Location: Children's Nutrition Research CenterTitle: Leucine supplementation does not restore diminished skeletal muscle satellite cell abundance and myonuclear accretion when protein intake is limiting in neonatal pigs
|RUDAR, MARKO - Children'S Nutrition Research Center (CNRC)|
|COLUMBUS, DANIEL - Children'S Nutrition Research Center (CNRC)|
|STEINHOFF-WAGNER, JULIA - Children'S Nutrition Research Center (CNRC)|
|SURYAWAN, AGUS - Children'S Nutrition Research Center (CNRC)|
|NGUYEN, HANH - Children'S Nutrition Research Center (CNRC)|
|FLEISCHMANN, RYAN - Children'S Nutrition Research Center (CNRC)|
|DAVIS, TERESA - Children'S Nutrition Research Center (CNRC)|
|FIOROTTO, MARTA - Children'S Nutrition Research Center (CNRC)|
Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2020
Publication Date: 1/1/2020
Citation: Rudar, M., Columbus, D.A., Steinhoff-Wagner, J., Suryawan, A., Nguyen, H.V., Fleischmann, R., Davis, T.A., Fiorotto, M.L. 2020. Leucine supplementation does not restore diminished skeletal muscle satellite cell abundance and myonuclear accretion when protein intake is limiting in neonatal pigs. Journal of Nutrition. 150(1):22-30. https://doi.org/10.1093/jn/nxz216.
Interpretive Summary: Skeletal muscle growth in the neonate is very rapid and is accomplished by the addition of protein and nuclei to the existing muscles. Protein synthesis is very sensitive to amino acid intake, and especially to leucine intake, but we do not know if the same is true for muscle nuclei. To determine this, we fed piglets for 21 days a complete diet that was optimized to support normal postnatal muscle growth. We measured rates of muscle protein synthesis, the rate at which muscle nuclei were added, and the abundance of satellite cells (the adult muscle stem cells responsible for the production of muscle nuclei). These responses were compared to those of piglets fed a diet that was similar to the control diet, but contained only half the amount of protein, or one supplemented with leucine so that its intake was similar to that of controls. We found that the protein-restricted piglets had smaller muscles with fewer satellite cells that divided more slowly, so that there were fewer total muscle nuclei. Supplementation with leucine was of no benefit. These results identified that in the neonate, satellite cells require an optimal amount of dietary protein to sustain the level of proliferation needed to grow muscles optimally. The decrease in accretion of muscle nuclei when protein intake is inadequate provides a mechanism that explains why many low birth weight infants who fail to receive adequate nutrition, particularly protein intake, in early life have less lean mass in adulthood.
Technical Abstract: Rapid growth of skeletal muscle in the neonate requires the coordination of protein deposition and myonuclear accretion. During this developmental stage, muscle protein synthesis is highly sensitive to amino acid supply, especially Leu, but we do not know if this is true for satellite cells, the source of muscle fiber myonuclei. We examined whether dietary protein restriction reduces myonuclear accretion in the neonatal pig, and if any reduction in myonuclear accretion is mitigated by restoring Leu intake. Neonatal pigs (1.53 +/- 0.2 kg) were fitted with jugular vein and gastric catheters and fed 1 of 3 isoenergetic milk replacers every 4 h for 21 d: high protein [HP; 22.5 g protein/(kg/d); n= 8]; restricted protein [RP; 11.2 g protein/(kg/d); n= 10]; or restricted protein with Leu [RPL; 12.0 g protein/(kg/d); n= 10]. Pigs were administered 5-bromo-2'-deoxyuridine (BrdU; 15 mg/kg) intravenously every 12 h from days 6 to 8. Blood was sampled on days 6 and 21 to measure plasma Leu concentrations. On day 21, pigs were killed and the longissimus dorsi (LD) muscle was collected to measure cell morphometry, satellite cell abundance, myonuclear accretion, and insulin-like growth factor (IGF) system expression. Compared with HP pigs, postprandial plasma Leu concentration in RP pigs was 37% and 47% lower on days 6 and 21, respectively (P < 0.05); Leu supplementation in RPL pigs restored postprandial Leu to HP concentrations. Dietary protein restriction reduced LD myofiber cross-sectional area by 21%, satellite cell abundance by 35%, and BrdU+ myonuclear abundance by 25% (P < 0.05); Leu did not reverse these outcomes. Dietary protein restriction reduced LD muscle IGF2 expression by 60%, but not IGF1 or IGF1R expression (P < 0.05); Leu did not rescue IGF2 expression. Satellite cell abundance and myonuclear accretion in neonatal pigs are compromised when dietary protein intake is restricted and are not restored with Leu supplementation.