Physiological Impact of Lipoxin A4 on Cystic Fibrosis Bronchial Epithelium
This thesis reports a novel role of lipoxin A4 (LXA4) in mediating physiological effects within the airways of cystic fibrosis (CF) patients. CF is caused by a mutation of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This mutation leads to a dysfunctional chloride transport system resulting in dehydration of the airway surface liquid (ASL) layer, impaired mucociliary clearance, lung infection and inflammation. The eicosanoid LXA4 described as a signal of the resolution of inflammation and produced at the site of inflammation has been reported to be decreased in the lungs of patients with CF. The decrease in LXA4 observed in CF lungs could participate to chronic airway inflammation in this disease. Using live cell imaging, we investigated the role of LXA4 on ASL height in non-CF and CF bronchial epithelial cells cultured in air/liquid interface. We also examined the effects of TA39, LXA4 stable analogue, in mediating ASL height. LXA4 and TA39 increase the ASL height in a dose and time dependent manner in both the non-CF and CF airway epithelium. The mechanism behind the increase in ASL height was also investigated and we found that LXA4 stimulated an apical adenosine triphosphate (ATP) release in bronchial epithelial cells to activate a purinoreceptor pathway, in particular the P2Y11 pathway, which increased intracellular calcium (Ca2+) and cyclic adenosine monophosphate (cAMP). Inhibition P2Y11 purino-receptor with NF340, prevented the ASL height increase induced by LXA4. The ASL height increase and ATP release induced by LXA4 were both blocked by the ALX/FPR2 receptor inhibitor, Boc-2. Our lab has previously reported the increase in tight junction formation in non-CF bronchial epithelium; however, the effect of LXA4 on C F tight junctions had yet to be reported. We examined the effect of LXA4 on tight junction formation in C F bronchial epithelium and the resulting physiological effects it may have on bacterial invasion and epithelial integrity. Using a gentamicin exclusion assay, confocal microscopy and Western blotting, we investigated the role of LXA4 on epithelial integrity of bronchial epithelial cells when infected with Psudomonas aeruginosa (P. aeruginsosa). Exposure of P. aeruginsosa to bronchial epithelial cells decreased the amount of ZO-1 protein (integral member of tight junction complex) synthesised and induced disruption of tight junctions. LXA4 not only increased ZO-1 protein synthesis but also prevented the decrease in expression of ZO-1 proteins and tight junction disruption induced by P. aeruginsosa in both non-CF and C F bronchial epithelium. Pre-treatment with LXA4 for 24 h prior to inoculation with P. aeruginosa, significantly delayed the invasion of non-CF and C F bronchial epithelial cells by P. aeruginosa, while LXA4 alone did not affect the growth of P. aeruginosa.
This thesis provides evidence for a novel effect of LXA4 in mediating physiological responses that result in the protection of C F bronchial epithelial cells from bacterial invasion.These novel findings may open a new therapeutic avenue for suffers of C F lung disease.