Dataset Information

TCF21 and the environmental sensor aryl-hydrocarbon receptor cooperate to activate a pro-inflammatory gene expression program in coronary artery smooth muscle cells.

ABSTRACT: Both environmental factors and genetic loci have been associated with coronary artery disease (CAD), however gene-gene and gene-environment interactions that might identify molecular mechanisms of risk are not easily studied by human genetic approaches. We have previously identified the transcription factor TCF21 as the causal CAD gene at 6q23.2 and characterized its downstream transcriptional network that is enriched for CAD GWAS genes. Here we investigate the hypothesis that TCF21 interacts with a downstream target gene, the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor that mediates the cellular response to environmental contaminants, including dioxin and polycyclic aromatic hydrocarbons (e.g., tobacco smoke). Perturbation of TCF21 expression in human coronary artery smooth muscle cells (HCASMC) revealed that TCF21 promotes expression of AHR, its heterodimerization partner ARNT, and cooperates with these factors to upregulate a number of inflammatory downstream disease related genes including IL1A, MMP1, and CYP1A1. TCF21 was shown to bind in AHR, ARNT and downstream target gene loci, and co-localization was noted for AHR-ARNT and TCF21 binding sites genome-wide in regions of HCASMC open chromatin. These regions of co-localization were found to be enriched for GWAS signals associated with cardio-metabolic as well as chronic inflammatory disease phenotypes. Finally, we show that similar to TCF21, AHR gene expression is increased in atherosclerotic lesions in mice in vivo using laser capture microdissection, and AHR protein is localized in human carotid atherosclerotic lesions where it is associated with protein kinases with a critical role in innate immune response. These data suggest that TCF21 can cooperate with AHR to activate an inflammatory gene expression program that is exacerbated by environmental stimuli, and may contribute to the overall risk for CAD.

SUBMITTER: Kim JB

PROVIDER: S-EPMC5439967 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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TCF21 and the environmental sensor aryl-hydrocarbon receptor cooperate to activate a pro-inflammatory gene expression program in coronary artery smooth muscle cells.

Kim Juyong Brian JB Pjanic Milos M Nguyen Trieu T Miller Clint L CL Iyer Dharini D Liu Boxiang B Wang Ting T Sazonova Olga O Carcamo-Orive Ivan I Matic Ljubica Perisic LP Maegdefessel Lars L Hedin Ulf U Quertermous Thomas T

PLoS genetics 20170508 5

Both environmental factors and genetic loci have been associated with coronary artery disease (CAD), however gene-gene and gene-environment interactions that might identify molecular mechanisms of risk are not easily studied by human genetic approaches. We have previously identified the transcription factor TCF21 as the causal CAD gene at 6q23.2 and characterized its downstream transcriptional network that is enriched for CAD GWAS genes. Here we investigate the hypothesis that TCF21 interacts wi ...[more]

PMID: 28481916

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Project description:Genome-wide association studies (GWAS) for coronary artery disease (CAD, also termed coronary heart disease, CHD) have discovered and validated 48 loci genome-wide and recent 1000-Genomes based meta-analyses have discovered additional 8 loci with significant association, however, true follow-up studies on the mechanisms of association are still scarce. Here we analyze the relationship of two transcription factors, TCF21, one of the lead GWAS candidate genes for coronary artery disease and AHR, aryl hydrocarbon receptor, which previously was not implicated as fundamental for the atherosclerotic process. We show that both the predicted and in-vivo ChIP-Seq binding sites for TCF and AHR colocalize in the human genome with over 400 predicted sites and 119 ChIP-Seq sites directly overlapping. TCF and AHR-ARNT predicted binding sites longitudinal phasing was observed near the transcription start sites, outlining the position of +1 nucleosome. AHR-ARNT matrix was highly enriched in both TCF21 ChIP-Seq peaks and ATAC-Seq open chromatin regions in human coronary artery smooth muscle cells (HCASMC), implicating the role of AHR in this important cell type for vascular biology. Co-expression modules of TCF21 and AHR showed high degree of connectivity. Separation of rotationally phased and unphased predicted binding sites for TCF and AHR resolved the roles of direct and indirect TCF-AHR interactions, and implicated as highly-modulated various inflammatory, interleukin and cytokine related processes, while ChIP-Seq co-localization of TCF21 and AHR/ARNT emphasized the role of calcium related processes. We performed TCF21 overexpression analysis in human coronary artery smooth muscle cells (HCASMC) and obtained GO ontologies that recapitulate in vivo pathophysiology of the atherosclerotic vessel wall, and a set of chronic inflammatory ontologies was established with the colocalization of TCF21 and AHR ChIP-Seq sites as well as with the binomial testing of GWAS SNP overrepresentation. We experimentally confirmed that TCF21 binds to and regulates AHR gene expression in HCASMC, as well as to elements near AHR downstream genes, such as CYP1A1, using reporter assays. The functional relevance of AHR pathway in HCASMC is confirmed using AHR ligands TCDD and oxidized LDL. Finally, we show that AHR is elevated in atherosclerotic arteries using laser capture microdissection in mice in vivo and in human ex vivo. In conclusion, we extend GWAS results to functional assays and show that TCF21 and AHR functional connectivity provides a novel mechanism for diseased coronary vessel wall biology.

