Expression of apoptosis-related genes after fetal tracheal occlusion in rabbits

Late-gestation lung remodeling is associated with alveolar type II cell apoptosis early in the saccular stage (day 28 in fetal rabbits). Intrauterine tracheal occlusion (TO), a potent stimulus of fetal lung growth and maturation, significantly increases type II cell apoptosis. The aim of this study was to determine the effect of fetal TO on the spatiotemporal expression of key apoptosis-related signaling molecules.

Tracheal occlusion of fetal rabbits was performed at gestational day 25 (term, 31 days), and apoptotic gene expression was studied between days 26 and 28.

At days 26 and 27, the protein levels of Fas and Fas-ligand (FasL) in lung lysates were similar in TO fetuses and sham-operated controls. At day 28, however, synchronous with the onset of TO-induced pulmonary distension and type II cell apoptosis, the FasL protein content was 8-fold higher in TO lungs compared with controls (P < .01), whereas Fas levels were comparable. In contrast, Bax and Bcl-2 protein levels were similar in TO and control fetuses at all time-points. TO significantly increased the cellular concentration of immunoreactive FasL in type II cells and bronchial epithelial Clara cells. Furthermore, bronchoalveolar lavage fluid (BAL) from TO fetuses at day 28 induced significantly more type II cell apoptosis in vitro compared with control BAL, an effect that was inhibited by neutralizing anti-FasL antibody.

Our findings show that TO results in time-specific increase of both cellular and soluble FasL in fetal lungs and implicate the Fas/FasL pathway as a pivotal autocrine and/or paracrine regulator of TO- induced type II cell apoptosis.