Muscle‐specific deletion of mTORC2 (Rictor) blocks insulin stimulated Akt Ser 473 phosphorylation and impairs submaximal but not maximal insulin induced glucose uptake

Abstract

ObjectiveTo test whether Rictor and Akt Ser437 phosphorylation is necessary for insulin‐stimulated glucose uptake in skeletal muscle.MethodsEDL muscle from muscle‐specific Rictor knock‐out mice (mKO) were incubated ex vivo with or without submaximal (100μU/ml) or maximal (100mU/ml) insulin concentrations. Akt Ser473 phosphorylation served as mTORC2 activity readout and muscle glucose uptake was measured with tritium‐labeled 2‐deoxyglucose.ResultsSubmaximal and maximal insulin stimulation increased Akt Ser437 phosphorylation 4‐fold and 21‐fold, respectively in EDL from WT mice (p < 0.01), but was blocked completely in mKO Rictor EDL. Akt1 and Akt2 expression in mKO Rictor muscle were reduced by 40% and 60%, respectively (p < 0.001). Conversely, expression of TRB3, a negative regulator of Akt activity, was increased 1.6‐fold (p < 0.05) in mKO Rictor muscle. Glucose uptake increased 2‐fold in WT mice with both submaximal and maximal insulin concentrations (p < 0.05). In mKO muscle submaximal insulin‐induced glucose uptake was completely blocked but was normal during maximal insulin stimulation.ConclusionDeletion of Rictor in muscle impairs Akt expression and blocks Akt Ser437 phosphorylation during insulin stimulation. Rictor and Akt Ser 473 phosphorylation are necessary for increasing muscle glucose uptake at submaximal but not maximal insulin concentrations.