Purpose/Aim: Exposure to hyperoxia leads to lung injury both in vivo and in vitro, molecular hydrogen has been reported to protect against hyperoxia-induced lung injury; however, the underlying molecular mechanisms remain largely unknown. The objective of this study was to characterize differentially regulated proteins and biological processes in hydrogen-treated hyperoxic primary type II alveolar epithelial cells (AECIIs) to elucidate the protective mechanism of hydrogen using quantitative proteomics. Materials and Methods: AECIIs were divided into three groups that were cultured for 24 h in three different conditions: control (21% oxygen), hyperoxia (95% oxygen), and hyperoxia + hydrogen. Morphologic examination, flow cytometric analysis, cell viability assessment and analysis of the expression of apoptosis-associated proteins Bax and Bcl-2 as well as AECI markers (AQP5, T1α) and an AECII marker (SP-C) were performed for each group. The TMT labeling quantitative proteome technique was used to detect changes in the protein expression profile, and bioinformatics analysis was performed. Results: Hydrogen plays a protective role in hyperoxia-induced damage in AECIIs, as evidenced by reduced apoptosis, increased viability and survival, improved morphology, and enhanced transdifferentiation of AECIIs into AECIs. A total of 5782 proteins were identified in our study, of which 162 were significantly altered in abundance after hyperoxia exposure, and 97 were significantly altered in abundance in response to hydrogen treatment. The Gene Ontology and KEGG enrichment analyses identified a large number of proteins and biological processes that may responsible for the protective effect of hydrogen, including VEGFA, PDGFB, IGFBP3, EDN1, NADPH oxidase, the coagulation cascade, etc. Conclusions: Molecular hydrogen protects AECIIs from hyperoxic injury by complex mechanisms involving a variety of proteins and biological processes, such as VEGFA, PDGFB, IGFBP3, EDN1, NADPH oxidase and the coagulation cascade. These findings suggest novel pathways that need to be investigated as possible therapeutic targets for hyperoxia-induced lung injury.
Keywords: hydrogen; hyperoxia; proteomics; type II alveolar epithelial cell.