title: Carnitine palmitoyltransferase 2 and carnitine/acylcarnitine translocase are involved in the mitochondrial synthesis and export of acylcarnitines.
abstract: Acylcarnitines are commonly used in the diagnosis of mitochondrial fatty acid β-oxidation disorders (mFAODs). It is generally assumed that this plasma acylcarnitine profile reflects the mitochondrial accumulation of acyl-CoAs. The identity of the enzymes and the mitochondrial and plasmalemmal transporters involved in the synthesis and export of these metabolites have remained undefined. We used lentiviral shRNA to knock down the expression of medium-chain acyl-CoA dehydrogenase (MCAD) in control and carnitine palmitoyltransferase 2 (CPT2)-, carnitine/acylcarnitine translocase (CACT)-, and plasmalemmal carnitine transporter (OCTN2)-deficient human fibroblasts. These cell lines, including mock-transduced controls, were loaded with decanoic acid and carnitine, followed by the measurement of the acylcarnitine profile in the extracellular medium. In control fibroblasts, MCAD knockdown markedly increased the production of octanoylcarnitine (3-fold, P<0.01). OCTN2-deficient cell lines also showed extracellular accumulation of octanoylcarnitine (2.8-fold, P<0.01), suggesting that the cellular export of acylcarnitines does not depend on OCTN2. In contrast, in CPT2- and CACT-deficient cells, the accumulation of octanoylcarnitine in the medium did not significantly increase in the MCAD knockdown. Similar results were obtained using pharmacological inhibition of CPT2 in fibroblasts from MCAD-deficient individuals. This shows that CPT2 and CACT are crucial for mitochondrial acylcarnitine formation and export to the extracellular fluids in mFAOD.
authors: Metabolism and Genetics Group, Research Institute for Medicines and Pharmaceutical Sciences (iMed.UL), Faculdade de Farmácia, Universidade de Lisboa, Lisbon, Portugal.
authors: Sara
authors: S
authors: Violante
authors: Lodewijk
authors: L
authors: Ijlst
authors: Heleen
authors: H
authors: Te Brinke
authors: Isabel
authors: I
authors: Tavares de Almeida
authors: Ronald J A
authors: RJ
authors: Wanders
authors: Fátima V
authors: FV
authors: Ventura
authors: Sander M
authors: SM
authors: Houten
mesh_terms: D042964:Acyl-CoA Dehydrogenase / Q000235:genetics / Q000378:metabolism; D002331:Carnitine / Q000031:analogs & derivatives* / Q000378:metabolism; D002333:Carnitine Acyltransferases / Q000172:deficiency / Q000378:metabolism*; D002334:Carnitine O-Palmitoyltransferase / Q000172:deficiency / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D028361:Mitochondrial Diseases / Q000378:metabolism*; D027701:Organic Cation Transport Proteins / Q000378:metabolism*; D000074058:Solute Carrier Family 22 Member 5
chemical_list: D026901:Membrane Transport Proteins; D027701:Organic Cation Transport Proteins; C492020:SLC22A5 protein, human; D000074058:Solute Carrier Family 22 Member 5; C116917:acylcarnitine; D042964:Acyl-CoA Dehydrogenase; C120109:SLC25A20 protein, human; D002333:Carnitine Acyltransferases; D002334:Carnitine O-Palmitoyltransferase; D002331:Carnitine