MMP9 and chronic obstructive pulmonary disease: Among them, CASP3 and MMP9 belong to one of the classes of cysteine proteases and matrix metalloproteinases, respectively, which are able to degrade all components of the extracellular matrix (ECM), leading to structural abnormalities of the airway wall, and are closely associated with lung diseases, such as COPD, pulmonary fibrosis and lung cancer.[15] The NFKB1 (p105/p50) subunit was an active regulatory factor of the NF-κB family genes, playing a crucial role in the inflammatory response in COPD.