[Hyperoxia induces AECII apoptosis of premature rats by reducing the activity of 20S proteasome].

Objective To establish a hyperoxia-exposed cell damage model of primary cultured premature rat alveolar type II epithelial cells (AECIIs) and investigate the effect of hyperoxia on ubiquitinated protein degradation and apoptosis of AECIIs. Methods Primary cultured premature rat AECIIs in vitro were divided into air group and hyperoxia group, which were exposed to air and 950 mL/L O2, respectively. After 24-, 48- and 72-hour exposure, isothiocyanate-labeled annexinV/propidium iodide (annexinV-FITC/PI) double staining combined with flow cytometry was utilized to detect the apoptosis of AECIIs. Real-time quantitative PCR and Western blotting were performed to observe the mRNA expression of ubiquitin and the protein levels of total ubiquitinated proteins, Bax/Bcl-2 ratio and caspase-3. Specific fluorescence substrate was used to measure the activity of 20S proteasome. Results Compared with the air group, the apoptosis of AEC II s in the hyperoxia group increased at each time point. The activity of 20S proteasome in AECIIs in the hyperoxia group decreased dramatically, while the levels of ubiquitin mRNA and total ubiquitinated protein increased. At the same time, the expression of caspase-3 and the Bax/Bcl-2 ratio were significantly raised. Conclusion Exposure to hyperoxia decreases the activity of 20S proteasome in AECIIs and the degradation of ubiquitinated proteins, which may induce the apoptosis of AECIIs by upregulating the expression of caspase-3 and the Bax/Bcl-2 ratio.