DNA damage as a molecular link in the pathogenesis of COPD in smokers

In this study, we investigated whether DNA double-strand breaks (DSBs) contribute to the pathogenesis of chronic obstructive pulmonary disease (COPD). We immunofluorescence-stained lung tissue samples obtained from COPD patients, asymptomatic smokers and nonsmokers for markers of DSBs. The numbers of DSB foci (phosphorylated histone 2AX (γH2AX), phosphorylated ATM (ataxia telangiectasia mutated) substrate and phosphorylated p53-binding protein-1 foci) per cell in alveolar type I and II cells and endothelial cells were higher in the COPD patients than in the asymptomatic smokers and nonsmokers. The lung tissue in which type II cells contained higher numbers of γH2AX foci per cell had higher percentages of type II cells that expressed p16(INK4a) (p16), phosphorylated nuclear factor (NF)-κB and interleukin (IL)-6, and of alveolar wall cells that expressed active caspase-3. The type II cells that contained higher numbers of γH2AX foci per cell had higher rates of expression of p16, phosphorylated NF-κB, and IL-6. Half of the alveolar wall cells that expressed active-caspase-3 contained γH2AX foci. Type II cells that stained positive for 8-hydroxy-2-deoxyguanosine contained a higher number of γH2AX foci per cell than the type II cells that stained negative. In conclusion, DSBs, at least in part caused by oxidative stress, appear to contribute to the pathogenesis of COPD by inducing apoptosis, cell senescence and pro-inflammatory responses.