Cathepsin S Contributes to Lung Inflammation in Acute Respiratory Distress Syndrome.

Rationale: Although the cysteine protease cathepsin S has been implicated in the pathogenesis of several inflammatory lung diseases, its role has not been examined in the context of acute respiratory distress syndrome, a condition that still lacks specific and effective pharmacological treatments. Objectives: To characterize the status of cathepsin S in acute lung inflammation and examine the role of cathepsin S in disease pathogenesis. Methods: Human and mouse model BAL fluid samples were analyzed for the presence and activity of cathepsin S and its endogenous inhibitors. Recombinant cathepsin S was instilled directly into the lungs of mice. The effects of cathepsin S knockout and pharmacological inhibition were examined in two models of acute lung injury. Protease-activated receptor-1 antagonism was used to test a possible mechanism for cathepsin S-mediated inflammation. Measurements and Main Results: Pulmonary cathepsin S concentrations and activity were elevated in acute respiratory distress syndrome, a phenotype possibly exacerbated by the loss of the endogenous antiprotease cystatin SN. Direct cathepsin S instillation into the lungs induced key pathologies of acute respiratory distress syndrome, including neutrophilia and alveolar leakage. Conversely, in murine models of acute lung injury, genetic knockdown and prophylactic or therapeutic inhibition of cathepsin S reduced neutrophil recruitment and protein leakage. Cathepsin S may partly mediate its pathogenic effects via protease-activated receptor-1, because antagonism of this receptor abrogated cathepsin S-induced airway inflammation. Conclusions: Cathepsin S contributes to acute lung injury and may represent a novel therapeutic target for acute respiratory distress syndrome.

The Effect of CFTR Modulators on Airway Infection in Cystic Fibrosis.

The advent of Cystic fibrosis transmembrane receptor (CFTR) modulators in 2012 was a critical event in the history of cystic fibrosis (CF) treatment. Unlike traditional therapies that target downstream effects of CFTR dysfunction, CFTR modulators aim to correct the underlying defect at the protein level. These genotype-specific therapies are now available for an increasing number of CF patients, transforming the way we view the condition from a life-limiting disease to one that can be effectively managed. Several studies have demonstrated the vast improvement CFTR modulators have on normalization of sweat chloride, CFTR function, clinical endpoints, and frequency of pulmonary exacerbation. However, their impact on other aspects of the disease, such as pathogenic burden and airway infection, remain under explored. Frequent airway infections as a result of increased susceptibility and impaired innate immune response are a serious problem within CF, often leading to accelerated decline in lung function and disease progression. Current evidence suggests that CFTR modulators are unable to eradicate pathogenic organisms in those with already established lung disease. However, this may not be the case for those with relatively low levels of disease progression and conserved microbial diversity, such as young patients. Furthermore, it remains unknown whether the restorative effects exerted by CFTR modulators extend to immune cells, such as phagocytes, which have the potential to modulate the response of people with CF (pwCF) to infection. Throughout this review, we look at the potential impact of CFTR modulators on airway infection in CF and their ability to shape impaired pulmonary defences to pathogens.

Deciphering Respiratory-Virus-Associated Interferon Signaling in COPD Airway Epithelium.

COPD is a chronic lung disorder characterized by a progressive and irreversible airflow obstruction, and persistent pulmonary inflammation. It has become a global epidemic affecting 10% of the population, and is the third leading cause of death worldwide. Respiratory viruses are a primary cause of COPD exacerbations, often leading to secondary bacterial infections in the lower respiratory tract. COPD patients are more susceptible to viral infections and associated severe disease, leading to accelerated lung function deterioration, hospitalization, and an increased risk of mortality. The airway epithelium plays an essential role in maintaining immune homeostasis, and orchestrates the innate and adaptive responses of the lung against inhaled and pathogen insults. A healthy airway epithelium acts as the first line of host defense by maintaining barrier integrity and the mucociliary escalator, secreting an array of inflammatory mediators, and initiating an antiviral state through the interferon (IFN) response. The airway epithelium is a major site of viral infection, and the interaction between respiratory viruses and airway epithelial cells activates host defense mechanisms, resulting in rapid virus clearance. As such, the production of IFNs and the activation of IFN signaling cascades directly contributes to host defense against viral infections and subsequent innate and adaptive immunity. However, the COPD airway epithelium exhibits an altered antiviral response, leading to enhanced susceptibility to severe disease and impaired IFN signaling. Despite decades of research, there is no effective antiviral therapy for COPD patients. Herein, we review current insights into understanding the mechanisms of viral evasion and host IFN antiviral defense signaling impairment in COPD airway epithelium. Understanding how antiviral mechanisms operate in COPD exacerbations will facilitate the discovery of potential therapeutic interventions to reduce COPD hospitalization and disease severity.

