EGR1 and chronic obstructive pulmonary disease: Transcriptomic analysis integrated with public datasets identified Early Growth Response 1 (EGR1) as a key exercise-response hub gene; its expression was downregulated in the COPD+NAFLD group after exercise but upregulated in the COPD-only group, correlating positively with M2 macrophages (derived from liver single-cell transcriptomic data) and negatively with monocytes.