As shown in Fig. 1H, COPD patients showed the decreased protein levels of PTEN at baseline, which was further reduced in the presence of CSE in a dose-dependent manner (Fig. 1H); therefore, PTEN protein expression was reduced in bronchial epithelial cells and the cells seemed to be an important target of exogenous oxidative stress with resultant PTEN reduction. Here, PTEN is linked to chronic obstructive pulmonary disease.