Attenuation of Free Fatty Acid (FFA)-Induced Skeletal Muscle Cell Insulin Resistance by Resveratrol is Linked to Activation of AMPK and Inhibition of mTOR and p70 S6K.

Danja J Den Hartogh,Filip Vlavcheski,Adria Giacca,Evangelia Tsiani

doi:10.3390/ijms21144900

Danja J Den Hartogh, Filip Vlavcheski + Show 2 more

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https://doi.org/10.3390/ijms21144900

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Abstract

Insulin resistance, a main characteristic of type 2 diabetes mellitus (T2DM), is linked to obesity and excessive levels of plasma free fatty acids (FFA). Studies indicated that significantly elevated levels of FFAs lead to skeletal muscle insulin resistance, by dysregulating the steps in the insulin signaling cascade. The polyphenol resveratrol (RSV) was shown to have antidiabetic properties but the exact mechanism(s) involved are not clearly understood. In the present study, we examined the effect of RSV on FFA-induced insulin resistance in skeletal muscle cells in vitro and investigated the mechanisms involved. Parental and GLUT4myc-overexpressing L6 rat skeletal myotubes were used. [3H]2-deoxyglucose (2DG) uptake was measured, and total and phosphorylated levels of specific proteins were examined by immunoblotting. Exposure of L6 cells to FFA palmitate decreased the insulin-stimulated glucose uptake, indicating insulin resistance. Palmitate increased ser307 (131% ± 1.84% of control, p < 0.001) and ser636/639 (148% ± 10.1% of control, p < 0.01) phosphorylation of IRS-1, and increased the phosphorylation levels of mTOR (174% ± 15.4% of control, p < 0.01) and p70 S6K (162% ± 20.2% of control, p < 0.05). Treatment with RSV completely abolished these palmitate-induced responses. In addition, RSV increased the activation of AMPK and restored the insulin-mediated increase in (a) plasma membrane GLUT4 glucose transporter levels and (b) glucose uptake. These data suggest that RSV has the potential to counteract the FFA-induced muscle insulin resistance.

Highlights

Skeletal muscle tissue accounts for nearly 75–80% of the postprandial insulin-mediated glucose uptake, thereby it plays a predominant role in maintaining glucose homeostasis
Evidence shows that free fatty acid (FFA) significantly impair the insulin signaling by increasing serine phosphorylation of insulin receptor substrate-1 (IRS-1) [11,12], through activation/phosphorylation of protein kinases, including mechanistic target of rapamycin [13,14], ribosomal protein S6 kinase (p70 S6K) [15,16], c-Jun N-terminal kinase (JNK) [12], protein kinase C (PKC) [15], glycogen synthase kinase 3 (GSK3) [17], and inhibitory kappa B (IκB) kinase (IKK) [7,18]
We investigated the effect of RSV on glucose uptake, glucose transporter 4 (GLUT4) plasma membrane levels, and Akt phosphorylation/expression in palmitate-treated insulin-resistant L6 cells

Summary

Introduction

Skeletal muscle tissue accounts for nearly 75–80% of the postprandial insulin-mediated glucose uptake, thereby it plays a predominant role in maintaining glucose homeostasis. Impairments in the IRS-1-PI3K-Akt signaling cascade results in insulin resistance and type 2 diabetes mellitus (T2DM) [3,4]. In vitro evidence showed that exposure of muscle cells to FFA palmitate resulted in insulin resistance [7,8]. Evidence shows that FFAs significantly impair the insulin signaling by increasing serine phosphorylation of IRS-1 [11,12], through activation/phosphorylation of protein kinases, including mechanistic target of rapamycin (mTOR) [13,14], ribosomal protein S6 kinase (p70 S6K) [15,16], c-Jun N-terminal kinase (JNK) [12], protein kinase C (PKC) [15], glycogen synthase kinase 3 (GSK3) [17], and inhibitory kappa B (IκB) kinase (IKK) [7,18]

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