Molecular basis for oxidative stress induced by simulated microgravity in nematode Caenorhabditis elegans

Impact of modeled microgravity stress on innate immunity in a beneficial animal-microbe symbiosis

The innate immune response is the first line of defense for all animals to not only detect invading microbes and toxins but also sense and interface with the environment. One such environment that can significantly affect innate immunity is spaceflight. In this study, we explored the impact of microgravity stress on key elements of the NFκB innate immune pathway. The symbiosis between the bobtail squid Euprymna scolopes and its beneficial symbiont Vibrio fischeri was used as a model system under a simulated microgravity environment. The expression of genes associated with the NFκB pathway was monitored over time as the symbiosis progressed. Results revealed that although the onset of the symbiosis was the major driver in the differential expression of NFκB signaling, the stress of simulated low-shear microgravity also caused a dysregulation of expression. Several genes were expressed at earlier time points suggesting that elements of the E. scolopes NFκB pathway are stress-inducible, whereas expression of other pathway components was delayed. The results provide new insights into the role of NFκB signaling in the squid-vibrio symbiosis, and how the stress of microgravity negatively impacts the host immune response. Together, these results provide a foundation to develop mitigation strategies to maintain host-microbe homeostasis during spaceflight.

β-Carbolines norharman and harman change neurobehavior causing neurological damage in Caenorhabditis elegans

β-Carbolines norharman and harman, belonging to the class of heterocyclic aromatic amines (HAAs), are typical hazardous substances produced during the thermal processing of food. Compared to other HAAs, there have been limited reports on the toxicity of β-carbolines. Nevertheless, the current studies are concerned with the neurotoxic effects of norharman and harman at high doses. It is still unknown whether the relatively low dose of β-carbolines in foods induces neurotoxicity and the mechanism of the toxicity. In this study, C. elegans was exposed to a series of gradients of norharman and harman (0, 0.05, 5, and 10 mg L-1). The survival rate and indicators of ethology (locomotor behaviors, foraging behavior, and chemotaxis ability) were assessed. The antioxidant system and the contents of neurotransmitters, as well as the activity of acetylcholinesterase (AChE), were evaluated. Additionally, the RNA-seq screening of differentially expressed genes (DEGs) revealed the potential molecular mechanisms of norharman- and harman-induced toxic effects. Our results indicated that the risk of long-term exposure to norharman and harman at low doses (food-related doses) should be emphasized. Moreover, β-carbolines might induce neurotoxicity by causing oxidative damage, regulating the content of neurotransmitters, and interfering with cytochrome P450 metabolism. This study would provide a toxicological basis for the neurotoxicity of β-carbolines and lay the foundation for the risk assessment of endogenous pollutants in food.

Simulated microgravity-induced oxidative stress and loss of osteogenic potential of osteoblasts can be prevented by protection of primary cilia

Oxidative stress has been considered to be closely related to spaceflight-induced bone loss; however, mechanism is elusive and there are no effective countermeasures. Using cultured rat calvarial osteoblasts exposed to microgravity simulated by a random positioning machine, this study addressed the hypotheses that microgravity-induced shortening of primary cilia leads to oxidative stress and that primary cilium protection prevents oxidative stress and osteogenesis loss. Microgravity was found to induce oxidative stress (as represented by increased levels of reactive oxygen species (ROS) and malondialdehyde production, and decreased activities of antioxidant enzymes), which was perfectly replicated in osteoblasts growing in NG with abrogated primary cilia (created by transfection of an interfering RNA), suggesting the possibility that shortening of primary cilia leads to oxidative stress. Oxidative stress was accompanied by mitochondrial dysfunction (represented by increased mitochondrial ROS and decreased mitochondrial membrane potential) and intracellular Ca2+ overload, and the latter was found to be caused by increased activity of Ca2+ channel transient receptor potential vanilloid 4 (TRPV4), as also evidenced by TRPV4 agonist GSK1016790A-elicited Ca2+ influx. Supplementation of HC-067047, a specific antagonist of TRPV4, attenuated microgravity-induced mitochondrial dysfunction, oxidative stress, and osteogenesis loss. Although TRPV4 was found localized in primary cilia and expressed at low levels in NG, microgravity-induced shortening of primary cilia led to increased TRPV4 levels and Ca2+ influx. When primary cilia were protected by miR-129-3p overexpression or supplementation with a natural flavonoid moslosooflavone, microgravity-induced increased TRPV4 expression, mitochondrial dysfunction, oxidative stress, and osteogenesis loss were all prevented. Our data revealed a new mechanism that primary cilia function as a controller for TRPV4 expression. Microgravity-induced injury on primary cilia leads to increased expression and overactive channel of TRPV4, causing intracellular Ca2+ overload and oxidative stress, and primary cilium protection could be an effective countermeasure against microgravity-induced oxidative stress and loss of osteogenic potential of osteoblasts.

