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Title: Investigating the role of eyes absent homolog 1 (EYA1) in aspirin-induced gastric ulceration
Author: Penrose, A. J.
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
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Non-selective NSAIDs are some of the mostly commonly used drugs worldwide; over 60 million US citizens regularly take NSAIDs while 30% of the general population use low-dose aspirin for cardiovascular disease prevention. NSAID use increases the risk of GI complications by 3-5 times compared to non-use. Estimates of NSAIDrelated mortality rates are between 3,200-16,500 in the USA and 400-1,000 in the UK, with the economic burden estimated to be over 3 billion USD a year in the USA alone. Whilst the majority of the adverse GI effects caused by NSAIDs are presumed to be dependent on the inhibition of COX-1-mediated prostaglandin synthesis, prostaglandin-independent mechanisms are also important in ulcer pathogenesis. Various genetic risk factors have been identified for NSAID-induced gastric injury. Uncovering the role of these polymorphisms has provided a better understanding of the mechanism through which NSAIDs cause gastric ulceration and bleeding. A genome-wide association study recently identified a novel association between a polymorphism in the Eyes Absent Homolog 1 (EYA1) gene and gastric ulceration. EYA1 is a transcriptional cofactor that plays an important role in organogenesis and has more recently shown to play a role in promoting DNA repair following genotoxic stress. The main aim of the thesis was to determine the role of EYA1 in aspirininduced gastric epithelial cell death using AGS cells, a gastric epithelial cell line. Aspirin induced time- and dose-dependent gastric epithelial cell death via the apoptotic pathway. EYA1 protein expression was barely detectable in AGS cells and several other cell lines. In view of the low expression, AGS cells were stably transfected with GFP-tagged human EYA1 via chemical co-transfection with a transposase plasmid, and isolated from puromycin selection to obtain the AGS-EYA1 cell line. EYA1-GFP localised to the nucleus of AGS cells, which is interesting considering most reports in rodent models require co-transfection of a SIX gene to translocate EYA1 from the cytosol to the nucleus. Using the native AGS cells as a control, aspirin-induced apoptosis was abolished in the AGS-EYA1 cell line. The protection provided by EYA1 overexpression occurred upstream of caspase-9 cleavage. BAX and MCL-1S protein expression was significantly reduced in AGS-EYA1 cells, which may suggest a mechanism for the protection against aspirin toxicity. Alternatively, EYA1 may reverse the apoptotic stimulus at the source, e.g. repair of damaged DNA; however, this hypothesis was not tested in this study. By analysing gene and protein expression data available from open source databases, EYA1 was found to have very low RNA expression in healthy stomach tissue. There were also no reports of EYA1 protein expression in stomach tissue. Moving forward it will be imperative to characterise the expression of EYA1 in healthy and ulcerative stomach tissue and the effects of genetic polymorphisms on EYA1 expression. In summary, the results presented in this thesis suggest that human EYA1 localises to the nucleus of gastric epithelial cells where it can provide protection against aspirininduced cytotoxicity. The mechanism of this protective effect may be due to EYA1- mediated downregulation of pro-apoptotic proteins or by the induction of genotoxic repair pathways. Validation of this association in non-tumorigenic tissues could provide novel strategies to prevent NSAID-induced gastropathy.
Supervisor: Pirmohamed, Munir ; Pushpakom, Sudeep ; Carr, Dan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral