MMP2 and chronic obstructive pulmonary disease: Specifically, based on the 4 selected COPD databases, 9 differentially expressed aging-related genes in COPD patients were identified with meta-analysis from the aging-related gene profile, including AREG, ATG3, E2F1, FOXO3, NUF2, HDAC1, MMP2, TP53 and TGFβ1.