Molecular evidence for the existence of an aryl hydrocarbon receptor pathway in scallops Chlamys farreri

Molecular responses of Mytilus coruscus hemocytes to lipopolysaccharide and peptidoglycan as revealed by 4D-DIA based quantitative proteomics analysis

Mytilus are sessile filter feeders that live in close contact with numerous marine microorganisms. Hemocytes, the immunocompetent cells of Mytilus, participate in the immune response in a very efficient manner. Lipopolysaccharide (LPS) and peptidoglycan (PGN) follow specific microbe/pathogen-associated molecular patterns (MAMPs or PAMPs) and are involved in immune stimulation in host cells. This study evaluated the molecular profiles and reactions at protein level of Mytilus hemocytes after stimulation with LPS and PGN. Mytilus coruscus was challenged in vivo with LPS and PGN. The hemocytes were collected after 48 h and analyzed for quantitative proteomics, cell subpopulations, and the free amino acid composition. 4D-DIA technology-based proteomic analysis revealed different protein profiles, as well as different responses at protein level, under either the LPS or PGN challenge. C-type lectins, collagens, and CD151 protein were highly upregulated in LPS-challenged mussels, while phospholipase A2 and dCMP deaminase were highly upregulated in PGN-challenged mussels. Moreover, LPS challenge disrupted dsRNA-mediated translation and stimulated energy-related metabolism, while PGN challenge stimulated proteins involved in the inflammatory response and suppressed amino acid metabolism. In addition, the LPS and PGN challenges differed in their effects on the free amino acid composition and granulocytes ratio of the hemocytes. These findings highlight the different strategies employed by mussel hemocytes in response to different MAMPs, providing insights into the effects of LPS and PGN on Mytilus.

Molecular Evolution of Aryl Hydrocarbon Receptor Signaling Pathway Genes

The Aryl hydrocarbon receptor is an ancient transcriptional factor originally discovered as a sensor of dioxin. In addition to its function as a receptor of environmental toxicants, it plays an important role in development. Although a significant amount of research has been carried out to understand the AHR signal transduction pathway and its involvement in species' susceptibility to environmental toxicants, none of them to date has comprehensively studied its evolutionary origins. Studying the evolutionary origins of molecules can inform ancestral relationships of genes. The vertebrate genome has been shaped by two rounds of whole-genome duplications (WGD) at the base of vertebrate evolution approximately 600 million years ago, followed by lineage-specific gene losses, which often complicate the assignment of orthology. It is crucial to understand the evolutionary origins of this transcription factor and its partners, to distinguish orthologs from ancient non-orthologous homologs. In this study, we have investigated the evolutionary origins of proteins involved in the AHR pathway. Our results provide evidence of gene loss and duplications, crucial for understanding the functional connectivity of humans and model species. Multiple studies have shown that 2R-ohnologs (genes and proteins that have survived from the 2R-WGD) are enriched in signaling components relevant to developmental disorders and cancer. Our findings provide a link between the AHR pathway's evolutionary trajectory and its potential mechanistic involvement in pathogenesis.

Bioaccumulation, Detoxification, and Biological Macromolecular Damage of Benzo[a]pyrene in Exposure in Tissues and Subcellular Fractions of Scallop Chlamys farreri

