Dioxin lethality: aryl hydrocarbon receptor (AHR)-mediated gene expression in a rat resistant model
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ABSTRACT:
ORGANISM(S): Rattus norvegicus
PROVIDER: GSE10083 | GEO | 2009/11/24
SECONDARY ACCESSION(S): PRJNA108649
REPOSITORIES: GEO
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Project description:Major toxicities of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) result from dysregulation of gene expression mediated by the aryl hydrocarbon receptor (AHR). Dioxin-like chemicals alter expression of numerous genes in liver but the specific genes whose dysregulation leads to toxicities such as wasting, hepatotoxicity and lethality have not been identified. We searched for genes that are most likely to be key to dioxin toxicity by using gene expression arrays to contrast hepatic gene expression after TCDD treatment in dioxin-sensitive rats (that carry wildtype AHR) with gene expression in H/W(Kuopio) rats which are highly resistant to dioxin toxicity due to a major deletion in the AHR's transactivation domain (TAD). The total number of TCDD-responsive genes was smaller in rats with the AHRH/W genotype than in rats with wildtype AHR. However, genes in the classic AH gene battery such as CYP1A1, CYP1A2 and CYP1B1 remained fully responsive to TCDD in AHRH/W rats; thus the TAD deletion selectively interferes with expression of a subset of hepatic genes rather than abolishing global AHR-mediated responses. Genes in the following functional categories differ in response to TCDD between dioxin-sensitive rats and dioxin-resistant rats: fatty acid oxidation, metabolism (xenobiotic, alcohol, amino acid, and fatty acid), phosphate transport, regulation of steroid biosynthesis, nitrogen compound catabolism, and generation of precursor metabolites and energy. Many of these differentially-responsive genes are integral parts of pathways such as: protein degradation and synthesis, fatty acid metabolism and synthesis, cytokinesis, cell growth, and apoptosis which may be part of mechanisms which lead to TCDD-induced wasting, hepatotoxicity, tumors, and death. These differentially-responsive genes are worthy candidates for further mechanistic studies to test their role in mediating or protecting from major dioxin toxicities. Experiment Overall Design: Four strains of rats were either treated with 100 ug/kg TCDD or cornoil vehicle and profiled at 19 hours, each with four replicates. Two strains were also analyzed at 3 hours, each with four replicates.
2009-12-02 | E-GEOD-10083 | biostudies-arrayexpress
Project description:The dioxin congener 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes a wide range of toxic effects in rodent species, all of which are mediated by a ligand-dependent transcription-factor, the aryl hydrocarbon receptor (AHR). The Han/Wistar (Kuopio) (H/W) strain shows exceptional resistance to many TCDD-induced toxicities; the LD50 of >9600 µg/kg for H/W rats is higher than for any other wild-type mammal known. We have previously shown that this resistance primarily results from H/W rats expressing a variant AHR isoform that has a substantial portion of the AHR transactivation domain deleted. Despite this large deletion, H/W rats are not entirely refractory to the effects of TCDD; the variant AHR in these animals remains fully competent to up-regulate well-known dioxin-inducible genes. TCDD-sensitive (Long-Evans, L-E) and resistant (H/W) rats were treated with either corn-oil (with or without feed-restriction) or 100 µg/kg TCDD for either four or ten days. Hepatic transcriptional profiling was done using microarrays, and was validated by RT-PCR analysis of 41 genes. . A core set of genes was altered in both strains at all time points tested, including CYP1A1, CYP1A2, CYP1B1, Nqo1, Aldh3a1, Tiparp, Exoc3, and Inmt. Outside this core, the strains differed significantly in the breadth of response: three-fold more genes were altered in L-E than H/W rats. At ten days almost all expressed genes were dysregulated in L-E rats, likely reflecting emerging toxic responses. Far fewer genes were affected by feed-restriction, suggesting that only a minority of the TCDD-induced changes are secondary to the wasting syndrome. Rats from sensitive (Long-Evans, LE) and resistant (Han/Wistar, HW) strains were treated with 100 ug/kg TCDD or corn oil vehicle and sacrificed either 4 or 10 days after treatment. LE control rats were either fed normally or feed-restricted to control for the wasting effects of TCDD treatment. Each treatment group contains four or five animals (biological replicates), each of which was assayed on an individual microarray.