Caenorhabditis elegans in microgravity: An omics perspective

The application of omics to study Caenorhabditis elegans (C. elegans) in the context of spaceflight is increasing, illuminating the wide-ranging biological impacts of spaceflight on physiology. In this review, we highlight the application of omics, including transcriptomics, genomics, proteomics, multi-omics, and integrated omics in the study of spaceflown C. elegans, and discuss the impact, use, and future direction of this branch of research. We highlight the variety of molecular alterations that occur in response to spaceflight, most notably changes in metabolic and neuromuscular gene regulation. These transcriptional features are reproducible and evident across many spaceflown species (e.g., mice and astronauts), supporting the use of C. elegans as a model organism to study spaceflight physiology with translational capital. Integrating tissue-specific, spatial, and multi-omics approaches, which quantitatively link molecular responses to phenotypic adaptations, will facilitate the identification of candidate regulatory molecules for therapeutic intervention and thus represents the next frontiers in C. elegans space omics research.

Integration of proteome and metabolome profiling to reveal heat stress response and tolerance mechanisms of Serratia sp. AXJ-M for the bioremediation of papermaking black liquor

The use of thermophilic bacteria for treating paper black liquor seems to be an efficient bioremediation strategy. In our previous work, the lignin-degrading bacterium Serratia sp. AXJ-M exhibited excellent heat tolerance ability. However, the molecular mechanism of its response to heat stress is unknown. Therefore, the heat stress response of AXJ-M was investigated using morphological and analytical methods. A comparative genomics analysis revealed interesting insights into the adaptability of the genetic basis of AXJ-M to harsh environments. Moreover, TMT quantitative proteomic analysis and parallel reaction monitoring (PRM) assays revealed that proteins related to both component systems, ABC transporters, carbohydrate, and amino metabolism, energy metabolism, etc., were differentially expressed. The non-targeted metabolome analysis revealed that the metabolic pathways associated with the fatty acid and amino acid biosynthesis and metabolism, together with the TCA cycle were most significantly enriched. Furthermore, integrated omics suggested that AXJ-M made metabolic adaptations to compensate for the increased energy demand caused by adverse environmental stimuli. The dominant heat regulator HspQ mediated heat adaptation of AXJ-M at high temperatures and modulated DyP expression. To summarize, the present study sheds light on the effect of high temperature on the lignin-degrading bacterium and its tolerance and underlying regulatory mechanisms.

Ecotoxicity induced by total, water soluble and insoluble components of atmospheric fine particulate matter exposure in Caenorhabditis elegans

Although PM_2.5 could cause toxicity in environmental organisms, the toxicity difference of PM_2.5 under different solubilities is still poorly understood. To acquire a better knowledge of the ecotoxicity of PM_2.5 under different solubilities, the model animal Caenorhabditis elegans (C. elegans) was exposed to Total-PM_2.5, water insoluble components of PM_2.5 (WIS-PM_2.5) and water soluble components of PM_2.5 (WS-PM_2.5). The physiological (growth, locomotion behavior, and reproduction), biochemical (germline apoptosis, and reactive oxygen species (ROS) production) indices, and the related gene expression were examined. According to the findings, acute exposure to these three components caused adverse physiological effects on growth and locomotion behavior, and significantly induced germline apoptosis or ROS production. In contrast, prolonged exposure showed stronger adverse effects than acute exposure. Additionally, the results of multiple toxicological endpoints showed that the toxicity effects of WIS-PM_2.5 are more intense than WS-PM_2.5, which means that insoluble components contributed more to the toxicity of PM_2.5. Prolonged exposure to 1000 mg/L WS-PM_2.5, WIS-PM_2.5, and Total-PM_2.5 dramatically altered the expression of stress-related genes, which further indicated that apoptosis, DNA damage and oxidative stress play a crucial part in toxicity induced by PM_2.5.

