Abstract
Background: Regional colonization of microbiota in local tissue gradually exhibited a critical role in disease progression. One of the clearest examples was the migration of mesenteric adipose tissue, also known as creeping fat (CrF) in Crohn’s disease (CD), which was associated with the postoperative recurrence. But the underlying mechanism of CrF formation in response to the translocated microbiota was far from clear.
Methods: We established three chronic colitis mice models (Il-10^-/- mice, DSS-induced colitis and surgical operation model) to mimic the formation of creeping fat. Mice with clodronate or anti-CSF antibody were applied to evaluate the role of macrophages in mesenteric adipogenesis. A clinical CD cohort was established for targeted metabolome of tryptophan metabolism and the Ido1^-/- mice model was subsequently constructed. Mesenteric scRNA sequencing from Ido1^-/- mice as well as the construction of Ido1^flox/flox Lyz2-Cre mice and Ahr^flox/flox Adipoq-Cre mice were used to confirm the impact of macrophages-derived kynurenine in adipogenesis. Engineering Escherichia coli strain BL21 that encoded kynurenine aminotransferase (KAT) was constructed to mediate the L-kynurenine metabolism.
Results: Mesenteric microbiota was found to induced colitis and mesenteric adipogenesis in three different mice models. But depletion of macrophages by clodronate or anti-CSF antibody improved the colitis and mesenteric adipogenesis. Targeted metabolome found that L-kynurenine was the most obviously enriched metabolite in creeping fat. Infiltration of macrophages was associated with an upregulation of key enzyme indoleamine 2,3-dioxygenase 1 (IDO1) in kynurenine metabolism. Improvement of mesenteric adipogenesis was found in Ido1^-/- mice but exacerbated in Ido1^-/- mice with L-kynurenine intervention. Further analysis of mesenteric scRNA from Ido1^-/- mice revealed the decreased potential of Ido1^-/-macrophages in adipogenesis. Subsequent Ido1^flox/flox Lyz2-Cre mice model verified the responsibility of IDO1 in macrophages in mesenteric adipogenesis. Mechanically, L-kynurenine-induced adipogenesis was associated with an upregulation of Sqstm1 in pre-adipocyte but alleviated in Ahr^flox/flox Adipoq-Cre mice. Combination of IDO1 inhibitor epacadostat and TNF-α antibody infliximab reversed the exacerbation of mesenteric adipogenesis. Downregulation of L-kynurenine by engineering bacteria BL21-KAT also exhibited a therapeutic role during the mesenteric adipogenesis.
Conclusion: Mesenteric associated microbiota mediated the mesenteric adipogenesis through an alteration of kynurenine metabolism in macrophages and subsequent activation of autophagy signaling in pre-adipocytes via Ahr-Sqstm1 axis.
Keywords: Crohn's disease, Creeping fat, macrophage, kynurenine, microbiota

Hongyu Xie

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