Function of RSKS-1-AAK-2-DAF-16 signaling cascade in enhancing toxicity of multi-walled carbon nanotubes can be suppressed by mir-259 activation in Caenorhabditis elegans

Design, Synthesis, and Anti-Infective Effect Against Candida Albicans of a New Urolithin Derivative

Deep mucosal and organ infections caused by the infestation of Candida albicans in immunocompromised patients represent a significant cause of mortality in hospitalized patients. The rise in fungal resistance is a consequence of the overuse of antibiotics. Therefore, innovative immunostimulants must be developed to combat pathogenic fungal infections. We used urolithin A (UA), an intestinal metabolite rich in the naturally occurring polyphenolic antioxidants ellagic acid (EA) or ellagitannin (ET), as a lead compound for structural modification. Through liquid screening of 17 synthesized compounds, we discovered compound 1e effectively inhibited C. albicans biofilm formation, thereby reducing its virulence. Furthermore, it protects animals from severe infections by enhancing tolerance to infection by intestinal pathogens and reducing oxidative stress. Moreover, our findings indicate that compound 1e exerts its effects through the p38 mitogen-activated protein kinase (MAPK) innate immune pathway, which is evolutionarily conserved. These observations not only enhance our comprehension of immune mechanisms but also provide a crucial foundation for the development of immune activators with the potential to resist pathogenic bacterial infections.

Exposure to 6-PPD quinone enhances glycogen accumulation in Caenorhabditiselegans

Glycogen metabolism is an important biological process for organisms. In Caenorhabditis elegans, effect of 6-PPD quinone (6-PPDQ) on glycogen accumulation and underlying mechanism were examined. Exposure to 6-PPDQ (1 and 10 μg/L) increased glycogen accumulation. Meanwhile, exposure to 6-PPDQ (1 and 10 μg/L) increased expression of gsy-1 encoding glycogen synthase and decreased expression of pygl-1 encoding glycogen phosphorylase. In 6-PPDQ exposed animals, glycogen content and glycogen accumulation were inhibited by RNAi of gsy-1 and enhanced by RNAi of pygl-1. RNAi of gsy-1 increased pygl-1 expression, and RNAi of pygl-1 increased gsy-1 expression after 6-PPDQ exposure. In 6-PPDQ exposed nematodes, daf-16 and aak-2 expressions were decreased and glycogen accumulation was suppressed by RNAi of daf-16 and aak-2, suggesting alteration in daf-16 and aak-2 expressions did not mediate glycogen accumulation. Moreover, resistance to 6-PPDQ toxicity on locomotion and brood size was observed in gsy-1(RNAi) animals, and susceptibility to 6-PPDQ toxicity was found in pygl-1(RNAi) animals. Therefore, glycogen accumulation could be enhanced by exposure to 6-PPDQ in nematodes. In addition, alteration in expressions of gsy-1 and pygl-1 governing this enhancement in glycogen accumulation mediated induction of 6-PPDQ toxicity.

Insulin and IGF-1 extend the lifespan of Caenorhabditis elegans by inhibiting insulin/insulin-like signaling and mTOR signaling pathways: C. elegans - Focused cancer research

The mutations in Caenorhabditis elegans (C. elegans) that extend lifespan slow down aging by interfering with several signaling pathways, including the insulin/IGF-1 signaling (IIS) pathway, AMP-activated protein kinase (AMPK), and mechanistic target of rapamycin (mTOR). The tumor suppressor pRb (retinoblastoma protein) is believed to be involved in almost all human cancers. Lin-35, the C. elegans orthologue of the tumor suppressor pRb, was included in the study to explore the effects of insulin and IGF-1 because it has been linked to cancer-related pRb function in mammals and exhibits a tumor suppressor effect by inhibiting mTOR or IIS signaling. According to our results, IGF-1 or insulin increased the lifespan of lin-35 worms compared to N2 worms by increasing fertilization efficiency, also causing a significant increase in body size. It was concluded that the expression of daf-2 and rsks-1 decreased after insulin or IGF-1 administration, thus extending the lifespan of C. elegans lin-35 worms through both IIS and mTOR-dependent mechanisms. This suggests that it was mediated by the combined effect of the TOR and IIS pathways. These results, especially obtained in cancer-associated mutant lin-35 worms, will be useful in elucidating the C. elegans cancer model in the future.