Prominent toxicity of isocyanates and maleic anhydrides to Caenorhabditis elegans: Multilevel assay for typical organic additives of biodegradable plastics

Biodegradable plastics (BDP) are increasingly applied; however, there has been of concerns about their environmental safety, especially from nondegradable additive compositions. Until now, data of ecotoxicity of BDP additives is scarce. Here, nematode C. elegans was used to comparatively evaluate toxicity of an isocyanate additive, i.e., Hexamethylene diisocyanate (HDI), a maleic anhydride, i.e., Diallyl maleate (DIM), and other four BDP organic additives. These additives caused lethality of nematodes at µg L^-1 level, of lowest LC₅₀ value of HDI/DIM. Uniform exposure to these additives resulted in various degrees of inhibitions in body volumes and longevity, indicating developmental toxicity. Moreover, BDP additives induced significant elevations of gst-4 expression, especially mean 123.54 %/234.29 % increase in HDI/DIM group, but reduced ges-1 expression, which indicates oxidative damages and mitochondrial dysfunction. BDP additives further caused inhibition in locomotor and food intake/excretion behavior, and related damages of glutamatergic neurons and GABAergic neurons, indicating their neurotoxicity. We found HDI and DIM presented relatively strong effects on susceptible endpoints including lethality, gst-4, mean lifespan, food intake and excretion behavior. Overall, this study suggests prominent ecotoxic risk of isocyanates and maleic anhydrides as BDP additives, which is significant for the selection of environmentally friendly BDP additives.

Reproductive toxicity and underlying mechanisms of fine particulate matter (PM2.5) on Caenorhabditis elegans in different seasons

Although numerous studies have investigated that atmospheric fine particulate matter (PM_2.5) can be toxic to environmental organisms, the research on the reproductive toxicity of PM_2.5 is limited, and the key toxic components and underlying mechanisms remain unknown. In this work, PM_2.5 samples of four seasons in Nanjing from March 1, 2021, to February 28, 2022 were collected and the chemical components were analyzed. Caenorhabditis elegans (C. elegans) was employed to conduct the toxicological testing. The reproductive toxicity of PM_2.5 to C. elegans in different seasons was evaluated by multiple reproductive endpoints. Exposure to high concentrations of PM_2.5 significantly decreased the brood size and the number of fertilized eggs in utero. PM_2.5 exposure also increased the number of germ cell corpses and caused abnormal expression of apoptosis-related genes (ced-9, ced-4, and ced-3), which confirmed that PM_2.5 induced germline apoptosis. In addition, PM_2.5 exposure significantly increased the production of reactive oxygen species (ROS) in C. elegans and the fluorescence intensity of HUS-1 protein in of transgenic strain WS1433. Meanwhile, the expression of genes related to DNA damage (cep-1, clk-2, egl-1, and hus-1) and oxidative stress (mev-1, isp-1, and gas-1) also significantly altered in C. elegans, suggesting induction of DNA damage and oxidative stress. According to Pearson correlation analyses, DNA damage and oxidative stress were significantly correlated with multiple reproductive endpoints in C. elegans. Thus, it was speculated that PM_2.5 caused reproductive dysfunction and germ cell apoptosis in C. elegans may be by inducing ROS and DNA damage. In addition, heavy metals in PM_2.5 were significantly correlated with multiple endpoints at physiological and biochemical, suggesting that the heavy metals might be an important contributor to the reproductive toxicity induced by PM_2.5.

Integrating transcriptomics and behavior tests reveals how the C. elegans responds to copper induced aging

