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Hepatic pyruvate kinase muscle isoform 2 (Pkm2) induction in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-elicited oxidative stress is independent of NRF2 (RNA-Seq)

ABSTRACT: Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces hepatic oxidative stress following activation of the aryl hydrocarbon receptor (AhR). Our recent studies revealed induction of pyruvate kinase muscle isoform 2 (Pkm2) as a novel antioxidant response in normal differentiated hepatocytes. To investigate cooperative regulation between nuclear factor, erythroid derived 2, like 2 (Nrf2) and the AhR, hepatic ChIP-seq analyses were integrated with RNA-seq time course data from mice treated with TCDD for 2 - 168h. ChIP-seq analysis 2h following TCDD treatment revealed genome-wide changes in NRF2 binding. 842 NRF2 enriched regions were in the regulatory region of differentially expressed genes (DEGs) while 579 DEGs showed both NRF2 and AhR enrichment. Sequence analysis showed over-representation of AhR and NRF2 binding motifs in these regions, though presence of motifs were largely independent. NRF2 was negligibly enriched within the Pkm gene loci in a closed chromatin region despite its role in antioxidant defenses. Furthermore, TCDD induced Pkm2 in primary hepatocytes from wild-type and Nrf2 null mice, indicating NRF2 is not required. Although NRF2 and AhR cooperate in the regulation of gene expression associated with antioxidant responses, the induction of Pkm2 by TCDD is not dependent on ROS-mediated activation of NRF2.

ORGANISM(S): Mus musculus

PROVIDER: GSE109863 | GEO | 2018/06/07

REPOSITORIES: GEO

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Project description:Background: Estrogen receptor (ERα) and aryl hydrocarbon receptor (AHR) are two nuclear receptors involved in regulating gene expression. ERα and AHR are regulated by estradiol(E2) and TCDD respectively. They are also regulated by dietary ligands including 3,3´diindolylmethane (DIM) and resveratrol (RES). DIM is an ERα and AHR agonist, while RES is an ERα agonist and AHR antagonist. Few studies have investigated the impact of RES and DIM on ERα and AHR signaling at a genome-wide level. This study assessed ERα and AHR binding and associated gene expression changes after treatment of MCF-7 human breast cancer cells with DIM, RES, E2, TCDD, and E2+TCDD for 1 hour and 6 hours before ChIP and RNA sequencing respectively. Results: 88% and 86% of the ERα bound sites after RES and DIM overlapped with E2 ERα sites. RES and DIM resulted in 577 and 446 differentially expressed genes (DEGs) respectively compared to 866 after E2. 68% and 62.3% of the DEGs after RES and DIM were closest to an ERα binding site. Motif analysis indicated enrichment for AHRE motif among DIM ERα sites but not among E2 or RES ERα sites. Both DIM and E2+TCDD resulted in greater genome wide binding of AHR than TCDD. DIM and E2+TCDD resulted in 10546 and 8904 AHR and ERα co-occupied sites respectively. While co-occupied sites for both enriched for the AHR and ERE motif among others, DIM mediated co-occupied sites enriched for Tcfcp2l1, Tgif1, Gata3 motifs while E2+TCDD mediated ones enriched for the NF1 and Ppara motifs. Overlap of coregulated DEGs after DIM and E2+TCDD indicated 123 were the same among both with 81 and 85 unique coregulated DEGs respectively. Enrichment analysis indicated that more enrichment terms were different than similar for coregulated genes after E2+TCDD and DIM. Conclusions: AHR activation is responsible for DIM mediated reduced regulation of gene expression by ERα relative to E2 and only a subset of the DEG’s after DIM and RES are ERα targets indicating future studies into other transcription factors regulated by DIM and RES are needed for insights into the regulation of gene expression by these ligands.

Project description:2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent environmental contaminant that disrupts normal hepatic function. This disruption leads to the development and progression of non-alcoholic fatty liver disease (NAFLD) pathologies, including steatosis, steatohepatitis, and fibrosis. TCDD exerts hepatotoxic effects through activation of the aryl hydrocarbon receptor (AHR) eliciting transcriptional changes. Although diverse liver cell types contribute to TCDD-induced hepatotoxicity, cell-specific transcriptional changes in response to acute TCDD exposure remain unclear. The objective of this project was to elucidate the cell-specific outcomes of AHR activation following acute TCDD exposure. We conducted liver single-nuclei RNA-sequencing from male C57BL/6 mice administered 30 μg/kg of TCDD or sesame oil and sacrificed at 2, 4, 8, 12, 18, 24, or 72 hours post-oral gavage. Leiden clustering and annotation identified 10 major liver cell types, and 2 macrophage and 8 endothelial cell (EC) subtypes. While most cell types maintained their relative abundance, neutrophils exhibited an increase at 72 hours in response to TCDD. Hepatocytes, ECs, and hepatic stellate cells (HSCs) were the only cell types with cell-specific gene expression changes with known AHR binding sites (1,550, 102, and 40, respectively). Functional enrichment analysis in response to TCDD revealed disruptions in the metabolism of steroids, primary bile acids, vitamins, retinols, and glutathione in addition to one-carbon metabolism. EC differential gene expression was associated with PI3-AKT signaling, as well as protein processing and transport pathways. HSCs were enriched in protein processing, ABC transporters, and the dysregulation of tryptophan and linoleic acid metabolism. Altogether, these results suggest that early responses to TCDD trigger cell-specific changes in gene expression in the liver, contributing to hepatotoxicity and the emergence of hepatic pathologies related to NAFLD.

Project description:Wild-type and AHR-KO rats harboring a 29-bp deletion mutation in exon 2 of the AHR gene were used in this study. Wild-type and AHR-KO rats were generated from heterozygous breeding stocks generated on a Sprague-Dawley outbred background and maintained at the Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina Persistent activation of the aryl hydrocarbon receptor (AHR) is believed to play a key role in the mode-of-action for TCDD induced rat liver tumorigenesis. It has been hypothesized that the cellular responses of hepatocytes to AHR activation may differ across regions of the liver lobule and that zone-specific effects of AHR agonists may play a role in the pathogenesis of rat liver tumorigenesis. Dose-dependent changes in gene expression were observed in both populations of hepatocytes collected from WT rats which were consistent with activation of AHR signaling. No significant or dose-dependent changes in gene expression were observed in samples from AHR-KO rats. In addition, evidence of inflammatory signaling pathway activation was observed only in centrilobular hepatocytes. Evidence of cell adhesion pathway enrichment was observed only in periportial hepatocytes. Benchmark dose analysis demonstrated that dose-dependent changes in gene expression occurred at lower doses in centrilobular as compared to periportal hepatocytes. These results indicate zone-specific differences in the sensitivity and response of hepatocytes to persistent AHR activation. AHR-KO and WT rats (n = 10 rats/dose/genotype) were dosed by oral gavage (4-5 doses / week, 19 total doses) with varying concentrations of TCDD in corn oil (0, 3, 22, 100, 300, 1000 ng/kg/day). Cryopreserved liver slices collected at necropsy were thawed, cryosectioned (12 Âµm thickness), fixed with ethanol and âquick-stainedâ with hematoxylin. Centrilobular and periportal hepatocytes were collected using laser capture microdissection. Total RNA was extracted, amplified and labeled using low-yield techniques and global transcriptomic profiles were obtained using Affymetrix Gene-Titan peg arrays.

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Hepatic pyruvate kinase muscle isoform 2 (Pkm2) induction in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-elicited oxidative stress is independent of NRF2 (RNA-Seq)

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