Regulation of muscle growth in neonates

Authors: Davis, Teresa; Fiorotto, Marta

Submitted to: Current Opinion in Clinical Nutrition and Metabolic Care
Publication Type: Review Article
Publication Acceptance Date: 10/22/2008
Publication Date: 1/1/2009
Citation: Davis, T.A., Fiorotto, M.L. 2009. Regulation of muscle growth in neonates. Current Opinion in Clinical Nutrition and Metabolic Care. 12(1):78-85.

Interpretive Summary: The skeletal muscle of healthy newborn infants grows at more rapid rates than the other tissues in their bodies. This is because the rate at which their muscles synthesize muscle protein increases profoundly when they eat. After eating, both the rise in amino acids, which are the building blocks of proteins, and the hormone insulin stimulate the synthesis of proteins in muscle. Intracellular signaling proteins stimulate the synthesis of muscle proteins by becoming activated in response to the rise in amino acids and insulin. The activity of these signaling proteins is elevated in muscle of the newborn and decreases with age. The high capacity of muscle in the newborn to activate these signaling components in skeletal muscle of the neonate contributes to the rapid growth of muscle in neonates. This capacity is further supported by enhanced proliferation of stem cells in muscle.

Technical Abstract: This review reports recent findings on the multiple factors that regulate skeletal muscle growth in neonates. Skeletal muscle is the fastest growing protein mass in neonates. The high rate of neonatal muscle growth is due to accelerated rates of protein synthesis accompanied by the rapid accumulation of muscle nuclei. Feeding profoundly stimulates muscle protein synthesis in neonates and the response decreases with age. The feeding-induced stimulation of muscle protein synthesis is modulated by enhanced sensitivity to the postprandial rise in insulin and amino acids. Insulin and amino acid signaling components have been identified that are involved in the feeding-induced stimulation of protein synthesis in neonatal muscle. The enhanced activation of these signaling components in skeletal muscle of the neonate contributes to the high rate of muscle protein synthesis and rapid gain in muscle protein mass in neonates. Recent findings suggest that the immature muscle has a heightened capacity to activate signaling cascades that promote translation initiation in response to the postprandial rise in insulin and amino acids, thereby enabling their efficient utilization for muscle growth. This capacity is further supported by enhanced satellite cell proliferation, but how these two processes are linked remains to be established.