Viscera and muscle protein synthesis in neonatal pigs is increased more by intermittent bolus than by continuous feeding

Infants unable to maintain oral feeding can be nourished by orogastric tube. We have shown that orogastric continuous feeding restricts muscle protein synthesis compared with intermittent bolus feeding in neonatal pigs. To determine whether leucine infusion can be used to enhance protein synthesis during continuous feeding, neonatal piglets received the same amount of formula enterally by orogastric tube for 25.25 h continuously (CON) with or without LEU or intermittently by bolus every 4 h (BOL). For the CON+LEU group, leucine pulses were administered parenterally (800 μmol·kg−1·h−1) every 4 h. Insulin and glucose concentrations increased after the BOL meal and were unchanged in groups fed continuously. LEU infusion during CON feeding increased plasma leucine after the leucine pulse and decreased essential amino acids compared with CON feeding. Protein synthesis in longissimus dorsi (LD), gastrocnemius, and soleus muscles, but not liver or heart, were greater in CON+LEU and BOL than in the CON group. BOL feeding increased protein synthesis in the small intestine. Muscle S6K1 and 4E-BP1 phosphorylation and active eIF4E·eIF4G complex formation were higher in CON+LEU and BOL than in CON but AMPKα, eIF2α, and eEF2 phosphorylation were unchanged. LC3-II-to-total LC3 ratio was lower in CON+LEU and BOL than in CON, but there were no differences in atrogin-1 and MuRF-1 abundance and FoxO3 phosphorylation. In conclusion, administration of leucine pulses during continuous orogastric feeding in neonates increases muscle protein synthesis by stimulating translation initiation and may reduce protein degradation via the autophagy-lysosome, but not the ubiquitin-proteasome pathway.

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Intermittent Bolus Compared with Continuous Feeding Enhances Insulin and Amino Acid Signaling to Translation Initiation in Skeletal Muscle of Pigs Born at Term (P08-071-19)

Current Developments in Nutrition ◽

10.1093/cdn/nzz044.p08-071-19 ◽

2019 ◽

Vol 3 (Supplement_1) ◽

Author(s):

Agus Suryawan ◽

Samer El-Kadi ◽

Hanh Nguyen ◽

Marta Fiorotto ◽

Teresa Davis

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Amino Acid ◽

Translation Initiation ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Intermittent Bolus ◽

Lean Growth ◽

Continuous Feeding ◽

Amino Acid Signaling

Abstract Objectives Our recent study in a piglet model of the human neonate born at full term showed that intermittent bolus feeding promotes greater rates of protein synthesis in skeletal muscle than continuous feeding, leading to an increase in lean growth. This enhanced rate of muscle protein synthesis with intermittent bolus feeding is associated with an increased activation of mTORC1-dependent translation initiation. However, the mechanism underlying this response is unknown. In this study, we aimed to identify the insulin and/or amino acid signaling components involved in the enhanced stimulation of lean growth by intermittent bolus compared to continuous feeding in term-born pigs. Methods Term piglets (2–3 d old) were fed for 21 d an equal amount (240 ml/kg body weight [BW]/d) of sow milk replacer containing 12.8 g protein and 175 kcal/kg BW/d. Feedings were administered by gastrostomy tube either as intermittent bolus meals every 4 h (INT) or by continuous infusion (CON). After 21 d, gastrocnemius muscle was collected from CON, INT-0 (before a meal) and INT-60 (60 min after a meal) groups. Upstream and downstream insulin and amino acid signaling components of relevance to mTORC1 activation and protein translation were measured. Results Phosphorylation of AKT and TCS2 was greater in INT-60 than in INT-0 and CON groups (P < 0.05). There was no significant difference between CON and INT groups in the phosphorylation of ERK 1/2 and AMPK. The association of Sestrin2, a leucine sensor, with GATOR2 was similar in CON and INT-0 but was lower in INT-60 (P < 0.05). The abundances of RagA-mTOR, RagC-mTOR, and Rheb-mTOR complexes were higher in INT-60 than in CON and INT-0 (P < 0.05). The phosphorylation of S6K1 and 4EBP1 was higher in INT-60 than CON and INT-0 groups (P < 0.05). Phosphorylation of eIF2alpha and eEF2 were not affected by treatments. Conclusions Our results demonstrate that, following a full-term birth, the enhanced rate of skeletal muscle protein synthesis and lean growth with intermittent bolus compared to continuous feeding is at least in part due to the enhanced activation of both insulin and amino acid signaling pathways leading to greater stimulation of translation initiation. Funding Sources NIH HD085573, USDA CRIS 6250-51000-055, NIH HD072891, USDA NIFA 2013-67015-20438.

