Histopathology of severe childhood asthma: a case series

Tezepelumab: patient selection and place in therapy in severe asthma

Asthma is a disease characterised by heterogeneous and multifaceted airway inflammation. Despite the availability of effective treatments, a substantial percentage of patients with the type 2 (T2)-high, but mainly the T2-low, phenotype complain of persistent symptoms, airflow limitation, and poor response to treatments. Currently available biologicals target T2 cytokines, but no monoclonal antibodies or other specific therapeutic options are available for non-T2 asthma. However, targeted therapy against alarmins is radically changing this perspective. The development of alarmin-targeted therapies, of which tezepelumab (TZP) is the first example, may offer broad action on inflammatory pathways as well as an enhanced therapeutic effect on epithelial dysfunction. In this regard, TZP demonstrated positive results not only in patients with severe T2 asthma but also those with non-allergic, non-eosinophilic disease. Therefore, it is necessary to identify clinical features of patients who can benefit from an upstream targeted therapy such as anti-thymic stromal lymphopoietin. The aims of this narrative review are to understand the role of alarmins in asthma pathogenesis and epithelial dysfunction, examine the rationale underlying the indication of TZP treatment in severe asthma, summarise the results of clinical studies, and recognise the specific characteristics of patients potentially eligible for TZP treatment.

A review of the pathophysiology and the role of ion channels on bronchial asthma

Asthma is one of the main non-communicable chronic diseases and affects a huge portion of the population. It is a multifactorial disease, classified into several phenotypes, being the allergic the most frequent. The pathophysiological mechanism of asthma involves a Th2-type immune response, with high concentrations of allergen-specific immunoglobulin E, eosinophilia, hyperreactivity and airway remodeling. These mechanisms are orchestrated by intracellular signaling from effector cells, such as lymphocytes and eosinophils. Ion channels play a fundamental role in maintaining the inflammatory response on asthma. In particular, transient receptor potential (TRP), stock-operated Ca2+ channels (SOCs), Ca2+-activated K+ channels (IKCa and BKCa), calcium-activated chloride channel (TMEM16A), cystic fibrosis transmembrane conductance regulator (CFTR), piezo-type mechanosensitive ion channel component 1 (PIEZO1) and purinergic P2X receptor (P2X). The recognition of the participation of these channels in the pathological process of asthma is important, as they become pharmacological targets for the discovery of new drugs and/or pharmacological tools that effectively help the pharmacotherapeutic follow-up of this disease, as well as the more specific mechanisms involved in worsening asthma.

Hedgehog Signaling as a Therapeutic Target for Airway Remodeling and Inflammation in Allergic Asthma

Genome-wide association studies (GWAS) have shown that variants of patched homolog 1 (PTCH1) are associated with lung function abnormalities in the general population. It has also been shown that sonic hedgehog (SHH), an important ligand for PTCH1, is upregulated in the airway epithelium of patients with asthma and is suggested to be involved in airway remodeling. The contribution of hedgehog signaling to airway remodeling and inflammation in asthma is poorly described. To determine the biological role of hedgehog signaling-associated genes in asthma, gene silencing, over-expression, and pharmacologic inhibition studies were conducted after stimulating human airway epithelial cells or not with transforming growth factor β1 (TGFβ1), an important fibrotic mediator in asthmatic airway remodeling that also interacts with SHH pathway. TGFβ1 increased hedgehog-signaling-related gene expression including SHH, GLI1 and GLI2. Knockdown of PTCH1 or SMO with siRNA, or use of hedgehog signaling inhibitors, consistently attenuated COL1A1 expression induced by TGFβ1 stimulation. In contrast, Ptch1 over-expression augmented TGFβ1-induced an increase in COL1A1 and MMP2 gene expression. We also showed an increase in hedgehog-signaling-related gene expression in primary airway epithelial cells from controls and asthmatics at different stages of cellular differentiation. GANT61, an inhibitor of GLI1/2, attenuated TGFβ1-induced increase in COL1A1 protein expression in primary airway epithelial cells differentiated in air–liquid interface. Finally, to model airway tissue remodeling in vivo, C57BL/6 wildtype (WT) and Ptch1^+/− mice were intranasally challenged with house dust mite (HDM) or phosphate-buffered saline (PBS) control. Ptch1^+/− mice showed reduced sub-epithelial collagen expression and serum inflammatory proteins compared to WT mice in response to HDM challenge. In conclusion, TGFβ1-induced airway remodeling is partially mediated through the hedgehog signaling pathway via the PTCH1-SMO-GLI axis. The Hedgehog signaling pathway is a promising new potential therapeutic target to alleviate airway tissue remodeling in patients with allergic airways disease.

Therapeutic effect of statins on airway remodeling during asthma

INTRODUCTION

Asthma is a chronic inflammatory disease of the airways, which is usually characterized by remodeling, hyperresponsiveness and episodic obstruction of the airways. The underlying chronic airway inflammation leads to pathological restructuring of both the large and small airways. Since the effects of current asthma medications on airway remodeling have been met with contradictions, many therapeutic agents have been redirected from their primary use for the treatment of asthma. Such treatments, which could target several signaling molecules implicated in the inflammatory and airway remodeling processes of asthma, would be an ideal choice.

AREAS COVERED

Statins are effective serum cholesterol-lowering agents that were found to have potential anti-inflammatory and anti-remodeling properties. Literature search was done for the past 10 years to include research and review articles in the field of statins and asthma complications. In this review, we discuss the role of statins in airway tissue remodeling and their potential therapeutic modalities in asthma.

EXPERT OPINION

With improved understanding of the role of statins in airway remodeling and inflammation, statins represent a potential therapeutic option for various asthma phenotypes. Further research is warranted to optimize statins for asthma therapy through inhalation as a possible route of administration.

Pathogenesis, clinical features of asthma COPD overlap (ACO), and therapeutic modalities

Both asthma and COPD are heterogeneous diseases identified by characteristic symptoms and functional abnormalities, with airway obstruction common in both diseases. Asthma COPD overlap (ACO) does not define a single disease but is a descriptive term for clinical use that includes several overlapping clinical phenotypes of chronic airways disease with different underlying mechanisms. This literature review was initiated to describe published studies, identify gaps in knowledge, and propose future research goals regarding the disease pathology of ACO, especially the airway remodelling changes and inflammation aspects. Airway remodelling occurs in asthma and COPD, but there are differences in the structures affected and the prime anatomic site at which they occur. Reticular basement membrane thickening and cellular infiltration with eosinophils and T-helper (CD4+) lymphocytes are prominent features of asthma. Epithelial squamous metaplasia, airway wall fibrosis, emphysema, bronchoalveolar lavage (BAL) neutrophilia and (CD8+) T-cytotoxic lymphocyte infiltrations in the airway wall are features of COPD. There is no universally accepted definition of ACO, nor are there clearly defined pathological characteristics to differentiate from asthma and COPD. Understanding etiological concepts within the purview of inflammation and airway remodelling changes in ACO would allow better management of these patients.

