AMPK activation increases uncoupling protein-3 expression and mitochondrial enzyme activities in rat muscle without fibre type transitions.
The present study examined the effect of chronic activation of 5'-AMP-activated protein kinase (AMPK) on the metabolic profile, including uncoupling protein-3 (UCP-3) and myosin heavy chain (MHC)-based fibre phenotype of rodent fast-twitch tibialis anterior muscle. Sprague-Dawley rats were given daily injections of 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), a known activator of AMPK, or vehicle (control) for 28 days. After AICAR treatment, UCP-3 expression at the mRNA level was elevated 1.6 +/- 0.1-fold (P < 0.006) and corresponded to a 3.3 +/- 0.2-fold increase in UCP-3 protein content (P < 0.0001). In addition, the activities of the mitochondrial reference enzymes citrate synthase (EC 4.1.3.7) and 3-hydroxyacyl-CoA-dehydrogenase (EC 1.1.1.35), which are known to increase in proportion to mitochondrial volume density, were elevated 1.6-fold (P < 0.006), while the activity of lactate dehydrogenase (EC 1.1.1.27) was reduced to 80 % of control (P < 0.02). No differences were detected after AICAR treatment in the activities of the glycolytic reference enzymes glyceraldehydephosphate dehydrogenase (EC 1.2.1.12) or phosphofructokinase (EC 2.7.1.11), nor were MHC-based fibre-type transitions observed, using immunohistochemical or electrophoretic analytical methods. These changes could not be attributed to variations in inter-organ signalling by metabolic substrates or insulin. We conclude that an AMPK-dependent pathway of signal transduction does mimic some of the metabolic changes associated with chronic exercise training, but does not affect expression of the MHC-based structural phenotype. Thus, the metabolic and MHC-based fibre types do not appear to be regulated in a co-ordinated way, but may be independently modified by different signalling pathways.
Putman
Charles T
CT
Exercise Biochemistry Laboratory, Faculty of Physical Education, University of Alberta, E-417 Van Vliet Centre, Edmonton, Alberta, Canada T6G 2H9. tputman@ualberta.ca
Kiricsi
Monika
M
Pearcey
Jean
J
MacLean
Ian M
IM
Bamford
Jeremy A
JA
Murdoch
Gordon K
GK
Dixon
Walter T
WT
Pette
Dirk
D
D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D007473:Ion Channels; D008297:Male; D008931:Mitochondria, Muscle / Q000201:enzymology*; D024101:Mitochondrial Proteins; D009097:Multienzyme Complexes; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012265:Ribonucleotides / Q000494:pharmacology; D000071247:Uncoupling Protein 3
D002352:Carrier Proteins; D007473:Ion Channels; D024101:Mitochondrial Proteins; D009097:Multienzyme Complexes; D012333:RNA, Messenger; D012265:Ribonucleotides; C000604394:Ucp3 protein, rat; D000071247:Uncoupling Protein 3; D000620:Aminoimidazole Carboxamide; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D018995:Myosin Heavy Chains; C031143:AICA ribonucleotide