TRIBUTYRIN, A BUTYRATE PRO-DRUG, AS A MUSCLE GROWTH PROMOTER IN A PORCINE MODEL
Murray, Robert Len
Stahl, Chad H.
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Postnatal muscle growth is dependent on myonuclear accretion and subsequent protein synthesis and accumulation. Altering the ability of muscle resident stem cells (satellite cells, SC), which provide nuclei to the growing muscle fiber, to progress through their myogenic lineage can have lifelong effects on muscle growth and repair. The use of butyrate, a histone deacetylase (HDAC) inhibitor, has promoted SC myogenesis in vitro. In animal models, dietary butyrate has improved growth performance and has had promising results in treating myopathic conditions, but the impact of dietary butyrate on SC activity and the direct promotion of muscle growth have not been examined. In the first experiment, we investigated whether the use of a physiologically relevant concentration of butyrate (0, 0.1, 0.5, or 1mM) could enhance the myogenic potential of porcine SC. We found increased expression of myogenin, the late stage myogenic regulatory factor, and increased SC fusion in the treated groups, suggesting an increased capacity during terminal differentiation. We further tested this hypothesis by conducting an animal study to test the effects of tributyrin, a butyrate pro-drug, on in vivo SC behavior. We found that tributyrin inclusion (0.25% and 0.5%) into the milk replacer of neonatal piglets led to significant increases in muscle DNA content, suggesting increased myonuclear accumulation. The neonatal portion (21-days) of the study was repeated, and the animals were then weaned and crossed into dry nursery treatment diets. At the end of the 37-day nursery feeding, animals that received tributyrin in their milk replacer formula weighed significantly more and had increased muscle hypertrophy than the untreated animals. Also, SC from treated animals responded similarly ex vivo to those in the first experiment, suggesting an increased capacity to progress through the differentiation process. We determined in our final experiment that tributyrin supplementation altered the epigenetic landscape of SC by globally reducing the transcriptionally repressive chromatin mark H3K27me3 around key genes. In addition, we found that this is not the sole mechanism through which butyrate alters SC behavior. These findings help support the notion that tributyrin may be used to enhance muscle growth and could prove useful at treating myopathies.