Akt substrate of 160 kDa is essential for the calorie restriction-induced increase in insulin-stimulated glucose uptake by skeletal muscle of female rats

Abstract

We evaluated effects of calorie restriction (CR; consuming 65% of ad libitum (AL) intake) for 8 weeks on female wildtype (WT) and Akt substrate of 160 kDa knockout (AS160-KO) rats. Insulin-stimulated glucose uptake (ISGU) was determined in isolated epitrochlearis muscles incubated with 0, 50, 100, or 500 µU/mL insulin. Phosphorylation of key insulin signaling proteins that control ISGU (Akt and AS160) was assessed by immunoblotting (Akt phosphorylation on Threonine-308, pAktThr308 and Serine-473, pAktSer473; AS160 phosphorylation on Serine-588, pAS160Ser588, and Threonine-642, pAS160Thr642). Abundance of proteins that regulate ISGU (GLUT4 glucose transporter protein and hexokinase II) was also determined by immunoblotting. The major results were as follows: ( i) WT-CR versus WT-AL rats had greater ISGU with 100 and 500 µU/mL insulin; ( ii) CR versus WT-AL rats had greater GLUT4 protein abundance; ( iii) WT-CR versus WT-AL rats had greater pAktThr308 with 500 µU/mL insulin; ( iv) WT-CR versus WT-AL rats did not differ for pAktSer473, pAS160Ser588, or pAS160Thr642 at any insulin concentration; ( v) AS160-KO versus WT rats with each diet had lower ISGU at each insulin concentration, but not lower pAkt on either phosphosite; ( vi) AS160-KO versus WT rats had lower muscle GLUT4 abundance regardless of diet; and ( vii) AS160-KO-CR versus AS160-KO-AL rats did not differ for ISGU, GLUT4 abundance, pAkt on either phosphosite, or pAS160 on either phosphosite. These novel results demonstrated that AS160 expression, but not greater pAS160 on key phosphosites, was essential for the CR-induced increases in muscle ISGU and GLUT4 abundance of female rats.