Evaluating the adverse effects and mechanisms of nanomaterial exposure on longevity of C. elegans: A literature meta-analysis and bioinformatics analysis of multi-transcriptome data

Exposure to large-size particulate air pollution (PM2.5 or PM10) has been reported to increase risks of aging-related diseases and human death, indicating the potential pro-aging effects of airborne nanomaterials with ultra-fine particle size (which have been widely applied in various fields). However, this hypothesis remains inconclusive. Here, a meta-analysis of 99 published literatures collected from electronic databases (PubMed, EMBASE and Cochrane Library; from inception to June 2023) was performed to confirm the effects of nanomaterial exposure on aging-related indicators and molecular mechanisms in model animal C. elegans. The pooled analysis by Stata software showed that compared with the control, nanomaterial exposure significantly shortened the mean lifespan [standardized mean difference (SMD) = -2.30], reduced the survival rate (SMD = -4.57) and increased the death risk (hazard ratio = 1.36) accompanied by upregulation of ced-3, ced-4 and cep-1, while downregulation of ctl-2, ape-1, aak-2 and pmk-1. Furthermore, multi-transcriptome data associated with nanomaterial exposure were retrieved from Gene Expression Omnibus (GSE32521, GSE41486, GSE24847, GSE59470, GSE70509, GSE14932, GSE93187, GSE114881, and GSE122728) and bioinformatics analyses showed that pseudogene prg-2, mRNAs of abu, car-1, gipc-1, gsp-3, kat-1, pod-2, acdh-8, hsp-60 and egrh-2 were downregulated, while R04A9.7 was upregulated after exposure to at least two types of nanomaterials. Resveratrol (abu, hsp-60, pod-2, egrh-2, acdh-8, gsp-3, car-1, kat-1, gipc-1), naringenin (kat-1, egrh-2), coumestrol (egrh-2) or swainsonine/niacin/ferulic acid (R04A9.7) exerted therapeutic effects by reversing the expression levels of target genes. In conclusion, our study demonstrates the necessity to use phytomedicines that target hub genes to delay aging for populations with nanomaterial exposure.

Exposure to multi-walled carbon nanotubes causes suppression in octopamine signal associated with transgenerational toxicity induction in C.elegans

Multi-walled carbon nanotube (MWCNT), a kind of carbon-based nanomaterials, has been extensively utilized in a variety of fields. In Caenorhabditis elegans, MWCNT exposure can result in toxicity not only at parental generation (P0-G) but also in the offspring. However, the underlying mechanisms remain still largely unknown. DAF-12, a transcriptional factor (TF), was previously found to be activated and involved in transgenerational toxicity control after MWCNT exposure. In this study, we observed that exposure to 0.1-10 μg/L MWCNTs caused the significant decrease in expression of tbh-1 encoding a tyramine beta-hydroxylase with the function to govern the octopamine synthesis, suggesting the inhibition in octopamine signal. After exposure to 0.1 μg/L MWCNT, the decrease in tbh-1 expression could be also detected in F1-G and F2-G. Moreover, in germline cells, the TF DAF-12 regulated transgenerational MWCNT toxicity by suppressing expression and function of TBH-1. Meanwhile, exposure to 0.1-10 μg/L MWCNTs induced the increase in octr-1 expression and the decrease in ser-6 expression. After exposure to 0.1 μg/L MWCNT, the increased octr-1 expression and the decreased ser-6 expression were further observed in F1-G and F2-G. Germline TBH-1 controlled transgenerational MWCNT toxicity by regulating the activity of octopamine receptors (SER-6 and OCTR-1) in offspring. Furthermore, in the offspring, SER-6 and OCTR-1 affected the induction of MWCNT toxicity by upregulating or downregulating the level of ELT-2, a GATA TF. Taken together, these findings suggested possible link between alteration in octopamine related signals and MWCNT toxicity induction in offspring in organisms.

