title: Metabolic flux analysis of mitochondrial uncoupling in 3T3-L1 adipocytes.
abstract: BACKGROUND
  Increasing energy expenditure at the cellular level offers an attractive option to limit adiposity and improve whole body energy balance. In vivo and in vitro observations have correlated mitochondrial uncoupling protein-1 (UCP1) expression with reduced white adipose tissue triglyceride (TG) content. The metabolic basis for this correlation remains unclear.
  
  
  RESULTS
  This study tested the hypothesis that mitochondrial uncoupling requires the cell to compensate for the decreased oxidation phosphorylation efficiency by up-regulating lactate production, thus redirecting carbon flux away from TG synthesis. Metabolic flux analysis was used to characterize the effects of non-lethal, long-term mitochondrial uncoupling (up to 18 days) on the pathways of intermediary metabolism in differentiating 3T3-L1 adipocytes. Uncoupling was induced by forced expression of UCP1 and chemical (FCCP) treatment. Chemical uncoupling significantly decreased TG content by ca. 35%. A reduction in the ATP level suggested diminished oxidative phosphorylation efficiency in the uncoupled adipocytes. Flux analysis estimated significant up-regulation of glycolysis and down-regulation of fatty acid synthesis, with chemical uncoupling exerting quantitatively larger effects.
  
  
  CONCLUSIONS
  The results of this study support our hypothesis regarding uncoupling-induced redirection of carbon flux into glycolysis and lactate production, and suggest mitochondrial proton translocation as a potential target for controlling adipocyte lipid metabolism.
authors.affiliation: Department of Biology, Tufts University, Medford, Massachusetts, USA.
authors.forename: Yaguang
authors.initials: Y
authors.lastname: Si
authors.forename: Hai
authors.initials: H
authors.lastname: Shi
authors.forename: Kyongbum
authors.initials: K
authors.lastname: Lee
mesh_terms: D041721:3T3-L1 Cells / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D017667:Adipocytes / Q000378:metabolism*; D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D002244:Carbon / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D006019:Glycolysis; D007473:Ion Channels / Q000378:metabolism; D007773:Lactates / Q000378:metabolism; D008055:Lipids / Q000737:chemistry; D051379:Mice; D024101:Mitochondrial Proteins / Q000378:metabolism; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism; D000071256:Uncoupling Protein 1
chemical_list: D005227:Fatty Acids; D007473:Ion Channels; D007773:Lactates; D008055:Lipids; D024101:Mitochondrial Proteins; D014280:Triglycerides; C000604372:Ucp1 protein, mouse; D000071256:Uncoupling Protein 1; D002244:Carbon; D000255:Adenosine Triphosphate; D010100:Oxygen