title: Niacin supplementation induces type II to type I muscle fiber transition in skeletal muscle of sheep.
abstract: BACKGROUND
  It was recently shown that niacin supplementation counteracts the obesity-induced muscle fiber transition from oxidative type I to glycolytic type II and increases the number of type I fibers in skeletal muscle of obese Zucker rats. These effects were likely mediated by the induction of key regulators of fiber transition, PPARδ (encoded by PPARD), PGC-1α (encoded by PPARGC1A) and PGC-1β (encoded by PPARGC1B), leading to type II to type I fiber transition and upregulation of genes involved in oxidative metabolism. The aim of the present study was to investigate whether niacin administration also influences fiber distribution and the metabolic phenotype of different muscles [M. longissimus dorsi (LD), M. semimembranosus (SM), M. semitendinosus (ST)] in sheep as a model for ruminants. For this purpose, 16 male, 11 wk old Rhoen sheep were randomly allocated to two groups of 8 sheep each administered either no (control group) or 1 g niacin per day (niacin group) for 4 wk.
  
  
  RESULTS
  After 4 wk, the percentage number of type I fibers in LD, SM and ST muscles was greater in the niacin group, whereas the percentage number of type II fibers was less in niacin group than in the control group (P < 0.05). The mRNA levels of PPARGC1A, PPARGC1B, and PPARD and the relative mRNA levels of genes involved in mitochondrial fatty acid uptake (CPT1B, SLC25A20), tricarboxylic acid cycle (SDHA), mitochondrial respiratory chain (COX5A, COX6A1), and angiogenesis (VEGFA) in LD, SM and ST muscles were greater (P < 0.05) or tended to be greater (P < 0.15) in the niacin group than in the control group.
  
  
  CONCLUSIONS
  The study shows that niacin supplementation induces muscle fiber transition from type II to type I, and thereby an oxidative metabolic phenotype of skeletal muscle in sheep as a model for ruminants. The enhanced capacity of skeletal muscle to utilize fatty acids in ruminants might be particularly useful during metabolic states in which fatty acids are excessively mobilized from adipose tissue, such as during the early lactating period in high producing cows.
authors.affiliation: Institute of Animal Nutrition and Nutrition Physiology, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 26-32, 35390 Giessen, Germany. klaus.eder@ernaehrung.uni-giessen.de.
authors.forename: Muckta
authors.initials: M
authors.lastname: Khan
authors.forename: Aline
authors.initials: A
authors.lastname: Couturier
authors.forename: Johanna F
authors.initials: JF
authors.lastname: Kubens
authors.forename: Erika
authors.initials: E
authors.lastname: Most
authors.forename: Frank-Christoph
authors.initials: FC
authors.lastname: Mooren
authors.forename: Karsten
authors.initials: K
authors.lastname: Krüger
authors.forename: Robert
authors.initials: R
authors.lastname: Ringseis
authors.forename: Klaus
authors.initials: K
authors.lastname: Eder
mesh_terms: D000818:Animals; D019587:Dietary Supplements; D005786:Gene Expression Regulation / Q000187:drug effects; D000960:Hypolipidemic Agents / Q000494:pharmacology; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects* / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D009525:Niacin / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D011897:Random Allocation; D012756:Sheep / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000960:Hypolipidemic Agents; D012333:RNA, Messenger; D014157:Transcription Factors; D009525:Niacin