SNAI1 and chronic obstructive pulmonary disease: Several genes known to be regulated downstream of TGF-β1 had a significantly lower expression level in cells on COPD scaffolds on day 0, including the genes for TGF-β receptor 1 (TGFBR1)25, Snail family transcriptional repressor 2 (SNAI2)26 and SMAD727 (Fig. 6B).