Response of DBL-1/TGF-β signaling-mediated neuron-intestine communication to nanopolystyrene in nematode Caenorhabditis elegans

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.

Neurotoxicity and accumulation of CPPD quinone at environmentally relevant concentrations in Caenorhabditis elegans

CPPD quinone (CPPDQ) is a member of PPDQs, which was widely distributed in different environments. Using Caenorhabditis elegans as an animal model, we here examined neurotoxicity and accumulation of CPPDQ and the underlying mechanism. After exposure to 0.01-10 μg/L CPPDQ, obvious body accumulation of CPDDQ was detected. Meanwhile, exposure to CPPDQ (0.01-10 μg/L) decreased head thrash, body bend, and forward turn, and increased backward turn. Nevertheless, only exposure to 10 μg/L CPPDQ induced neurodegeneration in GABAergic system. Exposure to CPPDQ (0.01-10 μg/L) further decreased expressions of daf-7 encoding TGF-β ligand, jnk-1 encoding JNK MAPK, and mpk-1 encoding ERK MAPK. Additionally, among examined G protein-coupled receptor (GPCR) genes, exposure to CPPDQ (0.01-10 μg/L) decreased dcar-1 expression and increased npr-8 expression. RNAi of daf-7, jnk-1, mpk-1, and dcar-1 resulted in susceptibility, and nhr-8 RNAi caused resistance to CPPDQ neurotoxicity and accumulation. Moreover, in CPPDQ exposed nematodes, RNAi of dcar-1 decreased jnk-1 and mpk-1 expressions, and RNAi of npr-8 increased mpk-1 expression. Therefore, exposure to CPPDQ potentially resulted in neurotoxicity by inhibiting TGF-β, JNK MAPK, and ERK MAPK signals. The inhibition in JNK MAPK and ERK MAPKs signals in CPPDQ exposed nematodes was further related to alteration in GPCRs of DCAR-1 and NHR-8 in nematodes.

Comparison of Transgenerational Neurotoxicity between Pristine and Amino-Modified Nanoplastics in C. elegans

Increasing evidence has suggested that nanoplastic pollution has become a global concern. More importantly, transgenerational toxicity can be induced by nanoplastics at predicted environmentally relevant doses (ERDs). Considering that amino modification could increase nanoplastic toxicity, we compared transgenerational neurotoxicity between pristine polystyrene nanoparticle (PS-NP) and amino-modified PS-NP (NH2-PS-NP) in Caenorhabditis elegans. At 0.1-10 μg/L, NH2-PS-NP caused more severe transgenerational toxicity on locomotion and neuronal development. Accompanied with a difference in transgenerational neuronal damage, compared to PS-NP (10 μg/L), NH2-PS-NP (10 μg/L) induced more severe transgenerational activation of mec-4, crt-1, itr-1, and tra-3, which are required for the induction of neurodegeneration. Moreover, NH2-PS-NP (10 μg/L) caused more severe transgenerational inhibition in expressions of mpk-1, jnk-1, dbl-1, and daf-7 than PS-NP (10 μg/L), and RNA interference (RNAi) of these genes conferred susceptibility to the toxicity of PS-NP and NH2-PS-NP on locomotion and neuronal development. NH2-PS-NP (10 μg/L) further caused more severe transgenerational activation of germline ligand genes (ins-3, ins-39, daf-28, lin-44, egl-17, efn-3, and lag-2) than PS-NP (10 μg/L), and RNAi of these ligand genes caused resistance to the toxicity of PS-NP and NH2-PS-NP on locomotion and neuronal development. Our results highlighted more severe exposure risk of amino-modified nanoplastics at ERDs in causing transgenerational neurotoxicity in organisms.

Polyethylene nanoparticles at environmentally relevant concentrations enhances neurotoxicity and accumulation of 6-PPD quinone in Caenorhabditis elegans

The exposure risk of 6-PPD quinone (6-PPDQ) has aroused increasing concern. In the natural environment, 6-PPDQ could interact with other pollutants, posing more severe environmental problems and toxicity to organisms. We here examined the effect of polyethylene nanoplastic (PE-NP) on 6-PPDQ neurotoxicity and the underling mechanisms in Caenorhabditis elegans. In nematodes, PE-NP (1 and 10 μg/L) decreased locomotion behavior, but did not affect development of D-type neurons. Exposure to PE-NP (1 and 10 μg/L) strengthened neurotoxicity of 6-PPDQ (10 μg/L) on the aspect of locomotion and neurodegeneration induction of D-type motor neurons. Exposure to PE-NPs (10 μg/L) caused increase in expressions of mec-4, asp-3, and asp-4 governing neurodegeneration in 10 μg/L 6-PPDQ exposed nematodes. Moreover, exposure to PE-NP (10 μg/L) increased expression of some neuronal genes (daf-7, dbl-1, jnk-1, and mpk-1) in 6-PPDQ exposed nematodes, and RNAi of these genes resulted in susceptibility to neurotoxicity of PE-NP and 6-PPDQ. 6-PPDQ could be adsorbed by PE-NPs, and resuspension of PE-NP and 6-PPDQ after adsorption equilibrium exhibited similar neurotoxicity to co-exposure of PE-NP and 6-PPDQ. In addition, exposure to PE-NP (1 and 10 μg/L) increased 6-PPDQ accumulation in body of nematodes and increased defecation cycle length in 6-PPDQ exposed nematodes. Therefore, 6-PPDQ could be adsorbed on nanoplastics (such as PE-NPs) and enhance both neurotoxicity and accumulation of 6-PPDQ in organisms.

Sublethal effects induced by different plastic nano-sized particles in Daphnia magna at environmentally relevant concentrations

A growing number of studies have reported the toxic effects of nanoplastics (NPs) on organisms. However, the focus of these studies has almost exclusively been on the use of polystyrene (PS) nanospheres. Herein, we aim to evaluate the sublethal effects on Daphnia magna juveniles of three different NP polymers: PS-NPs with an average size of 200 nm, polyethylene [PE] NPs and polyvinyl chloride [PVC] NPs with a size distribution between 50 and 350 nm and a comparable mean size. For each polymer, five environmentally relevant concentrations were tested (from 2.5 to 250 μg/L) for an exposure time of 48 h. NP effects were assessed at the biochemical level by investigating the amount of reactive oxygen species (ROS) and the activity of the antioxidant enzyme catalase (CAT) and at the behavioral level by evaluating the swimming behavior (distance moved). Our results highlight that exposure to PVC-NPs can have sublethal effects on Daphnia magna at the biochemical and behavioral levels. The potential role of particle size on the measured effects cannot be excluded as PVC and PE showed a wider size range distribution than PS, with particles displaying sizes from 50 to 350 nm. However, we infer that the chemical structure of PVC, which differs from that of PE of the same range size, concurs to explain the observed effects. Consequently, as PS seems not to be the most hazardous polymer, we suggest that the use of data on PS toxicity alone can lead to an underestimation of NP hazards.

Tire-rubber related pollutant 6-PPD quinone: A review of its transformation, environmental distribution, bioavailability, and toxicity

The antioxidant 6-PPD has been widely used to prevent cracking and thermal oxidative degradation and to extend the service life of tire rubber. 6-PPD quinone (6-PPDQ) is formed via the reaction of 6-PPD with O3. Due to its acute lethality in coho salmon, 6-PPDQ has become an emerging pollutant of increasing concern. In this review, we provide a critical overview of the generation, environmental distribution, bioavailability, and potential toxicity of 6-PPDQ. The transformation pathways from 6-PPD to 6-PPDQ include the N-1,3-dimethylbutyl-N-phenyl quinone diamine (QDI), intermediate phenol, and semiquinone radical pathways. 6-PPDQ has been frequently detected in water, dust, air particles, soil, and sediments, indicating its large-scale and potentially global pollution trend. 6-PPDQ is bioavailable to both aquatic animals and mammals and acute exposure to 6-PPDQ can be lethal to some organisms. Exposure to 6-PPDQ at environmentally relevant concentrations could induce several types of toxicity, including neurotoxicity, intestinal toxicity, and reproductive toxicity. This review also identifies and discusses knowledge gaps and research needs for the study of 6-PPDQ. This review facilitates a better understanding of the environmental occurrence and exposure risk of 6-PPDQ.

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.

TGF-β pathways in aging and immunity: lessons from Caenorhabditis elegans

The Transforming Growth Factor-β (TGF-β) superfamily of signaling molecules plays critical roles in development, differentiation, homeostasis, and disease. Due to the conservation of these ligands and their signaling pathways, genetic studies in invertebrate systems including the nematode Caenorhabditis elegans have been instrumental in identifying signaling mechanisms. C. elegans is also a premier organism for research in longevity and healthy aging. Here we summarize current knowledge on the roles of TGF-β signaling in aging and immunity.

Combinational exposure to hydroxyatrazine increases neurotoxicity of polystyrene nanoparticles on Caenorhabditis elegans

Using Caenorhabditis elegans as an animal model, we investigated combinational effect between 2-hydroxyatrazine (HA) and polystyrene nanoparticle (PS-NP) on function and development of D-type motor neurons. Exposure to HA (10 and 100 μg/L) alone caused decreases in body bend, head thrash, and forward turn and increase in backward turn. Exposure to 100 μg/L HA also caused neurodegeneration of D-type motor neurons. Moreover, combinational exposure to HA (0.1 and 1 μg/L) induced enhancement in PS-NP (10 μg/L) toxicity in inhibiting body bend, head thrash, and forward turn, and in increasing backward turn. In addition, combinational exposure to HA (1 μg/L) could result in neurodegeneration of D-type motor neurons in PS-NP (10 μg/L) exposed nematodes. Combinational exposure to HA (1 μg/L) and PS-NP (10 μg/L) increased expressions of crt-1, itr-1, mec-4, asp-3, and asp-4, which govern the induction of neurodegeneration. Moreover, combinational exposure to HA (0.1 and 1 μg/L) strengthened PS-NP (10 μg/L)-induced decreases in glb-10, mpk-1, jnk-1, and daf-7 expressions, which encode neuronal signals regulating response to PS-NP. Therefore, our results demonstrated the effect of combinational exposure to HA and nanoplastics at environmentally relevant concentrations in causing toxic effect on nervous system in organisms.

