S100A4 and chronic obstructive pulmonary disease: We observed the increased expression of the mesenchymal markers, Vimentin and S100A4, in the small airway epithelium and RBM in the NLFS, COPD-CS and COPD-ES groups compared to the NC, the epithelial marker E-cadherin junctional expression was reduced in these groups compared to NC, indicating the epithelial cells transitioning to mesenchymal phenotype (Figure 7).