Activation of Aryl Hydrocarbon Receptor Induces Vascular Inflammation and Promotes Atherosclerosis in Apolipoprotein E−/− Mice

Abstract

Objective— Exposure to dioxins has been shown to contribute to the development of inflammatory diseases, such as atherosclerosis. Macrophage-mediated inflammation is a critical event in the initiation of atherosclerosis. Previously, we showed that treatment of macrophages with 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD) leads to aryl hydrocarbon receptor (AhR)–dependent activation of inflammatory mediators and the formation of cholesterol-laden foam cells. However, the mechanisms responsible for the formation of atherosclerotic lesions mediated through AhR have not been identified. Methods and Results— An in vitro macrophage and an apolipoprotein E (ApoE)−/− mouse model were used to determine whether chemokines and their receptors are responsible for the AhR-mediated atherogenesis. Exposure of ApoE−/− mice to TCDD caused a time-dependent progression of atherosclerosis, which was associated with induction of inflammatory genes, including interleukin-8, as well as F4/80 and matrix metalloproteinase-12. A high-fat diet enhanced the TCDD-mediated inflammatory response and aggravated the formation of complex atheromas. Treatment with a CXCR2 inhibitor and an AhR antagonist reduced the TCDD-induced progression of early atherosclerotic lesions in ApoE−/− mice. Conclusion— The results suggest that CXCR2 mediates the atherogenic activity of environmental pollutants, such as dioxins, and contributes to the development of atherosclerosis through the induction of a vascular inflammatory response by activating the AhR-signaling pathway.