Acute treatment with TNF-α attenuates insulin-stimulated protein synthesis in cultures of C2C12 myotubes through a MEK1-sensitive mechanism

2005 ◽  
Vol 289 (1) ◽  
pp. E95-E104 ◽  
Author(s):  
David L. Williamson ◽  
Scot R. Kimball ◽  
Leonard S. Jefferson
Keyword(s):  
Protein Synthesis ◽  
Translational Control ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Mammalian Target Of Rapamycin ◽  
C2c12 Myotubes ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis ◽  
Tnf Α ◽  
Stimulation Of

Insulin and TNF-α exert opposing effects on skeletal muscle protein synthesis that are mediated in part by the rapamycin-sensitive mammalian target of rapamycin (mTOR) pathway and the PD-98059-sensitive, extracellular signal-regulated kinase (ERK)1/2 pathway. The present study examined the separate and combined effects of insulin (INS), TNF, PD-98059, or dnMEK1 adenovirus on the translational control of protein synthesis in C2C12 myotubes. Cultures were treated with INS, TNF, PD-98059, dnMEK1, or a combination of INS + TNF with PD-98059 or dnMEK1. INS stimulated protein synthesis, enhanced eIF4E·eIF4G association, and eIF4G phosphorylation and repressed eIF4E·4E-BP1 association vs. control. INS also promoted phosphorylation of ERK1/2, S6K1, and 4E-BP1 and dephosphorylation of eIF4E. TNF alone did not have an effect on protein synthesis (vs. control), eIF4E·eIF4G association, or the phosphorylation of eIF4G, S6K1, or 4E-BP1, although it transiently increased ERK1/2 and eIF4E phosphorylation. When myotubes were treated with TNF + INS, the cytokine blocked the insulin-induced stimulation of protein synthesis. This appeared to be due to an attenuation of insulin-stimulated eIF4E·eIF4G association, because other stimulatory effects of INS, e.g., phosphorylation of ERK1/2, 4E-BP1, S6K1, eIF4G, and eIF4E and eIF4E·4E-BP1 association, were unaffected. Finally, treatment of myotubes with PD-98059 or dnMEK1 adenovirus before TNF + INS addition resulted in a derepression of protein synthesis and the association of eIF4G with eIF4E. These findings suggest that TNF abrogates insulin-induced stimulation of protein synthesis in myotubes through a decrease in eIF4F complex assembly independently of S6K1 and 4E-BP1 signaling and dependently on a MEK1-sensitive signaling pathway.

scholarly journals Insulin Stimulates Human Skeletal Muscle Protein Synthesis via an Indirect Mechanism Involving Endothelial-Dependent Vasodilation and Mammalian Target of Rapamycin Complex 1 Signaling

2010 ◽  
Vol 24 (6) ◽  
pp. 1306-1306
Author(s):  
Kyle L. Timmerman ◽  
Jessica L. Lee ◽  
Hans C. Dreyer ◽  
Shaheen Dhanani ◽  
Erin L. Glynn ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Mammalian Target Of Rapamycin ◽  
Skeletal Muscle Protein ◽  
Capillary Recruitment ◽  
Isotope Tracers ◽  
Skeletal Muscle Protein Synthesis ◽  
Mtorc1 Signaling

Abstract Objective: Our objective was to determine whether endothelial-dependent vasodilation is an essential mechanism by which insulin stimulates human skeletal muscle protein synthesis and anabolism. Subjects: Subjects were healthy young adults (n = 14) aged 31 ± 2 yr. Design: Subjects were studied at baseline and during local leg infusion of insulin alone (control, n = 7) or insulin plus the nitric oxide synthase inhibitor NG-monomethyl-l-arginine (L-NMMA, n = 7) to prevent insulin-induced vasodilation. Methods: We measured skeletal muscle protein metabolism with stable isotope tracers, blood flow with indocyanine green, capillary recruitment with contrast enhanced ultrasound, glucose metabolism with stable isotope tracers, and phosphorylation of proteins associated with insulin (Akt) and amino acid-induced mammalian target of rapamycin(mTOR) complex 1 (mTORC1) signaling (mTOR, S6 kinase 1, and eukaryotic initiation factor 4Ebinding protein 1) with Western blot analysis. Results: No basal differences between groups were detected. During insulin infusion, blood flow and capillary recruitment increased in the control (P < 0.05) group only; Akt phosphorylation and glucose uptake increased in both groups (P < 0.05), with no group differences; and mTORC1 signaling increased more in control (P < 0.05) than in l-NMMA. Phenylalanine net balance increased (P < 0.05) in both groups, but with opposite mechanisms: increased protein synthesis (basal, 0.051 ± 0.006%/h; insulin, 0.077 ± 0.008%/h; P < 0.05) with no change in proteolysis in control and decreased proteolysis (P < 0.05) with no change in synthesis (basal, 0.061 ± 0.004%/h; insulin, 0.050 ± 0.006%/h; P value not significant) in l-NMMA. Conclusions: Endothelial-dependent vasodilation and the consequent increase in nutritive flow and mTORC1 signaling, rather than Akt signaling, are fundamental mechanisms by which insulin stimulates muscle protein synthesis in humans. Additionally, these data underscore that insulin modulates skeletal muscle proteolysis according to its effects on nutritive flow.

