Background: TGF-beta has been postulated to play an important role in the maintenance of epithelial homeostasis and the development of epithelium-derived cancers. However, most of previous studies are mainly focused on the function of TGF-beta in immune cells to the development of allergic asthma and how TGF-beta signaling in airway epithelium itself in allergic inflammation is largely unknown. Furthermore, the in vivo TGF-beta function specifically in the airway epithelium during lung cancer development has been largely elusive.
Methodology/principal findings: To evaluate the in vivo contribution of TGF-beta signaling in lung epithelium to the development of allergic disease and lung cancer, we generated a transgenic mouse model with Smad7, an intracellular inhibitor of TGF-beta signaling, constitutively expressed in mouse airway Clara cells using a mouse CC10 promoter. The mice were subjected to the development of OVA-induced allergic asthma and urethane-induced lung cancer. The Smad7 transgenic animals significantly protected from OVA-induced asthma, with reduced airway inflammation, airway mucus production, extracellular matrix deposition, and production of OVA-specific IgE. Further analysis of cytokine profiles in lung homogenates revealed that the Th2 cytokines including IL-4, IL-5 and IL-13, as well as other cytokines including IL-17, IL-1, IL-6, IP10, G-CSF, and GM-CSF were significantly reduced in the transgenic mice upon OVA induction. In contrast, the Smad7 transgenic animals had an increased incidence of lung carcinogenesis when subjected to urethane treatment.
Conclusion/significance: These studies, therefore, demonstrate for the first time the in vivo function of TGF-beta signaling specifically in airway epithelium during the development of allergic asthma and lung cancer.