Regulation of gastric metaplasia, dysplasia and neoplasia by Bone Morphogenetic Protein signaling

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It has been proposed that chronic inflammation causes aberrations in the normal functions of gastric epithelial cells leading to the development of metaplasia and dysplasia and, ultimately, to neoplasia. Both Intestinal Metaplasia (IM) and spasmolytic polypeptide expressing metaplasia (SPEM) have been associated with inflammation-induced gastric neoplasms. The bone morphogenetic proteins, (BMPs) regulate the growth and differentiation of gastrointestinal tissues. The BMPs are also known to inhibit inflammation, cell proliferation and the growth of gastric neoplasms. The Lgr5 gene marks gastric epithelial cells that can self renew and exhibit multi-lineage differentiation capacity. An increased number of Lgr5+ve cells has been detected in gastric tumors. Moreover, Lgr5+ve cells appear to be a major cell-of origin of gastric neoplasms. The mechanisms that regulate Lgr5+ve cells and their role in the development of gastric neoplasia are currently unknown. In studies conducted in Lgr5-EGFP-ires-CreERT2 mice, we observed Lgr5+ve cells at the base of antral glands and along the lesser curvature, an area that frequently gives rise to gastric neoplasms. We also reported that inhibition of BMP signaling in the oxyntic mucosa by transgenic expression of the BMP inhibitor noggin (H+/k+-Nog mice) enhances Helicobacter-induced inflammation leading to increased epithelial cell proliferation and to the development of SPEM and dysplasia. Lineage tracing studies conducted in the presence of both noggin and H. felis demonstrated expression of markers of SPEM in Lgr5-derived cells. Moreover, deletion of Bmpr1a and infection with H. felis, caused the development of dysplasia and of significant cellular changes of the gastric mucosa, which were characterized by increased expression in Lgr5+ve cells of both CD44 and Sox2, molecules that have been linked to the development of gastric metaplasia and neoplasia. In this study we will test the hypothesis that inflammation and inhibition/loss of BMP signaling induce the activation of Lgr5+ve cells that give rise to metaplastic and dysplastic epithelial lineages, and ultimately, to neoplasia. In the first aim using Lgr5- EGFP-ires-CreERT2 mice lines crossed to both noggin-tomato reporter mice and to Bmpr1aflox/flox mice, we will investigate the fate of Lgr5 cells during inflammation. In addition, we will determine if BMP signaling modulates the expression of Sox2 and CD44 in Lgr5 cells and if these molecules mediate the biological response of Lgr5 cells to inflammatory stimuli. In the second aim, we will test the hypothesis that inflammatory molecules regulate the proliferation and differentiation of Lgr5 cells in vitro and that BMP signaling modulates this event, using gastric organoids derived from both mice stomachs and human gastric biopsies. In the third aim, in order to determine the significance of BMP signaling in human diseases, we will measure the expression of BMPs, inflammatory mediators, stem cell markers and of components of the BMP signal transduction pathway in samples derived from patients with gastric cancer, gastritis and IM. In additional studies, we will assess the response of gastric cancer organoids to cytokines and BMPs.