Upregulated Kynurenine pathway enzymes in aortic atherosclerotic aneurysm: Macrophage kynureninase downregulates inflammation

Abstract

Aims: Inflammation and hypertension contribute to the progression of atherosclerotic aneurysm in the aorta. Vascular cell metabolism is regarded to modulate atherogenesis, but the metabolic alterations that occur in ath-erosclerotic aneurysm remain unknown. The present study aimed to identify metabolic pathways and metabolites in aneurysmal walls and examine their roles in atherogenesis. Methods: Gene expression using microarray and metabolite levels in the early atherosclerotic lesions and aneu-rysmal walls obtained from 42 patients undergoing aortic surgery were investigated (early lesion n=11, aneurysm n =35) and capillary electrophoresis–time-of-flight mass spectrometry (early lesion n =14, aneurysm n =38). Using immunohistochemistry, the protein expression and localization of the identified factors were examined (early lesion n=11, non-aneurysmal advanced lesion n=8, aneurysm n =11). The roles of the factors in athero-genesis were analyzed in macrophages derived from human peripheral blood mononuclear cells. Results: Enrichment analysis using 35 significantly upregulated genes (log2 ratio, ＞3) revealed the alteration of the kynurenine pathway. Metabolite levels of tryptophan, kynurenine, and quinolinic acid and the kynurenine-to-tryptophan ratio were increased in the aneurysmal walls. Gene and protein expression of kynureninase and kynurenine 3-monooxygenase were upregulated and localized in macrophages in the aneurysmal walls. The silencing of kynureninase in the cultured macrophages enhanced the expression of interleukin-6 and indoleamine 2,3-dioxygenase 1. Conclusion: Our study suggests the upregulation of the kynurenine pathway in macrophages in aortic athero-sclerotic aneurysm. Kynureninase may negatively regulate inflammation via the kynurenine pathway itself in macrophages.