Overexpression of UCP3 in cultured human muscle lowers mitochondrial membrane potential, raises ATP/ADP ratio, and favors fatty acid vs. glucose oxidation.
The skeletal muscle mitochondrial uncoupling protein-3 (UCP3) promotes substrate oxidation, but direct evidence for its metabolic role is lacking. Here, we show that UCP3 overexpression in cultured human muscle cells decreased mitochondrial membrane potential (DYm). Despite this, the ATP content was not significantly decreased compared with control cells, whereas ADP content was reduced and thus the ATP/ADP ratio raised. This finding was contrasts with the effect caused by the chemical protonophoric uncoupler, CCCP, which lowered DYm, ATP, and the ATP/ADP ratio. UCP3-overexpression enhanced oxidation of oleate, regardless of the presence of glucose, whereas etomoxir, which blocks fatty acid entry to mitochondria, suppressed the UCP3 effect. Glucose oxidation was stimulated in UCP3-overexpressing cells, but this effect was inhibited by oleate. UCP3 caused weak increase of both 2-Deoxyglucose uptake and glycolytic rate, which differed from the marked stimulation by CCCP. We concluded that UCP3 promoted nutrient oxidation by lowering DYm and enhanced fatty acid-dependent inhibition of glucose oxidation. Unlike the uncoupler CCCP, however, UCP3 raised the ATP/ADP ratio and modestly increased glucose uptake and glycolysis. We propose that this differential effect provides a biological significance to UCP3, which is up-regulated in metabolic stress situations where it could be involved in nutrient partitioning.
García-Martinez
C
C
Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, 08028 Barcelona, Spain.
Sibille
B
B
Solanes
G
G
Darimont
C
C
Macé
K
K
Villarroya
F
F
Gómez-Foix
A M
AM
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D005227:Fatty Acids / Q000378:metabolism*; D015870:Gene Expression; D005947:Glucose / Q000378:metabolism*; D006019:Glycolysis; D006801:Humans; D007425:Intracellular Membranes / Q000502:physiology*; D007473:Ion Channels; D008564:Membrane Potentials / Q000502:physiology; D008931:Mitochondria, Muscle / Q000502:physiology*; D024101:Mitochondrial Proteins; D009132:Muscles / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D010084:Oxidation-Reduction; D014475:Uncoupling Agents; D000071247:Uncoupling Protein 3
D002352:Carrier Proteins; D005227:Fatty Acids; D007473:Ion Channels; D024101:Mitochondrial Proteins; C000604392:UCP3 protein, human; D014475:Uncoupling Agents; D000071247:Uncoupling Protein 3; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D005947:Glucose