Functional significance of apoptosis in chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) is a highly prevalent airway disease characterized by an abnormal inflammatory response of the lungs to noxious particles and gases. Cigarette smoking remains a major risk factor in COPD development. Accumulating evidence suggests that apoptosis, a regulated form of cell death, may play an important role in COPD pathogenesis. Increased numbers of apoptotic cells can be detected in lung tissue and airways of human subjects with COPD, relative to normal lungs or those from smokers without COPD. Alveolar wall destruction associated with emphysema development, may involve increased apoptosis of alveolar structural cells. Several intervention-induced apoptotic models (e.g., cigarette smoke, vascular-endothelial growth factor inhibition, and interferon-gamma) cause emphysematous changes in vitro and in vivo. Increased apoptosis in COPD can also imply defects in the normal physiological clearance of apoptotic cells. Additional factors that relate to perpetuation of the pathogenesis of COPD, including protease/antiprotease imbalance, inflammation and oxidative stress, may mutually promote apoptosis or contribute to impaired clearance of apoptotic cells. Given that cigarette smoking is the most common cause of COPD, identification of the pathways of cigarette smoke-induced apoptosis may further the understanding of COPD pathogenesis. However, apoptosis rate is not diminished after cessation of cigarette smoking, indicating that other mechanisms perpetuate apoptosis in COPD. Therefore, understanding functional relationships between apoptosis and protease/antiprotease imbalance, inflammation, oxidative stress and other factors potentially involved in COPD pathogenesis may uncover crucial therapeutic targets.