CFTR Regulates Early Pathogenesis of Chronic Obstructive Lung Disease in βENaC-Overexpressing Mice

Mall MA (2012) CFTR Regulates Early Pathogenesis of Chronic Obstructive Lung Disease in bENaC- Overexpressing Mice. PLoS ONE 7(8): e44059. doi:10.1371/journal.pone.0044059 CFTR Regulates Early Pathogenesis of Chronic Obstructive Lung Disease in bENaC-Overexpressing Mice Bjarki Johannesson 0 Stephanie Hirtz 0 Jolanthe Schatterny 0 Carsten Schultz 0 Marcus A. Mall 0 Neeraj Vij, Johns Hopkins School of Medicine, United States of America 0 1 Department of Translational Pulmonology, Translational Lung Research Center Heidelberg (TLRC), Member of the German Center for Lung Research, University of Heidelberg , Heidelberg, Germany , 2 Division of Pediatric Pulmonology and Allergy and Cystic Fibrosis Center, Department of Pediatrics III, University of Heidelberg , Heidelberg, Germany , 3 Cell Biology and Biophysics Unit, European Molecular Biology Laboratory , Heidelberg, Germany, 4 Molecular Medicine Partnership Unit , University of Heidelberg and European Molecular Biology Laboratory , Heidelberg , Germany Background: Factors determining the onset and severity of chronic obstructive pulmonary disease remain poorly understood. Previous studies demonstrated that airway surface dehydration in bENaC-overexpressing (bENaC-Tg) mice on a mixed genetic background caused either neonatal mortality or chronic obstructive lung disease suggesting that the onset of lung disease was modulated by the genetic background. Methods: To test this hypothesis, we backcrossed bENaC-Tg mice onto two inbred strains (C57BL/6 and BALB/c) and studied effects of the genetic background on neonatal mortality, airway ion transport and airway morphology. Further, we crossed bENaC-Tg mice with CFTR-deficient mice to validate the role of CFTR in early lung disease. Results: We demonstrate that the C57BL/6 background conferred increased CFTR-mediated Cl2 secretion, which was associated with decreased mucus plugging and mortality in neonatal bENaC-Tg C57BL/6 compared to bENaC-Tg BALB/c mice. Conversely, genetic deletion of CFTR increased early mucus obstruction and mortality in bENaC-Tg mice. Conclusions: We conclude that a decrease or absence of CFTR function in airway epithelia aggravates the severity of early airway mucus obstruction and related mortality in bENaC-Tg mice. These results suggest that genetic or environmental factors that reduce CFTR activity may contribute to the onset and severity of chronic obstructive pulmonary disease and that CFTR may serve as a novel therapeutic target. - Funding: This study was supported by the German Research Foundation (DFG MA 2081/3-3 and MA 2081/4-1), the Federal Ministry of Education and Research (BMBF German Centre for Lung Research [DZL]), and the European Commission (MEXT-CT-2004013666). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have read the journals policy and have the following conflicts: MAM is listed on a patent application filed by the University of North Carolina, describing the bENaC-overexpressing mouse (patent number: 7514593; filing date: May 2003). Of note, the bENaC-overexpressing mouse has been deposited at the Jackson Laboratory for general deposition. This does not alter the authors adherence to all the PLoS ONE policies on sharing data and materials, as detailed online in the guide for authors. The other authors (BJ, SH, JS, CS) have declared that no competing interests exist. Chronic obstructive pulmonary disease (COPD) characterized by airflow obstruction due to chronic bronchitis with airways mucus plugging and/or emphysema belongs to the most common chronic diseases and has evolved as a leading cause of death worldwide [1]. Although it is well established that most COPD is caused by cigarette smoke and exposure to other environmental pollutants, the onset and severity of the disease in individuals who were exposed to similar levels of cigarette smoke is highly variable, and emerging evidence suggests that the risk of developing COPD is influenced by genetic factors [2,3]. However, the role of genetic factors and their contribution to disease-causing mechanisms in the in vivo pathogenesis of COPD remain poorly understood. Previous studies in a mouse model with airway-specific overexpression of the b-subunit of the amiloride-sensitive Na+ channel (ENaC), which constitutes a limiting pathway for absorption of Na+ and fluid across airway epithelia, identified airway surfaces liquid (ASL) dehydration as a disease-causing mechanism of COPD and established a model to study its pathogenesis in vivo [4]. Proper regulation of ASL volume by coordinate regulation of ENaC-mediated Na+ absorption and Cl2 secretion mediated by the cystic fibrosis transmembrane conductance regulator (CFTR) and Ca2+-activated Cl2 channels (CaCC) plays a crucial role in maintaining normal mucociliary clearance, which constitutes an important innate defense mechanism of the lung [5,6]. In bENaCoverexpressing (bENaC-Tg) mice, an imbalance between Na+ absorption and Cl2 secretion results in volume depletion (dehydration) of airway surfaces causing a spontaneous lung disease that shares key features with COPD in humans including impaired mucus clearance, airway mucus obstruction, goblet cell metaplasia, chronic neutrophilic inflammation with increased levels of the IL-8 homologue KC, reduced clearance of bacterial pathogens and emphysema [4,7,8]. Of note, a series of recent studies showed that cigarette smoke impairs CFTR-mediated Cl2 secretion across airway epithelia in vitro and in vivo indicating that impaired ASL hydration may also be implicated in the pathogenesis of COPD in humans [912]. When bENaC-overexpressing (bENaC-Tg) mice were maintained on a mixed genetic background (C3H/He x C57BL/6), we noted that the pulmonary phenotype was highly variable. Around 50% of bENaC-Tg mice died during the neonatal period due to severe mucus plugging of the trachea associated with hypoxic degeneration of airway epithelial cells and asphyxia, whereas the surviving bENaC-Tg mice developed chronic bronchitis and emphysema [4,13]. These observations suggested that similar to COPD in humans, the COPD-like lung disease in this model may also be modulated by the genetic background. In the present study, we therefore backcrossed bENaC-Tg mice onto two distinct inbred mouse strains (C57BL/6 and BALB/c) and performed quantitative phenotyping to test the hypothesis that dehydration-induced lung disease can be influenced by the genetic background. Because lung disease in bENaC-Tg mice is caused by a dysbalance between absorption and secretion of NaCl and fluid across airway surfaces, a focus of our studies was on the impact of the genetic background on ENaC-mediated Na+ transport and Cl2 secretion mediated by CFTR and Ca2+2activated Cl2 channels (CaCC) in freshly excised airway tissues. Further, we studied the effects of the genetic background on mortality and other chara (...truncated)