Therapeutic Inhibition of Cathepsin S Reduces Inflammation and Mucus Plugging in Adult ßENaC-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 ß-epithelial Na+ channel-overexpressing transgenic (ßENaC-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 ßENaC-Tg mice with established disease. METHODS: ßENaC-Tg mice and wild-type (WT) littermates were treated with a CatS inhibitor from 4 to 6 weeks of age, and CatS-/- ßENaC-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, ßENaC-Tg mice developed significant airway inflammation, lung tissue damage, and mucus plugging when compared to WT mice. CatS-/- ßENaC-Tg mice and ßENaC-Tg mice receiving inhibitor had significantly reduced airway mononuclear and polymorphonuclear (PMN) cell counts as well as mucus plugging. However, in contrast to CatS-/- ßENaC-Tg mice, therapeutic inhibition of CatS in ßENaC-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.

Proteases, Mucus, and Mucosal Immunity in Chronic Lung Disease.

Dysregulated protease activity has long been implicated in the pathogenesis of chronic lung diseases and especially in conditions that display mucus obstruction, such as chronic obstructive pulmonary disease, cystic fibrosis, and non-cystic fibrosis bronchiectasis. However, our appreciation of the roles of proteases in various aspects of such diseases continues to grow. Patients with muco-obstructive lung disease experience progressive spirals of inflammation, mucostasis, airway infection and lung function decline. Some therapies exist for the treatment of these symptoms, but they are unable to halt disease progression and patients may benefit from novel adjunct therapies. In this review, we highlight how proteases act as multifunctional enzymes that are vital for normal airway homeostasis but, when their activity becomes immoderate, also directly contribute to airway dysfunction, and impair the processes that could resolve disease. We focus on how proteases regulate the state of mucus at the airway surface, impair mucociliary clearance and ultimately, promote mucostasis. We discuss how, in parallel, proteases are able to promote an inflammatory environment in the airways by mediating proinflammatory signalling, compromising host defence mechanisms and perpetuating their own proteolytic activity causing structural lung damage. Finally, we discuss some possible reasons for the clinical inefficacy of protease inhibitors to date and propose that, especially in a combination therapy approach, proteases represent attractive therapeutic targets for muco-obstructive lung diseases.

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, ß-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.

Cathepsin S: investigating an old player in lung disease pathogenesis, comorbidities, and potential therapeutics.

Dysregulated expression and activity of cathepsin S (CTSS), a lysosomal protease and a member of the cysteine cathepsin protease family, is linked to the pathogenesis of multiple diseases, including a number of conditions affecting the lungs. Extracellular CTSS has potent elastase activity and by processing cytokines and host defense proteins, it also plays a role in the regulation of inflammation. CTSS has also been linked to G-coupled protein receptor activation and possesses an important intracellular role in major histocompatibility complex class II antigen presentation. Modulated CTSS activity is also associated with pulmonary disease comorbidities, such as cancer, cardiovascular disease, and diabetes. CTSS is expressed in a wide variety of immune cells and is biologically active at neutral pH. Herein, we review the significance of CTSS signaling in pulmonary diseases and associated comorbidities. We also discuss CTSS as a plausible therapeutic target and describe recent and current clinical trials examining CTSS inhibition as a means for treatment.

Protein Phosphatase 2A Reduces Cigarette Smoke-induced Cathepsin S and Loss of Lung Function.

