Pulmonary inflammation and emphysema are common features of cystic fibrosis (CF) and other acquired forms of chronic obstructive pulmonary diseases (COPD), which have emerged as a major cause of death worldwide. In a recent detailed histopathological characterization, we demonstrated that mice with CF-like lung disease (the ENaC-transgenic mouse) also develop emphysema with increased lung volumes, enlarged alveolar airspaces, and increased lung compliance (Mall. M. et al, Am. J. Respir. Crit. Care. Med., 2008).
The overall goal of this project is to further elucidate the molecular mechanisms leading to emphysema formation in CF lung disease. A protease/anti-protease imbalance leading to increased activity of proteolytic enzymes in the lung has long been implicated as a cause of damage of alveolar structures and development of emphysema. However, it has not been possible to quantitate and visualize protease activity in biological samples or in vivo. We, therefore, developed a set of novel soluble and membrane bound FRET probes to monitor the activity of macrophage elastase (MMP12), a major proteolytic enzyme in the lung. Using these FRET probes, we were recently able to visualize MMP12 activity at the surface of activated macrophages obtained from bronchoalveolar lavages from a mouse model of acute pulmonary inflammation (Cobos-Correa A. et al, Nat Chem Biol., 2009).
Based on these results, we currently focus on applying these novel FRET probes to measure MMP12 activity and elucidate its role in the pathogenesis of CF lung disease in pre-clinical models as well as in biological samples from patients. Further, we plan to develop FRET probes for other protease family members and determine their specific roles in the pathogenesis of inflammation and emphysema formation, which may ultimately lead to novel therapeutic targets. Since these activity based assays are non-invasive, they are also applicable in the clinical diagnostic setting. Therefore, we predict that these FRET reporters may become useful to measure protease activity as a novel biomarker for early diagnosis and monitoring of disease activity in CF and other chronic inflammatory lung diseases in the future.