Bronchoconstriction Induces TGF-beta Release and Airway Remodelling in Guinea Pig Lung Slices

Airway remodelling, including smooth muscle remodelling, is a primary cause of airflow limitation in asthma. Recent evidence links bronchoconstriction to airway remodelling in asthma. The mechanisms involved are poorly understood. A possible player is the multifunctional cytokine TGF-beta, which plays an important role in airway remodelling. Guinea pig lung slices were used as an in vitro model to investigate mechanisms involved in bronchoconstriction-induced airway remodelling. To address this aim, mechanical effects of bronchoconstricting stimuli on contractile protein expression and TGF-beta release were investigated. Lung slices were viable for at least 48 h. Both methacholine and TGF-beta(1) augmented the expression of contractile proteins (sm-alpha-actin, sm-myosin, calponin) after 48 h. Confocal fluorescence microscopy showed that increased sm-myosin expression was enhanced in the peripheral airways and the central airways. Mechanistic studies demonstrated that methacholine-induced bronchoconstriction mediated the release of biologically active TGF-beta, which caused the increased contractile protein expression, as inhibition of actin polymerization (latrunculin A) or TGF-beta receptor kinase (SB431542) prevented the methacholine effects, whereas other bronchoconstricting agents (histamine and KCl) mimicked the effects of methacholine. Collectively, bronchoconstriction promotes the release of TGF-beta, which induces airway smooth muscle remodelling. This study shows that lung slices are a useful in vitro model to study mechanisms involved in airway remodelling.