movement, and hormonal secretions

AMP-activated protein kinase (AMPK) is an evolutionarily conserved master regulator of metabolism and a therapeutic target in type 2 diabetes. As an energy sensor, AMPK activity is responsive to both metabolic inputs, for instance the ratio of AMP to ATP, and numerous hormonal cues. As in mammals, each of two genes, aak-1 and aak-2, encode for the catalytic subunit of AMPK in C. elegans. Here we show that in C. elegans loss of aak-2 mimics the effects of elevated serotonin signaling on fat reduction, slowed movement, and promoting exit from dauer arrest. Reconstitution of aak-2 in only the nervous system restored wild type fat levels and movement rate to aak-2 mutants and reconstitution in only the ASI neurons was sufficient to significantly restore dauer maintenance to the mutant animals. As in elevated serotonin signaling, inactivation of AAK-2 in the ASI neurons caused enhanced secretion of dense core vesicles from these neurons. The ASI neurons are the site of production of the DAF-7 TGF-β ligand and the DAF-28 insulin, both of which are secreted by dense core vesicles and play critical roles in whether animals stay in dauer or undergo reproductive development. These findings show that elevated levels of serotonin promote enhanced secretions of systemic regulators of pro-growth and differentiation pathways through inactivation of AAK-2. As such, AMPK is not only a recipient of hormonal signals but can also be an upstream regulator. Our data suggest that some of the physiological phenotypes previously attributed to peripheral AAK-2 activity on metabolic targets may instead be due to the role of this kinase in neural serotonin signaling.

Serotonin control of thermotaxis memory behavior in nematode Caenorhabditis elegans

Caenorhabditis elegans is as an ideal model system for the study of mechanisms underlying learning and memory. In the present study, we employed C. elegans assay system of thermotaxis memory to investigate the possible role of serotonin neurotransmitter in memory control. Our data showed that both mutations of tph-1, bas-1, and cat-4 genes, required for serotonin synthesis, and mutations of mod-5 gene, encoding a serotonin reuptake transporter, resulted in deficits in thermotaxis memory behavior. Exogenous treatment with serotonin effectively recovered the deficits in thermotaxis memory of tph-1 and bas-1 mutants to the level of wild-type N2. Neuron-specific activity assay of TPH-1 suggests that serotonin might regulate the thermotaxis memory behavior by release from the ADF sensory neurons. Ablation of ADF sensory neurons by expressing a cell-death activator gene egl-1 decreased the thermotaxis memory, whereas activation of ADF neurons by expression of a constitutively active protein kinase C homologue (pkc-1(gf)) increased the thermotaxis memory and rescued the deficits in thermotaxis memory in tph-1 mutants. Moreover, serotonin released from the ADF sensory neurons might act through the G-protein-coupled serotonin receptors of SER-4 and SER-7 to regulate the thermotaxis memory behavior. Genetic analysis implies that serotonin might further target the insulin signaling pathway to regulate the thermotaxis memory behavior. Thus, our results suggest the possible crucial role of serotonin and ADF sensory neurons in thermotaxis memory control in C. elegans.

The role of Akt/FoxO3a in the protective effect of venlafaxine against corticosterone-induced cell death in PC12 cells

RATIONALE

Antidepressants could exert neuroprotective effects against various insults and the antidepressant-like effect may result from its neuroprotective effects. The phosphatidylinositol-3-kinase/protein kinase B/Forkhead box O3 (PI3K/Akt/FoxO3a) pathway is a key signaling pathway in mediating cell survival. However, no information is available regarding the interaction of FoxO3a and antidepressants.

OBJECTIVES

PC12 cells treated with corticosterone were used as a model to study the protective effect of venlafaxine and underlying mechanisms.

METHODS

Methyl thiazolyl tetrazolium (MTT) assay, Hoechst staining, and the observation of FoxO3a subcellular location were used to study the protective effect of venlafaxine against cell damage caused by corticosterone. Pretreatments with various pathway inhibitors were used to investigate the possible pathways involved in the protection of venlafaxine. The phosphorylation of Akt and FoxO3a was analyzed by Western blot.