2011-11-14 | E-GEOD-13513 | biostudies-arrayexpress
Project description:The dioxin congener 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes a wide range of toxic effects in rodent species, all of which are mediated by a ligand-dependent transcription-factor, the aryl hydrocarbon receptor (AHR). The Han/Wistar (Kuopio) (H/W) strain shows exceptional resistance to many TCDD-induced toxicities; the LD50 of >9600 µg/kg for H/W rats is higher than for any other wild-type mammal known. We have previously shown that this resistance primarily results from H/W rats expressing a variant AHR isoform that has a substantial portion of the AHR transactivation domain deleted. Despite this large deletion, H/W rats are not entirely refractory to the effects of TCDD; the variant AHR in these animals remains fully competent to up-regulate well-known dioxin-inducible genes. TCDD-sensitive (Long-Evans, L-E) and resistant (H/W) rats were treated with either corn-oil (with or without feed-restriction) or 100 µg/kg TCDD for either four or ten days. Hepatic transcriptional profiling was done using microarrays, and was validated by RT-PCR analysis of 41 genes. . A core set of genes was altered in both strains at all time points tested, including CYP1A1, CYP1A2, CYP1B1, Nqo1, Aldh3a1, Tiparp, Exoc3, and Inmt. Outside this core, the strains differed significantly in the breadth of response: three-fold more genes were altered in L-E than H/W rats. At ten days almost all expressed genes were dysregulated in L-E rats, likely reflecting emerging toxic responses. Far fewer genes were affected by feed-restriction, suggesting that only a minority of the TCDD-induced changes are secondary to the wasting syndrome.
2011-11-14 | GSE13513 | GEO
Project description:2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent aryl hydrocarbon receptor (AhR) agonist that elicits a broad spectrum of dose-dependent effects in the liver, including hepatic lipid accumulation coupled with inflammation. To determine the role of inflammatory lipid mediators in TCDD-mediated hepatotoxicity, eicosanoid metabolism was investigated in female Sprague-Dawley (SD) rats. Rats were gavaged with sesame oil vehicle or 0.01-10 µg/kg TCDD every 4 days for 28 days. Hepatic RNA-Seq data from female SD rats was compared with data from female C57BL/6 mice and functionally annotated to determine key toxicogenomic differences between the two species regarding TCDD exposure. Hepatic RNA-Seq data from female SD rats integrated with untargeted metabolomics of liver, serum, and urine identified dose-dependent changes in linoleic acid (LA) and arachidonic acid (AA) metabolism. TCDD also elicited dose-dependent differential gene expression associated with cyclooxygenase, lipoxygenase, and cytochrome P450 epoxidation/ hydroxylation pathways with corresponding changes in omega-6 (e.g. AA and LA) and omega-3 polyunsaturated fatty acids (PUFAs) as well as their eicosanoid metabolites. Overall, total omega-6 PUFAs increased, while total omega-3 PUFAs decreased. Phospholipase A2 (Pla2g12a) was induced 6-fold consistent with increased AA metabolism, while AA utilization by lipoxygenases Alox5 (2-fold) and Alox15 (10-fold) increased leukotrienes (LTs), important mediators signaling an inflammatory response. More specifically, TCDD increased pro-inflammatory eicosanoids, including leukotriene (LT) B4 (3-fold), and LTB3 (5-fold), known signals for the recruitment of neutrophils to areas of tissue damage. Dose-response modeling of metabolite and gene expression changes suggests the cytochrome P450 hydroxylase/epoxygenase and the lipoxygenase pathways are the most sensitive to TCDD. While several differentially expressed genes (DEGs) associated with eicosanoid biosynthesis contained putative dioxin response elements (pDRE) within their regulatory region, ChIP-Seq analysis showed little AhR enrichment, suggesting TCDD-elicited induction of eicosanoid biosynthesis is not a direct effect of AhR activation.
