In vivo monitoring of cystic fibrosis-like lung disease in mice by volumetric computed tomography

Airway remodeling heterogeneity in asthma and its relationship to disease outcomes

Asthma affects an estimated 262 million people worldwide and caused over 461,000 deaths in 2019. The disease is characterized by chronic airway inflammation, reversible bronchoconstriction, and airway remodeling. Longitudinal studies have shown that current treatments for asthma (inhaled bronchodilators and corticosteroids) can reduce the frequency of exacerbations, but do not modify disease outcomes over time. Further, longitudinal studies in children to adulthood have shown that these treatments do not improve asthma severity or fixed airflow obstruction over time. In asthma, fixed airflow obstruction is caused by remodeling of the airway wall, but such airway remodeling also significantly contributes to airway closure during bronchoconstriction in acute asthmatic episodes. The goal of the current review is to understand what is known about the heterogeneity of airway remodeling in asthma and how this contributes to the disease process. We provide an overview of the existing knowledge on airway remodeling features observed in asthma, including loss of epithelial integrity, mucous cell metaplasia, extracellular matrix remodeling in both the airways and vessels, angiogenesis, and increased smooth muscle mass. While such studies have provided extensive knowledge on different aspects of airway remodeling, they have relied on biopsy sampling or pathological assessment of lungs from fatal asthma patients, which have limitations for understanding airway heterogeneity and the entire asthma syndrome. To further understand the heterogeneity of airway remodeling in asthma, we highlight the potential of in vivo imaging tools such as computed tomography and magnetic resonance imaging. Such volumetric imaging tools provide the opportunity to assess the heterogeneity of airway remodeling within the whole lung and have led to the novel identification of heterogenous gas trapping and mucus plugging as important predictors of patient outcomes. Lastly, we summarize the current knowledge of modification of airway remodeling with available asthma therapeutics to highlight the need for future studies that use in vivo imaging tools to assess airway remodeling outcomes.

Genetic Deletion of Mmp9 Does Not Reduce Airway Inflammation and Structural Lung Damage in Mice with Cystic Fibrosis-like Lung Disease

Elevated levels of matrix metalloprotease 9 (MMP-9) and neutrophil elastase (NE) are associated with bronchiectasis and lung function decline in patients with cystic fibrosis (CF). MMP-9 is a potent extracellular matrix-degrading enzyme which is activated by NE and has been implicated in structural lung damage in CF. However, the role of MMP-9 in the in vivo pathogenesis of CF lung disease is not well understood. Therefore, we used β-epithelial Na+ channel-overexpressing transgenic (βENaC-Tg) mice as a model of CF-like lung disease and determined the effect of genetic deletion of Mmp9 (Mmp9-/-) on key aspects of the pulmonary phenotype. We found that MMP-9 levels were elevated in the lungs of βENaC-Tg mice compared with wild-type littermates. Deletion of Mmp9 had no effect on spontaneous mortality, inflammatory markers in bronchoalveolar lavage, goblet cell metaplasia, mucus hypersecretion and emphysema-like structural lung damage, while it partially reduced mucus obstruction in βENaC-Tg mice. Further, lack of Mmp9 had no effect on increased inspiratory capacity and increased lung compliance in βENaC-Tg mice, whereas both lung function parameters were improved with genetic deletion of NE. We conclude that MMP-9 does not play a major role in the in vivo pathogenesis of CF-like lung disease in mice.

µCT to quantify muco-obstructive lung disease and effects of neutrophil elastase knockout in mice

Muco-obstructive lung diseases are characterized by airway obstruction and hyperinflation, which can be quantified by imaging. Our aim was to evaluate µCT for longitudinal quantification of muco-obstructive lung disease in β-epithelial Na⁺ channel overexpressing (Scnn1b-TG) mice and of the effects of neutrophil elastase (NE) knockout on its progression. Lungs from wild-type (WT), NE^-/-, Scnn1b-TG, and Scnn1b-TG/NE^-/- mice were scanned with 9 µm resolution at 0, 5, 14 and 60 days of age, and airway and parenchymal disease was quantified. Mucus adhesion lesions (MAL) were persistently increased in Scnn1b-TG compared to WT mice from 0 days (20.25±6.50 vs. 9.60±2.07, P<0.05), and this effect was attenuated in Scnn1b-TG/NE^-/- mice (5.33±3.67, P<0.001). Airway wall area percentage (WA%) was increased in Scnn1b-TG mice compared to WT from 14 days onward (59.2±6.3% vs. 49.8±9.0%, P<0.001) but was similar in Scnn1b-TG/NE^-/- compared to WT at 60 days (46.4±9.2% vs. 45.4±11.5%, P=0.97). Air proportion (Air%) and mean linear intercept (Lm) were persistently increased in Scnn1b-TG compared to WT from 5 days on (53.9±4.5% vs. 30.0±5.5% and 78.82±8.44µm vs. 65.66±4.15µm, respectively, P<0.001), whereas in Scnn1b-TG/NE^-/- Air% and Lm were similar to WT from birth (27.7±5.5% vs.27.2±5.9%, P =0.92 and 61.48±9.20µm vs. 61.70±6.73µm, P=0.93, respectively). Our results suggest that µCT is sensitive to detect the onset and progression of muco-obstructive lung disease and effects of genetic deletion of NE on morphology of airways and lung parenchyma in Scnn1b-TG mice, and that it may serve as a sensitive endpoint for preclinical studies of novel therapeutic interventions for muco-obstructive lung diseases.

Therapeutic Inhibition of Cathepsin S Reduces Inflammation and Mucus Plugging in Adult βENaC-Tg Mice

BACKGROUND

Elevated levels of the cysteine protease cathepsin S (CatS) are associated with chronic mucoobstructive lung diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). We have previously demonstrated that prophylactic treatment with a CatS inhibitor from birth reduces inflammation, mucus plugging, and lung tissue damage in juvenile β-epithelial Na+ channel-overexpressing transgenic (βENaC-Tg) mice with chronic inflammatory mucoobstructive lung disease. In this study, we build upon this work to examine the effects of therapeutic intervention with a CatS inhibitor in adult βENaC-Tg mice with established disease.

METHODS

βENaC-Tg mice and wild-type (WT) littermates were treated with a CatS inhibitor from 4 to 6 weeks of age, and CatS-/- βENaC-Tg mice were analysed at 6 weeks of age. Bronchoalveolar lavage (BAL) fluid inflammatory cell counts were quantified, and lung tissue destruction and mucus obstruction were analysed histologically.

