title: Resistance exercise increases AMPK activity and reduces 4E-BP1 phosphorylation and protein synthesis in human skeletal muscle.
abstract: Resistance exercise is a potent stimulator of muscle protein synthesis and muscle cell growth, with the increase in protein synthesis being detected within 2-3 h post-exercise and remaining elevated for up to 48 h. However, during exercise, muscle protein synthesis is inhibited. An increase in AMP-activated protein kinase (AMPK) activity has recently been shown to decrease mammalian target of rapamycin (mTOR) signalling to key regulators of translation initiation. We hypothesized that the cellular mechanism for the inhibition of muscle protein synthesis during an acute bout of resistance exercise in humans would be associated with an activation of AMPK and an inhibition of downstream components of the mTOR pathway (4E-BP1 and S6K1). We studied 11 subjects (seven men, four women) before, during, and for 2 h following a bout of resistance exercise. Muscle biopsy specimens were collected at each time point from the vastus lateralis. We utilized immunoprecipitation and immunoblotting methods to measure muscle AMPKalpha2 activity, and mTOR-associated upstream and downstream signalling proteins, and stable isotope techniques to measure muscle fractional protein synthetic rate (FSR). AMPKalpha2 activity (pmol min(-1) (mg protein)(-1)) at baseline was 1.7 +/- 0.3, increased immediately post-exercise (3.0 +/- 0.6), and remained elevated at 1 h post-exercise (P < 0.05). Muscle FSR decreased during exercise and was significantly increased at 1 and 2 h post-exercise (P < 0.05). Phosphorylation of 4E-BP1 at Thr37/46 was significantly reduced immediately post-exercise (P < 0.05). We conclude that AMPK activation and a reduced phosphorylation of 4E-BP1 may contribute to the inhibition of muscle protein synthesis during resistance exercise. However, by 1-2 h post-exercise, muscle protein synthesis increased in association with an activation of protein kinase B, mTOR, S6K1 and eEF2.
authors.affiliation: University of Texas Medical Branch, Department of Physical Therapy, Division of Rehabilitation Sciences, 301 University Blvd, Galveston, TX 77555-1144, USA.
authors.forename: Hans C
authors.initials: HC
authors.lastname: Dreyer
authors.forename: Satoshi
authors.initials: S
authors.lastname: Fujita
authors.forename: Jerson G
authors.initials: JG
authors.lastname: Cadenas
authors.forename: David L
authors.initials: DL
authors.lastname: Chinkes
authors.forename: Elena
authors.initials: E
authors.lastname: Volpi
authors.forename: Blake B
authors.initials: BB
authors.lastname: Rasmussen
mesh_terms: D055372:AMP-Activated Protein Kinases; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000328:Adult; D000596:Amino Acids / Q000378:metabolism; D001706:Biopsy; D018797:Cell Cycle Proteins; D015444:Exercise / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000493:pharmacokinetics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000378:metabolism; D008297:Male; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000378:metabolism* / Q000473:pathology; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012039:Regional Blood Flow / Q000502:physiology; D058570:TOR Serine-Threonine Kinases; D014891:Weight Lifting / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D007773:Lactates; D009097:Multienzyme Complexes; D009124:Muscle Proteins; D010750:Phosphoproteins; D011494:Protein Kinases; C546842:MTOR protein, human; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D005947:Glucose