title: Mitochondrial glycerol-3-phosphate acyltransferase-1 directs the metabolic fate of exogenous fatty acids in hepatocytes.
abstract: Because excess triacylglycerol (TAG) in nonadipose tissues is closely associated with the development of insulin resistance, interest has increased in the metabolism of long-chain acyl-CoAs toward beta-oxidation or the synthesis and storage of TAG. To learn whether a mitochondrial isoform of glycerol-3-phosphate acyltransferase (mtGPAT1) competes with carnitine palmitoyltransferase I (CPT I) for acyl-CoAs and whether it contributes to the formation of TAG, we overexpressed rat mtGPAT1 13-fold in primary hepatocytes obtained from fasted rats. When 100, 250, or 750 microM oleate was present, both TAG mass and the incorporation of [14C]oleate into TAG increased more than twofold in hepatocytes overexpressing mtGPAT1 compared with vector controls. Although the incorporation of [14C]oleate into CO2 and acid-soluble metabolites increased with increasing amounts of oleate in the media, these metabolites were approximately 40% lower in the Ad-mtGPAT1 infected cells, consistent with competition for acyl-CoAs between CPT I and mtGPAT1. A 50-60% decrease was also observed in [14C]oleate incorporation into cholesteryl ester. With increasing amounts of exogenous oleate, [14C]TAG secretion increased appropriately in vector control-infected hepatocytes, suggesting that the machinery for VLDL-TAG biogenesis and secretion was unaffected. Despite the marked increases in TAG synthesis and storage in the Ad-mtGPAT1 cells, however, the Ad-mtGPAT1 cells secreted the same amount of [14C]TAG as the vector control cells. Thus, in isolated hepatocytes, mtGPAT1 may synthesize a cytosolic pool of TAG that cannot be secreted.
authors.affiliation: Department of Nutrition, University of North Carolina, Chapel Hill, NC 27599, USA.
authors.forename: Tal M
authors.initials: TM
authors.lastname: Lewin
authors.forename: Shuli
authors.initials: S
authors.lastname: Wang
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Nagle
authors.forename: Cynthia G
authors.initials: CG
authors.lastname: Van Horn
authors.forename: Rosalind A
authors.initials: RA
authors.lastname: Coleman
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005227:Fatty Acids / Q000008:administration & dosage / Q000493:pharmacokinetics; D005992:Glycerol-3-Phosphate O-Acyltransferase / Q000235:genetics / Q000378:metabolism*; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D019301:Oleic Acid / Q000008:administration & dosage / Q000493:pharmacokinetics*; D010084:Oxidation-Reduction; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D005227:Fatty Acids; D011994:Recombinant Proteins; D014280:Triglycerides; D019301:Oleic Acid; D005992:Glycerol-3-Phosphate O-Acyltransferase