Alcohol impairs leucine-mediated phosphorylation of 4E-BP1, S6K1, eIF4G, and mTOR in skeletal muscle

2003 ◽  
Vol 285 (6) ◽  
pp. E1205-E1215 ◽  
Author(s):  
Charles H. Lang ◽  
Robert A. Frost ◽  
Nobuko Deshpande ◽  
Vinayshree Kumar ◽  
Thomas C. Vary ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Translational Control ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Plasma Concentrations ◽  
Mammalian Target Of Rapamycin ◽  
Initiation Factor ◽  
Skeletal Muscle Protein ◽  
Corticosterone Concentration

Acute alcohol (EtOH) intoxication impairs skeletal muscle protein synthesis. Although this impairment is not associated with a decrease in the total plasma amino acid concentration, EtOH may blunt the anabolic response to amino acids. To examine this hypothesis, rats were administered EtOH or saline (Sal) and 2.5 h thereafter were orally administered either leucine (Leu) or Sal. The gastrocnemius was removed 20 min later to assess protein synthesis and signaling components important in translational control of protein synthesis. Oral Leu increased muscle protein synthesis by the same magnitude in Sal- and EtOH-treated rats. However, the increase in the latter group was insufficient to overcome the suppressive effect of EtOH, and the rate of synthesis remained lower than that observed in rats from the Sal-Sal group. Leu markedly increased phosphorylation of Thr residues 36, 47, and 70 on 4E-binding protein (BP)1 in muscle from rats not receiving EtOH, and this response was associated with a redistribution of eukaryotic initiation factor (eIF) 4E from the inactive eIF4E · 4E-BP1 to the active eIF4E · eIF4G complex. In EtOH-treated rats, the Leu-induced phosphorylation of 4E-BP1 and changes in eIF4E availability were partially abrogated. EtOH also prevented the Leu-induced increase in phosphorylation of eIF4G, the serine/threonine protein kinase S6K1, and the ribosomal protein S6. Moreover, EtOH attenuated the Leu-induced phosphorylation of the mammalian target of rapamycin (mTOR). The ability of EtOH to blunt the anabolic effects of Leu could not be attributed to differences in the plasma concentrations of insulin, insulin-like growth factor I, or Leu. Finally, although EtOH increased the plasma corticosterone concentration, inhibition of glucocorticoid action by RU-486 was unable to prevent EtOH-induced defects in the ability of Leu to stimulate 4E-BP1, S6K1, and mTOR phosphorylation. Hence, ethanol produces a leucine resistance in skeletal muscle, as evidenced by the impaired phosphorylation of 4E-BP1, eIF4G, S6K1, and mTOR, that is independent of elevations in endogenous glucocorticoids.

scholarly journals Insulin Stimulates Human Skeletal Muscle Protein Synthesis via an Indirect Mechanism Involving Endothelial-Dependent Vasodilation and Mammalian Target of Rapamycin Complex 1 Signaling

2010 ◽  
Vol 95 (8) ◽  
pp. 3848-3857 ◽  
Author(s):  
Kyle L. Timmerman ◽  
Jessica L. Lee ◽  
Hans C. Dreyer ◽  
Shaheen Dhanani ◽  
Erin L. Glynn ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Mammalian Target Of Rapamycin ◽  
Skeletal Muscle Protein ◽  
Capillary Recruitment ◽  
Isotope Tracers ◽  
Skeletal Muscle Protein Synthesis ◽  
Mtorc1 Signaling

Objective: Our objective was to determine whether endothelial-dependent vasodilation is an essential mechanism by which insulin stimulates human skeletal muscle protein synthesis and anabolism. Subjects: Subjects were healthy young adults (n = 14) aged 31 ± 2 yr. Design: Subjects were studied at baseline and during local leg infusion of insulin alone (control, n = 7) or insulin plus the nitric oxide synthase inhibitor NG-monomethyl-l-arginine (l-NMMA, n = 7) to prevent insulin-induced vasodilation. Methods: We measured skeletal muscle protein metabolism with stable isotope tracers, blood flow with indocyanine green, capillary recruitment with contrast enhanced ultrasound, glucose metabolism with stable isotope tracers, and phosphorylation of proteins associated with insulin (Akt) and amino acid-induced mammalian target of rapamycin (mTOR) complex 1 (mTORC1) signaling (mTOR, S6 kinase 1, and eukaryotic initiation factor 4E-binding protein 1) with Western blot analysis. Results: No basal differences between groups were detected. During insulin infusion, blood flow and capillary recruitment increased in the control (P < 0.05) group only; Akt phosphorylation and glucose uptake increased in both groups (P < 0.05), with no group differences; and mTORC1 signaling increased more in control (P < 0.05) than in l-NMMA. Phenylalanine net balance increased (P < 0.05) in both groups, but with opposite mechanisms: increased protein synthesis (basal, 0.051 ± 0.006 %/h; insulin, 0.077 ± 0.008 %/h; P < 0.05) with no change in proteolysis in control and decreased proteolysis (P < 0.05) with no change in synthesis (basal, 0.061 ± 0.004 %/h; insulin, 0.050 ± 0.006 %/h; P value not significant) in l-NMMA. Conclusions: Endothelial-dependent vasodilation and the consequent increase in nutritive flow and mTORC1 signaling, rather than Akt signaling, are fundamental mechanisms by which insulin stimulates muscle protein synthesis in humans. Additionally, these data underscore that insulin modulates skeletal muscle proteolysis according to its effects on nutritive flow.