PAR-2-activated secretion by airway gland serous cells: role for CFTR and inhibition by Pseudomonas aeruginosa

Airway submucosal gland serous cells are important sites of fluid secretion in conducting airways. Serous cells also express the cystic fibrosis (CF) transmembrane conductance regulator (CFTR). Protease-activated receptor 2 (PAR-2) is a G protein-coupled receptor that activates secretion from intact airway glands. We tested if and how human nasal serous cells secrete fluid in response to PAR-2 stimulation using Ca²⁺ imaging and simultaneous differential interference contrast imaging to track isosmotic cell shrinking and swelling reflecting activation of solute efflux and influx pathways, respectively. During stimulation of PAR-2, serous cells exhibited dose-dependent increases in intracellular Ca²⁺. At stimulation levels >EC₅₀ for Ca²⁺, serous cells simultaneously shrank ∼20% over ∼90 s due to KCl efflux reflecting Ca²⁺-activated Cl^- channel (CaCC, likely TMEM16A)-dependent secretion. At lower levels of PAR-2 stimulation (<EC₅₀ for Ca²⁺), shrinkage was not evident due to failure to activate CaCC. Low levels of cAMP-elevating VIP receptor (VIPR) stimulation, also insufficient to activate secretion alone, synergized with low-level PAR-2 stimulation to elicit fluid secretion dependent on both cAMP and Ca²⁺ to activate CFTR and K⁺ channels, respectively. Polarized cultures of primary serous cells also exhibited synergistic fluid secretion. Pre-exposure to Pseudomonas aeruginosa conditioned media inhibited PAR-2 activation by proteases but not peptide agonists in primary nasal serous cells, Calu-3 bronchial cells, and primary nasal ciliated cells. Disruption of synergistic CFTR-dependent PAR-2/VIPR secretion may contribute to reduced airway surface liquid in CF. Further disruption of the CFTR-independent component of PAR-2-activated secretion by P. aeruginosa may also be important to CF pathophysiology.

EGFR activation-induced decreases in claudin1 promote MUC5AC expression and exacerbate asthma in mice

Claudin1 plays a critical role in maintaining the epithelial barrier, and mucus hypersecretion induced by epidermal growth factor receptor (EGFR) activation is a pivotal pathological feature of asthma. The relationship between claudin1 expression and mucus hypersecretion and EGFR activation is still poorly understood. In this report, we showed that claudin1 expression correlated with asthma stage, in both patients with asthma and in the house dust mite (HDM)-induced mouse asthma model. Claudin1 knockdown induced MUC5AC overexpression both in 16HBE cells and in mouse airways. In addition, claudin1 expression negatively correlated with asthma severity as demonstrated by significantly higher MUC5AC expression, more severe airway inflammation, and increased airway hyperreactivity in mouse lungs with claudin1 knockdown following HDM challenge. EGFR activation reduced claudin1 expression and increased MUC5AC expression, both in vitro and in vivo. Erlotinib alleviated murine allergic airway inflammation, restored claudin1 expression and decreased MUC5AC expression. These results suggest that EGFR activation-induced decreases in claudin1 promote goblet-cell metaplasia, and restoring claudin1 to maintain barrier integrity by EGFR antagonism may provide a novel therapeutic strategy for asthma.

Airway Remodeling in Asthma

Asthma is an inflammatory disease of the airways that may result from exposure to allergens or other environmental irritants, resulting in bronchoconstriction, wheezing, and shortness of breath. The structural changes of the airways associated with asthma, broadly referred to as airway remodeling, is a pathological feature of chronic asthma that contributes to the clinical manifestations of the disease. Airway remodeling in asthma constitutes cellular and extracellular matrix changes in the large and small airways, epithelial cell apoptosis, airway smooth muscle cell proliferation, and fibroblast activation. These pathological changes in the airway are orchestrated by crosstalk of different cell types within the airway wall and submucosa. Environmental exposures to dust, chemicals, and cigarette smoke can initiate the cascade of pro-inflammatory responses that trigger airway remodeling through paracrine signaling and mechanostimulatory cues that drive airway remodeling. In this review, we explore three integrated and dynamic processes in airway remodeling: (1) initiation by epithelial cells; (2) amplification by immune cells; and (3) mesenchymal effector functions. Furthermore, we explore the role of inflammaging in the dysregulated and persistent inflammatory response that perpetuates airway remodeling in elderly asthmatics.

Polarization of protease-activated receptor 2 (PAR-2) signaling is altered during airway epithelial remodeling and deciliation

Protease-activated receptor 2 (PAR-2) is activated by secreted proteases from immune cells or fungi. PAR-2 is normally expressed basolaterally in differentiated nasal ciliated cells. We hypothesized that epithelial remodeling during diseases characterized by cilial loss and squamous metaplasia may alter PAR-2 polarization. Here, using a fluorescent arrestin assay, we confirmed that the common fungal airway pathogen Aspergillus fumigatus activates heterologously-expressed PAR-2. Endogenous PAR-2 activation in submerged airway RPMI 2650 or NCI-H520 squamous cells increased intracellular calcium levels and granulocyte macrophage-colony-stimulating factor, tumor necrosis factor α, and interleukin (IL)-6 secretion. RPMI 2650 cells cultured at an air-liquid interface (ALI) responded to apically or basolaterally applied PAR-2 agonists. However, well-differentiated primary nasal epithelial ALIs responded only to basolateral PAR-2 stimulation, indicated by calcium elevation, increased cilia beat frequency, and increased fluid and cytokine secretion. We exposed primary cells to disease-related modifiers that alter epithelial morphology, including IL-13, cigarette smoke condensate, and retinoic acid deficiency, at concentrations and times that altered epithelial morphology without causing breakdown of the epithelial barrier to model early disease states. These altered primary cultures responded to both apical and basolateral PAR-2 stimulation. Imaging nasal polyps and control middle turbinate explants, we found that nasal polyps, but not turbinates, exhibit apical calcium responses to PAR-2 stimulation. However, isolated ciliated cells from both polyps and turbinates maintained basolateral PAR-2 polarization, suggesting that the calcium responses originated from nonciliated cells. Altered PAR-2 polarization in disease-remodeled epithelia may enhance apical responses and increase sensitivity to inhaled proteases.

Airway hyperresponsiveness, remodeling and inflammation in infants with wheeze

BACKGROUND

The relationship of airway hyperresponsiveness to airway remodeling and inflammation in infants with wheeze is unclear.

OBJECTIVE

To investigate airway hyperresponsiveness, remodeling and inflammation in infants with wheeze and troublesome breathing.

METHODS

Inclusion criteria were as follows: full-term, 3-23 months of age; doctor -diagnosed wheeze and persistent recurrent troublesome breathing; without obvious structural defect, suspicion of ciliary dyskinesia, cystic fibrosis, immune deficiency or specified use of corticosteroids. Airway hyperresponsiveness (AHR) was evaluated by performing a methacholine bronchial challenge test combined with whole body plethysmography and rapid thoracoabdominal compression. Endobronchial biopsies were analysed for remodeling (thickness of reticular basement membrane and amount of airway smooth muscle) and for inflammation (numbers of inflammatory cells). Correlation analyses were performed.

RESULTS

Forty-nine infants fulfilled the inclusion criteria for the present study. Median age was 1.06 years (IQR 0.6; 1.5). Lung function was impaired in 39/49 (80%) children, at the median age of 1.1 years. Methacholine challenge was successfully performed in 38/49 children. Impaired baseline lung function was correlated with AHR (P = .047, Spearman). In children with the most sensitive quartile of AHR, the percentage of median bronchial airway smooth muscle % and the number of bronchial mast cells in airway smooth muscle were not significantly higher compared to others (P = .057 and 0.056, respectively). No association was found between AHR and thickness of reticular basement membrane or inflammatory cells. Only a small group of children with both atopy and AHR (the most reactive quartile) had thicker airway smooth muscle area than non-atopics with AHR (P = .031).

