What is more, upregulation of phenotypic markers of EMT such as matrix metallopeptidase-9 (MMP-9), vimentin, and nicotinamide adenine dinucleotide phosphate oxidase-4 (NOX4) was found in bronchial epithelial cells of both large and small bronchi from smokers and COPD patients [57]. This evidence concerns the gene MMP9 and chronic obstructive pulmonary disease.