Evidence that inflammation-associated fibroblasts (IAFs) originate from Edil3 stromal "mesitocytes" in the colon following radiation injury

Stromal cells present in the colon crypt provide proliferation and differentiation signals to the epithelial cells, thereby maintaining their integrity and stimulating the regeneration process. Cancer patients treated for tumors located in the abdominopelvic region may develop radiation proctitis, a condition characterized by a strong mucosal inflammation. In this work, single-cell RNA sequencing approaches were combined with spatial transcriptomics to characterize colonic stromal cells in depth, both in control conditions and in the context of radiation-induced ulceration. The present study identifies a novel stromal marker, Edil3 (EGF-like repeats and discoidin domains 3), which defines the major stromal population of the colon. This population is spatially and functionally distinct from telocytes and trophocytes and is expressed along the crypt with a functional proliferation-differentiation axis . This population, which we propose to name "mesitocytes," cooperates with vascular cells to control inflammation and epithelial proliferation. We demonstrate that radiation-induced ulcerated areas are characterized by the presence of inflammation-associated fibroblasts (IAFs) deriving from mesitocytes.