CONCLUSIONS AND CLINICAL RELEVANCE

These findings do not support the concept that AHR in very young children with wheeze is determined by eosinophilic inflammation or clear-cut remodeling although it is associated with impaired baseline lung function. The possible association of increased airway smooth muscle area among atopic children with AHR remains to be confirmed.

Bronchoscopy in severe childhood asthma: Irresponsible or irreplaceable?

For children with severe asthma, guideline-based management focuses on the escalation of anti-inflammatory and bronchodilatory medications while addressing comorbid conditions. Bronchoscopy, in this context, has been relegated to ruling out asthma mimickers. More recently, however, there have been questions surrounding the clinical utility of bronchoscopy in severe childhood asthma. In this solicited lecture summary, we discuss the past, present, and potential future applications of bronchoscopy in severe childhood asthma.

Quantitative assessment of airway remodelling and response to allergen in asthma

BACKGROUND AND OBJECTIVE

In vivo evaluation of the microstructural differences between asthmatic and non-asthmatic airways and their functional consequences is relevant to understanding and, potentially, treating asthma. In this study, we use endobronchial optical coherence tomography to investigate how allergic airways with asthma differ from allergic non-asthmatic airways in baseline microstructure and in response to allergen challenge.

METHODS

A total of 45 subjects completed the study, including 20 allergic, mildly asthmatic individuals, 22 non-asthmatic allergic controls and 3 healthy controls. A 3-cm airway segment in the right middle and right upper lobe were imaged in each subject immediately before and 24 h following segmental allergen challenge to the right middle lobe. Relationships between optical airway measurements (epithelial and mucosal thicknesses, mucosal buckling and mucus) and airway obstruction (FEV1 /FVC (forced expiratory volume in 1 s/forced vital capacity) and FEV1 % (FEV1 as a percentage of predictive value)) were investigated.

RESULTS

Significant increases at baseline and in response to allergen were observed for all four of our imaging metrics in the asthmatic airways compared to the non-asthmatic airways. Epithelial thickness and mucosal buckling exhibited a significant relationship to FEV1 /FVC in the asthmatic group.

CONCLUSION

Simultaneous assessments of airway microstructure, buckling and mucus revealed both structural and functional differences between the mildly asthmatic and control groups, with airway buckling seeming to be the most relevant factor. The results of this study demonstrate that a comprehensive, microstructural approach to assessing the airways may be important in future asthma studies as well as in the monitoring and treatment of asthma.

Early Airway Pathological Changes in Children: New Insights into the Natural History of Wheezing

Asthma is a heterogeneous condition characterized by reversible airflow limitation, with different phenotypes and clinical expressions. Although it is known that asthma is influenced by age, gender, genetic background, and environmental exposure, the natural history of the disease is still incompletely understood. Our current knowledge of the factors determining the evolution from wheezing in early childhood to persistent asthma later in life originates mainly from epidemiological studies. The underlying pathophysiological mechanisms are still poorly understood. The aim of this review is to converge epidemiological and pathological evidence early in the natural history of asthma to gain insight into the mechanisms of disease and their clinical expression.

[Effect of acupuncture on TGF-β1/Smads pathway in mice with airway remodeling mic]

OBJECTIVE

To investigate the effect of acupuncture on TGF-β1/Smads signaling pathway in the lung tissue of mice with airway remodeling.

METHODS

Thirty specific pathogen-free mice were randomly divided into blank group, model group and acupuncture group (n=10). Mouse models of asthma were established in the model group and the acupuncture group, and the mice in the latter group received 7 acupuncture therapies (at bilateral Fei Shu, Da Zhui and Zu Sanli, 20 min each time) every other day, starting on the 10th day after the modeling. At 24 h after the last acupuncture, the mice were subjected to inhalation of 1% OVA for 3 days, and 24 h after the last challenge, the mice were given methacholine chloride (Mch) inhalation at different concentrations for measurement of lung resistance using a noninvasive stroke volume meter. HE staining was used to observe the pathological changes in the lung tissues, and TGF-β1 levels in the the bronchoalveolar lavage fluid (BALF) and serum were detected using ELISA; Western blotting was used to detect the differential protein expressions in the airway smooth muscles between the two groups. The airway smooth muscle cells were isolated from the mice in the acupuncture group and treated with a TGF- β1 inhibitor (LY2157299), and the relative expressions of type-Ⅰ and Smads proteins were detected using Western blotting.

RESULTS

The mice in the model showed obvious tracheal fistula with airway pathologies including lumen narrowing, bronchial mucosa thickening, dissociation of the epithelial cells, and thickening of the alveolar septum and airway smooth muscles. These pathological changes were obviously milder in the acupuncture group. The asthmatic mice exhibited significantly increased lung resistance in positive correlation with Mch concentration. Serum TGF-β1 level was significantly elevated in asthmatic mice (P &lt; 0.05); TGF-β1 levels in the serum and BALF were significantly lower in the acupuncture group than in the model group (P &lt; 0.05). In the model group, the expressions of α-SMA, TGF-β1 and Smads in the airway smooth muscles were significantly higher than those in the other two groups (both P &lt; 0.05). In cultured airway smooth muscle cells, the expressions of type-Ⅰ and Smads were significantly higher in cells treated with LY2157299 than in the control cells (P&gt;0.05).

CONCLUSIONS

Acupuncture can inhibit airway remodeling by inhibiting the expression of airway TGF-β1 and down-regulating the expression of Smads and α-SMA to reduce airway inflammatory response. Airway expressions of type-Ⅰ and Smads proteins remain high after inhibiting TGF-β1. Acupuncture may control asthma progression through the TGF-β1/Smads pathway.

Revisiting asthma therapeutics: focus on WNT signal transduction

Asthma is a complex disease of the airways that develops as a consequence of both genetic and environmental factors. This interaction has highlighted genes important in early life, particularly those that control lung development, such as the Wingless/Integrase-1 (WNT) signalling pathway. Although aberrant WNT signalling is involved with an array of human conditions, it has received little attention within the context of asthma. Yet it is highly relevant, driving events involved with inflammation, airway remodelling, and airway hyper-responsiveness (AHR). In this review, we revisit asthma therapeutics by examining whether WNT signalling is a valid therapeutic target for asthma.

Spectrum of T-lymphocyte activities regulating allergic lung inflammation

Despite advances in the treatment of asthma, optimization of symptom control remains an unmet need in many patients. These patients, labeled severe asthma, are responsible for a substantial fraction of the disease burden. In these patients, research is needed to define the cellular and molecular pathways contributing to disease which in large part are refractory to corticosteroid treatment. The causes of steroid-resistant asthma are multifactorial and result from complex interactions of genetics, environmental factors, and innate and adaptive immunity. Adaptive immunity, addressed here, integrates the activities of distinct T-cell subsets and by definition is dynamic and responsive to an ever-changing environment and the influences of epigenetic modifications. These T-cell subsets exhibit different susceptibilities to the actions of corticosteroids and, in some, corticosteroids enhance their functional activation. Moreover, these subsets are not fixed in lineage differentiation but can undergo transcriptional reprogramming in a bidirectional manner between protective and pathogenic effector states. Together, these factors contribute to asthma heterogeneity between patients but also in the same patient at different stages of their disease. Only by carefully defining mechanistic pathways, delineating their sensitivity to corticosteroids, and determining the balance between regulatory and effector pathways will precision medicine become a reality with selective and effective application of targeted therapies.