Ribavirin extends the lifespan of Caenorhabditis elegans through AMPK-TOR Signaling

Aging is a process accompanied by widespread degenerative changes which are a major cause of human disease and disability. One goal of aging research is to develop interventions or drugs that can extend organism lifespan and treat age-related diseases. Here, we report the identification of a broad spectrum anti-viral agent, ribavirin, as a potential pharmacological aging intervention. Ribavirin extended the lifespan and healthspan of Caenorhabditis elegans by inhibiting Target of Rapamycin (TOR) signaling and activating AMP-activated protein kinase (AMPK). Moreover, our data indicate that ribavirin activated AMPK by reducing the levels of adenosine triphosphate (ATP) and lysosomal v-ATPase-Ragulator-AXIN Complex. Thus, our studies successfully identify ribavirin as a potential anti-aging drug, and indicate that its anti-aging effect is mediated via AMPK-TOR signaling.

The critical role of epigenetic mechanisms involved in nanotoxicology

Over the past decades, nanomaterials (NMs) have been widely applied in the cosmetic, food, engineering, and medical fields. Along with the prevalence of NMs, the toxicological characteristics exhibited by these materials on health and the environment have gradually attracted attentions. A growing number of evidences have indicated that epigenetics holds an essential role in the onset and development of various diseases. NMs could cause epigenetic alterations such as DNA methylation, noncoding RNA (ncRNA) expression, and histone modifications. NMs might alternate either global DNA methylation or the methylation of specific genes to affect the biological function. Abnormal upregulation or downregulation of ncRNAs might also be a potential mechanism for the toxic effects caused by NMs. In parallel, the phosphorylation, acetylation, and methylation of histones also take an important part in the process of NMs-induced toxicity. As the adverse effects of NMs continue to be explored, mechanisms such as chromosomal remodeling, genomic imprinting, and m⁶ A modification are also gradually coming into the limelight. Since the epigenetic alterations often occur in the early development of diseases, thus the relevant studies not only provide insight into the pathogenesis of diseases, but also screen for the prospective biomarkers for early diagnosis and prevention. This review summarizes the epigenetic alterations elicited by NMs, hoping to provide a clue for nanotoxicity studies and security evaluation of NMs. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

Multi-walled carbon nanotubes induce transgenerational toxicity associated with activation of germline long non-coding RNA linc-7 in C.elegans

With the increase in application, multi-walled carbon nanotubes (MWCNTs) are potentially bioavailable to environmental organisms. However, the potential transgenerational effect of MWCNTs and underlying mechanisms remains still unclear. Here, we examined transgenerational MWCNT toxicity and the underlying mechanism mediated by germline long non-coding RNAs (lncRNAs) in Caenorhabditis elegans. Exposure to 0.1-10 μg/L MWCNT caused transgenerational toxicity reflected by endpoints of brood size and locomotion behavior. Meanwhile, among germline lncRNAs, expression of 5 lncRNAs were dysregulated by MWCNT exposure. Among these 5 dysregulated lncRNAs, only germline RNAi of linc-7 affected MWCNT toxicity. Increase in germline linc-7 expression was observed transgenerationally, and transgenerational MWCNT toxicity was prevented in linc-7(RNAi) nematodes. Moreover, germline linc-7 controlled transgenerational MWCNT toxicity by activating downstream DAF-12, a transcriptional factor. Therefore, our data indicated the association between induction of transgenerational MWCNT toxicity and increase in germline linc-7 expression in organisms.

Research Advances on the Adverse Effects of Nanomaterials in a Model Organism, Caenorhabditis elegans

Along with the rapid development of nanotechnology, the biosafety assessment of nanotechnology products, including nanomaterials (NMs), has become more and more important. The nematode Caenorhabditis elegans is a valuable model organism that has been widely used in the field of biology because of its excellent advantages, including low cost, small size, short life span, and highly conservative genomes with vertebral animals. In recent years, the number of nanotoxicological researchers using C. elegans has been growing. According to these available studies, the present review classified the adverse effects of NMs in C. elegans into systematic, cellular, and molecular toxicity, and focused on summarizing and analyzing the underlying mechanisms of metal, metal oxide, and nonmetallic NMs causing toxic effects in C. elegans. Our findings provide insights into what further studies are needed to assess the biosafety of NMs in the ecosystem using C. elegans. Environ Toxicol Chem 2021;40:2406-2424. © 2021 SETAC.