RESULTS

At 6 weeks of age, βENaC-Tg mice developed significant airway inflammation, lung tissue damage, and mucus plugging when compared to WT mice. CatS-/- βENaC-Tg mice and βENaC-Tg mice receiving inhibitor had significantly reduced airway mononuclear and polymorphonuclear (PMN) cell counts as well as mucus plugging. However, in contrast to CatS-/- βENaC-Tg mice, therapeutic inhibition of CatS in βENaC-Tg mice had no effect on established emphysema-like lung tissue damage.

CONCLUSIONS

These results suggest that while early CatS targeting may be required to prevent the onset and progression of lung tissue damage, therapeutic CatS targeting effectively inhibited airway inflammation and mucus obstruction. These results indicate the important role CatS may play in the pathogenesis and progression of mucoobstructive lung disease.

Lack of IL-1 Receptor Signaling Reduces Spontaneous Airway Eosinophilia in Juvenile Mice with Muco-Obstructive Lung Disease

Previous studies demonstrated spontaneous type 2 airway inflammation with eosinophilia in juvenile Scnn1b (sodium channel, non-voltage-gated 1, β-subunit)-transgenic (Scnn1b-Tg) mice with muco-obstructive lung disease. IL-1 receptor (IL-1R) signaling has been implicated in allergen-driven airway disease; however, its role in eosinophilic inflammation in muco-obstructive lung disease remains unknown. In this study, we examined the role of IL-1R signaling in the development of airway eosinophilia and type 2 inflammation in juvenile Scnn1b-Tg mice. We determined effects of genetic deletion of Il1r1 (IL-1 receptor type I) on eosinophil counts, transcript levels of key type 2 cytokines, markers of eosinophil activation and apoptosis, and tissue morphology in lungs of Scnn1b-Tg mice at different time points during neonatal development. Furthermore, we measured endothelial surface expression of intercellular adhesion molecule 1 (ICAM-1), an integrin involved in eosinophil transendothelial migration, and determined effects of eosinophil depletion using an anti-IL-5 antibody on lung morphology. Lack of IL-1R reduced airway eosinophilia and structural lung damage, but it did not reduce concentrations of type 2 cytokines and associated eosinophil activation in Scnn1b-Tg mice. Structural lung damage in Scnn1b-Tg mice was also reduced by eosinophil depletion. Lack of IL-1R was associated with reduced expression of ICAM-1 on lung endothelial cells and reduced eosinophil counts in lungs from Scnn1b-Tg mice. We conclude that IL-1R signaling is implicated in airway eosinophilia independent of type 2 cytokines in juvenile Scnn1b-Tg mice. Our data suggest that IL-1R signaling may be relevant in the pathogenesis of eosinophilic airway inflammation in muco-obstructive lung diseases, which may be mediated in part by ICAM-1-dependent transmigration of eosinophils into the lungs.

Compromised DNA repair is responsible for diabetes-associated fibrosis

Diabetes-associated organ fibrosis, marked by elevated cellular senescence, is a growing health concern. Intriguingly, the mechanism underlying this association remained unknown. Moreover, insulin alone can neither reverse organ fibrosis nor the associated secretory phenotype, favoring the exciting notion that thus far unknown mechanisms must be operative. Here, we show that experimental type 1 and type 2 diabetes impairs DNA repair, leading to senescence, inflammatory phenotypes, and ultimately fibrosis. Carbohydrates were found to trigger this cascade by decreasing the NAD⁺ /NADH ratio and NHEJ-repair in vitro and in diabetes mouse models. Restoring DNA repair by nuclear over-expression of phosphomimetic RAGE reduces DNA damage, inflammation, and fibrosis, thereby restoring organ function. Our study provides a novel conceptual framework for understanding diabetic fibrosis on the basis of persistent DNA damage signaling and points to unprecedented approaches to restore DNA repair capacity for resolution of fibrosis in patients with diabetes.

Intravital microscopic optical coherence tomography imaging to assess mucus-mobilizing interventions for muco-obstructive lung disease in mice

Airway mucus obstruction is a hallmark of chronic lung diseases such as cystic fibrosis, asthma, and COPD, and the development of more effective mucus-mobilizing therapies remains an important unmet need for patients with these muco-obstructive lung diseases. However, methods for sensitive visualization and quantitative assessment of immediate effects of therapeutic interventions on mucus clearance in vivo are lacking. In this study, we determined whether newly developed high-speed microscopic optical coherence tomography (mOCT) is sensitive to detect and compare in vivo effects of inhaled isotonic saline, hypertonic saline, and bicarbonate on mucus mobilization and clearance in Scnn1b-transgenic mice with muco-obstructive lung disease. In vivo mOCT imaging showed that inhaled isotonic saline-induced rapid mobilization of mucus that was mainly transported as chunks from the lower airways of Scnn1b-transgenic mice. Hypertonic saline mobilized a significantly greater amount of mucus that showed a more uniform distribution compared with isotonic saline. The addition of bicarbonate-to-isotonic saline had no effect on mucus mobilization, but also led to a more uniform mucus layer compared with treatment with isotonic saline alone. mOCT can detect differences in response to mucus-mobilizing interventions in vivo, and may thus support the development of more effective therapies for patients with muco-obstructive lung diseases.

Emerging Concepts and Therapies for Mucoobstructive Lung Disease

A spectrum of intrapulmonary airway diseases, for example, cigarette smoke-induced bronchitis, cystic fibrosis, primary ciliary dyskinesia, and non-cystic fibrosis bronchiectasis, can be categorized as "mucoobstructive" airway diseases. A common theme for these diseases appears to be the failure to properly regulate mucus concentration, producing mucus hyperconcentration that slows mucus transport and, importantly, generates plaque/plug adhesion to airway surfaces. These mucus plaques/plugs generate long diffusion distances for oxygen, producing hypoxic niches within adherent airway mucus and subjacent epithelia. Data suggest that concentrated mucus plaques/plugs are proinflammatory, in part mediated by release of IL-1α from hypoxic cells. The infectious component of mucoobstructive diseases may be initiated by anaerobic bacteria that proliferate within the nutrient-rich hypoxic mucus environment. Anaerobes ultimately may condition mucus to provide the environment for a succession to classic airway pathogens, including Staphylococcus aureus, Haemophilus influenzae, and ultimately Pseudomonas aeruginosa. Novel therapies to treat mucoobstructive diseases focus on restoring mucus concentration. Strategies to rehydrate mucus range from the inhalation of osmotically active solutes, designed to draw water into airway surfaces, to strategies designed to manipulate the relative rates of sodium absorption versus chloride secretion to endogenously restore epithelial hydration. Similarly, strategies designed to reduce the mucin burden in the airways, either by reducing mucin production/secretion or by clearing accumulated mucus (e.g., reducing agents), are under development. Thus, the new insights into a unifying process, that is, mucus hyperconcentration, that drives a significant component of the pathogenesis of mucoobstructive diseases promise multiple new therapeutic strategies to aid patients with this syndrome.

Auto-measure emphysematous parameters and pathophysiological gene expression profiles in experimental mouse models of acute and chronic obstructive pulmonary diseases

Pulmonary emphysema, inflammation and senescence-like phenotype are pathophysiological characteristics of chronic obstructive pulmonary disease (COPD). Recently, a murine model of COPD has been established by inducing airway-specific overexpression of epithelial Na⁺ channel β subunit (βENaC-Tg mice). However, little is known about the histological and biochemical differences between βENaC-Tg mice and an existing acute emphysematous mouse model (elastase-induced model). Here, we first utilized whole lung image-based quantification method for histological analysis to determine auto-measure parameters, including alveolar area, alveolar perimeter, (major axis + minor axis)/2 and Feret diameter. Even though the extent of emphysema was similar in both models, the coefficient of variation (CV) of all histological parameters was smaller in βENaC-Tg mice, indicating that βENaC-Tg mice show homogeneous emphysema as compared with elastase-induced acute model. Expression analysis of lung tissue RNAs further revealed that elastase-induced model exhibits transient changes of inflammation markers (Kc, Il-6, Lcn2) and senescence-related markers (Sirt1, p21) at emphysema-initiation stage (1 day), which does not last until emphysema-manifestation stage (3 weeks); while the up-regulation is stable at emphysema-manifestation stage in βENaC-Tg mice (14-week old). Thus, these studies demonstrate that βENaC-Tg mice exhibit diffuse-type emphysema with stable expression of inflammatory and senescence-like markers.

Airway Epithelium Dysfunction in Cystic Fibrosis and COPD

Cystic fibrosis is a genetic disease caused by mutations in the CFTR gene, whereas chronic obstructive pulmonary disease (COPD) is mainly caused by environmental factors (mostly cigarette smoking) on a genetically susceptible background. Although the etiology and pathogenesis of these diseases are different, both are associated with progressive airflow obstruction, airway neutrophilic inflammation, and recurrent exacerbations, suggesting common mechanisms. The airway epithelium plays a crucial role in maintaining normal airway functions. Major molecular and morphologic changes occur in the airway epithelium in both CF and COPD, and growing evidence suggests that airway epithelial dysfunction is involved in disease initiation and progression in both diseases. Structural and functional abnormalities in both airway and alveolar epithelium have a relevant impact on alteration of host defences, immune/inflammatory response, and the repair process leading to progressive lung damage and impaired lung function. In this review, we address the evidence for a critical role of dysfunctional airway epithelial cells in chronic airway inflammation and remodelling in CF and COPD, highlighting the common mechanisms involved in the epithelial dysfunction as well as the similarities and differences of the two diseases.

Homeostatic nuclear RAGE-ATM interaction is essential for efficient DNA repair

The integrity of genome is a prerequisite for healthy life. Indeed, defects in DNA repair have been associated with several human diseases, including tissue-fibrosis, neurodegeneration and cancer. Despite decades of extensive research, the spatio-mechanical processes of double-strand break (DSB)-repair, especially the auxiliary factor(s) that can stimulate accurate and timely repair, have remained elusive. Here, we report an ATM-kinase dependent, unforeseen function of the nuclear isoform of the Receptor for Advanced Glycation End-products (nRAGE) in DSB-repair. RAGE is phosphorylated at Serine³⁷⁶ and Serine³⁸⁹ by the ATM kinase and is recruited to the site of DNA-DSBs via an early DNA damage response. nRAGE preferentially co-localized with the MRE11 nuclease subunit of the MRN complex and orchestrates its nucleolytic activity to the ATR kinase signaling. This promotes efficient RPA2^S4-S8 and CHK1^S345 phosphorylation and thereby prevents cellular senescence, IPF and carcinoma formation. Accordingly, loss of RAGE causatively linked to perpetual DSBs signaling, cellular senescence and fibrosis. Importantly, in a mouse model of idiopathic pulmonary fibrosis (RAGE^−/−), reconstitution of RAGE efficiently restored DSB-repair and reversed pathological anomalies. Collectively, this study identifies nRAGE as a master regulator of DSB-repair, the absence of which orchestrates persistent DSB signaling to senescence, tissue-fibrosis and oncogenesis.

SPX-101 Is a Novel Epithelial Sodium Channel-targeted Therapeutic for Cystic Fibrosis That Restores Mucus Transport

RATIONALE

Cystic fibrosis (CF) lung disease is caused by the loss of function of the cystic fibrosis transmembrane conductance regulator (CFTR) combined with hyperactivation of the epithelial sodium channel (ENaC). In the lung, ENaC is responsible for movement of sodium. Hyperactivation of ENaC, which creates an osmotic gradient that pulls fluid out of the airway, contributes to reduced airway hydration, causing mucus dehydration, decreased mucociliary clearance, and recurrent acute bacterial infections. ENaC represents a therapeutic target to treat all patients with CF independent of their underlying CFTR mutation.

OBJECTIVES

To investigate the in vitro and in vivo efficacy of SPX-101, a peptide mimetic of the natural regulation of ENaC activity by short palate, lung, and nasal epithelial clone 1, known as SPLUNC1.

METHODS

ENaC internalization by SPX-101 in primary human bronchial epithelial cells from healthy and CF donors was assessed by surface biotinylation and subsequent Western blot analysis. SPX-101's in vivo therapeutic effect was assessed by survival of β-ENaC-transgenic mice, mucus transport in these mice, and mucus transport in a sheep model of CF.

MEASUREMENTS AND MAIN RESULTS

SPX-101 binds selectively to ENaC and promotes internalization of the α-, β-, and γ-subunits. Removing ENaC from the membrane with SPX-101 causes a significant decrease in amiloride-sensitive current. The peptide increases survival of β-ENaC-transgenic mice to greater than 90% with once-daily dosing by inhalation. SPX-101 increased mucus transport in the β-ENaC mouse model as well as the sheep model of CF.

CONCLUSIONS

These data demonstrate that SPX-101 promotes durable reduction of ENaC membrane concentration, leading to significant improvements in mucus transport.

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.

