Altered Epithelial Gene Expression in Peripheral Airways of Severe Asthma

Abstract

Management of severe asthma remains a challenge despite treatment with glucocorticosteroid therapy. The majority of studies investigating disease mechanisms in treatment-resistant severe asthma have previously focused on the large central airways, with very few utilizing transcriptomic approaches. The small peripheral airways, which comprise the majority of the airway surface area, remain an unexplored area in severe asthma and were targeted for global epithelial gene expression profiling in this study. Differences between central and peripheral airways were evaluated using transcriptomic analysis (Affymetrix HG U133 plus 2.0 GeneChips) of epithelial brushings obtained from severe asthma patients (N = 17) and healthy volunteers (N = 23). Results were validated in an independent cohort (N = 10) by real-time quantitative PCR. The IL-13 disease signature that is associated with an asthmatic phenotype was upregulated in severe asthmatics compared to healthy controls but was predominantly evident within the peripheral airways, as were genes related to mast cell presence. The gene expression response associated with glucocorticosteroid therapy (i.e. FKBP5) was also upregulated in severe asthmatics compared to healthy controls but, in contrast, was more pronounced in central airways. Moreover, an altered epithelial repair response (e.g. FGFBP1) was evident across both airway sites reflecting a significant aspect of disease in severe asthma unadressed by current therapies. A transcriptomic approach to understand epithelial activation in severe asthma has thus highlighted the need for better-targeted therapy to the peripheral airways in severe asthma, where the IL-13 disease signature persists despite treatment with currently available therapy.

Epithelial IL-6 trans-signaling defines a new asthma phenotype with increased airway inflammation

“…Hierarchical clustering of transcriptomic data based on the IL-6TS-specific 8-gene signature was done in a cohort including 38 patients with mild-to-moderate or severe asthma (replication cohort 1) 41,42 and in a cohort including 17 patients with severe asthma (replication cohort 2) with epithelial brushing samples from central and/or peripheral airways. 43 This analysis clearly clustered patients from both cohorts into an IL-6TS-high and an IL-6TS-low subsets (see Fig E4, A and B, in this article's Online Repository at www.jacionline.org). Importantly, the IL-6TShigh subset was again associated with gene upregulation related to TLR signaling, including TLR2, MYD88, TREM1, and CCL4 (see Fig E4, C).…”

“…The potential connection between the IL-6TS-high subset and microbial colonization is supported by a recent publication showing increased sputum bacterial numbers in a subset of patients with asthma and chronic obstructive pulmonary disease, the so-called cluster 2 or IL-1b-high cluster, which is also characterized by significantly increased sputum IL-6 and sIL-6R levels. 44 In a replication cohort of patients with treatment-resistant severe asthma all receiving high doses of inhaled steroids, 43 the IL-6TS-specific signature was present in nearly half of the patients, suggesting that the IL-6TS-high phenotype correlates with disease severity. In yet another replication cohort consisting of patients with mild-to-moderate and severe asthma, 41,42 the IL-6TS-high subset overlapped with the majority of patients with severe asthma, further strengthening the association of epithelial IL-6TS with asthma severity.…”

Whole blood transcriptional variations between responders and non‐responders in asthma patients receiving omalizumab

“…However, analysis of heatmaps of differently expressed genes was not powerful enough to reveal differences between responders and non‐responders, and direct comparisons of responders with non‐responders yielded no transcripts that passed FDR correction (Figure 1). In addition to the heterogeneity of asthma, common medications prescribed to moderate‐to‐severe asthma patients, including steroid and β‐agonist, could also interfere with the genes induced by omalizumab 64,65 . To overcome this challenge, we analysed the variances in the expressions of groups of genes, using cluster and module analyses.…”

Small RNA Species and microRNA Profiles are Altered in Severe Asthma Nanovesicles from Broncho Alveolar Lavage and Associate with Impaired Lung Function and Inflammation

“…The microRNAs down-regulated in BALF from SA patients are different from the ones dysregulated in mild asthma [6], which suggests that airway intercellular communication and disease mechanisms are quite distinct. Furthermore, there is little overlap with the cellular microRNAs dysregulated in sputum from patients with SA [7], which suggests that the altered microRNA cargo in BALF exosomes is not directly a consequence of lower levels of microRNAs in the inflammatory cells present in the airway lumen and, in addition, highlights the distinction between central and peripheral airway biology in severe asthma [16]. Whether the reduced nanovesicle microRNA content in SA reflects deficient nanovesicle loading or reflects altered activation status of the cellular source, such as alveolar macrophages or bronchial epithelial cells, cannot be determined with the extraction protocol that does not recover the whole nanovesicles but does purify RNA.…”