This study reveals the critical immune-stromal interaction mechanisms underlying fibrosis in Crohn's disease, providing new S100A8/A9 and CCR1 intervention strategies for targeting intestinal fibrosis. It highlights the need to focus on the communication network between macrophage subsets and fibroblasts in experimental design.
Literature Overview
The article titled "S100A8/A9-High Macrophages Activate Intestinal Fibroblasts via mCCL6/hCCL15-CCR1 Axis to Drive Intestinal Fibrosis in Crohn's Disease," published in Advanced Science, systematically explores the cellular origins and molecular mechanisms of intestinal fibrosis in Crohn's disease (CD). Specifically, it identifies a profibrotic macrophage subset with high S100A8/A9 expression and delineates the specific pathway by which this subset activates fibroblasts via a chemokine axis.Background Knowledge
Crohn's disease is a chronic inflammatory bowel disease (IBD), with intestinal fibrotic strictures being one of its most severe complications, necessitating surgical intervention in approximately 75% of patients. Currently, effective anti-fibrotic drugs are lacking. The key challenge addressed by this study is the lack of clarity regarding the upstream immune cell subsets and critical signaling molecules that drive excessive fibroblast activation and abnormal extracellular matrix (ECM) deposition. The specific mechanisms of S100A8/A9 or CCR1 in intestinal fibrosis remain unclear, and preclinical validation targeting this axis is absent. This study leverages re-analysis of single-cell sequencing data to pinpoint a macrophage subset highly expressing S100A8/A9. Through in vivo adoptive transfer and in vitro co-culture systems, it confirms that this subset drives fibrosis by secreting mCCL6 (the human homolog is hCCL15), which activates the CCR1 receptor on fibroblasts.
Research Methods and Core Experiments
Authors first utilized single-cell RNA sequencing (scRNA-seq) data from full-thickness Crohn's disease tissues. Through cell-cell communication analysis (CellChat) and cell distance analysis (scDist), they screened for an S100A8/A9-high macrophage subset enriched in stenotic regions with the strongest communication with fibroblasts. To verify causality, a chronic DSS-induced colitis mouse model was constructed. Adoptive transfer technology was employed to reinfuse in vitro-induced S100A8/A9hi macrophages into mice to observe their impact on intestinal fibrosis. Additionally, reverse validation was performed using S100a9-knockdown macrophages, and pharmacological interventions were conducted using an S100A8/A9 inhibitor (Paquinimod) and an mCCL6 neutralizing antibody. At the mechanistic level, proteomic analysis was used to screen for key secreted factors. Combined with co-immunoprecipitation, chromatin immunoprecipitation (ChIP), and dual-luciferase reporter assays, the study elucidated the molecular mechanism wherein S100A9 activates STAT3 via TLR4, thereby transcriptionally regulating CCL6 expression.Key Conclusions and Perspectives
Research Significance and Prospects
This discovery offers new target combinations for drug development; inhibitors targeting the S100A8/A9 complex, STAT3, or CCR1 may become effective treatments for intestinal fibrosis in Crohn's disease. In terms of clinical monitoring, serum hCCL15 levels could serve as a biomarker for assessing the risk of intestinal strictures and disease activity. For disease modeling, this study suggests that when constructing fibrosis models for inflammatory bowel disease, priority should be given to the reprogramming of macrophage subsets and their interactions with stromal cells. Utilizing gene-edited mice or humanized models to further validate the therapeutic potential of this axis is recommended.
Conclusion
This study provides an in-depth analysis of the complex immune microenvironment in Crohn's disease-associated intestinal fibrosis, establishing for the first time the pivotal role of S100A8/A9hi macrophages as core effector cells. By elucidating the complete signaling axis of S100A8/A9-TLR4-STAT3-CCL6/CCR1, the research not only reveals the molecular switch governing fibrosis but also provides clear intervention targets for clinical translation. From mechanistic elucidation in the laboratory to preclinical efficacy validation, this work lays a solid theoretical foundation for developing novel therapies that block the progression of intestinal fibrosis. It holds the potential to shift the current passive treatment paradigm for Crohn's patients, which primarily relies on surgical resection of strictured bowel segments, and provides crucial scientific support for building a more comprehensive care system for Crohn's disease.
