Notch1 and Notch2 Receptors Regulate Human and Mouse Gastric Epithelial Cell Homeostasis.

The gastric epithelium undergoes constant turnover that is maintained by a population of gastric stem cells. Gastric stem cells are under the regulation of multiple signaling pathways to promote proper epithelial homeostasis. Previous studies have shown that the Notch signaling pathway plays a crucial role in regulating epithelial differentiated cell fate, stem cell function, and epithelial cell proliferation in the stomach. My thesis work has focused on identifying the mechanisms by which Notch signaling regulates gastric epithelial cell homeostasis. I identified NOTCH1 and NOTCH2 as the key receptors contributing to the regulation of gastric epithelial cells by Notch. Using inhibitory antibodies targeting NOTCH1 and NOTCH2, I observed a marked reduction in proliferation of both corpus and antral epithelial cells that mimicked the reduced proliferation observed with global Notch inhibition. Inhibition of NOTCH1 or NOTCH2 signaling led to an intermediate reduction in proliferation in both regions of the glandular stomach. In the antrum, inhibition of both receptors resulted in a general increase in expression of markers of differentiated cells, including enteroendocrine, surface mucous, and deep mucous cells. Inhibition of both receptors also led to increased secretory granules in antral cells and expression of secretory products from other regions of the gastrointestinal tract, including the corpus and intestine. To investigate if Notch signaling is intrinsic to the epithelium, I refined the conditions for gastric organoid establishment from mouse and human antrum and corpus tissue. In mouse and human antral and corpus organoids, inhibition of NOTCH1 and NOTCH2 resulted in a reduction of organoid growth similar to that seen with global Notch inhibition. In corpus organoids, inhibition of either NOTCH1 or NOTCH2 resulted in an intermediate disruption of organoid growth. However, in antral organoids, inhibition of NOTCH1 mimicked growth similar to that seen with global inhibition, suggesting that NOTCH1 may play a more significant role in antral organoid growth than NOTCH2. In summary, my thesis work has expanded the understanding of the role of Notch in gastric epithelial homeostasis. I have illustrated an important role for the NOTCH1 and NOTCH2 receptors in regulating gastric epithelial proliferation and differentiation in vivo and in vitro.PhDMolecular and Integrative PhysiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120753/1/gcbutler_2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/120753/2/gcbutler_1.pd