title: A leucine-supplemented diet restores the defective postprandial inhibition of proteasome-dependent proteolysis in aged rat skeletal muscle.
abstract: We tested the hypothesis that skeletal muscle ubiquitin-proteasome-dependent proteolysis is dysregulated in ageing in response to feeding. In Experiment 1 we measured rates of proteasome-dependent proteolysis in incubated muscles from 8- and 22-month-old rats, proteasome activities, and rates of ubiquitination, in the postprandial and postabsorptive states. Peptidase activities of the proteasome decreased in the postabsorptive state in 22-month-old rats compared with 8-month-old animals, while the rate of ubiquitination was not altered. Furthermore, the down-regulation of in vitro proteasome-dependent proteolysis that prevailed in the postprandial state in 8-month-old rats was defective in 22-month-old rats. Next, we tested the hypothesis that the ingestion of a 5% leucine-supplemented diet may correct this defect. Leucine supplementation restored the postprandial inhibition of in vitro proteasome-dependent proteolysis in 22-month-old animals, by down-regulating both rates of ubiquitination and proteasome activities. In Experiment 2, we verified that dietary leucine supplementation had long-lasting effects by comparing 8- and 22-month-old rats that were fed either a leucine-supplemented diet or an alanine-supplemented diet for 10 days. The inhibited in vitro proteolysis was maintained in the postprandial state in the 22-month-old rats fed the leucine-supplemented diet. Moreover, elevated mRNA levels for ubiquitin, 14-kDa ubiquitin-conjugating enzyme E2, and C2 and X subunits of the 20S proteasome that were characteristic of aged muscle were totally suppressed in 22-month-old animals chronically fed the leucine-supplemented diet, demonstrating an in vivo effect. Thus the defective postprandial down-regulation of in vitro proteasome-dependent proteolysis in 22-month-old rats was restored in animals chronically fed a leucine-supplemented diet.
authors.affiliation: Human Nutrition Research Centre of Clermont-Ferrand and Institut National de la Recherche Agronomique, Nutrition and Protein Metabolism Unit, 63122 Ceyrat, France.
authors.forename: Lydie
authors.initials: L
authors.lastname: Combaret
authors.forename: Dominique
authors.initials: D
authors.lastname: Dardevet
authors.forename: Isabelle
authors.initials: I
authors.lastname: Rieu
authors.forename: Marie-Noëlle
authors.initials: MN
authors.lastname: Pouch
authors.forename: Daniel
authors.initials: D
authors.lastname: Béchet
authors.forename: Daniel
authors.initials: D
authors.lastname: Taillandier
authors.forename: Jean
authors.initials: J
authors.lastname: Grizard
authors.forename: Didier
authors.initials: D
authors.lastname: Attaix
mesh_terms: D000375:Aging; D000409:Alanine / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001835:Body Weight; D019587:Dietary Supplements; D006868:Hydrolysis; D007930:Leucine / Q000008:administration & dosage* / Q000494:pharmacology; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D019518:Postprandial Period; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics / Q000502:physiology
chemical_list: D009124:Muscle Proteins; D012333:RNA, Messenger; D025801:Ubiquitin; D044763:Ubiquitin-Conjugating Enzymes; D046988:Proteasome Endopeptidase Complex; D007930:Leucine; D000409:Alanine