NOX4 and chronic obstructive pulmonary disease: The present research mostly found that: (1) Pulmonary and serum DJ-1 was decreased in COPD patients; (2) Pulmonary VDR and Nrf-2 were reduced in COPD patients; (3) Pulmonary HO-1 and NOX-4 were elevated in COPD patients; (4) There were positive correlations among pulmonary function, DJ-1, VDR and Nrf-2 in lung tissues of COPD patients.