title: Activation of mammalian target of rapamycin signaling in skeletal muscle of neonatal chicks: effects of dietary leucine and age.
abstract: The mammalian target of rapamycin (mTOR) signaling pathway is necessary for cellular protein synthesis regulation. Leucine was reported to stimulate muscle protein synthesis in mammalian embryos and neonates, but in higher animals (chickens) the effect of dietary leucine on mTOR signaling is unknown. Thus, we investigated the effects of dietary leucine and age on mRNA expression and phosphorylation of mTOR as well as its downstream targets, ribosomal protein S6 kinase (S6K1) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1) in chick pectoral muscles. One hundred eighty newly hatched male chicks were randomly assigned to 1 of 3 dietary leucine treatment groups (1.43, 1.73, and 2.03% leucine) for 14 d, respectively. Each treatment group consisted of 6 cages with 10 chicks each. On d 3, 7, and 14, plasma insulin and leucine were measured and target gene expression and phosphorylation was assessed. Dietary leucine influenced plasma leucine but not insulin, and plasma leucine and insulin declined with chick age. The mTOR, S6K1, and 4E-BP1 mRNA expression and phosphorylation within chick pectoral muscles were upregulated with increased dietary leucine but downregulated with increased chick age. Thus, high dietary leucine activates target of rapamycin signaling pathways in skeletal muscle of neonatal chicks to stimulate muscle protein synthesis, and this pathway is attenuated with aging.
authors.affiliation: Feed Research Institute, Chinese Academy of Agricultural Sciences, No. 12, Zhong-guan-cun Nandajie, Haidian, Beijing 100081, China.
authors.forename: Huiling
authors.initials: H
authors.lastname: Deng
authors.forename: Aijuan
authors.initials: A
authors.lastname: Zheng
authors.forename: Guohua
authors.initials: G
authors.lastname: Liu
authors.forename: Wenhuan
authors.initials: W
authors.lastname: Chang
authors.forename: Shu
authors.initials: S
authors.lastname: Zhang
authors.forename: Huiyi
authors.initials: H
authors.lastname: Cai
mesh_terms: D000375:Aging; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D000831:Animals, Newborn; D002645:Chickens / Q000254:growth & development / Q000378:metabolism*; D004032:Diet / Q000662:veterinary*; D004305:Dose-Response Relationship, Drug; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects* / Q000502:physiology; D007930:Leucine / Q000494:pharmacology*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D007930:Leucine
keywords: chick; leucine; skeletal muscle; target of rapamycin