Label-free quantitative proteomics of rat liver exposed to simulated microgravity

Abstract

Microgravity affects the content of carbohydrates, lipids and proteins in liver. Since liver is the major metabolic organ of endogenous and exogenous compounds, a deep understanding of microgravity-induced effects on liver could be of great importance. Therefore, livers from tail-suspension simulated microgravity (SM) rat model were analyzed using a label-free quantitative proteomic method in the present study. The results indicated that hepatic metabolic functions were obviously disrupted by SM. After short-term SM, enzymes for oxidizing nutrients were greatly increased and thus glucose, non-ester fatty acids and amino acids in liver were heavily consumed. Meanwhile, proteins for oxidative phosphorylation were also remarkably regulated. Therefore, the vast electrons generated from oxygenolysis could not be fully transferred to dioxygen and subsequently strong oxidative stress was triggered in liver. On the other hand, antioxidants were increased compensatorily. With the restoration of most energy-metabolic proteins and the continuous up-regulation of antioxidants, hepatic oxidative status returned to physiological level after long-term SM. Moreover, several enzymes involved in xenobiotic metabolism, such as cytochrome P450s and UDP-glucuronosyltransferases were also regulated by SM in a duration-dependent way. Our data might be helpful in understanding the effects of microgravity on liver and would support the design of protective measures for manned space missions.