The Role of Helicobacter Pylori Virulence and Host Genetic Factors in Gastroduodenal Disease
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The role of Helicobacter pylori virulence and host genetic factors in gastroduodenal disease Heather-Marie Ann Schmidt A thesis submitted as fulfilment of the requirement for the degree of Doctor of Philosophy (PhD) School of Biotechnology and Biomolecular Sciences University of New South Wales 2010 Abstract Helicobacter pylori, a gastric bacterial pathogen, colonises >50% of the world’s population. Colonisation invariably leads to chronic gastritis, with a small but significant proportion progressing to peptic ulcer disease and gastric cancer (GC). The reason why some individuals progress to severe disease is unknown, but is likely the result of an as yet unidentified combination of bacterial, host and environmental factors. This thesis aimed to elucidate the contribution of host genetics and H. pylori virulence to severe disease, particularly GC, in patients from different ethnicities. Papers I, II and III investigated a comprehensive set of H. pylori virulence factors for their association with pro-inflammatory signalling in gastric epithelial cells in vitro and disease development. The major H. pylori virulence factors, including the cag PAI, vacA, babA and oipA were highly prevalent in all three ethnic groups resident in Malaysia and Singapore irrespective of the disease state of the host, suggesting all strains from this region are highly virulent. There was significant ethnic variation in the CagA EPIYA-motifs, HP0521 alleles and dupA, confirming that distinct H. pylori strains circulate within particular populations. Paper IV assessed strains isolated from patients with different levels of inflammation for their ability to cause dendritic cell maturation and activation, and induce pro- inflammatory signalling in gastric epithelial cells in vitro. Strains from a higher inflammatory background induced higher levels of pro-inflammatory cytokine secretion in vitro. Paper V examined a novel range of host genetic polymorphisms from genes in immune and cell signalling pathways for associations with susceptibility to H. pylori infection or GC. The prevalence of many polymorphisms varied significantly between the ethnic groups (Chinese, Indian and Malay), and several polymorphisms were associated with H. pylori infection (EBBR2+1963G) or GC (PTGS2-1195G, IL1B-1473C) in ethnic Chinese resident in Malaysia and Singapore. In conclusion, substantial variation exists in the prevalence of genetic polymorphisms and the diversity of circulating strains among ethnic groups, as well as the ability of strains to induce inflammation; these findings may underlie differences in GC development and H. pylori infection. A combination of these factors in the same individual may provide a more complete picture. Statement of Originality ‘I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgment is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged.’ Signed……………………………………………………………………………………. Date………………………………………………………………………………………. 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Authenticity Statement ‘I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format.’ Signed……………………………………………………………………………………. Date………………………………………………………………………………………. Acknowledgements This thesis would not have been possible without the help and support of so many amazing people. I would especially like to thank the following: Hazel Mitchell, truly the most wonderful supervisor I could have wished for. Thank you for so many things, personally and professionally; the opportunities to travel, to work in different labs, to present at conferences in Australia and abroad; the encouragement to get things done and to do things better – lab work, papers, thesis; the cakes and wine; the valuable discussions about where to go next with my research; your formidable editing skills. I am grateful for your continual support, though I must have frustrated you immensely sometimes. Thank you for your kindness and your friendship throughout these past few years. Thank you for so much more than I can ever really put down on paper. I have so many happy memories and I am so glad that I stayed to do a PhD with you. Lars Engstrand, the best sort of co-supervisor! Thank you adopting me wholeheartedly into Bakteriella Tarmpatogener, I loved being a member of your group as much for the excellent science as for the social program. Sönke Andres, my lab-buddy and co-author extraordinaire. Thank you for being such a great friend, inside the lab and out, and it didn’t hurt that you are a superb scientist too. Christina Nilsson, a brilliant scientist, mentor and co-author. I am grateful for all of your help, advice and patience over the years, and I feel very privileged to call you a friend. Nadeem Kaakoush, thank you for the discussions that were all too often about anything but science, and for all of your help in the lab, especially towards the end. You’ve been a super co-author and unexpected friend. Zsuzsanna Kovach, thank you for sharing some of the burden in the lab, for being a supportive co-author and for just being there when I needed a chat. KL Goh and KM Fock, thank you for the specimens. Faye Taylor, Jenny Barrett and David Forman, thank you for your help with statistics. Mai Dung Ha, thank you for everything you did in the lab. Thank you to all my co-authors for your helpful suggestions and support. The members of Lab 301 (UNSW, Sydney, Australia), past and present, thank you for the good times and for never making it feel like I’ve been away for very long. Jani O’Rourke, thank you for your support, your interest in what I was up to, your friendship and, of course, the teaching opportunities. Si Ming Man, thank you for being a good friend and a talented scientist, I really enjoyed spending time in and out of the lab with you. Li Zhang, thank you for your help in the lab when I first started so many years ago and for your support and friendship ever since. John Wilson, thank you for passion for microbiology, you always made it fun to be both a student and a tutor. Ruiting, Jacob, Sophie, Alfred, Johnny, Natalia, Alex, Ping and all the other lab members, thank you also for the help in the lab, the chats, the advice and the fun we’ve had. The members of the pylori pinglorna (Karolinksa Institutet, Stockholm and Smittskyddsinstitutet, Solna, Sweden) past, present and honorary, thank you for making me feel at home at SMI. The one and a half years I spent in Stockholm was one of the best times of my life, I have so many happy memories, and it was mostly because you are all such amazing people. Tack så jätte mycket. Mathilda Lindberg, thank you for being a friend and a great Swedish tutor. Karin Wreiber and Roger Lundberg, thank you for being so absolutely kind, I cannot tell you how much your friendship means to me. Helene Kling-Bäckhead and Anna Skoglund, thank you for the Swedish lessons and generally being fun to be around. Sandra Rodin, thank you for being such a sweetie. Laura Plant, thank you for all your help in the lab. Annelie Lundin, thank you for your friendship. Thank you Lena, Kristina, Marianne, Britta, Cia, Hedvig, Valteri, Anders, Wilhelm, Britt-Marie and Zong-Li, and everyone else at SMI and KI for making me feel welcome and a part of the group. Thank you to the members of the Thomas Borén group at Umeå Universitet for for taking me under your wing(s) for those few weeks in the freezing north. All my girls here in Oz and mina kompisar i Stockholm, thank you for your friendship, your distractions, your support, your advice and for so often not mentioning I was in the middle of a PhD. Julie Wood thank you for understanding what I was going through. And finally, my family, thank you for simply putting up with me sometimes and for being proud of me always, I love you. Thank you especially to my wonderful Mum, words cannot express the gratitude I feel for everything you have done for me. Your support, encouragement, and unconditional love mean the world to me. Thank you for your faith in me, for forcing me to sit down and work, for sharing the ups and downs and for being there when I just needed someone to listen.