Sulfonate-Modified Polystyrene Nanoparticle at Precited Environmental Concentrations Induces Transgenerational Toxicity Associated with Increase in Germline Notch Signal of Caenorhabditis elegans

Recently, the transgenerational toxicity of nanoplastics has received increasing attention. Caenorhabditis elegans is a useful model to assess the transgenerational toxicity of different pollutants. In nematodes, the possibility of early-life exposure to sulfonate-modified polystyrene nanoparticle (PS-S NP) causing transgenerational toxicity and its underlying mechanisms were investigated. After exposure at the L1-larval stage, transgenerational inhibition in both locomotion behavior (body bend and head thrash) and reproductive capacity (number of offspring and fertilized egg number in uterus) was induced by 1-100 μg/L PS-S NP. Meanwhile, after exposure to 1-100 μg/L PS-S NP, the expression of germline lag-2 encoding Notch ligand was increased not only at the parental generation (P0-G) but also in the offspring, and the transgenerational toxicity was inhibited by the germline RNA interference (RNAi) of lag-2. During the transgenerational toxicity formation, the parental LAG-2 activated the corresponding Notch receptor GLP-1 in the offspring, and transgenerational toxicity was also suppressed by glp-1 RNAi. GLP-1 functioned in the germline and the neurons to mediate the PS-S NP toxicity. In PS-S NP-exposed nematodes, germline GLP-1 activated the insulin peptides of INS-39, INS-3, and DAF-28, and neuronal GLP-1 inhibited the DAF-7, DBL-1, and GLB-10. Therefore, the exposure risk in inducing transgenerational toxicity through PS-S NP was suggested, and this transgenerational toxicity was mediated by the activation of germline Notch signal in organisms.

Activation of FGF signal in germline mediates transgenerational toxicity of polystyrene nanoparticles at predicted environmental concentrations in Caenorhabditis elegans

Nanoplastics in the environment could cause the ecological and health risks. Recently, the transgenerational toxicity of nanoplastic has been observed in different animal models. In this study, using Caenorhabditis elegans as an animal model, we aimed to examine the role of alteration in germline fibroblast growth factor (FGF) signal in mediating the transgenerational toxicity of polystyrene nanoparticle (PS-NP). Exposure to 1-100 μg/L PS-NP (20 nm) induced transgenerational increase in expressions of germline FGF ligand/EGL-17 and LRP-1 governing FGF secretion. Germline RNAi of egl-17 and lrp-1 resulted in resistance to transgenerational PS-NP toxicity, indicating the requirement of FGF ligand activation and secretion in formation of transgenerational PS-NP toxicity. Germline overexpression of EGL-17 increased expression of FGF receptor/EGL-15 in the offspring, and RNAi of egl-15 at F1 generation (F1-G) inhibited transgenerational toxicity of PS-NP exposed animals overexpressing germline EGL-17. EGL-15 functions in both the intestine and the neurons to control transgenerational PS-NP toxicity. Intestinal EGL-15 acted upstream of DAF-16 and BAR-1, and neuronal EGL-15 functioned upstream of MPK-1 to control PS-NP toxicity. Our results suggested the important role of activation in germline FGF signal in mediating the induction of transgenerational toxicity in organisms exposed to nanoplastics in the range of μg/L.

BuShen HuoXue decoction improves fertility through intestinal hsp-16.2-mediated heat-shock signaling pathway in Caenorhabditis elegans

Introduction: BuShen HuoXue (BSHX) decoction is commonly used in the clinical treatment of premature ovarian failure because it can increase estradiol level and decrease follicle-stimulating hormone level. In this study, we determined the potential therapeutic effects of BSHX decoction via anti-stress pathway and the underlying mechanism by using the nematode Caenorhabditis elegans as an assay system. Methods: Bisphenol A (BPA, 175 μg/mL) was used to establish a fertility-defective C. elegans model. Nematodes were cultivated according to standard methods. Brood size, DTC, the number of apoptotic cells and oocytes were used to evaluate the fertility of nematodes. Nematodes were cultivated at 35°C as heat stress. RNA isolation and RT-qPCR were used to detect the mRNA expression level of genes. Intestinal ROS and intestinal permeability were used to evaluate the function of intestinal barrier. BSHX decoction was extracted with water and analyzed by LC/Q-TOF. Results and Discussion: In BPA-treated N2 nematodes, 62.5 mg/mL BSHX decoction significantly improved the brood size and the oocytes quality at different developmental stages. BSHX decoction improved resistance to heat stress through the hsf-1-mediated heat-shock signaling pathway. Further analysis showed that the decoction significantly improved the transcriptional levels of hsf-1 downstream target genes, such as hsp-16.1, hsp-16.2, hsp-16.41, and hsp-16.48. Other than hsp-16.2 expression in the gonad, the decoction also affected intestinal hsp-16.2 expression and significantly reversed the adverse effects induced by BPA. Moreover, the decoction ameliorated intestinal ROS and permeability. Thus, BSHX decoction can improve fertility by increasing intestinal barrier function via hsp-16.2-mediated heat-shock signaling pathway in C. elegans. These findings reveal the underlying regulatory mechanisms of hsp-16.2-mediated heat resistance against fertility defect.

