Activation of TGF-β/Smad2 signaling is associated with airway remodeling in asthma

Background: Transforming growth factor beta (TGF-beta) has been suggested to play an important role in the development of airway remodeling in asthma; this suggestion is based on evidence that expression levels of TGF-beta are correlated with unique parameters of airway remodeling, such as thickness of basement membrane. However, the relevant studies were inconclusive because they were unable to demonstrate active signaling mediated by the cytokine in the airways of asthmatic individuals. Objective: We sought to determine whether TGF-beta signaling was active in the airways of asthmatic subjects and, if so, whether it was correlated with clinicopathologic features associated with the development of airway remodeling in asthma. Methods: We examined the phosphorylation status of Smad2 in bronchial biopsy samples obtained from 40 asthmatic subjects as a marker of active TGF-beta signaling, and we studied its correlation with basement membrane thickness. Results: Expression levels of phosphorylated Smad2 in bronchial biopsy specimens from asthmatic subjects were higher than those in specimens from normal subjects, and they were correlated with basement membrane thickness in asthma. Conclusion: The findings provide evidence that TGF-beta signaling was active in asthmatic airways and that the activity was associated with the development of airway remodeling in asthma.