title: Effects of advanced age on whole-body protein synthesis and skeletal muscle mechanistic target of rapamycin signaling in horses.
abstract: OBJECTIVE
  To determine the effects of advanced age on whole-body protein synthesis and activation of the mechanistic target of rapamycin (mTOR) signaling pathway in skeletal muscle of horses.
  
  
  METHODS
  Six 22- to 26-year-old (aged) and six 7- to 14-year-old (mature) horses.
  
  
  METHODS
  Whole-body protein synthesis was measured with a 2-hour primed constant infusion of (13)C sodium bicarbonate, followed by a 4-hour primed constant infusion of 1-(13)C phenylalanine. After the infusions, a biopsy specimen was obtained from a gluteus medius muscle and activation of protein kinase B (Akt), p70 riboprotein S6 kinase (S6K1), riboprotein S6 (rpS6), and eukaryotic initiation factor 4E binding protein 1 (4EBP1) was determined with western immunoblot analysis. For all horses, inflammatory cytokine expression in muscle and blood samples was measured with quantitative real-time PCR analysis.
  
  
  RESULTS
  Advanced age had no effect on whole-body protein synthesis or the phosphorylation of Akt, rpS6, and 4EBP1; however, muscle specimens of aged horses had 42% lower phosphorylation of S6K1 than did those of mature horses. Aged and mature horses had similar inflammatory cytokine expression in muscle and blood samples.
  
  
  CONCLUSIONS
  The lower S6K1 activation for aged horses, compared with that for mature horses, could be indicative of low rates of muscle protein synthesis in aged horses. However, advanced age had no effect on any other indicators of whole-body or muscle protein synthesis or on measures of systemic or muscle inflammation, which suggested that protein metabolism and subsequently requirements may not differ between healthy mature and aged horses.
authors.affiliation: Department of Animal and Food Sciences, College of Agriculture, and the Center for Muscle Biology, College of Medicine, University of Kentucky, Lexington, KY 40546.
authors.forename: Ashley L
authors.initials: AL
authors.lastname: Wagner
authors.forename: Kristine L
authors.initials: KL
authors.lastname: Urschel
authors.forename: Alejandra
authors.initials: A
authors.lastname: Betancourt
authors.forename: Amanda A
authors.initials: AA
authors.lastname: Adams
authors.forename: David W
authors.initials: DW
authors.lastname: Horohov
mesh_terms: D000375:Aging; D000818:Animals; D015153:Blotting, Western / Q000662:veterinary; D005260:Female; D006736:Horses / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D014176:Protein Biosynthesis; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D015398:Signal Transduction; D020123:Sirolimus / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus