Neutrophil elastase and matrix metalloproteinase 12 in cystic fibrosis lung disease

Abstract

Chronic lung disease remains the major cause of morbidity and mortality in patients with cystic fibrosis (CF). Recent studies in young children with CF diagnosed by newborn screening identified neutrophil elastase (NE), a major product released from neutrophils in inflamed airways, as a key risk factor for the onset and early progression of CF lung disease. However, the understanding of how NE and potentially other proteases contribute to the complex in vivo pathogenesis of CF lung disease remains limited. In this review, we summarize recent progress in this area based on studies in βENaC-overexpressing (βENaC-Tg) mice featuring CF-like lung disease and novel protease-specific Förster resonance energy transfer (FRET) sensors for localization and quantification of protease activity in the lung. These studies demonstrated that NE is implicated in several key features of CF lung disease such as neutrophilic airway inflammation, mucus hypersecretion, and structural lung damage in vivo. Furthermore, these studies identified macrophage elastase (matrix metalloproteinase 12 (MMP12)) as an additional protease contributing to early lung damage in βENaC-Tg mice. Collectively, these results suggest that NE and MMP12 released from activated neutrophils and macrophages in mucus-obstructed airways play important pathogenetic roles and may serve as potential therapeutic targets to prevent and/or delay irreversible structural lung damage in patients with CF.

Keywords: Airway inflammation; Cystic fibrosis; FRET reporter; Matrix metalloproteinase 12; Neutrophil elastase.

Fig. 1

Neutrophil elastase (NE) and matrix metalloproteinase 12 (MMP12) activity is increased at the surface of bronchoalveolar neutrophils and macrophages and is associated with structural lung damage in βENaC-Tg mice. Protease activity was measured on the surface of neutrophils from bronchoalveolar lavage (BAL) using a lipidated FRET reporter for NE (NEmo-2) and representative ratio images calculated from donor and acceptor fluorescence are shown (left upper panels). NEmo-2 detects increased NE activity (green color) on neutrophils from βENaC-Tg compared to wild-type (WT) mice, and the specificity of the NEmo-2 FRET signal is confirmed by genetic deletion of NE (NE^−/− and βENaC-Tg/NE^−/− mice). Representative morphology of distal airspaces shows that increased NE activity on BAL neutrophils is associated with airspace enlargement and destruction in βENaC-Tg mice that is substantially reduced by genetic deletion of NE (left lower panels). Corresponding experiments using a lipidated FRET reporter for MMP12 (LaRee-1) show activity (green color) on macrophages from βENaC-Tg mice, but not from wild-type (WT) mice or mice that lack MMP12 (MMP12^−/− and βENaC-Tg/MMP12^−/− mice) (right upper panels). Representative morphology of lung sections from WT, βENaC-Tg, MMP12^−/−, and βENaC-Tg/MMP12^−/− mice demonstrates that increased MMP12 activity on BAL macrophages also contributes to structural lung damage (right lower panels). Reprinted from [15, 52] with permission from the American Thoracic Society