Modulation of the assay system for the sensory integration of 2 sensory stimuli that inhibit each other in nematode Caenorhabditis elegans

Microcystin-LR induces neuronal damage through mitophagy defects resulted from the downregulated transcription of Scd2 by directly targeting IGF-1R

Microcystin-LR (MC-LR), a prevalent cyanotoxin present in hazardous cyanobacterial blooms, is recognized as a neurotoxic environmental pollutant that induces brain damage and neurobehavioral deficits. However, the mechanisms underlying MC-LR-induced neurotoxicity remain unclear. This study aims to elucidate the role of mitophagy in MC-LR-induced neurotoxicity both in vitro and in vivo. We found that administration of 10 μg/kg body weight (intraperitoneally) MC-LR impaired learning and memory abilities and induced neuronal damage and apoptosis in the CA1 region of the hippocampus in rats. Exposure to MC-LR (1 μM-10 μM) resulted in cellular damage and apoptosis in PC-12 and HT22 cells. MC-LR induced mitophagy through the PINK1/Parkin pathway but hindered mitophagy progression by repressing Scd2 transcription in neurons. These inhibitory effects were reversed by Scd2 overexpression. Furthermore, MC-LR was found to repress Scd2 transcription by directly binding to type 1 insulin-like growth factor receptor (IGF-1R) and competitively inhibiting its activation by Insulin-like growth factor 1 (IGF-1). Overexpression of IGF-1R and administration of exogenous IGF-1 mitigated the MC-LR-induced inhibition of Scd2 and the associated mitophagy defects. These findings indicate that IGF-1R is the direct target of MC-LR in neurons. MC-LR initiates mitophagy defects and apoptosis by inhibiting Scd2 transcription through binding to IGF-1R.

Zinc homeostasis may reverse the synergistic neurotoxicity of heavy metal mixtures in Caenorhabditis elegans

Heavy metal mixtures can cause nerve damage. However, the combined effects of metal mixtures are extremely complex and rarely studied. Zinc (Zn) homeostasis plays an integral role in neural function, but the role of Zn homeostasis in the toxicity of metal mixtures is not well understood. Here, we investigated the combined effects of manganese (Mn), lead (Pb) and arsenic (As) on nerves and the effect of Zn homeostasis on metal toxicity. Caenorhabditis elegans (Maupas, 1900) were exposed to single and multiple metals for 8 days, their movement, behavior, neurons and metal concentration were detected to evaluate the combined effect of metal mixtures. After nematodes were co-treated with metal mixtures and Zn, the nerve function, Zn concentration and redox balance were detected to evaluate the effect of Zn homeostasis on metal toxicity. The results showed that Mn + Pb and Pb + As mixtures induced synergistic toxicity for nematode nerves, which damaged movement, behavior and neurons, and decreased Zn concentration. While Zn supplementation recovered Zn homeostasis and promoted redox balance on nematodes, and then improved the nerve function. Our study demonstrated the combined effects of metal mixtures and the neuroprotective effect of Zn homeostasis. Therefore, assessment of metal mixtures toxicity should consider their interaction and the impacts of essential metals homeostasis.

A neuropeptide signal confers ethanol state dependency during olfactory learning in Caenorhabditis elegans

Alcohol intoxication can impact learning and this may contribute to the development of problematic alcohol use. In alcohol (ethanol)-induced state-dependent learning (SDL), information learned while an animal is intoxicated is recalled more effectively when the subject is tested while similarly intoxicated than if tested while not intoxicated. When Caenorhabditis elegans undergoes olfactory learning (OL) while intoxicated, the learning becomes state dependent such that recall of OL is only apparent if the animals are tested while intoxicated. We found that two genes known to be required for signal integration, the secreted peptide HEN-1 and its receptor tyrosine kinase, SCD-2, are required for SDL. Expression of hen-1 in the ASER neuron and scd-2 in the AIA neurons was sufficient for their functions in SDL. Optogenetic activation of ASER in the absence of ethanol during learning could confer ethanol state dependency, indicating that ASER activation is sufficient to signal ethanol intoxication to the OL circuit. To our surprise, ASER activation during testing did not substitute for ethanol intoxication, demonstrating that the effects of ethanol on learning and recall rely on distinct signals. Additionally, intoxication-state information could be added to already established OL, but state-dependent OL did not lose state information when the intoxication signal was removed. Finally, dopamine is required for state-dependent OL, and we found that the activation of ASER cannot bypass this requirement. Our findings provide a window into the modulation of learning by ethanol and suggest that ethanol acts to modify learning using mechanisms distinct from those used during memory access.

