Objective      To investigate the effect of cigarette smoke extract (CSE) on the apoptosis of rat type Ⅱ alveolar epithelial cells (RLE-6TN)

and explore the possible mechanism.       Methods      Different concentrations of CSE were used to culture the RLE-6TN cells for 48 h

and transforming growth factor-β1 (TGF-β1) type Ⅰ receptor inhibitor SB431542 was administered prior to CSE exposure. Morphological changes of apoptotic cells were observed with a fluorescence microscope after Hoechst staining. Cell apoptostic rate was measured by flow cytometry

and the expression levels of TGF-β1， p-Smad2 and apoptosis related protein Cleaved Caspase-3 were examined by Western blotting.       Results      Hoechst staining showed that the cells treated with CSE showed chromatin condensation and typical apoptotic morphological changes

and the cell apoptosis rate was increased from (5.270±0.526)% to (32.580±0.413)% (P0.001). The expression of TGF-β1

p-Smad2 and Cleaved Caspase-3 was obviously increased after exposure to CSE

but the outcome could be abrogated by SB431542.       Conclusion      TGF-β1/Smad2 signal pathway may be involved in the CSE-induced apoptosis of the rat alveolar epithelial cells.