BRAF Controls the Effects of Metformin on Neuroblast Cell Divisions in C. elegans

Metformin has demonstrated substantial potential for use in cancer treatments. Liver kinase B (LKB)-AMP-activated protein kinase (AMPK) and mTOR are reported to be the main targets of metformin in relation to its ability to prevent cancer cell proliferation. However, the role of metformin in the control of neoplastic cancer cell growth is possibly independent of LKB-AMPK and mTOR. Using C. elegans as a model, we found that the neuronal Q-cell divisions in L1-arrested worms were suppressed following metformin treatment in AMPK-deficient mutants, suggesting that the mechanism by which metformin suppresses these cell divisions is independent of AMPK. Our results showed that the mTOR pathway indeed played a role in controlling germ cell proliferation, but it was not involved in the neuronal Q-cell divisions occurring in L1-arrested worms. We found that the neuronal Q-cells divisions were held at G1/S cell stage by metformin in vivo. Additionally, we demonstrated that metformin could reduce the phosphorylation activity of BRAF and block the BRAF-MAPK oncogenesis pathway to regulate neuronal Q-cell divisions during L1 arrest. This work discloses a new mechanism by which metformin treatment acts to promote neuronal cancer prevention, and these results will help promote the study of the anticancer mechanisms underlying metformin treatments.

The C. elegans miR-235 regulates the toxicity of graphene oxide via targeting the nuclear hormone receptor DAF-12 in the intestine

The increased application of graphene oxide (GO), a new carbon-based engineered nanomaterial, has generated a potential toxicity in humans and the environment. Previous studies have identified some dysregulated microRNAs (miRNAs), such as up-regulated mir-235, in organisms exposed to GO. However, the detailed mechanisms of the dysregulation of miRNA underlying GO toxicity are still largely elusive. In this study, we employed Caenorhabditis elegans as an in vivo model to investigate the biological function and molecular basis of mir-235 in the regulation of GO toxicity. After low concentration GO exposure, mir-235 (n4504) mutant nematodes were sensitive to GO toxicity, implying that mir-235 mediates a protection mechanism against GO toxicity. Tissue-specific assays suggested that mir-235 expressed in intestine is required for suppressing the GO toxicity in C. elegans. daf-12, a gene encoding a member of the steroid hormone receptor superfamily, acts as a target gene of mir-235 in the nematode intestine in response to GO treatment, and RNAi knockdown of daf-12 suppressed the sensitivity of mir-235(n4503) to GO toxicity. Further genetic analysis showed that DAF-12 acted in the upstream of DAF-16 in insulin/IGF-1 signaling pathway and PMK-1 in p38 MAPK signaling pathway in parallel to regulate GO toxicity. Altogether, our results revealed that mir-235 may activate a protective mechanism against GO toxicity by suppressing the DAF-12-DAF-16 and DAF-12-PMK-1 signaling cascade in nematodes, which provides an important molecular basis for the in vivo toxicity of GO at the miRNA level.

The NLRP3-Mediated Neuroinflammatory Responses to CdTe Quantum Dots and the Protection of ZnS Shell

Introduction

Since CdTe quantum dots (QDs) are still widely considered as advanced fluorescent probes because of their far superior optical performance and fluorescence efficiency over non-cadmium QDs, it is important to find ways to control their toxicity.

Methods

In this study, the adverse effects of two cadmium-containing QDs, ie, CdTe QDs and CdTe@ZnS QDs, on the nervous system of nematode C. elegans, the hippocampus of mice, and cultured microglia were measured in order to evaluate the neuroinflammation caused by cadmium-containing QDs and the potential mechanisms.

Results

Firstly, we observed that cadmium-containing QD exposure-induced immune responses and neurobehavioral deficit in nematode C. elegans. In the mice treated with QDs, neuroinflammatory responses to QDs in the hippocampus, including microglial activation and IL-1ß release, occurred as well. When investigating the mechanisms of cadmium-containing QDs causing IL-1ß-mediated inflammation, the findings suggested that cadmium-containing QDs activated the NLRP3 inflammasome by causing excessive ROS generation, and resulted in IL-1ß release.

