Probing the link between citrate and malonyl-CoA in perfused rat hearts.
Little is known about the sources of cytosolic acetyl-CoA used for the synthesis of malonyl-CoA, a key regulator of fatty acid oxidation in the heart. We tested the hypothesis that citrate provides acetyl-CoA for malonyl-CoA synthesis after its mitochondrial efflux and cleavage by cytosolic ATP-citrate lyase. We expanded on a previous study where we characterized citrate release from perfused rat hearts (Vincent G, Comte B, Poirier M, and Des Rosiers C. Citrate release by perfused rat hearts: a window on mitochondrial cataplerosis. Am J Physiol Endocrinol Metab 278: E846-E856, 2000). In the present study, we show that citrate release rates, ranging from 6 to 22 nmol/min, can support a net increase in malonyl-CoA concentrations induced by changes in substrate supply, at most 0.7 nmol/min. In experiments with [U-(13)C](lactate + pyruvate) and [1-(13)C]oleate, we show that the acetyl moiety of malonyl-CoA is derived from both pyruvate and long-chain fatty acids. This (13)C-labeling of malonyl-CoA occurred without any changes in its concentration. Hydroxycitrate, an inhibitor of ATP-citrate lyase, prevents increases in malonyl-CoA concentrations and decreases its labeling from [U-(13)C](lactate + pyruvate). Our data support at least a partial role of citrate in the transfer from the mitochondria to cytosol of acetyl units for malonyl-CoA synthesis. In addition, they provide a dynamic picture of malonyl-CoA metabolism: even when the malonyl-CoA concentration remains constant, there appears to be a constant need to supply acetyl-CoA from various carbon sources, both carbohydrates and lipids, for malonyl-CoA synthesis.
Poirier
Myriame
M
Department of Biochemistry, University of Montreal, Québec, Canada H3C 3J7.
Vincent
Geneviève
G
Reszko
Aneta E
AE
Bouchard
Bertrand
B
Kelleher
Joanne K
JK
Brunengraber
Henri
H
Des Rosiers
Christine
C
D001275:ATP Citrate (pro-S)-Lyase / Q000378:metabolism; D000105:Acetyl Coenzyme A / Q000378:metabolism; D000818:Animals; D002247:Carbon Isotopes; D002951:Citrates / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism*; D002952:Citric Acid Cycle / Q000502:physiology; D008401:Gas Chromatography-Mass Spectrometry; D066298:In Vitro Techniques; D008297:Male; D008316:Malonyl Coenzyme A / Q000378:metabolism*; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D019289:Pyruvic Acid / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley
D002247:Carbon Isotopes; D002951:Citrates; D019343:Citric Acid; D008316:Malonyl Coenzyme A; D000105:Acetyl Coenzyme A; D019289:Pyruvic Acid; C007999:hydroxycitric acid; D001275:ATP Citrate (pro-S)-Lyase