Stem Cell Dynamics in Colonic Epithelial Repair

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PROJECT SUMMARY The study of the regeneration of adult organs has undergone a major revolution with the discovery of specific molecular markers of adult stem cells and development of techniques to grow organ-like structures outside the body. In the mouse small intestine, the finding of multiple, distinctly marked populations of epithelial stem cells has shaped our view of how self-renewing populations interact and are differentially utilized in physiological contexts such as homeostasis and injury. Here we focus on stem cell populations in the mouse colon (large intestine). The colonic epithelium is maintained by Lgr5-positive stem cells during normal tissue maintenance, but the stem cell populations utilized in injury and their rules of interaction have not been elucidated. The markers of injury-activated stem cell populations in the small intestine do not label stem cells in the colon. Our goal is to characterize stem cell dynamics and signaling during mouse colonic epithelial repair states, especially those that accompany or follow inflammatory injuries seen in human patients with inflammatory bowel disease. This is possible in mouse colon because of the relative wealth of injury models and our recent development of an imaging platform that allows stem cells to be visualized in the context of specialized tissue repair structures over a large region. Preliminary data obtained for this application suggest that stem cell population dynamics in repair are fundamentally different from those in homeostasis and that injury-induced stem cells have a distinct molecular identity. These stem cells originate from both intestinal and squamous tissues, and their repair dynamics result in a dramatic loss in clonal diversity. Specific aims for this project are: (1) To analyze the cellular origins and dynamics of crypt regeneration in distal colon, (2) to determine the origins and growth mechanisms of injury-induced squamous metaplasia in distal mouse colon, and (3) to characterize the role of epidermal growth factor receptor (EGFR) signaling in stem cell responses to injury. Primary methodologies used in our approach include lineage tracing, colonic organoid culture from mouse and human tissue, high throughput sequencing, and utilization of advanced models of EGFR dysfunction. This work will help identify specific cellular populations and processes to target for next generation therapies focusing on the underutilized mucosal healing pathway in inflammatory bowel disease.