Adverse effects, expression of defense-related genes, and oxidative stress-induced MAPK pathway in the benzo[α]pyrene-exposed rotifer Brachionus rotundiformis

Changes in life history parameters and expression of key genes of Brachionus plicatilis exposed to a combination of organic and inorganic ultraviolet filters

The increasing use of ultraviolet filters has become an emerging contaminant on the coast, posing potential ecological risks. Rotifers are essential components of marine ecosystems, serving as an association between primary producers and higher-level consumers. These organisms frequently encounter ultraviolet filters in coastal waters. This study aimed to assess the comprehensive effects of organic ultraviolet filters, specifically 2-ethylhexyl-4-methoxycinnamate (EHMC), and inorganic ultraviolet filters, namely, titanium dioxide nanoparticles (TiO2 NPs), on the rotifer Brachionus plicatilis. We exposed B. plicatilis to multiple combinations of different concentrations of EHMC and TiO2 NPs to observe changes in life history parameters and the expression of genes related to reproduction and antioxidant responses. Our findings indicated that increased EHMC concentrations significantly delayed the age at first reproduction, reduced the total offspring, and led to considerable alterations in the expression of genes associated with reproduction and stress. Exposure to TiO2 NPs resulted in earlier reproduction and decreased total offspring, although these changes were not synchronised in gene expression. The two ultraviolet filters had a significant interaction on the age at first reproduction and the total offspring of rotifer, with these interactions extending to the first generation. This research offers new insights into the comprehensive effects of different types of ultraviolet filters on rotifers by examining life history parameters and gene expression related to reproduction and stress, highlighting the importance of understanding the impacts of sunscreen products on zooplankton health.

Tangeretin Supplementation Mitigates the Aging Toxicity Induced by Dietary Benzo[a]pyrene Exposure with Aberrant Proteostasis and Heat Shock Responses in Caenorhabditis elegans

Benzo[a]pyrene (BaP) is a common food contaminant that can impair organismal aging. Tangeretin (TAN) may mitigate aging toxicities as a dietary supplement. This study used Caenorhabditis elegans to investigate the effects of chronic exposure to BaP on aging and to determine whether TAN supplementation could alleviate BaP-induced toxicity. Early life exposure to BaP (10 μM) significantly inhibited growth by 5%, and exposure to 0.1 to 10 μM BaP impaired C. elegans motility, resulting in a 3.4-6.5% reduction in motility. Chronic exposure to BaP (10 μM) age-dependently aggravated aberrant protein aggregation (7% increase) and shortened the median lifespan of the worms from 20 to 16 days. In addition, BaP worsened the age-dependent decline in motility and pharyngeal pumping, as well as the accumulation of reactive oxygen species. Furthermore, exposure to BaP resulted in significantly higher relative transcript levels of approximately 1.8-2.0-fold for the hsp-16.1, hsp-16.2, hsp-16.49, and hsp-70 genes. Stressed worms exposed to BaP exhibited significantly lower survival under heat stress. Dietary TAN supplementation alleviated the BaP-induced decline in motility, pumping, and poly-Q accumulation and restored heat shock proteins' transcript levels. Our findings suggest that chronic BaP exposure adversely affects aging and that TAN exposure mitigates the BaP-induced aging toxicity.

Molecular Mechanisms Associated with Protecting IEC-6 Cells from Acrylamide-Induced Tight Junction Damage by Ganoderma atrum Polysaccharide

SCOPE

The previous in vivo studies show Ganoderma atrum polysaccharide (PSG-F₂ ) has a protective effect against the acrylamide (AA)-induced intestinal oxidative damage in rats. Now, this study aims to explore the protective mechanism with IEC-6 cell model.

