Characterization of Cigarette Smoke Extract (CSE)-induced Cell Death in Lung Epithelial Cells

Choi, Eun Kyung; Kim, Yun Seup; Park, Jae Seuk; Jee, Young Koo; Lee, Kye Young

Abstract

Emphysema is characterized by air space enlarge?ment and alveolar destruction. The mechanism responsible for the development of emphysema was thought to be protease/antiprotease imbalance and oxidative stress. A very recent study shows that alveolar cell apoptosis causes lung destruction and emphysematous changes. Thus, this study was per?formed to support the evidence for the role of apoptosis in the development of emphysema by characterizing cigarette smoke extract (CSE)-induced apoptosis in A549 (type II pneumocyte) lung epithelial cells. CSE induced apoptosis at low concentration (10% or less) and both apoptosis and necrosis at high concentration (20%). Apoptosis was demonstrated by DNA fragmentation using FACScan for subG1 fraction. Discrimination between apoptosis and necrosis was done by morphologic analysis using fluorescent microscopy with Hoecst 33342/propium iodide double staing and electron microscopy. Cy?tochrome c release was confirmed by using immuno?fluorescence with monoclonal anti-cytochrome c antibody. However, CSE-induced cell death did not show the activation of caspase 3 and was not blocked by caspase inhibitors. This suggests that CSE-induced apoptosis might be caspase-independent apoptosis. CSE-induced cell death was near com?pletely blocked by N-acetylcystein and bcl-2 over?expression protected CSE-induced cell death. This results suggests that CSE might induce apoptosis through intracellular oxidative stress. CSE also activated p53 and functional knock-out of p53 using stable overexpression of HPV-E6 protein inhibited CSE-induced cell death. The characterization of CSE-induced cell death in lung epithelial cells could support the role of lung cell apoptosis in the patho?genesis of emphysema.