Exposure to 6-PPD Quinone at Environmentally Relevant Concentrations Causes Abnormal Locomotion Behaviors and Neurodegeneration in Caenorhabditis elegans

6-PPD quinone (6-PPDQ) can be transformed from 6-PPD through ozonation. Nevertheless, the potential neurotoxicity of 6-PPDQ after long-term exposure and the underlying mechanism are largely unclear. In Caenorhabditis elegans, we here observed that 0.1-10 μg/L of 6-PPDQ caused several forms of abnormal locomotion behaviors. Meanwhile, the neurodegeneration of D-type motor neurons was observed in 10 μg/L of 6-PPDQ-exposed nematodes. The observed neurodegeneration was associated with the activation of the Ca²⁺ channel DEG-3-mediated signaling cascade. In this signaling cascade, expressions of deg-3, unc-68, itr-1, crt-1, clp-1, and tra-3 were increased by 10 μg/L of 6-PPDQ. Moreover, among genes encoding neuronal signals required for the control of stress response, expressions of jnk-1 and dbl-1 were decreased by 0.1-10 μg/L of 6-PPDQ, and expressions of daf-7 and glb-10 were decreased by 10 μg/L of 6-PPDQ. RNAi of jnk-1, dbl-1, daf-7, and glb-10 resulted in the susceptibility to 6-PPDQ toxicity in decreasing locomotory ability and in inducing neurodegeneration, suggesting that JNK-1, DBL-1, DAF-7, and GLB-10 were also required for the induction of 6-PPDQ neurotoxicity. Molecular docking analysis further demonstrated the binding potential of 6-PPDQ to DEG-3, JNK-1, DBL-1, DAF-7, and GLB-10. Together, our data suggested the exposure risk of 6-PPDQ at environmentally relevant concentrations in causing neurotoxicity in organisms.

Phenolic Compounds from Sonchus arvensis Linn. and Hemerocallis citrina Baroni. Inhibit Sucrose and Stearic Acid Induced Damage in Caenorhabditis elegans

Sonchus arvensis Linn. and Hemerocallis citrina Baroni. have been reported to improve body resistance. However, the underlying mechanism is not clear. In this study, Sonchus arvensis Linn. phenolic compounds (SAP) and Hemerocallis citrina Baroni. phenolic compounds (HCP) were extracted and their protective effects in Caenorhabditis elegans evaluated. SAP and HCP showed considerably different phenolic compositions. In the normal C. elegans model, HCP exhibited better effects in promoting growth than SAP. In the sucrose-incubated C. elegans model, both SAP and HCP showed positive effects against the high-sucrose-induced damage. In the stearic acid-incubated C. elegans model, both SAP and HCP improved lifespan, reproductive ability and growth, while HCP had a more evident effect than SAP on reproductive ability. The TGF-β signaling pathway was confirmed to be involved in the protective effects of SAP and HCP. The antioxidant ability of SAP was also found to be related to skn-1. Our study shows that both SAP and HCP have protective effects against high sucrose- or high stearic acid-induced damage.

Nanoplastics in the soil environment: Analytical methods, occurrence, fate and ecological implications

Soils play a very important role in ecosystems sustainability, either natural or agricultural ones, serving as an essential support for living organisms of different kinds. However, in the current context of extremely high plastic pollution, soils are highly threatened. Plastics can change the chemical and physical properties of the soils and may also affect the biota. Of particular importance is the fact that plastics can be fragmented into microplastics and, to a final extent into nanoplastics. Due to their extremely low size and high surface area, nanoplastics may even have a higher impact in soil ecosystems. Their transport through the edaphic environment is regulated by the physicochemical properties of the soil and plastic particles themselves, anthropic activities and biota interactions. Their degradation in soils is associated with a series of mechanical, photo-, thermo-, and bio-mediated transformations eventually conducive to their mineralisation. Their tiny size is precisely the main setback when it comes to sampling soils and subsequent processes for their identification and quantification, albeit pyrolysis coupled with gas chromatography-mass spectrometry and other spectroscopic techniques have proven to be useful for their analysis. Another issue as a consequence of their minuscule size lies in their uptake by plants roots and their ingestion by soil dwelling fauna, producing morphological deformations, damage to organs and physiological malfunctions, as well as the risks associated to their entrance in the food chain, although current conclusions are not always consistent and show the same pattern of effects. Thus, given the omnipresence and seriousness of the plastic menace, this review article pretends to provide a general overview of the most recent data available regarding nanoplastics determination, occurrence, fate and effects in soils, with special emphasis on their ecological implications.

