Leucine induces myofibrillar protein accretion in cultured skeletal muscle through mTOR dependent and -independent control of myosin heavy chain mRNA levels.
METHODS
Nutritional intervention during muscle wasting aims to attenuate net muscle protein loss. Branched chain amino acids, especially leucine, are able to stimulate the anabolic mammalian target of rapamycin (mTOR) signalling cascade and protein synthesis. It has been suggested that muscle myofibrillar protein expression is more responsive to amino acid supplementation compared to cytoplasmic proteins, although accretion of myofibrillar proteins has not extensively been investigated. We hypothesized that leucine specifically increases myofibrillar protein synthesis in skeletal muscle.


RESULTS
This hypothesis was investigated in C2C12 skeletal muscle cells using physiologically relevant culture conditions. Leucine supplementation specifically increased myofibrillar protein accretion, including myosin heavy chain-slow and -fast and myosin light chain 1 and -3 in C2C12 cells. Neither total protein content, nor de novo protein synthesis was affected, despite leucine-induced increased 4E-BP1 and S6K1 phosphorylation. Leucine supplementation did not affect myogenesis, measured by creatine kinase activity and myoblast fusion, either. Remarkably, leucine-induced increased myofibrillar protein accretion was accompanied by elevated MyHC mRNA levels, which involved mTOR-dependent and -independent regulation of MyHC-4 and MyHC-7 gene-expression, respectively.


CONCLUSIONS
This study clearly demonstrates myofibrillar and not generic protein accretion in skeletal muscle following leucine supplementation, and suggests this involves pre-translational control of MyHC expression by leucine.
Top Institute Food & Nutrition-TIFN, Wageningen, The Netherlands. a.haegens@maastrichtuniversity.nl
Astrid
A
Haegens
Annemie M
AM
Schols
Anon L
AL
van Essen
Luc J
LJ
van Loon
Ramon C
RC
Langen
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D003402:Creatine Kinase / Q000378:metabolism; D019587:Dietary Supplements; D039642:Eukaryotic Initiation Factors; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology; D007930:Leucine / Q000494:pharmacology*; D051379:Mice; D024510:Muscle Development / Q000187:drug effects; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D009210:Myofibrils / Q000187:drug effects / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics* / Q000378:metabolism; D018994:Myosin Light Chains / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C499527:Eif4ebp1 protein, mouse; D039642:Eukaryotic Initiation Factors; D009124:Muscle Proteins; D018994:Myosin Light Chains; D010750:Phosphoproteins; D007334:Insulin-Like Growth Factor I; C546843:mTOR protein, mouse; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse; D058570:TOR Serine-Threonine Kinases; D003402:Creatine Kinase; D018995:Myosin Heavy Chains; D007930:Leucine