2018-12-01 | GSE110293 | GEO
Project description:2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent aryl hydrocarbon receptor (AhR) agonist that elicits a broad spectrum of dose-dependent effects in the liver, including hepatic lipid accumulation coupled with inflammation. To determine the role of inflammatory lipid mediators in TCDD-mediated hepatotoxicity, eicosanoid metabolism was investigated in female Sprague-Dawley (SD) rats. Rats were gavaged with sesame oil vehicle or 0.01-10 µg/kg TCDD every 4 days for 28 days. Hepatic RNA-Seq data from female SD rats was compared with data from female C57BL/6 mice and functionally annotated to determine key toxicogenomic differences between the two species regarding TCDD exposure. Hepatic RNA-Seq data from female SD rats integrated with untargeted metabolomics of liver, serum, and urine identified dose-dependent changes in linoleic acid (LA) and arachidonic acid (AA) metabolism. TCDD also elicited dose-dependent differential gene expression associated with cyclooxygenase, lipoxygenase, and cytochrome P450 epoxidation/ hydroxylation pathways with corresponding changes in omega-6 (e.g. AA and LA) and omega-3 polyunsaturated fatty acids (PUFAs) as well as their eicosanoid metabolites. Overall, total omega-6 PUFAs increased, while total omega-3 PUFAs decreased. Phospholipase A2 (Pla2g12a) was induced 6-fold consistent with increased AA metabolism, while AA utilization by lipoxygenases Alox5 (2-fold) and Alox15 (10-fold) increased leukotrienes (LTs), important mediators signaling an inflammatory response. More specifically, TCDD increased pro-inflammatory eicosanoids, including leukotriene (LT) B4 (3-fold), and LTB3 (5-fold), known signals for the recruitment of neutrophils to areas of tissue damage. Dose-response modeling of metabolite and gene expression changes suggests the cytochrome P450 hydroxylase/epoxygenase and the lipoxygenase pathways are the most sensitive to TCDD. While several differentially expressed genes (DEGs) associated with eicosanoid biosynthesis contained putative dioxin response elements (pDRE) within their regulatory region, ChIP-Seq analysis showed little AhR enrichment, suggesting TCDD-elicited induction of eicosanoid biosynthesis is not a direct effect of AhR activation.
2018-12-01 | GSE110282 | GEO
Project description:Dioxin-like chemicals are well-known for their ability to upregulate expression of numerous genes via the AH receptor (AHR). However, recent transcriptomic analyses in several laboratories indicate that dioxin-like chemicals or AHR genotype itself also can downregulate levels of mRNAs encoded by numerous genes. The mechanism responsible for such downregulation is unknown. We hypothesized that microRNAs (miRNAs), which have emerged as powerful negative regulators of mRNA levels in several systems, might be responsible for mRNA downregulation in dioxin/AHR pathways. We used the Exiqon miRNA array platform as well as quantitative RT-PCR to measure miRNA levels in dioxin-sensitive Long-Evans (Turku/AB; L-E) rats vs. dioxin-resistant Han/Wistar(Kuopio; H/W) rats. Treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in vivo caused few changes in miRNA levels in rat livers and those changes that were statistically significant were of modest magnitude. AHR genotype had little effect on hepatic miRNA levels, either in constitutive expression or in response to TCDD – only a few miRNAs differed in expression between between L-E rats (that have wildtype AHR) compared to H/W rats (whose AHR has a large deletion in the transactivation domain). It is unlikely that mRNA downregulation by dioxins is mediated by miRNAs, nor are miRNAs likely to play a significant role in dioxin toxicity in adult rodent liver. We conducted a thorough investigation to address the following questions: (1) does AHR genotype itself affect constitutive expression of microRNAs? (2) does TCDD affect microRNA levels and, if so, is this response dependent on the AHR? (3) does TCDD affect microRNA levels differently in animals that are sensitive to dioxin toxicity versus those that are dioxin-resistant? We assessed the in vivo effect of TCDD on microRNA levels in liver at multiple time points after TCDD treatment using microRNA arrays along with quantitative RT-PCR. The cumulative results of our experiments indicate that downregulation of mRNA levels by dioxins in adult rodent livers is very unlikely to involve microRNAs. Manuscript Submitted: Moffat ID, Boutros PC, Celius T, Pohjanvirta R & Okey AB. Micro-RNAs in rodent liver are refractory to dioxin treatment. Toxicological Sciences May, 2007. Keywords: miRNA expression, Time course, response to xenobiotics, genetic modification, comparative genome hybridization We examined strain differences in miRNA expression independent of TCDD: 19-h vehicle-treated dioxin-resistant H/W AHRH/W/H/W rats (HC19) vs. vehicle- control dioxin-sensitive L-E AHRWT/WT rats (LC19). In the dioxin-sensitive rats we compared miRNA expression levels 3 h (LT3) or 19 h (LT19) post-TCDD treatment vs. LC19. In the dioxin-resistant rats we compared miRNA levels 3 h (HT3), 19 h (HT19), or 96 h (HT96) post-TCDD treatment vs. HC19.
