Wnt Pathway Regulation of Gastric Stem Cell Function

PROJECT SUMMARY This resubmission of a new R01 application proposes to define mechanisms of gastric stem cell regulation, investigating the role of Wnt signaling to maintain tissue homeostasis and to promote epithelial cell proliferation in the stomach. Our proposed studies are directly relevant to human disease, focusing on mechanisms of gastric polyp formation in patients with familial adenomatous polyposis (FAP). FAP is a genetic disorder resulting from germline APC gene mutations that dysregulate Wnt signaling, with extreme gastrointestinal (GI) proliferative disease resulting from Wnt promotion of stem cell proliferation. Although Wnt is well known to regulate GI stem cells, questions remain regarding sensitivity to Wnt dysregulation in different regions of the GI tract. Colonic manifestations in FAP patients are extreme, with aggressive disease characterized by early adenoma and cancer development, which commonly leads to colectomy at a young age. The consequences of Wnt dysregulation in gastric stem cells is less well understood, although polyp, adenoma and cancer development are enhanced in the FAP patient stomach. Notably, almost all FAP patients exhibit frequent hyperproliferative polyps localized to the proximal fundic/corpus region of the stomach, while, in contrast, the distal antral/pylorus region of the stomach is relatively spared from these polyps and develops more occasional adenomatous growths. The basis for the regional effect of FAP mutations on corpus vs. antral stem cells and gastric tissue responses is unknown. To address this important question, this project focuses on defining Wnt regulation of gastric stem cells to uncover the differential effects of pathway activation in the proximal vs. distal stomach. We will pursue the mechanisms of FAP polyp formation in the stomach by functional and genetic analysis of gastric polyp and non-polyp organoids and tissues from a biobank of human FAP gastric tissue samples that will be built as a component of this study. Human FAP organoid studies will be complemented by mouse genetic, pharmacologic and organoid models to gain deeper mechanistic insight into regional Wnt regulation of gastric stem cells. The studies are framed by the “Just Right Hypothesis” which defines differential sensitivities along the GI tract based on region-specific stem cell responses to different levels of Wnt activation. Together the proposed studies will determine how dysregulated Wnt signaling leads to differential gastric epithelial cell proliferation and polyp formation in proximal vs. distal stomach. This information will establish a scientific framework to help define the gastric manifestations in FAP patients. In addition, the studies will provide functional insights to develop a deeper understanding of Wnt pathway regulation of gastrointestinal stem cells. Furthermore, understanding mechanisms of Wnt pathway regulation of gastric stem cell function is important to refine strategies to propagate adult stem cells in culture for regenerative therapies as well as to develop diagnostic criteria and potential therapies for gastric hyperproliferative diseases.