Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle

P. L. Greenhaff, L. G. Karagounis, N. Peirce, E. J. Simpson, M. Hazell, R. Layfield, H. Wackerhage, K. Smith, P. Atherton, A. Selby, M. J. Rennie

Research output: Contribution to journalArticle

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Abstract

We determined the effects of intravenous infusion of amino acids (AA) at serum insulin of 5, 30, 72, and 167 mU/l on anabolic signaling, expression of ubiquitin-proteasome components, and protein turnover in muscles of healthy young men. Tripling AA availability at 5 mU/l insulin doubled incorporation of [1-C-13] leucine [i.e., muscle protein synthesis ( MPS), P < 0.01] without affecting the rate of leg protein breakdown (LPB; appearance of d(5)-phenylalanine). While keeping AA availability constant, increasing insulin to 30 mU/l halved LPB (P < 0.05) without further inhibition at higher doses, whereas rates of MPS were identical to that at 5 mU/l insulin. The phosphorylation of PKB Ser(473) and (p)70(S6k) Thr(389) increased concomitantly with insulin, but whereas raising insulin to 30 mU/l increased the phosphorylation of mTOR Ser(2448), 4E-BP1 Thr(37/46), or GSK3 beta Ser(9) and decreased that of eEF2 Thr(56), higher insulin doses to 72 and 167 mU/l did not augment these latter responses. MAFbx and proteasome C2 subunit proteins declined as insulin increased, with MuRF-1 expression largely unchanged. Thus increasing AA and insulin availability causes changes in anabolic signaling and amounts of enzymes of the ubiquitin-proteasome pathway, which cannot be easily reconciled with observed effects on MPS or LPB.

Original languageEnglish
Pages (from-to)E595-E604
Number of pages10
JournalAmerican Journal of Physiology: Endocrinology and Metabolism
Volume295
Issue number3
Early online date24 Jun 2008
DOIs
Publication statusPublished - Sep 2008

Keywords

  • muscle protein synthesis
  • muscle protein breakdown
  • human skeletal-muscle
  • physiological hyperinsulinemia
  • euglycemic hyperinsulinemia
  • human forearm
  • healthy man
  • whole-body
  • proteolysis
  • availability
  • metabolism
  • infusion

Cite this

Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle. / Greenhaff, P. L.; Karagounis, L. G.; Peirce, N.; Simpson, E. J.; Hazell, M.; Layfield, R.; Wackerhage, H.; Smith, K.; Atherton, P.; Selby, A.; Rennie, M. J.

In: American Journal of Physiology: Endocrinology and Metabolism, Vol. 295, No. 3, 09.2008, p. E595-E604.

Research output: Contribution to journalArticle

Greenhaff, PL, Karagounis, LG, Peirce, N, Simpson, EJ, Hazell, M, Layfield, R, Wackerhage, H, Smith, K, Atherton, P, Selby, A & Rennie, MJ 2008, 'Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle', American Journal of Physiology: Endocrinology and Metabolism, vol. 295, no. 3, pp. E595-E604. https://doi.org/10.1152/ajpendo.90411.2008
Greenhaff, P. L. ; Karagounis, L. G. ; Peirce, N. ; Simpson, E. J. ; Hazell, M. ; Layfield, R. ; Wackerhage, H. ; Smith, K. ; Atherton, P. ; Selby, A. ; Rennie, M. J. / Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle. In: American Journal of Physiology: Endocrinology and Metabolism. 2008 ; Vol. 295, No. 3. pp. E595-E604.
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AU - Greenhaff, P. L.

AU - Karagounis, L. G.

AU - Peirce, N.

AU - Simpson, E. J.

AU - Hazell, M.

AU - Layfield, R.

AU - Wackerhage, H.

AU - Smith, K.

AU - Atherton, P.

AU - Selby, A.

AU - Rennie, M. J.

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N2 - We determined the effects of intravenous infusion of amino acids (AA) at serum insulin of 5, 30, 72, and 167 mU/l on anabolic signaling, expression of ubiquitin-proteasome components, and protein turnover in muscles of healthy young men. Tripling AA availability at 5 mU/l insulin doubled incorporation of [1-C-13] leucine [i.e., muscle protein synthesis ( MPS), P < 0.01] without affecting the rate of leg protein breakdown (LPB; appearance of d(5)-phenylalanine). While keeping AA availability constant, increasing insulin to 30 mU/l halved LPB (P < 0.05) without further inhibition at higher doses, whereas rates of MPS were identical to that at 5 mU/l insulin. The phosphorylation of PKB Ser(473) and (p)70(S6k) Thr(389) increased concomitantly with insulin, but whereas raising insulin to 30 mU/l increased the phosphorylation of mTOR Ser(2448), 4E-BP1 Thr(37/46), or GSK3 beta Ser(9) and decreased that of eEF2 Thr(56), higher insulin doses to 72 and 167 mU/l did not augment these latter responses. MAFbx and proteasome C2 subunit proteins declined as insulin increased, with MuRF-1 expression largely unchanged. Thus increasing AA and insulin availability causes changes in anabolic signaling and amounts of enzymes of the ubiquitin-proteasome pathway, which cannot be easily reconciled with observed effects on MPS or LPB.

AB - We determined the effects of intravenous infusion of amino acids (AA) at serum insulin of 5, 30, 72, and 167 mU/l on anabolic signaling, expression of ubiquitin-proteasome components, and protein turnover in muscles of healthy young men. Tripling AA availability at 5 mU/l insulin doubled incorporation of [1-C-13] leucine [i.e., muscle protein synthesis ( MPS), P < 0.01] without affecting the rate of leg protein breakdown (LPB; appearance of d(5)-phenylalanine). While keeping AA availability constant, increasing insulin to 30 mU/l halved LPB (P < 0.05) without further inhibition at higher doses, whereas rates of MPS were identical to that at 5 mU/l insulin. The phosphorylation of PKB Ser(473) and (p)70(S6k) Thr(389) increased concomitantly with insulin, but whereas raising insulin to 30 mU/l increased the phosphorylation of mTOR Ser(2448), 4E-BP1 Thr(37/46), or GSK3 beta Ser(9) and decreased that of eEF2 Thr(56), higher insulin doses to 72 and 167 mU/l did not augment these latter responses. MAFbx and proteasome C2 subunit proteins declined as insulin increased, with MuRF-1 expression largely unchanged. Thus increasing AA and insulin availability causes changes in anabolic signaling and amounts of enzymes of the ubiquitin-proteasome pathway, which cannot be easily reconciled with observed effects on MPS or LPB.

KW - muscle protein synthesis

KW - muscle protein breakdown

KW - human skeletal-muscle

KW - physiological hyperinsulinemia

KW - euglycemic hyperinsulinemia

KW - human forearm

KW - healthy man

KW - whole-body

KW - proteolysis

KW - availability

KW - metabolism

KW - infusion

U2 - 10.1152/ajpendo.90411.2008

DO - 10.1152/ajpendo.90411.2008

M3 - Article

VL - 295

SP - E595-E604

JO - American Journal of Physiology: Endocrinology and Metabolism

JF - American Journal of Physiology: Endocrinology and Metabolism

SN - 0193-1849

IS - 3

ER -