Nanoplastic Exposure at Predicted Environmental Concentrations Induces Activation of Germline Ephrin Signal Associated with Toxicity Formation in the Caenorhabditis elegans Offspring

In nematode Caenorhabditis elegans, exposure to polystyrene nanoparticles (PS-NPs) at predicted environmental concentrations can cause induction of transgenerational toxicity. However, the underlying mechanisms for toxicity formation of PS-NP in the offspring remain largely unknown. In this study, based on high-throughput sequencing, Ephrin ligand EFN-3 was identified as a target of KSR-1/2 (two kinase suppressors of Ras) in the germline during the control of transgenerational PS-NP toxicity. At parental generation (P0-G), exposure to 0.1-10 μg/L PS-NP caused the increase in expression of germline efn-3, and this increase in germline efn-3 expression could be further detected in the offspring, such as F1-G and F2-G. Germline RNAi of efn-3 caused a resistance to transgenerational PS-NP toxicity, suggesting that the activation of germline EFN-3 at P0-G mediated transgenerational PS-NP toxicity. In the offspring, Ephrin receptor VAB-1 was further activated by the increased EFN-3 caused by PS-NP exposure at P0-G, and RNAi of vab-1 also resulted in resistance to transgenerational PS-NP toxicity. VAB-1 acted in both the neurons and the germline to control toxicity of PS-NP in the offspring. In the neurons, VAB-1 regulated PS-NP toxicity by suppressing expressions of DBL-1, JNK-1, MPK-1, and GLB-10. In the germline, VAB-1 regulated PS-NP toxicity by increasing NDK-1 and LIN-23 expressions and decreasing EGL-1 expression. Therefore, germline Ephrin ligand EFN-3 and its receptor VAB-1 acted together to mediate the formation of transgenerational PS-NP toxicity. Our data highlight the important role of activation in germline Ephrin signals in mediating transgenerational toxicity of nanoplastics at predicted environmental concentrations in organisms.

Reduced bone morphogenic protein signaling along the gut-neuron axis by heat shock factor promotes longevity

Aging is a complex and highly regulated process of interwoven signaling mechanisms. As an ancient transcriptional regulator of thermal adaptation and protein homeostasis, the Heat Shock Factor, HSF-1, has evolved functions within the nervous system to control age progression; however, the molecular details and signaling dynamics by which HSF-1 modulates age across tissues remain unclear. Herein, we report a nonautonomous mode of age regulation by HSF-1 in the Caenorhabditis elegans nervous system that works through the bone morphogenic protein, BMP, signaling pathway to modulate membrane trafficking in peripheral tissues. In particular, HSF-1 represses the expression of the neuron-specific BMP ligand, DBL-1, and initiates a complementary negative feedback loop within the intestine. By reducing receipt of DBL-1 in the periphery, the SMAD transcriptional coactivator, SMA-3, represses the expression of critical membrane trafficking regulators including Rab GTPases involved in early (RAB-5), late (RAB-7), and recycling (RAB-11.1) endosomal dynamics and the BMP receptor binding protein, SMA-10. This reduces cell surface residency and steady-state levels of the type I BMP receptor, SMA-6, in the intestine and further dampens signal transmission to the periphery. Thus, the ability of HSF-1 to coordinate BMP signaling along the gut-brain axis is an important determinate in age progression.

Nanoplastics: Status and Knowledge Gaps in the Finalization of Environmental Risk Assessments

Nanoplastics (NPs) are particles ranging in size between 1 and 1000 nm, and they are a form of environmental contaminant of great ecotoxicological concern. Although NPs are widespread across ecosystems, they have only recently garnered growing attention from both the scientific community and regulatory bodies. The present study reviews scientific literature related to the exposure and effects of NPs and identifies research gaps that impede the finalization of related environmental risk assessments (ERAs). Approximately 80 articles published between 2012 and 2021 were considered. Very few studies (eight articles) focused on the presence of NPs in biotic matrices, whereas the majority of the studies (62 articles) assessed the lethal and sublethal effects of NPs on aquatic and terrestrial organisms. Whilst many studies focused on nude NPs, only a few considered their association with different aggregates. Amongst NPs, the effects of polystyrene are the most extensively reported to date. Moreover, the effects of NPs on aquatic organisms are better characterized than those on terrestrial organisms. NP concentrations detected in water were close to or even higher than the sublethal levels for organisms. An ERA framework specifically tailored to NPs is proposed.

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.

