Preterm Lung Exhibits Distinct Spatiotemporal Proteome Expression at Initiation of Lung Injury.

Objectives: To characterize time-dependent and regionally-specific injury patterns associated with early ventilation of the preterm lung using a mass-spectrometry based proteomic approach. Methods: Preterm lambs delivered at gestational age 124-127d were randomized to receive 15-min (n=7) or 90-min (n=10) of mechanical ventilation at standardized settings (positive end-expiratory pressure 8 cmH2 O, tidal volume 6-8 mL/kg) and were compared with unventilated control lambs (n=7). At study completion, lung tissue was taken from standardized gravity-dependent and non-dependent regions, and assessed for lung injury via histology, qPCR and by proteomic analysis via Orbitrap-mass spectrometry. Ingenuity Pathway Analysis Software was used to identify temporal and region-specific enrichments in pathways and functions. Measurements and Main Results: Apoptotic cell numbers were 9-fold higher in non-dependent lung at 15- and 90-minutes compared to controls, whilst proliferative cells were increased 4-fold in the dependent lung at 90-minutes. The relative gene expression of lung injury markers was increased at 90-minutes in non-dependent lung (p<0.05) and unchanged in dependent lung. Within the proteome the number of differentially expressed proteins was 4-fold higher in the non-dependent lung than the dependent lung. The number of differential proteins increasing over time in both lung regions. 95% of enriched canonical pathways and 94% of enriched cellular and molecular functions were identified only in non-dependent lung tissue from the 90-min ventilation group. Conclusions: Complex injury pathways are initiated within the preterm lung after 15 minutes of ventilation and amplified by continuing ventilation. Injury development is region-specific with greater alterations within the proteome of non-dependent lung.