Because of the persistence and high toxicity of benzo[a]pyrene (B[a]P), the bioaccumulation and detoxification mechanisms of B[a]P have been studied extensively at the tissue level; but the data at the subcellular level in bivalves have not been reported. The present study was conducted to investigate the effects of B[a]P exposure on bioaccumulation, detoxification, and biomacromolecular damage in gills, digestive glands, and their subcellular fractions of the scallop Chlamys farreri. The subcellular fraction contains cytoplasm, mitochondria, microsome, nucleus, cell membrane, and overall organelle. The results demonstrated that B[a]P accumulation showed a clear time-dose effect. Based on the time-dependent accumulation of B[a]P in subcellular fractions, we speculated that the intracellular migration order of B[a]P was cell membrane, organelle, and nucleus in turn. Considering the difference of B[a]P accumulation may be related to B[a]P metabolism, we have further confirmed that the activities of B[a]P metabolizing enzymes in scallop tissues and subcellular fractions were significantly tempted by B[a]P (p < 0.05), including 7-ethoxyresorufin O-deethylase (increased), glutathione-S-transferase (GST; decreased), and superoxide dismutase (increased). First, GST was detected in bivalve cytoplasm and microsome. Second, B[a]P exposure also caused biomacromolecules damage. The results demonstrated that mitochondria and microsome were more vulnerable to lipid peroxidation than cell membrane and nucleus. Taken together, the present study fills some of the gaps in our knowledge of the bioaccumulation and detoxification mechanisms of C. farreri exposed to B[a]P in subcellular fractions and deeply explores the transportation and the main metabolic and damage sites of polycyclic aromatic hydrocarbons (PAHs) in cells, which helped us to comprehensively understand the toxic mechanism of PAHs on bivalves. Environ Toxicol Chem 2022;41:2353-2364. © 2022 SETAC.

Identification of Modulators of the C. elegans Aryl Hydrocarbon Receptor and Characterization of Transcriptomic and Metabolic AhR-1 Profiles

The Aryl hydrocarbon Receptor (AhR) is a xenobiotic sensor in vertebrates, regulating the metabolism of its own ligands. However, no ligand has been identified to date for any AhR in invertebrates. In C.&nbsp;elegans, the AhR ortholog, AHR-1, displays physiological functions. Therefore, we compared the transcriptomic and metabolic profiles of worms expressing AHR-1 or not and investigated the putative panel of chemical AHR-1 modulators. The metabolomic profiling indicated a role for AHR-1 in amino acids, carbohydrates, and fatty acids metabolism. The transcriptional profiling in neurons expressing AHR-1, identified 95 down-regulated genes and 76 up-regulated genes associated with neuronal and metabolic functions in the nervous system. A gene reporter system allowed us to identify several AHR-1 modulators including bacterial, dietary, or environmental compounds. These results shed new light on the biological functions of AHR-1 in C.&nbsp;elegans and perspectives on the evolution of the AhR functions across species.

An insight on microbial degradation of benzo[a]pyrene: current status and advances in research

Benzo[a]pyrene (BaP) is a high molecular weight polycyclic aromatic hydrocarbon produced as a result of incomplete combustion of organic substances. Over the years, the release of BaP in the atmosphere has increased rapidly, risking human lives. BaP can form bonds with DNA leading to the formation of DNA adducts thereby causing cancer. Therefore addressing the problem of its removal from the environment is quite pertinent though it calls for a very cumbersome and tedious process owing to its recalcitrant nature. To resolve such issues many efforts have been made to develop physical and chemical technologies of BaP degradation which have neither been cost-effective nor eco-friendly. Microbial degradation of BaP, on the other hand, has gained much attention due to added advantage of the high level of microbial diversity enabling great potential to degrade the substance without impairing environmental sustainability. Microorganisms produce enzymes like oxygenases, hydrolases and cytochrome P450 that enable BaP degradation. However, microbial degradation of BaP is restricted due to several factors related to its bio-availability and soil properties. Technologies like bio-augmentation and bio-stimulation have served to enhance the degradation rate of BaP. Besides, advanced technologies such as omics and nano-technology have opened new doors for a better future of microbial degradation of BaP and related compounds.

