- Title
- The impact of respiratory virus infection on airway epithelial cell differentiation and barrier formation in asthma
- Creator
- Li, Ngan Fung
- Resource Type
- thesis
- Date
- 2021
- Description
- Professional Doctorate - Doctor of Philosophy (PhD)
- Description
- The airway epithelium constitutes an anatomical interface between the body and external environment. Differentiated airway epithelial cells (AECs) are polarized for luminal mucociliary clearance to prevent infections. This epithelial structure is mediated by formation of intercellular junctions: tight junction (TJ) and adherens junction (AJ) responsible for both cell-cell adhesion and stabilization of apical-basolateral polarity across the epithelium. Loss of junctional integrity demonstrated by increased barrier leakiness and dissociated junction proteins is evident in airway epithelium of patients with asthma. This thesis aimed to identify key junctional components responsible for barrier dysfunction in asthma and assess how virus infection modifies junctional interaction to perpetuate barrier dysfunction in asthma. This was achieved by using airway epithelial cells obtained by bronchoscopy from the airways of healthy and asthmatic donors. These airway epithelial cells, enriched in lung progenitor cells were cultured in vitro and differentiated in air-liquid interface to recapitulate a model of injured and regenerating airway epithelium for studying of junctional formation in the absence and presence of virus infection. This thesis describes studies that identified junction proteins associated with promoting barrier dysfunction in AECs from patients with asthma. In chapter 3, spatial-temporal mapping of junction proteins revealed that barrier formation was impaired in differentiating AECs from asthmatic donors. Reduced expression of zonula occludens-1 (ZO-1), claudin-4 and -7 with disorganized actin cytoskeleton were evident, resulting in reduced barrier function. Infection by respiratory viruses, the major triggers of asthma exacerbations, mediate junctional dissociation in differentiated airway epithelium. However, it remains unclear whether viral infection contributes to impaired barrier function widely reported in airway epithelium from patients with asthma. Chapter 4 investigated the effect of two respiratory viruses – rhinovirus (RV) and influenza A virus (IAV) in impairing barrier formation in differentiating AEC cultures from healthy and asthmatic donors. RV infection reduced ZO-1 expression in differentiated AECs from healthy donors with no apparent change in barrier function. This was in contrast to IAV-mediated barrier disruption where increased barrier permeability and loss of ZO-1 and claudin-4 expression were observed in differentiating AECs from both healthy and asthmatic donors. Previous studies showed that activated TLR2 signalling enhanced transepithelial resistance (TER) of an intestinal epithelial barrier through enhancing ZO-1 protein expression to the junctional region. This suggests an alternative function of TLR2 signalling in epithelial barrier regulation. Chapter 5 aimed to investigate the functional significance of activated TLR-2 signalling in repairing RV-induced junctional dysfunction in differentiating AECs from healthy donors. TLR-2 agonist INNA-X in the absence of infection was able to improve barrier function by increasing TER in differentiating AECs from healthy donors. Stimulated TLR2 by INNA-X enhanced junction expression of ZO-1 and claudin-4 in differentiated AECs infected by RV. In summary, this thesis identified several junction-associated components responsible for intrinsic barrier defects seen in asthma. In addition to this, TLR2-mediated restoration of junction expression in injured epithelium implies that this pathway is a potential target for developing therapeutics for patients with asthma, in which compromised barrier function represents a pathological determinant in disease progression.
- Subject
- asthma; rhinovirus; airway epithelial cells; tight junctions; zonula occluden; virus infection
- Identifier
- http://hdl.handle.net/1959.13/1508325
- Identifier
- uon:56118
- Rights
- Copyright 2021 Ngan Fung Li
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 3 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 242 KB | Adobe Acrobat PDF | View Details Download |