Mucosal macrophages govern intestinal regeneration in response to injury.

Cancer patients treated with radiotherapy in the abdominal and pelvic cavity develop radiation-induced enteritis, a condition that impairs their quality of life. Radiation injury depletes proliferative intestinal stem cells (ISCs); in response to this, the epithelium activates a regenerative program that facilitates the healing of the intestine. However, the mechanisms that induce the activation of the intestinal regenerative program are poorly characterized. In this study, we induced radiation-induced enteritis in mice through abdominal irradiation, mimicking clinical scenarios. Through imaging and flow cytometric analysis, we investigated the recruitment of macrophages to the small intestine during injury and healing. Additionally, we developed a co-culture system for mouse and human intestinal organoids and macrophages to explore the crosstalk between these cells. Then combining in vivo ablation of macrophages, fluorescent lineage tracing, imaging, bulk RNA-sequencing (RNA-seq), single-cell RNA sequencing (scRNA-seq), human intestinal organoids and cell trajectory analysis, we study at cellular and molecular level the macrophage induction of intestinal regeneration. Our findings revealed that macrophages are recruited around the intestinal stem cell compartment upon radiation injury, promoting a fetal-like reprogramming and proliferation of epithelial cells that drives the regeneration process. In contrast macrophage ablation led to compromised regeneration. Moreover, our scRNA-seq analysis identified key secreted molecules, nrg1 and spp1, as pivotal players in regulating this process. Additionally, characterization of human macrophage/organoid co-cultures and cell trajectory inference confirmed the conservation of macrophages' role in triggering the regenerative program in primary human cells. This study identifies macrophages as essential contributors to intestinal regeneration beyond their innate immune response. Targeting macrophages therapeutically may hold promise in enhancing regeneration and improving the quality of life for cancer survivors.