Mucus Obstruction Research Articles

Association between the length of the MUC8-minisatellite 5 region and susceptibility to chronic obstructive pulmonary disease (COPD).

In asthma and chronic obstructive pulmonary disease (COPD), mucins display disease-related alterations caused by airway mucus obstruction. MUC5AC, MUC5B and MUC8 are known as the major secretory mucins in human airway epithelial cells. Analysis of mucin genes has identified the presence of several features with a variable number of tandem repeats (VNTR; minisatellites) in the central region of each mucin. In our previous study, six minisatellites in the region of the MUC8 gene were identified, and the MUC8-MS5 minisatellite showed the highest heterozygosity among them. In this study, we evaluated the relationship between MUC8-MS5 and susceptibility to asthma and COPD. A case-control study was performed with 229 controls, 123 COPD cases and 77 asthma cases. A significant association (OR 3.96) between short alleles (2/2 repeats) and the occurrence of COPD was observed [95% confidence interval (CI) 1.32-11.88; p = 0.008]. Hence, the increased frequency of 2/2 homo-short alleles were also found in asthma cases (3.11; CI 0.88-11.05; p = 0.066), though this association was not statistically significant. These results revealed a genetic association between MUC8 and COPD, and that the specific short minisatellite alleles (2/2) of MUC8-MS5 may be a risk factor for COPD.

Early Postnatal Secondhand Smoke Exposure Disrupts Bacterial Clearance and Abolishes Immune Responses in Muco-Obstructive Lung Disease.

Secondhand smoke (SHS) exposure has been linked to the worsening of ongoing lung diseases. However, whether SHS exposure affects the manifestation and natural history of imminent pediatric muco-obstructive airway diseases such as cystic fibrosis remains unclear. To address these questions, we exposed Scnn1b transgenic (Scnn1b-Tg+) mice to SHS from postnatal day (PND) 3-21 and lung phenotypes were examined at PND22. Although a majority of filtered air (FA)-exposed Scnn1b-Tg+ (FA-Tg+) mice successfully cleared spontaneous bacterial infections by PND22, the SHS-exposed Scnn1b-Tg+ (SHS-Tg+) mice failed to resolve these infections. This defect was associated with suppressed antibacterial defenses, i.e., phagocyte recruitment, IgA secretion, and Muc5b expression. Whereas the FA-Tg+ mice exhibited marked mucus obstruction and Th2 responses, SHS-Tg+ mice displayed a dramatic suppression of these responses. Mechanistically, downregulated expression of IL-33, a stimulator of type II innate lymphoid cells, in lung epithelial cells was associated with suppression of neutrophil recruitment, IgA secretions, Th2 responses, and delayed bacterial clearance in SHS-Tg+ mice. Cessation of SHS exposure for 21 d restored previously suppressed responses, including phagocyte recruitment, IgA secretion, and mucous cell metaplasia. However, in contrast with FA-Tg+ mice, the SHS-Tg+ mice had pronounced epithelial necrosis, alveolar space consolidation, and lymphoid hyperplasia; indicating lagged unfavorable effects of early postnatal SHS exposure in later life. Collectively, our data show that early postnatal SHS exposure reversibly suppresses IL-33 levels in airspaces which, in turn, results in reduced neutrophil recruitment and diminished Th2 response. Our data indicate that household smoking may predispose neonates with muco-obstructive lung disease to bacterial exacerbations.

MUC5AC and a Glycosylated Variant of MUC5B Alter Mucin Composition in Children With Acute Asthma