Optimizing and Evaluating the Antihelminthic Activity of the Biocompatible Zinc Oxide Nanoparticles Against the Ascaridid Nematode, Parascaris equorum In Vitro

PURPOSE

In the present study, the effect of different biocompatible concentrations from ZnO nanoparticles (ZnO NPs) on the physiological state and surface topography of the nematode P. equorum was determined in vitro.

METHODS

Different concentrations of ZnO NPs (100, 200, 300 and 400 mg/l) synthesized using the egg white were prepared followed by the incubation of parasitic worms with these concentrations in vitro. The physiological state of treated worms such as oxidative stress markers, enzymatic activities and biochemical parameters in addition to the surface topography was determined and compared with control untreated worms.

RESULTS

In comparison to control worms, it was observed that at high concentrations of ZnO NPs, most of the treated worms showed an increase in the levels of ALT, AST and ALP (worm muscle damage, and gonad injury); enhancement of the total protein content (worm cellular dysfunction); significant increase in MDA level (free radical-mediated worm cell membrane damage); depletion in GST and GSH activities (reduced ability to clear toxic compounds like lipid peroxides); CAT depletion (superoxide dismutase and hydrogen peroxide toxicity) and NO increase (detoxification activity and stressful conditions on worms). SEM showed that there was a modified morphological appearance in the surface of treated worms; lips were wrinkled with irregularly arranged denticles, weathering of cuticle, bursts of cuticle layers, disruption of surface annulations and erosion of surface papillae of male around the cloacal opening.

CONCLUSION

ZnO NPs at environmentally relevant concentrations achieved a significant antihelminthic activity against P. equorum which represents a successful model used in parasite control experiments.

A Receptor Tyrosine Kinase Plays Separate Roles in Sensory Integration and Associative Learning in C. elegans

Associative learning and sensory integration are two behavioral processes that involve the sensation and processing of stimuli followed by an altered behavioral response to these stimuli, with learning requiring memory formation and retrieval. We found that the cellular and molecular actions of scd-2 dissociate sensory integration and associative learning. This was discovered through investigation of a Caenorhabditis elegans mutation (lrn-2 (mm99)) affecting both processes. After mapping and sequencing, lrn-2 was found to be allelic to the gene, scd-2. scd-2-mediated associative learning and sensory integration operate in separate neurons as separate processes. We also find that memories can form from associations that are processed and stored independently from the integration of stimuli preceding an immediate behavioral decision.

Dysregulation of Neuronal Gαo Signaling by Graphene Oxide in Nematode Caenorhabditis elegans

Exposure to graphene oxide (GO) induced some dysregulated microRNAs (miRNAs), such as the increase in mir-247, in nematode Caenorhabditis elegans. We here further identified goa-1 encoding a Gαo and pkc-1 encoding a serine/threonine protein kinase as the targets of neuronal mir-247 in the regulation of GO toxicity. GO exposure increased the expressions of both GOA-1 and PKC-1. Mutation of goa-1 or pkc-1 induced a susceptibility to GO toxicity, and suppressed the resistance of mir-247 mutant to GO toxicity. GOA-1 and PKC-1 could also act in the neurons to regulate the GO toxicity, and neuronal overexpression of mir-247 could not affect the resistance of nematodes overexpressing neuronal goa-1 or pkc-1 lacking 3'-UTR to GO toxicity. In the neurons, GOA-1 acted upstream of diacylglycerol kinase/DGK-1 and PKC-1 to regulate the GO toxicity. Moreover, DGK-1 and GOA-1 functioned synergistically in the regulation of GO toxicity. Our results highlight the crucial role of neuronal Gαo signaling in response to GO in nematodes.

