|O'connor, Pamela m.j.|
Submitted to: American Journal of Physiology - Endocrinology and Metabolism
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/30/2007
Publication Date: 6/5/2007
Citation: Jeyapalan, A.S., Orellana, R.A., Suryawan, A., O'Connor, P.M.J., Nguyen, H.V., Escobar, J., Frank, J.W., Davis, T.A. 2007. Glucose stimulates protein synthesis in skeletal muscle of neonatal pigs through an AMPK- and mTOR-independent process. American Journal of Physiology Endocrinology and Metabolism. 293(2):E595-E603. Interpretive Summary: Some studies suggest that glucose plays a role in allowing protein synthesis regulation in the muscle of neonates to enhance growth. This study aimed to determine whether glucose, independently of insulin and amino acids, is involved in augmenting protein synthesis in skeletal muscle of neonates. In this study, we manipulated hormones to allow stimulation of protein synthesis in muscle by glucose in neonatal pigs. We found that glucose alone increased protein synthesis in muscles but not in other tissues of neonates, and there were cellular changes that explained the possible molecular mechanism. The results suggest that glucose stimulates protein synthesis in neonates, independently of insulin and amino acids. This phenomenon is important to understand the medical management of neonates that are kept fasting and solely with dextrose in intravenous fluids.
Technical Abstract: Skeletal muscle protein synthesis is elevated in neonates in part due to an enhanced response to the rise in insulin and amino acids after eating. In vitro studies suggest that glucose plays a role in protein synthesis regulation. To determine whether glucose, independently of insulin and amino acids, is involved in the postprandial rise in skeletal muscle protein synthesis, pancreatic-substrate clamps were performed in neonatal pigs. Insulin secretion was inhibited with somatostatin and insulin was infused to reproduce fasting or fed levels, while glucose and amino acids were clamped at fasting or fed levels. Fractional protein synthesis rates and translational control mechanisms were examined. Raising glucose alone increased protein synthesis in fast-twitch glycolytic muscles but not in other tissues. The response in muscle was associated with increased phosphorylation of protein kinase B (PKB) and enhanced formation of the active eIF4E•eIF4G complex but no change in phosphorylation of AMP-activated protein kinase (AMPK), tuberous sclerosis complex 2 (TSC2), mammalian target of rapamycin (mTOR), 4E-binding protein-1 (4E-BP1), ribosomal protein S6 kinase (S6K1), or eukaryotic elongation factor 2 (eEF2). Raising glucose, insulin, and amino acids increased protein synthesis in most tissues. The response in muscle was associated with phosphorylation of PKB, mTOR, S6K1, and 4E-BP1 and enhanced eIF4E•eIF4G formation. The results suggest that the postprandial rise in glucose, independently of insulin and amino acids, stimulates protein synthesis in neonates, and this response is specific to fast-twitch glycolytic muscle and occurs by AMPK- and mTOR-independent pathways.