title: 25-Hydroxycholecalciferol Enhances Male Broiler Breast Meat Yield through the mTOR Pathway.
abstract: BACKGROUND
  In recent years, there has been a growing body of evidence indicating that replacing cholecalciferol (vitamin D₃) with 25-hydroxycholecalciferol [25(OH)D₃] through dietary supplementation enhances breast meat yield in broiler chickens. However, the underlying molecular mechanisms are still unknown.
  
  
  OBJECTIVE
  We investigated the effect of 25(OH)D₃ on male broiler growth performance (body weight, feed intake, feed conversion ratio, and breast meat yield), muscle protein synthesis, and the potential underlying molecular mechanisms.
  
  
  METHODS
  Male Cobb 500 broiler chickens were divided into 4 body weight-matched groups and received a control diet with normal cholecalciferol (2760 IU/kg feed) for 42 d, a diet with high concentrations of cholecalciferol (5520 IU/kg feed) for 42 d, or a diet with 25(OH)D₃ (5520 IU/kg feed) for 42 d (HyD-42). A fourth group consumed the HyD-42 for 21 d and then control feed for 21 d (HyD-21) (n = 360 birds, 12 replicates/treatment). Food and clean water were available for ad libitum consumption. At the end of the 42-d experiment, protein turnover was measured by phenylalanine flooding dose. Breast muscle tissues were collected and protein synthesis-related gene and protein expression were measured by real time polymerase chain reaction and Western blot, respectively. Functional studies were performed in vitro with the use of a quail myoblast (QM7) cell line. QM7 cells were treated with 2 doses (1 nM and 10 nM) of cholecalciferol or 25(OH)D₃ alone or in combination with 100 nM rapamycin, and cell proliferation was determined by cell proliferation assay. Protein synthesis-related gene and protein expression were also determined.
  
  
  RESULTS
  The HyD-42 increased 25(OH)D₃ circulating concentrations by 126% (P < 0.05), enhanced breast meat yield (P < 0.05), and increased the fractional rate of protein synthesis by 3-fold (P < 0.05) compared with the control diet. Molecular analyses revealed that breast muscle from chickens consuming the HyD-42 expressed significantly higher concentrations of vitamin D receptor (VDR), phospho mechanistic target of rapamycin(Ser2481), phospho ribosomal P70 S6 kinase (RPS6K)(Thr421/Ser424), and antigen Ki-67 (Ki67) compared with the other groups. In line with the in vivo data, in vitro functional studies showed that cells treated with 25(OH)D₃ for 24 h had increased VDR expression, and activated the mechanistic target of rapamycin (mTOR)/S6 kinase (S6K) pathway, enhanced Ki67 protein concentrations, and induced QM7 cell proliferation compared with untreated or cholecalciferol-treated cells. Blocking the mTOR pathway with rapamycin reversed these effects.
  
  
  CONCLUSIONS
  Taken together, our findings provide evidence that the effects of 25(OH)D₃ on male broiler breast muscle are likely mediated through the mTOR-S6K pathway.
authors: Center of Excellence for Poultry Science and.
authors: Karen
authors: K
authors: Vignale
authors: Center of Excellence for Poultry Science and.
authors: Elizabeth S
authors: ES
authors: Greene
authors: Center of Excellence for Poultry Science and.
authors: Justina V
authors: JV
authors: Caldas
authors: Center of Excellence for Poultry Science and.
authors: Judith A
authors: JA
authors: England
authors: Center of Excellence for Poultry Science and.
authors: Nirun
authors: N
authors: Boonsinchai
authors: Center of Excellence for Poultry Science and.
authors: Phiphob
authors: P
authors: Sodsee
authors: University of Arkansas Stable Isotope Laboratory, Department of Biological Sciences, University of Arkansas, Fayetteville, AR.
authors: Erik D
authors: ED
authors: Pollock
authors: Center of Excellence for Poultry Science and dridi@uark.edu.
authors: Sami
authors: S
authors: Dridi
authors: Center of Excellence for Poultry Science and dridi@uark.edu.
authors: Craig N
authors: CN
authors: Coon
mesh_terms: D000818:Animals; D017849:Animals, Inbred Strains; D001131:Arkansas; D030161:Avian Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D002112:Calcifediol / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002645:Chickens / Q000097:blood / Q000254:growth & development* / Q000378:metabolism; D004032:Diet / Q000662:veterinary*; D002149:Energy Intake; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D008297:Male; D008460:Meat / Q000032:analysis; D024510:Muscle Development; D009124:Muscle Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010369:Pectoralis Muscles / Q000254:growth & development* / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D055550:Protein Stability / Q000187:drug effects; D011784:Quail; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015430:Weight Gain
chemical_list: D030161:Avian Proteins; D009124:Muscle Proteins; D047428:Protein Kinase Inhibitors; D058570:TOR Serine-Threonine Kinases; D002112:Calcifediol
keywords: 25(OH)D3; VDR; broiler breast muscle; gene expression; mTOR pathway; protein expression; protein synthesis