METHODS AND RESULTS

Based on RNA Sequencing (RNA-Seq), the study screens MAPK signaling pathway as one of the most crucial pathways for pretreatment with PSG-F₂   against AA-induced damage in IEC-6 cells. In total, six key MAPK signaling pathway-related proteins (p-P38/P38, p-ERK/ERK, and p-JNK/JNK), and three tight junction key proteins (Zonula Occludens protein-1, Claudin-1, and Occludin) are detected by Western blot and immunofluorescence, which verify the RNA-Seq data. Moreover, PD98059 interference inhibits critical proteins in the MAPK signaling pathway, thus uncovering the precise molecular mechanisms of MAPK/ERK signaling pathway involve in the protective effects of PSG-F₂ against AA-induced intestinal barrier damage.

CONCLUSION

These findings confirm that PSG-F₂ can be used as a daily dietary supplement to protect the intestinal cells from damage caused by thermal processing hazards AA.

Di(2-ethylhexyl) phthalate disturbs cholesterol metabolism through oxidative stress in rat liver

Di(2-ethylhexyl) phthalate (DEHP) is widely used and has been implicated in hepatotoxicity, although the mechanism is unclear. Here, we investigated the effect of DEHP on hepatic cholesterol metabolism in SD rats exposed to 0 and 300 mg/kg/day DEHP for 12 weeks. An RNA-Seq analysis was performed to describe the hepatic responses to long-term DEHP exposure in combination with serological and oxidative stress parameter measurements. DEHP increased the serum levels of total cholesterol (TC), high-density lipoprotein (HDL), and alanine transaminase (ALT). Moreover, DEHP increased the content of malondialdehyde (MDA) and decreased antioxidant enzyme activities in the liver. Transcriptomic results revealed that DEHP dramatically changed the cholesterol metabolism pathway and oxidation-reduction process and depressed gene expression involved in cholesterol efflux and monooxygenase activity. Total antioxidant capacity (T-AOC) positively correlated with Abcg5 and Abcg8. Overall, this study showed the mechanisms underlying hepatotoxicity caused by DEHP, providing new insights into understanding DEHP poisoning.

De-coupled phytoplankton growth and microzooplankton grazing in a simulated oil spill event in mesocosms

Microzooplankton (<200 μm) are essential intermediates between primary production and organisms at the higher trophic levels. Their ecological functions could be substantially affected by crude oil pollution. A natural plankton community was exposed to 10 μL L^-1 of chemically dispersed crude oil (DOil) in outdoor mesocosms for 7 days, with control (Ctrl) mesocosms set up for comparison. Dilution experiments were conducted to estimate the grazing rates of microzooplankton on the 2nd and 6th days of the pollutants exposure. Results showed 0.36-2.28 d^-1 microzooplankton grazing rates in the Ctrl mesocosms on both days but negative rates in the DOil mesocosms. A significant linear relationship between in situ phytoplankton growth and microzooplankton grazing rates was found in the Ctrl treatment but not in the DOil treatment. This suggests a de-coupling between phytoplankton growth and microzooplankton and the potential for the formation of phytoplankton blooms in seawater after an oil spill event.

Global expression response of genes in sex-undifferentiated Nile tilapia gonads after exposure to trace letrozole

The aromatase inhibitor letrozole can be found in rivers, effluents, and even drinking water. Studies have demonstrated that letrozole affects various metabolic pathways and may cause reproductive toxicity, especially in fish exposed during development. However, studies on the effect of a low concentration of letrozole at the whole-gonad transcriptomic level in the early stage of fish sexual development have not been investigated. The aim of our study was to explore the potential effects of a low concentration of letrozole on the gonad transcriptome of Nile tilapia at an early stage of sexual development. In this study, 9 dpf (days postfertilization) Nile tilapia were exposed to trace letrozole for 12 days. Letrozole exposure from 9 dpf to 21 dpf persistently altered phenotypic sex development and induced the male-biased sex ratio. The transcriptome results showed that 1173 differentially expressed genes (DEGs) were present in the female control vs 1.5 μg/L letrozole-treated female comparison group and that 1576 DEGs were present in the 1.5 μg/L letrozole-treated female vs male control comparison group. Differentially expressed gene enrichment analysis revealed several crucial pathways, including the drug metabolism-cytochrome P450 pathway, the ErbB-PI3K/Akt/mTOR pathway, and the calcium signalling pathway. Further analysis of these identified DEGs indicated that some key genes correlated with metabolism and epigenetic regulation were significantly affected by letrozole, such as UDP-glucuronosyltransferase (Ugt), glutathione S-transferase omega-1 (Gsto1), lysine-specific demethylase 6bb (Kdm6bb, original name is Kdm6a), jumonji and AT-rich interaction domain containing 2 (Jarid2b, original name is Jarid2), growth arrest and DNA damage inducible gamma (Gadd45g), and chromobox protein 7 (Cbx7). The qRT-PCR validation results for twelve DEGs showed that the Pearson's correlation of the log₁₀^{fold change} values between the qPCR and RNA-Seq results was 0.90, indicating the accuracy and reliability of the RNA-Seq results. Our study is the first to report the effect of letrozole on the transcriptome of gonads from fish during early-stage sexual development. These findings will be useful for understanding the toxic effects and molecular mechanisms of letrozole exposure at the early stage of gonad development on the sexual development of aquatic organisms.

