Erin D. Gordon

A protective role for periostin and TGF-β in IgE-mediated allergy and airway hyperresponsiveness

The pathophysiology of asthma involves allergic inflammation and remodelling in the airway and airway hyperresponsiveness (AHR) to cholinergic stimuli, but many details of the specific underlying cellular and molecular mechanisms remain unknown. Periostin is a matricellular protein with roles in tissue repair following injury in both the skin and heart. It has recently been shown to be up‐regulated in the airway epithelium of asthmatics and to increase active TGF‐β. Though one might expect periostin to play a deleterious role in asthma pathogenesis, to date its biological role in the airway is unknown.

Alternative splicing of interleukin-33 and type 2 inflammation in asthma

Significance Type 2 inflammation occurs in a large subgroup of asthmatics and is the target of multiple novel therapies for asthma; however, the mechanisms that drive type 2 inflammation in chronic asthma are poorly understood. In this study, we identify a previously unidentified mechanism of IL-33 activity involving alternative RNA transcript splicing and provide evidence that mast cells and basophils are major cellular targets of IL-33 activity driving type 2 cytokine production in stable asthma. These data advance our understanding of the mechanisms of type 2-high asthma and guide the selection of asthmatics likely to benefit from IL-33 inhibitor therapies. Type 2 inflammation occurs in a large subgroup of asthmatics, and novel cytokine-directed therapies are being developed to treat this population. In mouse models, interleukin-33 (IL-33) activates lung resident innate lymphoid type 2 cells (ILC2s) to initiate airway type 2 inflammation. In human asthma, which is chronic and difficult to model, the role of IL-33 and the target cells responsible for persistent type 2 inflammation remain undefined. Full-length IL-33 is a nuclear protein and may function as an “alarmin” during cell death, a process that is uncommon in chronic stable asthma. We demonstrate a previously unidentified mechanism of IL-33 activity that involves alternative transcript splicing, which may operate in stable asthma. In human airway epithelial cells, alternative splicing of the IL-33 transcript is consistently present, and the deletion of exons 3 and 4 (Δ exon 3,4) confers cytoplasmic localization and facilitates extracellular secretion, while retaining signaling capacity. In nonexacerbating asthmatics, the expression of Δ exon 3,4 is strongly associated with airway type 2 inflammation, whereas full-length IL-33 is not. To further define the extracellular role of IL-33 in stable asthma, we sought to determine the cellular targets of its activity. Comprehensive flow cytometry and RNA sequencing of sputum cells suggest basophils and mast cells, not ILC2s, are the cellular sources of type 2 cytokines in chronic asthma. We conclude that IL-33 isoforms activate basophils and mast cells to drive type 2 inflammation in chronic stable asthma, and novel IL-33 inhibitors will need to block all biologically active isoforms.

Claudin-18 deficiency is associated with airway epithelial barrier dysfunction and asthma

Background: Epithelial barrier dysfunction and increased permeability may contribute to antigen sensitization and disease progression in asthma. Claudin‐18.1 is the only known lung‐specific tight junction protein, but its contribution to airway barrier function or asthma is unclear. Objectives: We sought to test the hypotheses that claudin‐18 is a determinant of airway epithelial barrier function that is downregulated by IL‐13 and that claudin‐18 deficiency results in increased aeroantigen sensitization and airway hyperresponsiveness. Methods: Claudin‐18.1 mRNA levels were measured in airway epithelial brushings from healthy controls and patients with asthma. In patients with asthma, claudin‐18 levels were compared with a three‐gene‐mean marker of TH2 inflammation. Airway epithelial permeability changes due to claudin‐18 deficiency were measured in 16HBE cells and claudin‐18 null mice. The effect of IL‐13 on claudin expression was determined in primary human airway epithelial cells and in mice. Airway hyperresponsiveness and serum IgE levels were compared in claudin‐18 null and wild‐type mice following aspergillus sensitization. Results: Epithelial brushings from patients with asthma (n = 67) had significantly lower claudin‐18 mRNA levels than did those from healthy controls (n = 42). Claudin‐18 levels were lowest among TH2‐high patients with asthma. Loss of claudin‐18 was sufficient to impair epithelial barrier function in 16HBE cells and in mouse airways. IL‐13 decreased claudin‐18 expression in primary human cells and in mice. Claudin‐18 null mice had significantly higher serum IgE levels and increased airway responsiveness following intranasal aspergillus sensitization. Conclusions: These data support the hypothesis that claudin‐18 is an essential contributor to the airway epithelial barrier to aeroantigens. Furthermore, TH2 inflammation suppresses claudin‐18 expression, potentially promoting sensitization and airway hyperresponsiveness.

Management of chronic obstructive pulmonary disease: moving beyond the asthma algorithm.

For many years, chronic obstructive pulmonary disease (COPD) was considered a disease of fixed airflow obstruction for which there was no good treatment. Out of desperation and frustration, health care providers extrapolated from asthma to COPD, and standard asthma therapy was adopted without evidence for efficacy. In recent years, we have gained a better understanding of the pathophysiologic differences between asthma and COPD, and prospective controlled trials have provided a rationale for therapy. Smoking cessation is critically important, both as primary prevention and as an effective way to slow the decrease in lung function in patients with established disease. beta(2)-Adrenergic and anticholinergic agonists improve lung function and relieve symptoms in most patients. Tiotropium improves exercise tolerance and quality of life and reduces exacerbations and hospitalizations. The increase in lung function seen with tiotropium is sustained with continued use over at least 3 to 4 years. Inhaled corticosteroids decrease exacerbations and improve quality of life, and their effect seems greatest in patients with lower lung function and in exacerbation-prone patients. There is no evidence that inhaled corticosteroids alone affect mortality, despite the reduction in exacerbations and increased risk of pneumonia. In some patient populations, inhaled fluticasone, salmeterol, or the combination might slow the rate of loss of lung function. Rather than reflexively using effective asthma therapy in the patient with COPD, current and future therapy for COPD is increasingly evidence based and targeted to specific inflammatory pathways that are important in patients with COPD.

