Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH2-terminal (sites 2+2a) phosphorylation

Martin Friedrichsen; Jesper Bratz Birk; Erik Richter; Rasmus Ribel-Madsen; Christian Pehmøller; Bo Falck Hansen; Henning Beck-Nielsen; Michael F Hirshman; Laurie J Goodyear; Allan Vaag; Pernille Poulsen; Jørgen Wojtaszewski

doi:10.1152/ajpendo.00494.2012

Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH2-terminal (sites 2+2a) phosphorylation

Martin Friedrichsen, Jesper Bratz Birk, Erik Richter, Rasmus Ribel-Madsen, Christian Pehmøller, Bo Falck Hansen, Henning Beck-Nielsen, Michael F Hirshman, Laurie J Goodyear, Allan Vaag, Pernille Poulsen, Jørgen Wojtaszewski

The August Krogh Section for Molecular Physiology

10 Citations (Scopus)

Abstract

Type 2 diabetes is characterized by reduced muscle glycogen synthesis. The key enzyme in this process, glycogen synthase (GS), is activated via proximal insulin signaling, but the exact molecular events remain unknown. Previously, we demonstrated that phosphorylation of Thr³⁰⁸ on Akt (p-Akt-Thr³⁰⁸), Akt2 activity, and GS activity in muscle were positively associated with insulin sensitivity. Here, in the same study population, we determined the influence of several upstream elements in the canonical PI3K signaling on muscle GS activation. One-hundred eighty-one nondiabetic twins were examined with the euglycemic hyperinsulinemic clamp combined with excision of muscle biopsies. Insulin signaling was evaluated at the levels of the insulin receptor, IRS-1-associated PI3K (IRS-1-PI3K), Akt, and GS employing activity assays and phosphospecific Western blotting. The insulin-stimulated GS activity was positively associated with p-Akt-Thr³⁰⁸ (P = 0.01) and Akt2 activity (P = 0.04) but not p-Akt-Ser⁴⁷³ or IRS-1-PI3K activity. Furthermore, p-Akt-Thr³⁰⁸ and Akt2 activity were negatively associated with NH₂-terminal GS phosphorylation (P = 0.001 for both), which in turn was negatively associated with insulin-stimulated GS activity (P = 0.001). We found no association between COOHterminal GS phosphorylation and Akt or GS activity. Employing whole body Akt2-knockout mice, we validated the necessity for Akt2 in insulin-mediated GS activation. However, since insulin did not affect NH₂-terminal phosphorylation in mice, we could not use this model to validate the observed association between GS NH₂-terminal phosphorylation and Akt activity in humans. In conclusion, our study suggests that although COOH-terminal dephosphorylation is likely necessary for GS activation, Akt2-dependent NH₂-terminal dephosphorylation may be the site for "fine-tuning" insulin-mediated GS activation in humans.

Original language	English
Journal	American Journal of Physiology: Endocrinology and Metabolism
Volume	304
Issue number	6
Pages (from-to)	E631-E639
Number of pages	9
ISSN	0193-1849
DOIs	https://doi.org/10.1152/ajpendo.00494.2012
Publication status	Published - 2013

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Friedrichsen, M., Birk, J. B., Richter, E., Ribel-Madsen, R., Pehmøller, C., Hansen, B. F., Beck-Nielsen, H., Hirshman, M. F., Goodyear, L. J., Vaag, A., Poulsen, P., & Wojtaszewski, J. (2013). Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH2-terminal (sites 2+2a) phosphorylation. American Journal of Physiology: Endocrinology and Metabolism, 304(6), E631-E639. https://doi.org/10.1152/ajpendo.00494.2012

Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH2-terminal (sites 2+2a) phosphorylation. / Friedrichsen, Martin; Birk, Jesper Bratz ; Richter, Erik et al.

In: American Journal of Physiology: Endocrinology and Metabolism, Vol. 304, No. 6, 2013, p. E631-E639.

Research output: Contribution to journal › Journal article › Research › peer-review

Friedrichsen, M, Birk, JB , Richter, E, Ribel-Madsen, R, Pehmøller, C, Hansen, BF, Beck-Nielsen, H, Hirshman, MF, Goodyear, LJ, Vaag, A, Poulsen, P & Wojtaszewski, J 2013, 'Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH2-terminal (sites 2+2a) phosphorylation', American Journal of Physiology: Endocrinology and Metabolism, vol. 304, no. 6, pp. E631-E639. https://doi.org/10.1152/ajpendo.00494.2012

@article{f691d5cf7aee485bb16a68f78f6be9de,

title = "Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH2-terminal (sites 2+2a) phosphorylation",

abstract = "Type 2 diabetes is characterized by reduced muscle glycogen synthesis. The key enzyme in this process, glycogen synthase (GS), is activated via proximal insulin signaling, but the exact molecular events remain unknown. Previously, we demonstrated that phosphorylation of Thr308 on Akt (p-Akt-Thr308), Akt2 activity, and GS activity in muscle were positively associated with insulin sensitivity. Here, in the same study population, we determined the influence of several upstream elements in the canonical PI3K signaling on muscle GS activation. One-hundred eighty-one nondiabetic twins were examined with the euglycemic hyperinsulinemic clamp combined with excision of muscle biopsies. Insulin signaling was evaluated at the levels of the insulin receptor, IRS-1-associated PI3K (IRS-1-PI3K), Akt, and GS employing activity assays and phosphospecific Western blotting. The insulin-stimulated GS activity was positively associated with p-Akt-Thr308 (P = 0.01) and Akt2 activity (P = 0.04) but not p-Akt-Ser473 or IRS-1-PI3K activity. Furthermore, p-Akt-Thr308 and Akt2 activity were negatively associated with NH2-terminal GS phosphorylation (P = 0.001 for both), which in turn was negatively associated with insulin-stimulated GS activity (P = 0.001). We found no association between COOHterminal GS phosphorylation and Akt or GS activity. Employing whole body Akt2-knockout mice, we validated the necessity for Akt2 in insulin-mediated GS activation. However, since insulin did not affect NH2-terminal phosphorylation in mice, we could not use this model to validate the observed association between GS NH2-terminal phosphorylation and Akt activity in humans. In conclusion, our study suggests that although COOH-terminal dephosphorylation is likely necessary for GS activation, Akt2-dependent NH2-terminal dephosphorylation may be the site for {"}fine-tuning{"} insulin-mediated GS activation in humans.",