Metallothioneins act downstream of insulin signaling to regulate toxicity of outdoor fine particulate matter (PM2.5) during Spring Festival in Beijing in nematode Caenorhabditis elegans

In this study, we performed the toxicological assessment of outdoor PM2.5 collected from Beijing during Spring Festival using the in vivo assay system of Caenorhabditis elegans. Acute exposure to outdoor PM2.5 at a concentration of 10 mg L-1 and prolonged exposure to outdoor PM2.5 at concentrations of 0.1-10 mg L-1 decreased locomotion behavior and caused significant induction of intestinal ROS production. Meanwhile, outdoor PM2.5 exposure induced significant expression of gene (mtl-1 and mtl-2) encoded metallothioneins in the intestine. Mutation of the mtl-1 or mtl-2 gene resulted in a susceptible property of nematodes to outdoor PM2.5 toxicity. Genetic assays suggested that mtl-1 and mtl-2 genes acted downstream of the daf-16 gene encoding a FOXO transcriptional factor and daf-2 gene encoding an insulin receptor in the insulin signaling pathway to regulate outdoor PM2.5 toxicity. DAF-2 further acted upstream of DAF-16 and suppressed the function of DAF-16 to regulate outdoor PM2.5 toxicity. Therefore, we identified a signaling cascade of DAF-2-DAF-16-MTL-1/2 in the control of outdoor PM2.5 toxicity in nematodes. Our study provides an important molecular basis for the potential toxicity of outdoor PM2.5 during Spring Festival in Beijing in nematodes. Especially, our study will highlight the potential adverse effects of outdoor PM2.5 during Spring Festival on environmental organisms.

Biological effects, translocation, and metabolism of quantum dots in the nematode Caenorhabditis elegans

Quantum dots (QDs), semiconductor nanomaterials with tiny light-emitting particles, act as important alternatives to conventional fluorescent dyes for biomedical imaging. With the increased tendency towards QD applications, concerns about the likelihood of adverse health impacts from exposure to QDs have also received attention. The nematode Caenorhabditis elegans is an important non-mammalian alternative model for the toxicological study of environmental toxicants including engineered nanomaterials. In this review, we summarize recent progress on the biological effects, translocation, and metabolism of QDs in the in vivo assay system of C. elegans. Moreover, certain perspectives or suggestions are further raised for the future toxicological study of QDs in nematodes.

FLP-4 neuropeptide and its receptor in a neuronal circuit regulate preference choice through functions of ASH-2 trithorax complex in Caenorhabditis elegans

Preference choice on food is an important response strategy for animals living in the environment. Using assay system of preference choice on bacterial foods, OP50 and PA14, we identified the involvement of ADL sensory neurons in the control of preference choice in Caenorhabditis elegans. Both genetically silencing and ChR2-mediated activation of ADL sensory neurons significantly affected preference choice. ADL regulated preference choice by inhibiting function of G protein-coupled receptor (GPCR)/SRH-220. ADL sensory neurons might regulate preference choice through peptidergic signals of FLP-4 and NLP-10, and function of FLP-4 or NLP-10 in regulating preference choice was regulated by SRH-220. FLP-4 released from ADL sensory neurons further regulated preference choice through its receptor of NPR-4 in AIB interneurons. In AIB interneurons, NPR-4 was involved in the control of preference choice by activating the functions of ASH-2 trithorax complex consisting of SET-2, ASH-2, and WDR-5, implying the crucial role of molecular machinery of trimethylation of histone H3K4 in the preference choice control. The identified novel neuronal circuit and the underlying molecular mechanisms will strengthen our understanding neuronal basis of preference choice in animals.

Dopamine receptors antagonistically regulate behavioral choice between conflicting alternatives in C. elegans

Caenorhabditis elegans is a useful model to study the neuronal or molecular basis for behavioral choice, a specific form of decision-making. Although it has been implied that both D1-like and D2-like dopamine receptors may contribute to the control of decision-making in mammals, the genetic interactions between D1-like and D2-like dopamine receptors in regulating decision-making are still largely unclear. In the present study, we investigated the molecular control of behavioral choice between conflicting alternatives (diacetyl and Cu2+) by D1-like and D2-like dopamine receptors and their possible genetic interactions with C. elegans as the assay system. In the behavioral choice assay system, mutation of dop-1 gene encoding D1-like dopamine receptor resulted in the enhanced tendency to cross the Cu2+ barrier compared with wild-type. In contrast, mutations of dop-2 or dop-3 gene encoding D2-like dopamine receptor caused the weak tendency to cross the Cu2+ barrier compared with wild-type. During the control of behavioral choice, DOP-3 antagonistically regulated the function of DOP-1. The behavioral choice phenotype of dop-2; dop-1dop-3 triple mutant further confirmed the possible antagonistic function of D2-like dopamine receptor on D1-like dopamine receptor in regulating behavioral choice. The genetic assays further demonstrate that DOP-3 might act through Gαo signaling pathway encoded by GOA-1 and EGL-10, and DOP-1 might act through Gαq signaling pathway encoded by EGL-30 and EAT-16 to regulate the behavioral choice. DOP-1 might function in cholinergic neurons to regulate the behavioral choice, whereas DOP-3 might function in GABAergic neurons, RIC, and SIA neurons to regulate the behavioral choice. In this study, we provide the genetic evidence to indicate the antagonistic relationship between D1-like dopamine receptor and D2-like dopamine receptor in regulating the decision-making of animals. Our data will be useful for understanding the complex functions of dopamine receptors in regulating decision-making in animals.

