Alteration in expressions of ion channels in Caenorhabditis elegans exposed to polystyrene nanoparticles

Amino-modified nanoplastics at predicted environmental concentrations cause transgenerational toxicity through activating germline EGF signal in Caenorhabditis elegans

In the real environment, some chemical functional groups are unavoidably combined on the nanoplastic surface. Reportedly, amino-modified polystyrene nanoparticles (PS-A NPs) exposure in parents can induce severe transgenerational toxicity, but the underlying molecular mechanisms remain largely unclear. Using Caenorhabditis elegans as the animal model, this study was performed to investigate the role of germline epidermal growth factor (EGF) signal on modulating PS-A NPs' transgenerational toxicity. As a result, 1-10 μg/L PS-A NPs exposure transgenerationally enhanced germline EGF ligand/LIN-3 and NSH-1 levels. Germline RNAi of lin-3 and nsh-1 was resistant against PS-A NPs' transgenerational toxicity, implying the involvement of EGF ligand activation in inducing PS-A NPs' transgenerational toxicity. Furthermore, LIN-3 overexpression transgenerationally enhanced EGF receptor/LET-23 expression in the progeny, and let-23 RNAi in F1-generation notably suppressed PS-A NPs' transgenerational toxicity in the exposed worms overexpressing germline LIN-3 at P0 generation. Finally, LET-23 functioned in neurons and intestine for regulating PS-A NPs' transgenerational toxicity. LET-23 acted at the upstream DAF-16/FOXO within the intestine in response to PS-A NPs' transgenerational toxicity. In neurons, LET-23 functioned at the upstream of DAF-7/DBL-1, ligands of TGF-β signals, to mediate PS-A NPs' transgenerational toxicity. Briefly, this work revealed the exposure risk of PS-A NPs' transgenerational toxicity, which was regulated through activating germline EGF signal in organisms.

Long-term exposure to polystyrene nanoparticles at environmentally relevant concentration causes suppression in heme homeostasis signal associated with transgenerational toxicity induction in Caenorhabditis elegans

Heme homeostasis related signaling participates in inducing a protective response when controlling nanopolystyrene toxic effects in parental generation. However, whether the heme homeostasis signal is involved in regulation of transgenerational toxicity of nanopolystyrene toxicity is still unclear. Herein, with the model organism of Caenorhabditis elegans, 0.1-10 μg/L nanopolystyrene particles (PS-NPs) at 20-nm treatment downregulated glb-18, and the decrease was also discovered in the offspring following PS-NPs exposure. Germline glb-18 RNAi induced susceptive property to transgenerational PS-NPs toxicity, suggesting that a decreased GLB-18 level mediated induction of transgenerational toxicity. Importantly, germline GLB-18 transgenerationally activated the function of intestinal HRG-4 in controlling transgenerational PS-NPs toxicity. In transgenerational toxicity control, HRG-1/ATFS-1/HSP-6 was recognized to be the downstream pathway of HRG-4. Briefly, germline GLB-18 in P0 generation can transgenerationally activate the downstream intestinal HRG-4/HRG-1/ATFS-1/HSP-6 pathway among offspring for controlling the transgenerational toxicity of PS-NPs. Findings in the present work strengthens the possible association of heme homeostasis signal changes with transgenerational nanoplastic toxicity within the organisms.

Sulfate-modified nanosized polystyrene impairs memory by inhibiting ionotropic glutamate receptors and the cAMP-response element binding protein (CREB) pathway in Caenorhabditis elegans

Nanoplastic contamination is an emerging environmental concern worldwide. In particular, sulfate anionic surfactants often appear along with nanosized plastic particles in personal care products, suggesting that sulfate-modified nanosized polystyrene (S-NP) may occur, remain, and spread into the environment. However, whether S-NP adversely affects learning and memory is unknown. In this study, we used a positive butanone training protocol to evaluate the effects of S-NP exposure on short-term associative memory (STAM) and long-term associative memory (LTAM) in Caenorhabditis elegans. We observed that long-term S-NP exposure impairs both STAM and LTAM in C. elegans. We also observed that mutations in the glr-1, nmr-1, acy-1, unc-43, and crh-1 genes eliminated the STAM and LTAM impairment induced by S-NP, and the mRNA levels of these genes were also decreased upon S-NP exposure. These genes encode ionotropic glutamate receptors (iGluRs), cyclic adenosine monophosphate (cAMP)/Ca²⁺ signaling proteins, and cAMP-response element binding protein (CREB)/CRH-1 signaling proteins. Moreover, S-NP exposure inhibited the expression of the CREB-dependent LTAM genes nid-1, ptr-15, and unc-86. Our findings provide new insights into long-term S-NP exposure and the impairment of STAM and LTAM, which involve the highly conserved iGluRs and CRH-1/CREB signaling pathways.