Rationale: CTSS (cathepsin S) is a cysteine protease that is observed at higher concentrations in BAL fluid and plasma of subjects with chronic obstructive pulmonary disease (COPD). Objectives: To investigate whether CTSS is involved in the pathogenesis of cigarette smoke-induced COPD and determine whether targeting upstream signaling could prevent the disease. Methods: CTSS expression was investigated in animal and human tissue and cell models of COPD. Ctss-/- mice were exposed to long-term cigarette smoke and forced oscillation and expiratory measurements were recorded. Animals were administered chemical modulators of PP2A (protein phosphatase 2A) activity. Measurements and Main Results: Here we observed enhanced CTSS expression and activity in mouse lungs after exposure to cigarette smoke. Ctss-/- mice were resistant to cigarette smoke-induced inflammation, airway hyperresponsiveness, airspace enlargements, and loss of lung function. CTSS expression was negatively regulated by PP2A in human bronchial epithelial cells isolated from healthy nonsmokers and COPD donors and in monocyte-derived macrophages. Modulating PP2A expression or activity, with silencer siRNA or a chemical inhibitor or activator, during acute smoke exposure in mice altered inflammatory responses and CTSS expression and activity in the lung. Enhancement of PP2A activity prevented chronic smoke-induced COPD in mice. Conclusions: Our study indicates that the decrease in PP2A activity that occurs in COPD contributes to elevated CTSS expression in the lungs and results in impaired lung function. Enhancing PP2A activity represents a feasible therapeutic approach to reduce CTSS activity and counter smoke-induced lung disease.

Airway Inflammation and Host Responses in the Era of CFTR Modulators.

The arrival of cystic fibrosis transmembrane conductance regulator (CFTR) modulators as a new class of treatment for cystic fibrosis (CF) in 2012 represented a pivotal advance in disease management, as these small molecules directly target the upstream underlying protein defect. Further advancements in the development and scope of these genotype-specific therapies have been transformative for an increasing number of people with CF (PWCF). Despite clear improvements in CFTR function and clinical endpoints such as lung function, body mass index (BMI), and frequency of pulmonary exacerbations, current evidence suggests that CFTR modulators do not prevent continued decline in lung function, halt disease progression, or ameliorate pathogenic organisms in those with established lung disease. Furthermore, it remains unknown whether their restorative effects extend to dysfunctional CFTR expressed in phagocytes and other immune cells, which could modulate airway inflammation. In this review, we explore the effects of CFTR modulators on airway inflammation, infection, and their influence on the impaired pulmonary host defences associated with CF lung disease. We also consider the role of inflammation-directed therapies in light of the widespread clinical use of CFTR modulators and identify key areas for future research.

Targeting of cathepsin S reduces cystic fibrosis-like lung disease.

Cathepsin S (CatS) is upregulated in the lungs of patients with cystic fibrosis (CF). However, its role in CF lung disease pathogenesis remains unclear.In this study, ß-epithelial Na+ channel-overexpressing transgenic (ßENaC-Tg) mice, a model of CF-like lung disease, were crossed with CatS null (CatS-/-) mice or treated with the CatS inhibitor VBY-999.Levels of active CatS were elevated in the lungs of ßENaC-Tg mice compared with wild-type (WT) littermates. CatS-/-ßENaC-Tg mice exhibited decreased pulmonary inflammation, mucus obstruction and structural lung damage compared with ßENaC-Tg mice. Pharmacological inhibition of CatS resulted in a significant decrease in pulmonary inflammation, lung damage and mucus plugging in the lungs of ßENaC-Tg mice. In addition, instillation of CatS into the lungs of WT mice resulted in inflammation, lung remodelling and upregulation of mucin expression. Inhibition of the CatS target, protease-activated receptor 2 (PAR2), in ßENaC-Tg mice resulted in a reduction in airway inflammation and mucin expression, indicating a role for this receptor in CatS-induced lung pathology.Our data indicate an important role for CatS in the pathogenesis of CF-like lung disease mediated in part by PAR2 and highlight CatS as a therapeutic target.

Characterisation of eppin function: expression and activity in the lung.

Eppin is a serine protease inhibitor expressed in male reproductive tissues.The aim of this study was to investigate the localisation and regulation of eppin expression in myeloid and epithelial cell lines, and explore its potential role as a multifunctional host defence protein.Using immunohistochemistry and Western blotting, eppin was detected in the lungs of patients with acute respiratory distress syndrome and cystic fibrosis lung disease. Expression of eppin in monocytic cells was unaffected by stimulation with Toll-like receptor agonists, cytokines and hormone receptor agonists. However, upregulated expression and secretion of eppin was observed following treatment of monocytes with epidermal growth factor. Incubation of recombinant eppin with monocytic cells resulted in significant inhibition of lipopolysaccharide-induced chemokine production. Furthermore, eppin inhibited lipopolysaccharide-induced NF-κB activation by a mechanism which involved accumulation of phosphorylated IκBα. In an in vivo model of lung inflammation induced by lipopolysaccharide, eppin administration resulted in decreased recruitment of neutrophils to the lung with a concomitant reduction in the levels of the neutrophil chemokine macrophage inflammatory protein-2.Overall, these results suggest a role for eppin outside of the reproductive tract and that eppin may have a role in the innate immune response in the lung.

