Comparative Effects of Dietary Methylmercury on Gene Expression in Liver, Skeletal Muscle, and Brain of the Zebrafish ( Danio rerio )

Université Bordeaux 1, Talence, Aquitaine, France
Environmental Science and Technology (Impact Factor: 5.33). 07/2005; 39(11):3972-80. DOI: 10.1021/es0483490
Source: PubMed

ABSTRACT Effects of dietary methylmercury (MeHg) on gene expression were examined in three organs (liver, skeletal muscle, and brain) of the zebrafish (Danio rerio). Adult male fish were fed over 7, 21, and 63 days on three different diets: one control diet (C0: 0.08 microg of Hg g(-1), dry wt) and two diets (C1 and C2) contaminated by MeHg at 5 and 13.5 microg of Hg g(-1), dry wt. Total Hg and MeHg concentrations were determined in the three organs after each exposure duration, and a demethylation process was evidenced only in the liver. Thirteen genes known to be involved in antioxidant defenses, metal chelation, active efflux of organic compounds, mitochondrial metabolism, DNA repair, and apoptosis were investigated by quantitative real-time RT-PCR and normalized according to actin gene expression. Surprisingly, no change in the expression levels of these genes was observed in contaminated brain samples, although this organ accumulated the highest mercury concentration (63.5 +/- 4.4 microg g(-1), dry wt after 63 days). This lack of genetic response could explain the high neurotoxicity of MeHg. coxI and cytoplasmic and mitochondrial sod gene expressions were induced early in skeletal muscle and later in liver, indicating an impact on the mitochondrial metabolism and production of reactive oxygen species. Results demonstrated that skeletal muscle was not only an important storage reservoir but was also affected by MeHg contamination. The expression of the metallothionein mt2 and the DNA repair rad51 genes was up-regulated in liver between 21 and 63 days, whereas in skeletal muscle, mt2 remained uninduced, and gadd and rad51 were found to be repressed.