Lycopene Preventing DEHP-Induced Renal Cell Damage Is Targeted by Aryl Hydrocarbon Receptor

Di (2-ethylhexyl) phthalate (DEHP) is an environmentally persistent and bioaccumulative plasticizer. Accumulation of DEHP in the body can eventually cause kidney damage. As a type of natural carotenoid, lycopene (LYC) has a potential protective effect on renal cells, but the protective mechanism has not yet been elucidated. The major goal of this study was to see how effective LYC was at treating DEHP-induced nephrotoxicity in mice. ICR mice were treated with DEHP (500 mg/kg BW/day or 1000 mg/kg BW/day) or LYC (5 mg/kg BW/day) for 28 days. Through histopathology and ultrastructure, we found that LYC attenuated DEHP-induced renal tubular cell and glomerular damage. LYC relieved DEHP-induced kidney injury evidenced by lower levels of blood urea nitrogen (Bun), creatinine (Cre), and uric acid (Uric). Meanwhile, the reduced expression of kidney injury molecule-1 (Kim-1) also supported it. Notably, LYC can alleviate the activity or content of cytochrome P450 system (CYP450s) interfered with by DEHP. In addition, LYC treatment reduced nuclear accumulation of DEHP-induced aromatic hydrocarbon receptor (AhR) and AhR nuclear transporter (Arnt), and its downstream target genes such as cytochrome P450-dependent monooxygenase (CYP) 1A1, 1A2, and 1B1 expression significantly decreased to normal in the LYC treatment group. In summary, LYC can mediate the AhR/Arnt signaling system to prevent kidney toxicity in mice caused by DEHP exposure.

Effects of Nrf2-Keap1 signaling pathway on antioxidant defense system and oxidative damage in the clams Ruditapes philippinarum exposure to PAHs

NF-E2-related factor 2 (Nrf2) is a master regulator of antioxidant defense system which can maintain the oxidation balance in the cell. In our previous study, we first cloned the Nrf2 gene in clams and preliminarily explored the role of the Nrf2 at the transcription level. In this study, RNA interference (RNAi) technology was used to interfere with the expression of Nrf2 after being exposed to benzo(a)pyrene (BaP) for 5 days to verify the role of Nrf2 in the antioxidant defense system. Besides, we examined the mRNA expression and enzyme activities of antioxidases and the oxidative damage. The positive correlations between the Nrf2 with the mRNA expression and the enzyme activities of antioxidases indicated that Nrf2 was required for the induction of these antioxidant genes. Additionally, the mRNA expression and the enzyme activities of the glutathione peroxidase (GPx) in the Nrf2-dsRNA group were significantly higher than those in the control groups on the fifth day, indicating that the GPx is more sensitive to oxidative stress. Moreover, the oxidative damage in the RpNrf2-dsRNA group was markedly increased than control groups, indicating that Nrf2 transcriptional regulation may play an essential role in defending against oxidative damage. This study provides a foundation for further research on the mechanism of detoxification and antioxidation of polycyclic aromatic hydrocarbons (PAHs) in the clams at the transcription level and the protein level.

Study on the AhR signaling pathway and phase II detoxification metabolic enzymes isoforms in scallop Chlamys farreri exposed to single and mixtures of PAHs

This study aimed to investigate the detoxification metabolism responses in scallop Chlamys farreri exposed to phenanthrene (PHE), chrysene (CHR), benzo[a]pyrene (B[a]P) and PHE + CHR + B[a]P for 15 days under laboratory conditions. The mRNA expression levels of AhR signaling pathway (AhR, HSP90, XAP2 and ARNT), detoxification system (phase I: CYP1A1 and CYP1B1; phase II: SULTs, UGT and GSTs) and ATP-binding cassette transporters (phase 0: ABCB1 and phase III: ABCC1, ABCG2) in digestive glands of scallops exposed to PHE (0.7, 2.1 μg/L), CHR (0.7, 2.1 μg/L), B[a]P (0.7, 2.1 μg/L), and PHE + CHR + B[a]P (0.7 + 0.7 +0.7, 2.1 + 2.1 + 2.1 μg/L) were detected. In present study, key genes (AhR, HSP90, XAP2 and ARNT) of the AhR signaling pathway can be significantly induced by pollutants, suggesting that the AhR/ARNT signaling pathway plays a role directly or indirectly. AhR, HSP90 and ARNT reached the maximum value on day 6, which can be preliminarily understood as the synchronization of their functions. Besides, the results also indicated that different genes had specific response to different pollution exposure. CYP1B1, GST-2, GST-omega and GST-microsomal could be potional indexes to PHE, ARNT, GST-sigma 2 and GST-3 were sensitive to CHR exposure, HSP90, GST-theta and ABCG2 were considered as potional indexes to BaP while CYP1A1 and UGT were possible to be indexes for monitoring the mix exposure of these three PAHs. These findings in C. farreri suggested that phase II detoxification metabolic enzymes isoforms played an essential role in detoxification mechanisms and mRNA expression levels of specific SULTs, UGTs and GSTs were potentially to be ideal indexes in PAHs pollution research. In summary, this study provides more valuable information for the risk assessments of different rings of PAHs.

