Dietary tributyrin alters satellite cell activity in neonatal swine

Abstract

Satellite cells (SC), skeletal muscle stem cells, are responsible for all postnatal muscle growth and repair. Recently, we have shown that physiologically relevant concentrations of butyrate altered myogenesis in SC by enhancing terminal differentiation and the upregulation of myogenin mRNA expression. Our objective in this study was to determine the effect of dietary inclusion of tributyrin (Tb), a butyrate pro‐drug, has on neonatal muscle growth. Thirty neonatal piglets (24±8hrs old) were fed a standard milk replacer formula or formula supplemented with 0.50% (dry matter) spray dried Tb for 17d. Skeletal muscle tissue and SC were isolated from the longissimus dorsi (LD) for analysis of muscle growth parameters. Body weights were recorded daily and showed no difference in average daily body weight gain or feed efficiency. Animals that had received the Tb treatment diet had a significant increase (P<0.05) in the DNA:protein ratio in muscle. However, total concentrations of mTOR and the ratio of phosphorylated‐mTOR: total mTOR were not different between treatments. There was no difference in the relative abundance of the transcription factors Pax7 or MyoD in muscle tissue; however, there was an increase in myogenin expression in the LD from the Tb treated group (P<0.15). There was a numerical increase of in vivo proliferation rates of SC from the Tb group as assessed by BrdU staining. For in vitro analysis of SC behavior, the isolated SC were cultured for 48h in proliferation media and then switched to differentiation media for 96h. RNA was collected every 24h and RT‐PCR reveled a 100‐fold increase over the control group in myogenin expression 24h after they were induced to differentiate (P<0.05). Myogenin expression remained elevated in the Tb treatment group during differentiation (P<0.20), while there was no difference in Pax7 or MyoD expression at any time point. After 48h of differentiation, satellite cell fusion rate was assessed by immunofluorescent staining for myosin heavy chain (MyHC). Satellite cells from tributyrin treated animals had doubled the rate of fusion (P=0.10) over the control animals. Butyrate is a known inhibitor of histone deacetylases (HDACs) and when applied to satellite cells in culture it has arrested cell proliferation and enhanced terminal differentiation. In the present study, we have shown using an in vivo rapid muscle growth model that dietary inclusion of Tb can alter SC dynamics by way of HDAC regulation. Further investigation into the epigenetic targets could elucidate candidate genes for disease pathways and pharmacologic manipulation. Furthermore, we have provided evidence of accelerated myonuclear accretion in the neonatal pig; this may result in enhanced life‐time lean muscle growth which would significantly improve the sustainability of the swine production industry.Support or Funding InformationMaryland Agriculture Experiment Station