BackgroundDiffuse airway mucus obstruction is an important feature of severe and fatal asthma. MUC5AC and MUC5B are the principal gel-forming mucins found in airway mucus. The mucin composition of airway mucus likely affects its functional properties.MethodsWe quantified the principal airway mucins MUC5AC and MUC5B in the sputum of age-matched children with acute and stable asthma and healthy control subjects by using Western blotting.ResultsSputum samples from 38 children (13 with acute asthma, 15 with stable asthma, 10 control subjects) were obtained. Sputum MUC5AC concentrations were 7.6 μg/mL in control subjects, 22.4 μg/mL in those with stable asthma (P = .17), and 44.7 μg/mL in those with acute asthma (P < .05). MUC5B concentrations showed less variation, with 238.5, 208.4 and 165.9 μg/mL in control subjects, those with stable asthma, and those with acute asthma, respectively. The greater MUC5AC concentration in those with acute asthma resulted in a significantly altered MUC5B:MUC5AC ratio between control subjects and those with acute asthma (P < .05). Significant differences in MUC5B glycoforms were present between the groups, with the low-charge-only glycoform being found uniquely in those with acute asthma.ConclusionsIncreased MUC5AC and the presence of a low-charge-only MUC5B glycoform significantly altered mucin composition in children with acute asthma. These changes may be important contributory factors to the airway mucus obstruction observed during acute asthma.

Phosphoinositide 3-Kinase in Asthma: Novel Roles and Therapeutic Approaches.

Asthma manifests as airway hyperresponsiveness and inflammation, including coughing, wheezing, and shortness of breath. Immune cells and airway structural cells orchestrate asthma pathophysiology, leading to mucus secretion, airway narrowing, and obstruction. Phosphoinositide 3-kinase, a lipid kinase, plays a crucial role in many of the cellular and molecular mechanisms driving asthma pathophysiology and represents an attractive therapeutic target. Here, we summarize the diverse roles of phosphoinositide 3-kinase in the pathogenesis of asthma and discuss novel therapeutic approaches to treatment.

MicroRNA-145 down-regulates mucin 5AC to alleviate airway remodeling and targets EGFR to inhibit cytokine expression.

This study aims to explore how microRNA-145 (miR-145) affects airway remodeling and cytokine expression by targeting epidermal growth factor receptor (EGFR) to regulate mucin 5AC (MUC5AC).Mice alveolar epithelial cells (AECs) were divided into a control, blank, miR-145 mimics, mimic control, miR-145 inhibitors, inhibitor control, si-EGFR and miR-145 inhibitors + si-EGFR group. Asthma mice models with airway remodeling were induced with an Ovalbumin (OVA) solution and randomly divided into a normal, asthma, asthma + miR-145 mimics, asthma + miR-145 mimic control, asthma + si-EGFR or asthma + si-EGFR NC group. Airway remodeling degree and histomorphology was measured using hematoxylin-eosin (HE), Masson and periodic acid-Schiff (PAS) staining. Flow cytometry was used to detect Th2 and Th17 cells in peripheral blood, ELISA was used to measure inflammatory factors. qRT-PCR and western blotting was adapted to detect the expressions of EGFR and the relevant cytokines that are regulated by miR-145.The control, miR-145 mimics and si-EGFR groups showed a higher expression of miR-145 and a lower expression of EGFR and cytokines than the blank, mimic control, inhibitor control and miR-145 inhibitor + si-EGFR groups. Mice in the asthma + miR-145 mimics and asthma + si-EGFR groups showed lower WAt/Pbm, WAi/Pbm and WAm/Pbm, less inflammatory cells, less airway modeling and alleviated goblet cell hyperplasia and mucus obstruction than the asthma group. Furthermore, the expressions of EGFR and cytokines of transfected cells and lung tissues were negatively related to those of miR-145. MiR-145 can down-regulate MUC5AC by negatively targeting EGFR and thereby relieving airway remodeling.

Long-term results of ileal ureteric replacement: a 25-year single-centre experience.

