A proteomic analysis of liver mitochondria during acute endotoxemia

Objective: Accumulating evidence indicates that mitochondrial function is impaired in vital organs during sepsis. In addition to oxidative phosphorylation, mitochondria participate in diverse cellular functions ranging from protein and lipid metabolism to programmed cell death. We analyzed liver mitochondrial protein expression patterns (i.e., proteomics) during acute endotoxemia to discover novel insights into mitochondrial responses to acute systemic inflammation. Design: A normotensive endotoxemia model was employed in which altered mitochondrial morphology occurs under conditions minimizing the potentially confounding effects of tissue hypoxia and acidosis. Setting: University medical research laboratory. Subjects: Random-source, adult, male cats. Interventions: Hemodynamic resuscitation and maintenance of acid-base balance and tissue oxygen availability were provided to preserve baseline homeostatic conditions. Treatment groups received isotonic saline vehicle ( control; n = 5) or endotoxin (lipopolysaccharide, LPS, at 3.0 mg/ kg intravenously; n = 5]. Liver samples were obtained 4 h posttreatment, and mitochondrial proteins were isolated and quantitatively compared using two-dimensional gel electrophoresis. Differentially expressed proteins (> 1.5-fold change relative to controls) were identified using mass spectrometry. Measurements and results: Among over 500 protein spots that were separated 14 were differentially expressed in mitochondria of LPS-treated animals relative to matching controls. Spectrometric analyses demonstrated increased expression of urea cycle enzymes, heat shock protein (HSP) 60 and manganese superoxide dismutase, whereas expression of HSP70, F1-ATPase and key enzymes regulating lipid metabolism was reduced. Conclusions: Considering the known functions of each of the proteins exhibiting altered expression, it is likely that the observed changes in liver mitochondrial protein expression are reflective of significant changes in mitochondrial function in response to endotoxemia.