Pharmacological and genetic reappraisals of protease and oxidative stress pathways in a mouse model of obstructive lung diseases

Protease-antiprotease imbalance and oxidative stress are considered to be major pathophysiological hallmarks of severe obstructive lung diseases including chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF), but limited information is available on their direct roles in the regulation of pulmonary phenotypes. Here, we utilized βENaC-transgenic (Tg) mice, the previously established mouse model of severe obstructive lung diseases, to produce lower-mortality but pathophysiologically highly useful mouse model by backcrossing the original line with C57/BL6J mice. C57/BL6J-βENaC-Tg mice showed higher survival rates and key pulmonary abnormalities of COPD/CF, including mucous hypersecretion, inflammatory and emphysematous phenotypes and pulmonary dysfunction. DNA microarray analysis confirmed that protease- and oxidative stress-dependent pathways are activated in the lung tissue of C57/BL6J-βENaC-Tg mice. Treatments of C57/BL6J-βENaC-Tg mice with a serine protease inhibitor ONO-3403, a derivative of camostat methylate (CM), but not CM, and with an anti-oxidant N-acetylcystein significantly improved pulmonary emphysema and dysfunction. Moreover, depletion of a murine endogenous antioxidant vitamin C (VC), by genetic disruption of VC-synthesizing enzyme SMP30 in C57/BL6J-βENaC-Tg mice, exaggerated pulmonary phenotypes. Thus, these assessments clarified that protease-antiprotease imbalance and oxidative stress are critical pathways that exacerbate the pulmonary phenotypes of C57/BL6J-βENaC-Tg mice, consistent with the characteristics of human COPD/CF.

Neutrophil elastase and matrix metalloproteinase 12 in cystic fibrosis lung disease

Chronic lung disease remains the major cause of morbidity and mortality in patients with cystic fibrosis (CF). Recent studies in young children with CF diagnosed by newborn screening identified neutrophil elastase (NE), a major product released from neutrophils in inflamed airways, as a key risk factor for the onset and early progression of CF lung disease. However, the understanding of how NE and potentially other proteases contribute to the complex in vivo pathogenesis of CF lung disease remains limited. In this review, we summarize recent progress in this area based on studies in βENaC-overexpressing (βENaC-Tg) mice featuring CF-like lung disease and novel protease-specific Förster resonance energy transfer (FRET) sensors for localization and quantification of protease activity in the lung. These studies demonstrated that NE is implicated in several key features of CF lung disease such as neutrophilic airway inflammation, mucus hypersecretion, and structural lung damage in vivo. Furthermore, these studies identified macrophage elastase (matrix metalloproteinase 12 (MMP12)) as an additional protease contributing to early lung damage in βENaC-Tg mice. Collectively, these results suggest that NE and MMP12 released from activated neutrophils and macrophages in mucus-obstructed airways play important pathogenetic roles and may serve as potential therapeutic targets to prevent and/or delay irreversible structural lung damage in patients with CF.

Cigarette smoke causes acute airway disease and exacerbates chronic obstructive lung disease in neonatal mice

Epidemiological evidence demonstrates a strong link between postnatal cigarette smoke (CS) exposure and increased respiratory morbidity in young children. However, how CS induces early onset airway disease in young children, and how it interacts with endogenous risk factors, remains poorly understood. We, therefore, exposed 10-day-old neonatal wild-type and β-epithelial sodium ion channel (β-ENaC)-transgenic mice with cystic fibrosis-like lung disease to CS for 4 days. Neonatal wild-type mice exposed to CS demonstrated increased numbers of macrophages and neutrophils in the bronchoalveolar lavage fluid (BALF), which was accompanied by increased levels of Mmp12 and Cxcl1 BALF from β-ENaC-transgenic mice contained greater numbers of macrophages, which did not increase following acute CS exposure; however, there was significant increase in airway neutrophilia compared with filtered air transgenic and CS-exposed wild-type controls. Interestingly, wild-type and β-ENaC-transgenic mice demonstrated epithelial airway and vascular remodeling following CS exposure. Morphometric analysis of lung sections revealed that CS exposure caused increased mucus accumulation in the airway lumen of neonatal β-ENaC-transgenic mice compared with wild-type controls, which was accompanied by an increase in the number of goblet cells and Muc5ac upregulation. We conclude that short-term CS exposure 1) induces acute airway disease with airway epithelial and vascular remodeling in neonatal wild-type mice; and 2) exacerbates airway inflammation, mucus hypersecretion, and mucus plugging in neonatal β-ENaC-transgenic mice with chronic lung disease. Our results in neonatal mice suggest that young children may be highly susceptible to develop airway disease in response to tobacco smoke exposure, and that adverse effects may be aggravated in children with underlying chronic lung diseases.

Quantification of heterogeneity in lung disease with image-based pulmonary function testing

Computed tomography (CT) and spirometry are the mainstays of clinical pulmonary assessment. Spirometry is effort dependent and only provides a single global measure that is insensitive for regional disease, and as such, poor for capturing the early onset of lung disease, especially patchy disease such as cystic fibrosis lung disease. CT sensitively measures change in structure associated with advanced lung disease. However, obstructions in the peripheral airways and early onset of lung stiffening are often difficult to detect. Furthermore, CT imaging poses a radiation risk, particularly for young children, and dose reduction tends to result in reduced resolution. Here, we apply a series of lung tissue motion analyses, to achieve regional pulmonary function assessment in β-ENaC-overexpressing mice, a well-established model of lung disease. The expiratory time constants of regional airflows in the segmented airway tree were quantified as a measure of regional lung function. Our results showed marked heterogeneous lung function in β-ENaC-Tg mice compared to wild-type littermate controls; identified locations of airway obstruction, and quantified regions of bimodal airway resistance demonstrating lung compensation. These results demonstrate the applicability of regional lung function derived from lung motion as an effective alternative respiratory diagnostic tool.

