84 Prolonged Ventilation Causes P27KIP1 Induced Cell Cycle Arrest in Newborn Rat Lung

Background: I n vitro studies have demonstrated that mechanical stretch can inhibit lung cell proliferation. This inhibition of cell growth may lead to reduction of alveolar formation and contribute to the development of bronchopulmonary dyplasia. Objective: To determine the effect of prolonged mechanical ventilation on cell-cycle regulation in a newborn rat model. Methods: 7-day old Wistar rats were ventilated with low/moderate tidal volume and room air for 24 h. Following ventilation arterial blood gas analysis was performed and the animal was killed. Lung tissues were processed for histological or molecular/protein analysis to determine (1) number of proliferating cells by BrdU and phospho-Histone H3 staining and (2) gene and protein expression of cell cycle regulatory proteins by real-time PCR and Western blotting. Results: After 24 h of ventilation arterial blood gas values were within normal range but alveolar formation was reduced. The number of proliferating cells was decreased (BrdU incorporation decreased from 10 to 3 % and phospho-histone H3 positive cells from 0.8 to 0.1%. Expression of CyclinD1 and E1 mRNA and protein was markedly down-regulated. Instead, protein expression of the CDK inhibitor p27 Kip1 was significantly increased while its phosphorylation at site T157, T198 and T187 was decreased. Interestingly, CDK inhibitor p16 Ink4a levels were decreased by ventilation. Conclusions: Prolonged mechanical ventilation causes cycle arrest of lung cells in newborn rats by increased transcription and nuclear localization of the CDK inhibitor p27 Kip1 . These data may in part explain the arrest in alveolarization by mechanical ventilation of the neonatal lung.