PROJECT SUMMARY/ABSTRACT The etiology of Barrett's esophagus (BE), a molecularly complex disorder of the distal esophagus, remains elusive. Patients with BE are at an increased risk of developing esophageal adenocarcinoma (EAC), a lethal, increasingly prevalent, and the most common esophageal malignancy in the U.S. Our long-term objective is to identify the causative mechanisms underlying the onset and malignant progression of BE, and to develop evidence-based biomarkers and chemopreventive/therapeutic strategies for subsequent clinical implementation. Project 1 of this program is based on our prior discovery of a novel germline susceptibility mutation in VSIG10L (S631G) that modulates the epithelial integrity of squamous epithelium. VSIG10L is expressed in suprabasal cells as squamous epithelium matures. Furthermore, we have generated mice that are either null for Vsig10l or carry the mouse ortholog of the human S631G variant. Homozygous Vsig10l knockout (KO) and homozygous S631G knockin (KI) mice are both viable. Electron microscopy imaging demonstrates decreased desmosomal cell to cell junctions in the suprabasal squamous cells of mice with altered VSIG10L. Further, both mouse genotypes initially develop multilayered epithelium at 12 months of age and BE like metaplasia by 24 months at the squamo-columnar junction (SCj) upon exposure to genotoxic/oxidative stress (Deoxycholate). The three Aims of Project 1 strategically address how mutations in VSIG10L lead to a susceptibility to BE. Aim 1 will define phenotypic and molecular alterations affected by VSIG10L mutations in three dimensional organotypic cultures. Aim 2 will define phenotype of our mouse models and identify molecular alterations that lead to BE like metaplasia and dysplasia. Aim 3 studies how VSIG10L expression is associated with a susceptibility to develop BE in human subjects. Collectively, our proposed studies will delineate the role of VSIG10L in esophageal homeostasis, uncovering novel mechanisms of BE-EAC pathogenesis.