Longitudinal micro-CT provides biomarkers of lung disease that can be used to assess the effect of therapy in preclinical mouse models, and reveal compensatory changes in lung volume

In vivo lung micro-computed tomography (micro-CT) is being increasingly embraced in pulmonary research because it provides longitudinal information on dynamic disease processes in a field in which ex vivo assessment of experimental disease models is still the gold standard. To optimize the quantitative monitoring of progression and therapy of lung diseases, we evaluated longitudinal changes in four different micro-CT-derived biomarkers [aerated lung volume, lung tissue (including lesions) volume, total lung volume and mean lung density], describing normal development, lung infections, inflammation, fibrosis and therapy. Free-breathing mice underwent micro-CT before and repeatedly after induction of lung disease (bleomycin-induced fibrosis, invasive pulmonary aspergillosis, pulmonary cryptococcosis) and therapy (imatinib). The four lung biomarkers were quantified. After the last time point, we performed pulmonary function tests and isolated the lungs for histology. None of the biomarkers remained stable during longitudinal follow-up of adult healthy mouse lungs, implying that biomarkers should be compared with age-matched controls upon intervention. Early inflammation and progressive fibrosis led to a substantial increase in total lung volume, which affects the interpretation of aerated lung volume, tissue volume and mean lung density measures. Upon treatment of fibrotic lung disease, the improvement in aerated lung volume and function was not accompanied by a normalization of the increased total lung volume. Significantly enlarged lungs were also present in models of rapidly and slowly progressing lung infections. The data suggest that total lung volume changes could partly reflect a compensatory mechanism that occurs during disease progression in mice. Our findings underscore the importance of quantifying total lung volume in addition to aerated lung or lesion volumes to accurately document growth and potential compensatory mechanisms in mouse models of lung disease, in order to fully describe and understand dynamic processes during lung disease onset, progression and therapy. This is highly relevant for the translation of therapy evaluation results from preclinical studies to human patients.

Genetic Deletion and Pharmacological Inhibition of PI3K γ Reduces Neutrophilic Airway Inflammation and Lung Damage in Mice with Cystic Fibrosis-Like Lung Disease

Purpose. Neutrophil-dominated airway inflammation is a key feature of progressive lung damage in cystic fibrosis (CF). Thus, reducing airway inflammation is a major goal to prevent lung damage in CF. However, current anti-inflammatory drugs have shown several limits. PI3Kγ plays a pivotal role in leukocyte recruitment and activation; in the present study we determined the effects of genetic deletion and pharmacologic inhibition of PI3Kγ on airway inflammation and structural lung damage in a mouse model of CF lung disease. Methods. βENaC overexpressing mice (βENaC-Tg) were backcrossed with PI3Kγ-deficient (PI3Kγ^KO) mice. Tissue damage was assessed by histology and morphometry and inflammatory cell number was evaluated in bronchoalveolar lavage fluid (BALF). Furthermore, we assessed the effect of a specific PI3Kγ inhibitor (AS-605240) on inflammatory cell number in BALF. Results. Genetic deletion of PI3Kγ decreased neutrophil numbers in BALF of PI3Kγ^KO/βENaC-Tg mice, and this was associated with reduced emphysematous changes. Treatment with the PI3Kγ inhibitor AS-605240 decreased the number of neutrophils in BALF of βENaC-Tg mice, reproducing the effect observed with genetic deletion of the enzyme. Conclusions. These results demonstrate the biological efficacy of both genetic deletion and pharmacological inhibition of PI3Kγ in reducing chronic neutrophilic inflammation in CF-like lung disease in vivo.

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

RATIONALE

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.

OBJECTIVES

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.

METHODS

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.

MEASUREMENTS AND MAIN RESULTS

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.

CONCLUSIONS

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 Surface Dehydration Aggravates Cigarette Smoke-Induced Hallmarks of COPD in Mice

INTRODUCTION

Airway surface dehydration, caused by an imbalance between secretion and absorption of ions and fluid across the epithelium and/or increased epithelial mucin secretion, impairs mucociliary clearance. Recent evidence suggests that this mechanism may be implicated in chronic obstructive pulmonary disease (COPD). However, the role of airway surface dehydration in the pathogenesis of cigarette smoke (CS)-induced COPD remains unknown.

OBJECTIVE

We aimed to investigate in vivo the effect of airway surface dehydration on several CS-induced hallmarks of COPD in mice with airway-specific overexpression of the β-subunit of the epithelial Na⁺ channel (βENaC).

METHODS

βENaC-Tg mice and wild-type (WT) littermates were exposed to air or CS for 4 or 8 weeks. Pathological hallmarks of COPD, including goblet cell metaplasia, mucin expression, pulmonary inflammation, lymphoid follicles, emphysema and airway wall remodelling were determined and lung function was measured.

RESULTS

Airway surface dehydration in βENaC-Tg mice aggravated CS-induced airway inflammation, mucin expression and destruction of alveolar walls and accelerated the formation of pulmonary lymphoid follicles. Moreover, lung function measurements demonstrated an increased compliance and total lung capacity and a lower resistance and hysteresis in βENaC-Tg mice, compared to WT mice. CS exposure further altered lung function measurements.

CONCLUSIONS

We conclude that airway surface dehydration is a risk factor that aggravates CS-induced hallmarks of COPD.

Emphysema Is Common in Lungs of Cystic Fibrosis Lung Transplantation Patients: A Histopathological and Computed Tomography Study

Background

Lung disease in cystic fibrosis (CF) involves excessive inflammation, repetitive infections and development of bronchiectasis. Recently, literature on emphysema in CF has emerged, which might become an increasingly important disease component due to the increased life expectancy. The purpose of this study was to assess the presence and extent of emphysema in endstage CF lungs.

Methods

In explanted lungs of 20 CF patients emphysema was semi-quantitatively assessed on histology specimens. Also, emphysema was automatically quantified on pre-transplantation computed tomography (CT) using the percentage of voxels below -950 Houndfield Units and was visually scored on CT. The relation between emphysema extent, pre-transplantation lung function and age was determined.

Results

All CF patients showed emphysema on histological examination: 3/20 (15%) showed mild, 15/20 (75%) moderate and 2/20 (10%) severe emphysema, defined as 0–20% emphysema, 20–50% emphysema and >50% emphysema in residual lung tissue, respectively. Visually upper lobe bullous emphysema was identified in 13/20 and more diffuse non-bullous emphysema in 18/20. Histology showed a significant correlation to quantified CT emphysema (p = 0.03) and visual emphysema score (p = 0.001). CT and visual emphysema extent were positively correlated with age (p = 0.045 and p = 0.04, respectively).

Conclusions

In conclusion, this study both pathologically and radiologically confirms that emphysema is common in end-stage CF lungs, and is age related. Emphysema might become an increasingly important disease component in the aging CF population.

Imaging regional lung function: a critical tool for developing inhaled antimicrobial therapies

Alterations in regional lung function due to respiratory infection have a significant effect on the deposition of inhaled treatments. This has consequences for treatment effectiveness and hence recovery of lung function. In order to advance our understanding of respiratory infection and inhaled treatment delivery, we must develop imaging techniques that can provide regional functional measurements of the lung. In this review, we explore the role of functional imaging for the assessment of respiratory infection and development of inhaled treatments. We describe established and emerging functional lung imaging methods. The effect of infection on lung function is described, and the link between regional disease, function, and inhaled treatments is discussed. The potential for lung function imaging to provide unique insights into the functional consequences of infection, and its treatment, is also discussed.

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.

Correlation of apical fluid-regulating channel proteins with lung function in human COPD lungs

Links between epithelial ion channels and chronic obstructive pulmonary diseases (COPD) are emerging through animal model and in vitro studies. However, clinical correlations between fluid-regulating channel proteins and lung function in COPD remain to be elucidated. To quantitatively measure epithelial sodium channels (ENaC), cystic fibrosis transmembrane conductance regulator (CFTR), and aquaporin 5 (AQP5) proteins in human COPD lungs and to analyze the correlation with declining lung function, quantitative western blots were used. Spearman tests were performed to identify correlations between channel proteins and lung function. The expression of α and β ENaC subunits was augmented and inversely associated with lung function. In contrast, both total and alveolar type I (ATI) and II (ATII)-specific CFTR proteins were reduced. The expression level of CFTR proteins was associated with FEV1 positively. Abundance of AQP5 proteins and extracellular superoxide dismutase (SOD3) was decreased and correlated with spirometry test results and gas exchange positively. Furthermore, these channel proteins were significantly associated with severity of disease. Our study demonstrates that expression of ENaC, AQP5, and CFTR proteins in human COPD lungs is quantitatively associated with lung function and severity of COPD. These apically located fluid-regulating channels may thereby serve as biomarkers and potent druggable targets of COPD.

Gene expression in whole lung and pulmonary macrophages reflects the dynamic pathology associated with airway surface dehydration

Background

Defects in airway mucosal defense, including decreased mucus clearance, contribute to the pathogenesis of human chronic obstructive pulmonary diseases. Scnn1b-Tg mice, which exhibit chronic airway surface dehydration from birth, can be used as a model to study the pathogenesis of muco-obstructive lung disease across developmental stages. To identify molecular signatures associated with obstructive lung disease in this model, gene expression analyses were performed on whole lung and purified lung macrophages collected from Scnn1b-Tg and wild-type (WT) littermates at four pathologically relevant time points. Macrophage gene expression at 6 weeks was evaluated in mice from a germ-free environment to understand the contribution of microbes to disease development.

Results

Development- and disease-specific shifts in gene expression related to Scnn1b over-expression were revealed in longitudinal analyses. While the total number of transgene-related differentially expressed genes producing robust signals was relatively small in whole lung (n = 84), Gene Set Enrichment Analysis (GSEA) revealed significantly perturbed biological pathways and interactions between normal lung development and disease initiation/progression. Purified lung macrophages from Scnn1b-Tg mice exhibited numerous robust and dynamic gene expression changes. The expression levels of Classically-activated (M1) macrophage signatures were significantly altered at post-natal day (PND) 3 when Scnn1b-Tg mice lung exhibit spontaneous bacterial infections, while alternatively-activated (M2) macrophage signatures were more prominent by PND 42, producing a mixed M1-M2 activation profile. While differentially-regulated, inflammation-related genes were consistently identified in both tissues in Scnn1b-Tg mice, there was little overlap between tissues or across time, highlighting time- and tissue-specific responses. Macrophages purified from adult germ-free Scnn1b-Tg mice exhibited signatures remarkably similar to non-germ-free counterparts, indicating that the late-phase macrophage activation profile was not microbe-dependent.

Conclusions

Whole lung and pulmonary macrophages respond independently and dynamically to local stresses associated with airway mucus stasis. Disease-specific responses interact with normal developmental processes, influencing the final state of disease in this model. The robust signatures observed in Scnn1b-Tg lung macrophages highlight their critical role in disease pathogenesis. These studies emphasize the importance of region-, cell-type-, and time-dependent analyses to fully dissect the natural history of disease and the consequences of disease on normal lung development.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-726) contains supplementary material, which is available to authorized users.

Nanoparticle uptake by airway phagocytes after fungal spore challenge in murine allergic asthma and chronic bronchitis

Background

In healthy lungs, deposited micrometer-sized particles are efficiently phagocytosed by macrophages present on airway surfaces; however, uptake of nanoparticles (NP) by macrophages appears less effective and is largely unstudied in lung disease. Using mouse models of allergic asthma and chronic obstructive pulmonary disease (COPD), we investigated NP uptake after challenge with common biogenic ambient air microparticles.

Methods

Bronchoalveolar lavage (BAL) cells from diseased mice (allergic asthma: ovalbumin [OVA] sensitized and COPD: Scnn1b-transgenic [Tg]) and their respective healthy controls were exposed ex vivo first to 3-μm fungal spores of Calvatia excipuliformis and then to 20-nm gold (Au) NP. Electron microscopic imaging was performed and NP uptake was assessed by quantitative morphometry.

Results

Macrophages from diseased mice were significantly larger compared to controls in OVA-allergic versus sham controls and in Scnn1b-Tg versus wild type (WT) mice. The percentage of macrophages containing AuNP tended to be lower in Scnn1b-Tg than in WT mice. In all animal groups, fungal spores were localized in macrophage phagosomes, the membrane tightly surrounding the spore, whilst AuNP were found in vesicles largely exceeding NP size, co-localized in spore phagosomes and occasionally, in the cytoplasm. AuNP in vesicles were located close to the membrane. In BAL from OVA-allergic mice, 13.9 ± 8.3% of all eosinophils contained AuNP in vesicles exceeding NP size and close to the membrane.

Conclusions

Overall, AuNP uptake by BAL macrophages occurred mainly by co-uptake together with other material, including micrometer-sized ambient air particles like fungal spores. The lower percentage of NP containing macrophages in BAL from Scnn1b-Tg mice points to a change in the macrophage population from a highly to a less phagocytic phenotype. This likely contributes to inefficient macrophage clearance of NP in lung disease. Finally, the AuNP containing eosinophils in OVA-allergic mice show that other inflammatory cells present on airway surfaces may substantially contribute to NP uptake.

Lack of neutrophil elastase reduces inflammation, mucus hypersecretion, and emphysema, but not mucus obstruction, in mice with cystic fibrosis-like lung disease

RATIONALE

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.

OBJECTIVES

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.

METHODS

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.

MEASUREMENTS AND MAIN RESULTS

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.

CONCLUSIONS

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.

CFTR: cystic fibrosis and beyond

Cystic fibrosis (CF) remains the most common fatal hereditary lung disease. The discovery of the cystic fibrosis transmembrane conductance regulator (CFTR) gene 25 years ago set the stage for: 1) unravelling the molecular and cellular basis of CF lung disease; 2) the generation of animal models to study in vivo pathogenesis; and 3) the development of mutation-specific therapies that are now becoming available for a subgroup of patients with CF. This article highlights major advances in our understanding of how CFTR dysfunction causes chronic mucus obstruction, neutrophilic inflammation and bacterial infection in CF airways. Furthermore, we focus on recent breakthroughs and remaining challenges of novel therapies targeting the basic CF defect, and discuss the next steps to be taken to make disease-modifying therapies available to a larger group of patients with CF, including those carrying the most common mutation ΔF508-CFTR. Finally, we will summarise emerging evidence indicating that acquired CFTR dysfunction may be implicated in the pathogenesis of chronic obstructive pulmonary disease, suggesting that lessons learned from CF may be applicable to common airway diseases associated with mucus plugging.

Early cystic fibrosis lung disease: Role of airway surface dehydration and lessons from preventive rehydration therapies in mice

Cystic fibrosis (CF) lung disease starts in the first months of life and remains one of the most common fatal hereditary diseases. Early therapeutic interventions may provide an opportunity to prevent irreversible lung damage and improve outcome. Airway surface dehydration is a key disease mechanism in CF, however, its role in the in vivo pathogenesis and as therapeutic target in early lung disease remains poorly understood. Mice with airway-specific overexpression of the epithelial Na(+) channel (βENaC-Tg) recapitulate airway surface dehydration and phenocopy CF lung disease. Recent studies in neonatal βENaC-Tg mice demonstrated that airway surface dehydration produces early mucus plugging in the absence of mucus hypersecretion, which triggers airway inflammation, promotes bacterial infection and causes early mortality. Preventive rehydration therapy with hypertonic saline or amiloride effectively reduced mucus plugging and mortality in neonatal βENaC-Tg mice. These results support clinical testing of preventive/early rehydration strategies in infants and young children with CF.

Hypertonic saline is effective in the prevention and treatment of mucus obstruction, but not airway inflammation, in mice with chronic obstructive lung disease

Recent evidence suggests that inadequate hydration of airway surfaces is a common mechanism in the pathogenesis of airway mucus obstruction. Inhaled hypertonic saline (HS) induces osmotic water flux, improving hydration of airway surfaces. However, trials in patients with obstructive lung diseases are limited. The aim of this study was to investigate effects of HS on mucus obstruction and airway inflammation in the prevention and treatment of obstructive lung disease in vivo. We, therefore, used the β-epithelial Na(+) channel (βENaC)-overexpressing mouse as a model of chronic obstructive lung disease and determined effects of preventive and late therapy with 3% HS and 7% HS on pulmonary mortality, airway mucus obstruction, and inflammation. We found that preventive treatment with 3% HS and 7% HS improved growth, reduced mortality, and reduced mucus obstruction in neonatal βENaC-overexpressing mice. In adult βENaC-overexpressing mice with chronic lung disease, mucus obstruction was significantly reduced by 7% HS, but not by 3% HS. Treatment with HS triggered airway inflammation with elevated keratinocyte chemoattractant levels and neutrophils in airways from wild-type mice, but reduced keratinocyte chemoattractant in chronic neutrophilic inflammation in adult βENaC-overexpressing mice. Our data demonstrate that airway surface rehydration with HS provides an effective preventive and late therapy of mucus obstruction with no consistent effects on inflammation in chronic lung disease. These results suggest that, through mucokinetic effects, HS may be beneficial for patients with a spectrum of obstructive lung diseases, and that additional strategies are required for effective treatment of associated airway inflammation.

Pulmonary emphysema in cystic fibrosis detected by densitometry on chest multidetector computed tomography

Background

Histopathological studies on lung specimens from patients with cystic fibrosis (CF) and recent results from a mouse model indicate that emphysema may contribute to CF lung disease. However, little is known about the relevance of emphysema in patients with CF. In the present study, we used computationally generated density masks based on multidetector computed tomography (MDCT) of the chest for non-invasive characterization and quantification of emphysema in CF.

Methods

Volumetric MDCT scans were acquired in parallel to pulmonary function testing in 41 patients with CF (median age 20.1 years; range 7-66 years) and 21 non-CF controls (median age 30.4 years; range 4-68 years), and subjected to dedicated software. The lung was segmented, low attenuation volumes below a threshold of -950 Hounsfield units were assigned to emphysema volume (EV), and the emphysema index was computed (EI). Results were correlated with forced expiratory volume in 1 s percent predicted (FEV1%), residual volume (RV), and RV/total lung capacity (RV/TLC).

Results

We show that EV was increased in CF (457±530 ml) compared to non-CF controls (78±90 ml) (P<0.01). EI was also increased in CF (7.7±7.5%) compared to the control group (1.2±1.4%) (P<0.05). EI correlated inversely with FEV1% (r_s=-0.66), and directly with RV (r_s=0.69) and RV/TLC (r_s=0.47) in patients with CF (P<0.007), but not in non-CF controls. Emphysema in CF was detected from early adolescence (~13 years) and increased with age (r_s=0.67, P<0.001).

Conclusions

Our results indicate that early onset emphysema detected by densitometry on chest MDCT is a characteristic pathology that contributes to airflow limitation and may serve as a novel endpoint for monitoring lung disease in CF.

Cellular uptake and localization of inhaled gold nanoparticles in lungs of mice with chronic obstructive pulmonary disease

Background

Inhalative nanocarriers for local or systemic therapy are promising. Gold nanoparticles (AuNP) have been widely considered as candidate material. Knowledge about their interaction with the lungs is required, foremost their uptake by surface macrophages and epithelial cells.

Diseased lungs are of specific interest, since these are the main recipients of inhalation therapy. We, therefore, used Scnn1b-transgenic (Tg) mice as a model of chronic obstructive pulmonary disease (COPD) and compared uptake and localization of inhaled AuNP in surface macrophages and lung tissue to wild-type (Wt) mice.

Methods

Scnn1b-Tg and Wt mice inhaled a 21-nm AuNP aerosol for 2 h. Immediately (0 h) or 24 h thereafter, bronchoalveolar lavage (BAL) macrophages and whole lungs were prepared for stereological analysis of AuNP by electron microscopy.

Results

AuNP were mainly found as singlets or small agglomerates of ≤ 100 nm diameter, at the epithelial surface and within lung-surface structures. Macrophages contained also large AuNP agglomerates (> 100 nm). At 0 h after aerosol inhalation, 69.2±4.9% AuNP were luminal, i.e. attached to the epithelial surface and 24.0±5.9% in macrophages in Scnn1b-Tg mice. In Wt mice, 35.3±32.2% AuNP were on the epithelium and 58.3±41.4% in macrophages. The percentage of luminal AuNP decreased from 0 h to 24 h in both groups. At 24 h, 15.5±4.8% AuNP were luminal, 21.4±14.2% within epithelial cells and 63.0±18.9% in macrophages in Scnn1b-Tg mice. In Wt mice, 9.5±5.0% AuNP were luminal, 2.2±1.6% within epithelial cells and 82.8±0.2% in macrophages. BAL-macrophage analysis revealed enhanced AuNP uptake in Wt animals at 0 h and in Scnn1b-Tg mice at 24 h, confirming less efficient macrophage uptake and delayed clearance of AuNP in Scnn1b-Tg mice.