Discussion

Even though the milder immune responses and neurotoxicity of CdTe@ZnS QDs compared with CdTe QDs indicated the protective role of ZnS coating, the inhibitions of NLRP3 expression and ROS production completely reduced the IL-1ß-mediated inflammation. This provided valuable information that inhibiting target molecules is an effective and efficient way to alleviate  the toxicity of cadmium-containing QDs, so it is important to evaluate QDs through a mechanism-based risk assessment.

Nitrate reductase-dependent nitric oxide is crucial for multi-walled carbon nanotube-induced plant tolerance against salinity

Although there have been some studies on the plant-carbonaceous nanomaterials (CNMs) interactions, related conclusions were controversial. Here, we report that multi-walled carbon nanotubes (MWCNTs) can enter into rapeseed (Brassica napus L.) seedling root, and transport to stem. Further results showed that salinity-inhibited rapeseed seedling growth was obviously alleviated by MWCNTs. Meanwhile, NaCl-induced nitrate reductase (NR)-dependent NO production was significantly intensified by MWCNTs. The redox and ion imbalance was reestablished as well, confirmed by the reduction in reactive oxygen species (ROS) overproduction, the decrease in thiobarbituric acid reactive substance production, and the lower Na+/K+ ratio. These beneficial effects could be explained by the changes in related antioxidant defense genes, sodium hydrogen exchanger 1 (NHX1), salt overly sensitive 1 (SOS1), and K+transporter 1 (KT1) transcripts. The above responses were separately abolished after the removal of endogenous NO with its scavengers or the addition of the NR inhibitor. Genetic evidence revealed that the NaCl-triggered NO level in wild-type seedling roots was partly abolished in either the nitric reductase mutant (nia1/2) or noa1 mutant (exhibiting indirectly a reduced endogenous NO level). Treatment with MWCNTs could totally rescue the impaired NO production in the noa1 mutant rather than the nia1/2 mutant, suggesting that NR-dependent NO acts as a downstream signaling molecule in MWCNT signaling. This point was verified by phenotypic analyses, histochemical staining, and ion analysis. qPCR analysis further demonstrated that MWCNTs stimulated antioxidant genes and ion balance-related genes through NR-mediated NO. The above molecular and genetic evidence indicated that NR-dependent NO acts downstream of MWCNTs in salinity tolerance, which requires the reestablishment of redox and ion homeostasis.

Caenorhabditis elegans as a complete model organism for biosafety assessments of nanoparticles

The number of biosafety evaluation studies of nanoparticles (NPs) using different biological models is increasing with the rapid development of nanotechnology. Thus far, nematode Caenorhabditis elegans (C. elegans), as a complete model organism, has become an important in vivo alternative assay system to assess the risk of NPs, especially at the environmental level. According to results of qualitative and quantitative analyses, it can be concluded that studies of nanoscientific research using C. elegans is persistently growing. However, the comprehensive conclusion and analysis of toxic effects of NPs in C. elegans are limited and chaotic. This review focused on the effects, especially sublethal ones, induced by NPs in C. elegans, including the development, intestinal function, immune response, neuronal function, and reproduction, as well as the underlying mechanisms of NPs causing these effects, including oxidative stress and alterations of several signaling pathways. Furthermore, we presented some factors that influence the toxic effects of NPs in C. elegans. The advantages and limitations of using nematodes in the nanotoxicology study were also discussed. Finally, we predicted that the application of C. elegans to assess long-term impacts of metal oxide NPs in the ecosystem would become a vital part of the nanoscientific research field, which provided an insight for further study.

Mechanisms of engineered nanoparticle induced neurotoxicity in Caenorhabditis elegans

The wide-spread implementation of nanoparticles poses a major health concern. Unique biokinetics allow them to transfer to neurons throughout the body and inflict neurotoxicity, which is challenging to evaluate solely in mammalian experimental models due to logistics, financial and ethical limitations. In recent years, the nematode Caenorhabditis elegans has emerged as a promising nanotoxicology experimental surrogate due to characteristics such as ease of culture, short life cycle and high number of progeny. Most importantly, this model organism has a well conserved and fully described nervous system rendering it ideal for use in neurotoxicity assessment of nanoparticles. In that context, this mini review aims to summarize the main mechanistic findings on nanoparticle related neurotoxicity in the setting of Caenorhabditis elegans screening. The injury pathway primarily involves changes in intestinal permeability and defecation frequency both of which facilitate translocation at the site of neurons, where toxicity formation is linked partly to oxidative stress and perturbed neurotransmission.

