FKBP5 and chronic obstructive pulmonary disease: Further analysis of the PPI network topology structure and gene expression revealed a hub gene signature that was significantly upregulated in PBMCs of COPD patients, including MDM2 (6.3-fold, p < 0.001), FKBP5 (7.0-fold, p < 0.001), and CTNNA1 (10.0-fold, p < 0.001).