The use of different sublethal endpoints to monitor atrazine toxicity in nematode Caenorhabditis elegans

In this work, Caenorhabditis elegans was employed as an in vivo model to determine the toxic effects of atrazine at different concentrations. After the exposure period from the larval stage L1 to adulthood day 1, atrazine (10 mg/L) significantly decreased the body length and lifespan of nematodes. In addition, exposure to ≥0.01 mg/L atrazine remarkably increased the intestinal reactive oxygen species (ROS) levels and reduced locomotion behavior of nematodes, while exposure to ≥ 1 mg/L atrazine decreased the brood size of nematodes. Moreover, atrazine (0.001-0.1 mg/L) upregulated the expression levels of hsp-6::GFP and hsp-6/60 in nematodes, indicating the activation of mitochondrial unfolded protein response (mtUPR). On the contrary, atrazine (1-10 mg/L) downregulated the expression levels of hsp-6::GFP and hsp-6/60 in nematodes. Furthermore, mtUPR induction governed by the RNAi knockdown of atfs-1 could increase the vulnerability of nematodes against atrazine toxicity. Overall, our findings highlighted the dynamic responses of nematodes toward different concentrations of atrazine, which could be monitored using different sublethal endpoints as bioindicators.

Response of tyramine and glutamate related signals to nanoplastic exposure in Caenorhabditis elegans

Neurotransmission related signals are involved in the control of response to toxicants. We here focused on the tyramine and the glutamate related signals to determine their roles in regulating nanoplastic toxicity in Caenorhabditis elegans. In the range of μg/L, exposure to nanopolystyrene (100 nm) increased the expression of tdc-1 encoding a tyrosine decarboxylase required for synthesis of tyramine, and decreased the expression of eat-4 encoding a glutamate transporter. Both TDC-1 and EAT-4 could act in the neurons to regulate the nanopolystyrene toxicity. Meanwhile, neuronal RNAi knockdown of tdc-1 induced a susceptibility to nanopolystyrene toxicity, and neuronal RNAi knockdown of eat-4 induced a resistance to nanopolystyrene toxicity. In the neurons, TYRA-2 functioned as the corresponding receptor of tyramine and acted upstream of MPK-1 signaling to regulate the nanopolystyrene toxicity. Moreover, during the control of nanopolystyrene toxicity, GLR-4 and GLR-8 were identified as the corresponding glutamate receptors, and acted upstream of JNK-1 signaling and DBL-1 signaling, respectively. Our results demonstrated the crucial roles of tyramine and glutamate related signals in regulating the toxicity of nanoplastics in organisms.

Acetylation regulation associated with the induction of protective response to polystyrene nanoparticles in Caenorhabditis elegans

Caenorhabditis elegans is a useful animal model to assess nanoplastic toxicity. Using polystyrene nanoparticles (PS-NPs) as the example of nanoplastics, we found that exposure to PS-NPs (1-100 μg/L) from L1-larvae for 6.5 days increased expression of cbp-1 encoding an acetyltransferase. The susceptibility to PS-NPs toxicity was observed in cbp-1(RNAi) worms, suggesting that CBP-1-mediated histone acetylation regulation reflects a protective response to PS-NPs. The functions of CBP-1 in intestine, neurons, and germline were required for formation of this protective response. In intestinal cells, CBP-1 controlled PS-NPs toxicity by modulating functions of insulin and p38 MAPK signaling pathways. In neuronal cells, CBP-1 controlled PS-NPs toxicity by affecting functions of DAF-7/TGF-β and JNK MAPK signaling pathways. In germline cells, CBP-1 controlled PS-NPs toxicity by suppressing NHL-2 activity, and NHL-2 further regulated PS-NPs toxicity by modulating insulin communication between germline and intestine. Therefore, our data suggested that the CBP-1-mediated histone acetylation regulation in certain tissues is associated with the induction of protective response to PS-NPs in C. elegans.

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

Ion channels on cytoplasmic membrane function to sense various environmental stimuli. We here determined the changes of genes encoding ion channels in Caenorhabditis elegans after exposure to polystyrene nanoparticles (PS-NPs). Exposure to 1-1000 μg/L PS-NPs could increase expressions of egl-19, mec-10, trp-4, trp-2, tax-4, cca-1, unc-2, and unc-93, and decrease the expressions of cng-3, mec-6, ocr-2, deg-1, exc-4, kvs-1, and eat-2. Among these 15 ion channel genes, RNAi knockdown of cng-3 or eat-2 caused resistance to PS-NPs toxicity and RNAi knockdown of egl-19, cca-1, tax-4, or unc-93 induced susceptibility to PS-NPs toxicity, suggesting that cng-3, eat-2, egl-19, cca-1, tax-4, and unc-93 were involved in the control of PS-NPs toxicity. EGL-19 and CCA-1 functioned in intestinal cells to control PS-NPs toxicity, and CNG-3, EAT-2, EGL-19, TAX-4, and UNC-93 functioned in neuronal cells to control PS-NPs. Moreover, in intestinal cells of PS-NPs exposed worms, cca-1 RNAi knockdown decreased elt-2 expression, and egl-19 RNAi knockdown decreased daf-16 and elt-2 expressions. In neuronal cells of PS-NPs exposed worms, eat-2 RNAi knockdown increased jnk-1, mpk-1, and dbl-1 expressions, unc-93 RNAi knockdown decreased mpk-1 and daf-7 expressions, and tax-4 RNAi knockdown decreased jnk-1 and daf-7 expressions. Therefore, two molecular networks mediated by ion channels in intestinal cells and neuronal cells were dysregulated by PS-NPs exposure in C. elegans. Our data suggested that the dysregulation in expressions of these ion channels mediated a protective response to PS-NPs in the range of μg/L in worms.