First evidence of transcriptional modulation by chlorothalonil in mussels Perna perna

Gills are considered a key player in organism defenses against environmental pollutants. Since it is the major site of uptake of waterborne chemicals, the modulation of important cellular defenses is expected in this tissue. Chlorothalonil, a fungicide presented in herbicides and antifouling paints, might be responsible for toxicity in marine biota. In this context, mussels were exposed to 0.1 μgL^-1 and 10 μgL^-1 of chlorothalonil for 24 h and 96 h. Genes from biotransformation and antioxidant defense pathways were investigated. Overall, we report, for the first time, an increase in the transcripts of the AhR-like, SULT1A1-like, CYP1A2-like, GSTO-like, MGST-like and SOD-like genes in the gills of the brown mussel Perna perna. This up-regulation was observed mostly after 96 h of exposure to chlorothalonil. Those results reinforce the important role of gills in xenobiotic metabolism and suggest the involvement of the mentioned genes in the detoxification of the compound. Throughout biotransformation and antioxidant defenses pathway, mussels exposed to chlorothalonil are activating mechanisms of defense against this contaminant.

The molecular mechanism of AhR-ARNT-XREs signaling pathway in the detoxification response induced by polycyclic aromatic hydrocarbons (PAHs) in clam Ruditapes philippinarum

The aryl hydrocarbon receptor (AhR) has been known primarily for its role in the regulation of several drug and xenobiotic metabolizing enzymes to mitigate environmental stresses. In this study, we interfere the expression of AhR gene to investigate the mechanism of AhR signaling pathway in the detoxification and antioxidation defense system that induced by Polycyclic Aromatic Hydrocarbons (PAHs) exposure by RNA interference (RNAi). The gene expressions of aryl hydrocarbon receptor nuclear translocator (ARNT), heat shock protein 90 (Hsp90) were evaluated after being exposed to benzo(a)pyrene (BaP) (4 μg/L) for 5 days and the positive correlations between AhR, ARNT, HSP90 indirectly indicating that AhR may have the ability to bind to ligands such as PAHs in Ruditapes philippinarum (R. philippinarum). Besides, the activities of detoxification enzymes were determined to investigate the role of AhR signaling pathway played in the metabolic detoxification. What's more, the gene expressions of protein kinase C (PKC) signaling pathway, mitogen-activated protein kinase (MAPKs) signaling pathway, NF-E2-related factor 2 (Nrf2) signaling pathway and antioxidant defense system indicated that AhR may regulate the Nrf2-Keap1 signaling pathway through Kelch-like ECH-associated protein-1 (Keap1) and MAPKs, PKC signaling pathways. In conclusion, adoption of RNA interference technology to explore the role of RpAhR gene played in the detoxification and antioxidation defense system under the PAHs stress at different time points can informe molecular endpoints for application towards ecotoxicology monitoring of bivalves.