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Stimulation of Muscle Protein Synthesis by Prolonged Parenteral Infusion of Leucine Is Dependent on Amino Acid Availability in Neonatal Pigs

Journal of Nutrition ◽

10.3945/jn.109.113621 ◽

2009 ◽

Vol 140 (2) ◽

pp. 264-270 ◽

Cited By ~ 52

Author(s):

Fiona A. Wilson ◽

Agus Suryawan ◽

Maria C. Gazzaneo ◽

Renán A. Orellana ◽

Hanh V. Nguyen ◽

...

Keyword(s):

Protein Synthesis ◽

Amino Acid ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Neonatal Pigs ◽

Amino Acid Availability ◽

Stimulation Of

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Developmental changes in the feeding-induced activation of the insulin-signaling pathway in neonatal pigs

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.2001.281.5.e908 ◽

2001 ◽

Vol 281 (5) ◽

pp. E908-E915 ◽

Cited By ~ 41

Author(s):

Agus Suryawan ◽

Hanh V. Nguyen ◽

Jill A. Bush ◽

Teresa A. Davis

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Insulin Receptor ◽

Insulin Signaling ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Skeletal Muscle Protein ◽

Neonatal Pigs ◽

Skeletal Muscle Protein Synthesis ◽

Primary Determinant

In neonatal animals, feeding stimulates skeletal muscle protein synthesis, a response that declines with development. Both the magnitude of the feeding response and its developmental decline can be reproduced by insulin infusion, suggesting that an altered responsiveness to insulin is a primary determinant of the developmental decline in the stimulation of protein synthesis by feeding. In this study, 7- and 26-day-old pigs were either fasted overnight or fed porcine milk after an overnight fast. We examined the abundance and degree of tyrosine phosphorylation of the insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and IRS-2 in skeletal muscle and, for comparison, liver. We also evaluated the association of IRS-1 and IRS-2 with phosphatidylinositol 3-kinase (PI 3-kinase). The abundance of IR protein in muscle was twofold higher at 7 than at 26 days, but IRS-1 and IRS-2 abundances were similar in muscle of 7- and 26-day-old pigs. The feeding-induced phosphorylations were greater at 7 than at 26 days of age for IR (28- vs. 13-fold), IRS-1 (14- vs. 8-fold), and IRS-2 (21- vs. 12-fold) in muscle. The associations of IRS-1 and IRS-2 with PI 3-kinase were also increased by refeeding to a greater extent at 7 than at 26 days (9- vs. 5-fold and 6- vs. 4-fold, respectively). In liver, the abundance of IR, IRS-1, and IRS-2 was similar at 7 and 26 days of age. Feeding increased the activation of IR, IRS-1, IRS-2, and PI 3-kinase in liver only twofold, and these responses were unaffected by age. Thus our findings demonstrate that the feeding-induced activation of IR, IRS-1, IRS-2, and PI 3-kinase in skeletal muscle decreases with development. Further study is needed to ascertain whether the developmental decline in the feeding-induced activation of early insulin-signaling components contributes to the developmental decline in translation initiation in skeletal muscle.

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Anabolic signaling and protein deposition are enhanced by intermittent compared with continuous feeding in skeletal muscle of neonates

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00516.2011 ◽

2012 ◽

Vol 302 (6) ◽

pp. E674-E686 ◽

Cited By ~ 36

Author(s):

Samer W. El-Kadi ◽

Agus Suryawan ◽

Maria C. Gazzaneo ◽

Neeraj Srivastava ◽

Renán A. Orellana ◽

...