Comparison of transgenerational reproductive toxicity induced by pristine and amino modified nanoplastics in Caenorhabditis elegans

Certain modifications can aggravate the toxicity of nanoplastics. However, the influence of surface amino modification on transgenerational impairment induced by nanoplastics remains largely unclear. Pristine nanopolystyrene (NPS) and amino modified NPS (NPS-NH₂) were used to determine their transgenerational toxicity in Caenorhabditis elegans. Exposure to 100 μg/L pristine NPS in parents (P0) cause a decrease in reproductive capacity in the F1-F3 generations and the damage on gonad development in the F1-F2 generations. In contrast, exposure to 10 μg/L NPS-NH₂ caused toxicity on reproductive capacity and gonad development in the F1 generation. The toxic effects of NPS-NH₂ on reproductive capacity and gonad development in the F1-F3 generations were more severe than those of pristine NPS. Moreover, amino modification could increase transgenerational toxicity of NPS in inducing apoptosis of germline and in affecting expressions of ced-1, ced-4, and ced-9. Our data demonstrate that surface modification of NPS with amino groups enhances transgenerational reproductive toxicity of NPS in C. elegans.

Induction of protective response to polystyrene nanoparticles associated with methylation regulation in Caenorhabditis elegans

The epigenetic regulation mechanisms for toxicity induction of nanoplastics in organisms remain largely unknown. In Caenorhabditis elegans, we found that prolonged exposure to 1-100 μg/L polystyrene nanoparticles (PS-NPs) decreased expression of MET-2, a H3K9 methyltransferase. Meanwhile, RNAi knockdown of met-2 suppressed the PS-NPs toxicity in inducing production of reactive oxygen species (ROS) and in decreasing locomotion behavior, which suggesting that the decrease in MET-2 expression reflected a protective response. This resistance to PS-NPs toxicity could be further detected in worms with met-2 RNAi knockdown in both intestinal cells and germline cells. In PS-NPs exposed worms, intestinal RNAi knockdown of met-2 significantly increased expressions of daf-16, bar-1, and elt-2. Intestinal RNAi knockdown of daf-16, bar-1, or elt-2 suppressed the resistance of met-2(RNAi) worms to PS-NPs toxicity, suggesting that MET-2 functioned upstream of ELT-2, BAR-1, and DAF-16 in intestinal cells to control PS-NPs toxicity. Moreover, in PS-NPs exposed worms, germline RNAi knockdown of met-2 significantly decreased expressions of wrt-3 and pat-12. RNAi knockdown of wrt-3 or pat-12 further inhibited the susceptibility of worms overexpressing germline MET-2 to PS-NPs toxicity, suggesting that MET-2 functioned upstream of PAT-12 and WRT-3 in germline cells to control PS-NPs toxicity. Therefore, our data provided an important molecular basis for MET-2-mediated methylation regulation in causing protective response to nanoplastics in organisms.

Induction of protective response to polystyrene nanoparticles associated with dysregulation of intestinal long non-coding RNAs in Caenorhabditis elegans

Intestinal barrier plays a crucial function during the response to polystyrene nanoparticles (PS-NPs) in nematode Caenorhabditis elegans. Long non-coding RNAs (lncRNAs) are involved in the control of various biological processes, including stress response. We here used C. elegans to determine intestinal lncRNAs dysregulated by PS-NPs (1-100 μg/L). In intestine of PS-NPs exposed worms, we found four lncRNAs (linc-61, linc-50, linc-9, and linc-2) in response to PS-NPs and with the function in controlling PS-NPs toxicity. The alteration in expressions of these four intestinal lncRNAs reflected a protective response to PS-NPs exposure. During the response to PS-NPs, limited number of transcriptional factors functioned as the downstream targets of these four lncRNAs. linc-2 acted upstream of DAF-16, linc-9 acted upstream of NHR-77, linc-50 functioned upstream of DAF-16, and linc-61 regulated the functions of DAF-16, DVE-1, and FKH-2 to control PS-NPs toxicity. The obtained data demonstrated the important role of lncRNAs in intestinal barrier to mediate a protective response to PS-NPs exposure at low concentrations.

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.

