Overexpression of carnitine palmitoyltransferase I in skeletal muscle in vivo increases fatty acid oxidation and reduces triacylglycerol esterification.
A key regulatory point in the control of fatty acid (FA) oxidation is thought to be transport of FAs across the mitochondrial membrane by carnitine palmitoyltransferase I (CPT I). To investigate the role of CPT I in FA metabolism, we used in vivo electrotransfer (IVE) to locally overexpress CPT I in muscle of rodents. A vector expressing the human muscle isoform of CPT I was electrotransferred into the right lateral muscles of the distal hindlimb [tibialis cranialis (TC) and extensor digitorum longus (EDL)] of rats, and a control vector expressing GFP was electrotransferred into the left muscles. Initial studies showed that CPT I protein expression peaked 7 days after IVE (+104%, P<0.01). This was associated with an increase in maximal CPT I activity (+30%, P < 0.001) and a similar increase in palmitoyl-CoA oxidation (+24%; P<0.001) in isolated mitochondria from the TC. Importantly, oxidation of the medium-chain FA octanoyl-CoA and CPT I sensitivity to inhibition by malonyl-CoA were not altered by CPT I overexpression. FA oxidation in isolated EDL muscle strips was increased with CPT I overexpression (+28%, P<0.01), whereas FA incorporation into the muscle triacylglycerol (TAG) pool was reduced (-17%, P<0.01). As a result, intramyocellular TAG content was decreased with CPT I overexpression in both the TC (-25%, P<0.05) and the EDL (-45%, P<0.05). These studies demonstrate that acute overexpression of CPT I in muscle leads to a repartitioning of FAs away from esterification and toward oxidation and highlight the importance of CPT I in regulating muscle FA metabolism.
Bruce
Clinton R
CR
Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst. clinton.bruce@baker.edu.au
Brolin
Camilla
C
Turner
Nigel
N
Cleasby
Mark E
ME
van der Leij
Feike R
FR
Cooney
Gregory J
GJ
Kraegen
Edward W
EW
D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002334:Carnitine O-Palmitoyltransferase / Q000235:genetics / Q000378:metabolism*; D018274:Electroporation; D004951:Esterification; D005227:Fatty Acids / Q000378:metabolism*; D006614:Hindlimb; D006801:Humans; D066298:In Vitro Techniques; D050356:Lipid Metabolism; D008297:Male; D008931:Mitochondria, Muscle / Q000201:enzymology; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction; D010168:Palmitates / Q000378:metabolism; D010171:Palmitoyl Coenzyme A / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014162:Transfection / Q000379:methods; D014280:Triglycerides / Q000378:metabolism*
D015415:Biomarkers; D005227:Fatty Acids; D010168:Palmitates; D014280:Triglycerides; D010171:Palmitoyl Coenzyme A; D002334:Carnitine O-Palmitoyltransferase