Study of the variation in expression and the significance of markers for alveolar epithelial cells in bronchopulmonary dysplasia newborn rats

Abstract

Objective To investigate the variation in expression and the significance of markers indicating typeⅠalveolar epithelial cells(AECⅠ) and type Ⅱ alveolar epithelial cells(AECⅡ) in hyperoxia induced bronchopulmonary dysplasia(BPD) model. Methods A total of 80 term normal Wistar rats were randomly devided into model group (85% oxygen) or control group (room air) within 12 h after birth, with 40 rats in each group.On day 7, day 14, day 21 after exposure, the pathological characteristics of lung tissues were observed using HE staining, the expression and location of AECⅠ marker aquaporin 5(AQP5) and AECⅡ marker surfactant protein-C (SP-C) were examined using immunofluorescence double staining.Western blot analysis was employed to examine the expressions levels of AQP5 and SP-C proteins, while real-time PCR was used to evaluate the mRNA expression of AQP5 and SP-C. Results Alveolar developmental disorder was observed in lung tissues of the model group, including fewer, larger, simplified alveoli, thicker alveolar walls, and fewer alveolar secondary septa.Immunofluorescence double staining showed increased and disorganized AQP5 and SP-C expression, with significantly higher ratio of double-stained cells/SP-C positive cells in the model group (P<0.001). Comparing to the control group, the expression of AQP5 and SP-C protein increased from 7 d after hyperoxia exposure, which continued to 21 d. The mRNA expression levels of these two markers both significantly increased in the model group compared with the control group, with AQP5 starting from 7 d while SP-C starting from 14 d after hyperoxia exposure (P<0.05), and the difference between two groups became more significant with the exposure time extending. Conclusion The expression of AECⅠ marker AQP5 and AECⅡ marker SP-C both increase in the lung tissues of hyperoxia induced BPD newborn rats, with more AECⅡ transdifferentiated into AECⅠ.These changes of the markers indicate that there is excessive transdifferentiation of AECⅡ in the recovery process after BPD lung injury. Key words: Transdifferentiation; Alveolar epithelial cell; Bronchopulmonary dysplasia; Hyperoxia; Rats