title: Regulation of muscle protein degradation, not synthesis, by dietary leucine in rats fed a protein-deficient diet.
abstract: The aim of this study was to elucidate the effects of long-term intake of leucine in dietary protein malnutrition on muscle protein synthesis and degradation. A reduction in muscle mass was suppressed by leucine-supplementation (1.5% leucine) in rats fed protein-free diet for 7 days. Furthermore, the rate of muscle protein degradation was decreased without an increase in muscle protein synthesis. In addition, to elucidate the mechanism involved in the suppressive effect of leucine, we measured the activities of degradation systems in muscle. Proteinase activity (calpain and proteasome) and ubiquitin ligase mRNA (Atrogin-1 and MuRF1) expression were not suppressed in animals fed a leucine-supplemented diet, whereas the autophagy marker, protein light chain 3 active form (LC3-II), expression was significantly decreased. These results suggest that the protein-free diet supplemented with leucine suppresses muscle protein degradation through inhibition of autophagy rather than protein synthesis.
authors.affiliation: United Graduate School of Agricultural Sciences, Iwate University, Morioka, Iwate, 020-8550, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Sugawara
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Ito
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Nishizawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Nagasawa
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects*; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D002154:Calpain / Q000378:metabolism; D018753:Diet, Protein-Restricted; D019587:Dietary Supplements; D007328:Insulin / Q000097:blood; D007930:Leucine / Q000008:administration & dosage*; D008297:Male; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D002154:Calpain; D007328:Insulin; D007930:Leucine; D008869:Microtubule-Associated Proteins; D009124:Muscle Proteins; D046988:Proteasome Endopeptidase Complex; D044767:Ubiquitin-Protein Ligases; C526109:Anxa3 protein, rat