Re-Adaption on Earth after Spaceflights Affects the Mouse Liver Proteome

Harsh environmental conditions including microgravity and radiation during prolonged spaceflights are known to alter hepatic metabolism. Our studies have focused on the analysis of possible changes in metabolic pathways in the livers of mice from spaceflight project "Bion-M 1". Mice experienced 30 days of spaceflight with and without an additional re-adaption period of seven days compared to control mice on Earth. To investigate mice livers we have performed proteomic profiling utilizing shotgun mass spectrometry followed by label-free quantification. Proteomic data analysis provided 12,206 unique peptides and 1,086 identified proteins. Label-free quantification using MaxQuant software followed by multiple sample statistical testing (ANOVA) revealed 218 up-regulated and 224 down-regulated proteins in the post-flight compared to the other groups. Proteins related to amino acid metabolism showed higher levels after re-adaption, which may indicate higher rates of gluconeogenesis. Members of the peroxisome proliferator-activated receptor pathway reconstitute their level after seven days based on a decreased level in comparison with the flight group, which indicates diminished liver lipotoxicity. Moreover, bile acid secretion may regenerate on Earth due to reconstitution of related transmembrane proteins and CYP superfamily proteins elevated levels seven days after the spaceflight. Thus, our study demonstrates reconstitution of pharmacological response and decreased liver lipotoxicity within seven days, whereas glucose uptake should be monitored due to alterations in gluconeogenesis.