Intestinal mitochondrial unfolded protein response induced by nanoplastic particles in Caenorhabditis elegans

In organisms, activation of mitochondrial unfolded protein response (mt UPR) provides the protective strategy against toxicity of environmental exposures. The aim of this study was to determine the activation of intestinal mt UPR and the underlying mechanisms in nanopolystyrene (100 nm) exposed Caenorhabditis elegans. The exposure was performed from L1-larvae for approximately 6.5-day. Activation of mt UPR as reflected by expressions of both HSP-6::GFP and hsp-6 in the intestine could be detected in nanopolystyrene (1-100 μg/L) exposed nematodes. Meanwhile, the susceptibility to nanoplastic toxicity was observed in hsp-6(RNAi) nematodes, suggesting the protective function of intestinal activation of mt UPR. After nanoplastic exposure, the activation of intestinal mt UPR was due to increase in expressions of ATFS-1, UBL-5, and DVE-1. Moreover, the activations of intestinal mt UPR mediated by ATFS-1, DVE-1, and UBL-5 was under the control of ELT-2 signaling, Wnt signaling, and insulin signaling, respectively. In the intestine, UBL-5, DVE-1, and ATFS-1 functioned in different pathways to control nanoplastic toxicity. Therefore, we provide an important molecular network of mt UPR activation in intestine of nematodes against the nanoplastic toxicity. Our findings highlight the importance of mt UPR activation in mediating a protective response to nanoplastics at low concentrations in organisms.

Intestinal long non-coding RNAs in response to simulated microgravity stress in Caenorhabditis elegans

Long non-coding RNAs (lncRNAs) are important in regulating the response to environmental stresses in organisms. In this study, we used Caenorhabditis elegans as an animal model to determine the functions of intestinal lncRNAs in regulating response to simulated microgravity stress. Among the intestinal lncRNAs, linc-2, linc-46, linc-61, and linc-78 were increased by simulated microgravity treatment, and linc-13, linc-14, linc-50, and linc-125 were decreased by simulated microgravity treatment. Among these 8 intestinal lncRNAs, RNAi knockdown of linc-2 or linc-61 induced a susceptibility to toxicity of simulated microgravity, whereas RNAi knockdown of linc-13, linc-14, or linc-50 induced a resistance to toxicity of simulated microgravity. In simulated microgravity treated nematodes, linc-50 potentially binds to three transcriptional factors (DAF-16, SKN-1, and HLH-30). RNAi knockdown of daf-16, skn-1, or hlh-30 could suppress resistance of linc-50(RNAi) nematodes to the toxicity of simulated microgravity. Therefore, our results provide an important basis for intestinal lncRNAs, such as the linc-50, in regulating the response to simulated microgravity in nematodes.

Epigenetic response to nanopolystyrene in germline of nematode Caenorhabditis elegans

microRNAs (miRNAs) provide an epigenetic regulation mechanism for the response to environmental toxicants. mir-38, a germline miRNA, was increased by exposure to nanopolystyrene (100 nm). In this study, we further found that germline overexpression of mir-38 decreased expressions of nhl-2 encoding a miRISC cofactor, ndk-1 encoding a homolog of NM23-H1, and wrt-3 encoding a homolog of PPIL-2. Meanwhile, germline-specific RNAi knockdown of nhl-2, ndk-1, or wrt-3 caused the resistance to nanopolystyrene toxicity. Additionally, mir-38 overexpression suppressed the resistance of nematodes overexpressing germline nhl-2, ndk-1, or wrt-3 containing 3'UTR, suggesting the role of NHL-2, NDK-1, and WRT-3 as the targets of germline mir-38 in regulating the response to nanopolystyrene. Moreover, during the control of response to nanopolystyrene, EKL-1, a Tudor domain protein, was identified as the downstream target of germline NHL-2, kinase suppressors of Ras (KSR-1 and KSR-2) were identified as the downstream targets of germline NDK-1, and ASP-2, a homolog of BACE1, was identified as the downstream target of germline WRT-3. Our results raised a mir-38-mediated molecular network in the germline in response to nanopolystyrene in nematodes. Our data provided an important basis for our understanding the response of germline of organisms to nanoplastic exposure.

microRNAs involved in the control of toxicity on locomotion behavior induced by simulated microgravity stress in Caenorhabditis elegans

microRNAs (miRNAs) post-transcriptionally regulate the expression of targeted genes. We here systematically identify miRNAs in response to simulated microgravity based on both expressions and functional analysis in Caenorhabditis elegans. After simulated microgravity treatment, we observed that 19 miRNAs (16 down-regulated and 3 up-regulated) were dysregulated. Among these dysregulated miRNAs, let-7, mir-54, mir-67, mir-85, mir-252, mir-354, mir-789, mir-2208, and mir-5592 were required for the toxicity induction of simulated microgravity in suppressing locomotion behavior. In nematodes, alteration in expressions of let-7, mir-67, mir-85, mir-252, mir-354, mir-789, mir-2208, and mir-5592 mediated a protective response to simulated microgravity, whereas alteration in mir-54 expression mediated the toxicity induction of simulated microgravity. Moreover, among these candidate miRNAs, let-7 regulated the toxicity of simulated microgravity by targeting and suppressing SKN-1/Nrf protein. In the intestine, a signaling cascade of SKN-1/Nrf-GST-4/GST-5/GST-7 required for the control of oxidative stress was identified to act downstream of let-7 to regulate the toxicity of simulated microgravity. Our data demonstrated the crucial function of miRNAs in regulating the toxicity of simulated microgravity stress in organisms. Moreover, our results further provided an important molecular basis for epigenetic control of toxicity of simulated microgravity.