[Proteome analysis of type II alveolar epithelial cell in hyperoxia induced lung injury]

To investigate the damage mechanism of type II alveolar epithelial cells (AEC II) after hyperoxia exposure by proteomics.

The primary AEC II of preterm Sprague-Dawley (SD) rats were divided into normoxia and hyperoxia groups, and cultured in room air (21% O₂) or hyperoxia (95% O₂) condition, respectively. The cell morphology change was observed under an inverted contrast microscope; the protein expressions of Bcl-2 and caspase-3 were detected by Western Blot to ensure a successful model. Total protein in AEC II was collected, and mass spectrometry-based tandem mass tag (TMT)-labeled quantitative proteomics were used to detect the change of protein profile. Proteins with changes greater than 1.5-fold and P < 0.05 were considered differentially expressed, and bioinformatics analysis was performed. According to the proteomic results, AEC II were divided into three groups: normoxia group, hyperoxia group and hyperoxia+MW167 group (γ-secretase inhibitor MW167 was added to culture medium 30 minutes before they were placed into the chamber). The cell viability was detected by the cell proliferation and toxicity kit (CCK-8), and the expressions of Hes1, Bax mRNA were detected by real-time fluorescence quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

(1) The cells in the normoxia group proliferated and prolonged significantly, and the cytoplasmic particulate matter was abundant. In the hyperoxia group, nucleus pyknosis and cytoplasmic particulate matter decreased significantly. Compared with the normoxia group, the expression of caspase-3 in the hyperoxia group was significantly increased, and the expression of Bcl-2 was significantly decreased (caspase-3/GAPDH: 1.352±0.086 vs. 0.769±0.080, Bcl-2/GAPDH: 0.614±0.060 vs. 1.361±0.078, both P < 0.01). (2) A total of 162 differentially expressed proteins were identified between normoxia and hyperoxia groups, the proteins up-regulated by hyperoxia were commonly associated with response processes to various stimuli, and located in the extracellular region; the proteins down-regulated by hyperoxia were commonly associated with synthesis of substances, and located in the cellular matrix. KEGG Pathway analyses suggested that metabolism by cytochrome P450, oxidative phosphorylation, and Notch signaling pathway were associated with the mechanism of hyperoxia injury on AEC II. (3) Compared with the normoxia group, the viability of cells in the hyperoxia group was significantly decreased, and the expressions of Hes1 and Bax mRNA were significantly increased [cell viability (A value): 0.060±0.003 vs. 1.058± 0.017, Hes1 mRNA (2^-ΔΔCt): 2.235±0.606 vs. 1.144±0.107, Bax mRNA (2^-ΔΔCt): 2.210±0.240 vs. 1.084±0.096, all P < 0.05]. Compared with the hyperoxia group, the viability of cells in the hyperoxia+MW167 group was significantly increased, and the expressions of Hes1 and Bax mRNA were significantly decreased [cell viability (A value): 0.271±0.025 vs. 0.060±0.003, Hes1 mRNA (2^-ΔΔCt): 0.489±0.046 vs. 2.235±0.606, Bax mRNA (2^-ΔΔCt): 1.289±0.041 vs. 2.210±0.240, all P < 0.05].

The mechanism of hyperoxia injury on AECII may be related to the metabolism by cytochrome P450, oxidative phosphorylation and activation of Notch signaling pathway.