EMT and the TGF-β/Smad pathway were activated in the AECs of rats with COPD or diabetes, and the combination of COPD and diabetes amplified those effects, as indicated by downregulation of Zo1 and upregulation of vimentin, TGF-β and Smad4 in immunohistochemical experiments. This evidence concerns the gene TJP1 and chronic obstructive pulmonary disease.