Disruption of Aryl Hydrocarbon Receptor Homeostatic Levels during Embryonic Stem Cell Differentiation Alters Expression of Homeobox Transcription Factors that Control Cardiomyogenesis

Abstract

Background: The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates the expression of xenobiotic detoxification genes and is a critical mediator of gene–environment interactions. Many AHR target genes identified by genome-wide gene expression profiling have morphogenetic functions, suggesting that AHR may play a role in embryonic development.Objectives: To characterize the developmental functions of the AHR, we studied the consequences of AHR activation by the agonist 2,3,7,8-tetrachlorodibenzo-p-doxin (TCDD), and the result of its repression by the antagonists 6,2,4-trimethoxyflavone and CH 223191 or by short-hairpin RNA (shRNA)-mediated Ahr knockdown during spontaneous differentiation of embryonic stem (ES) cells into cardiomyocytes.Methods: We generated an AHR-positive cardiomyocyte lineage differentiated from mouse ES cells that expresses puromycin resistance and enhanced green fluorescent protein (eGFP) under the control of the Cyp1a1 (cytochrome P450 1a1) promoter. We used RNA sequencing (RNA.Seq) to analyze temporal trajectories of TCDD-dependent global gene expression in these cells during differentiation.Results: Activation, inhibition, and knockdown of Ahr significantly inhibited the formation of contractile cardiomyocyte nodes. Global expression analysis of AHR-positive cells showed that activation of the AHR/TCDD axis disrupted the concerted expression of genes that regulate multiple signaling pathways involved in cardiac and neural morphogenesis and differentiation, including dozens of genes encoding homeobox transcription factors and Polycomb and trithorax group proteins.Conclusions: Disruption of AHR expression levels resulted in gene expression changes that perturbed cardiomyocyte differentiation. The main function of the AHR during development appears to be the coordination of a complex regulatory network responsible for attainment and maintenance of cardiovascular homeostasis.Citation: Wang Q, Chen J, Ko CI, Fan Y, Carreira V, Chen Y, Xia Y, Medvedovic M, Puga A. 2013. Disruption of aryl hydrocarbon receptor homeostatic levels during embryonic stem cell differentiation alters expression of homeobox transcription factors that control cardiomyogenesis. Environ Health Perspect 121:1334–1343; http://dx.doi.org/10.1289/ehp.1307297

In utero exposure of rats to high-fat diets perturbs gene expression profiles and cancer susceptibility of prepubertal mammary glands

“…Clustering was performed with the GENE-E algorithm (http://www.broadinstitute.org/cancer/software/GENE-E/). The gene expression data and results [34] have been deposited in the Gene Expression Omnibus (GEO, GSE73604). The expression level of each gene was determined, and the differences of gene expression between two groups were determined by t-test, and the false discovery rate was based on previously published protocols [34].…”

“…The gene expression data and results [34] have been deposited in the Gene Expression Omnibus (GEO, GSE73604). The expression level of each gene was determined, and the differences of gene expression between two groups were determined by t-test, and the false discovery rate was based on previously published protocols [34]. Genes differentially expressed in HFBUTTER in mammary transcriptomes were analyzed further by knowledge-based Ingenuity Pathways (IPA) network online software (www.ingenuity.com).…”

Does the aryl hydrocarbon receptor regulate pluripotency?

“…Ahr mRNA expression completely disappears during the cleavage divisions and becomes de novo detectable in early blastocysts [24, 25, 27]. After implantation, the earliest that AHR expression has been detected is in E7.5 embryos [9], becoming thereafter detectable in almost all developing organs [24, 28]. These observations suggest that the AHR may play a stage-dependent developmental function, possibly behaving as a differentiation-promoting factor that opposses pluripotency.…”

“…AHR repression may provide the ICM cells with the opportunity to reprogram gene expression, implementing epigenetic mechanisms that bring about global changes in DNA methylation [22-27]. In addition, the AHR might also play a significant role in the determination of cell fate decisions, as suggested by the correlation between AHR expression and lineage specification after implantation [9, 28]. The fact that the pattern of AHR expression parallels these changes suggests that the association of the receptor with a repressive chromatin configuration might ultimately play a determinant role in differentiation.…”

Aryl hydrocarbon receptor (AHR): “pioneer member” of the basic-helix/loop/helix per - Arnt - sim (bHLH/PAS) family of “sensors” of foreign and endogenous signals

“…Jup -encoded plakoglobin plays a pivotal role in intercellular junctions; when Jup is suppressed by AHR — cell adherence and proliferation become dysregulated (Prochazkova et al , 2013). Disruption of AHR-signaling activity thus perturbs cardiomyocyte differentiation; reasons for this perturbation include alterations in expression of homeobox transcription factors (Wang et al , 2013). …”