An investigation of the response of airway epithelial cells to pathogens associated with Acute Exacerbations of Chronic Obstructive Pulmonary Disease (AECOPD).

  • Stephen Carson

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Chronic Obstructive Pulmonary Disease (COPD) is a progressive and preventable disease associated with loss of lung function following exposure to noxious particles or gases. Exacerbations of COPD are acute periods associated with an increase in hyperinflation and gas trapping and characterised by reduced expiratory flow and increased airway inflammation. Although exacerbations are commonly associated with respiratory infections from bacteria or viruses, there remains an incomplete understanding on the interaction between pathogens and airway epithelial cells (AECs) in the triggering and progression of these events.

The initial aim of the study was to assess the responses of airway epithelial cells to different pathogenic stimulus associated with infections in COPD. Treatment of primary bronchial epithelial cells (PBEC), from a healthy and COPD donor, with heat-inactivated strains of Streptococcus pneumoniae and Haemophilus influenzae led to an increase in a number of inflammatory mediators as analysed using the Bioplex human inflammatory mediator panel (37-plex). Of particular interest was thymic stromal lymphopoietin (TSLP). TSLP is a cytokine that has been associated with airways disease including allergic asthma but its role in bacterial infections is less established. In the PBEC model, S. pneumoniae stimulation increased TSLP levels to a greater extent than H. influenzae in both healthy and COPD cells. Further investigation using COPD PBEC indicated a similar increase in TSLP expression following 6-hour treatment with clinical isolates of both H. influenzae and S. pneumoniae.

Another aim of the project was to investigate the effect of pathogen-associated immune cell stimulus on AEC responses. Sterile-filtered cell-conditioned media from the differentiated macrophage-like THP-1 cells, infected with strains of H. influenzae (TCCM), was used to treat cells. Optimisation of the model on 16HBE14o- cells (HBE cells) led to significant increases in IL-8 levels (p<0.01) following treatment with TCCM. PBEC from two healthy and COPD donors were treated with TCCM, with levels of 36 inflammatory mediators analysed using the Proteome Profiler Human Cytokine Antibody Array screen, with subsequent validation in changes in expression of genes of interest by qPCR. TCCM treatment stimulated both the production and expression of a number of inflammatory mediators in PBEC from all donors including IL-8. Two potential targets for further work were identified, G-CSF and SERPIN E1. There was a reduction in G-CSF production and lower levels expression of the gene coding for G-CSF from the COPD donor PBEC compared to the levels produced by the healthy PBEC following treatment with TCCM. SERPIN E1 levels and SERPINE1 gene expression levels were reduced in PBEC from both healthy and COPD donors treated with TCCM, compared to the untreated and vehicle controls. Treatment for 96 hours of COPD PBEC grown at air-liquid interface with TCCM from cells infected with H. influenzae ELB 008 at MOI 50 led to increase mucociliary clearance (MCC), with a decrease in CXCL8 and MUC5AC expression.

The final aim of this study was to investigate the effect of first-in-class, small molecule furin inhibitors, BOS-857 and BOS-318 on ICAM-1, a cell-surface adhesion molecule used to facilitate initial adherence of pathogens, including H. influenzae and the human rhinovirus strain, RV-A16. There was an indication of reduced ICAM-1 expression in PBEC treated with BOS-857 and BOS-318 but no clear reduction in ICAM-1 protein levels. Whilst treatment of HBE cells with furin inhibitors did not reduce ICAM-1 levels in those cells infected with H. influenzae (shown to stimulate a pro-inflammatory response, increasing levels of IL-8 and ICAM-1) they did seem to lead to a reduction in IL-8 levels. Furin inhibition was not shown to have an effect on RV-A16 replication in HBE cells or within PBEC from a healthy and COPD donor.

In conclusion, this project increased our understanding of the inflammatory responses of airway epithelial cells to pathogenic stimulus which included the identification of a number of inflammatory mediators of interest for future studies. Studies using infected immune cells showed that inflammation within airway epithelial cells could be driven above levels seen from direct bacterial stimulation alone and that this inflammatory response may lead to unexpected increases in MCC and reductions in MUC5AC expression, priming future studies. Whilst there was no clear change in ICAM-1 levels following furin inhibition, IL-8 was identified as an inflammatory mediator of interest for further studies. Future work will build upon the results within project, expanding it to include PBEC from a greater number of healthy donors and COPD donors and to further refine models developed within this project to give further insight into the inflammatory responses of airway epithelial cells in COPD

Thesis embargoed until 31 July 2024
Date of AwardJul 2022
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsBREATH (Border REgions Airway Training Hub) & Special EU Programmes Body
SupervisorLorraine Martin (Supervisor), Fionnuala Lundy (Supervisor) & Lorcan McGarvey (Supervisor)

Keywords

  • Chronic obstructive pulmonary disease
  • Haemophilus influenzae
  • primary bronchial epithelial cells
  • Furin inhibition
  • inflammation

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