In addition, based on the 4 selected COPD-related databases, meta-analysis of the candidate 25 aging-related genes showed that 9 genes (FOXO3, TP53, TGFβ1, MMP2, HDAC1, NUF2, ATG3, AREG and E2F1) were significantly altered in the COPD group compared to the control group (Table 2 and Additional file 3). The gene discussed is MMP2; the disease is chronic obstructive pulmonary disease.