Abstract: Cancer patients treated with radiotherapy in the abdomen suffer from bleeding and malabsorption that impairs their quality of life. Radiation injury depletes the proliferative intestinal stem cells and progenitors, in response to this the intestine is reprogrammed into a fetal-like primitive state where committed cells de-differentiate giving rise de novo to the intestinal stem cells. Macrophages have garnered significant attention due to their multifaceted functions. While their role in inflammation and injury is well-established the putative contribution of macrophages to the intricate process of intestinal regeneration remains elusive. Using a plethora of approaches such as in vivo ablation of macrophages, bulk and single-cell RNA-seq, lineage tracing, 3D imaging, mouse and human organoid co-cultures we demonstrate that macrophages crosstalk with the intestinal epithelium to lead the process of regeneration. Our findings show that upon injury, macrophages are massively recruited near the intestinal stem cell compartment, acting as a temporary niche for de-differentiating epithelial cells by secreting two critical factors. NRG1 activates the regenerative genetic program, while SPP1 promotes the acquisition of ISC transcriptional traits. In the absence of macrophages, intestinal proliferation and de-differentiation are disrupted after injury. Moreover, co-culture experiments with human intestinal organoids and polarized macrophages show that macrophages influence cell differentiation trajectories and enhance organoids recovery after radiation injury. Consequently, we have identified a novel role of macrophages beyond their traditional innate immune functions that can be exploited to boost the process of intestinal regeneration to avoid anti-cancer treatments side effects.
