Impaired epithelium in asthma: mechanisms driving ciliary dysfunction
thesisposted on 28.06.2013, 14:35 by Wing Yan Heidi Wan
Rationale: Epithelial ciliary dysfunction is a feature of asthma that is believed to contribute to persistent symptoms and recurrent exacerbations. However, the mechanism underlying this dysfunction is unknown. Hypotheses: The ciliary dysfunction of asthmatic airway epithelial cells is due to an intrinsic abnormality that leads to a high susceptibility of these cells to an environmental challenge, which results in a chronic inflammation and thus a predisposition of asthma exacerbations. Methods: Primary airway epithelial cells from basal cells and ciliated cultures, and fresh ciliated strips, were used. Baseline protein and gene expression were assessed by protein quantification and microarrays. Ciliary function was studied using video-microscopy. Asthmatic sputa were used as the environmental stimuli; microbiology was assessed. Oxidative stress and the role of NADPH oxidase (NOX) 4 were assessed using immunohistology, reactive oxygen species (ROS) quantification, quantitative gene expression, and the NOX1/4 inhibitor GKT137831. Results: In ex vivo ciliated cultures, ciliary dysfunction did not persist but was evident in cells from asthmatics following asthmatic sputum inoculation. Bacterial 16S load increased equally in asthmatic and control samples. Oxidative burden in asthmatic bronchial epithelium was increased and was related to the percentage of sputum neutrophils. NOX4 expression and hydrogen peroxide-induced intracellular ROS generation were significantly elevated in epithelial cells from neutrophilic subjects, with the latter being attenuated by NOX4 inhibition. In asthmatic ciliated cells obtained directly from bronchoscopy, inhibiting NOX4 markedly improved ciliary function and was related to the intensity of neutrophilic inflammation. Summary: The up-regulation of NOX4 expression that is evident in asthmatic ALI cultures might promote the susceptibility of the bronchial epithelium to the development of ciliary dysfunction in the presence of an abnormal microenvironment, implicating NOX4 as a potential therapeutic target for neutrophilic asthma. An increase in the sample size is required to increase the strength of this conclusion.