Differential responses in the biotransformation systems of the oyster Crassostrea gasar (Adanson, 1757) elicited by pyrene and fluorene: molecular, biochemical and histological approach - Part I

Polycyclic aromatic hydrocarbons (PAHs) are among the main contaminants in aquatic environments. PAHs can affect organisms due to their carcinogenic, mutagenic and/or teratogenic characteristics. Depending on the PAHs, concentration, and period of exposure, biological damage can occur leading to histopathologic alterations. This study aimed to evaluate the molecular, biochemical and histological responses of the oyster Crassostrea gasar exposed to pyrene (0.25 and 0.5 μM) and fluorene (0.6 and 1.2 μM), after exposure for 24 and 96 h. Concentrations of both PAHs were quantified in the water and in oyster tissues. Transcript levels of phase I (CYP3475C1, CYP2-like, CYP2AU1 and CYP356A) and phase II (GSTO-like, MGST-like and SULT-like) biotransformation-related genes and the activities of ethoxyresorufin-O-deethylase (EROD), total and microsomal glutathione S-transferase (GST and MGST) were evaluated in the gills. Also, histological changes and localization of mRNA transcripts CYP2AU1 in gills, mantle, and digestive diverticula were evaluated. Both PAHs accumulated in oyster tissues. Pyrene half-life in water was significantly lower than fluorene. Transcript levels of all genes were higher in oysters exposed to of pyrene 0.5 μM (24 h). Only CYP2AU1 gene was up-regulated by fluorene exposure. EROD and MGST activities were higher in oysters exposed to pyrene. Tubular atrophy in the digestive diverticula and an increased number of mucous cells in the mantle were observed in oysters exposed to pyrene. CYP2AU1 transcripts were observed in different tissues of pyrene-exposed oysters. A significant correlation was observed between tubular atrophy and the CYP2AU1 hybridization signal in oysters exposed to pyrene, suggesting the sensibility of the species to this PAH. These results suggest an important role of biotransformation-related genes and enzymes and tissue alterations associated to pyrene metabolism but not fluorene. In addition, it reinforces the role of CYP2AU1 gene in the biotransformation process of PAHs in the gills of C. gasar.

The molecular mechanism of Nrf2-Keap1 signaling pathway in the antioxidant defense response induced by BaP in the scallop Chlamys farreri

In this study, we cloned the full-length cDNA of the Kelch-like ECH-associated protein 1 (Keap1) from the scallops Chlamys farreri (C. farreri). Sequences alignment and phylogenetic analysis showed that CfKeap1 was highly specific in the scallops, and the amino acid sequence identity value is closer to that in zebrafish Keap1b and Nothobranchius furzeri Keap1b than Keap1a. The highest transcription level of CfKeap1 expression was detected in the digestive glands. The gene expressions of CfKeap1, NF-E2-related nuclear factor 2 (Nrf2), Superoxide Dismutase (SOD), Catalase (CAT) and Glutathione Peroxidase (GPx) in digestive glands were evaluated by quantitative real-time PCR (qRT-PCR) after being exposed to benzo(a)pyrene (BaP) (0.25, 1and 4 μg/L) for 15 days, which indicated that the activation of Nrf2 and Keap1 expression can be significantly induced under BaP exposure. RNA interference (RNAi) experiments were conducted to examine the expression profiles of CfKeap1, Nrf2, antioxidant genes (Cu/Zn-SOD, CAT and GPx), mitogen-activated protein kinase (MAPKs) and protein kinase C (PKC) signaling pathways key genes in digestive glands and gills when exposed to BaP. Results showed that the mRNA level of CfKeap1 was significantly decreased by 60.69% and59.485%. The changes of CfKeap1 and Nrf2 suggested that the enhancement of Keap1 expression stimulating Nrf2 degradation. Furthermore, the expression of antioxidant genes were consistent with the Nrf2 gene, which suggesting that Nrf2-Keap1 signaling pathway is required for the induction of antioxidant genes. Besides, the changes of PKC, c-Jun N-terminal kinase (JNK) and p38 genes expression suggested that PKC and MAPKs signaling pathways played a synergistic role with Nrf2-Keap1 signaling pathway in the anti-oxidative defense system of bivalve molluscs. In conclusion, these data demonstrated that Keap1 can sense nucleophilic or oxidative stress factors to regulate the Nrf2 signaling pathway together with Cul3-based E3 Ubiquitin Ligase (E3), and the Nrf2-Keap1 signaling pathway played an important role in modulating gene expression of antioxidant enzymes in bivalve mollusks.

