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Related Experiment Videos

Insulin and exercise decrease glycogen synthase kinase-3 activity by different mechanisms in rat skeletal muscle.

J F Markuns1, J F Wojtaszewski, L J Goodyear

  • 1Research Division, Joslin Diabetes Center, and the Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02215, USA.

The Journal of Biological Chemistry
|August 24, 1999
PubMed
Summary
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Both exercise and insulin activate glycogen synthase in skeletal muscle. Insulin uses Akt to deactivate glycogen synthase kinase-3 (GSK-3), while exercise employs an independent pathway.

Area of Science:

  • Muscle physiology
  • Metabolic regulation
  • Cell signaling

Background:

  • Insulin and exercise stimulate glycogen synthase activity in skeletal muscle.
  • Akt signaling and glycogen synthase kinase-3 (GSK-3) are implicated in this process.
  • Understanding the precise regulatory mechanisms is crucial for metabolic research.

Purpose of the Study:

  • To investigate the roles of Akt and GSK-3 in muscle glycogen synthesis regulation.
  • To compare the effects of insulin and exercise on Akt and GSK-3 activity and phosphorylation.
  • To elucidate the signaling pathways involved in muscle glycogen regulation.

Main Methods:

  • Time course experiments were conducted on male rat hindlimb skeletal muscle.
  • Insulin injection and treadmill running were used as stimuli.

Related Experiment Videos

  • Measurements included glycogen synthase activity, Akt phosphorylation/activity, and GSK-3 phosphorylation/activity.

    • Main Results:

    • Both insulin and exercise increased glycogen synthase activity.
    • Insulin increased Akt phosphorylation and activity, leading to GSK-3 serine phosphorylation and deactivation.
    • Exercise deactivated GSK-3 but did not affect Akt phosphorylation or Ser(21) phosphorylation.

    Conclusions:

    • GSK-3 is constitutively active and tyrosine phosphorylated in resting muscle.
    • Both exercise and insulin effectively regulate GSK-3 activity in vivo.
    • Insulin deactivates GSK-3 via Akt-dependent serine phosphorylation, while exercise uses an Akt-independent mechanism.