Immunohistology and remodeling in fatal pediatric and adolescent asthma

Background

Thickening of reticular basement membrane, increased airway smooth muscle mass and eosinophilic inflammation are found in adult fatal asthma. At the present study the histopathology of fatal paediatric and adolescent asthma is evaluated.

Methods

Post-mortem lung autopsies from 12 fatal asthma cases and 8 non-asthmatic control subjects were examined. Thickness of reticular basement membrane (RBM) and percentage of airway smooth muscle (ASM%) mass area were measured and inflammatory cells were counted. Patient records were reviewed for clinical history.

Results

The age range of the cases was from 0.9 to 19.5 years, eight were males and five had received inhaled corticosteroids. Thickened RBM was detected in majority of the cases without any correlation to treatment delay, age at onset of symptoms or diagnosis. In the large airways ASM was clearly increased in one third of the cases whereas the median ASM% did not differ from that in healthy controls (14.0% vs. 14.0%). In small airways no increase of ASM was found, instead mucous plugs were seen in fatal asthma. The number of eosinophils, plasmacytoid dendritic cells, macrophages, and B-cells were significantly increased in fatal asthma cases compared with controls and the two latter correlated with the length of the fatal exacerbation.

Conclusions

The findings highlight the strong presence of eosinophils and mucous plugs even in small airways in children and adolescents with fatal asthma. Thickened RBM was obvious in majority of the patients. Contrary to our hypothesis, increased ASM% was detected in only one third of the patients.

Japanese guidelines for childhood asthma 2017

The Japanese Guideline for the Diagnosis and Treatment of Allergic Diseases 2017 (JAGL 2017) includes a minor revision of the Japanese Pediatric Guideline for the Treatment and Management of Asthma 2012 (JPGL 2012) by the Japanese Society of Pediatric Allergy and Clinical Immunology. The section on child asthma in JAGL 2017 provides information on how to diagnose asthma between infancy and adolescence (0-15 years of age). It makes recommendations for best practices in the management of childhood asthma, including management of acute exacerbations and non-pharmacological and pharmacological management. This guideline will be of interest to non-specialist physicians involved in the care of children with asthma. JAGL differs from the Global Initiative for Asthma Guideline in that JAGL emphasizes diagnosis and early intervention of children with asthma at <2 years or 2-5 years of age. The first choice of treatment depends on the severity and frequency of symptoms. Pharmacological management, including step-up or step-down of drugs used for long-term management based on the status of asthma control levels, is easy to understand; thus, this guideline is suitable for the routine medical care of children with asthma. JAGL also recommends using a control test in children, so that the physician aims for complete control by avoiding exacerbating factors and appropriately using anti-inflammatory drugs (for example, inhaled corticosteroids and leukotriene receptor antagonists).

Impacts of allergic airway inflammation on lung pathology in a mouse model of influenza A virus infection

Influenza A virus is the respiratory pathogen responsible for influenza. Infection by the 2009 pandemic influenza A (H1N1) virus caused severe lower airway inflammation and pneumonia. Asthma is a chronic inflammatory disorder of the airways that affects the entire brachial tree, and was one of the commonest underlying medical conditions among patients hospitalized with the 2009 pandemic influenza virus infection. Although respiratory virus infections are the major causes of asthma exacerbation, the mechanism by which influenza exacerbates asthma is poorly understood. Animal models of disease comorbidity are crucial to understanding host-pathogen interactions and elucidating complex pathologies. Existing murine models of influenza virus infection in asthmatics show that asthmatic mice are highly resistant to influenza virus infection, which contradicts clinical observations in humans. Here, we developed a murine model of influenza virus/asthma comorbidity using NC/Nga mice, which are highly sensitive to allergic reactions such as atopic dermatitis and allergic airway inflammation. This model was then used to examine the impact of allergic airway inflammation on lung pathology in the 2009 pandemic influenza virus infected mice. The results showed that induction of acute allergic airway inflammation in pre-existing influenza virus infection had additive effects on exacerbation of lung pathology, which mirrors findings in human epidemiological studies. In contrast, pre-existing allergic airway inflammation protected from subsequent influenza virus infection, which was compatible with those of previous murine models of influenza virus infection in asthmatic mice. These variable outcomes of this murine model indicate that the temporal relation between allergic airway inflammation and influenza virus infection might play a critical role in asthma and influenza comorbidity. Thus, this murine model will further our understanding of how influenza virus infection affects an asthmatic host and may aid the development of strategies to improve treatments and outcomes for asthmatics harboring influenza virus infection.

Epithelial and endothelial cell plasticity in chronic obstructive pulmonary disease (COPD)

Chronic Obstructive Pulmonary Disease (COPD) is mainly caused by smoking and presents with shortness of breath that is progressive and irreversible. It is a worldwide health problem and the fourth most common cause of chronic disability and mortality (even in developed countries). It is a complex disease involving both the airway and lung parenchyma. Small-airway fibrosis is the main contributor to physiological airway dysfunction in COPD. One potential mechanism contributing to small-airway fibrosis is epithelial mesenchymal transition (EMT). When associated with angiogenesis (EMT-type-3), EMT may well also be linked to the development of airway epithelial cancer, which is closely associated with COPD and predominantly observed in large airways. Vascular remodeling has also been widely reported in smokers and patients with COPD but the mechanisms behind it are poorly understood. It is quite possible that the process of endothelial to mesenchymal transition (EndMT) is also active in COPD lungs, in addition to EMT. Understanding these pathological mechanisms will greatly enhance our knowledge of the immunopathology of smoking-related lung disease. Only by understanding these processes can new therapies be developed.

Mechanisms Mediating Pediatric Severe Asthma and Potential Novel Therapies

Although a rare disease, severe therapy-resistant asthma in children is a cause of significant morbidity and results in utilization of approximately 50% of health-care resources for asthma. Improving control for children with severe asthma is, therefore, an urgent unmet clinical need. As a group, children with severe asthma have severe and multiple allergies, steroid resistant airway eosinophilia, and significant structural changes of the airway wall (airway remodeling). Omalizumab is currently the only add-on therapy that is licensed for use in children with severe asthma. However, limitations of its use include ineligibility for approximately one-third of patients because of serum IgE levels outside the recommended range and lack of clinical efficacy in a further one-third. Pediatric severe asthma is thus markedly heterogeneous, but our current understanding of the different mechanisms underpinning various phenotypes is very limited. We know that there are distinctions between the factors that drive pediatric and adult disease since pediatric disease develops in the context of a maturing immune system and during lung growth and development. This review summarizes the current data that give insight into the pathophysiology of pediatric severe asthma and will highlight potential targets for novel therapies. It is apparent that in order to identify novel treatments for pediatric severe asthma, the challenge of undertaking mechanistic studies using age appropriate experimental models and airway samples from children needs to be accepted to allow a targeted approach of personalized medicine to be achieved.

Selective targeting of CREB-binding protein/β-catenin inhibits growth of and extracellular matrix remodelling by airway smooth muscle

BACKGROUND AND PURPOSE

Asthma is a heterogeneous chronic inflammatory disease, characterized by the development of structural changes (airway remodelling). β-catenin, a transcriptional co-activator, is fundamentally involved in airway smooth muscle growth and may be a potential target in the treatment of airway smooth muscle remodelling.