Keyword(s):

Protein Synthesis ◽

Protein Degradation ◽

Muscle Protein ◽

Mrna Translation ◽

Initiation Factor ◽

Whole Body ◽

Signaling Proteins ◽

Protein Deposition ◽

Intermittent Bolus ◽

Continuous Feeding

Orogastric tube feeding is indicated for neonates with impaired ability to ingest and can be administered by intermittent bolus or continuous schedule. Our aim was to determine whether feeding modalities affect muscle protein deposition and to identify mechanisms involved. Neonatal pigs were overnight fasted (FAS) or fed the same amount of food continuously (CON) or intermittently (INT; 7 × 4 h meals) for 29 h. For 8 h, between hours 20 and 28, pigs were infused with [2H5]phenylalanine and [2H2]tyrosine, and amino acid (AA) net balances were measured across the hindquarters. Insulin, branched-chain AA, phenylalanine, and tyrosine arterial concentrations and whole body phenylalanine and tyrosine fluxes were greater for INT after the meal than for CON or FAS. The activation of signaling proteins leading to initiation of mRNA translation, including eukaryotic initiation factor (eIF)4E·eIF4G complex formation in muscle, was enhanced by INT compared with CON feeding or FAS. Signaling proteins of protein degradation were not affected by feeding modalities except for microtubule-associated protein light chain 3-II, which was highest in the FAS. Across the hindquarters, AA net removal increased for INT but not for CON or FAS, with protein deposition greater for INT. This was because protein synthesis increased following feeding for INT but remained unchanged for CON and FAS, whereas there was no change in protein degradation across any dietary treatment. These results suggest that muscle protein accretion in neonates is enhanced with intermittent bolus to a greater extent than continuous feeding, mainly by increased protein synthesis.

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Physiological rise in plasma leucine stimulates muscle protein synthesis in neonatal pigs by enhancing translation initiation factor activation

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00510.2004 ◽

2005 ◽

Vol 288 (5) ◽

pp. E914-E921 ◽

Cited By ~ 93

Author(s):

Jeffery Escobar ◽

Jason W. Frank ◽

Agus Suryawan ◽

Hanh V. Nguyen ◽

Scot R. Kimball ◽

...

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Amino Acid ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Mrna Translation ◽

Translation Initiation Factor ◽

Initiation Factor ◽

Neonatal Pigs ◽

Plasma Leucine

Protein synthesis in skeletal muscle of adult rats increases in response to oral gavage of supraphysiological doses of leucine. However, the effect on protein synthesis of a physiological rise in plasma leucine has not been investigated in neonates, an anabolic population highly sensitive to amino acids and insulin. Therefore, in the current study, fasted pigs were infused intra-arterially with leucine (0, 200, or 400 μmol·kg−1·h−1), and protein synthesis was measured after 60 or 120 min. Protein synthesis was increased in muscle, but not in liver, at 60 min. At 120 min, however, protein synthesis returned to baseline levels in muscle but was reduced below baseline values in liver. The increase in protein synthesis in muscle was associated with increased plasma leucine of 1.5- to 3-fold and no change in plasma insulin. Leucine infusion for 120 min reduced plasma essential amino acid levels. Phosphorylation of eukaryotic initiation factor (eIF)-4E-binding protein-1 (4E-BP1), ribosomal protein (rp) S6 kinase, and rpS6 was increased, and the amount of eIF4E associated with its repressor 4E-BP1 was reduced after 60 and 120 min of leucine infusion. No change in these biomarkers of mRNA translation was observed in liver. Thus a physiological increase in plasma leucine stimulates protein synthesis in skeletal muscle of neonatal pigs in association with increased eIF4E availability for eIF4F assembly. This response appears to be insulin independent, substrate dependent, and tissue specific. The results suggest that the branched-chain amino acid leucine can act as a nutrient signal to stimulate protein synthesis in skeletal muscle of neonates.

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