Kim Y B, Zhu J S, Zierath J R, Shen H Q, Baron A D, Kahn B B
Department of Medicine, Beth Israel-Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
Diabetes. 1999 Feb;48(2):310-20. doi: 10.2337/diabetes.48.2.310.
Glucosamine, a metabolite of glucose via the hexosamine biosynthetic pathway, potently induces insulin resistance in skeletal muscle by impairing insulin-induced GLUT4 translocation to the plasma membrane. Activation of phosphoinositide (PI) 3-kinase is necessary for insulin-stimulated GLUT4 translocation, and the serine/threonine kinase Akt/protein kinase B (PKB) is a downstream mediator of some actions of PI 3-kinase. To determine whether glucosamine-induced insulin resistance could be due to impaired signaling, we measured insulin receptor substrate (IRS)-1 and insulin receptor tyrosine phosphorylation; PI 3-kinase activity associated with IRS-1, IRS-2, and phosphotyrosine; and Akt activity and phosphorylation in skeletal muscle of rats infused for 2 h with glucosamine (6.0 mg x kg(-1) x min(-1)) or saline. Euglycemic-hyperinsulinemic clamp studies (12 mU x kg(-1) x min(-1) insulin) in awake rats showed that glucosamine infusion resulted in rapid induction of insulin resistance, with a 33% decrease in glucose infusion rate (P < 0.01). Tissues were harvested after saline alone (basal), 1 min after an insulin bolus (10 U/kg), or after 2 h of insulin clamp in saline- and glucosamine-infused rats. After 1 min of insulin stimulation, phosphorylation of IRS-1 and insulin receptor increased 6- to 8-fold in saline-infused rats and 7- to 10-fold in glucosamine-infused rats. In saline-infused rats, 1 min of insulin stimulation increased PI 3-kinase activity associated with IRS-1, IRS-2, or phosphotyrosine 7.6-, 6.4-, and 10-fold, respectively. In glucosamine-infused rats treated for 1 min with insulin, PI 3-kinase activity associated with IRS-1 was reduced 28% (P < 0.01) and that associated with phosphotyrosine was reduced 43% (P < 0.01). Insulin for 1 min stimulated Akt/PKB activity approximately 5-fold in both saline- and glucosamine-infused rats; insulin-induced hyperphosphorylation of Akt/PKB was not different between groups. Glucosamine infusion alone had no effect on tyrosine phosphorylation of the insulin receptor or IRS-1 or on stimulation of PI 3-kinase or Akt/PKB activity. However, 2 h of insulin clamp reduced PI 3-kinase activity associated with IRS-1, IRS-2, or phosphotyrosine to <30% of that seen with 1 min of insulin. No effect of glucosamine was seen on these signaling events when compared with 2 h of insulin clamp without glucosamine. Our data show that 1) glucosamine infusion in rats is associated with an impairment in the early activation of PI 3-kinase by insulin in skeletal muscle, 2) this insulin-resistant state does not involve alterations in the activation of Akt/PKB, and 3) prolonged insulin infusion under clamp conditions results in a blunting of the PI 3-kinase response to insulin.
氨基葡萄糖是葡萄糖经己糖胺生物合成途径生成的代谢产物，它通过损害胰岛素诱导的葡萄糖转运蛋白4（GLUT4）向质膜的转位，从而在骨骼肌中强力诱导胰岛素抵抗。磷酸肌醇（PI）3激酶的激活是胰岛素刺激的GLUT4转位所必需的，而丝氨酸/苏氨酸激酶Akt/蛋白激酶B（PKB）是PI 3激酶某些作用的下游介质。为了确定氨基葡萄糖诱导的胰岛素抵抗是否可能归因于信号转导受损，我们测量了胰岛素受体底物（IRS）-1和胰岛素受体酪氨酸磷酸化；与IRS-1、IRS-2和磷酸酪氨酸相关的PI 3激酶活性；以及在输注氨基葡萄糖（6.0 mg·kg⁻¹·min⁻¹）或生理盐水2小时的大鼠骨骼肌中的Akt活性和磷酸化。清醒大鼠的正常血糖-高胰岛素钳夹研究（12 mU·kg⁻¹·min⁻¹胰岛素）表明，输注氨基葡萄糖导致胰岛素抵抗迅速诱导，葡萄糖输注速率降低33%（P < 0.01）。在单独输注生理盐水（基础）、胰岛素推注（10 U/kg）1分钟后或在输注生理盐水和氨基葡萄糖的大鼠中进行2小时胰岛素钳夹后采集组织。胰岛素刺激1分钟后，输注生理盐水的大鼠中IRS-1和胰岛素受体的磷酸化增加6至8倍，输注氨基葡萄糖的大鼠中增加7至10倍。在输注生理盐水的大鼠中，胰岛素刺激1分钟使与IRS-1、IRS-2或磷酸酪氨酸相关的PI 3激酶活性分别增加7.6倍、6.4倍和10倍。在输注氨基葡萄糖的大鼠中，用胰岛素处理1分钟后，与IRS-1相关的PI 3激酶活性降低28%（P < 0.01），与磷酸酪氨酸相关的降低43%（P < 0.01）。胰岛素刺激1分钟在输注生理盐水和氨基葡萄糖的大鼠中均使Akt/PKB活性增加约5倍；胰岛素诱导的Akt/PKB过度磷酸化在两组之间没有差异。单独输注氨基葡萄糖对胰岛素受体或IRS-1的酪氨酸磷酸化或对PI 3激酶或Akt/PKB活性的刺激没有影响。然而，2小时的胰岛素钳夹使与IRS-1、IRS-2或磷酸酪氨酸相关的PI 3激酶活性降至胰岛素刺激1分钟时的<30%。与无氨基葡萄糖的2小时胰岛素钳夹相比，未观察到氨基葡萄糖对这些信号转导事件有影响。我们的数据表明：1）在大鼠中输注氨基葡萄糖与骨骼肌中胰岛素对PI 3激酶的早期激活受损有关；2）这种胰岛素抵抗状态不涉及Akt/PKB激活的改变；3）在钳夹条件下长时间输注胰岛素导致PI 3激酶对胰岛素的反应减弱。