A review of transgenerational and multigenerational toxicology in the in vivo model animal Caenorhabditis elegans

A large number of pollutants existing in the environment can last for a long time, and their potential toxic effects can transfer from parents to their offspring. Thus, it is necessary to investigate the toxicity of environmental pollutants across multigenerations and the underlying mechanisms in organisms. Due to its short life cycle and sensitivity to environmental exposures, Caenorhabditis elegans is an important animal model for toxicity assessment of environmental pollutants across multigenerations. In this review, we introduced the transgenerational and multigenerational toxicity caused by various environmental pollutants in C. elegans. Moreover, we discussed the underlying mechanisms for the observed transgenerational and multigenerational toxicity of environmental contaminants in C. elegans.

Hazard of polystyrene micro-and nanospheres to selected aquatic and terrestrial organisms

Plastics contamination in the environment is a major concern. Risk assessment of micro- and nanoplastics (MPL and NPL) poses significant challenges due to MPL and NPL heterogeneity regarding compositional polymers, particle sizes and morphologies in the environment. Yet, there exists considerable toxicological literature on commercial polystyrene (PS) micro- and nanospheres. Although such particles do not directly represent the environmental MPL and NPL, their toxicity data should be used to advance the hazard assessment of plastics. Here, toxicity data of PS micro- and nanospheres for microorganisms, aquatic and terrestrial invertebrates, fish, and higher plants was collected and analyzed. The evaluation of 294 papers revealed that aquatic invertebrates were the most studied organisms, nanosized PS was studied more often than microsized PS, acute exposures prevailed over chronic exposures, the toxicity of PS suspension additives was rarely addressed, and ∼40 % of data indicated no organismal effects of PS. Toxicity mechanisms were mainly studied in fish and nematode Caenorhabditis elegans, providing guidance for relevant studies in higher organisms. Future studies should focus on environmentally relevant plastics concentrations, wide range of organisms, co-exposures with other pollutants, and method development for plastics identification and quantification to fill the gap of bioaccumulation assessment of plastics.

Polystyrene nanoparticles cause dynamic alteration in mitochondrial unfolded protein response from parents to the offspring in C. elegans

The mitochondrial unfolded protein response (mt UPR) is important for organisms against the toxicity from toxicants and stresses. Polystyrene nanoparticle (PS-NP), one of the emerging pollutants, has aroused increasing concern for its toxicity in the offspring. Nevertheless, the molecular basis for this transgenerational toxicity remains largely unclear. In this study, the role of mt UPR in the induction of transgenerational toxicity was determined in Caenorhabditis elegans (C. elegans) after parental exposure to PS-NP. After exposure to PS-NP (1-100 μg/L), the suppression in mt UPR showed the concentration-dependent in nematodes from P0 generation (P0-G) to F2-G. Moreover, the decreased expression of genes required for controlling mt UPR (atfs-1, dve-1, and ubl-5 genes) were observed from P0-G to F2-G after exposure to PS-NP (1 μg/L). The adverse effects on locomotion and reproductive capacity were more severe over generations in nematodes with RNAi of these three genes, indicating that these genes were involved in controlling transgenerational toxicity. After parental PS-NP exposure (1 μg/L), the mt UPR was significantly inhibited by RNAi of atfs-1, dve-1, and ubl-5, indicating the association between the transgenerational PS-NP toxicity and mt UPR suppression. Additionally, during the transgenerational process, RNAi of atfs-1, dve-1, and ubl-5 enhanced the PS-NP toxicity by suppressing mt UPR, while RNAi of daf-2 encoding an insulin receptor inhibited the PS-NP toxicity by increasing mt UPR. Therefore, our data highlighted the role of inhibition in mt UPR in mediating the transgenerational nanoplastic toxicity in nematodes.

Induction of transgenerational toxicity is associated with the activated germline insulin signals in nematodes exposed to nanoplastic at predicted environmental concentrations

Exposure to nanoplastics can induce toxicity on organisms at both parental generation (P0-G) and the offspring. However, the underlying mechanism remains unknown. Using Caenorhabditis elegans as a model organism, exposure to 20-nm polystyrene nanoparticle (PS-NP) (1-100 μg/L) upregulated the expressions of insulin ligands (INS-39, INS-3, and DAF-28), and this increase could be further detected in the offspring after PS-NP exposure. Germline ins-39, ins-3, and daf-28 RNAi induced resistance to transgenerational toxicity of PS-NP, indicating that increase in expression of these three insulin ligands mediated induction of transgenerational toxicity. These three insulin ligands transgenerationally activated function of insulin receptor DAF-2 to control transgenerational toxicity of PS-NP. Exposure to 1-100 μg/L PS-NP further upregulated DAF-2, AGE-1, and AKT-1 expressions and downregulated DAF-16 expression. During transgenerational toxicity control, DAF-16/AKT-1/AGE-1 was identified as downstream signaling cascade of DAF-2. Moreover, transcriptional factor DAF-16 activated two downstream targets of HSP-6 (a mitochondrial UPR marker) and SOD-3 (a mitochondrial SOD) to modulate transgenerational toxicity of PS-NP. Our findings indicate a crucial link between activation of insulin signaling and induction of transgenerational toxicity of nanoplastics at low concentrations in organisms.