author = "Martin Friedrichsen and Birk, {Jesper Bratz} and Erik Richter and Rasmus Ribel-Madsen and Christian Pehm{\o}ller and Hansen, {Bo Falck} and Henning Beck-Nielsen and Hirshman, {Michael F} and Goodyear, {Laurie J} and Allan Vaag and Pernille Poulsen and J{\o}rgen Wojtaszewski",

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T1 - Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH2-terminal (sites 2+2a) phosphorylation

AU - Friedrichsen, Martin

AU - Birk, Jesper Bratz

AU - Richter, Erik

AU - Ribel-Madsen, Rasmus

AU - Pehmøller, Christian

AU - Hansen, Bo Falck

AU - Beck-Nielsen, Henning

AU - Hirshman, Michael F

AU - Goodyear, Laurie J

AU - Vaag, Allan

AU - Poulsen, Pernille

AU - Wojtaszewski, Jørgen

N1 - CURIS 2013 NEXS 012

PY - 2013

Y1 - 2013

N2 - Type 2 diabetes is characterized by reduced muscle glycogen synthesis. The key enzyme in this process, glycogen synthase (GS), is activated via proximal insulin signaling, but the exact molecular events remain unknown. Previously, we demonstrated that phosphorylation of Thr308 on Akt (p-Akt-Thr308), Akt2 activity, and GS activity in muscle were positively associated with insulin sensitivity. Here, in the same study population, we determined the influence of several upstream elements in the canonical PI3K signaling on muscle GS activation. One-hundred eighty-one nondiabetic twins were examined with the euglycemic hyperinsulinemic clamp combined with excision of muscle biopsies. Insulin signaling was evaluated at the levels of the insulin receptor, IRS-1-associated PI3K (IRS-1-PI3K), Akt, and GS employing activity assays and phosphospecific Western blotting. The insulin-stimulated GS activity was positively associated with p-Akt-Thr308 (P = 0.01) and Akt2 activity (P = 0.04) but not p-Akt-Ser473 or IRS-1-PI3K activity. Furthermore, p-Akt-Thr308 and Akt2 activity were negatively associated with NH2-terminal GS phosphorylation (P = 0.001 for both), which in turn was negatively associated with insulin-stimulated GS activity (P = 0.001). We found no association between COOHterminal GS phosphorylation and Akt or GS activity. Employing whole body Akt2-knockout mice, we validated the necessity for Akt2 in insulin-mediated GS activation. However, since insulin did not affect NH2-terminal phosphorylation in mice, we could not use this model to validate the observed association between GS NH2-terminal phosphorylation and Akt activity in humans. In conclusion, our study suggests that although COOH-terminal dephosphorylation is likely necessary for GS activation, Akt2-dependent NH2-terminal dephosphorylation may be the site for "fine-tuning" insulin-mediated GS activation in humans.

AB - Type 2 diabetes is characterized by reduced muscle glycogen synthesis. The key enzyme in this process, glycogen synthase (GS), is activated via proximal insulin signaling, but the exact molecular events remain unknown. Previously, we demonstrated that phosphorylation of Thr308 on Akt (p-Akt-Thr308), Akt2 activity, and GS activity in muscle were positively associated with insulin sensitivity. Here, in the same study population, we determined the influence of several upstream elements in the canonical PI3K signaling on muscle GS activation. One-hundred eighty-one nondiabetic twins were examined with the euglycemic hyperinsulinemic clamp combined with excision of muscle biopsies. Insulin signaling was evaluated at the levels of the insulin receptor, IRS-1-associated PI3K (IRS-1-PI3K), Akt, and GS employing activity assays and phosphospecific Western blotting. The insulin-stimulated GS activity was positively associated with p-Akt-Thr308 (P = 0.01) and Akt2 activity (P = 0.04) but not p-Akt-Ser473 or IRS-1-PI3K activity. Furthermore, p-Akt-Thr308 and Akt2 activity were negatively associated with NH2-terminal GS phosphorylation (P = 0.001 for both), which in turn was negatively associated with insulin-stimulated GS activity (P = 0.001). We found no association between COOHterminal GS phosphorylation and Akt or GS activity. Employing whole body Akt2-knockout mice, we validated the necessity for Akt2 in insulin-mediated GS activation. However, since insulin did not affect NH2-terminal phosphorylation in mice, we could not use this model to validate the observed association between GS NH2-terminal phosphorylation and Akt activity in humans. In conclusion, our study suggests that although COOH-terminal dephosphorylation is likely necessary for GS activation, Akt2-dependent NH2-terminal dephosphorylation may be the site for "fine-tuning" insulin-mediated GS activation in humans.

U2 - 10.1152/ajpendo.00494.2012

DO - 10.1152/ajpendo.00494.2012

M3 - Journal article

C2 - 23321478

SN - 0193-1849

VL - 304

SP - E631-E639

JO - American Journal of Physiology - Endocrinology and Metabolism

JF - American Journal of Physiology - Endocrinology and Metabolism

IS - 6

ER -

Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH2-terminal (sites 2+2a) phosphorylation

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