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