Defective Epithelial Barrier Function In Asthma

Abstract

Asthma is a complex disease involving gene and environment interactions (Holgate). Although atopy is a strong predisposing Rationale risk factor for asthma, local tissue susceptibilities also contribute to disease expression (Moffitt). The bronchial epithelium forms the interface with the external environment and is pivotally involved in controlling tissue homeostasis through provision of a physical barrier controlled by tight junction complexes (Swindle et al, 2009). To explain the link between environment exposures and airway vulnerability, our previous studies based on a small number of volunteers have shown that tight junctions are abnormal in asthma. To confirm the previous findings and strengthen the concept of defective epithelial barrier function in asthma, we studied a much bigger population of asthmatics to assess their epithelial barrier integrity and permeability.Non-asthmatic normal and asthmatic subjects were recruited and clinically characterised in accordance with GINA guidelines. Methods:Bronchial brushings were obtained by fibreoptic bronchoscopy following ethical approval and informed consent. Primary bronchial epithelial cells (pBECs) were expanded from brushings then seeded onto collagen I coated porous transwells and differentiated at in vitro an air-liquid interface (ALI) for 3-4 weeks. Transepithelial electrical resistance (TER) was monitored as an indication of tight junction formation and epithelial integrity using a set of chopstick electrodes and a voltohmmeter. Paracellular permeability was quantified by FITC-dextran flux assay.We studied differentiated bronchial epithelial cultures (n=83) grown from bronchial brushings obtained from normal (40) Results:in vitro or asthmatic (n=43) volunteers. Tight junction function assessed by TER measurement was significantly lower in cultures from asthmatic donors compared to normals (median (interquartile range) = 346 (248-536) Ω·cm 428 (340-593) -analysis of the data revealed that 2 versus TER was significantly decreased as a function of disease severity (p<0.05). TER measurements were inversely correlated with permeability to fluorescently conjugated 20 or 4 kDa dextrans indicating alterations to both ionic and macromolecular permeability in asthma.Our results show that the bronchial epithelial barrier in asthma is compromised. This defect may facilitate the passage of low Conclusions: molecular weight allergens and other agents into the airway tissue leading to immune activation and may thus contribute to the end organ expression of asthma. This work suggests that addressing the barrier defect in asthma may offer a novel therapeutic approach for difficult-to-treat asthmatic subjects who fail to respond to conventional therapy. This abstract is funded by:

Barrier function of airway tract epithelium

“…57 In fact, enhanced surface expression and phosphorylation of EGF receptors in the airway epithelium has been observed in patients with asthma who show impaired mucosal barrier function. 121 Recently, we demonstrated that EGF receptor phosphorylation is also increased in COPD airway epithelial cells, which retains the phenotype of goblet cell hyperplasia. 122,123 β-catenin cooperates with E-cadherin to form adherens junctions.…”

Pollen exposure weakens innate defense against respiratory viruses

“…Primary bronchial epithelial cells were expanded in bronchial epithelial growth medium (BEBM) (Lonza) up to passage 1 as previously described. 18 Differentiation of PBECs was induced at passage 2. Primary bronchial epithelial cells were plated on transwell permeable supports (diameter 6.5 mm, polyester membrane with 0.4 µm pores, Corning Life Sciences, Amsterdam, the Netherlands) and differentiated at an air-liquid interface (ALI) for 21 days.…”

Effects of human rhinovirus on epithelial barrier integrity and function in children with asthma

“…We performed immunofluorescence confocal microscopy to examine have investigated levels of TJ gene and protein expression following various insults, 11,32,33 these studies were performed using either established epithelial cell lines or AECs from adults. Hence, there is a paucity of data on the intrinsic gene and protein expression of epithelial tight junction complexes in asthmatic children.…”