RESULTS

Corticosterone decreased the phosphorylation of Akt and FoxO3a and led to the nuclear localization of FoxO3a and the apoptosis of PC12 cells. Venlafaxine concentration-dependently protected PC12 cells against corticosterone. The protective effect of venlafaxine was reversed by LY294002 and wortmannin, two PI3K inhibitors, and Akt inhibitor VIII, whereas mitogen-activated protein kinase kinase (MAPK kinase) inhibitor PD98059 and the p38 MAPK inhibitor PD160316 had no effect. Western blot analyses showed that venlafaxine induced the phosphorylation of Akt and FoxO3a by the PI3K/Akt pathway and reversed the reduction of the phosphorylated Akt and FoxO3a, and the nuclear translocation of Foxo3a induced by corticosterone.

CONCLUSIONS

Venlafaxine protects PC12 cells against corticosterone-induced cell death by modulating the activity of the PI3K/Akt/FoxO3a pathway.

Neuropeptidergic regulation of reproduction in insects

Successful animal reproduction depends on multiple physiological and behavioral processes that take place in a timely and orderly manner in both mating partners. It is not only necessary that all relevant processes are well coordinated, they also need to be adjusted to external factors of abiotic and biotic nature (e.g. population density, mating partner availability). Therefore, it is not surprising that several hormonal factors play a crucial role in the regulation of animal reproductive physiology. In insects (the largest class of animals on planet Earth), lipophilic hormones, such as ecdysteroids and juvenile hormones, as well as several neuropeptides take part in this complex regulation. While some peptides can affect reproduction via an indirect action (e.g. by influencing secretion of juvenile hormone), others exert their regulatory activity by directly targeting the reproductive system. In addition to insect peptides with proven activities, several others were suggested to also play a role in the regulation of reproductive physiology. Because of the long evolutionary history of many insect orders, it is not always clear to what extent functional data obtained in a given species can be extrapolated to other insect taxa. In this paper, we will review the current knowledge concerning the neuropeptidergic regulation of insect reproduction and situate it in a more general physiological context.

Functional analysis of neuronal microRNAs in Caenorhabditis elegans dauer formation by combinational genetics and Neuronal miRISC immunoprecipitation

Identifying the physiological functions of microRNAs (miRNAs) is often challenging because miRNAs commonly impact gene expression under specific physiological conditions through complex miRNA::mRNA interaction networks and in coordination with other means of gene regulation, such as transcriptional regulation and protein degradation. Such complexity creates difficulties in dissecting miRNA functions through traditional genetic methods using individual miRNA mutations. To investigate the physiological functions of miRNAs in neurons, we combined a genetic “enhancer” approach complemented by biochemical analysis of neuronal miRNA-induced silencing complexes (miRISCs) in C. elegans. Total miRNA function can be compromised by mutating one of the two GW182 proteins (AIN-1), an important component of miRISC. We found that combining an ain-1 mutation with a mutation in unc-3, a neuronal transcription factor, resulted in an inappropriate entrance into the stress-induced, alternative larval stage known as dauer, indicating a role of miRNAs in preventing aberrant dauer formation. Analysis of this genetic interaction suggests that neuronal miRNAs perform such a role partly by regulating endogenous cyclic guanosine monophosphate (cGMP) signaling, potentially influencing two other dauer-regulating pathways. Through tissue-specific immunoprecipitations of miRISC, we identified miRNAs and their likely target mRNAs within neuronal tissue. We verified the biological relevance of several of these miRNAs and found that many miRNAs likely regulate dauer formation through multiple dauer-related targets. Further analysis of target mRNAs suggests potential miRNA involvement in various neuronal processes, but the importance of these miRNA::mRNA interactions remains unclear. Finally, we found that neuronal genes may be more highly regulated by miRNAs than intestinal genes. Overall, our study identifies miRNAs and their targets, and a physiological function of these miRNAs in neurons. It also suggests that compromising other aspects of gene expression, along with miRISC, can be an effective approach to reveal miRNA functions in specific tissues under specific physiological conditions.

MicroRNAs (miRNAs) are important in the regulation of gene expression and are present in many organisms. To identify specific biological processes that are regulated by miRNAs, we disturbed total miRNA function under a certain genetic background and searched for defects. Interestingly, we found a prominent developmental defect that was dependent on a mutation in another gene involved in regulating transcription in neurons. Thus, by compromising two different aspects of gene regulation, we were able to identify a specific biological function of miRNAs. By investigating this defect, we determined that neuronal miRNAs likely function to help modulate cyclic guanosine monophosphate signaling. We then took a systematic approach and identified many miRNAs and genes that are likely to be regulated by neuronal miRNAs, and in doing so, we found genes involved in the initial defect. Additionally, we found many other genes, and show that genes expressed in neurons seem to be more regulated by miRNAs than genes in the intestine. Through our study, we identify a biological function of neuronal miRNAs and provide data that will help in identifying other important, novel, and exciting roles of this important class of small RNAs.