Copper (Cu) pollution in water and agricultural soil has always been a worldwide concern. This research aims to investigate the health effects of copper exposure on Caenorhabditis elegans (C. elegans) under the existing environmental quality standards (1 mg/L and 2 mg/L) via lifespan, reproduction, biological markers and transcriptome analysis. The results showed that copper of these two environmental standards shorten the lifespan of nematodes, reduced the brood size, reduced the frequency of pharyngeal pumps and prolonged defecation time as aging-related behaviors, and increased the levels of aging-related markers ROS, MDA and H₂O₂. There was a certain effect trend for the two exposure concentrations. Further, the possible molecular mechanism of copper-induced aging and reproductive effects on C. elegans was explored. Differential gene expression analysis was performed, and 2332 genes (567 up- and 1765 down-regulated genes) in the 1 mg/L group, 2449 DEGs (724 up- and 1725 down-regulated genes) in the 2 mg/L group in response to copper treatment. The top 20 regulated genes were vit (vit-1, vit-3, vit-4) genes, col genes (col-35, col-72, col-114, col-123, col-164, col-183, col-185), eea-1, him-18 and grl-20, which suggested that cuticle collagen synthesis and yolk expression were disrupted by copper. Analysis of KEGG pathway showed copper exposure widely affects longevity regulation pathways, thereby promoting aging. In summary, the sequencing results extensively and deeply reveal the health hazards of environmentally relevant doses of copper exposure to C. elegans, and behavioral testing verified that copper promoted aging of C. elegans.

Cerium Oxide Nanoparticle Administration to Skeletal Muscle Cells under Different Gravity and Radiation Conditions

For their remarkable biomimetic properties implying strong modulation of the intracellular and extracellular redox state, cerium oxide nanoparticles (also termed "nanoceria") were hypothesized to exert a protective role against oxidative stress associated with the harsh environmental conditions of spaceflight, characterized by microgravity and highly energetic radiations. Nanoparticles were supplied to proliferating C2C12 mouse skeletal muscle cells under different gravity and radiation levels. Biological responses were thus investigated at a transcriptional level by RNA next-generation sequencing. Lists of differentially expressed genes (DEGs) were generated and intersected by taking into consideration relevant comparisons, which led to the observation of prevailing effects of the space environment over those induced by nanoceria. In space, upregulation of transcription was slightly preponderant over downregulation, implying involvement of intracellular compartments, with the majority of DEGs consistently over- or under-expressed whenever present. Cosmic radiations regulated a higher number of DEGs than microgravity and seemed to promote increased cellular catabolism. By taking into consideration space physical stressors alone, microgravity and cosmic radiations appeared to have opposite effects at transcriptional levels despite partial sharing of molecular pathways. Interestingly, gene ontology denoted some enrichment in terms related to vision, when only effects of radiations were assessed. The transcriptional regulation of mitochondrial uncoupling protein 2 in space-relevant samples suggests perturbation of the intracellular redox homeostasis, and leaves open opportunities for antioxidant treatment for oxidative stress reduction in harsh environments.

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.

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.

Intergenerational toxicity of nonylphenol ethoxylate (NP-9) in Caenorhabditis elegans

The ethoxylated isomers of nonylphenol (NPEs, NP-9) are one of the main active ingredients present in nonionic surfactants employed as herbicides, cosmetics, paints, plastics, disinfectants and detergents. These chemicals and their metabolites are commonly found in environmental matrices. The aim of this work was to evaluate the intergenerational toxicity of NP-9 in Caenorhabditis elegans. The lethality, length, width, locomotion and lifespan were investigated in the larval stage L4 of the wild strain N2. Transgenic green fluorescent protein (GFP) strains were employed to estimate changes in relative gene expression. RT-qPCR was utilized to measure mRNA expression for neurotoxicity-related genes (unc-30, unc-25, dop-3, dat-1, mgl-1, and eat-4). Data were obtained from parent worms (P0) and the first generation (F1). Lethality of the nematode was concentration-dependent, with 48 h-LC₅₀ values of 3215 and 1983 μM in P0 and F1, respectively. Non-lethal concentrations of NP-9 reduced locomotion. Lifespan was also decreased by the xenobiotic, but the negative effect was greater in P0 than in F1. Non-monotonic concentration-response curves were observed for body length and width in both generations. The gene expression profile in P0 was different from that registered in F1, although the expression of sod-4, hsp-70, gpx-6 and mtl-2 increased with the surfactant concentration in both generations. None of the tested genes followed a classical concentration-neurotoxicity relationship. In P0, dopamine presented an inverted-U curve, while GABA and glutamate displayed a bimodal type. However, in F1, inverted U-shaped curves were revealed for these genes. In summary, NP-9 induced intergenerational responses in C. elegans through mechanisms involving ROS, and alterations of the GABA, glutamate, and dopamine pathways.

