Atheroma plaque microenvironment stimulates kynurenine production by macrophages to induce endothelial adhesion molecules in the context of atherogenesis

Cardiovascular diseases, including atherosclerosis, are major causes of morbidity and mortality worldwide. Here, we investigate the role of the kynurenine pathway (KP) in macrophages in the context of atheroma plaque microenvironment and its impact on atherogenesis. Using an in vitro model of primary human macrophages, we observed that exposure to plaque homogenates induces a marked increase in the early steps of the KP which impacts on kynurenine production. This was confirmed by immunostaining on human plaque of carotid arteries. Further investigation into the underlying molecular mechanisms revealed that LXR signaling contributes to this plaque microenvironment-induced KP activation. We showed that kynurenine released from macrophages affected endothelial cells, leading to increased expression of ICAM-1 and VCAM-1 in an AhR-dependent manner. Consistently with the proatherogenic effects, in a cohort of atherosclerotic patients, we observed higher levels of plasma kynurenine in patients with lower extremity arterial disease. In line with the results of in vitro investigations, the plasma kynurenine levels were associated plaque oxysterol content. Using a multiple logistic regression model, we showed that plasma kynurenine was independently associated with lower extremity arterial disease in atherosclerotic patients. Altogether, our data indicate that the activation of KP in macrophages in the context of atheroma plaque is partially mediated by LXR axis and leads to the release of kynurenine. This, in turn, contributes to the exacerbation of both local and peripheral atherosclerosis particularly through the activation of endothelial cells.