Author: Cameron Michael Smith
Smith, Cameron Michael, 2012 Investigation of MicroRNA's in the Gastroesophageal Reflux - Barrett's Oesophagus - Adenocarcinoma Sequence, Flinders University, School of Medicine
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Gastrointestinal reflux disease can lead to the development of Barrett's oesophagus (conversion of oesophageal squamous epithelium to columnar epithelium with intestinal metaplasia) and oesophageal adenocarcinoma. However, the molecular mechanisms driving the reflux-Barrett's oesophagus-oesophageal adenocarcinoma sequence are not fully understood. MicroRNAs (miRNAs) are a class of small RNA molecules involved in almost every cellular process investigated. In this study quantitative assessment identified seven differentially expressed miRNAs in Barrett's oesophagus compared with squamous epithelium including: increased expression of miR-21, miR-143, miR-145, miR-194, miR-215 and decreased expression of miR-203 and miR-205. miR-143, miR-145 and miR-205 were also increased in gastroesophageal reflux disease. MiR-143, miR-145 and miR-215 were decreased in oesophageal adenocarcinoma. Gastroesophageal reflux disease: Unravelling roles for miRNAs in the oesophagus Subsequent studies were performed to explore the biological consequences of these changes in miRNA expression. Investigation of increased miR-143, miR-145 and miR-205 levels in an oesophageal squamous cell line identified these miRNAs can regulate proliferation and apoptosis. We therefore hypothesized that these miRNAs might act as regulators of oesophageal epithelial restitution in response to reflux. Investigation of miRNA and mRNA expression in tissues identified correlations between miR-143 and both BMP4, a key promoter of columnar specific gene expression and CK8, a marker of a columnar phenotype. This data is consistent with a possible role for miRNA expression in development of Barrett's oesophagus. Tumour suppressor miRNAs in oesophageal adenocarcinoma Studies using an oesophageal adenocarcinoma cell line revealed that decreased miR-143, miR-145 and miR-215 expression likely contributes to a reduction in proliferative and apoptotic control in this cancer. Further, this reduction is likely mediated by a number of miRNA directed changes in gene expression. In-situ hybridisation identified localisation of these miRNAs to the crypts within the Barrett's oesophagus epithelium. Dysplasia is thought to originate from the crypts of the Barrett's oesophagus epithelium, so we hypothesized that miR-143, miR-145 and miR-215 play a role in regulating proliferation and apoptosis in these crypts, with decreased expression promoting the development cancer development in these areas. The miR-200 family: Involvement in Barrett's oesophagus and oesophageal adenocarcinoma Decreased expression of miR-141 and miR-200c, members of the miR-200 family was found to distinguish Barrett's oesophagus from related gastric and intestinal epithelia. Bioinformatic analysis provided computational evidence that this decreased miRNA expression might contribute to the abnormal proliferative and apoptotic status of Barrett's oesophagus epithelium. We observed decreased expression of the miR-200 family (miR-141, miR-200a, miR-200b, miR-200c and miR-429) and increased expression of ZEB1 and ZEB2 in oesophageal adenocarcinoma. The miR-200 family regulates the epithelial to mesenchymal transition, a key process in tumour metastasis, by targeting the transcription factors ZEB1 and ZEB2. These results provided the first evidence implicating miRNAs in the epithelial to mesenchymal transition in oesophageal adenocarcinoma. Moving forward This study provides an exciting platform to build from, especially for further investigating a miRNA mechanism for the development of both Barrett's oesophagus and oesophageal adenocarcinoma. In addition, this study provides preliminary support for the development of miRNA based tools for (1) assessing the efficacy of reflux control, (2) classifying patients at risk of developing Barrett's oesophagus and oesophageal adenocarcinoma, and (3) therapies targeted towards modulating miRNA expression to reduce oesophageal adenocarcinoma tumour growth.
Keywords: Gastroesophageal reflux,Barrett's oesophagus,oesophageal adenocarcinoma,microRNAs,tumour suppressor,metastasis
Subject: Medicine thesis, Surgery thesis
Thesis type: Doctor of Philosophy
School: School of Medicine
Supervisor: Dr Damian Hussey