EXPERIMENTAL APPROACH

We assessed the ability of small-molecule compounds that selectively target β-catenin breakdown or its interactions with transcriptional co-activators to inhibit airway smooth muscle remodelling in vitro and in vivo.

KEY RESULTS

ICG-001, a small-molecule compound that inhibits the β-catenin/CREB-binding protein (CBP) interaction, strongly and dose-dependently inhibited serum-induced smooth muscle growth and TGFβ1-induced production of extracellular matrix components in vitro. Inhibition of β-catenin/p300 interactions using IQ-1 or inhibition of tankyrase 1/2 using XAV-939 had considerably less effect. In a mouse model of allergic asthma, β-catenin expression in the smooth muscle layer was found to be unaltered in control versus ovalbumin-treated animals, a pattern that was found to be similar in smooth muscle within biopsies taken from asthmatic and non-asthmatic donors. However, β-catenin target gene expression was highly increased in response to ovalbumin; this effect was prevented by topical treatment with ICG-001. Interestingly, ICG-001 dose-dependently reduced airway smooth thickness after repeated ovalbumin challenge, but had no effect on the deposition of collagen around the airways, mucus secretion or eosinophil infiltration.

CONCLUSIONS AND IMPLICATIONS

Together, our findings highlight the importance of β-catenin/CBP signalling in the airways and suggest ICG-001 may be a new therapeutic approach to treat airway smooth muscle remodelling in asthma.

Airway Remodeling in Preschool Children with Severe Recurrent Wheeze

RATIONALE

Airway wall structure in preschoolers with severe recurrent wheeze is poorly described.

OBJECTIVES

To describe airway wall structure and inflammation in preschoolers with severe recurrent wheeze.

METHODS

Flexible bronchoscopy was performed in two groups of preschoolers with severe recurrent wheeze: group 1, less than or equal to 36 months (n = 20); group 2, 36-59 months (n = 29). We assessed airway inflammation, reticular basement membrane (RBM) thickness, airway smooth muscle (ASM), mucus gland area, vascularity, and epithelial integrity. Comparisons were then made with biopsies from 21 previously described schoolchildren with severe asthma (group 3, 5-11.2 yr).

MEASUREMENTS AND MAIN RESULTS

RBM thickness was lower in group 1 than in group 2 (3.3 vs. 3.9 μm; P = 0.02), was correlated with age (P < 0.01; ρ = 0.62), and was higher in schoolchildren than in preschoolers (6.8 vs. 3.8 μm; P < 0.01). ASM area was lower in preschoolers than in schoolchildren (9.8% vs. 16.5%; P < 0.01). Vascularity was higher in group 1 than in group 2 (P = 0.02) and group 3 (P < 0.05). Mucus gland area was higher in preschoolers than in schoolchildren (16.4% vs. 4.6%; P < 0.01). Inflammatory cell counts in biopsies were not correlated with airway wall structure. ASM area was higher in preschoolers with atopy than without atopy (13.1% vs. 7.7%; P = 0.01). Airway morphometrics and inflammation were similar in viral and multiple-trigger wheezers.

CONCLUSIONS

In preschoolers with severe recurrent wheeze, markers of remodeling and inflammation are unrelated, and atopy is associated with ASM. In the absence of control subjects, we cannot determine whether differences observed in RBM thickness and vascularity result from disease or normal age-related development.

Update on the current methods for the diagnosis and treatment of severe childhood asthma

The level of asthma control is the key outcome towards which asthma management is evaluated. The majority of children with asthma can obtain adequate control of symptoms through avoidance of triggering factors and/or with the help of low to moderate doses of current available medications. However, there is still a group of children with poor symptom control despite intensive treatment. The current review will provide an overview of a standardized approach to characterize this heterogeneous group of severely sick children. Factors that attenuate the effect of the prescribed treatment and make asthma difficult to treat are discussed. In addition, the usefulness of current methods of assessing asthma severity, pulmonary function, allergy and airway inflammation is also described. Finally, an overview of therapeutic options for children with severe asthma is provided.

Should lung biopsies be performed in patients with severe asthma?

Asthma, and severe asthma, in particular, is increasingly recognised as a heterogeneous disease. Identifying these different phenotypes of asthma and assigning patients to phenotype-specific treatments is one of the current conundrums in respiratory medicine. Any diagnostic procedure in severe asthma (or any disease) should have two aims: 1) better understanding or identifying the diagnosis, and 2) providing information on the heterogeneity of asthma phenotypes to guide therapy with the objective of improving outcomes. Lung biopsies can target the large and small airways as well as the lung parenchyma. All compartments are affected in severe asthma; however, knowledge on the distal lung is limited. At this point, it remains uncertain whether lung specimens routinely add diagnostic information that is unable to be obtained otherwise. Indeed, whether a lung biopsy is indicated in the workup of a patient with severe asthma remains an individual decision. It is hoped this review will support rational decision-making and provide a detailed synopsis of the varied histopathological features seen in biopsies of patients with a diagnosis of severe asthma. Due to limited data on this topic this review is primarily based on opinion with recommendations arising primarily from the personal experience of the authors.

Japanese Guideline for Childhood Asthma 2014

The Japanese Guideline for the Diagnosis and Treatment of Allergic Diseases 2013 (JAGL 2013) describes childhood asthma after the Japanese Pediatric Guideline for the Treatment and Management of Asthma 2012 (JPGL 2012) by the Japanese Society of Pediatric Allergy and Clinical Immunology. JAGL 2013 provides information on diagnosis by age group from infancy to puberty (0-15 years of age), treatment for acute exacerbations, long-term management by anti-inflammatory drugs, daily life guidance, and patient education to allow non-specialist physicians to refer to this guideline for routine medical treatment. JAGL differs from the Global Initiative for Asthma Guideline (GINA) in that JAGL emphasizes early diagnosis and intervention at <2 years and 2-5 years of age. A management method, including step-up or step-down of long-term management drugs based on the status of asthma control levels, as in JAGL, is easy to understand, and thus the Guideline is suitable as a frame of reference for routine medical treatment. JAGL has also introduced treatment and management using a control test on children, recommending that the physician aim at complete control by avoiding exacerbation factors and by appropriate use of anti-inflammatory drugs.

Bronchoconstriction and airway biology: potential impact and therapeutic opportunities

Recent work has demonstrated that mechanical forces occurring in the airway as a consequence of bronchoconstriction are sufficient to not only induce symptoms but also influence airway biology. Animal and human in vitro and in vivo work demonstrates that the airways are structurally and functionally altered by mechanical stress induced by bronchoconstriction. Compression of the airway epithelium and mechanosensing by the airway smooth muscle trigger the activation and release of growth factors, causing cell proliferation, extracellular matrix protein accumulation, and goblet cell differentiation. These effects of bronchoconstriction are of major importance to asthma pathophysiology and appear sufficient to induce remodeling independent of the inflammatory response. We review these findings in detail and discuss previous studies in light of this new evidence regarding the influence of mechanical forces in the airways. Furthermore, we highlight potential impacts of therapies influencing mechanical forces on airway structure and function in asthma.