Serotonin promotes the proliferation of serum-deprived hepatocellular carcinoma cells via upregulation of FOXO3a

Background

Peripheral serotonin is involved in tumorigenesis and induces a pro-proliferative effect in hepatocellular carcinoma (HCC) cells; however, the intracellular mechanisms by which serotonin exerts a mitogenic effect remain unclear. In this research, we examined whether FOXO3a, a transcription factor at the interface of crucial cellular processes, plays a role downstream of serotonin in HCC cells.

Results

The cell viability and expression of FOXO3a was assessed in three HCC cell lines (Huh7, HepG2 and Hep3B) during serum deprivation in the presence or absence of serotonin. Serum free media significantly inhibited HCC proliferation and led to reduced expression and nuclear accumulation of FOXO3a. Knockdown of FOXO3a enhanced the ability of serum deprivation to inhibit HCC cells proliferation. And overexpression of non-phosphorylated FOXO3a in HCC cells reversed serum-deprivation-induced growth inhibition. Serotonin reversed the serum-deprivation-induced inhibition of cell proliferation and upregulated FOXO3a in Huh7 cells; however, serotonin had no effect on the proliferation of serum-deprived HepG2 or Hep3B cells. In addition to proliferation, serotonin also induced phosphorylation of AKT and FOXO3a in serum-deprived Huh7 cells but not in HepG2 and Hep3B cells. However, the phosphorylation of FOXO3a induced by serotonin did not export FOXO3a from nucleus to cytoplasm in serum-deprived Huh7 cells. Consequently, we demonstrated that serotonin promoted the proliferation of Huh7 cells by increasing the expression of FOXO3a. We also provide preliminary evidence that different expression levels of the 5-HT2B receptor (5-HT_2BR) may contribute to the distinct effects of serotonin in different serum-deprived HCC cells.

Conclusions

This study demonstrates that FOXO3a functions as a growth factor in serum-deprived HCC cells and serotonin promotes the proliferation of serum-deprived HCC cells via upregulation of FOXO3a, in the presence of sufficient levels of the serotonin receptor 5-HT_2BR. Drugs targeting the serotonin-5-HT_2BR-FOXO3a pathway may provide a novel target for anticancer therapy.

Recognition of familiar food activates feeding via an endocrine serotonin signal in Caenorhabditis elegans

Familiarity discrimination has a significant impact on the pattern of food intake across species. However, the mechanism by which the recognition memory controls feeding is unclear. Here, we show that the nematode Caenorhabditis elegans forms a memory of particular foods after experience and displays behavioral plasticity, increasing the feeding response when they subsequently recognize the familiar food. We found that recognition of familiar food activates the pair of ADF chemosensory neurons, which subsequently increase serotonin release. The released serotonin activates the feeding response mainly by acting humorally and directly activates SER-7, a type 7 serotonin receptor, in MC motor neurons in the feeding organ. Our data suggest that worms sense the taste and/or smell of novel bacteria, which overrides the stimulatory effect of familiar bacteria on feeding by suppressing the activity of ADF or its upstream neurons. Our study provides insight into the mechanism by which familiarity discrimination alters behavior.DOI:http://dx.doi.org/10.7554/eLife.00329.001.

FOXO1 orchestrates the bone-suppressing function of gut-derived serotonin

Serotonin is a critical regulator of bone mass, fulfilling different functions depending on its site of synthesis. Brain-derived serotonin promotes osteoblast proliferation, whereas duodenal-derived serotonin suppresses it. To understand the molecular mechanisms of duodenal-derived serotonin action on osteoblasts, we explored its transcriptional mediation in mice. We found that the transcription factor FOXO1 is a crucial determinant of the effects of duodenum-derived serotonin on bone formation We identified two key FOXO1 complexes in osteoblasts, one with the transcription factor cAMP-responsive element-binding protein 1 (CREB) and another with activating transcription factor 4 (ATF4). Under normal levels of circulating serotonin, the proliferative activity of FOXO1 was promoted by a balance between its interaction with CREB and ATF4. However, high circulating serotonin levels prevented the association of FOXO1 with CREB, resulting in suppressed osteoblast proliferation. These observations identify FOXO1 as the molecular node of an intricate transcriptional machinery that confers the signal of duodenal-derived serotonin to inhibit bone formation.