Differential Regulation of Protein Synthesis and mTOR Signaling in Skeletal Muscle and Visceral Tissues of Neonatal Pigs after a Meal

Abstract

Neonates have a high rate of growth driven by elevated rates of skeletal muscle protein synthesis. Feeding stimulates protein synthesis but the time course of the changes in different tissues has not been determined. The aim of this study was to evaluate the time course of the changes in protein synthesis rates and translation initiation factor activation in skeletal muscle and visceral tissues after a meal. Neonatal pigs (n=36; 5–7 day old) received a meal providing one‐sixth of daily requirements and were sacrificed at 0, 30, 60, 90, 120, or 240 min after feeding. Protein synthesis increased 30 to 120 min in glycolytic muscles, 30 to 90 min in mixed fiber type muscle and did not increase in oxidative muscle post‐feeding. Protein synthesis increased in liver 30 to 120 min, jejunum 30 to 60 min and pancreas 30 min post‐feeding and did not increase in kidney and heart. Eukaryotic initiation factor (eIF) 4E binding protein (4EBP1) and rp S6 kinase 1 (S6K1) phosphorylation increased 30 to 90 min in all tissues. These results suggest that feeding stimulates mTOR signaling in skeletal muscle and visceral tissues. However, mTOR activation alone was not sufficient to stimulate protein synthesis in all tissues. (Supported by NIH grants AR‐44474 and AR‐51563 and USDA/ARS 6250510000‐33).Grant Funding Source: NIH grants AR‐44474 and AR‐51563 and USDA/ARS 6250510000‐33