Acid Sphingomyelinase Inhibition Attenuates Cell Death in Mechanically-Ventilated Newborn Rat Lung.

RATIONALE: Premature infants subjected to mechanical ventilation (MV) are prone to lung injury that may result in bronchopulmonary dysplasia. Mechanical ventilation causes epithelial cell death and halts alveolar development. The exact mechanism of MV-induced epithelial cell death is unknown.

OBJECTIVE: To determine the contribution of autophagy to MV-induced epithelial cell death in newborn rat lungs.

METHODS: Newborn rat lungs and fetal rat lung epithelial (FLRE) cells were exposed to MV and cyclic stretch, respectively, and were then analyzed by immunoblotting and mass spectrometry for autophagy, apoptosis and bioactive sphingolipids.

MEASUREMENTS AND MAIN RESULTS: Both MV and stretch first induces autophagy (ATG5/12 and LC3B-II formation) followed by extrinsic apoptosis (cleaved CASP8/3 and PARP formation). Stretch-induced apoptosis was attenuated by inhibiting autophagy. Co-immunoprecipitation revealed that stretch promoted an interaction between LC3B and the FAS cell death receptor in FRLE cells. Ceramide levels, in particular C16 ceramide, were rapidly elevated in response to ventilation and stretch, and C16 ceramide treatment of FRLE cells induced autophagy and apoptosis in a temporal pattern similar to that seen with mechanical ventilation and stretch. Sphingomyelin phosphodiesterase 1 (SMPD1) was activated by ventilation and stretch, and its inhibition prevented ceramide production, LC3B-II formation, LC3B/FAS interaction, CASP3 activation, and ultimately FLRE cell death. SMPD1 inhibition also attenuated ventilation-induced autophagy and apoptosis in newborn rats.

CONCLUSIONS: Ventilation-induced ceramides promote autophagy-mediated cell death, and identifies SMPD1 as a potential therapeutic target for the treatment of ventilation-induced lung injury in newborns.