Gastroesophageal reflux disease (GERD) and Barrett's esophagus (BE) are the major risk factors for esophageal adenocarcinoma. To prevent this deadly cancer, patients with BE are advised to have regular endoscopic surveillance for dysplasia and, when dysplasia is discovered, to have it treated with radiofrequency ablation (RFA). Unfortunately, surveillance does not appear to prevent deaths from esophageal cancer in BE patients, and recurrence of Barrett's metaplasia occurs frequently after RFA. Surveillance failures and metaplasia recurrences might be due to a condition called subsquamous intestinal metaplasia (SSIM), in which metaplastic glands are located in the lamina propria underneath a layer of squamous epithelium that hides them from the endoscopist and protects them from destruction by RFA. Initially, SSIM was thought to develop as a consequence of ablation procedures. However, recent studies have shown that SSIM is present under squamous epithelium close to the squamo-Barrett's epithelial junction in the large majority of patients withBE, even in the absence of ablation procedures. This SSIM might be the source of tumors missed by endoscopic surveillance, and the nidus for recurrent metaplasia after RFA. Thus, SSIM appears to be a frequent and important condition that is thwarting attempts to prevent cancer in BE. Epithelial-mesenchymal transition (EMT) is the process in which epithelial cells acquire mesenchymal cell characteristics such as motility and invasiveness. In BE, EMT could result in SSIM by enabling metaplastic epithelial cells to move into the lamina propria underneath the adjacent squamous epithelium. This notion is supported by a mouse model of pancreatic cancer in which metaplastic pancreatic cells in inflamed areas acquire markers of EMT and invade the pancreatic stroma. Our preliminary data demonstrate that exposures to acid and bile salts cause non-neoplastic Barrett's epithelial cells to acquire features of EMT. GERD can cause reflux esophagitis, and inflamed tissues often are hypoxic, a condition that can activate hypoxia inducible factors (HIFs). Our preliminary data show that Barrett's epithelial cells exposed to acid and bile salts exhibit a strong and sustained increase in nuclear HIF-1a and HIF-2a. Recent data suggest that HIF- 1a and HIF-2a can promote EMT in cancers by causing tumor cells to secrete vascular endothelial growth factor (VEGF), which binds the cells' VEGF receptors in an autocrine fashion to induce VEGF signaling, which results in EMT. Our preliminary data show that acid and bile salts induce autocrine VEGF signaling in non- neoplastic Barrett's epithelial cells. Therefore, we hypothesize that reflux-induced activation of HIFs in Barrett's epithelial cells causes VEGF secretion with autocrine VEGF signaling, which initiates the EMT program and causes SSIM.
The aims of this study are to elucidate the mechanism(s) whereby acid and bile salts activate HIFs to cause VEGF production, and to explore the role of autocrine VEGF signaling in the EMT program induced by acid and bile salts in non-neoplastic Barrett's cells in vitro, and in patients with BE in vivo.
Barrett's esophagus; the condition in which abnormal glands that are predisposed to develop cancer replace the normal (squamous) lining of the esophagus; is the major risk factor for cancer of the esophagus. To prevent this deadly cancer; patients with Barrett's esophagus are advised to have biopsies and endoscopic procedures directed at those abnormal glands; but those procedures may not be effective because the glands often are hidden under a layer of normal squamous lining in a condition called subsquamous intestinal metaplasia (SSIM). Our project will determine how SSIM develops; and the relevance to public health is that this understanding is essential to devise new medical treatments to prevent Barrett's esophagus from forming; and to prevent the development of cancer in Barrett's esophagus.
