Introduction Airway remodelling describes the histopathological changes in tissue architecture observed in obstructive lung diseases such as asthma and may have a negative impact on lung function. These changes do not appear to be treated by current asthma treatments. Changes observed during airway remodelling include increased thickness of airway smooth muscle (ASM) layer and enhanced extracellular matrix (ECM) deposition. Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes, which facilitate tissue remodelling via ECM protein degradation. Matrix metalloproteinase-1 (MMP-1) and mast cells are present in the airways of patients with asthma (but not in healthy people). MMPs expression is highly regulated in lungs and is increased in disease states. My project aimed to assess MMP-1, -2 and -9 expression and activity in asthma airways. Furthermore, the underlying mechanism of MMP-1 activation and subsequently its role in airway remodelling and worsening asthma severity was investigated in the context of asthma exacerbation, which is thought to be an exaggerated lower airway inflammatory response to an environmental exposure such as respiratory virus infection. Methods Patients with stable asthma and healthy controls underwent spirometry, methacholine airway (PC20 ) challenge, exhaled nitric oxide (FeNO) test, bronchoscopy/bronchial washings and primary airway smooth muscle (ASM) cell cultures. A second asthma group (mild to moderate severity) and controls had symptom scores, spirometry and bronchoalveolar lavage (BAL) before and after rhinovirus inoculation. ECM was prepared from decellularised primary ASM cultures. MMP-1 protein levels and activity were assessed in bronchial fluid samples by enzyme-linked immunosorbent assay (ELISA), western blotting and fluorescent activity assay. ASM cell growth was measured by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) reduction assay and cell counts. Bronchial fluid gelatinase (MMP-2 and -9) expression and activity was assessed by gelatin zymography. Results MMP-1 and MMP-9 expression was enhanced in both stable asthma and during asthma exacerbations, whilst MMP-2 expression was only increased during asthma exacerbations. MMP-1 can be activated by tryptase, which is an inflammatory product of mast cell degranulation. Activated (degranulated) mast cells enhanced proliferation of both control and asthma ASM cells via the production of a pro-proliferative ECM in vitro and the proliferative effect was dependent on MMP-1. In patients with asthma, mast cells numbers within ASM bundles were associated with ASM growth. MMP-1 protein levels were related to bronchial reactivity and MMP-1 activity increased during asthma exacerbations, where its levels were related to exacerbation severity. Conclusion This study suggests that MMP-1 plays an important role in asthma pathophysiology and that ASM/mast cell interactions contribute to asthma severity by transiently increasing MMP-1 activation, ASM growth and airway responsiveness. Moreover, there is increased expression of MMP-2 and -9 during asthma exacerbations compared with stable asthma. As both MMP-2 and -9 act as mediators of inflammation (Okada, S. et al., 1997) (Elkington, P.T.G., 2006) and tissue remodelling (Oshita, Y. et al., 2003), an increase in gelatinolytic activity linked to MMP-2 and MMP-9 is also likely to play a significant role in the pathophysiology of asthma exacerbations.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:748393 |
| Date | January 2018 |
| Creators | Naveed, Shams-un-nisa |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/50577/ |
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