title: Glycine Regulates Protein Turnover by Activating Protein Kinase B/Mammalian Target of Rapamycin and by Inhibiting MuRF1 and Atrogin-1 Gene Expression in C2C12 Myoblasts.
abstract: BACKGROUND
  The regulation of protein turnover in skeletal muscle is essential for the maintenance of integrity, growth, and function of this tissue. We recently reported that glycine enhances skeletal muscle growth in young pigs. However, the underlying mechanisms remain unknown.
  
  
  OBJECTIVE
  This study was conducted with a mouse myoblast cell line, C2C12, to test the hypothesis that glycine activates protein kinase B/mammalian target of rapamycin (Akt/mTOR), as well as inhibits 5'-adenosine monophosphate-activated protein kinase (AMPK) and the expression of genes for proteolysis.
  
  
  METHODS
  C2C12 myoblasts were cultured with 0, 0.25 (physiologic concentration in mouse plasma), 0.5, or 1.0 mmol glycine/L. Cell proliferation, activation of mammalian target of rapamycin complex 1 (mTORC1), AMPK signaling, mRNA levels of atrogin-1 and muscle-specific ring finger protein 1 (MuRF1), and protein synthesis and degradation were measured in the absence or presence of an Akt inhibitor, LY294002, or an AMPK activator, 5-aminoimidazole-4-carboxyamide ribonucleoside (AICAR).
  
  
  RESULTS
  Compared with control cells, 0.25-1.0 mmol glycine/L enhanced cell growth (by 12-15%) after 24 h (P < 0.05). Glycine treatment led to increased DNA replication (by 70-80%) while enhancing mTORC1 activation by upregulating Akt and inhibiting AMPK signaling (P < 0.05). Accordingly, glycine exposure increased (P < 0.05) the rate of protein synthesis (by 20-80%) and inhibited (P < 0.05) the rate of protein degradation (by 15-30%) in a concentration-dependent manner in C2C12 cells. These observations were validated by the use of an Akt inhibitor, LY294002, or an AMPK activator, AICAR. Moreover, glycine addition resulted in decreased mRNA levels for atrogin-1 and MuRF1 (by 20-40% and 30-50%, respectively; P < 0.05). The repressing effect of glycine on the expression of MuRF1, instead of atrogin-1, was abolished by LY294002 (P < 0.05).
  
  
  CONCLUSIONS
  These findings indicate that glycine plays a previously unrecognized role in enhancing protein synthesis and inhibiting protein degradation in C2C12 cells. Glycine regulates protein turnover by activating mTORC1 and by inhibiting the expression of genes for proteolysis. Our results indicate that glycine is a functional amino acid that improves muscle cell growth.
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: KaiJi
authors: K
authors: Sun
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and bio2046@hotmail.com.
authors: Zhenlong
authors: Z
authors: Wu
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Yun
authors: Y
authors: Ji
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.|Department of Animal Science, Texas A&M University, College Station, TX.
authors: Guoyao
authors: G
authors: Wu
mesh_terms: D000818:Animals; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D005998:Glycine / Q000494:pharmacology*; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D032446:Myoblasts / Q000187:drug effects* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000070584:Tripartite Motif Proteins / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D002867:Chromones; D009025:Morpholines; D009124:Muscle Proteins; D000070584:Tripartite Motif Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C486691:Fbxo32 protein, mouse; D044843:SKP Cullin F-Box Protein Ligases; C499084:Trim63 protein, mouse; D044767:Ubiquitin-Protein Ligases; C546843:mTOR protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D005998:Glycine
keywords: AMPK; C2C12; PI3K/Akt; glycine; mTOR; protein turnover