The role of whey acidic protein four-disulfide-core proteins in respiratory health and disease.

Members of the whey acidic protein (WAP) or WAP four-disulfide-core (WFDC) family of proteins are a relatively under-explored family of low molecular weight proteins. The two most prominent WFDC proteins, secretory leukocyte protease inhibitor (SLPI) and elafin (or the precursor, trappin-2), have been shown to possess multiple functions including anti-protease, anti-bacterial, anti-viral and anti-inflammatory properties. It is therefore of no surprise that both SLPI and elafin/trappin-2 have been developed as potential therapeutics. Given the abundance of SLPI and elafin/trappin-2 in the human lung, most work in the area of WFDC research has focused on the role of WFDC proteins in protecting the lung from proteolytic attack. In this review, we will outline the current evidence regarding the expanding role of WFDC protein function with a focus on WFDC activity in lung disease as well as emerging data regarding the function of some of the more recently described WFDC proteins.

A functional variant of elafin with improved anti-inflammatory activity for pulmonary inflammation.

Elafin is a serine protease inhibitor produced by epithelial and immune cells with anti-inflammatory properties. Research has shown that dysregulated protease activity may elicit proteolytic cleavage of elafin, thereby impairing the innate immune function of the protein. The aim of this study was to generate variants of elafin (GG- and QQ-elafin) that exhibit increased protease resistance while retaining the biological properties of wild-type (WT) elafin. Similar to WT-elafin, GG- and QQ-elafin variants retained antiprotease activity and susceptibility to transglutaminase-mediated fibronectin cross-linking. However, in contrast to WT-elafin, GG- and QQ-elafin displayed significantly enhanced resistance to degradation when incubated with bronchoalveolar lavage fluid from patients with cystic fibrosis. Intriguingly, both variants, particularly GG-elafin, demonstrated improved lipopolysaccharide (LPS) neutralization properties in vitro. In addition, GG-elafin showed improved anti-inflammatory activity in a mouse model of LPS-induced acute lung inflammation. Inflammatory cell infiltration into the lung was reduced in lungs of mice treated with GG-elafin, predominantly neutrophilic infiltration. A reduction in MCP-1 levels in GG-elafin treated mice compared to the LPS alone treatment group was also demonstrated. GG-elafin showed increased functionality when compared to WT-elafin and may be of future therapeutic relevance in the treatment of lung diseases characterized by a protease burden.

A role for whey acidic protein four-disulfide-core 12 (WFDC12) in the regulation of the inflammatory response in the lung.

INTRODUCTION: Secretory leucocyte protease inhibitor and elafin are members of the whey acidic protein (WAP), or WAP four disulfide-core (WFDC), family of proteins and have multiple contributions to innate defence including inhibition of neutrophil serine proteases and inhibition of the inflammatory response to lipopolysaccharide (LPS). This study aimed to explore potential activities of WFDC12, a previously uncharacterised WFDC protein expressed in the lung. METHODS: Recombinant expression and purification of WFDC12 were optimised in Escherichia coli. Antiprotease, antibacterial and immunomodulatory activities of recombinant WFDC12 were evaluated and levels of endogenous WFDC12 protein were characterised by immunostaining and ELISA. RESULTS: Recombinant WFDC12 inhibited cathepsin G, but not elastase or proteinase-3 activity. Monocytic cells pretreated with recombinant WFDC12 before LPS stimulation produced significantly lower levels of the pro-inflammatory cytokines interleukin-8 and monocyte chemotactic protein-1 compared with cells stimulated with LPS alone. Recombinant WFDC12 became conjugated to fibronectin in a transglutaminase-mediated reaction and retained antiprotease activity. In vivo WFDC12 expression was confirmed by immunostaining of human lung tissue sections. WFDC12 levels in human bronchoalveolar lavage fluid from healthy and lung-injured patients were quantitatively compared, showing WFDC12 to be elevated in both patients with acute respiratory distress syndrome and healthy subjects treated with LPS, relative to healthy controls. CONCLUSIONS: Together, these results suggest a role for this lesser known WFDC protein in the regulation of lung inflammation.

miR-31 dysregulation in cystic fibrosis airways contributes to increased pulmonary cathepsin S production.

