Effects of hyperoxia on the dynamic expression of Aquaporin5 in premature rats lung development

To explore the dynamic expression and role of Aquaporin5 (AQP5) in lung development and hyperoxia lung injury, gestation 21-day Sprague-Dawley (SD) rats (term=22 days) were randomly assigned to air group and hyperoxia group within 12-24 h after birth. The rats in hyperoxia group were continuously exposed to about 85% oxygen and those in air group to room air. After 1 to 14 days of exposure, total lung RNA was extracted and the expression of AQP5 mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR). Immunohistochemistry and western-blot were used to detect the expression of AQP5 protein. The results showed that the expression of AQP5 in premature rats lung could be detected at various time points after birth, and the positive staining was restricted to the type I alveolar epithelial cells. In air group, the AQP5 expression was detected in a very low level at day 1, but exhibited a persistent increase after birth. Compared with the air group, the expression of AQP5 in hyperoxia group was increased at day 1, and had significant difference in mRNA level (P<0.05), but decreased significantly in mRNA and protein levels after 4 to 14 days (P<0.01 or P<0.05 respectively). It was concluded that AQP5 might play a key role in the alveolar period of premature rats by regulating the lung water balance. Hyperoxia exposure leads to a down-regulation of the AQP5 expression, which may be an important factor for the development of hyperoxia lung injury.