Intestinal mir-794 responds to nanopolystyrene by linking insulin and p38 MAPK signaling pathways in nematode Caenorhabditis 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.

Nanoplastics: Focus on the role of microRNAs and long non-coding RNAs

When plastic objects in our surroundings are degraded, they may produce particles ranging in size from 1 to 100 nm therefore called nanoplastics. The environmental chemicals including nanoplastics may be able to affect biological processes in the nuclear level like altering DNA methylation and regulating microRNAs (miRNAs) as well as long non-coding RNAs (lncRNAs) expression and therefore are implicated in chronic human diseases like neoplasms. The regulatory role of miRNAs and lncRNAs in gene expression is appreciated. In vitro as well as in vivo experiments have shown that environmental elements including nanoplastics are able to dysregulate miRNAs and lncRNAs expression with possible genetic consequences that increase the risk of cancer development. In the current article, we review the biological effects of miRNAs and lncRNAs alterations following nanoplastics exposure.

Long-term exposure to nanoplastics alters molecular and functional traits related to the carcinogenic process

Micro/nanoplastics (MNPLs) are considered emergent pollutants widely spread over all environmental compartments. Although their potential biological effects are being intensively evaluated, many doubts remain about their potential health effects in humans. One of the most underdeveloped fields is the determination of the potential tumorigenic risk of MNPLs exposure. To shed light on this topic, we have designed a wide battery of different hallmarks of cancer applied to prone-to-transformed progress MEF cells exposed to polystyrene nanoplastics (PSNPLs) in the long term (6 months). Interestingly, most of the evaluated hallmarks of cancer are exacerbated after exposure, independently if they are associated with an early tumoral phenotype (changes in stress-related genes, or microRNA deregulation), advanced tumoral phenotype (growing independently of anchorage ability, and migration capacity), or an aggressive tumoral phenotype (invasion potential, changes in pluripotency markers, and ability to grow to form tumorspheres). This set of obtained data constitutes a relevant warning on the potential carcinogenic risk associated with long-term exposures to MNPLs, specifically that induced by the PSNPLs evaluated in this study.

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.

Untoward Effects of Micro- and Nanoplastics: An Expert Review of Their Biological Impact and Epigenetic Effects

The production of plastic has dramatically increased in the last 50 y. Because of their stability and durability, plastics are ubiquitously incorporated in both marine and terrestrial ecosystems. Plastic is acted upon by biological, chemical, and physical agents, leading to fragmentation into small pieces [i.e., microplastics (MPs) or nanoplastics (NPs)], classified depending on their size. MPs range from 0.1 to 5000 μm and NPs are fragments between 0.001 to 0.1 μm. MPs and, especially NPs, are easily incorporated into living beings via ingestion. The penetration of MPs and NPs into the food system is an important issue, for both food security and health risk assessment. Ingestion of different MPs and NPs has been associated with different issues in the intestine, such as direct physical damage, increased intestinal permeability, diminished microbiota diversity, and increases in local inflammatory response. However, the potential harmful effects of low-dose dietary plastic are still unclear. Some evidence indicates that intestinal uptake of plastic particles is relatively low and is mostly dependent on the particle's size. However, other evidence highlights that NPs dysregulate key molecular signaling pathways, modify the gut microbiota composition, and may induce important epigenetic changes, including transgenerational effects that might be involved in the onset of many different metabolic disorders. Until now, experiments have been mostly performed on marine organisms, Caenorhabditis elegans, and mouse models, but some research indicates accidental plastic dietary consumption by humans, raising the issue of detrimental health effects of MPs and NPs. This review discusses the impact that MPs and NPs could have on the intestinal tract and the biodistribution and systemic, cellular, and molecular levels. Accumulated evidence of MPs' effects on the human gut suggests that large exposure to MPs and NPs may have phenotypical untoward effects in humans, calling for urgent research in this field.

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.

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.

Response of G protein-coupled receptor CED-1 in germline to polystyrene nanoparticles in Caenorhabditis elegans

The deposition of a certain amount of nanopolystyrene (NPS) can be observed in the gonad of Caenorhabditis elegans. However, we still know little about the response of germline towards NPS exposure. In the germline of C. elegans, NPS (1-1000 μg L^-1) increased the expression levels of two G protein-coupled receptors (GPCRs), namely PAQR-2 and CED-1. Moreover, susceptibility to NPS toxicity was observed in ced-1(RNAi) worms, which suggested that the protective response of germline was mediated by GPCR CED-1. In the germline, five proteins (CED-10, VPS-34, SNX-1, RAB-7, and RAB-14) functioned as downstream targets of GPCR CED-1 in controlling NPS toxicity. Furthermore, these five targets in the germline regulated NPS toxicity by affecting the activities of p38 MAPK and insulin signaling pathways in intestinal cells. Therefore, we raised a GPCR CED-1-mediated signaling cascade in the germline in response to NPS exposure, which is helpful for understanding the molecular basis of the germline in response to NPS exposure.

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.

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.