Wnt-Retinoic Acid Regulation of Gastric Epithelial Cells

About This Grant

PROJECT SUMMARY This new R01 application proposes to define a novel signaling axis regulating gastric epithelial cell homeostasis and response to injury. The gastric mucosa is organized into gastric glands lined with a columnar epithelium that is renewed by gastric stem cells throughout lifespan. Wnt is an essential niche pathway regulating stem cell function, with activation associated with hyperproliferative gastric disease. Wnt signaling regulates two important cellular functions in the glandular stomach: stem/progenitor cell proliferation and chief cell differentiation. Although these roles have been established, questions remain about how Wnt promotes these gastric epithelial cell functions. Interestingly, chief cells, differentiated cells that secrete digestive enzymes, also operate as reserve stem cells in the gastric glands, remodeling after injury into proliferating metaplastic cells to repair the epithelium. How Wnt signaling regulates this regenerative process is not known. Our extensive preliminary findings identified retinoic acid signaling as a potential novel Wnt effector pathway in the gastric epithelium, regulating both gastric stem cell function and chief cell identity. This project tests the hypothesis that Wnt activates retinoic acid signaling to maintain gastric epithelial cell homeostasis and to regulate chief cell remodeling after injury. To address this hypothesis, we will independently manipulate Wnt and retinoid acid signaling in the gastric epithelium in mouse in vivo models and in vitro organoid models, and gastric stem cell and chief cell (reserve stem cell) function will be measured. High dose tamoxifen treatment will be used to induce gastric injury to activate chief cell remodeling in mouse. Histological analysis and lineage tracing will measure gastric epithelial cell proliferation and differentiation during homeostasis and after injury. Because both Wnt and retinoic acid signaling are transcriptional pathways, our studies include bulk and single cell RNAseq analysis to identify cellular changes, and gene and pathway targets. In addition to using genetic and pharmacologic approaches to manipulate Wnt and retinoic acid signaling, mice will be fed Vitamin A deficient diet to deplete body retinol stores to uncover retinoic acid function in the stomach. Gastric organoid studies will define epithelial specific responses to Wnt and retinoic acid signaling. Notably, both mouse and human gastric organoids will be analyzed, including previously characterized high-Wnt organoids established from Familial Adenomatous Polyposis patient gastric polyps. Together the proposed studies will establish a Wnt-retinoic acid signaling axis in the stomach regulating epithelial cell function. The information learned from this project will provide functional insights to develop a deeper understanding of Wnt and retinoic acid pathway regulation of gastric stem cells (active and reserve). Furthermore, defining mechanisms of Wnt-retinoic acid 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 potential therapies for gastric hyperproliferative diseases.