α2 Isoform-specific activation of 5′ adenosine monophosphate-activated protein kinase by 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside at a physiological level activates glucose transport and increases glucose transporter 4 in mouse skeletal muscle

5' Adenosine monophosphate-activated protein kinase (AMPK) has been implicated in exercise-induced stimulation of glucose metabolism in skeletal muscle. Although skeletal muscle expresses both the alpha 1 and alpha 2 isoforrns of AMPK, the alpha 2 isoform is activated predominantly in response to moderate-intensity endurance exercise in human and animal muscles. The purpose of this study was to determine whether activation of alpha 2 AMPK plays a role in increasing the rate of glucose transport, promoting glucose transporter 4 (GLUT4) expression, and enhancing insulin sensitivity in skeletal muscle. To selectively activate the alpha 2 isoform, we used 5-aminoimidazole-4carboxamide-1-beta-D-ribonucleoside (AICAR), which is metabolized in muscle cells and preferentially stimulates the alpha 2 isoform Subcutaneous administration of 250 mg/kg AICAR activated the alpha 2 isoform for 90 minutes, but not the alpha 1 isoform in hind limb muscles of the C57/B6J mouse. The maximal activation of the alpha 2 isoform was observed 30 to 60 minutes after administration of AICAR and was 172 similar to the activation induced by a 30-minute swim in a current pool. The increase in alpha 2 activity paralleled the phosphorylation of Thr(172), the essential residue for full kinase activation, and the activity of acetyl-coenzyme A carboxylase beta, a known substrate of AMPK in skeletal muscle. Subcutaneous injection of AICAR rapidly increased, by 30%, the rate of 2-deoxyglucose (2DG) transport into soleus muscle; 2DG transport increased within 30 minutes and remained elevated for 4 hours after administration of AICAR. Repeated intraperitoneal injection of AICAR, 3 times a day for 4 to 7 days, increased soleus GLUT4 protein by 30% concomitant with a significant 20% increase in insulin-stimulated 2DG transport. These data suggest that moderate endurance exercise promotes glucose transport, GLUT4 expression, and insulin sensitivity in skeletal muscle at least partially via activation of the alpha 2 isoform of AMPK. (c) 2006 Elsevier Inc. All rights reserved.