Functional disruption in epidermal barrier enhances toxicity and accumulation of graphene oxide

In Caenorhabditis elegans, mutation of mlt-7 causes the deficits in epidermal barrier. Using the nematodes with epidermal-specific RNA interference (RNAi) knockdown of mlt-7 as a genetic tool, we found that epidermal-specific RNAi knockdown of mlt-7 resulted in a susceptibility to graphene oxide (GO) toxicity, and enhanced GO accumulation in the body. Epidermal-development related proteins of BLI-1 and IFB-1 acted as downstream targets of MLT-7, and mediated the function of MLT-7 in maintaining the epidermal barrier. Antimicrobial proteins of NLP-30 and CNC-2 also acted as downstream targets of MLT-7 in the regulation of GO toxicity. Epidermal-specific RNAi knockdown of nlp-30 or cnc-2 enhanced GO toxicity and accumulation in bli-1(RNAi) or ifb-1(RNAi) nematodes. Our data highlights the importance of maintaining normal epidermal barrier for nematodes against the GO toxicity.

Deficit in the epidermal barrier induces toxicity and translocation of PEG modified graphene oxide in nematodes

The developmental basis for the epidermal barrier against the translocation of nanomaterials is still largely unclear in organisms. We here investigated the effect of deficits in the epidermal barrier on the translocation and toxicity of PEG modified graphene oxide (GO-PEG) in Caenorhabditis elegans. In wild-type or NR222 nematodes, GO-PEG exposure did not cause toxicity and affect the expression of epidermal-development related genes. However, GO-PEG exposure resulted in toxicity in mlt-7(RNAi) nematodes with deficit in the function of epidermal barrier. Epidermal RNAi knockdown of mlt-7 allowed GO-PEG accumulation and translocation into targeted organs through the epidermal barrier. Epidermal-development related proteins of BLI-1 and IFB-1 were identified as targets for MLT-7 in the regulation of GO-PEG toxicity and accounted for MLT-7 function in maintaining the epidermal barrier. AAK-2, a catalytic α subunit of AMP-activated protein kinase, was identified as another target for MLT-7 in the regulation of GO-PEG toxicity. AAK-2 functioned synergistically with BLI-1 or IFB-1 in the regulation of GO-PEG toxicity. Our data provide the molecular basis for the role of epidermal barrier against the toxicity and translocation of nanomaterials in organisms.

Functional Interactions Between rsks-1/S6K, glp-1/Notch, and Regulators of Caenorhabditis elegans Fertility and Germline Stem Cell Maintenance

The proper accumulation and maintenance of stem cells is critical for organ development and homeostasis. The Notch signaling pathway maintains stem cells in diverse organisms and organ systems. In Caenorhabditis elegans, GLP-1/Notch activity prevents germline stem cell (GSC) differentiation. Other signaling mechanisms also influence the maintenance of GSCs, including the highly-conserved TOR substrate ribosomal protein S6 kinase (S6K). Although C. elegans bearing either a null mutation in rsks-1/S6K or a reduction-of-function (rf) mutation in glp-1/Notch produce half the normal number of adult germline progenitors, virtually all these single mutant animals are fertile. However, glp-1(rf) rsks-1(null) double mutant animals are all sterile, and in about half of their gonads, all GSCs differentiate, a distinctive phenotype associated with a significant reduction or loss of GLP-1 signaling. How rsks-1/S6K promotes GSC fate is unknown. Here, we determine that rsks-1/S6K acts germline-autonomously to maintain GSCs, and that it does not act through Cyclin-E or MAP kinase in this role. We found that interfering with translation also enhances glp-1(rf), but that regulation through rsks-1 cannot fully account for this effect. In a genome-scale RNAi screen for genes that act similarly to rsks-1/S6K, we identified 56 RNAi enhancers of glp-1(rf) sterility, many of which were previously not known to interact functionally with Notch. Further investigation revealed at least six candidates that, by genetic criteria, act linearly with rsks-1/S6K. These include genes encoding translation-related proteins, cacn-1/Cactin, an RNA exosome component, and a Hedgehog-related ligand. We found that additional Hedgehog-related ligands may share functional relationships with glp-1/Notch and rsks-1/S6K in maintaining germline progenitors.

