title: Effect of branched-chain amino acid supplementation during unloading on regulatory components of protein synthesis in atrophied soleus muscles.
abstract: Maintenance of skeletal muscle mass depends on the equilibrium between protein synthesis and protein breakdown; diminished functional demand during unloading breaks this balance and leads to muscle atrophy. The current study analyzed time-course alterations in regulatory genes and proteins in the unloaded soleus muscle and the effects of branched-chain amino acid (BCAA) supplementation on muscle atrophy and abundance of molecules that regulate protein turnover. Short-term (6 days) hindlimb suspension of rats resulted in significant losses of myofibrillar proteins, total RNA, and rRNAs and pronounced atrophy of the soleus muscle. Muscle disuse induced upregulation and increases in the abundance of the eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), increases in gene and protein amounts of two ubiquitin ligases (muscle RING-finger protein 1 and muscle atrophy F-box protein), and decreases in the expression of cyclin D1, the ribosomal protein S6 kinase 1, the mammalian target of rapamycin (mTOR), and ERK1/2. BCAA addition to the diet did not prevent muscle atrophy and had no apparent effect on regulators of proteasomal protein degradation. However, BCAA supplementation reduced the loss of myofibrillar proteins and RNA, attenuated the increases in 4E-BP1, and partially preserved cyclin D1, mTOR and ERK1 proteins. These results indicate that BCAA supplementation alone does not oppose protein degradation but partly preserves specific signal transduction proteins that act as regulators of protein synthesis and cell growth in the non-weight-bearing soleus muscle.
authors.affiliation: Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601, Japan.
authors.forename: Gustavo
authors.initials: G
authors.lastname: Bajotto
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Sato
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Kitaura
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Shimomura
mesh_terms: D000597:Amino Acids, Branched-Chain / Q000494:pharmacology*; D000818:Animals; D019587:Dietary Supplements; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects; D019417:Hindlimb Suspension / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D009133:Muscular Atrophy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D010805:Physical Conditioning, Animal / Q000502:physiology; D014176:Protein Biosynthesis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D000597:Amino Acids, Branched-Chain