| Summary: | The urokinase plasminogen activator receptor (uPAR, PLAUR) is a cell surface receptor actively involved in the regulation of cell homeostasis. Expression is elevated in the bronchial epithelium in vivo and also in serum and sputum in asthma and elevated expression often indicates poor prognosis in a number of human diseases. The relative contribution of uPAR to asthma disease mechanisms is not fully understood and the functional roles of uPAR isoforms remains to be resolved. The key aims of this thesis were to i) investigate how the uPAR pathway may influence bronchial epithelial barrier properties; ii) investigate the gene expression patterns in the bronchial epithelium in asthma; iii) identify functions of different forms of uPAR in human bronchial epithelial cells (HBEC) and to iv) investigate the association between genetic polymorphisms spanning the PLAUR gene with clinical features and the presentation of asthma in moderate to severe asthma. Using two cell based approaches we identified an inverse relationship between soluble-cleaved uPAR expression and epithelial barrier properties. Importantly, we demonstrated that blocking uPAR-integrin interactions provides a potential therapeutic opportunity to improve epithelial barrier function. Using whole transcriptome analysis genes differentially expressed between cultured asthma and control subjects were identified which were related to cell growth, repair and immune regulation. Furthermore, uPAR expression was elevated in epithelial cells in asthma subjects compared to healthy controls, suggesting expression is inherently altered in the bronchial epithelium in asthma. Transcriptomics was used to provide novel insight into the specific and overlapping functions of uPAR isoforms and to determine the effects of elevated uPAR expression on HBEC function. Finally, the contribution of PLAUR genetic variants to clinical and immunological traits within asthma were investigated and found that PLAUR single nucleotide polymorphisms (SNPs) did not show an association with the traits measured in a severe asthma population. Overall this work has provided new insight into the function of uPAR as a regulator of the bronchial epithelium in asthma.
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