Comparative transcriptome analysis between the short-term stress and long-term adaptation of the Ruditapes philippinarum in response to benzo[a]pyrene

In order to monitor the pollution of polycyclic aromatic hydrocarbons (PAHs) in the seawater environment, screening biomarkers capable of monitoring PAHs is the focus of many studies. The transcriptomic profiles of the digestive gland tissue from the R. philippinarum groups after the exposure to BaP (4 μg/L) at four time points (0, 0.5, 6 and 15 days) were investigated to globally screen the key genes and pathways involved in the responses to short-term stress and long-term adaptation of BaP resistance. By comparative transcriptome analysis, 233, 282 and 58 differentially expressed genes (DEGs) were identified at 0.5 day, 6 day and 15 day (vs 0 day). The differential expression genes were related to stress response, detoxification metabolic process and innate immunity. DEGs of each group at different stages were clustered in six profiles based on gene expression pattern. Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis were used on all genes to determine the biological functions and processes. We selected Multidrug resistance protein 3 (MRP3), transcriptional regulator ATRX-like isoform X2 (ATRX) as biomarker indicator genes for short-term pollution monitoring and NADH dehydrogenase [ubiquinone] 1 (NQO1), Complement C1q-like protein 4 (C1q), Glutathione-S-transferase theta (GST), E3 ubiquitin-protein ligase (E3) for long-term pollution monitoring based on the different expression patterns and the function in detoxification and antioxidant defense system. Besides, the expression of seven genes was measured through Quantitative real-time PCR (qPCR) according to their gene expression patterns which was confirmed by the DGE analysis. Taken together, adoption of transcriptomic analysis to explore the bivalves' mRNA abundance changes and detoxification metabolic mechanism under the BaP stress at different time points can aid the development of sensitive and informed molecular endpoints for application towards ecotoxicogenomic monitoring of bivalves.

Gene expression and genotoxicity in Manila clam (Ruditapes philippinarum) modulated by sediment contamination and lagoon dynamics in the Po river delta

The lagoons of the Po River delta are potentially exposed to complex mixtures of contaminants, nevertheless, there is a substantial lack of information about the biological effects of these contaminants in the Po delta lagoons. These environments are highly dynamic and the interactions between chemical and environmental stressors could prevent the proper identification of biological effects and their causes. In this study, we aimed to disentangle such interactions focusing on Manila clams, previously exposed to six lagoons of the Po delta, adopting three complementary tools: a) the detailed description via modelling techniques of lagoon dynamics for salinity and water temperature; b) the response sensitivity of a number of target genes (ahr, cyp4, ρ-gst, σ-gst, hsp22, hsp70, hsp90, ikb, dbh, ach, cat, Mn-sod, Cu/Zn-sod, cyp-a, flp, grx, TrxP) investigated in clam digestive glands by Real Time PCR; and c) the relevance of DNA adducts determined in clams as markers of exposure to genotoxic chemicals. The lagoons showed specific dynamics, and two of them (Marinetta and Canarin) could induce osmotic stress. A group of genes (ahr, cyp4, Mn-sod, σ-gst, hsp-22, cyp-a, TrxP) seemed to be associated with overall lagoon characteristics as may be described by salinity and its variations. Lagoon modelling and a second group of genes (hsp70, hsp90, cat, ikb, ach, grx, Cu/Zn-sod) also suggested that moderate increases of river discharge may imply worse exposure conditions. Oxidative stress seemed to be associated with such events but it was slightly evident also under normal exposure conditions. DNA adduct formation was mainly associated with overwhelmed antioxidant defences (e.g. low Cu/Zn-sod) or seemingly with their lack of response in due time. In Po delta lagoons, Manila clam can be affected by chemical and environmental factors which can contribute to induce oxidative stress, DNA adduct formation and, ultimately, to affect clam condition and health.

The role of Nrf2-Keap1 signaling pathway in the antioxidant defense response induced by PAHs in the calm Ruditapes philippinarum

The NF-E2-related factor 2 (Nrf2) is a master regulator of cellular responses against environmental stresses. In this study we cloned the full-length cDNAs of the RpNrf2 encompassed 2823 bp from the clam Ruditapes philippinarum (R. philippinarum). Sequences alignment and phylogenetic analysis showed that Nrf2 was highly specific in the clams. RpNrf2 expression was detected in gill, digestive gland, mantle and adductor, which the highest transcription level was observed in gill and digestive gland. The gene expressions of RpNrf2, Kelch-like-ECH-associated Protein 1 (Keap1), Cul3-based E3 Ubiquitin Ligase (E3), Glutathione S-transferase (GST-pi), Superoxide Dismutase (SOD), Catalase (CAT) and Glutathione Peroxidase (GPx) in digestive gland was evaluated by real-time PCR after being exposed to benzo(a)pyrene (BaP) (0.25, 1and 4 μg/L) for 15 days, which showed that the expression of Nrf2 significantly increased at day 1 and day 6 after exposure (p < 0.05), and there was a negative relationship between the mRNA levels of Nrf2 and Keap1 that indicates the enhancement of Keap1 expression stimulating Nrf2 degradation. RNA interference experiments were conducted to examine the expression profiles of RpNrf2, antioxidant and detoxification genes (GST-pi, Cu/Zn-SOD, CAT and GPx) and Lipid Peroxidase (LPO) level in digestive gland exposed to BaP. The results showed that the mRNA level of Nrf2 was significantly decreased by 63.2%, and the changes of antioxidant and detoxification genes expression were consistent with the Nrf2 gene suggesting that Nrf2 is required for the induction of antioxidant and detoxification genes. Besides, the LPO levels expressed by malondialdehyde (MDA) contents were significant higher compared with the control group at 72 h post dsRNA-Nrf2 injection. In conclusion, our data demonstrated that Keap1 can sense nucleophilic or oxidative stress factors to regulate the Nrf2 signaling pathway together with E3 and Nrf2 signaling pathway plays an important role in modulating gene expression of antioxidant enzymes in bivalve mollusks.

Expression profiles of different glutathione S-transferase isoforms in scallop Chlamys farreri exposed to benzo[a]pyrene and chrysene in combination and alone

Aquatic organisms are increasingly exposed to polycyclic aromatic hydrocarbons (PAHs) due to anthropogenic pressure. This study aimed at evaluating the response of Glutathione S-transferases (GSTs) in scallop Chlamys farreri against benzo[a]pyrene (BaP) and chrysene (CHR) exposure under laboratory conditions. Nine published GST genes were classified into six subfamilies and a new member of rho family was identified for the first time. Twelve GSTs (including nine published GST genes and three in transcriptome established by our laboratory) mRNA transcript levels in the gills, digestive glands, adductor muscle, mantle, testis, ovaries, blood cells of scallops were measured by real-time PCR. The results showed that the mRNA transcript levels of twelve GSTs, except GST-zeta, GST-mu and GST-microsomal, were highest in digestive gland. Accordingly, the mRNA expression levels of GSTs were measured in digestive glands of scallops exposed to BaP (0.1μg/L and 1μg/L), CHR (0.1μg/L and 1μg/L) and their mixtures (0.1μg/L BaP +0.1μg/L CHR and 1μg/L BaP +1μg/L CHR). The results indicated that different GST had specific response to different pollution exposure. In BaP exposure experiment, the mRNA expression level of GST-theta was a potential suitable biomarker. GST-sigma-2 and GST-3, which belonged to sigma class, were sensitive to CHR exposure while GST-microsomal was considered a potential ideal bioindicator to joint exposure of BaP and CHR. In summary, this study investigated the classification of GSTs and provided information about the expression profiles of different class GSTs after PAHs exposure.

