Abstract Background Inflammatory bowel disease pathogenesis involves genetic susceptibility, environmental factors, and intestinal microbiota dysbiosis. A key mechanism is the dysfunction of autophagy within intestinal epithelial cells, a critical process for maintaining cellular homeostasis and barrier integrity. Defective autophagy disrupts mucosal immunity, antimicrobial defense, and epithelial repair, promoting inflammation. The kynurenine pathway of tryptophan metabolism is altered in IBD, but the specific roles of its metabolites, particularly Quinolinic Acid (QA), remain poorly defined in the gut. This study therefore focuses on elucidating the role of QA in disrupting autophagy-dependent intestinal barrier homeostasis. Methods Untargeted fecal metabolomics compared 34 active IBD patients (23 CD, 11 UC) to 29 non-IBD controls. Functional validation was performed in vitro models (HT-29 cells, colon organoids) and in vivo colitis models (DSS- and TNBS-induced colitis). Apoptosis was assessed via TUNEL staining and Annexin V, and autophagy was evaluated by Western blot (LC3B, Beclin-1, ATG16L1, ATG12-5) and transcriptomics profiling. Interventions included QA administration, autophagy activator rapamycin, inhibitor 3-MA, and an ULK1 inhibitor. Molecular docking and biotin-streptavidin pulldown assays were performed to identify QA-binding targets. Results Metabolomics identified significantly accumulated QA in IBD feces (p 0.001), correlating with CD severity (p 0.01). QA administration exacerbated murine DSS- and TNBS-induced colitis, evidenced by increased weight loss, disease activity index (DAI), colon shortening, histopathological damage, apoptosis (TUNEL+ cells: 1.14% vs 0.69%, p 0.05), and mortality (HR = 3.156, p 0.05). Transcriptomics analysis revealed QA upregulated apoptosis-related genes and suppressed autophagy pathways. QA synergized with TNF-α to promote apoptosis in HT-29 cells and organoids (p 0.01), reversible by rapamycin. QA treatment downregulated autophagy markers in colon tissue and epithelial cells. Autophagy inhibitor 3-MA did not further enhance QA-induced apoptosis, while rapamycin alone alleviated colitis but showed no additive benefit with QA. Pulldown assays and molecular docking identified ULK1 as a direct QA target, forming hydrogen bonds at LYS-46, ASP-165, ALA-28, and PHE-27. Pharmacological ULK1 inhibition abrogated QA-mediated autophagy suppression, confirming ULK1 as a key mechanistic target. Conclusion QA is a critical metabolic driver that directly binds and inhibits ULK1, suppressing intestinal epithelial autophagy, synergizing with TNF-α to promote apoptosis, and exacerbating IBD pathogenesis. Targeting the QA-ULK1-autophagy axis represents a potential therapeutic strategy for IBD. References: 1.Wang S, Dong Z, Wan X. Global, regional, and national burden of inflammatory bowel disease and its associated anemia, 1990 to 2019 and predictions to 2050: An analysis of the global burden of disease study 2019. Autoimmun Rev. 2024;23(3):103498. doi:10.1016/j.autrev.2023.103498 2.Larabi A, Barnich N, Nguyen HTT. New insights into the interplay between autophagy, gut microbiota and inflammatory responses in IBD. Autophagy. 2020;16(1):38-51. doi:10.1080/15548627.2019.1635384 3.Pott J, Kabat AM, Maloy KJ. Intestinal Epithelial Cell Autophagy Is Required to Protect against TNF-Induced Apoptosis during Chronic Colitis in Mice. Cell Host Microbe. 2018;23(2):191-202.e4. doi:10.1016/j.chom.2017.12.017 Conflict of interest: Xia, Wenhao: No conflict of interest Yao, Lingya: No conflict of interest Xu, Yining: No conflict of interest Cao, Qian: No conflict of interest
Xia et al. (Thu,) studied this question.