238 Leucine Supplementation Enhances Protein Synthesis in Lean Tissue Through a Sestrin2-GATOR2 and Raga-mTORC1 Signaling Pathway in a Preterm Piglet Model

Abstract

Abstract Extrauterine growth restriction is common in preterm infants and is associated with reduced lean growth and long-term morbidities. We previously showed that leucine (Leu) acts as a nutrient signal to stimulate protein synthesis, and that in neonatal pigs born at term intermittent parenteral Leu pulses during continuous feeding increases skeletal muscle mTORC1 signaling and protein synthesis. The objective of this study was to determine the validity of the hypothesis that leu pulsing during continuous feeding enhances mTORC1 signaling via a Sestrin-mediated pathway to increase protein synthesis in lean tissue in the preterm piglet. Pigs delivered by cesarean section at 105 d gestation were continuously fed a protein and energy balanced milk-replacer diet [195 kcal ME and 13.5 g protein (kg body weight; BW)-1·d-1)]. Pigs (n = 11-12) were randomly assigned to Leu (LEU) or Alanine (ALA, isonitrogenous control) groups and treatments were administered as a pulse (1.6 mmol·kg BW-1·h-1) for 1 h every 4 h for 21 d. Indices of amino acid signaling and mTORC1 activation were determined postprandially, 60 min after initiation of the last pulse on day 24. Final body weight was greater (P < 0.05) and longissimus muscle weight was heavier in LEU than ALA pigs (P = 0.01). Upstream of mTORC1 activation, the abundance of the Sestrin2-GATOR2 complex was less and the RagA-mTORC1 complex was greater in longissimus muscle and gastrocnemius muscle of LEU compared with ALA pigs (P < 0.05). Downstream of mTORC1, the phosphorylation of S6K1 and 4EBP1 and abundance of the eIF4E-eIF4G complex were greater in longissimus muscle and gastrocnemius muscle of LEU compared with ALA pigs (P < 0.05). Fractional rates of protein synthesis in longissimus muscle and gastrocnemius muscle were greater in LEU compared with ALA pigs (P < 0.05). These results show that leucine supplementation enhances mTORC1-activated translation initiation in skeletal muscle of the preterm piglet via a Leu-sensing pathway mediated bySestrin2 and the Rag proteins. This leucine-mediated cascade promotes skeletal muscle and body weight gain by increasing muscle protein synthesis.