To report the long-term outcomes of ileal ureteric replacement (IUR) in complex reconstruction of the urinary tract. From 1991 to 2016, IUR was performed in 157 patients with structural or functional ureteric loss. In 52 patients, bilateral IUR became necessary. Implantation sites where either the native urinary bladder (n = 79) or intestinal reservoirs (n = 78). In the latter group, the technique was used at the time of primary urinary diversion (n = 34), in a secondary approach (n = 29), and in undiversion or conversion procedures (n = 15). Anti-refluxive implantation was performed in 37 patients. In eight patients the ileal ureter was implanted into the cutis as an ileal conduit. All patients were followed prospectively according to a standardised protocol. The mean follow-up was 54.1 months. In 114 patients with dilatation of the upper urinary tract before surgery a significant improvement of the dilatation was confirmed in 98 patients. Serum creatinine levels decreased or remained stable in 147 of the 157 patients. Reflux was present in all cases without and in six cases with an anti-reflux mechanism. In six patients, operative revision became necessary because of severe metabolic acidosis, mucus obstruction or stenosis of the ileal ureter. To our knowledge, this is the world's largest single-centre series of IUR reported to date. Long-term follow-up confirms that this approach is a safe and reliable solution, even under complex conditions. Anti-refluxive implantation is recommended for intestinal reservoirs, whereas reflux prevention seems to be of minor importance when the native bladder is chosen as the site of implantation.

Airway mucus, inflammation and remodeling: emerging links in the pathogenesis of chronic lung diseases.

Airway mucus obstruction is a hallmark of many chronic lung diseases including rare genetic disorders such as cystic fibrosis (CF) and primary ciliary dyskinesia, as well as common lung diseases such as asthma and chronic obstructive pulmonary disease (COPD), which have emerged as a leading cause of morbidity and mortality worldwide. However, the role of excess airway mucus in the in vivo pathogenesis of these diseases remains poorly understood. The generation of mice with airway-specific overexpression of epithelial Na+ channels (ENaC), exhibiting airway surface dehydration (mucus hyperconcentration), impaired mucociliary clearance (MCC) and mucus plugging, led to a model of muco-obstructive lung disease that shares key features of CF and COPD. In this review, we summarize recent progress in the understanding of causes of impaired MCC and in vivo consequences of airway mucus obstruction that can be inferred from studies in βENaC-overexpressing mice. These studies confirm that mucus hyperconcentration on airway surfaces plays a critical role in the pathophysiology of impaired MCC, mucus adhesion and airway plugging that cause airflow obstruction and provide a nidus for bacterial infection. In addition, these studies support the emerging concept that excess airway mucus per se, probably via several mechanisms including hypoxic epithelial necrosis, retention of inhaled irritants or allergens, and potential immunomodulatory effects, is a potent trigger of chronic airway inflammation and associated lung damage, even in the absence of bacterial infection. Finally, these studies suggest that improvement of mucus clearance may be a promising therapeutic strategy for a spectrum of muco-obstructive lung diseases.

Hypoxia and sterile inflammation in cystic fibrosis airways: mechanisms and potential therapies.

Cystic fibrosis is one of the most common autosomal recessive genetic diseases in Caucasian populations. Diagnosis via newborn screening and targeted nutritional and antibiotic therapy have improved outcomes, however respiratory failure remains the key cause of morbidity and mortality. Progressive respiratory disease in cystic fibrosis is characterised by chronic neutrophilic airway inflammation associated with structural airway damage leading to bronchiectasis and decreased lung function. Mucus obstruction is a characteristic early abnormality in the cystic fibrosis airway, associated with neutrophilic inflammation often in the absence of detectable infection. Recent studies have suggested a link between hypoxic cell death and sterile neutrophilic inflammation in cystic fibrosis and other diseases via the IL-1 signalling pathway. In this review, we consider recent evidence regarding the cellular responses to respiratory hypoxia as a potential driver of sterile neutrophilic inflammation in the lung, current knowledge on hypoxia as a pathogenic mechanism in cystic fibrosis and the potential for current and future therapies to alleviate hypoxia-driven sterile inflammation.

Hydrator Therapies for Chronic Bronchitis. Lessons from Cystic Fibrosis.

