Citrullination of CAMP exacerbating mucosal inflammation in inflammatory bowel disease.

BACKGROUND: Cathelicidin (CAMP), plays important roles in pathogen defense, immune regulation, and epithelial barrier maintenance. While previous studies have highlighted its protective function, the post-translational modifications and downstream immune-metabolic effects of CAMP in the pathogenesis of inflammatory bowel disease remain unclear. METHODS: A dextran sodium sulfate (DSS)-induced colitis mouse model was employed to assess the role of CAMP and its citrullination mediated by peptidyl arginine deiminase 4 (PAD4). Proteomic and metaproteomic analyses were performed to investigate microbiota composition and functional shifts. We generated gene-deficient mouse models, CAMP knockout (KO) and PAD4-KO mice, to dissect molecular mechanisms. Epithelial integrity, inflammatory markers, and immune responses have been evaluated at both the protein and mRNA levels. Bone marrow-derived dendritic cells and primary CD4⁺ T cells were co-cultured to examine the effects of CAMP-related metabolites on antigen presentation and Th17 differentiation. Furthermore, we evaluated the impact of CAMP peptide supplementation and the effects of CAMP-KO mice on DSS-induced colitis. RESULTS: CAMP citrullination was significantly elevated in DSS-induced colitis mice but restored by PAD4 deletion. Citrullination was found to reduce CAMP protein levels without affecting its transcriptional expression. The absence of CAMP exacerbated intestinal inflammation in DSS-treated mice. Metaproteomic analysis identified 70 differentially expressed proteins and 15 altered microbiota families associated with CAMP deficiency. Elevated levels of arginase-1 and its metabolites, particularly polyamines, enhanced dendritic cell maturation and increased Th17 polarization in CAMP-KO mice. CONCLUSIONS: Our findings highlight that the protein level of CAMP decreased after PAD4-mediated citrullination, thus playing a vital role in regulating taxonomic community structure, restricting arginine metabolism, and regulating dendritic cell-Th17 immune responses in IBD.