International Symposium on Ruminant Physiology: Nutrient signaling to skeletal muscle and adipose tissue

Accretion of key carcass tissues such as skeletal muscle and adipose tissue is a direct effect of the specific nutrients available to support the growth and development of these key tissues. Whereas these nutrients vary greatly, many often are key regulators of important cell signaling pathways that regulate the growth and differentiation of these tissues. Postnatal skeletal muscle growth is a result of hypertrophy of the existing skeletal muscle fibers in animals. A major driver of skeletal muscle hypertrophy is protein accretion in the existing muscle fibers. This is a result of the balance between rate of protein synthesis and rate of protein degradation. Certain signaling pathways can alter the myosin heavy chain (MyHC) isoform type in postnatal skeletal muscle. Alterations in the various MyHC isoforms result in different degrees of postnatal skeletal muscle hypertrophy. An enzyme, AMP-activated protein kinase α, has been shown to affect expression of MyHC depending on sources and availability of energy to the skeletal muscle. The mTOR signaling pathway has been shown to be a critical regulator of protein synthesis in tissues such as skeletal muscle. Different components of this mTOR pathway are regulated by key nutrients such as individual AA. In many meat animals, such as cattle and sheep, there are different types of adipose tissue depots that grow and differentiate differently from each other. Two key types of adipose tissue in ruminants that have economic importance are subcutaneous and intramuscular adipose tissue. Many of the genes that control preadipocyte differentiation of these different adipose tissues in cattle are regulated by fatty acids circulating in plasma. It appeared that various fatty acids could affect cell signaling through a membrane bound G protein-coupled receptor signaling pathway. These nutrients, as well as micronutrients such as chromium, all have economic viability in the cattle feeding industry.