Patients with the chronic bronchitis form of chronic obstructive pulmonary disease and cystic fibrosis share similar clinical features, including mucus obstruction of airways and the development of chronic/recurrent airways infections that often manifest as disease exacerbations. There is growing evidence that these diseases may have parallels in disease pathogenesis as well, including cystic fibrosis transmembrane conductance regulator dysfunction, mucus dehydration, and defective mucociliary clearance. As progress is made in the development of therapies that target the basic defects that lead to cystic fibrosis lung disease, it is possible that similar approaches could also benefit patients with chronic bronchitis. A deeper understanding of how tobacco smoke and other triggers of chronic bronchitis actually lead to disease, and exploration of the concept that therapies that restore cystic fibrosis transmembrane conductance regulator function, mucus hydration, and/or mucociliary clearance may benefit patients with chronic bronchitis, hold the prospect of significant progress in treating this prevalent disease.

Altered protease and antiprotease balance during a COPD exacerbation contributes to mucus obstruction.

BackgroundProteases have been shown to degrade airway mucin proteins and to damage the epithelium impairing mucociliary clearance. There are increased proteases in the COPD airway but changes in protease-antiprotease balance and mucin degradation have not been investigated during the course of a COPD exacerbation. We hypothesized that increased protease levels would lead to mucin degradation in acute COPD exacerbations.MethodsWe measured neutrophil elastase (NE) and alpha 1 protease inhibitor (A1-PI) levels using immunoblotting, and conducted protease inhibitor studies, zymograms, elastin substrate assays and cigarette smoke condensate experiments to evaluate the stability of the gel-forming mucins, MUC5AC and MUC5B, before and 5–6 weeks after an acute pulmonary exacerbation of COPD (n = 9 subjects).ResultsUnexpectedly, mucin concentration and mucin stability were highest at the start of the exacerbation and restored to baseline after 6 weeks. Consistent with these data, immunoblots and zymograms confirmed decreased NE concentration and activity and increased A1-PI at the start of the exacerbation. After recovery there was an increase in NE activity and a decrease in A1-PI levels. In vitro, protease inhibitor studies demonstrated that serine proteases played a key role in mucin degradation. Mucin stability was further enhanced upon treating with cigarette smoke condensate (CSC).ConclusionThere appears to be rapid consumption of secreted proteases due to an increase in antiproteases, at the start of a COPD exacerbation. This leads to increased mucin gel stability which may be important in trapping and clearing infectious and inflammatory mediators, but this may also contribute acutely to mucus retention.

IL-1 receptor anatagonist anakinra reduces neutrophilic airway inflammation in mice with cystic fibrosis-like lung disease

Hypoxic degeneration and necrosis of epithelial cells associated with airway mucus obstruction precedes neutrophilic airway inflammation in βENaC-overexpressing (βENaC-Tg) mice with cystic fibrosis (CF)-like lung disease (Mall MA et al., Am J Respir Crit Care Med., 2008). In many organs sterile neutrophilic inflammation is triggered by necrosis via release of Interleukin-1 alpha (IL-1α) and IL-1 receptor (IL-1R) signaling (Chen CJ et al., Nat Med., 2007). Recently we demonstrated that lack of IL-1R improved survival and reduced neutrophilic airway inflammation, structural lung damage and mucus obstruction in βENaC-Tg mice (Zhou-Suckow Z et al., Pediatr Pulmonol., Suppl 2013). In the present day, we hypothesized that treatment with the IL-1R antagonist anakinra may reduce neutrophilic airway inflammation and ameliorate CF-like lung disease in βENaC-Tg mice. To test this hypothesis, we treated 4 to 6 week old βENaC-Tg mice in established lung disease and wild-type littermates with anakinra (200 mg/kg body weight) or vehicle (NaCl 0.9%) alone by subcutaneous injection twice per day for one week. At the endpoint, we performed bronchoalveolar lavage (BAL) to determine differential cell counts and KC levels, and analyzed histology and morphometry for airway epithelial necrosis, airway mucus obstruction and emphysema. As expected from previous studies of βENaC-Tg mice with genetic deletion of IL-1R, treatment with anakinra had no effect on hypoxic epithelial degeneration. However, anakinra treatment significantly reduced neutrophilic inflammation and KC levels in BAL. Furthermore, mean linear intercepts and destructive index were also reduced by anakinra indicating less structural lung damage in βENaC-Tg mice. These results demonstrate that inhibition of IL-1R signalling provides an effective therapy of CF-like lung disease in mice and suggest anakinra as a potential anti-inflammatory therapy to limit neutrophilic inflammation and associated lung damage in patients with CF and potentially other muco-obstructive lung diseases.