Mucus plugs in patients with asthma linked to eosinophilia and airflow obstruction

BACKGROUND. The link between mucus plugs and airflow obstruction has not been established in chronic severe asthma, and the role of eosinophils and their products in mucus plug formation is unknown. METHODS. In clinical studies, we developed and applied a bronchopulmonary segment–based scoring system to quantify mucus plugs on multidetector computed tomography (MDCT) lung scans from 146 subjects with asthma and 22 controls, and analyzed relationships among mucus plug scores, forced expiratory volume in 1 second (FEV1), and airway eosinophils. Additionally, we used airway mucus gel models to explore whether oxidants generated by eosinophil peroxidase (EPO) oxidize cysteine thiol groups to promote mucus plug formation. RESULTS. Mucus plugs occurred in at least 1 of 20 lung segments in 58% of subjects with asthma and in only 4.5% of controls, and the plugs in subjects with asthma persisted in the same segment for years. A high mucus score (plugs in ≥ 4 segments) occurred in 67% of subjects with asthma with FEV1 of less than 60% of predicted volume, 19% with FEV1 of 60%–80%, and 6% with FEV1 greater than 80% (P < 0.001) and was associated with marked increases in sputum eosinophils and EPO. EPO catalyzed oxidation of thiocyanate and bromide by H2O2 to generate oxidants that crosslink cysteine thiol groups and stiffen thiolated hydrogels. CONCLUSION. Mucus plugs are a plausible mechanism of chronic airflow obstruction in severe asthma, and EPO-generated oxidants may mediate mucus plug formation. We propose an approach for quantifying airway mucus plugging using MDCT lung scans and suggest that treating mucus plugs may improve airflow in chronic severe asthma. TRIAL REGISTRATION. Clinicaltrials.gov NCT01718197, NCT01606826, NCT01750411, NCT01761058, NCT01761630, NCT01759186, NCT01716494, and NCT01760915. FUNDING. NIH grants P01 HL107201, R01 HL080414, U10 HL109146, U10 HL109164, U10 HL109172, U10 HL109086, U10 HL109250, U10 HL109168, U10 HL109257, U10 HL109152, and P01 HL107202 and National Center for Advancing Translational Sciences grants UL1TR0000427, UL1TR000448, and KL2TR000428.

IL1RL1 asthma risk variants regulate airway type 2 inflammation

Genome-wide association studies of asthma have identified genetic variants in the IL1RL1 gene, but the molecular mechanisms conferring risk are unknown. IL1RL1 encodes the ST2 receptor (ST2L) for IL-33 and an inhibitory decoy receptor (sST2). IL-33 promotes type 2 inflammation, which is present in some but not all asthmatics. We find that two single nucleotide polymorphisms (SNPs) in IL1RL1 - rs1420101 and rs11685480 - are strongly associated with plasma sST2 levels, though neither is an expression quantitative trait locus (eQTL) in whole blood. Rather, rs1420101 and rs11685480 mark eQTLs in airway epithelial cells and distal lung parenchyma, respectively. We find that the genetically determined plasma sST2 reservoir, derived from the lung, neutralizes IL-33 activity, and these eQTL SNPs additively increase the risk of airway type 2 inflammation among asthmatics. These risk variants define a population of asthmatics at risk of IL-33-driven type 2 inflammation.

Corticosteroid and Long‐Acting ß‐Agonist Therapy Reduces Epithelial Goblet Cell Metaplasia

Bronchial epithelial goblet cell metaplasia (GCM) with hyperplasia is a prominent feature of asthma, but the effects of treatment with corticosteroids alone or in combination with a long‐acting β2‐adrenergic receptor agonist (LABA) on GCM in the bronchial epithelium are unknown.

Cadherin-26 (CDH26) regulates airway epithelial cell cytoskeletal structure and polarity

Polarization of the airway epithelial cells (AECs) in the airway lumen is critical to the proper function of the mucociliary escalator and maintenance of lung health, but the cellular requirements for polarization of AECs are poorly understood. Using human AECs and cell lines, we demonstrate that cadherin-26 (CDH26) is abundantly expressed in differentiated AECs, localizes to the cell apices near ciliary membranes, and has functional cadherin domains with homotypic binding. We find a unique and non-redundant role for CDH26, previously uncharacterized in AECs, in regulation of cell–cell contact and cell integrity through maintaining cytoskeletal structures. Overexpression of CDH26 in cells with a fibroblastoid phenotype increases contact inhibition and promotes monolayer formation and cortical actin structures. CDH26 expression is also important for localization of planar cell polarity proteins. Knockdown of CDH26 in AECs results in loss of cortical actin and disruption of CRB3 and other proteins associated with apical polarity. Together, our findings uncover previously unrecognized functions for CDH26 in the maintenance of actin cytoskeleton and apicobasal polarity of AECs.