E2F1 and chronic obstructive pulmonary disease: Among all the 9 genes, the mRNA expression of FOXO3, TP53, TGFβ1, HDAC1, NUF2, ATG3, AREG and E2F1 was significantly down-regulated in the COPD group compared with the control group (Fig. 1), which was consistent with previous meta-analysis results.