ABSTRACT
Whereas cigarette smoking remains the main risk factor for emphysema, recent studies in ß-epithelial Na(+) channel-transgenic (ßENaC-Tg) mice demonstrated that airway surface dehydration, a key pathophysiological mechanism in cystic fibrosis (CF), caused emphysema in the absence of cigarette smoke exposure. However, the underlying mechanisms remain unknown. The aim of this study was to elucidate mechanisms of emphysema formation triggered by airway surface dehydration. We therefore used expression profiling, genetic and pharmacological inhibition, Foerster resonance energy transfer (FRET)-based activity assays, and genetic association studies to identify and validate emphysema candidate genes in ßENaC-Tg mice and patients with CF. We identified matrix metalloproteinase 12 (Mmp12) as a highly up-regulated gene in lungs from ßENaC-Tg mice, and demonstrate that elevated Mmp12 expression was associated with progressive emphysema formation, which was reduced by genetic deletion and pharmacological inhibition of MMP12 in vivo. By using FRET reporters, we show that MMP12 activity was elevated on the surface of airway macrophages in bronchoalveolar lavage from ßENaC-Tg mice and patients with CF. Furthermore, we demonstrate that a functional polymorphism in MMP12 (rs2276109) was associated with severity of lung disease in CF. Our results suggest that MMP12 released by macrophages activated on dehydrated airway surfaces may play an important role in emphysema formation in the absence of cigarette smoke exposure, and may serve as a therapeutic target in CF and potentially other chronic lung diseases associated with airway mucus dehydration and obstruction.
Subject(s)
Airway Obstruction/immunology , Macrophage Activation/immunology , Macrophages, Alveolar/immunology , Matrix Metalloproteinase 12/immunology , Mucus/immunology , Pulmonary Emphysema/immunology , Airway Obstruction/metabolism , Animals , Bronchoalveolar Lavage Fluid/immunology , Cystic Fibrosis/genetics , Cystic Fibrosis/immunology , Cystic Fibrosis/metabolism , Dehydration/immunology , Dehydration/metabolism , Genomics , Macrophages, Alveolar/metabolism , Matrix Metalloproteinase 12/genetics , Matrix Metalloproteinase 12/metabolism , Mice, Knockout , Mucus/metabolism , Polymorphism, Single Nucleotide/genetics , Pulmonary Disease, Chronic Obstructive/immunology , Pulmonary Disease, Chronic Obstructive/metabolism , Pulmonary Emphysema/metabolism , STAT6 Transcription Factor/genetics , STAT6 Transcription Factor/immunology , STAT6 Transcription Factor/metabolism , Signal Transduction/immunologyABSTRACT
MMP12 is a metalloproteinase implicated in inflammation. To monitor its activity, we synthesized a membrane-targeted reporter (LaRee1) based on Foerster resonance energy transfer (FRET). Unlike existing sensors, LaRee1 detects MMP12 activity by loss of FRET plus internalization of the lipidated fragment. In bronchoalveolar lavages from a mouse model of pulmonary inflammation, LaRee1 detected MMP12 activity at the surface of activated macrophages. LaRee1 may become a powerful tool for monitoring lung disease.
