Comparisons of differential gene expression elicited by TCDD, PCB126, βNF, or ICZ in mouse hepatoma Hepa1c1c7 cells and C57BL/6 mouse liver

Abstract

The aryl hydrocarbon receptor (AhR) is a promiscuous receptor activated by structurally diverse synthetic and natural compounds. AhR activation may lead to ligand-specific changes in gene expression despite similarities in mode of action. Therefore, differential gene expression elicited by four structurally diverse, high affinity AhR ligands (2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 10 nM, 30 µg/kg), 3,3′,4,4′,5-pentachlorobiphenyl (PCB126; 100 nM, 300 µg/kg), β-naphthoflavone (βNF; 10 µM, 90 mg/kg), and indolo[3,2-b]carbazole (ICZ; 1 µM)) in mouse Hepa1c1c7 hepatoma cells and C57BL/6 mouse liver samples were compared. A total of 288, 183, 119, and 131 Hepa1c1c7 genes were differentially expressed (|fold-change| ≥ 1.5, P1(t) ≥ 0.9999) by TCDD, βNF, PCB126, and ICZ, respectively. Only ~35% were differentially expressed by all 4 ligands in Hepa1c1c7 cells. In vivo, 661, 479, and 265 hepatic genes were differentially expressed following treatment with TCDD, βNF, and PCB126, respectively. Similar to Hepa1c1c7 cells, ≤34% of gene expression changes were common across all ligands. Principal components analysis identified time-dependent gene expression divergence. Comparisons of ligand-elicited expression between Hepa1c1c7 cells and mouse liver identified only 11 common gene expression changes across all ligands. Although metabolism may explain some ligand-specific gene expression changes, PCB126, βNF, and ICZ also elicited divergent expression compared to TCDD, suggestive of selective AhR modulation.

The Aryl Hydrocarbon Receptor in Barrier Organ Physiology, Immunology, and Toxicology

“…Other tryptophan derivatives, the kynurenines, and further downstream products such as the newly identified cinnabarinic acid (stimulates IL-22) display large potential as well (Mezrich et al, 2010;Lowe et al, 2014). Although global gene expression profiles and promoter studies have shed some light on the activities of SAhRMs, AhR antagonists and agonists, and selective modulators for other receptors (Sun et al, 2004;Nohara et al, 2006;Suzuki and Nohara, 2007;Nault et al, 2013), the factors important for the selectivity of a specific AhR ligand are not well understood and require further investigation.…”

SEURAT-1 liver gold reference compounds: a mechanism-based review

“…However, a close correspondence between a conserved core of gene expression patterns and the key events that represent the nodes or events downstream of the nodes would be an ideal result. We can expect that we will need on the order of five reference compounds for each MIE to prove such a relation (Nault et al 2013).…”

“…The AHR target genes that have been most often studied specifically in liver are involved in phases I and II xenobiotic metabolism. Of these, activation of CYP1A1 is seen in diverse tissues in many species and is a sensitive marker due to its low background expression levels; other metabolic enzymes upregulated in the liver include CYP1A2, NQO1, and TIPARP (TCDD-inducible poly [ADP-ribose] polymerase) (Birnbaum and Tuomisto 2000;Nault et al 2013;Safe 1995). Interestingly, AHR also increases Nrf2 transcription, which does not activate the pathway but may act as a priming mechanism .…”

“…Since both interaction with a given response element and crosstalk with other receptors are dependent on ligand structure, ligand structure represents a point of variability in gene expression profiles, which can be extreme. A study of four AHR ligands in a human hepatocyte cell line, for example, showed a total of 440 genes activated, with 287 unique to a specific ligand and only 41 common to all ligands (Nault et al 2013).…”

The aryl hydrocarbon receptor as a moderator of host-microbiota communication

“…For example, might we expect potent agonists like TCDD or FICZ to exhibit the same metabolomic profile or can distinct metabolic profiles be obtained that differentiate toxicity from health promoting benefits? Suggestions from studies in Hepa1c1c7 and C57Bl/6 mice exposed to TCDD, 3,3′,4,4′,5-pentachlorobiphenyl (PCB-126), β-naphthoflavone, and indolo[3,2-b]carbazole suggest that indeed selective AHR modulation might exert different metabolic effects [38]. These studies of course are not without their complications given that dose considerations must take into account factors like differential binding affinity as well as half-life.…”