Development of Confocal Reflection Microscopy for the Study of Airway Surface Liquid Dysregulation in Cystic Fibrosis

In cystic fibrosis(CF) patients and βENaC-overexpressing mice, impaired airway epithelial ion transport produces airway surface liquid(ASL) depletion, leading to mucociliary dysfunction, mucus obstruction, chronic airway inflammation and infection. ASL homeostasis can be studied by measuring ASL height in primary epithelial cultures from murine and human airways. The height can be determined using confocal fluorescence microscopy; however the current protocol requires fluorescently labelled liquid addition to the apical side of the epithelium resulting in nonphysiological conditions.

Small molecule inhibitor of neutrophil elastase reduces emphysema in mice with cystic fibrosis-like lung disease

Background: Increased neutrophil elastase (NE) activity in bronchoalveolar lavage (BAL) fluid in newborns with cystic fibrosis (CF) has been shown to correlate with lung damage in juvenile age. Mice with airway- specific overexpression of the epithelial Na+ channel (βENaC-Tg) phenocopy CF lung disease with mucus obstruction, chronic inflammation and emphysema. Genetic deletion of NE in βENaC-Tg mice reduced airway inflammation and emphysema, indicating that NE may serve as a therapeutic target.

Dysregulation of epithelial miR-148b contributes to goblet cell metaplasia, inflammation and alveolar damage in cystic fibrosis lung disease

Cystic fibrosis (CF) lung disease is primarily characterized by chronic mucus obstruction, inflammation and structural damage. While mutations in the CFTR gene are an initial trigger, molecular mechanisms underlying CF pathogenesis remains poorly understood. miRNAs are key regulators of diverse biological and pathological processes. Here, we identified association of miR-148b during the in vivo pathogenesis of CF using Scnn1b-overexpressing (Scnn1b-Tg) mice as a model of CF-like lung disease. miR-148b expression was elevated in the lung tissue of Scnn1b-Tg mice and is localized mainly in airway and alveolar epithelial cells. We demonstrate that ERBB receptor feedback inhibitor 1 (Errfi1) is one of the target genes of miR-148b. Antagomir-mediated selective silencing of miR-148b resulted in reduced goblet cell metaplasia, mucus hypersecretion, neutrophilic inflammation, and emphysema in the lungs of Scnn1b-Tg mice compared to wild-type. Our human studies demonstrate differential upregulation of miR-148b in the bronchial brushing of CF compared to non-CF individuals and localization in airway and alveolar epithelial cells. Further, we found that the allele distribution at MIR148B-Sat, a polymorphic marker that reflects the genetic variation at the human MIR148B gene, is associated with disease severity in F508del-CFTR homozygous sibling pairs. Together, this study provides a functional link between miR-148b and in vivo pathogenesis of CF and may have a potential for the development of novel therapeutic target.

WS10.2 Hypoxic epithelial necrosis triggers neutrophilic inflammation via IL-1 receptor signaling in cystic fibrosis-like lung disease