Pathobiology of severe asthma

Severe asthma (SA) afflicts a heterogeneous group of asthma patients who exhibit poor responses to traditional asthma medications. SA patients likely represent 5-10% of all asthma patients; however, they have a higher economic burden when compared with milder asthmatics. Considerable research has been performed on pathological pathways and structural changes associated with SA. Although limitations of the pathological approaches, ranging from sampling, to quantitative assessments, to heterogeneity of disease, have prevented a more definitive understanding of the underlying pathobiology, studies linking pathology to molecular markers to targeted therapies are beginning to solidify the identification of select molecular phenotypes. This review addresses the pathobiology of SA and discusses the current limitations of studies, the inflammatory cells and pathways linked to emerging phenotypes, and the structural and remodeling changes associated with severe disease. In all cases, an effort is made to link pathological findings to specific clinical/molecular phenotypes.

Lung function, airway remodeling, and inflammation in infants: outcome at 8 years

BACKGROUND

Associations between early deficits of lung function, infant airway disease, and outcome at school age in symptomatic infants are still unclear.

OBJECTIVE

To report follow-up data on a unique cohort of children investigated invasively in infancy to determine predictive value of airway disease for school-aged respiratory outcomes.

METHODS

Fifty-three infants previously studied using bronchoscopy and airway conductance were approached at 8 years of age. Symptoms, lung volumes, and airway responsiveness were reassessed. Data on lifetime purchase of asthma medication were obtained. Lung function was compared with that of 63 healthy nonasthmatic children.

RESULTS

Forty-seven children were reevaluated. Physician-diagnosed asthma was present in 39 children (83%). Twenty-five children (53%) had current and 14 children (30%) had past asthma. No pathologic feature in infancy correlated with any outcome parameter. As expected, study children had significantly reduced lung function and increased airway responsiveness compared with healthy controls, and very early symptoms were risk factors for reduced lung function. Current asthma was associated with reduced infant lung function and parental asthma. Reduced lung function in infancy was associated with purchase of inhaled corticosteroids when 6 to 8 and 0 to 8 years of age.

CONCLUSION

The lack of predictive value of any pathologic measure in infancy, reported here for the first time to our knowledge, demonstrates that pathologic processes determining the inception of asthma, which are as yet undescribed, are different from the eosinophilic inflammation associated with ongoing disease.

Th2-type cytokine-induced mucus metaplasia decreases susceptibility of human bronchial epithelium to rhinovirus infection

Human rhinoviruses (RVs) are a major cause of exacerbations in asthma and other chronic airway diseases. A characteristic feature of asthmatic epithelium is goblet cell metaplasia and mucus hypersecretion. Bronchial epithelium is also an important source of lipid mediators, including pro- and antiinflammatory eicosanoids. By using air-liquid interface cultures of airway epithelium from patients with asthma and nonasthmatic control subjects, we compared RV16 replication-induced changes in mRNA expression of asthma candidate genes and eicosanoid production in the epithelium with or without IL-13-induced mucus metaplasia. Mucus metaplastic epithelium was characterized by a 20-fold less effective replication of RV16 and blunted changes in gene expression; this effect was seen to the same extent in patients with asthma and control subjects. We identified ciliary cells as the main target for RV16 by immunofluorescence imaging and demonstrated that the numbers of ciliary cells decreased in RV16-infected epithelium. RV16 infection of mucociliary epithelium resulted in overexpression of genes associated with bronchial remodeling (e.g., MUC5AC, FGF2, and HBEGF), induction of cyclooxygenase-2, and increased secretion of prostaglandins. These responses were similar in both studied groups. These data indicate that structural changes associated with mucus metaplasia renders airway epithelium less susceptible to RV infection. Thus, exacerbations of the lung disease caused by RV may result from severe impairment in mucociliary clearance or activation of immune defense rather than from preferential infection of mucus metaplastic epithelium. Repeated rhinoviral infections of compromised epithelium may contribute to the remodeling of the airways.

Airway collagen and elastic fiber content correlates with lung function in equine heaves

The consequences on lung function and inflammation of alterations in the extracellular matrix affecting the peripheral airway wall in asthma are largely unknown. We hypothesized that remodeling of collagen and elastic fibers in the peripheral airway wall leads to airway obstruction and contributes to neutrophilic airway inflammation. Animals used were six heaves-affected horses and five controls. Large peripheral lung biopsies were obtained from horses with heaves in clinical remission (Baseline) and during disease exacerbation and from age-matched controls. The area of collagen and elastic fiber content in the lamina propria was measured by histological staining techniques and corrected for airway size. Collagen type 1 and type 3 content was further assessed from additional horses after postmortem lung samples by immunohistochemistry. The collagen breakdown products proline-glycine-proline (PGP) and N-acetylated-PGP (N-α-PGP) were also measured in bronchoalveolar lavage fluids (BALF) by mass spectrometry. Compared with controls, heaves-affected horses had an increase in collagen (P = 0.05) and elastic fiber contents (P = 0.04) at baseline. Collagen types 1 and 3 content was also significantly increased in diseased horses (P = 0.015) when both collagen types were combined. No further change in collagen content was observed after a 30-day antigenic challenge. Airway collagen at baseline was positively correlated with pulmonary resistance in asthmatic horses (r(2) = 0.78, P = 0.03) and elastic fiber content was positively associated with pulmonary elastance in controls (r(2) = 0.95, P = 0.02). No difference between groups was appreciated in PGP and N-α-PGP peptides in BALF. Increased airway wall collagen and elastic fiber content may contribute to residual obstruction in the asthmatic airways.

Epithelial injury and repair in airways diseases

Asthma is a common chronic disease characterized by variable respiratory distress with underlying airway inflammation and airflow obstruction. The incidence of asthma has risen inexorably over the past 50 years, suggesting that environmental factors are important in its etiology. All inhaled environmental stimuli interact with the lung at the respiratory epithelium, and it is a testament to the effectiveness of the airway innate defenses that the majority of inhaled substances are cleared without the need to elicit an inflammatory response. However, once this barrier is breached, effective communication with immune and inflammatory cells is required to protect the internal milieu of the lung. In asthma, the respiratory epithelium is known to be structurally and functionally abnormal. Structurally, the epithelium shows evidence of damage and has more mucus-producing cells than normal airways. Functionally, the airway epithelial barrier can be more permeable and more sensitive to oxidants and show a deficient innate immune response to respiratory virus infection compared with that in normal individuals. The potential of a susceptible epithelium and the underlying mesenchyme to create a microenvironment that enables deviation of immune and inflammatory responses to external stimuli may be crucial in the development and progression of asthma. In this review, we consider three important groups of environmental stimuli on the epithelium in asthma: oxidants, such as environmental pollution and acetaminophen; viruses, including rhinovirus; and agents that cause barrier disruption, such as house dust mite allergens. The pathology associated with each stimulus is considered, and potential future treatments arising from research on their effects are presented.

Remodeling, inflammation and airway responsiveness in early childhood asthma

PURPOSE OF REVIEW

Remodeling and inflammation together with airway hyperresponsiveness are essential components of asthma but their role in development of the disease is still obscure.

RECENT FINDINGS

Recent data imply that remodeling can occur early in childhood, not necessarily subsequent to but rather, in parallel with inflammation. The assumption of thickening of the reticular basement membrane being a prerequirement for chronic asthma is questioned but development of airway responsiveness is a significant factor. Airway responsiveness is at least partially linked to bronchial inflammation but there are several other genes and pathways regulating airway responsiveness. Increased airway smooth muscle in early childhood is associated with later development of asthma and may be one link between inflammation and airway responsiveness. Novel findings on genetic variation in genes regulating lung growth and remodeling in early childhood shed light on the pathophysiological mechanisms leading to chronic asthma.

