CLN5 and chronic obstructive pulmonary disease: TGF-β family members, including BMPs, GDFs, endogenous inhibitor FZD receptors, and down-stream mediators such as SMADs, SNAILs, and TWIST, have been shown to be involved in the EMT that occurs in the bronchial epithelial cells of COPD patients or smokers [16,23,26,72,73,74].