RATIONALE: Cathepsin S (CTSS) activity is increased in bronchoalveolar lavage (BAL) fluid from patients with cystic fibrosis (CF). This activity contributes to lung inflammation via degradation of antimicrobial proteins, such as lactoferrin and members of the ß-defensin family. OBJECTIVES: In this study, we investigated the hypothesis that airway epithelial cells are a source of CTSS, and mechanisms underlying CTSS expression in the CF lung. METHODS: Protease activity was determined using fluorogenic activity assays. Protein and mRNA expression were analyzed by ELISA, Western blotting, and reverse-transcriptase polymerase chain reaction. MEASUREMENTS AND MAIN RESULTS: In contrast to neutrophil elastase, CTSS activity was detectable in 100% of CF BAL fluid samples from patients without Pseudomonas aeruginosa infection. In this study, we identified epithelial cells as a source of pulmonary CTSS activity with the demonstration that CF airway epithelial cells express and secrete significantly more CTSS than non-CF control cells in the absence of proinflammatory stimulation. Furthermore, levels of the transcription factor IRF-1 correlated with increased levels of its target gene CTSS. We discovered that miR-31, which is decreased in the CF airways, regulates IRF-1 in CF epithelial cells. Treating CF bronchial epithelial cells with a miR-31 mimic decreased IRF-1 protein levels with concomitant knockdown of CTSS expression and secretion. CONCLUSIONS: The miR-31/IRF-1/CTSS pathway may play a functional role in the pathogenesis of CF lung disease and may open up new avenues for exploration in the search for an effective therapeutic target.

The Role of Serine Proteases and Antiproteases in the Cystic Fibrosis Lung.

Cystic fibrosis (CF) lung disease is an inherited condition with an incidence rate of approximately 1 in 2500 new born babies. CF is characterized as chronic infection of the lung which leads to inflammation of the airway. Sputum from CF patients contains elevated levels of neutrophils and subsequently elevated levels of neutrophil serine proteases. In a healthy individual these proteases aid in the phagocytic process by degrading microbial peptides and are kept in homeostatic balance by cognate antiproteases. Due to the heavy neutrophil burden associated with CF the high concentration of neutrophil derived proteases overwhelms cognate antiproteases. The general effects of this protease/antiprotease imbalance are impaired mucus clearance, increased and self-perpetuating inflammation, and impaired immune responses and tissue. To restore this balance antiproteases have been suggested as potential therapeutics or therapeutic targets. As such a number of both endogenous and synthetic antiproteases have been trialed with mixed success as therapeutics for CF lung disease.

Proteolytic cleavage of elafin by 20S proteasome may contribute to inflammation in acute lung injury.

RATIONALE: We hypothesise that elafin levels in acute lung injury (ALI) decrease over time due, in part, to proteolytic degradation as observed in other lung diseases. OBJECTIVES: The aim of this study was to characterise temporal changes in elafin concentration in patients with ALI and to evaluate whether a decrease in elafin levels is due to elevated protease activity. METHODS: Bronchoalveolar lavage fluid (BALF) was obtained from patients with ALI within 48 h of onset of ALI (day 0), at day 3 and at day 7. Elafin levels were quantified by ELISA. Elafin susceptibility to proteolytic cleavage by ALI BALF was assessed by Western blot and by high-performance liquid chromatography-mass spectrometry. MEASUREMENTS AND MAIN RESULTS: Elafin levels were found to be significantly increased at the onset of ALI compared with healthy volunteers and fell significantly by day 7 compared with day 0. In contrast, levels of secretory leukocyte protease inhibitor did not decrease over time. This decrease in elafin was due to cleavage by the 20S proteasome which was significantly increased in ALI BALF. Incubation of ALI BALF with the proteasome inhibitor epoxomicin confirmed that 20S proteasome protease activity was responsible for proteolytic cleavage of elafin, resulting in diminished anti-elastase activity. In addition, free neutrophil elastase activity significantly increased in ALI BALF from day 0 to day 7. CONCLUSIONS: Elafin concentrations fall within the pulmonary compartment over the course of ALI as a result of proteolytic degradation. This loss of elafin may predispose people, in part, to excessive inflammation in ALI.