NOD-like receptor signaling pathway activation: A potential mechanism underlying negative effects of benzo(α)pyrene on zebrafish

Benzo(α)pyrene (BaP) is one of typical polycyclic aromatic hydrocarbons (PAHs) in aquatic environments and has been shown to cause toxic effects to aquatic animals. Although the negative effects of BaP have been investigated, the potential toxic mechanisms remain uncharacterized. To explore the potential mechanisms mediating the toxic effects of BaP, zebrafish (Danio rerio) were exposed to BaP for 15 days and the toxic effects of BaP in zebrafish liver were investigated using physiological and transcriptomic analyses. After 15-day BaP exposure, zebrafish liver exhibited abnormalities including increased cytoplasmic vacuolation, inflammatory cell infiltration, swelled nuclei and irregular pigmentation. BaP exposure also induced oxidative stress to the liver of zebrafish. Transcriptomic profiles revealed 5129 differentially expressed genes (DEGs) after 15-days of BaP exposure, and the vast majority of DEGs were up-regulated under BaP treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggest that genes related to immune response were significantly dysregulated. Furthermore, the nucleotide-binding, oligomerization domain (NOD)-like receptor signaling pathway was significantly enriched and most of the genes in this pathway exhibited enhanced expression after BaP exposure. These results partially explained the mechanisms underlying the toxic effects of BaP on zebrafish liver. In conclusion, BaP has the potential to induce physiological responses in zebrafish liver through altering associated genes.

Molecular mechanisms of Mycoredoxin-1 in resistance to oxidative stress in Corynebacterium glutamicum

Glutaredoxins (Grxs) with Cys-Pro-Phe (Tyr)-Cys motif and a thioredoxin fold structure play an important role in the anti-oxidant system of bacteria by catalyzing a variety of thiol-disulfide exchange reactions with a 2-Cys mechanism or a 1-Cys mechanism. However, the catalytic and physiological mechanism of Corynebacterium glutamicum Mycoredoxin 1 (Mrx1) that shares a high amino acid sequence similarity to Grxs has not been fully elucidated. Here, we report that Mrx1 has a protective function against various adverse conditions, and the decrease of cell viability to various stress conditions by deletion of the Mrx1 in C. glutamicum was confirmed in the mrx1 mutant. The physiological roles of Mrx1 in defence to oxidative stress were corroborated by its induced expression under various stresses, regulated directly by the stress-responsive extracytoplasmic function-sigma (ECF-σ) factor SigH. As well as reducing mycothiol (MSH) mixed disulfide bonds via a 1-Cys mechanism, C. glutamicum Mrx1 catalytically reduced the disulfides in the Ib RNR, insulin and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) by exclusively linking the MSH/Mtr (mycothiol disulfide reductase)/NADPH electron pathway via a 2-Cys mechanism. Thus, we present the first evidence that the Mrx1 is able to protect against the damaging effects of various exogenous stresses by acting as a disulfide oxidoreductase, thereby giving a new insight in how C. glutamicum survives oxidative stressful conditions.

