REGULATION OF ATROPHY-INDUCED PROGENITOR CELLS IN THE GASTRIC CORPUS

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PROJECT SUMMARY/ABSTRACT This project seeks to define the molecular mechanisms that stem cells use to differentiate into acid-pumping parietal cells in the gastric epithelium. Abnormalities related to parietal cell abundance and activity are associated with a variety of stomach conditions, including peptic ulcers, gastroesophageal reflux disease, autoimmune gastritis, and Helicobacter pylori infection with chronic atrophic gastritis and pyloric metaplasia. Despite the array of human health conditions related to parietal cell dysfunction, little is known about how parietal cells emerge from stem cells at homeostasis or in diseases where parietal cells are lost. During the prior funding period for this project, we have shown that parietal cell death requires IFNγ and IL-17 signaling and that AMPK and AMPK-regulated proteins like PGC1α and CD36 are critical for parietal cell differentiation and function. Here, we will show preliminary data that the nuclear hormone transcription factor Estrogen- related receptor gamma (ERRγ, encoded by the gene Esrrg) is first expressed in parietal progenitor cells as they differentiate from induced stem cells, and deletion of Esrrg abrogates parietal cell differentiation. Thus, we hypothesize that ERRγ is critical and sufficient for parietal cell fate choice and differentiation from stem cells. We propose three aims to test our hypothesis. In Aim 1, we will characterize the molecular and cellular steps involved in stem cell differentiation to parietal cells during mouse development and after parietal cell ablation using ERRγ in combination with other gastric lineage markers, immunostaining, and electron microscopic approaches. We will use newly generated ERRγ-RFP mice to flow sort ERRγ+ parietal cell progenitors at various time points after ablation and identify novel molecular regulators of PC differentiation via RNA-Seq. We will grow ERRγ+ sorted and whole-corpus organoids in 2D/3D conditions with varying growth factors, which we have optimized for maintaining stem cells or generating parietal cells. In Aim 2, we will determine how and when ERRγ is necessary for parietal cell differentiation using Esrrg-floxed mice crossed with strains expressing inducible Cre recombinase in stem cells, progenitors, and mature parietal cells, including a newly generated EsrrgCreERT2 line. We will also perform ChIP-seq to identify ERRγ genetic targets and mass spectrometry of co- immunoprecipitated proteins to identify co-activators and modulators. In Aim 3, we will examine ERRγ and other gastric lineage markers to reveal the unexpected presence of abundant parietal cell progenitors in patients lacking mature parietal cells due to autoimmune gastritis. We will transduce ERRγ into mouse and human organoids and/or treat organoids and mouse models with ERRγ activating and inhibiting drugs to assess sufficiency of ERRγ to generate parietal cells and establish a pipeline to identify agents that can treat parietal cell disorders by regulating parietal cell differentiation. We expect this work will generate a more robust understanding of parietal cell differentiation and lead to novel therapeutic approaches for treating parietal cell disorders.