SUMMARY

Even young children with chronic asthma have detectable elements of airway remodeling, inflammation and increased airway responsiveness, which all contribute to impaired lung function.

Phenotypes and endotypes of severe asthma in children

Severe childhood asthma is a complicated and heterogeneous disorder with distinct phenotypes. Children with severe asthma have more persistent symptoms despite receiving treatment, more atopy, greater airway obstruction, and more air trapping than those with mild-to-moderate asthma. They also have higher morbidity and substantial airflow limitations that persist throughout adulthood. Identification of the phenotype clusters and endotypes of severe asthma can allow further modulation of the natural history of severe asthma and may provide the pathophysiologic rationale for appropriate management strategies.

Association between eosinophilic airway inflammation and persistent airflow limitation

OBJECTIVE

We aimed to evaluate the association between eosinophilic inflammation in induced sputum and pulmonary function and persistent airflow limitation in children.

METHODS

A total of 92 asthmatic children and 72 controls were enrolled in this study. Eosinophil count (%) and eosinophil cationic protein (ECP) levels were measured in induced sputum. We performed spirometry and a methacholine challenge test, and measured total eosinophil count, total serum IgE, and serum ECP in all subjects.

RESULTS

Asthmatic children had significantly higher levels of sputum eosinophils (9% vs. 0%; P < 0.001) and sputum ECP (2.3 ± 0.7 vs. 1.6 ± 0.6 log µg/L, p < .001) than controls. Sputum ECP levels showed a significant negative correlation with post-bronchodilator (post-BD) FEV(1) (r = -0.307; p = .001) and post-BD FEV(1)/FVC (r = -0.286; p = .002), whereas sputum eosinophils showed no correlation with post-BD FEV(1) and post-BD FEV(1)/FVC. However, no significant differences in sputum ECP and sputum eosinophil counts were observed in asthmatic children with and without persistent airflow limitation.

CONCLUSIONS

Our findings suggest that sputum eosinophilic inflammation, especially ECP, is associated with pulmonary function and persistent airflow limitation, which is manifested by low post-BD FEV(1)/FVC.

Functional phenotype of airway myocytes from asthmatic airways

In asthma, the airway smooth muscle (ASM) cell plays a central role in disease pathogenesis through cellular changes which may impact on its microenvironment and alter ASM response and function. The answer to the long debated question of what makes a 'healthy' ASM cell become 'asthmatic' still remains speculative. What is known of an 'asthmatic' ASM cell, is its ability to contribute to the hallmarks of asthma such as bronchoconstriction (contractile phenotype), inflammation (synthetic phenotype) and ASM hyperplasia (proliferative phenotype). The phenotype of healthy or diseased ASM cells or tissue for the most part is determined by expression of key phenotypic markers. ASM is commonly accepted to have different phenotypes: the contractile (differentiated) state versus the synthetic (dedifferentiated) state (with the capacity to synthesize mediators, proliferate and migrate). There is now accumulating evidence that the synthetic functions of ASM in culture derived from asthmatic and non-asthmatic donors differ. Some of these differences include an altered profile and increased production of extracellular matrix proteins, pro-inflammatory mediators and adhesion receptors, collectively suggesting that ASM cells from asthmatic subjects have the capacity to alter their environment, actively participate in repair processes and functionally respond to changes in their microenvironment.

Corticosteroids: still at the frontline in asthma treatment?

Inhaled corticosteroids (ICS) have led to improved asthma control and reduced asthma mortality in the Western world. ICS are effective in combating T-helper type 2-driven inflammation featuring mast cell and eosinophilic airway infiltration. Their effect on innate immunity-driven neutrophilic inflammation is poor and their ability to prevent airway remodeling and accelerated lung decline is controversial. Although ICS remain pivotal drugs in asthma management, research is needed to find drugs complementary to the combination ICS/long-acting β2-agonist in refractory asthma and perhaps a new class of drugs as a first-line treatment in mild to moderate noneosinophilic asthma.

Exhaled breath 8-isoprostane as a marker of asthma severity

INTRODUCTION

Oxidative stress is a non-specific feature of airway inflammation in asthmatics. 8-Isoprostane (8-IP), a prostaglandin-F(2α) isomer, is a relatively new marker of oxidative stress and may be measured in exhaled breath condensate (EBC) of patients with asthma. This research study aimed to evaluate the usefulness of EBC 8-IP as a marker of severity and control of severe adult asthma.

MATERIAL AND METHODS

Twenty-seven severe, never-smoking asthmatics were studied. According to positive or negative reversibility testing, this group was subdivided into reversible and irreversible asthma groups. All participants were observed for 8 weeks during which they completed daily diary observations including day and night symptoms, number of awakenings, peak expiratory flow (PEF) variability, daily rescue medication usage and oral steroids consumption. They attended the clinic 3 times and on these occasions spirometry assessments, EBC collection and asthma control tests (ACT) were done. Two control groups were included: 11 healthy never-smokers and 16 newly diagnosed and never-treated, non-smoking mild asthmatics.

RESULTS

There were no statistically significant differences between severe asthma and healthy control or never-treated asthma groups in concentrations of EBC 8-IP (median and interquartile range: 4.67; 2.50-27.92 vs. 6.93; 2.5-12.98 vs. 3.80; 2.50-10.73, respectively). No correlations were found between EBC 8-IP and asthma control parameters, such as ACT results, night and day symptoms, consumption of rescue medication, percentage of days free of oral steroids, PEF diurnal variation, lung function test results, forced expiratory volume in the 1 s reversibility, and markers of systemic inflammation.

CONCLUSIONS

Our study results suggest that EBC 8-IP measurements are not useful for asthma monitoring.

Asthma and COPD - The C/EBP Connection

Asthma and chronic obstructive pulmonary disease (COPD) are the two most prominent chronic inflammatory lung diseases with increasing prevalence. Both diseases are associated with mild or severe remodeling of the airways. In this review, we postulate that the pathologies of asthma and COPD may result from inadequate responses and/or a deregulated balance of a group of cell differentiation regulating factors, the CCAAT/Enhancer Binding Proteins (C/EBPs). In addition, we will argue that the exposure to environmental factors, such as house dust mite and cigarette smoke, changes the response of C/EBPs and are different in diseased cells. These novel insights may lead to a better understanding of the etiology of the diseases and may provide new aspects for therapies.

Mechanisms of remodeling in asthmatic airways

Asthma is a chronic inflammatory airway disorder characterized by airway hyperresponsiveness and reversible airflow obstruction. Subgroups of asthma patients develop airflow obstruction that is irreversible or only partially reversible and experience an accelerated rate of lung function decline. The structural changes in the airways of these patients are referred to as airway remodeling. All elements of the airway wall are involved, and remodeled airway wall thickness is substantially increased compared to normal control airways. Airway remodeling is thought to contribute to the subphenotypes of irreversible airflow obstruction and airway hyperresponsiveness, and it has been associated with increased disease severity. Reversal of remodeling is therefore of paramount therapeutic importance, and mechanisms responsible for airway remodeling are feasible therapeutic targets for asthma treatment. This paper will focus on our current understanding of the mechanisms of airway remodeling in asthma and potential targets for future intervention.

