The goal of this proposal is to define a 5-year plan to prepare Brian Muegge, M.D., Ph.D., to become an independent physician-scientist studying the role of intestinal enteroendocrine cells during gut injury. He obtained his M.D. and Ph.D. degrees at Washington University, where he studied the intestinal microbiome. After clinical training in Internal Medicine and Endocrinology, Dr. Muegge joined the lab of Dr. Thaddeus Stappenbeck. There he has identified that intestinal enteroendocrine cells are dynamically altered during injury to increase the expression of factors that promote intestinal healing. The finding that rare enteroendocrine cells undergo adaptive reprogramming during injury establishes an important new paradigm in intestinal biology. He has extended these findings by developing new in vitro model systems to grow and injure enteroendocrine cells, along with experimental and analytic methods to isolate and transcriptionally profile single nuclei from these cells. This work serves as the basis for the aims in the proposal. The central guidance for this project will be provided by the mentor, Dr. Stappenbeck. Dr. Stappenbeck, a physician-scientist, is an internationally recognized expert in intestinal stem cells and wound repair. He has a distinguished track record of training physician-scientists as they prepare for independent careers. In addition. Dr. Muegge has assembled an advisory committee of faculty with expertise in endocrinology, developmental biology, and single nuclear RNA sequencing who will provide crucial scientific and career guidance. Washington University is an ideal place to receive this training, with outstanding resources and expertise readily available. The primary research goal of this proposal is to address how subtypes of enteroendocrine cells change their activity (secretion) or state of differentiation in response to injury signals. Dr. Stappenbeck?s lab has previously characterized how absorptive cells of the intestine use altered, adaptive reprogramming to achieve new phenotypes that restore epithelial integrity. Dr. Muegge?s work has provided the first evidence that similar reprogramming may occur in the enteroendocrine lineage. He has used computational methods to identify candidate regulators of enteroendocrine cell secretion and will test those hypotheses using novel injury models in vitro and in vivo. He will identify mechanisms of EEC cellular and transcriptional adaptation to injury with single cell RNA sequencing. These efforts promise to fundamentally change our understanding of epithelial differentiation and identify new therapeutic targets to treat chronic injury. This K08 award will provide the necessary resources and skills that Dr. Muegge will require to become a successful independent investigator