Postdoctoral Fellow University of Toronto Toronto, Ontario, Canada
Disclosure(s):
Tapas Mukherjee, PhD: No financial relationships to disclose
Introduction/Rationale: 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.
