The Combined Deletion of S6K1 and Akt2 Deteriorates Glycemic Control in a High-Fat Diet

Abstract

Signaling downstream of mechanistic target of rapamycin complexes 1 and 2 (mTORC1 and mTORC2) controls specific and distinct aspects of insulin action and nutrient homeostasis in an interconnected and as yet unclear way. Mice lacking the mTORC1 substrate S6 kinase 1 (S6K1) maintain proper glycemic control with a high-fat diet. This phenotype is accompanied by insulin hypersensitivity, Akt- and AMP-activated kinase upregulation, and increased lipolysis in adipose tissue and skeletal muscle. Here, we show that, when S6K1 inactivation is combined with the deletion of the mTORC2 substrate Akt2, glucose homeostasis is compromised due to defects in both insulin action and β-cell function. After a high-fat diet, the S6K1^−/− Akt2^−/− double-mutant mice do not become obese, though they are severely hyperglycemic. Our data demonstrate that S6K1 is required for pancreatic β-cell growth and function during adaptation to insulin resistance states. Strikingly, the inactivation of two targets of mTOR and phosphatidylinositol 3-kinase signaling is sufficient to reproduce major hallmarks of type 2 diabetes.

ACKNOWLEDGMENTS

We thank the Novartis Foundation and the George Thomas laboratory for the use of S6K mutant mice. We thank Gilles Mithieux for providing us the anti-G6Pase antibody. We are grateful to the members of INSERM U845 for support. We thank Sophie Berissi for excellent technical support.

This work was supported by grants to M.P. from the European Research Council, from INSERM-Fondation pour la Recherche Médicale-Juvenile Diabetes Research Foundation International, from Fondation de la Recherche Medicale, and from Fondation Schlumberger pour l'Education et la Recherche.