Ceramide- and oxidant-induced insulin resistance involve loss of insulin-dependent rac-activation and actin remodeling in muscle cells
Ceramide- and oxidant-induced insulin resistance involve loss of insulin-dependent rac-activation and actin remodeling in muscle cells
复制标题
DOI：
10.2337/db06-0823
复制
发表时间：
2007-02-01
期刊：
影响因子：
7.7
通讯作者：
Klip, Amira
中科院分区：
文献类型：
--
作者：
JeBailey, Lellean;Wanono, Oshrit;Klip, Amira
在肌肉细胞中，胰岛素引起葡萄糖转运蛋白 GLUT4 募集至质膜。该过程涉及从胰岛素受体底物 (IRS)-1 到磷脂酰肌醇的顺序信号传导。 (PI) 3-激酶和丝氨酸/苏氨酸激酶 Akt。 GLUT4 易位还需要丝状肌动蛋白的不依赖于 Akt、但依赖于 PI 3 激酶和 Rac 的重塑。尽管 IRS-1 磷酸化在体内胰岛素抵抗状态下通常会降低，但在细胞培养中引发胰岛素抵抗的几种条件可以避免这一早期步骤。在这里，我们表明，当 L6 肌管暴露于 C2-神经酰胺或产生氧化剂的葡萄糖氧化酶剂量分别低至 12.5 μmol/l 和 12.5 mU/ml 时，胰岛素依赖性 Rac 激活及其随后的肌动蛋白重塑被消除。在 25 μmol/l 和 25 mU/ml 浓度下，葡萄糖氧化酶和 C2-神经酰胺显着减少 GLUT4 易位和葡萄糖摄取，并降低 Ser473 和 Thr308 上的 Akt 磷酸化，但它们既不影响 IRS-1 酪氨酸磷酸化，也不影响其与 p85 和 PI 3 激酶活性的关联。小干扰 RNA 依赖性 Rac1 敲低可阻止肌动蛋白重塑和 GLUT4 易位，但不会影响 Akt 磷酸化，这表明 Rac 和肌动蛋白重塑对 Akt 整体激活没有贡献。我们认为，神经酰胺和氧化应激可以分别影响胰岛素向 GLUT4 发出信号的两个独立臂，即 Rac-GTP 负载和 Akt 磷酸化。
In muscle cells, insulin elicits recruitment of the glucose transporter GLUT4 to the plasma membrane. This process engages sequential signaling from insulin receptor substrate (IRS)-1 to phosphatidylinositol. (PI) 3-kinase and the serine/threonine kinase Akt. GLUT4 translocation also requires an Akt-independent but PI 3-kinase- and Rac-dependent remodeling of filamentous actin. Although IRS-1 phosphorylation is often reduced in insulin-resistant states in vivo, several conditions eliciting insulin resistance in cell culture spare this early step. Here, we show that insulin-dependent Rac activation and its consequent actin remodeling were abolished upon exposure of L6 myotubes beginning at doses of C2-ceramide or oxidant-producing glucose oxidase as low as 12.5 mu mol/l and 12.5 mU/ml, respectively. At 25 mu mol/l and 25 mU/ml, glucose oxidase and C2-ceramide markedly reduced GLUT4 translocation and glucose uptake and lowered Akt phosphorylation on Ser473 and Thr308, yet they affected neither IRS-1 tyrosine phosphorylation nor its association with p85 and PI 3-kinase activity. Small interfering RNA-dependent Rac1 knockdown prevented actin remodeling and GLUT4 translocation but spared Akt phosphorylation, suggesting that Rac and actin remodeling do not contribute to overall Akt activation. We propose that ceramide and oxidative stress can each affect two independent arms of insulin signaling to GLUT4 at distinct steps, Rac-GTP loading and Akt phosphorylation.