Downregulated Translation Initiation Signaling Predisposes Low-Birth-Weight Neonatal Pigs to Slower Rates of Muscle Protein Synthesis

Skeletal muscle protein synthesis is reduced in neonatal pigs in response to endotoxemia. To examine the role of insulin in this response, neonatal pigs were infused with endotoxin (LPS, 0 and 10 μg·kg−1·h−1), whereas glucose and amino acids were maintained at fasting levels and insulin was clamped at fasting or fed (2 or 10 μU/ml) levels. Fractional rates of protein synthesis and translational control mechanisms were examined in longissimus dorsi muscle and liver. In the presence of fasting insulin, LPS reduced muscle protein synthesis (−29%), and increasing insulin to fed levels accelerated muscle protein synthesis in both groups (controls, +44%; LPS, +64%). LPS, but not insulin, increased liver protein synthesis by +28%. In muscle of fasting neonatal pigs, LPS reduced 4E-BP1 phosphorylation and eIF4E to eIF4G binding. In muscle of controls, but not LPS pigs, raising insulin to fed levels increased 4E-BP1 and S6K1 phosphorylation and eIF4E to eIF4G binding. In muscle and liver, neither LPS nor insulin altered eIF2B activity. eEF2 phosphorylation decreased in response to insulin in both LPS and control animals. The results suggest that, in endotoxemic neonatal animals, the response of protein synthesis to insulin is maintained despite suppression of mTOR-dependent translation initiation and eIF4E availability for eIF4F assembly. Maintenance of an anabolic response to the feeding-induced rise in insulin likely exerts a protective effect for the neonate to the catabolic processes induced by sepsis.

Download Full-text

Amino Acids Augment Muscle Protein Synthesis in Neonatal Pigs During Endotoxemia by Modulating Translation Initiation

The FASEB Journal ◽

10.1096/fasebj.20.4.a9-a ◽

2006 ◽

Vol 20 (4) ◽

Author(s):

Renan A Orellana ◽

Jeffery Escobar ◽

Asumpthia S Jeyapalan ◽

Hanh V Nguyen ◽

Agus Suryawan ◽

...

Keyword(s):

Amino Acids ◽

Protein Synthesis ◽

Translation Initiation ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Neonatal Pigs

Download Full-text

Amino acids augment muscle protein synthesis in neonatal pigs during acute endotoxemia by stimulating mTOR-dependent translation initiation

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00146.2007 ◽

2007 ◽

Vol 293 (5) ◽

pp. E1416-E1425 ◽

Cited By ~ 22

Author(s):

Renán A. Orellana ◽

Asumthia Jeyapalan ◽

Jeffery Escobar ◽

Jason W. Frank ◽

Hanh V. Nguyen ◽

...

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Protein Synthesis ◽

Amino Acid ◽

Translation Initiation ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Synthesis Rate ◽

Protein Synthesis Rate ◽

Neonatal Pigs

In skeletal muscle of adults, sepsis reduces protein synthesis by depressing translation initiation and induces resistance to branched-chain amino acid stimulation. Normal neonates maintain a high basal muscle protein synthesis rate that is sensitive to amino acid stimulation. In the present study, we determined the effect of amino acids on protein synthesis in skeletal muscle and other tissues in septic neonates. Overnight-fasted neonatal pigs were infused with endotoxin (LPS, 0 and 10 μg·kg−1·h−1), whereas glucose and insulin were maintained at fasting levels; amino acids were clamped at fasting or fed levels. In the presence of fasting insulin and amino acids, LPS reduced protein synthesis in longissimus dorsi (LD) and gastrocnemius muscles and increased protein synthesis in the diaphragm, but had no effect in masseter and heart muscles. Increasing amino acids to fed levels accelerated muscle protein synthesis in LD, gastrocnemius, masseter, and diaphragm. LPS stimulated protein synthesis in liver, lung, spleen, pancreas, and kidney in fasted animals. Raising amino acids to fed levels increased protein synthesis in liver of controls, but not LPS-treated animals. The increase in muscle protein synthesis in response to amino acids was associated with increased mTOR, 4E-BP1, and S6K1 phosphorylation and eIF4G-eIF4E association in control and LPS-infused animals. These findings suggest that amino acids stimulate skeletal muscle protein synthesis during acute endotoxemia via mTOR-dependent ribosomal assembly despite reduced basal protein synthesis rates in neonatal pigs. However, provision of amino acids does not further enhance the LPS-induced increase in liver protein synthesis.

Download Full-text

Intravenous administration of amino acids during anesthesia stimulates muscle protein synthesis and heat accumulation in the body

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00333.2005 ◽

2006 ◽

Vol 290 (5) ◽

pp. E882-E888 ◽

Cited By ~ 24

Author(s):

Ippei Yamaoka ◽

Masako Doi ◽

Mitsuo Nakayama ◽

Akane Ozeki ◽

Shinji Mochizuki ◽

...

Keyword(s):

Protein Synthesis ◽

Protein Kinase ◽

Intravenous Administration ◽

Translation Initiation ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Mammalian Target Of Rapamycin ◽

The Body ◽

Initiation Factor ◽

Heat Accumulation

The present study was conducted to determine the contribution of muscle protein synthesis to the prevention of anesthesia-induced hypothermia by intravenous administration of an amino acid (AA) mixture. We examined the changes of intraperitoneal temperature (Tcore) and the rates of protein synthesis ( Ks) and the phosphorylation states of translation initiation regulators and their upstream signaling components in skeletal muscle in conscious (Nor) or propofol-anesthetized (Ane) rats after a 3-h intravenous administration of a balanced AA mixture or saline (Sal). Compared with Sal administration, the AA mixture administration markedly attenuated the decrease in Tcore in rats during anesthesia, whereas Tcore in the Nor-AA group became slightly elevated during treatment. Stimulation of muscle protein synthesis resulting from AA administration was observed in each case, although Ks remained lower in the Ane-AA group than in the Nor-Sal group. AA administration during anesthesia significantly increased insulin concentrations to levels ∼6-fold greater than in the Nor-AA group and enhanced phosphorylation of eukaryotic initiation factor 4E-binding protein-1 (4E-BP1) and ribosomal protein S6 protein kinase relative to all other groups and treatments. The alterations in the Ane-AA group were accompanied by hyperphosphorylation of protein kinase B and the mammalian target of rapamycin (mTOR). These results suggest that administration of an AA mixture during anesthesia stimulates muscle protein synthesis via insulin-mTOR-dependent activation of translation initiation regulators caused by markedly elevated insulin and, thereby, facilitates thermal accumulation in the body.

Download Full-text

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

Download Full-text

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.

Download Full-text

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.

Download Full-text