2007-08-15 | E-GEOD-8470 | biostudies-arrayexpress
Project description:Dioxin-like chemicals are well-known for their ability to upregulate expression of numerous genes via the AH receptor (AHR). However, recent transcriptomic analyses in several laboratories indicate that dioxin-like chemicals or AHR genotype itself also can downregulate levels of mRNAs encoded by numerous genes. The mechanism responsible for such downregulation is unknown. We hypothesized that microRNAs (miRNAs), which have emerged as powerful negative regulators of mRNA levels in several systems, might be responsible for mRNA downregulation in dioxin/AHR pathways. We used the Ambion miRNA array platform as well as quantitative RT-PCR to measure miRNA levels in dioxin-sensitive Long-Evans (Turku/AB; L-E) rats vs. dioxin-resistant Han/Wistar(Kuopio; H/W) rats. Treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in vivo caused no significant changes in miRNA levels in rat livers. AHR genotype had no effect on hepatic miRNA levels in response to TCDD – no miRNAs differed in expression between between L-E rats (that have wildtype AHR) compared to H/W rats (whose AHR has a large deletion in the transactivation domain). It is unlikely that mRNA downregulation by dioxins is mediated by miRNAs, nor are miRNAs likely to play a significant role in dioxin toxicity in adult rodent liver. Manuscript Submitted: Moffat ID, Boutros PC, Celius T, Pohjanvirta R & Okey AB. Micro-RNAs in rodent liver are refractory to dioxin treatment. Toxicological Sciences May, 2007. Keywords: miRNA expression, response to xenobiotics, genetic modification, comparative genome hybridization In the dioxin-sensitive L-E rats we compared miRNA expression levels 19 h post-TCDD treatment vs. corn oil vehicle treatment. In the dioxin-resistant H/W rats we compared miRNA levels 19 h post-TCDD treatment vs.corn oil vehicle treatment.
2007-08-15 | E-GEOD-8467 | biostudies-arrayexpress
Project description:We previously reported that TCDD-inducible poly-ADP-ribose polymerase (TIPARP), an aryl hydrocarbon receptor (AHR) target gene and mono-ADP-ribosyltransferase, acts as part of a negative feedback loop to repress AHR signalling, a process that prevented by a single H532A mutation that destroys TIPARP catalytic activity. Moreover, whole body or hepatocyte specific-deletion of, increases the sensitivity of mice to dioxin-induced toxicities. Based on these findings, we hypothesized that the loss of TIPARP catalytic activity would increase sensitivity to TCDD-induced toxicity in vivo. To test the hypothesis, we created a catalytically deficient mouse line (TiparpH532A) by introducing a single H532A mutation in Tiparp. Treatment of mouse embryonic fibroblasts (MEFs) or hepatocytes isolated from TiparpH532A mice confirmed the increased TCDD-induced expression of the AHR target genes, Cyp1a1, Cyp1b1 and Tiparp. We also confirmed TCDD-dependent increases in Tiparp protein levels, as well as increased protein stabilization of TiparpH532A compared Tiparp+/+ protein. TiparpH532A mice given a single injection of 10 ug/kg dioxin, a non-lethal dose in Tiparp+/+ mice, did not survive beyond day 10. All Tiparp+/+ mice survived the 30-day treatment. Dioxin treated TiparpH532A mice displayed increased expression of Ahr target genes, increased steatohepatitis and hepatotoxicity as indicated by increased alanine aminotransferase activity compared with wildtypes. Taken together, these data further support TIPARP as a key negative regulator of AHR activity and its specific loss of its catalytic activity is sufficient to increase the sensitivity to dioxin-induced hepatosteatosis and lethality. TIPARP has recently emerged as a potential anti-cancer therapeutic; however, AHR signalling and toxicity will need to be carefully considered in determining the consequences of TIPARP inhibition.
