Background: Airway remodeling is an important feature of chronic obstructive pulmonary disease (COPD) that is associated with disease severity and irreversible airflow limitation. An extensive alteration of the extracellular matrix (ECM) surrounding the airway smooth muscle (ASM) bundle is one of the pathological manifestations of airway remodeling, which contributes to the decline in lung function. Tiotropium, a long-acting inhaled muscarinic receptor antagonist, has been confirmed to play a role in preventing airway remodeling including ECM deposition beyond bronchodilation in vivo, but the relationship between ASM cell (ASMC) relaxation and ECM production remains unclear. 
Purpose: In this study, we attempted to investigate the influence of tiotropium on ECM production by ASMCs and the underlying mechanism. 
Methods: Tiotropium was added 30 minutes before the addition of methacholine to primary cultured human ASMCs. Protein expression was analylized by Western Blot and mRNA abundance was determined by real-time PCR. 
Results: We found that tiotropium reduced collagen I protein expression, and the mRNA abundance of collagen I , fibronectin , and versican . β-catenin signaling was inactivated by inhibiting glycogen synthase kinase 3β (GSK3β) phosphorylation in this process. Tiotropum inhibited the amount of active β-catenin and its transcription activity. Furthermore, overexpression of active β-catenin by adenoviruses carrying the S33Y mutant resisted the suppressive effect of tiotropium on collagen I protein expression. However, silencing β-catenin  by specific small interfering RNA enhanced the negative effect of tiotropium. 
Conclusion: These findings suggest that relaxation of ASMCs by tiotropium can prevent ECM production through β-catenin signaling.
Keywords: tiotropium, collagen I, β-catenin, airway smooth muscle cell