Involvement of Transforming Growth Factor-β-Associated Kinase 1 in Fixed Airway Obstruction in Asthmatic Patients with Longer Disease Duration Independent on Airway Eosinophilia

Abstract

Objective: Transforming growth factor-β-associated kinase 1 (TAK1) mediates non-canonical TGF-β signalling by promoting adhesive, migratory, proliferative and contractile responses of fibroblasts to TGF-β₁. However, TAK1 expression status in asthmatic patients with or without fixed airway obstruction (FAO) is unknown.

Patients and methods: A total of 60 adult asthmatics with FAO were recruited and compared to 43 those without FAO (nFAO). TGF-β₁ concentrations, and total TAK1 and phosphorylated TAK1 (p-TAK1) levels were determined in sputum supernatants, cytospin, and whole cell lysate by ELISA, immunocytochemistry, and Western blot analysis, respectively, in asthmatics with and without FAO.

Results: Asthmatic patients with FAO had much greater sputum TGF-β₁ concentrations than those without FAO. This was independent of airway eosinophilia as there was no significant difference in TGF-β₁ levels between high and low eosinophil counts within FAO and nFAO groups. In contrast, patients with FAO in the presence of sputum eosinophilia had greater expression of TAK1 and p-TAK1 than those without sputum eosinophilia (P=0.0032 and P=0.0061, respectively). The Western Blot data of total TAK1 and p-TAK1 were consistent with the immunocytochemistry, showing upregulation in all sputum cell types (neutrophils, eosinophils, macrophages, lymphocytes and airway epithelial cells). In addition, total TAK1 expression negatively correlated with pre- and post-bronchodilator FEV₁/FVC ratio.

Conclusion: TAK1 may play a key role in asthmatic patients with fixed airway obstruction, which was independent of eosinophilic airway inflammation. The interruption of TAK1 might have favourable clinical impact.

Keywords: asthma; fixed airway obstruction; transforming growth factor-β-associated kinase 1.

Figure 1

TGF-β₁ levels of asthmatics with FAO and non-FAO (nFAO) in the presence or absence of airway eosinophilia as indicated. TGF-β₁ was quantified by ELISA in sputum fluid of FAO and nFAO asthmatic patients with sputum eosinophilia and without sputum eosinophilia. Results are depicted as bar column, with median values, 25th and 75th quartile and the range of values. Mann–Whitney U-test was used for the statistical analysis, and there was no statistical significance within group and associated P values between groups are indicated. ***P < 0.001.

Figure 2

The levels of TAK1 and p-TAK1 in total sputum cells was analyzed by Western blot analysis of whole cell lysate from asthmatics with FAO and without FAO (non-FAO). GAPDH served as the standard.

Figure 3

Correlations between total TAK1 immunopositive cells in sputum of asthmatics with FAO, expressed as percentage, and the pulmonary function tests, including pre-bronchodilator (A) and post-bronchodilator FEV₁/FVC ratios (B). Spearman rank correlation has shown significant negative correlations between TAK1 levels and FEV₁/FVC ratios.

Figure 4

TAK1 and p-TAK1 immunopositive cells (%) in sputum of asthmatics with FAO and without FAO (nFAO) in the presence or absence of airway eosinophilia as indicated. (A) The difference in TAK1 immunopositive cell numbers within and between groups. (B) The difference in p-TAK1 immunopositive cell numbers between patients with and without airway eosinophilia. Results are depicted as bar, column, with median values, 25th and 75th quartile and the range of values. Mann–Whitney U-test and associated P-values are indicated. ***P < 0.001 for comparison with FAO with eosinophilia. ψ for comparison with FAO without eosinophilia (P < 0.001).