TGFB1 and chronic obstructive pulmonary disease: We also treated the CS-exposed epithelium with inhibitors of pathways that have been implicated in the development of COPD, namely inhibitors of the MAPK/ERK kinase (U0126; Favata et al., 1998), TGFβ1 (1D11; Edwards et al., 2010) and Wnt signaling pathways (DKK1; Glinka et al., 1998) .