Combinational effect of titanium dioxide nanoparticles and nanopolystyrene particles at environmentally relevant concentrations on nematode Caenorhabditis elegans

The possible adverse effects of nanoplastics have received the great attention recently; however, their effects at environmentally relevant concentration on organisms are still largely unclear. We here employed Caenorhabditis elegans to investigate the combinational effects of titanium dioxide nanoparticles (TiO₂-NPs) and nanopolystyrene particles at environmentally relevant concentrations on organisms. In wild-type nematodes, prolonged exposure to nanopolystyrene particles (1 μg/L) could enhance the toxicity of TiO₂-NPs (1 μg/L) in decreasing locomotion behavior and in inducing intestinal reactive oxygen species (ROS) production. Meanwhile, combinational exposure to TiO₂-NPs (1 μg/L) and nanopolystyrene particles (1 μg/L) altered the molecular basis for oxidative stress in wild-type nematodes. Moreover, prolonged exposure to nanopolystyrene particles (0.1 μg/L) could further enhance the toxicity of TiO₂-NPs (1 μg/L) in decreasing locomotion behavior and in inducing intestinal ROS production in sod-3 mutant nematodes. Our data suggest the potential role of nanopolystyrene particles at environmentally relevant concentrations in enhancing the toxicity of ENMs in the environment.

Biosafety assessment of water samples from Wanzhou watershed of Yangtze Three Gorges Reservior in the quiet season in Caenorhabditis elegans

We here employed a model animal of Caenorhabditis elegans to perform toxicity assessment of original surface water samples collected from Three Gorges Reservoir (TGR) in the quiet season in Wanzhou, Chongqing. Using some sublethal endpoints, including lifespan, body length, locomotion behavior, brood size, and intestinal reactive oxygen species (ROS) induction, we found that the examined five original surface water samples could not cause toxicity on wild-type nematodes. Nevertheless, the surface water sample collected from backwater area induced the significant increase in expressions of genes (sod-2 and sod-3) encoding Mn-SODs in wild-type nematodes. Among the examined five original surface water samples, exposure to the original surface water sample collected from backwater area could further cause the toxicity in decreasing locomotion behavior and in inducing intestinal ROS production in sod-3 mutant nematodes. Moreover, the solid phase of surface water sample collected from backwater area might mainly contribute to the observed toxicity in sod-3 mutant nematodes. Our results are helpful for understanding the potential effects of surface water in the TGR region in the quiet season on environmental organisms.

Toxicity evaluation of Wanzhou watershed of Yangtze Three Gorges Reservior in the flood season in Caenorhabditis elegans

Three Gorges Reservoir (TGR) in the upper stream of Yangtze River in China is a reservoir with the largest and the longest yearly water-level drop. Considering the fact that most of safety assessments of water samples collected from TGR region were based on chemical analysis, we here employed Caenorhabditis elegans to perform in vivo safety assessment of original surface water samples collected from TGR region in the flood season in Wanzhou, Chongqing. Among the examined five original surface water samples, only exposure to original surface water sample collected from backwater area could induce the significant intestinal ROS production, enhance the intestinal permeability, and decrease the locomotion behavior. Additionally, exposure to original surface water sample collected from backwater area altered the expressions of sod-2, sod-5, clk-1, and mev-1. Moreover, mutation of sod-2 or sod-5 was susceptible to the potential toxicity of original surface water sample collected from backwater area on nematodes. Together, our results imply that exposure to surface water sample from the backwater area may at least cause the adverse effects on intestinal function and locomotion behavior in nematodes.