Conclusions

Inhaled AuNP rapidly bound to the alveolar epithelium in both Wt and Scnn1b-Tg mice. Scnn1b-Tg mice showed less efficient AuNP uptake by surface macrophages and concomitant higher particle internalization by alveolar type I epithelial cells compared to Wt mice. This likely promotes AuNP depth translocation in Scnn1b-Tg mice, including enhanced epithelial targeting. These results suggest AuNP nanocarrier delivery as successful strategy for therapeutic targeting of alveolar epithelial cells and macrophages in COPD.

Loss of Cftr function exacerbates the phenotype of Na(+) hyperabsorption in murine airways

Airway surface hydration depends on the balance between transepithelial Na(+) absorption and Cl(-) secretion. In adult mice, absence of functional cystic fibrosis transmembrane conductance regulator (Cftr) fails to recapitulate human cystic fibrosis (CF) lung disease. In contrast, overexpression of the epithelial Na(+) channel β subunit in transgenic mice (βENaC-Tg) produces unregulated Na(+) hyperabsorption and results in CF-like airway surface dehydration, mucus obstruction, inflammation, and increased neonatal mortality. To investigate whether the combination of airway Na(+) hyperabsorption and absent Cftr-mediated Cl(-) secretion resulted in more severe lung pathology, we generated double-mutant ΔF508 CF/βENaC-Tg mice. Survival of ΔF508 CF/βENaC-Tg mice was reduced compared with βENaC-Tg or ΔF508 CF mice. Absence of functional Cftr did not affect endogenous or transgenic ENaC currents but produced reduced basal components of Cl(-) secretion and tracheal cartilaginous defects in both ΔF508 CF and ΔF508 CF/βENaC-Tg mice. Neonatal ΔF508 CF/βENaC-Tg mice exhibited higher neutrophilic pulmonary inflammation and club cell (Clara cell) necrosis compared with βENaC-Tg littermates. Neonatal ΔF508 CF/βENaC-Tg mice also exhibited spontaneous bacterial infections, but the bacterial burden was similar to that of βENaC-Tg littermates. Adult ΔF508 CF/βENaC-Tg mice exhibited pathological changes associated with eosinophilic crystalline pneumonia, a phenotype not observed in age-matched βENaC-Tg mice. Collectively, these data suggest that the combined abnormalities in Na(+) absorption and Cl(-) secretion produce more severe lung disease than either defect alone. Airway cartilage abnormalities, airway cell necrosis, and exaggerated neutrophil infiltration likely interact with defective mucus clearance caused by βENaC overexpression and absent CFTR-mediated Cl(-) secretion to produce the increased neonatal mortality observed in ΔF508 CF/βENaC-Tg mice.

Non-contact respiration monitoring for in-vivo murine micro computed tomography: characterization and imaging applications

A cone beam micro-CT has previously been utilized along with a pressure-tracking respiration sensor to acquire prospectively gated images of both wild-type mice and various adult murine disease models. While the pressure applied to the abdomen of the subject by this sensor is small and is generally without physiological effect, certain disease models of interest, as well as very young animals, are prone to atelectasis with added pressure, or they generate too weak a respiration signal with this method to achieve optimal prospective gating. In this work we present a new fibre-optic displacement sensor which monitors respiratory motion of a subject without requiring physical contact. The sensor outputs an analogue signal which can be used for prospective respiration gating in micro-CT imaging. The device was characterized and compared against a pneumatic air chamber pressure sensor for the imaging of adult wild-type mice. The resulting images were found to be of similar quality with respect to physiological motion blur; the quality of the respiration signal trace obtained using the non-contact sensor was comparable to that of the pressure sensor and was superior for gating purposes due to its better signal-to-noise ratio. The non-contact sensor was then used to acquire in-vivo micro-CT images of a murine model for congenital diaphragmatic hernia and of 11-day-old mouse pups. In both cases, quality CT images were successfully acquired using this new respiration sensor. Despite the presence of beam hardening artefacts arising from the presence of a fibre-optic cable in the imaging field, we believe this new technique for respiration monitoring and gating presents an opportunity for in-vivo imaging of disease models which were previously considered too delicate for established animal handling methods.

CFTR regulates early pathogenesis of chronic obstructive lung disease in βENaC-overexpressing mice

Background

Factors determining the onset and severity of chronic obstructive pulmonary disease remain poorly understood. Previous studies demonstrated that airway surface dehydration in βENaC-overexpressing (βENaC-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 βENaC-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 βENaC-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 Cl⁻ secretion, which was associated with decreased mucus plugging and mortality in neonatal βENaC-Tg C57BL/6 compared to βENaC-Tg BALB/c mice. Conversely, genetic deletion of CFTR increased early mucus obstruction and mortality in βENaC-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 βENaC-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.

Mucus clearance, MyD88-dependent and MyD88-independent immunity modulate lung susceptibility to spontaneous bacterial infection and inflammation

It has been postulated that mucus stasis is central to the pathogenesis of obstructive lung diseases. In Scnn1b-transgenic (Scnn1b-Tg⁺ mice, airway-targeted overexpression of the epithelial Na⁺ channel β subunit causes airway surface dehydration, which results in mucus stasis and inflammation. Bronchoalveolar lavage from neonatal Scnn1b-Tg⁺ mice, but not wild-type littermates, contained increased mucus, bacteria, and neutrophils, which declined with age. Scnn1b-Tg⁺ mice lung bacterial flora included environmental and oropharyngeal species, suggesting inhalation and/or aspiration as routes of entry. Genetic deletion of the Toll-interleukin-1 receptor adapter molecule MyD88 in Scnn1b-Tg⁺ mice did not modify airway mucus obstruction, but caused defective neutrophil recruitment and increased bacterial infection, which persisted into adulthood. Scnn1b-Tg⁺ mice derived into germ-free conditions exhibited mucus obstruction similar to conventional Scnn1b-Tg⁺ mice and sterile inflammation. Collectively, these data suggest that dehydration-induced mucus stasis promotes infection, compounds defects in other immune mechanisms, and alone is sufficient to trigger airway inflammation.