Sox9 drives columnar differentiation of esophageal squamous epithelium: A possible role in the pathogenesis of Barrett's esophagus

The molecular mechanism underlying the development of Barrett s esophagus (BE), the precursor to esophageal adenocarcinoma (EAC) remains unknown. Our previous work implicated sonic hedgehog (Shh) signaling as a possible driver of BE via bone morphogenic protein 4 (Bmp4) and Sox9. Here we have utilized a novel in vivo tissue reconstitution model to investigate the relative roles of Bmp4 and Sox9 in driving metaplasia. Epithelia reconstituted from squamous epithelial cells or empty vector (EV) transduced cells had a stratified squamous phenotype, reminiscent of normal esophagus. Expression of Bmp4 in the stromal compartment activated signaling in the epithelium but did not alter the squamous phenotype. In contrast, expression of Sox9 in squamous epithelial cells induced formation of columnar-like epithelium with expression of the columnar differentiation marker Ck8 and the intestinal specific glycoprotein, A33. In patient tissue, A33 protein was expressed specifically in BE and not normal esophagus. Expression of Cdx2, another putative driver of BE alone had no affect on reconstitution of a squamous epithelium. Furthermore, epithelium co-expressing Cdx2 and Sox9 had a similar phenotype to epithelium expressing Sox9 alone. Our results demonstrate that Sox9 is sufficient to drive columnar differentiation of squamous epithelium and expression of an intestinal differentiation marker, reminiscent of BE. These data suggest that Shh-mediated expression of Sox9 may be an important early event in the development of BE, and that the potential for inhibitors of the hedgehog signaling pathway to be used in the treatment of BE and/or EAC could be tested in the near future