AMPK-independent pathways regulate skeletal muscle fatty acid oxidation.
The activation of AMP-activated protein kinase (AMPK) and phosphorylation/inhibition of acetyl-CoA carboxylase 2 (ACC2) is believed to be the principal pathway regulating fatty acid oxidation. However, during exercise AMPK activity and ACC Ser-221 phosphorylation does not always correlate with rates of fatty acid oxidation. To address this issue we have investigated the requirement for skeletal muscle AMPK in controlling aminoimidazole-4-carboxymide-1-beta-d-ribofuranoside (AICAR) and contraction-stimulated fatty acid oxidation utilizing transgenic mice expressing a muscle-specific kinase dead (KD) AMPK alpha2. In wild-type (WT) mice, AICAR and contraction increased AMPK alpha2 and alpha1 activities, the phosphorylation of ACC2 and rates of fatty acid oxidation while tending to reduce malonyl-CoA levels. Despite no activation of AMPK in KD mice, ACC2 phosphorylation was maintained, malonyl-CoA levels were reduced and rates of fatty acid oxidation were comparable between genotypes. During treadmill exercise both KD and WT mice had similar values of respiratory exchange ratio. These studies suggested the presence of an alternative ACC2 kinase(s). Using a phosphoproteomics-based approach we identified 18 Ser/Thr protein kinases whose phosphorylation was increased by greater than 25% in contracted KD relative to WT muscle. Utilizing bioinformatics we predicted that extracellular regulated protein-serine kinase (ERK1/2), inhibitor of nuclear factor (NF)-kappaB protein-serine kinase beta (IKKbeta) and protein kinase D (PKD) may phosphorylate ACC2 at Ser-221 but during in vitro phosphorylation assays only AMPK phosphorylated ACC2. These data demonstrate that AMPK is not essential for the regulation of fatty acid oxidation by AICAR or muscle contraction.
Dzamko
Nicolas
N
St Vincent's Institute, 9 Princes Street, Fitzroy, Victoria 3065, Australia. gsteinberg@svi.edu.au
Schertzer
Jonathan D
JD
Ryall
James G
JG
Steel
Rohan
R
Macaulay
S Lance
SL
Wee
Sheena
S
Chen
Zhi-Ping
ZP
Michell
Belinda J
BJ
Oakhill
Jonathan S
JS
Watt
Matthew J
MJ
Jørgensen
Sebastian Beck
SB
Lynch
Gordon S
GS
Kemp
Bruce E
BE
Steinberg
Gregory R
GR
D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000103:Acetyl-CoA Carboxylase / Q000737:chemistry / Q000378:metabolism; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002334:Carnitine O-Palmitoyltransferase / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004852:Epoxy Compounds / Q000494:pharmacology; D005227:Fatty Acids / Q000378:metabolism*; D015151:Immunoblotting; D008316:Malonyl Coenzyme A / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D008822:Mice, Transgenic; D009043:Motor Activity / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D010084:Oxidation-Reduction; D019308:Palmitic Acid / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D012265:Ribonucleotides / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology*; D002787:Sterol Esterase / Q000378:metabolism
D004791:Enzyme Inhibitors; D004852:Epoxy Compounds; D005227:Fatty Acids; D012265:Ribonucleotides; D019308:Palmitic Acid; D000620:Aminoimidazole Carboxamide; D008316:Malonyl Coenzyme A; D002334:Carnitine O-Palmitoyltransferase; C534978:Prkaa2 protein, mouse; D055372:AMP-Activated Protein Kinases; D002787:Sterol Esterase; C498191:Acacb protein, mouse; D000103:Acetyl-CoA Carboxylase; C031143:AICA ribonucleotide; C054207:etomoxir