The genome of the marine monogonont rotifer Brachionus rotundiformis and insight into species-specific detoxification components in Brachionus spp

The monogonont rotifer Brachionus spp. have been widely used for ecotoxicological studies because of their advantages as one of the most suitable laboratory experimental species. In the present study, we obtained and assembled the whole genome sequence of the rotifer Brachionus rotundiformis, consisting of 13,612 annotated genes with 213 scaffolds and 58 Mb in total length. Focusing on ecotoxicological aspects, we conducted a comparative genome analysis on the gene families involved in detoxification, including four to six sulfotransferase gene families, seven uridine 5'-diphospho-glucuronosyltransferase gene families, and 58, 61, or 70 ATP-binding cassette genes in the genus Brachionus including Brachionus koreanus and Brachionus plicatilis. Our results suggest that these gene families have undergone a species- and/or lineage-specific evolution in response to the surrounding environmental pressure. Our genome resource for B. rotundiformis would be highly useful for future ecotoxicological studies and also provides a better understanding on the view of evolutionary mechanism of detoxification in the genus Brachionus spp.

Effects of temperature changes on life parameters, oxidative stress, and antioxidant defense system in the monogonont marine rotifer Brachionus plicatilis

Global warming is a big concern for all organisms and many efforts have been made to reveal the potential effects of temperature elevation on aquatic organisms. However, limited studies on molecular mechanistic approaches on physiological effects due to temperature changes are available. Here, we investigated the effects of temperature changes on life parameters (e.g., population growth [total number of rotifers], and lifespan), oxidative stress levels and antioxidant activities (e.g., glutathione S-transferase [GST], catalase [CAT], superoxide dismutase [SOD]) with expression levels in the monogonont marine rotifer Brachionus plicatilis. The changes in temperatures led to significant reduction (P < 0.05) in lifespan, possibly due to significant decrease (P < 0.05) in antioxidant activities, reducing the potential to cope with significant elevation in the temperature-induced oxidative stress in B. plicatilis. To further assess the actual induction and clearance of reactive oxygen species (ROS), N-acetyl-L-cysteine was used to examine whether the temperature-induced oxidative stress could be successfully scavenged. Furthermore, expression patterns of the antioxidant-related genes (GSTs, SODs, and CATs) were down- or upregulated (P < 0.05) in response to different temperatures in B. plicatilis. Overall, these findings indicate that ROS-mediated oxidative stress led to cellular damage and antioxidant defense system, resulting in deleterious effects on life parameters in rotifer.

The genome of the marine rotifer Brachionus koreanus sheds light on the antioxidative defense system in response to 2-ethyl-phenanthrene and piperonyl butoxide

BRACHIONUS: spp. (Rotifera: Monogononta) have been introduced as ecotoxicological model-organisms that are widely distributed in aquatic environments. Among the Brachionus spp., the monogonont rotifer Brachionus koreanus has been widely used for ecology, ecotoxicology, and evolution, thus, providing the whole genome data of B. koreanus is important for further understandings of in-depth molecular mechanisms. In this study, the completed assembly and characterization of the B. koreanus genome resulted in a total length of 85.7 Mb with 14,975 annotated genes. The final number of scaffolds was 567 with an N50 value and a GC content of 1.86 Mb and 24.35 %, respectively. Based on the fully constructed genome database, a total of 24 CYPs, 23 GSTs, two SODs, and a single CAT genes were identified and analyzed antioxidant activities (CAT, SOD, and GST), and transcriptional regulation of the entire CYPs, GSTs, SODs, and CAT in response to 2-ethyl-phenanthrene (2-ethyl-PHE) and piperonyl butoxide (PBO), to demonstrate the usefulness of the whole genome library of B. koreanus in response xenobiotic-induced oxidative stress. The assembled B. koreanus genome will provide a better understanding on the molecular ecotoxicology in the view of molecular mechanisms underlying toxicological responses, particularly on xenobiotic detoxification processes in the rotifer B. koreanus.