The regulatory effect of hyperoxia exposure on the transdifferentiation level of type II alveolar epithelial cells in newborn rats

Abstract

Objective To investigate the effect of hyperoxia on the transdifferentiation level of type Ⅱ alveolar epithelial cells (AEC Ⅱ)in vivo and in vitro, in order to illuminate the mechanism of epithelial injury in bronchopulmonary dysplasia (BPD). Methods Newborn Wistar rats were randomly devided into control group (room air inhalation)or model group (85% oxygen inhalation)after birth.Lung tissue sampling and AEC Ⅱ isolation was conducted on 7 d, 14 d, 21 d. Type Ⅰ alveolar epithelial cells (AEC Ⅰ)marker aquaporin 5(AQP5)and AEC Ⅱ marker surfactant protein C (SP-C)were examined by Western blot and florescent real-time PCR.AEC Ⅱ isolated from normal newborn rats was randomly devided into normoxia group (21% oxygen)or hyperoxia group (85% oxygen)after 24 h culture, and continued culturing for another 48 h in vitro.Then the morphological changes of cells were observed under inverted phase contrast microscope.The expression and location of markers for AEC Ⅰ and AEC Ⅱ was examined by immunofluorescence double staining.The protein expression of AQP5 and SP-C was evaluated by Western blot, and the mRNA expression of these markers was examined by florescent real-time PCR. Results In AEC Ⅱ isolated from the animal models, the AQP5 protein expression increased from 7 d while the SP-C expression decreased from 14 d in the model group comparing with the control group.In the model group, AQP5 mRNA expression increased and SP-C mRNA expression decreased since 7 d after hyperoxia exposure (P<0.05), with the difference between groups more obvious as exposure time extending.After culturing in vitro, AEC Ⅱ isolated from normal newborn rats expressed more AQP5 and less SP-C, with more cells double stained in the hyperoxia group compared with the normoxia group, examined by immunofluorescence double staining.The protein and mRNA examination results both showed that AQP5 expression increased and SP-C expression decreased in the hyperoxia group compared with the normoxia group (P<0.01). Conclusion After hyperoxia exposure, no matter in vivo or in vitro, the expression of AEC Ⅱ marker SP-C decreases while the expression of AEC Ⅰ marker AQP5 increases.These results indicate that the excessive transdifferentiation of AEC Ⅱ takes part in the recovery process after hyperoxia induced lung injury. Key words: Alveolar epithelial cell; Transdifferentiation; Hyperoxia; Lung injury; Bronchopulmonary dysplasia