Assessment of nanopolystyrene toxicity under fungal infection condition in Caenorhabditis elegans

Due to the potential of release and accumulation in the environment, nanoplastics have attracted an increasing attention. In this study, we investigated the effect of exposure to nanopolystyrene (30 nm) in nematode Caenorhabditis elegans after the fungal infection. After Candida albicans infection, exposure to nanopolystyrene (10 and 100 μg/L) for 24-h could cause the more severe toxicity on lifespan and locomotion behavior compared with fungal infection alone. The more severe activation of oxidative stress and suppression of SOD-3:GFP expression and mitochondrial unfolded protein response (mt UPR) were associated with this observed toxicity enhancement induced by nanopolystyrene exposure. Moreover, the more severe C. albicans colony formation and suppression of innate immune response as indicated by the alteration in expression of anti-microbial genes (abf-2, cnc-4, cnc-7, and fipr-22/23) further contributed to the formation of this toxicity enhancement induced by nanopolystyrene exposure. Our results demonstrated that short-term exposure to nanopolystyrene in the range of μg/L potentially enhances the adverse effects of fungal infection on organisms.

Omics approach reveals perturbation of metabolism and phenotype in Caenorhabditis elegans triggered by perfluorinated compounds

Perfluorinated compounds (PFCs) are widely used in consumer products because of their remarkable endurance. However, their distinct stability prolongs degradation, resulting in bioaccumulation in the environment which is a severe environmental issue. Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are principal constituents in the PFCs. In this study, the potential toxic effects of PFOS and PFOA were evaluated by adopting an in vivo animal model, Caenorhabditis elegans (C. elegans). The uptake of PFCs was confirmed by the quantification of internal concentration in C. elegans. Metabolomics and lipidomics were applied along with reproduction assay and reactive oxygen species (ROS) assay. In the C. elegans exposed to PFOS and PFOA, amino acids including phenylalanine, tyrosine, and tryptophan, were significantly affected. Also, various species that belong to glycerophospholipids and triacylglycerol were perturbed in the exposed groups. The alteration patterns of the lipidome in PFOS and PFOA treated C. elegans were significantly different. Additionally, dichlorodihydrofluorescein diacetate (H₂DCFDA)-based ROS assay revealed increased internal ROS in PFOS (1.5 fold, p-value = 0.0067) and PFOA (1.46 fold, p-value = 0.0253) groups. Decrease in reproduction was confirmed in PFOS (0.53 fold, p-value < 0.0001) and PFOA (0.69 fold, p-value = 0.0003) by counting progeny. Collectively, our findings suggest that exposure to PFCs in C. elegans leads to perturbation of various phenotypes as well as crucial amino acid and lipid metabolism.

Response of canonical Wnt/β-catenin signaling pathway in the intestine to microgravity stress in Caenorhabditis elegans

Considering the short life-cycle property, Caenorhabditis elegans is a suitable animal model to evaluate the long-term effects of microgravity stress on organisms. Canonical Wnt/β-catenin signaling is evolutionarily conserved in various organisms. We here investigated the response of canonical Wnt/β-catenin signaling pathway to microgravity stress in nematodes. We observed the noticeable response of canonical Wnt/β-catenin signaling to microgravity stress. In contrast, we did not detect the obvious response of non-canonical Wnt/β-catenin signaling to microgravity stress. The canonical β-catenin BAR-1 acted in the intestine to regulate the response to simulated microgravity. Moreover, in the intestine, we identified a signaling cascade of canonical Wnt/β-catenin signaling pathway in response to simulated microgravity, and this signaling cascade contained Frizzled receptor MIG-1, Disheveled protein DSH-2, GSK3A/GSK-3, and β-catenin transcriptional factor BAR-1. Our data suggests an important protective response of canonical Wnt/β-catenin signaling to simulated microgravity in nematodes.

Damage on functional state of intestinal barrier by microgravity stress in nematode Caenorhabditis elegans

Due to short life cycle, nematode Caenorhabditis elegans is a suitable animal model for assessing the effect of long-term simulated microgravity treatment on organisms. We here investigated the effect of simulated microgravity treatment for 24-h on development and functional state of intestinal barrier in nematodes. Simulated microgravity treatment not only caused a broadened intestinal lumen, but also enhanced intestinal permeability. Intestinal overexpression of SOD-2, a mitochondrial Mn-SOD protein, prevented the damage on functional state of intestinal barrier by simulated microgravity and induced a resistance to toxicity of simulated microgravity, suggesting the crucial role of oxidative stress in inducing the damage on functional state of intestinal barrier in simulated microgravity treated nematodes. For the molecular basis of damage on functional state of intestinal barrier, we observed significant decrease in expressions of some genes (acs-22, erm-1, and hmp-2) required for maintenance of functional state of intestinal barrier in simulated microgravity treated nematodes. Our results highlight the potential of long-term simulated microgravity treatment in inducing intestinal damage in animals.

