Microbiota-induced alteration of kynurenine metabolism in macrophages drives formation of creeping fat in Crohn's disease.

Hyperplasia of mesenteric tissues in Crohn's disease, called creeping fat (CrF), is associated with surgical recurrence. Although microbiota translocation and colonization have been found in CrF, convincing mouse phenotypes and the underlying mechanisms of CrF formation remain unclear. Utilizing single-nucleus RNA (snRNA) sequencing of CrF and different mouse models, we demonstrate that the commensal Achromobacter pulmonis induces mesenteric adipogenesis through macrophage alteration. Targeted metabolome analysis reveals that L-kynurenine is the most enriched metabolite in CrF. Upregulation of indoleamine 2,3-dioxygenase 1 (IDO1) enhances kynurenine metabolism and drives mesenteric adipogenesis. Leveraging single-cell RNA (scRNA) sequencing of mouse mesenteric tissues and macrophage-specific IDO1 knockout mice, we verify the role of macrophage-sourced L-kynurenine in mesenteric adipogenesis. Mechanistically, L-kynurenine-induced adipogenesis is mediated by the aryl hydrocarbon receptors in adipocytes. Administration of an IDO1 inhibitor or bacteria engineered to degrade L-kynurenine alleviates mesenteric adipogenesis in mice. Collectively, our study demonstrates that microbiota-induced modulation of macrophage metabolism potentiates CrF formation.