Quantification of collagen and proteoglycan deposition in a murine model of airway remodelling

Background: Sub- epithelial extracellular matrix deposition is a feature of asthmatic airway remodelling associated with severity of disease, decline in lung function and airway hyperresponsiveness. The composition of, and mechanisms leading to, this increase in subepithelial matrix, and its importance in the pathogenesis of asthma are unclear. This is partly due to limitations of the current models and techniques to assess airway remodelling. Methods: In this study we used a modified murine model of ovalbumin sensitisation and challenge to reproduce features of airway remodelling, including a sustained increase in sub- epithelial matrix deposition. In addition, we have established techniques to accurately and specifically measure changes in sub- epithelial matrix deposition, using histochemical and immunohistochemical staining in conjunction with digital image analysis, and applied these to the measurement of collagen and proteoglycans. Results: 24 hours after final ovalbumin challenge, changes similar to those associated with acute asthma were observed, including inflammatory cell infiltration, epithelial cell shedding and goblet cell hyperplasia. Effects were restricted to the bronchial and peribronchial regions with parenchymal lung of ovalbumin sensitised and challenged mice appearing histologically normal. By 12 days, the acute inflammatory changes had largely resolved and increased sub- epithelial staining for collagen and proteoglycans was observed. Quantitative digital image analysis confirmed the increased deposition of sub- epithelial collagen ( 33%, p < 0.01) and proteoglycans ( 32%, p < 0.05), including decorin ( 66%, p < 0.01). In addition, the increase in sub- epithelial collagen deposition was maintained for at least 28 days ( 48%, p < 0.001). Conclusion: This animal model reproduces many of the features of airway remodelling found in asthma and allows accurate and reproducible measurement of sub- epithelial extra- cellular matrix deposition. As far as we are aware, this is the first demonstration of increased sub- epithelial proteoglycan deposition in an animal model of airway remodelling. This model will be useful for measurement of other matrix components, as well as for assessment of the molecular mechanisms contributing to, and agents to modulate airway remodelling.