P0051 DUOX2-Mediated Innate Immune Hyperactivation Drives Macrophage M1 Polarization via the APP-CD74 Axis in Inflammatory Bowel Disease

Abstract Background Inflammatory bowel disease (IBD) pathogenesis is predominantly attributed to adaptive immune dysregulation, while the contribution of innate immune effectors, particularly the reactive oxygen species (ROS)-generating enzyme DUOX2, remains less clear. This study investigates the role of DUOX2 in bridging epithelial innate immunity and chronic inflammation in IBD. Methods We integrated transcriptomic datasets from IBD patients and healthy controls to identify common differentially expressed genes (DEGs). DUOX2 expression and epithelial-specific localization were confirmed in clinical biopsies via immunofluorescence. Functional validation was pursued in a dextran sulfate sodium (DSS)-induced colitis model using DUOX2-knockout mice. Single-cell RNA sequencing (scRNA-seq) and cellular communication analysis were employed to characterize DUOX2-high enterocytes. The interaction between APP and CD74 was evaluated using molecular docking. Regulation of DUOX2 by the gut microbiota was examined via antibiotic treatment, fecal microbiota transplantation (FMT), and in vitro LPS stimulation of NCM460 cells. Results DUOX2 was identified as the most significantly upregulated gene among shared DEGs in IBD. Immunofluorescence confirmed its specific localization to intestinal epithelial cells, corroborating scRNA-seq findings. DUOX2 deficiency markedly attenuated DSS-induced colitis, accompanied by reduced epithelial apoptosis, neutrophil infiltration, and M1 macrophage polarization. scRNA-seq revealed that DUOX2-high enterocytes exhibited enhanced intercellular communication, specifically via the APP-CD74 ligand-receptor pair. Molecular docking demonstrated a high-affinity interaction between APP and CD74 (docking score: -13.3 kcal/mol), involving four hydrogen bonds (E121-R264, R301-S246, E139-R266, P299-R266). All interacting residues were located within the APP ectodomain, suggesting that the cleaved product sAPPα acts as the functional ligand. Finally, DUOX2 expression was upregulated by gut microbiota-derived LPS via the TLR4–NF-κB pathway. Conclusion Our findings delineate a novel pathogenic circuit in IBD: microbiota-induced DUOX2 overexpression in enterocytes promotes the APP-CD74 signaling axis, which is postulated to drive macrophage M1 pro-inflammatory polarization. The high-affinity interaction between APP and CD74 provides a mechanistic basis for this signaling. Future work validating that DUOX2-driven APP/sAPPα production directly induces M1 polarization via CD74 will solidify this model, positioning the DUOX2-APP-CD74 axis as a promising innate immune-specific therapeutic target in IBD. Conflict of interest: Ms. Xu, Yalan: No conflict of interest Chen, Ning: No conflict of interest