Mitochondrial Unfolded Protein Response to Microgravity Stress in Nematode Caenorhabditis elegans

Caenorhabditis elegans is useful for assessing biological effects of spaceflight and simulated microgravity. The molecular response of organisms to simulated microgravity is still largely unclear. Mitochondrial unfolded protein response (mt UPR) mediates a protective response against toxicity from environmental exposure in nematodes. Using HSP-6 and HSP-60 as markers of mt UPR, we observed a significant activation of mt UPR in simulated microgravity exposed nematodes. The increase in HSP-6 and HSP-60 expression mediated a protective response against toxicity of simulated microgravity. In simulated microgravity treated nematodes, mitochondria-localized ATP-binding cassette protein HAF-1 and homeodomain-containing transcriptional factor DVE-1 regulated the mt UPR activation. In the intestine, a signaling cascade of HAF-1/DVE-1-HSP-6/60 was required for control of toxicity of simulated microgravity. Therefore, our data suggested the important role of mt UPR activation against the toxicity of simulated microgravity in organisms.

Anti-aging effects of long-term space missions, estimated by heart rate variability

Reports that aging slows down in space prompted this investigation of anti-aging effects in humans by analyzing astronauts' heart rate variability (HRV). Ambulatory 48-hour electrocardiograms from 7 astronauts (42.1 ± 6.8 years; 6 men) 20.6 ± 2.7 days (ISS01) and 138.6 ± 21.8 days (ISS02) after launch were divided into 24-hour spans of relative lower or higher magnetic disturbance, based on geomagnetic measures in Tromso, Norway. Magnetic disturbances were significantly higher on disturbed than on quiet days (ISS01: 72.01 ± 33.82 versus 33.96 ± 17.90 nT, P = 0.0307; ISS02: 71.06 ± 51.52 versus 32.53 ± 27.27 nT, P = 0.0308). SDNNIDX was increased on disturbed days (by 5.5% during ISS01, P = 0.0110), as were other HRV indices during ISS02 (SDANN, 12.5%, P = 0.0243; Triangular Index, 8.4%, P = 0.0469; and TF-component, 17.2%, P = 0.0054), suggesting the action of an anti-aging or longevity effect. The effect on TF was stronger during light (12:00-17:00) than during darkness (0:00-05:00) (P = 0.0268). The brain default mode network (DMN) was activated, gauged by increases in the LF-band (9.7%, P = 0.0730) and MF1-band (9.9%, P = 0.0281). Magnetic changes in the magnetosphere can affect and enhance HRV indices in space, involving an anti-aging or longevity effect, probably in association with the brain DMN, in a light-dependent manner and/or with help from the circadian clock.

Dysregulation of let-7 by PEG modified graphene oxide in nematodes with deficit in epidermal barrier

In nematode Caenorhabditis elegans, epidermal RNA interference (RNAi) knockdown of bli-1 encoding a cuticular collagen caused the toxicity induction of GO-PEG (PEG surface modified graphene oxide). In this study, we further found that epidermal RNAi knockdown of bli-1 increased expression of a microRNA let-7, and let-7 mutation suppressed the susceptibility of bli-1(RNAi) nematodes to GO-PEG toxicity. let-7 regulated the toxicity induction of GO-PEG by suppressing expression and function of its direct targets (HBL-1 and LIN-41). Like the nematodes with epidermal RNAi knockdown of bli-1, epidermal RNAi knockdown of hbl-1 or lin-41 also induced functional abnormality in epidermal barrier. Therefore, a signaling cascade of BLI-1-let-7-HBL-1/LIN-41 was raised to be involved in GO-PEG toxicity induction. Our data imply the dysregulation of let-7-mediated molecular machinery for developmental timing control by GO-PEG in nematodes with deficit in epidermal barrier caused by bli-1(RNAi).