Developmental changes in the feeding-induced stimulation of translation initiation in muscle of neonatal pigs

2000 ◽  
Vol 279 (6) ◽  
pp. E1226-E1234 ◽  
Author(s):  
Teresa A. Davis ◽  
Hanh V. Nguyen ◽  
Agus Suryawan ◽  
Jill A. Bush ◽  
Leonard S. Jefferson ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Developmental Changes ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis ◽  
Hyperphosphorylated Form ◽  
Stimulation Of

The rapid gain in skeletal muscle mass in the neonate is associated with a marked elevation in skeletal muscle protein synthesis in response to feeding. The feeding-induced response decreases with development. To determine whether the response to feeding is regulated at the level of translation initiation, the expression, phosphorylation, and function of a number of eukaryotic initiation factors (eIF) were examined. Pigs at 7 and 26 days of age were either fasted overnight or fed porcine milk after an overnight fast. In muscle of 7-day-old pigs, the hyperphosphorylated form of the eIF4E repressor protein, 4E-binding protein 1 (4E-BP1), was undetectable in the fasting state but rose to 60% of total 4E-BP1 after feeding; eIF4E phosphorylation was unaffected by feeding status. The amount of eIF4E in the inactive 4E-BP1 · eIF4E complex was reduced by 80%, and the amount of eIF4E in the active eIF4E · eIF4G complex was increased 14-fold in muscle of 7-day-old pigs after feeding. The amount of 70-kDa ribosomal protein S6 (p70S6) kinase in the hyperphosphorylated form rose 2.5-fold in muscle of 7-day-old pigs after feeding. Each of these feeding-induced responses was blunted in muscle of 26-day-old pigs. eIF2B activity in muscle was unaffected by feeding status but decreased with development. Feeding produced similar changes in eIF characteristics in liver and muscle; however, the developmental changes in liver were not as apparent as in skeletal muscle. Thus the results demonstrate that the developmental change in the acute stimulation of skeletal muscle protein synthesis by feeding is regulated by the availability of eIF4E for 48S ribosomal complex formation. The results further suggest that the overall developmental decline in skeletal muscle protein synthesis involves regulation by eIF2B.

scholarly journals Stimulation of muscle protein synthesis by somatotropin in pigs is independent of the somatotropin-induced increase in circulating insulin

2008 ◽  
Vol 295 (1) ◽  
pp. E187-E194 ◽  
Author(s):  
Fiona A. Wilson ◽  
Renán A. Orellana ◽  
Agus Suryawan ◽  
Hanh V. Nguyen ◽  
Asumthia S. Jeyapalan ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Growing Pigs ◽  
Initiation Factor ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis ◽  
Stimulation Of

Chronic treatment of growing pigs with porcine somatotropin (pST) promotes protein synthesis and doubles postprandial levels of insulin, a hormone that stimulates translation initiation. This study aimed to determine whether the pST-induced increase in skeletal muscle protein synthesis was mediated through an insulin-induced stimulation of translation initiation. After 7–10 days of pST (150 μg·kg−1·day−1) or control saline treatment, pancreatic glucose-amino acid clamps were performed in overnight-fasted pigs to reproduce 1) fasted (5 μU/ml), 2) fed control (25 μU/ml), and 3) fed pST-treated (50 μU/ml) insulin levels while glucose and amino acids were maintained at baseline fasting levels. Fractional protein synthesis rates and indexes of translation initiation were examined in skeletal muscle. Effectiveness of pST treatment was confirmed by reduced urea nitrogen and elevated insulin-like growth factor I levels in plasma. Skeletal muscle protein synthesis was independently increased by both insulin and pST. Insulin increased the phosphorylation of protein kinase B and the downstream effectors of the mammalian target of rapamycin, ribosomal protein S6 kinase, and eukaryotic initiation factor (eIF)4E-binding protein-1 (4E-BP1). Furthermore, insulin reduced inactive 4E-BP1·eIF4E complex association and increased active eIF4E·eIF4G complex formation, indicating enhanced eIF4F complex assembly. However, pST treatment did not alter translation initiation factor activation. We conclude that the pST-induced stimulation of skeletal muscle protein synthesis in growing pigs is independent of the insulin-associated activation of translation initiation.

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