Transgenerational effects of traffic-related fine particulate matter (PM₂.₅) on nematode Caenorhabditis elegans

Numerous studies have demonstrated the toxic effects of fine particle matter less than 2.5 μm (PM2.5) on health of human. However, little information is available on PM2.5 ecotoxicity. We employed Caenorhabditis elegans to investigate the adverse effects of traffic-related PM2.5 on exposed animals and their progeny. Acute exposure to high concentrations of PM2.5 in the range of mg/L caused adverse effects on development, lifespan, reproduction, and locomotion behavior of nematodes. In contrast, prolonged exposure to low concentrations of PM2.5 in the range of μg/L resulted in adverse effects on development, lifespan, reproduction, locomotion behavior, and intestinal development of nematodes. Prolonged exposure to PM2.5 could even cause adverse effects on lifespan, reproduction, locomotion behavior, and intestinal development in progeny of exposed nematodes. PM2.5 toxicity was only partially recovered in progeny of exposed nematodes. For the PM2.5 toxicity on nematodes and their progeny, we hypothesize that it might be the combinational effects of oxidative stress, damage on intestinal barrier, and abnormal defecation behavior. Our data here imply the potential toxic effects of long-term exposure to traffic-related PM2.5 on environmental organisms. Our results further highlight the possible crucial roles of biological barrier and defecation behavior in regulating the PM2.5 toxicity.

Changes to cuticle surface ultrastructure and some biological functions in the nematode Caenorhabditis elegans exposed to excessive copper

Copper is an essential metal, but its toxic effects are pronounced when organisms are exposed to it in excessive amounts. However, information about the effects of chronic copper exposure on the cuticle ultrastructure of organisms is insufficient. Studies of the model organism, Caenorhabditis elegans, could further our understanding of the effect of chronic excessive copper exposure on human health. In this study, the cuticle surface ultrastructure of C. elegans was observed using scanning electron microscopy after excessive copper exposure. In addition to this, some biological functions, such as chemotaxis, reproduction, and development, were also analyzed. After chronic excessive copper exposure, the worms' body surface from vulva to tail was extensively wrinkled and folded along with the annulus. The worm's vulva size was significantly decreased, and the middle ridge of the alae was disrupted. Furthermore, some of the biological functions of nematodes were also affected: the chemotaxis index was partially changed, bags-of-worms were induced, development was delayed, and egg-laying number was decreased by copper treatment. The results of the present study shed new light on the effects of copper on C. elegans cuticle as well as some biological functions.

Biosafety assessment of titanium dioxide nanoparticles in acutely exposed nematode Caenorhabditis elegans with mutations of genes required for oxidative stress or stress response

We used Caenorhabditis elegans to investigate whether acute exposure to TiO2-NPs at the concentration of 20 μg L(-1) reflecting predicted environmental relevant concentration and 25 mg L(-1) reflecting concentration in food can cause toxicity on nematodes with mutations of susceptible genes. Among examined mutants associated with oxidative stress and stress response, we found that genes of sod-2, sod-3, mtl-2, and hsp-16.48 might be susceptible for TiO2-NPs toxicity. Mutations of these genes altered functions of both possible primary and secondary targeted organs in nematodes exposed to 25 mg L(-1) of TiO2-NPs for 24-h. Mutations of these genes caused similar expression patterns of genes required for oxidative stress in TiO2-NPs exposed mutant nematodes, implying their similar mechanisms to form the susceptible property. Nevertheless, acute exposure to 20 μg L(-1) of TiO2-NPs for 24-h and 25 mg L(-1) of TiO2-NPs for 0.48-h or 5.71-h did not influence functions of both possible primary and secondary targeted organs in sod-2, sod-3, mtl-2, and hsp-16.48 mutants. Therefore, our results suggest the relatively safe property of acute exposure to TiO2-NPs with certain durations at predicted environmental relevant concentrations or concentrations comparable to those in food in nematodes with mutations of some susceptible genes.