Background: IDO1 (indoleamine 2,3-dioxygenase 1) is the rate-limiting enzyme for tryptophan metabolism. IDO1 malfunction is involved in the pathogenesis of atherosclerosis. Vascular smooth muscle cells (VSMCs) with an osteogenic phenotype promote calcification and features of plaque instability. However, it remains unclear whether aberrant IDO1-regulated tryptophan metabolism causes VSMCs osteogenic reprogramming and calcification. Methods: We generated global Apoe ( apolipoprotein E ) and Ido1 double knockout mice, and Apoe knockout mice with specific deletion of IDO1 in VSMCs or macrophages. Arterial intimal calcification was evaluated by a Western diet–induced atherosclerotic calcification model. Results: Global deficiency of IDO1 boosted calcific lesion formation without sex bias in vivo. Conditional IDO1 loss of function in VSMCs rather than macrophages promoted calcific lesion development and the abundance of RUNX2 (runt-related transcription factor 2). In contrast, administration of kynurenine via intraperitoneal injection markedly delayed the progression of intimal calcification in parallel with decreased RUNX2 expression in both Apoe ^−/− and Apoe ^−/− Ido1 ^−/− mice. We found that IDO1 deletion restrained RUNX2 from proteasomal degradation, which resulted in enhanced osteogenic reprogramming of VSMCs. Kynurenine administration downregulated RUNX2 in an aryl hydrocarbon receptor–dependent manner. Kynurenine acted as the endogenous ligand of aryl hydrocarbon receptor, controlled resultant interactions between cullin 4B and aryl hydrocarbon receptor to form an E3 ubiquitin ligase that bound with RUNX2, and subsequently promoted ubiquitin-mediated instability of RUNX2 in VSMCs. Serum samples from patients with coronary artery calcification had impaired IDO1 activity and decreased kynurenine catabolites compared with those without calcification. Conclusions: Kynurenine, an IDO1-mediated tryptophan metabolism main product, promotes RUNX2 ubiquitination and subsequently leads to its proteasomal degradation via an aryl hydrocarbon receptor–dependent nongenomic pathway. Insufficient kynurenine exerts the deleterious role of IDO1 ablation in promoting RUNX2-mediated VSMCs osteogenic reprogramming and calcification in vivo.

Background: Abnormal amino acid metabolism is associated with vascular disease. However, the causative link between dysregulated tryptophan metabolism and abdominal aortic aneurysm (AAA) is unknown. Methods: Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting enzyme in the kynurenine pathway of tryptophan metabolism. Mice with deficiencies in both apolipoprotein e (Apoe) and IDO (Apoe ^–/– /IDO ^–/– ) were generated by cross-breeding IDO ^–/– mice with Apoe ^–/– mice. Results: The acute infusion of angiotensin II markedly increased the incidence of AAA in Apoe ^–/– mice, but not in Apoe ^–/– /IDO ^–/– mice, which presented decreased elastic lamina degradation and aortic expansion. These features were not altered by the reconstitution of bone marrow cells from IDO ^+/+ mice. Moreover, angiotensin II infusion instigated interferon-γ, which induced the expression of IDO and kynureninase and increased 3-hydroxyanthranilic acid (3-HAA) levels in the plasma and aortas of Apoe ^–/– mice, but not in IDO ^–/– mice. Both IDO and kynureninase controlled the production of 3-HAA in vascular smooth muscle cells. 3-HAA upregulated matrix metallopeptidase 2 via transcription factor nuclear factor-κB. Furthermore, kynureninase knockdown in mice restrained 3-HAA, matrix metallopeptidase 2, and resultant AAA formation by angiotensin II infusion. Intraperitoneal injections of 3-HAA into Apoe ^–/– and Apoe ^–/– /IDO ^–/– mice for 6 weeks increased the expression and activity of matrix metallopeptidase 2 in aortas without affecting metabolic parameters. Finally, human AAA samples had stronger staining with the antibodies against 3-HAA, IDO, and kynureninase than those in adjacent nonaneurysmal aortic sections of human AAA samples. Conclusions: These data define a previously undescribed causative role for 3-HAA, which is a product of tryptophan metabolism, in AAA formation. Furthermore, these findings suggest that 3-HAA reduction may be a new target for treating cardiovascular diseases.

Rationale: Nicotine has been reported to be a strong risk factor for atherosclerosis. However, the underlying mechanism by which nicotine controls atherosclerotic plaque stability remain largely unknown.

Vascular aging, characterized by arterial thickening, reduced elasticity, and endothelial dysfunction, significantly compromises vascular health and accelerates the progression of cardiovascular diseases (CVDs). Emerging research highlights the gut–vascular axis as a critical mediator of vascular health, with the gut microbiota (GM) playing a pivotal role in modulating vascular aging and CVDs. This review presents a thorough and up-to-date discussion of the fundamental mechanisms driving vascular aging and explores how GM and its metabolites influence these processes. Furthermore, we place particular emphasis on therapeutic strategies, including probiotics and food-derived natural products, that foster beneficial bacterial growth and support cardiovascular health, while also exploring the underlying mechanisms. By targeting GM composition and function, these approaches offer promising strategies to mitigate vascular aging and lower CVD risk. Future studies aimed at deepening our understanding of the interplay between GM, its metabolites, and vascular health could pave the way for novel preventive and therapeutic interventions against vascular aging and CVDs.

Endothelial cell (EC) dysfunction is a hallmark of obesity and Type 2 diabetes mellitus (T2DM), yet the mechanisms linking vascular stress to systemic metabolic diseases remain unclear. Here, we investigated the role of the mitochondrial protein FUN14 domain-containing 1 (FUNDC1) in EC under nutritional overload. Using high-fat diet (HFD)-fed EC-specific Fundc1 knockout mice, human umbilical vein ECs, primary ECs, and vascular tissues from patients with obese/T2DM, we find that endothelial FUNDC1 expression is elevated under diabetic conditions, whereas its deletion protects mice from HFD-induced obesity, insulin resistance, and metabolic disorders. Mechanistically, overnutrition triggers nuclear export of the long isoform of SIRT3 (SIRT3-L) to mitochondria via FUNDC1, disinhibiting GATA2 and enhancing endothelin-1 (ET-1) production. Loss of FUNDC1 in ECs retains SIRT3-L in the nucleus, promoting GATA2 degradation and reducing ET-1. Endothelial FUNDC1 levels correlated positively with plasma ET-1 in individuals with obesity/T2DM. These findings identify endothelial FUNDC1 as a key regulator of vasculature-metabolic organ cross talks and obesity-diabetes transition.