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Available from: Jean-Charles Massabuau, Nov 28, 2014
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    • "Fish studies suggest that MeHg may disturb reproductive hormones, mediating smaller gonad development or atrophy, delays in spawning and effects on fecundity (Klaper et al., 2006, 2008), and act gender-specifically (Liu et al., 2013). Oxidative stress and apoptosis have been suggested to be two of the main effects of MeHg exposure in fish (Gonzalez et al., 2005; Klaper et al., 2008; Berg et al., 2010; Cambier et al., 2010; Richter et al., 2011). Conducting studies with Atlantic salmon (Salmo salar), it has recently been shown that oxidative stress is one of the major effects of MeHg exposure (Olsvik et al., 2011a; Nøstbakken et al., 2012a,b). "
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    ABSTRACT: Recent findings have shown that deep-water fish from coastal areas may contain elevated levels of mercury (Hg). Tusk (Brosme brosme) was collected from six locations in Hardangerfjord, a fjord system where the inner parts are contaminated by metals due to historic industrial activity. ICPMS was used to determine the accumulated levels of metals (Hg, MeHg, Cd, Pb, As, and Se) in the fish, whereas oxidative status of the liver was assessed by measuring TBARS, vitamin C, vitamin E and catalase activity. To find out whether accumulated Hg triggers toxicologically relevant transcriptional responses and in order to gain genomic knowledge from a non-model species, the liver transcriptome of the gadoid fish was sequenced and assembled, and RNA-seq and RT-qPCR were used to screen for effects of Hg. The results showed high levels of accumulated Hg in tusk liver, probably reflecting an adaptation to deep-water life history, and only a weak declining outward fjord gradient of Hg concentration in tusk liver. MeHg only accounted for about 17% of total Hg in liver, suggesting hepatotoxicity of both inorganic and organic Hg. Pathway analysis suggested an effect of Hg exposure on lipid metabolism and beta-oxidation in liver. Oxidative stress markers glutathione peroxidase 1 and ferritin mRNA, as well as vitamin C and vitamin E (alpha and gamma tocopherol) showed a significant correlation with accumulated levels of Hg. Many transcripts of genes encoding established markers for Hg exposure were co-regulated in the fish. In conclusion, tusk from Hardangerfjord contains high levels of Hg, with possible hepatic effects on lipid metabolism and oxidative stress.
    Aquatic toxicology (Amsterdam, Netherlands) 10/2013; 144-145C:172-185. DOI:10.1016/j.aquatox.2013.10.002 · 3.45 Impact Factor
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    • "They were however, down-regulated following MeHgCl exposure. Previous publications in a variety of species report inconsistent induction of metallothioneins in response to MeHgCl exposure [41-44]. The present study is the first to report a down-regulation of metallothionein gene expression in response to MeHgCl exposure. "
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    ABSTRACT: Mercury is a ubiquitous environmental toxicant that exists in multiple chemical forms. A paucity of information exists regarding the differences or similarities by which different mercurials act at the molecular level. Transcriptomes of mixed-stage C. elegans following equitoxic sub-, low- and high-toxicity exposures to inorganic mercuric chloride (HgCl2) and organic methylmercury chloride (MeHgCl) were analyzed. In C. elegans, the mercurials had highly different effects on transcription, with MeHgCl affecting the expression of significantly more genes than HgCl2. Bioinformatics analysis indicated that inorganic and organic mercurials affected different biological processes. RNAi identified 18 genes that were important in C. elegans response to mercurial exposure, although only two of these genes responded to both mercurials. To determine if the responses observed in C. elegans were evolutionarily conserved, the two mercurials were investigated in human neuroblastoma (SK-N-SH), hepatocellular carcinoma (HepG2) and embryonic kidney (HEK293) cells. The human homologs of the affected C. elegans genes were then used to test the effects on gene expression and cell viability after using siRNA during HgCl2 and MeHgCl exposure. As was observed with C. elegans, exposure to the HgCl2 and MeHgCl had different effects on gene expression, and different genes were important in the cellular response to the two mercurials. These results suggest that, contrary to previous reports, inorganic and organic mercurials have different mechanisms of toxicity. The two mercurials induced disparate effects on gene expression, and different genes were important in protecting the organism from mercurial toxicity.
    BMC Genomics 10/2013; 14(1):698. DOI:10.1186/1471-2164-14-698 · 3.99 Impact Factor
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    • "The zebrafish is a useful model organism for studying embryonic development and is increasingly being used in vertebrate toxicology studies (Gonzalez et al. 2005; Korbas et al. 2008; Kusik et al. 2008; Samson et al. 2001; Weber et al. 2008). Previously, embryonic and larval zebrafish have been used to study the toxic effects of MeHg exposure on the entire body (Samson et al. 2001; Weber et al. 2008) and at the molecular level (Gonzalez et al. 2005; Korbas et al. 2008). Because the nucleotide sequence and expression of the zebrafish OCTN1 gene homolog has been characterized (Nilsson et al. 2009; Weber et al. 2005), OCTN1-deficient embryos can be generated by microinjection of an antisense morpholino oligo (MO) and used for the study of MeHg toxicity. "
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    ABSTRACT: The selenium (Se)-containing antioxidant selenoneine (2-selenyl-Nα,Nα,Nα-trimethyl-l-histidine) has recently been discovered to be the predominant form of organic Se in tuna blood. Although dietary intake of fish Se has been suggested to reduce methylmercury (MeHg) toxicity, the molecular mechanism of MeHg detoxification by Se has not yet been determined. Here, we report evidence that selenoneine accelerates the excretion and demethylation of MeHg, mediated by a selenoneine-specific transporter, organic cations/carnitine transporter-1 (OCTN1). Selenoneine was incorporated into human embryonic kidney HEK293 cells transiently overexpressing OCTN1 and zebrafish blood cells by OCTN1. The Km for selenoneine uptake was 13.0 μM in OCTN1-overexpressing HEK293 cells and 9.5 μM in zebrafish blood cells, indicating high affinity of OCTN1 for selenoneine in human and zebrafish cells. When such OCTN1-expressing cells and embryos were exposed to MeHg–cysteine (MeHgCys), MeHg accumulation was decreased and the excretion and demethylation of MeHg were enhanced by selenoneine. In addition, exosomal secretion vesicles were detected in the culture water of embryos that had been microinjected with MeHgCys, suggesting that these may be responsible for MeHg excretion and demethylation. In contrast, OCTN1-deficient embryos accumulated MeHg, and MeHg excretion and demethylation were decreased. Furthermore, Hg accumulation was decreased in OCTN1-overexpressing HEK293 cells, but not in mock vector-transfected cells, indicating that selenoneine and OCTN1 can regulate MeHg detoxification in human cells. Thus, the selenoneine-mediated OCTN1 system regulates secretory lysosomal vesicle formation and MeHg demethylation. Electronic supplementary material The online version of this article (doi:10.1007/s10126-013-9508-1) contains supplementary material, which is available to authorized users.
    Marine Biotechnology 05/2013; 15(5). DOI:10.1007/s10126-013-9508-1 · 3.27 Impact Factor
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