Using acs-22 mutant Caenorhabditis elegans to detect the toxicity of nanopolystyrene particles

In this study, we employed Caenorhabditis elegans with acs-22 mutation to examine the in vivo effect of functional deficit in intestinal barrier on toxicity and translocation of nanopolystyrene particles. Mutation of acs-22 leads to deficit in intestinal barrier. After prolonged exposure, nanopolystyrene particles at concentrations ≥1 μg/L could cause toxicity on acs-22 mutant nematodes. acs-22 mutation resulted in translocation of nanopolystyrene particles into targeted organs through intestinal barrier in nanopolystyrene particles (1 μg/L) exposed nematodes. After prolonged exposure, nanopolystyrene particles (1 μg/L) dysregulated expressions of some genes required for the control of oxidative stress and activated expression of Nrf signaling pathway. Therefore, under certain pathological conditions, our results suggest the potential toxicity of nanoplastic particles at predicted environmental concentration on organisms after long-term exposure.

Di (2-ethylhexyl) phthalate-induced reproductive toxicity involved in dna damage-dependent oocyte apoptosis and oxidative stress in Caenorhabditis elegans

Di-(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer with a high environmental exposure level. As a persistent organic pollutant, DEHP causes reproductive and developmental toxicity in mammals. In this paper, the reproductive toxicity of DEHP was discussed using the model organism Caenorhabditis elegans to determine the sensitivity indices for evaluating the ecotoxicological effects of DEHP. L4 C. elegans larvae to evaluate the LC50 of DEHP and the changes in brood size and generation time, we found that the LC50 of DEHP to C. elegans exceeded 100 mg/L. And 10 mg/L DEHP exposure significantly reduced the brood sizes but not the generation time. Results of oocyte and distal-tip cell (DTC) counting suggested that the number of oocytes were decreased and apoptotic cells that from the unilateral gonad arm were increased in the 1 mg/L and 10 mg/L DEHP exposed groups. In contrast, there was no significant difference in the fluorescence intensity of DTC. Fluorescence analysis of HUS-1 showed that HUS-1 protein was overexpressed after DEHP exposure. The H₂O₂ level and DNA damage were measured by Bradford protein assay and AP staining respectively. The results showed that there was no significant difference in H₂O₂ level after DEHP exposure, in contrast, DNA damage was increased significantly. Moreover, 10 mg/L concentration DEHP exposure significantly increased the expression levels of apoptosis-related genes cep-1, egl-1, ced-4, and ced-3 and decreased the expression levels of ced-9. It suggested that cep-1, egl-1, ced-4, and ced-3 genes promote apoptosis and the ced-9 gene inhibits apoptosis. Meanwhile, 10 mg/L concentration DEHP exposure decreased the expression of oxidative stress-related genes mev-1 and gas-1. The mev-1 and gas-1 are mainly involved in the inhibition of oxidative stress in nematodes. In short, the decreased oocyte numbers and increased apoptosis oocyte numbers in C. elegans when exposed to DEHP, which may involve in the DNA damage induced by oxidative stress.

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

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

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

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

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

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

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

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

Regulation of the Response of Caenorhabditis elegans to Simulated Microgravity by p38 Mitogen-Activated Protein Kinase Signaling

The in vivo function of p38 mitogen-activated protein kinase (MAPK) signaling in regulating the response to simulated microgravity is still largely unclear. Using Caenorhabditis elegans as an assay system, we investigated the in vivo function of p38 MAPK signaling in regulating the response of animals to simulated microgravity and the underlying molecular mechanism. Simulated microgravity treatment significantly increased the transcriptional expressions of genes (pmk-1, sek-1, and nsy-1) encoding core p38 MAPK signaling pathway and the expression of phosphorylated PMK-1/p38 MAPK. The pmk-1, sek-1, or nsy-1 mutant was susceptible to adverse effects of simulated microgravity. The intestine-specific activity of PMK-1 was required for its function in regulating the response to simulated microgravity, and the entire p38 MAPK signaling pathway could act in the intestine to regulate the response to simulated microgravity. In the intestine, SKN-1 and ATF-7, two transcriptional factors, were identified as downstream targets for PMK-1 in regulating the response to simulated microgravity. Therefore, the activation of p38 MAPK signaling may mediate a protection mechanism for nematodes against the adverse effects of simulated microgravity. Additionally, our results highlight the potential crucial role of intestinal cells in response to simulated microgravity in nematodes.