Effects of Space Flight on the Expression of Liver Proteins in the Mouse

Raw data derived from mass spectroscopic (MS) analyses of formalin-fixed paraffin-embedded (FFPE) tissue sections of the essential metabolic organ, liver, allocated by the provider (Amgen) from mice subjected to 13 days of microgravity on NASA Flight STS-118 were analyzed by two different search engines using shotgun proteomics. With the eight statistically significant readouts in hand, Ingenuity Pathway Analysis (IPA) was employed to visualize probable biologic pathway relationships among proteins that might be associated with alterations in liver biochemistry due to space flight. Most noteworthy was the finding of up-regulation of the first urea cycle enzyme carbamoyl-phosphate synthetase, consistent with increased amino acid catabolism resulting from gravitational changes and/or other stress associated with missions in space. Down-regulation of fructose-bisphosphate aldolase B, regucalcin, ribonuclease UK114, alpha enolase, glycine N-methyltransferase and S-adenosyl methionine synthetase isoform type-1 was observed. 60 kDa heat shock protein was elevated. This protein data set (67 proteins) represents the potential of utilizing FFPE tissue for conducting studies of this type and represents a beginning understanding of what takes place in the mammalian liver with weightlessness followed by stress of landing. Eight of the 67 proteins show statistical differences between FLT and GRD. Six were mapped by IPA. Some of these are linked to detoxification pathways within the liver (carbamoyl-phosphate synthetase, glycine N-methyltransferase, S-adenosylmethionine synthetase) and some to carbohydrate metabolism (fructose-bisphosphate aldolase B, alpha-enolase). 60 kDa heat shock protein was up-regulated, probably because of its relation to stress. Regucalcin was highly down-regulated possibly limiting osteoporosis which is a major problem with space flight. Ribonuclease UK114, also known as heat-responsive protein 12 was down-regulated possibly due to the stress of space flight as well.