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.

Long-term exposure to polystyrene nanoparticles causes transgenerational toxicity by affecting the function and expression of MEV-1 and DAF-2 signals in Caenorhabditis elegans

In this study, we determined the roles of oxidative stress and related signals in mediating transgenerational toxicity of 30 nm polystyrene nanoparticles (PS-NPs) in Caenorhabditis elegans. Using brood size and locomotion behavior as endpoints, exposure to 1-100 μg/L PS-NPs caused transgenerational toxicity. Meanwhile, the activation of reactive oxygen species (ROS) was also observed transgenerationally after exposure to 1-100 μg/L PS-NPs. After exposure to 1 μg/L PS-NPs, the transgenerational toxicity was monitored until F2 generation (F2-G) and recovered at F3-G. At the F1-G of 1 μg/L PS-NPs-exposed nematodes, RNAi knockdown of daf-2 with function to inhibit oxidative stress suppressed the transgenerational toxicity and increased the mitochondrial SOD-3 expression. In contrast, at F3-G of 1 μg/L PS-NPs-exposed nematodes, RNAi knockdown of mev-1 with function to induce oxidative stress promoted locomotion and brood size, and suppressed the SOD-3 expression. Moreover, we observed the dynamic expressions of mev-1, daf-2, and sod-2 transgenerationally after exposure to 1 μg/L PS-NPs at P0-G, which further suggested the involvement of MEV-1, DAF-2, and SOD-3 in affecting induction of transgenerational PS-NP toxicity. Therefore, we provided the evidence to suggest the roles of oxidative stress activation and related molecular signals in mediating induction of transgenerational PS-NP toxicity. Our data highlights the crucial function of oxidative stress-related signals during induction of transgenerational PS-NP toxicity.

Neuronal Gα subunits required for the control of response to polystyrene nanoparticles in the range of μg/L in C. elegans

The aim of this study was to identify Gα proteins mediating function of neuronal G protein-coupled receptors (GPCRs) in controlling the response to polystyrene nanoparticles (PS-NPs). Caenorhabditis elegans was used as an animal model, and both gene expression and functional analysis were performed to identify the Gα proteins in controlling PS-NPs toxicity. In nematodes, exposure to PS-NPs (1-100 μg/L) significantly altered transcriptional expressions of some neuronal Gα genes, including gpa-5, gpa-10, gpa-11, gpa-15 gsa-1, egl-30, and goa-1. Among these 7 Gα genes, only neuronal RNAi knockdown of gsa-1, gpa-10, and goa-1 affected toxicity of PS-NPs in inducing ROS production and in decreasing locomotion behavior. Some neuronal GPCRs (such as GTR-1, DCAR-1, DOP-2, NPR-8, NPR-12, NPR-9, and DAF-37) functioned upstream of GOA-1, some neuronal GPCRs (such as DCAR-1, DOP-2, NPR-9, NPR-8, and DAF-37) functioned upstream of GSA-1, and some neuronal GPCRs (such as DOP-2, NPR-8, DAF-37, and DCAR-1) functioned upstream of GPA-10 to regulate the toxicity of PS-NPs. Moreover, GOA-1 acted upstream of MPK-1/ERK MAPK, JNK-1/JNK MAPK, DBL-1/TGF-β, and DAF-7/ TGF-β, GSA-1 functioned upstream of MPK-1/ERK MAPK, JNK-1/JNK MAPK, and DBL-1/TGF-β, and GPA-10 functioned upstream of GLB-1/Globin and DBL-1/TGF-β to control the PS-NPs toxicity. Therefore, neuronal Gα proteins of GOA-1, GSA-1, and GPA-10 functioned to transduce signals of multiple GPCRs to different downstream signaling pathways during the control of PS-NPs toxicity in nematodes. Our results provide clues for understanding the important function of GPCRs-Gα signaling cascade in the neurons in controlling response to nanoplastics in organisms.

