Citrullination of CAMP exacerbating mucosal inflammation in inflammatory bowel disease

Abstract 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.