Long-term exposure to thiolated graphene oxide in the range of μg/L induces toxicity in nematode Caenorhabditis elegans

The in vivo toxicity and translocation of thiolated graphene oxide (GO-SH) are still largely unclear. We hypothesized that long-term exposure to GO-SH may cause the adverse effects on environmental organisms. We here employed in vivo assay system of Caenorhabditis elegans to investigate the possible toxicity and translocation of GO-SH after long-term exposure. In wild-type nematodes, we observed that prolonged exposure to GO-SH at concentrations>100μg/L resulted in the toxicity on functions of both primary targeted organs such as the intestine and secondary targeted organs such as the neurons and the reproductive organs. The severe accumulation of GO-SH was further detected in the body of wild-type nematodes. The translocation of GO-SH into secondary targeted organs such as reproductive organs through intestinal barrier might be associated with the enhancement in intestinal permeability in GO-SH exposed wild-type nematodes. Prolonged exposure to GO-SH (100μg/L) decreased the expression of gas-1 encoding a subunit of mitochondrial complex I, and mutation of gas-1 caused the formation of GO-SH toxicity at concentration>10μg/L and more severe accumulation of GO-SH in the body of animals. Therefore, our results confirm the possibility for prolonged exposure to GO-SH in inducing adverse effects on nematodes. Our data highlight the potential adverse effects of GO-SH in the range of μg/L on environmental organisms after long-term exposure.

Coal combustion related fine particulate matter (PM2.5) induces toxicity in Caenorhabditis elegans by dysregulating microRNA expression

We employed an in vivo assay system of Caenorhabditis elegans to determine if and which microRNAs (miRNAs) were dysregulated upon exposure to coal combustion related fine particulate matter (PM2.5) by profiling the miRNAs using SOLiD sequencing. From this, expression of 25 miRNAs was discovered to become dysregulated by exposure to PM2.5. Using the corresponding C. elegans deletion mutants, 5 miRNAs (mir-231, mir-232, mir-230, mir-251 and mir-35) were found to be involved in the control of PM2.5 toxicity. Furthermore, mutation of mir-231 or mir-232 induced a resistance to PM2.5 toxicity, whereas mutation of mir-230, mir-251, or mir-35 induced a susceptibility to PM2.5 toxicity. SMK-1, an ortholog of the mammalian SMEK protein, was identified as a molecular target for mir-231 in the regulation of PM2.5 toxicity. In addition, the genes of sod-3, sod-4 and ctl-3, which are necessary for protection against oxidative stress, were determined to be important downstream targets of smk-1 in the regulation of PM2.5 toxicity. The triggering of this mir-231-SMK-1-SOD-3/SOD-4/CTL-3 signaling pathway may be a critical molecular basis for the role of oxidative stress in the induction of coal combustion related PM2.5 toxicity.

Neuronal ERK signaling in response to graphene oxide in nematode Caenorhabditis elegans

ERK signaling is one of the important mitogen-activated protein kinases (MAPKs). However, the role of ERK signaling in the regulation of response to engineered nanomaterial exposure is still largely unclear. In this study, using in vivo assay system of Caenorhabditis elegans, we investigated the function of ERK signaling in response to graphene oxide (GO) exposure and the underlying molecular mechanism. GO exposure increased the expression of MEK-2/MEK and MPK-1/ERK in the ERK signaling pathway. Mutation of mek-2 or mpk-1 resulted in a susceptibility to GO toxicity. Both the MEK-2 and the MPK-1 acted in neurons to regulate the response to GO exposure, and the neuronal expression of MEK-2 or MPK-1 caused a resistance to GO toxicity. In the neurons, SKN-1b/Nrf acted downstream of the MPK-1, and AEX-3, a guanine exchange factor for GTPase, further acted downstream of the SKN-1b to regulate the response to GO exposure. Therefore, a signaling cascade of MEK-2-MPK-1-SKN-1b/-AEX-3 was identified in the neurons required for the regulation of response to GO exposure. Moreover, genetic interaction assay demonstrated that the neuronal ERK signaling-mediated signaling pathway and the intestinal p38 MAPK-mediated signaling pathway functioned synergistically in the regulation of response to GO exposure. Our results highlight the crucial function of the neuronal ERK signaling in the regulation of response to nanomaterial exposure in organisms.