2021-09-08 | GSE167205 | GEO
Project description:Dioxin-like chemicals are well-known for their ability to upregulate expression of numerous genes via the AH receptor (AHR). However, recent transcriptomic analyses in several laboratories indicate that dioxin-like chemicals or AHR genotype itself also can downregulate levels of mRNAs encoded by numerous genes. The mechanism responsible for such downregulation is unknown. We hypothesized that microRNAs (miRNAs), which have emerged as powerful negative regulators of mRNA levels in several systems, might be responsible for mRNA downregulation in dioxin/AHR pathways. We used the Exiqon miRNA array platform as well as quantitative RT-PCR to measure miRNA levels in dioxin-sensitive Long-Evans (Turku/AB; L-E) rats vs. dioxin-resistant Han/Wistar(Kuopio; H/W) rats. Treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in vivo caused few changes in miRNA levels in rat livers and those changes that were statistically significant were of modest magnitude. AHR genotype had little effect on hepatic miRNA levels, either in constitutive expression or in response to TCDD – only a few miRNAs differed in expression between between L-E rats (that have wildtype AHR) compared to H/W rats (whose AHR has a large deletion in the transactivation domain). It is unlikely that mRNA downregulation by dioxins is mediated by miRNAs, nor are miRNAs likely to play a significant role in dioxin toxicity in adult rodent liver. We conducted a thorough investigation to address the following questions: (1) does AHR genotype itself affect constitutive expression of microRNAs? (2) does TCDD affect microRNA levels and, if so, is this response dependent on the AHR? (3) does TCDD affect microRNA levels differently in animals that are sensitive to dioxin toxicity versus those that are dioxin-resistant? We assessed the in vivo effect of TCDD on microRNA levels in liver at multiple time points after TCDD treatment using microRNA arrays along with quantitative RT-PCR. The cumulative results of our experiments indicate that downregulation of mRNA levels by dioxins in adult rodent livers is very unlikely to involve microRNAs. Manuscript Submitted: Moffat ID, Boutros PC, Celius T, Pohjanvirta R & Okey AB. Micro-RNAs in rodent liver are refractory to dioxin treatment. Toxicological Sciences May, 2007. Keywords: miRNA expression, Time course, response to xenobiotics, genetic modification, comparative genome hybridization
2007-08-15 | GSE8470 | GEO
Project description:The aryl hydrocarbon receptor (AHR) is a ligand activated transcription factor that mediates the toxic effects of the environmental contaminant, dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD). Dioxin causes a diverse range of toxic responses, including hepatic damage and lethal wasting syndrome; however, the mechanisms of dioxin-induced toxicity are still unknown. Here we show that the loss of TCDD-inducible poly(ADP-ribose) polymerase (TIPARP; ARTD14), an ADP-ribosyltransferase and AHR repressor, increases sensitivity to dioxin-induced toxicity and lethality. Tiparp-/- mice treated with a single injection of 100 mg/kg dioxin display an accelerated lethal wasting syndrome with no Tiparp-/- mice surviving beyond day 5; all Tiparp+/+ mice survived up to 30 days post treatment. Tiparp-/- mice displayed dramatic increases in liver steatosis and hepatotoxicity. At the molecular level, TIPARP selectively ADP-ribosylates AHR, but not AHR nuclear translocator (ARNT) and the Tiparp-dependent repression of AHR is reversed by the ADP-ribosylase and macrodomain containing protein MacroD1, but not MacroD2. These results describe previously unidentified roles for Tiparp, MacroD1, and ADP-ribosylation in AHR signaling, dioxin toxicity and lethality.
2015-05-14 | GSE61534 | GEO