In many organs, hypoxic cell death triggers sterile neutrophilic inflammation via Interleukin-1 receptor (IL-1R) signaling. Although hypoxia is common in airways from patients with cystic fibrosis (CF), its role in neutrophilic inflammation remains unknown. We recently demonstrated that hypoxic epithelial necrosis due to airway mucus obstruction precedes neutrophilic inflammation in Scnn1b -transgenic ( Scnn1b -Tg) mice with CF-like lung disease. To determine the role of hypoxic epithelial necrosis and IL-1R signaling in the development of neutrophilic inflammation, mucus obstruction and structural lung damage in CF lung disease, we used genetic deletion and pharmacological inhibition of IL-1R in Scnn1b -Tg mice and studied effects on airway epithelial necrosis, levels of IL-1α, keratinocyte chemoattractant (KC), neutrophils in bronchoalveolar lavage and mortality, mucus obstruction and emphysema. We evaluated lung tissues from patients with CF and COPD and controls for airway epithelial necrosis and mucus obstruction. Lack of IL-1R abrogated airway neutrophilia and reduced mortality, mucus obstruction and emphysema in Scnn1b -Tg mice. Treatment with IL-1R antagonist anakinra in adult Scnn1b -Tg mice showed similar protective effects. Numbers of necrotic airway epithelial cells were elevated and correlated with mucus obstruction in patients with CF and COPD. Our results support an important role of hypoxic epithelial necrosis in the pathogenesis of neutrophilic airway inflammation independent of bacterial infection and suggest IL-1R as a novel target for antiinflammatory therapy in CF and potentially other muco-obstructive airway diseases. Supported by DFG (DFG MA 2081/3–2).

WS06.6 Mucociliary transport is impaired in cystic fibrosis pig airways

Objectives The basic defect in cystic fibrosis (CF) is well characterized, but the link between defects in the CF transmembrane conductance regulator (CFTR) and the phenomenon of stagnant mucus is not well understood. We have shown that the ileal mucus in CFTR mutant mice adheres to the epithelium, is denser, and is less penetrable than that of wildtype mice and that addition of 115 mM NaHCO 3 to mucus partially normalizes this mucus phenotype. Using this knowledge of effects on ileal mucus, we are developing an airway experimental set-up. Methods Excised airways from CFTR knockout (CF) and wildtype (WT) pigs are pinned to a chamber, alcian blue mucosal stain is added to visualize the mucus and the transport is recorded. During the experiment, mucus is collected for proteomics using masspectrometry. Scanning electron microscopy is used to visualize the properties of the mucus, and transmission electron microscopy is used to study mucin secretion in detail. Results Average clearance rates of strands in CF pig airways are lower than in WT pig airways. Preliminary results suggest that the initial defect in newborn pigs involves clearance of Muc5b from the glands. Furthermore, we show that removal of bicarbonate from WT airways reduces the average clearance rate to the level of CF airways. Conclusion Evidence suggests the importance of bicarbonate in the proper unpacking and secretion of mucins. Thus, restoration of bicarbonate to the apical surface of the epithelium in combination with osmolytes may induce proper mucin unpacking in CF epithelia, and therefore could relieve the mucus obstruction that causes clinical problems for cystic fibrosis patients.

138 Dysregulation of epithelial miR-148b contributes to goblet cell metaplasia, inflammation and alveolar damage in cystic fibrosis lung disease

Cystic fibrosis (CF) lung disease is primarily characterized by chronic mucus obstruction, inflammation and structural damage. While mutations in the CFTR gene are an initial trigger, molecular mechanisms underlying CF pathogenesis remains poorly understood. miRNAs are key regulators of diverse biological and pathological processes. Here, we identified association of miR-148b during the in vivo pathogenesis of CF using Scnn1b-overexpressing (Scnn1b-Tg) mice as a model of CF-like lung disease. miR-148b expression was elevated in the lung tissue of Scnn1b-Tg mice and is localized mainly in airway and alveolar epithelial cells. We demonstrate that ERBB receptor feedback inhibitor 1 (Errfi1) is one of the target genes of miR-148b. Antagomir-mediated selective silencing of miR-148b resulted in reduced goblet cell metaplasia, mucus hypersecretion, neutrophilic inflammation, and alveolar damage in the lungs of Scnn1b-Tg mice compared to wild-type. Our human studies demonstrate differential upregulation of miR-148b in the bronchial brushing of CF compared to non-CF individuals and localization in airway and alveolar epithelial cells. Further, we found that the allele distribution at MIR148B-Sat, a polymorphic marker that reflects the genetic variation at the human MIR148B gene, is associated with disease severity in F508del-CFTR homozygous sibling pairs. Together, this study provides a functional link between miR-148b and in vivo pathogenesis of CF and may have a potential for the development of novel therapeutic target.

