CX3CR1+ myeloid cell-intrinsic NOD2 signaling limits Crohn’s disease-associated intestinal fibrosis 2254570

Introduction Crohn’s disease (CD) is a chronic inflammatory bowel disease that often progresses to fibrostenotic disease, requiring surgical intervention. Intestinal fibrosis (IF) is a debilitating outcome of chronic inflammation, excessive collagen deposition, abnormal cellular functions and defective tissue remodeling. CD stems from a complex interplay of host genetics, immune dysregulation, microbial imbalance, and environmental cues. Notably, loss-of-function variants in nucleotide-binding oligomerization domain-containing protein 2 (NOD2) — a cytosolic innate-immune receptor and the strongest genetic risk factor for CD — increase susceptibility to IF. Yet, the cell-intrinsic mechanisms by which NOD2 deficiency promotes IF remain unclear. Methods We employed single-cell RNA sequencing (scRNA-seq) in a chronic chemical-induced colitis model using littermate wild-type and Nod2-/- mice. Complementary approaches, including qRT-PCR, immunohistochemistry, RNA in situ hybridization, flow cytometry, and conditional knockout mice, were used to validate cell populations and molecular signatures associated with IF. Results scRNA-seq revealed a distinct Pi16+ progenitor population, termed FAET (Fibroblast and Endothelial Transition) cells, emerging in the fibrotic gut. Trajectory analysis indicated that FAET cells in Nod2-/- mice aberrantly differentiate into inflammation-associated fibroblasts (IAFs) rather than endothelial cells (EndoCs), leading to crypt microvasculature loss. Cellular interactome and genetic studies identified CX3CR1+ myeloid cell-intrinsic NOD2 signaling maintains CX3CR1+CD206+ gut resident macrophages that favor a niche conducive for FAET-to-EndoC transition over IAF differentiation, promoting wound healing. Consistently, ileal biopsies of CD patients carrying NOD2 variants showed reduced CD206+ macrophages and disrupted stromal-immune communication networks. Conclusion CX3CR1+ myeloid cell-intrinsic NOD2 signaling establishes a pro-restitutive stromal-immune niche that constrains IF in CD. Funding Source The American Association of Immunologists (AAI) Intersect Fellowship Program for Computational Scientists and Immunologists, Canadian Institute of Health Research (CIHR) Fellowship Program Topic Categories Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)