Project description:Atmospheric particulate matter (PM) is a complex component of air pollution and the leading environmental risk factor for death worldwide. PM is formed from a combination of primary sources that emit PM directly into the atmosphere and secondary sources that emit gaseous precursors which oxidize in the atmosphere to form PM and composed of both inorganic and organic components. Currently, all PM is regulated by total mass. This regulatory strategy does not consider individual chemical constituents and assumes all PM is equally toxic. The chemically-extracted organic fraction (OF) of PM retains most organic constituents such as polycyclic aromatic hydrocarbons (PAHs) and excludes inorganics. PAHs are ubiquitous environmental toxicants and known aryl hydrocarbon receptor (AHR) ligands. This study addressed the role of individual components, specifically PAHs, of PM and how differences in chemical composition of real-world samples drive differential responses. This study tested the hypothesis that real-world extracts containing different combinations and concentrations of PAHs activate the AHR and enhance T helper (Th)17 differentiation to different degrees based on specific PAHs present in each sample, and not simply the mass of PM. The ability of the real-world OF, with different PAH compositions, to enhance Th17 differentiation and activate the AHR was tested in vitro. Cumulatively, the results identified PAHs as possible candidate components of PM contributing to increased inflammation and demonstrated that the sum concentration of PAHs does not determine the extent to which each PM activates the AHR and enhances Th17 differentiation suggesting individual components of each PM, and interactions of those components with others in the mixture, contribute to the inflammatory response. This demonstrates that not all PM are the same and suggests that when regulating PM based on its ability to cause human pathology, a strategy based on PM mass may not reduce pathologic potential of exposures.

Project description:Recent genome wide association studies have identified a number of genes that contribute to the risk for coronary heart disease. One such gene, TCF21, encodes a basic-helix-loop-helix transcription factor believed to serve a critical role in the development of epicardial progenitor cells that give rise to coronary artery smooth muscle cells (SMC) and cardiac fibroblasts. Using reporter gene and immunolocalization studies with mouse and human tissues we have found that vascular TCF21 expression in the adult is restricted primarily to adventitial cells associated with coronary arteries and also medial SMC in the proximal aorta of mouse. Genome wide RNA-Seq studies in human coronary artery SMC (HCASMC) with siRNA knockdown found a number of putative TCF21 downstream pathways identified by enrichment of terms related to CAD, including "vascular disease," "disorder of artery," and "occlusion of artery," as well as disease-related cellular functions including "cellular movement" and "cellular growth and proliferation." In vitro studies in HCASMC demonstrated that TCF21 expression promotes proliferation and migration and inhibits SMC lineage marker expression. Detailed in situ expression studies with reporter gene and lineage tracing revealed that vascular wall cells expressing Tcf21 before disease initiation migrate into vascular lesions of ApoE-/- and Ldlr-/- mice. While Tcf21 lineage traced cells are distributed throughout the early lesions, in mature lesions they contribute to the formation of a subcapsular layer of cells, and others become associated with the fibrous cap. The lineage traced fibrous cap cells activate expression of SMC markers and growth factor receptor genes. Taken together, these data suggest that TCF21 may have a role regulating the differentiation state of SMC precursor cells that migrate into vascular lesions and contribute to the fibrous cap and more broadly, in view of the association of this gene with human CAD, provide evidence that these processes may be a mechanism for CAD risk attributable to the vascular wall.

Dataset Information

TCF21 and the environmental sensor aryl-hydrocarbon receptor cooperate to activate a pro-inflammatory gene expression program in coronary artery smooth muscle cells.

Publications

TCF21 and the environmental sensor aryl-hydrocarbon receptor cooperate to activate a pro-inflammatory gene expression program in coronary artery smooth muscle cells.

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