The detoxification responses, damage effects and bioaccumulation in the scallop Chlamys farreri exposed to single and mixtures of benzo[a]pyrene and chrysene

This study aimed to investigate the detoxification responses, damage effects and biotransformation in scallop Chlamys farreri exposed to benzo[a]pyrene (BaP) (0.1, 1μg/L), chrysene (CHR) (0.1, 1μg/L) and BaP+CHR (0.1+0.1, 1+1μg/L) for 15days. Results demonstrated that BaP and CHR concentration (BaP<CHR) in tissues increased rapidly in a time and dose effect. The mRNA expression of aryl hydrocarbon receptor (AhR), cytochrome P450 1A1 (CYP1A1), CYP1B1, multidrug resistance protein 1 (MRP1/ABCC1), breast cancer resistance protein (BCRP/ABCG2) and P-glycoprotein (P-gp) were induced especially in the mixtures of BaP and CHR. Heat shock protein 90 (HSP90) and aryl hydrocarbon receptor nuclear translocator (ARNT) mRNA expression was significantly elevated at days 1, 10 and 15. Detoxification enzymes of 7-ethoxyresorufin O-deethylase (EROD), uridine-diphosphate-glucuronyl-transferase (UGT) and sulfotransferase (SULT) were significantly induced and then became stable gradually while glutathione-S-transferase (GST) was inhibited in the mixtures of BaP and CHR at days 10 and 15. Superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and glutathione (GSH) were all stimulated especially in the mixtures of BaP and CHR. The levels of DNA strand breaks, lipid peroxidation (LPO) and protein carbonyl (PC) contents showed damage effects exposed BaP and CHR. All the results indicated that BaP and CHR have similar induced effect and a majority of the biomarkers pointed to a more toxic effect when BaP and CHR were mixed. These will provide a solid foundation for the study of PAHs detoxification mechanism in bivalves and valuable information for marine pollution monitoring.

Identification of interacting proteins with aryl hydrocarbon receptor in scallop Chlamys farreri by yeast two hybrid screening

The aryl hydrocarbon receptor (AhR) belongs to the basic-helix-loop helix (bHLH) Per-Arnt-Sim (PAS) family of transcription factors. AhR has been known primarily for its role in the regulation of several drug and xenobiotic metabolizing enzymes, as well as the mediation of the toxicity of certain xenobiotics, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Although the AhR is well-studied as a mediator of the toxicity of certain xenobiotics in marine bivalves, the normal physiological function remains unknown. In order to explore the function of the AhR, the bait protein expression plasmid pGBKT7-CfAhR and the cDNA library of gill from Chlamys farreri were constructed. By yeast two hybrid system, after multiple screening with the high screening rate medium, rotary verification, sequencing and bioinformatics analysis, the interactions of the CfAhR with receptor for activated protein kinase C 1 (RACK1), thyroid peroxidase-like protein (TPO), Toll-like receptor 4(TLR 4), androglobin-like, store-operated Ca(2+) entry (SocE), ADP/ATP carrier protein, cytochrome b, thioesterase, actin, ferritin subunit 1, poly-ubiquitin, short-chain collagen C4-like and one hypothetical protein in gill cells were identified. This study suggests that the CfAhR played fundamental roles in immune system homeostasis, oxidative stress response, and in grow and development of C. farreri. The elucidation of these protein interactions is of much importance both in understanding the normal physiological function of AhR, and as potential targets for further research on protein function in AhR interactions.