Abstract 703: Dioxin-induced Smooth Muscle Cell Phenotypic Modulation And Atherosclerosis Worsens In The Absence Of AHR

Abstract

Background: Dioxin (TCDD, 2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin) is an active constituent of tobacco smoke and air pollution that activates the aryl hydrocarbon receptor (AHR). Dioxin has been linked to an increased risk of coronary artery disease (CAD). However, the corresponded molecular mechanisms remain unclear. Smooth muscle cells (SMC) play a critical role in atherosclerotic plaque remodeling due to their phenotypic plasticity. In this study, we aimed to understand the role of AHR in modulating the effect of dioxin on vascular SMC and atherosclerosis phenotype. Methods: SMC lineage-tracing (SMC Lin ) mice ( Tg Myh11-CreERT2 , ROSA tdT/tdT , ApoE -/- ) without any TCDD injection were used as control. TCDD were injected to both SMC Lin mice, and SMC-specific Ahr knockout mice. High fat diet (HFD) and TCDD injection started at 8 weeks of age and aortic roots were harvested at 24 weeks of age for either histology or single-cell sequencing (10X Genomics, triplicates). Histology analysis was performed at the aortic sinus of control mice (n=9), TCDD injected SMC Lin mice (n=12) and TCDD injected SMC-specific Ahr knockout mice (n=9). Immunohistochemistry was performed with anti-SM22α antibody and CD68 antibody. Results: The histological analysis of the aortic sinus showed increased lesion area after TCDD treatment in the SMC Lin control mice. In the SMC-specific knockout of Ahr , the lesion area was significantly larger compared to the SMC Lin control mice when treated with TCDD along with significantly increased presence of Tagln + cells in the lesion. These results indicated TCDD leads to adverse remodeling of atherosclerosis and that the presence of Ahr gene is protective against the athero-promoting effects of dioxin. The scRNA-seq of SMC Lin control mice treated with TCDD exposure showed that the SMC phenotypic modulation was markedly inhibited, leading to the presence of fewer fibromyocytes (FMC). Increased FMC to chondromyocytes (CMC) modulation resulted in further reduction of FMC population in the Ahr -KO mice treated with TCDD. Conclusion: Dioxin adversely remodels atherosclerotic plaque, and the lack of AHR in SMC can exacerbate the atherosclerotic process, suggesting that dioxin may exhibit its harmful effect via non-AHR dependent pathway.