Hyperoxia inhibits protein synthesis and increases eIF2α phosphorylation in the newborn rat lung

Prolonged exposure to hyperoxia contributes to aberrant lung growth in premature infants. Of the deleterious effects induced by hyperoxia, alterations in protein synthesis are likely to be of great importance to the developing lung. Regulation of mRNA translation occurs predominantly at the level of initiation via control of mRNA/ribosome binding by proteins known as eukaryotic initiation factors (eIF). Although hyperoxia is known to suppress mRNA translation in adult lungs, little is known regarding the effects in newborns or the involved mechanism. This study was performed to determine the effect of exposure to 95% O(2) on pulmonary protein synthesis in 4-day-old Sprague-Dawley rat pups. We found that hyperoxia suppressed the incorporation of [(3)H]phenylalanine into lung protein over time, resulting in a 23% reduction after 72 h compared with pups reared in room air. This effect was preceded by a shift in total lung RNA to lower order polysomes. Hyperoxia increased eIF4G-eIF4E binding, a surrogate maker of eIF4F complex assembly, and initially activated, then suppressed, the phosphorylation of ribosomal S6 kinase 1 and ribosomal S6 protein, downstream targets of mammalian target of rapamycin. Exposure to 95% O(2) enhanced the phosphorylation of the translational repressor eIF2α in whole lung extracts and the immunoreactivity of phosphorylated eIF2α in epithelial cells. Cell culture studies further demonstrated that hyperoxia increases eIF2α phosphorylation in lung epithelial cells, but not in lung fibroblasts. These findings illustrate that hyperoxia-induced suppression of mRNA translation in the newborn lung is accompanied by increased phosphorylation of eIF2α in the epithelium.