Hypoxic epithelial necrosis triggers neutrophilic inflammation via IL-1 receptor signaling in cystic fibrosis lung disease.

In many organs, hypoxic cell death triggers sterile neutrophilic inflammation via IL-1R signaling. Although hypoxia is common in airways from patients with cystic fibrosis (CF), its role in neutrophilic inflammation remains unknown. We recently demonstrated that hypoxic epithelial necrosis caused by airway mucus obstruction precedes neutrophilic inflammation in Scnn1b-transgenic (Scnn1b-Tg) mice with CF-like lung disease. To determine the role of epithelial necrosis and IL-1R signaling in the development of neutrophilic airway inflammation, mucus obstruction, and structural lung damage in CF lung disease. We used genetic deletion and pharmacologic inhibition of IL-1R in Scnn1b-Tg mice and determined effects on airway epithelial necrosis; levels of IL-1α, keratinocyte chemoattractant, and neutrophils in bronchoalveolar lavage; and mortality, mucus obstruction, and structural lung damage. Furthermore, we analyzed lung tissues from 21 patients with CF and chronic obstructive pulmonary disease and 19 control subjects for the presence of epithelial necrosis. Lack of IL-1R had no effect on epithelial necrosis and elevated IL-1α, but abrogated airway neutrophilia and reduced mortality, mucus obstruction, and emphysema in Scnn1b-Tg mice. Treatment of adult Scnn1b-Tg mice with the IL-1R antagonist anakinra had protective effects on neutrophilic inflammation and emphysema. Numbers of necrotic airway epithelial cells were elevated and correlated with mucus obstruction in patients with CF and chronic obstructive pulmonary disease. Our results support an important role of hypoxic epithelial necrosis in the pathogenesis of neutrophilic inflammation independent of bacterial infection and suggest IL-1R as a novel target for antiinflammatory therapy in CF and potentially other mucoobstructive airway diseases.

Airway mucus obstruction triggers macrophage activation and matrix metalloproteinase 12-dependent emphysema.

Whereas cigarette smoking remains the main risk factor for emphysema, recent studies in β-epithelial Na(+) channel-transgenic (βENaC-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 βENaC-Tg mice and patients with CF. We identified matrix metalloproteinase 12 (Mmp12) as a highly up-regulated gene in lungs from βENaC-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 βENaC-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.

Lack of Neutrophil Elastase Reduces Inflammation, Mucus Hypersecretion, and Emphysema, but Not Mucus Obstruction, in Mice with Cystic Fibrosis–like Lung Disease

Recent evidence from clinical studies suggests that neutrophil elastase (NE) released in neutrophilic airway inflammation is a key risk factor for the onset and progression of lung disease in young children with cystic fibrosis (CF). However, the role of NE in the complex in vivo pathogenesis of CF lung disease remains poorly understood. To elucidate the role of NE in the development of key features of CF lung disease including airway inflammation, mucus hypersecretion, goblet cell metaplasia, bacterial infection, and structural lung damage in vivo. We used the Scnn1b-Tg mouse as a model of CF lung disease and determined effects of genetic deletion of NE (NE(-/-)) on the pulmonary phenotype. Furthermore, we used novel Foerster resonance energy transfer (FRET)-based NE reporter assays to assess NE activity in bronchoalveolar lavage from Scnn1b-Tg mice and sputum from patients with CF. Lack of NE significantly reduced airway neutrophilia, elevated mucin expression, goblet cell metaplasia, and distal airspace enlargement, but had no effect on airway mucus plugging, bacterial infection, or pulmonary mortality in Scnn1b-Tg mice. By using FRET reporters, we show that NE activity was elevated on the surface of airway neutrophils from Scnn1b-Tg mice and patients with CF. Our results suggest that NE plays an important role in the in vivo pathogenesis and may serve as a therapeutic target for inflammation, mucus hypersecretion, and structural lung damage and indicate that additional rehydration strategies may be required for effective treatment of airway mucus obstruction in CF.