Rationale: Cystic fibrosis transmembrane conductance regulator (CFTR) protein is a chloride channel regulating fluid homeostasis at epithelial surfaces. Its loss of function induces hypohydration, mucus accumulation, and bacterial infections in CF and potentially other lung chronic diseases. Objectives: To test whether neutrophil elastase (NE) and neutrophil-mediated inflammation negatively impact CFTR structure and function, in vitro and in vivo. Methods: Using an adenovirus-CFTR overexpression approach, we showed that NE degrades wild-type (WT)- and ΔF508-CFTR in vitro and WT-CFTR in mice through a new pathway involving the activation of intracellular calpains. Measurements and Main Results: CFTR degradation triggered a loss of function, as measured in vitro by channel patch-clamp and in vivo by nasal potential recording in mice. Importantly, this mechanism was also shown to be operative in a Pseudomonas aeruginosa lung infection murine model, and was NE-dependent, because CFTR integrity was significantly protected in NE^−/− mice compared with WT mice. Conclusions: These data provide a new mechanism and show for the first time a link between NE-calpains activation and CFTR loss of function in bacterial lung infections relevant to CF and to other chronic inflammatory lung conditions.

Inflammation plays a critical role in lung disease progression in cystic fibrosis (CF). This inflammatory process is dominated by a neutrophil influx in the airways. To determine whether the accumulation of neutrophils in the airways of CF patients is associated with an altered function, we analyzed the capacity of neutrophils isolated from the lung compartment and the blood to release the major neutrophil pro- and anti-inflammatory cytokines IL-8 and IL-1-receptor antagonist (ra) spontaneously and in the presence of LPS. Comparison of cytokine production by blood neutrophils from CF patients and from control subjects showed significantly increased IL-8 and decreased IL-1ra release by CF neutrophils. Comparison of cytokine production by airway and blood neutrophils from CF patients also documented distinct profiles: the spontaneous release of IL-8 and IL-1ra by airway neutrophils was significantly higher than that from blood neutrophils. Culture in the presence of LPS failed to further enhance cytokine production. Analysis of the effect of dexamethasone confirmed the difference in the responsiveness of lung and blood neutrophils in CF. Used at a concentration effective in reducing IL-8 production by blood neutrophils, dexamethasone (10⁻⁶M) was unable to repress secretion of IL-8 by airway neutrophils. In addition, comparison of cytokine production by airway neutrophils from children with CF and children with dyskinetic cilia syndrome also documented distinct profiles of secretion. These results are consistent with a dysregulated cytokine production by lung and blood neutrophils in CF. They provide support to the hypothesis that not only the CF genotype but also the local environment may modify the functional properties of the neutrophils.