Extra-cellular matrix inducible collagenase activity in asthma: a potential drug target against airway remodelling.

Asthma effects more than 5 million people in the UK and is responsible for 70,000 hospital admissions and 13,000 deaths each year. Despite treatment many patients still experience significant symptoms. Patients with chronic asthma can develop structural airway changes called airway remodelling which increase the frequency and severity of their symptoms. Airway remodelling is not well counted by current asthma therapies and new approaches to treat remodelling are urgently required. Extracellular matrix proteins surround all cells providing support but also effecting cell function. In remodelling, excessive amounts of the extracellular matrix proteins collagen 1 and tenascin-C are deposited in the airways. We have shown that these proteins can cause increased expression of enzymes called MMPs. We think that MMP-1, made by smooth muscle cells in the airways in response to signals from collagen 1 and tenascin-C leads to increased airway contraction and asthma symptoms. In this study, we will examine how collagen 1 and tenascin-C act on smooth muscle cells to produce more MMP-1. Next, we will determine how these extracellular matrix proteins and MMP-1 lead to increased airway contraction in an experimental model of asthma. We will then confirm our findings in human asthma: we will use samples from people with no lung disease and compare them with patients with asthma, with mild and stronger airway narrowing in response to a standard asthma trigger. By studying the expression of MMP-1, collagen I and tenascin-C in the lungs of these patients and if they have more airway narrowing and worse asthma symptoms. We hope this study will provide potential new targets for drugs to treat airway remodelling, reduce asthma symptoms and improve quality of life for those with asthma.

Despite current therapies, patients with asthma develop progressive structural airway changes termed airway remodelling leading to airflow obstruction, bronchial hyper responsiveness, and worsening asthma symptoms. Airway smooth muscle (ASM) hyperplasia and increased extracellular matrix deposition are key features of remodelling, with collagen I and tenascin-C particularly over expressed. We and others have shown that matrix factors enhance ASM proliferation, survival and strongly induce the expression of matrix metalloproteinase-1 (MMP-1), a collagenase causing increased airway contraction in model systems. Here we will test the hypothesis that collagen I and tenascin-C increase MMP-1 activity worsening airway responsiveness and asthma symptoms. Studies will be conducted in patients and primary ASM obtained from three groups: normal volunteers, those with asthma and mild BHR (methacholine PC20 5-8mg/ml) and those with asthma and moderate to strong BHR with a methacholine (PC20 less than 1mg). Patients will be evaluated for asthma control and airway function and will undergo bronchoscopy, bronchial washings and airway biopsy. ASM cells will be cultured from patients and used in the following studies. We will investigate the receptors and signalling pathways linking collagen I and tenascin-C to increased MMP-1 transcription, the proteases are responsible for MMP-1 activation and if this is different in asthma derived cells. To determine if enhanced MMP-1 activity increases airway contraction we will use a lung slice model. Lung slices from normal animals and those over-expressing MMP-1 will be treated with chronic allergen exposure to develop airway remodelling and the response to contractile agonists determined. Finally we will examine the effect of collagenase activity on airway contraction in human asthma: firstly by studying the expression and co-localisation of MMP-1, collagen I and tenascin C in the airways of patients with asthma by immunohistochemistry and in situ zymography. We will then examine if MMP-1 protein and collagenase activity in bronchial washings and biopsies are associated with airway reactivity as determined by bronchial reactivity and methocholine and peak flow variability using multiple logistic regression in different asthma phenotypes. The experiments will determine the role of these matrix factors in remodelling, particularly with regard to airway contraction and highlight targets for therapeutic intervention.