The proliferation of intestinal stem cells is maintained by EGF, a key component of the medium required to support organoids ex vivo. Here, we identified that NRG1, not EGF, is up-regulated during tissue repair following injury. NRG1 is expressed in mesenchymal stromal cells, macrophages and Paneth cells. Knockout of NRG1 produced a decrease in cell proliferation within crypts and a reduced capacity to regenerate following injury. Treatment with NRG1 robustly stimulated proliferation in crypts and budding of organoids. Molecular characterisation of the effects of NRG1 revealed an elevated and sustained activation of MAPK and AKT and a proliferative signature. NRG1 also had a strong impact on the expression of stem cell markers, the ability of progenitor cells to initiate organoid growth and enhanced regeneration. Our data suggest mesenchymal-derived NRG1 is a potent mediator of tissue regeneration and may inform the development of NRG1-based therapies for enhancing intestinal repair after injury.

Gastrointestinal infections often induce epithelial damage that must be repaired for optimal gut function. While intestinal stem cells are critical for this regeneration process [R. C. van der Wath, B. S. Gardiner, A. W. Burgess, D. W. Smith,PLoS One8, e73204 (2013); S. Kozaret al.,Cell Stem Cell13, 626–633 (2013)], how they are impacted by enteric infections remains poorly defined. Here, we investigate infection-mediated damage to the colonic stem cell compartment and how this affects epithelial repair and recovery from infection. Using the pathogenClostridioides difficile,we show that infection disrupts murine intestinal cellular organization and integrity deep into the epithelium, to expose the otherwise protected stem cell compartment, in a TcdB-mediated process. Exposure and susceptibility of colonic stem cells to intoxication compromises their function during infection, which diminishes their ability to repair the injured epithelium, shown by altered stem cell signaling and a reduction in the growth of colonic organoids from stem cells isolated from infected mice. We also show, using both mouse and human colonic organoids, that TcdB from epidemic ribotype 027 strains does not require Frizzled 1/2/7 binding to elicit this dysfunctional stem cell state. This stem cell dysfunction induces a significant delay in recovery and repair of the intestinal epithelium of up to 2 wk post the infection peak. Our results uncover a mechanism by which an enteric pathogen subverts repair processes by targeting stem cells during infection and preventing epithelial regeneration, which prolongs epithelial barrier impairment and creates an environment in which disease recurrence is likely.