Size-dependent transgenerational toxicity induced by nanoplastics in nematode Caenorhabditis elegans

Nanoplastic exposure can potentially cause the severe transgenerational toxicity in organisms. However, the transgenerational nanoplastic toxicity and the underlying mechanisms are still largely unclear. Using Caenorhabditis elegans as an animal model, we here compared the transgenerational toxicity of two sizes of polystyrene nanoparticles (PS-NPs, 20 and 100 nm). The nematodes were exposed to PS-NPs at the P0 generation, and from the F1 generation the nematodes were grown under the normal condition. Exposure to 20 nm PS-NPs resulted in more severe transgenerational toxicity than exposure to 100 nm PS-NPs. At the concentration of 100 μg/L, the toxicity of 20 nm PS-NPs on locomotion and reproduction was detected at the F1-F6 generations, whereas the toxicity of 100 nm PS-NPs could only be observed at the F1-F3 generations. The difference in transgeneration toxicity between PS-NPs (20 nm) and PS-NPs (100 nm) was associated with the difference in transgenerational activation of oxidative stress. Based on observations on SOD-3::GFP, HSP-6::GFP, and HSP-4::GFP expressions, PS-NPs (20 nm) and PS-NPs (100 nm) further induced different transgenerational responses of anti-oxidation, mt UPR, and ER UPR. Our data suggested that the induction of transgenerational toxicity of PS-NPs was size dependent in nematodes. The results are helpful for our understanding the cellular mechanisms for the induction of transgenerational nanoplastic toxicity in organisms.

Biosafety assessment of Acinetobacter strains isolated from the Three Gorges Reservoir region in nematode Caenorhabditis elegans

Acinetobacter has been frequently detected in backwater areas of the Three Gorges Reservoir (TGR) region. We here employed Caenorhabditis elegans to perform biosafety assessment of Acinetobacter strains isolated from backwater area in the TGR region. Among 21 isolates and 5 reference strains of Acinetobacter, exposure to Acinetobacter strains of AC1, AC15, AC18, AC21, A. baumannii ATCC 19606T, A. junii NH88-14, and A. lwoffii DSM 2403T resulted in significant decrease in locomotion behavior and reduction in lifespan of Caenorhabditis elegans. In nematodes, exposure to Acinetobacter strains of AC1, AC15, AC18, AC21, A. baumannii, A. junii and A. lwoffii also resulted in significant reactive oxygen species (ROS) production. Moreover, exposure to Acinetobacter isolates of AC1, AC15, AC18, and AC21 led to significant increase in expressions of both SOD-3::GFP and some antimicrobial genes (lys-1, spp-12, lys-7, dod-6, spp-1, dod-22, lys-8, and/or F55G11.4) in nematodes. The Acinetobacter isolates of AC1, AC15, AC18, and AC21 had different morphological, biochemical, phylogenetical, and virulence gene properties. Our results suggested that exposure risk of some Acinetobacter strains isolated from the TGR region exists for environmental organisms and human health. In addition, C. elegans is useful to assess biosafety of Acinetobacter isolates from the environment.

Dysregulated mir-76 mediated a protective response to nanopolystyrene by modulating heme homeostasis related molecular signaling in nematode Caenorhabditis elegans

The underlying mechanisms of microRNAs (miRNAs) in regulating nanoplastic toxicity are still largely unclear in organisms. In nanopolystyrene (NPS) exposed Caenorhabditis elegans, the expression of mir-76 (a neuronal miRNA) was significantly decreased, and the mir-76 mutant was resistant to the toxicity of NPS. The aim of this study was to determine the molecular basis of mir-76 in controlling NPS toxicity in nematodes. The mir-76 mutation increased expression of glb-10 encoding a globin protein in NPS (1 μg/L) exposed nematodes. Exposure to NPS (1-100 μg/L) increased the glb-10 expression, and the glb-10(RNAi) worm was susceptible to NPS toxicity in inducing reactive oxygen species (ROS) production and in decreasing locomotion behavior. Using ROS production and locomotion behavior as endpoints, mutation of glb-10 inhibited resistance of mir-76 mutant to NPS toxicity, and neuronal overexpression of mir-76 inhibited the resistance to NPS toxicity in nematodes overexpressing neuronal glb-10 containing 3' untranslated region (3'UTR). Thus, GLB-10 functioned as a target of mir-76 in the neurons to regulate the NPS toxicity. Moreover, a signaling cascade of HRG-7-HRG-5 required for the control of heme homeostasis was identified to function downstream of neuronal GLB-10 to regulate the NPS toxicity. In this signaling cascade, the neuronal HRG-7 regulated the NPS toxicity by antagonizing function of intestinal HRG-5. Furthermore, in the intestine, HRG-5 controlled NPS toxicity by inhibiting functions of hypoxia-inducible transcriptional factor HIF-1 and transcriptional factor ELT-2. Our results highlight the crucial function of heme homeostasis related signaling in regulating the NPS toxicity in organisms.

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.