Abstract 17671: TCF21 Regulates Coronary Artery Disease Causing Aryl-hydrocarbon Receptor Gene Expression and its Downstream Pathway Activation by Environmental Ligands

Abstract

Background: Recently, the TCF21 gene was linked to the highly replicated coronary artery disease (CAD) associated polymorphism in the 6q23 locus. TCF21 is especially compelling as a causal gene since it is a transcription factor that is known to play a critical role in the development of coronary arteries. One downstream target gene identified through preliminary studies was AHR. AHR is a ligand-activated transcription factor that mediates the cellular response to environmental contaminants, including dioxin and polycyclic aromatic hydrocarbons (eg. cigarette smoke), and has recently been associated with CAD in mice and humans. We set out to identify the TCF21 downstream pathways that are related to CAD. Methods: We performed chromatin immunoprecipitation sequencing (ChIP-Seq) and RNA-sequencing using primary human coronary artery smooth muscle cells (HCASMC) to survey the targets of TCF21 binding and the regulated downstream pathways. The peaks from ChIP-Seq were identified using MACSv2 according to ENCODE parameters. RNA-Seq was analyzed using edgeR to identify the differentially expressed genes. The effect of TCF21 on Aryl-hydrocarbon receptor (AHR) pathway activation was tested using knockdown and overexpression lentivirus transduction of HCASMC followed by 2,3,7,8-Tetrachlorodibenxo- p -dioxin (TCDD) treatment and qPCR. Results: RNA-Seq studies identified AHR as a significantly regulated mRNA downstream of TCF21 (p=1.4x10 -5 ). Also, the ChIP-Seq identified multiple TCF21 binding peaks in the AHR gene. We found a significant overlap of the AHR and TCF21 binding peaks (p<1x10 -15 ) and genes differentially regulated by TCF21 and AHR (p=1x10 -5 ), among publicly available datasets. Furthermore, we found that the TCF21 level modulated the magnitude of the ligand-dependent activation of AHR pathway genes by TCDD. Conclusion: We identified a novel interaction between TCF21 and AHR, a gene involved in environmental xenobiotic response that was recently associated with CAD. The functional link between TCF21 and AHR provides an opportunity to explore gene by environment interactions in the pathogenesis of CAD.