Akt Activity Negatively Regulates Phosphorylation of AMP-activated Protein Kinase in the Heart

Suzanne Kovacic,Carrie-Lynn M Soltys,Amy J Barr,Ichiro Shiojima,Kenneth Walsh,Jason R.B Dyck

doi:10.1074/jbc.m305371200

Suzanne Kovacic, Carrie-Lynn M Soltys + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m305371200

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Abstract

In the heart, insulin stimulates a variety of kinase cascades and controls glucose utilization. Because insulin is able to activate Akt and inactivate AMP-activated protein kinase (AMPK) in the heart, we hypothesized that Akt can regulate the activity of AMPK. To address the potential existence of this novel signaling pathway, we used a number of experimental protocols to activate Akt in cardiac myocytes and monitored the activation status of AMPK. Mouse hearts perfused in the presence of insulin demonstrated accelerated glycolysis and glucose oxidation rates as compared with non-insulin-perfused hearts. In addition, insulin caused an increase in Akt phosphorylation and a decrease in AMPK phosphorylation at its major regulatory site (threonine 172 of the alpha catalytic subunit). Transgenic mice overexpressing a constitutively active mutant form of Akt1 displayed decreased phosphorylation of cardiac alpha-AMPK. Isolated neonatal cardiac myocytes infected with an adenovirus expressing constitutively active mutant forms of either Akt1 or Akt2 also suppressed AMPK phosphorylation. However, Akt-dependent depression of alpha-AMPK phosphorylation could be overcome in the presence of the AMPK activator, metformin, suggesting that an override mechanism exists that can restore AMPK activity. Taken together, this study suggests that there is cross-talk between the AMPK and Akt pathways and that Akt activation can lead to decreased AMPK activity. In addition, our data suggest that the ability of insulin to inhibit AMPK may be controlled via an Akt-mediated mechanism.

Highlights

In the heart, insulin stimulates a variety of kinase cascades and controls glucose utilization
A similar profile is observed in these hearts with respect to glucose oxidation rates, with glucose oxidation rates increasing ϳ8-fold in the insulin-perfused group as compared with controls (Fig. 1B)
Using insulin- perfused mouse hearts, hearts from transgenic mice expressing constitutively active Akt, and isolated cardiac myocytes expressing constitutively active Akt, our data suggest that the ability of insulin to inhibit AMPK can be controlled via Akt

Summary

Introduction

Insulin stimulates a variety of kinase cascades and controls glucose utilization. Insulin has been shown to stimulate myocardial glucose uptake [1, 2] and accelerate glycolysis [2, 3] and glucose oxidation rates [2, 4] as well as promote glycogen synthesis [5, 6] These effects of insulin on glucose metabolism are important because a significant amount of glucose-derived ATP is used for maintaining proper cardiac function. Recent evidence in heart indicates that the presence of elevated exogenous palmitate inhibits insulin-induced Akt phosphorylation [2], suggesting that Akt may be more central to the control of cardiac energy substrate preference than previously thought. Insulin can antagonize ischemia-induced activation of AMPK, presumably by preventing phosphorylation at the activation site (Thr-172) of the catalytic subunit of AMPK by the upstream AMPK kinase [29]

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