Protease-activated receptor 2-dependent fluid secretion from airway submucosal glands by house dust mite extract

BACKGROUND

The submucosal gland (SMG) is important in the control of airway surface fluid. Protease-activated receptor (PAR) 2 contributes to the pathophysiology of allergies in response to nonspecific allergens bearing proteases and anion secretion. House dust mites (HDMs) have abundant proteases that can activate PAR2, but little is known about the direct effect of HDM on SMG secretion.

OBJECTIVE

The aim of this study was to investigate the effect of HDMs on glandular secretion and its mechanism in allergic patients, patients with chronic rhinosinusitis (CRS), or both.

METHODS

Inferior nasal turbinates were harvested from 55 patients and classified into 4 groups (the control, allergic rhinitis [AR], CRS, and AR+CRS groups). A microscope attached to a digital camera was used to quantify mucus bubbles from individual SMGs while stimulated with HDM extract, PAR2-activating peptide, and carbachol. PAR2 expression in the SMG was determined by means of immunostaining with anti-PAR2 mAb.

RESULTS

HDM induced a significantly higher secretion rate and number of responding glands in the AR and AR+CRS groups than in the control group. Interestingly, patients in the CRS group, who had no HDM-specific IgE antibody, showed a higher response than the control group, and its response was suppressed by a PAR2-selective antagonist. The responses to PAR2-activating peptide were similar to those to HDM, and their secretion rates positively correlated with HDM responses. PAR2 was highly expressed in all 3 disease groups with immunostaining.

CONCLUSIONS

HDM allergens can induce glandular secretion in patients with AR, CRS, or both, and PAR2 represents a possible mechanism for nonspecific hyperreactivity in inflammatory airway diseases.

Function and mechanisms of TSLP/TSLPR complex in asthma and COPD

Thymic stromal lymphopoietin (TSLP) is a key pro-allergic cytokine that has recently been linked to chronic airway diseases, such as asthma and chronic obstructive pulmonary disease (COPD). High levels of TSLP were detected in bronchial mucosa of asthma and COPD patients suggesting TSLP's biological role beyond a signature 'Th2-favoring' or 'pro-allergic cytokine'. Besides inflammatory cells, airway structural cells produce and are targets of TSLP suggesting a potential autocrine loop that may have a profound effect on local inflammatory response and airway remodelling. This review sums up diverse mechanisms that mediate TSLP/TSLP receptor-signalling network in chronic airway diseases.

Hypertrophic airway smooth muscle mass correlates with increased airway responsiveness in a murine model of asthma

The increase of airway smooth muscle (ASM) mass in asthma results from hypertrophic and hyperplastic stimuli, and leads to an increase in cellular contractile proteins. However, little evidence correlates the relative contributions of hypertrophic and hyperplastic muscle with functional effects on airway resistance. We performed a ventilator-based assessment of respiratory mechanics and responsiveness to methacholine in a murine model of acute (3-week) ovalbumin (OVA)-induced airway inflammation, compared with a chronic (12-week) model. We correlated functional changes in airways Newtonian resistance (RN), peripheral tissue damping (G), and elastance (H) with the relative contributions of proliferation, hypertrophy, and apoptosis to increased ASM mass. Immunohistochemical analyses of treated (OVA-sensitized and OVA-challenged; OVA/OVA) and control (OVA-sensitized and saline-challenged; OVA/PBS) murine lungs showed an increase in ASM area in chronic, but not acute, OVA/OVA-treated mice that correlated positively with increased airway resistance to methacholine. Acute OVA/OVA-treated ASM exhibited an increase in proliferation with diminished apoptosis, which resolved in the chronic OVA/OVA model. Chronic OVA/OVA-treated ASM exhibited hypertrophy. Distinct temporal differences exist in the response of murine airways to antigenic challenge. We report that ASM proliferation and diminished apoptosis occur during the acute phase, followed by the development of smooth muscle hypertrophy and an increased muscle mass with chronic challenge, that correlate strongly with increased airway Newtonian resistance. The identification of a functionally relevant hypertrophic bronchial muscle mass highlights the possibility of regulating airway muscle hypertrophy as a novel therapeutic target in asthma.

Is there a regulatory role of immunoglobulins on tissue forming cells relevant in chronic inflammatory lung diseases?

Epithelial cells, fibroblasts and smooth muscle cells together form and give structure to the airway wall. These three tissue forming cell types are structure giving elements and participate in the immune response to inhaled particles including allergens and dust. All three cell types actively contribute to the pathogenesis of chronic inflammatory lung diseases such as asthma and chronic obstructive pulmonary disease (COPD). Tissue forming cells respond directly to allergens through activated immunoglobulins which then bind to their corresponding cell surface receptors. It was only recently reported that allergens and particles traffic through epithelial cells without modification and bind to the immunoglobulin receptors on the surface of sub-epithelial mesenchymal cells. In consequence, these cells secrete pro-inflammatory cytokines, thereby extending the local inflammation. Furthermore, activation of the immunoglobulin receptors can induce proliferation and tissue remodeling of the tissue forming cells. New studies using anti-IgE antibody therapy indicate that the inhibition of immunoglobulins reduces the response of tissue forming cells. The unmeasured questions are: (i) why do tissue forming cells express immunoglobulin receptors and (ii) do tissue forming cells process immunoglobulin receptor bound particles? The focus of this review is to provide an overview of the expression and function of various immunoglobulin receptors.

Extracellular 14-3-3 from human lung epithelial cells enhances MMP-1 expression

Airway remodelling in asthma involves various mediators modulating the production/breakdown of collagen by lung fibroblasts. Matrix metalloproteinase-1 (MMP-1) plays an important role in collagen breakdown. We recently showed that epithelial cell-derived extracellular form of 14-3-3σ is an important inducer of MMP-1 expression in skin fibroblasts. Thus, we hypothesized that 14-3-3 proteins are important regulators of MMP-1 expression in the respiratory airway. We examined the presence of extracellular 14-3-3 proteins in conditioned media obtained from primary lung epithelial cells, A549 and HS24 cells, and their effect on MMP-1 expression by lung fibroblasts (IMR-90). In addition, we evaluated IMR-90 response to 14-3-3 proteins in the presence of transforming growth factor-β(1) (TGF-β(1)), a cytokine known to decrease MMP-1 expression by fibroblasts. Extracellular 14-3-3α/β, but not -σ, is released by the human-derived lung epithelial cell lines, A549 and HS24. Unlike dermal fibroblasts, IMR-90 cells do not produce MMP-1 in response to 14-3-3σ. Conversely, MMP-1 production was induced following treatment of IMR-90 with recombinant or lung epithelial cell-derived 14-3-3α/β. These findings were also confirmed using primary human bronchial epithelial cells and lung fibroblasts obtained from non-asthmatic patients. The MMP-1-inducing effect of 14-3-3α/β on IMR-90 was not inhibited by TGF-β(1). Lung epithelial cell-derived 14-3-3α/β has a potent MMP-1-inducing effect on airway fibroblasts. Modulation of MMP-1 by 14-3-3α/β, may be important in the alteration of collagenase production associated with airway remodelling in obstructive lung diseases. Our data indicate that 14-3-3 proteins may be potential targets for future therapeutic strategies aimed at modulating tissue remodelling in asthma.