EARLY ALTERATION OF INSULIN STIMULATION OF PI 3-KINASE IN MUSCLE AND ADIPOCYTE FROM GOLD THIOGLUCOSE OBESE MICE
EARLY ALTERATION OF INSULIN STIMULATION OF PI 3-KINASE IN MUSCLE AND ADIPOCYTE FROM GOLD THIOGLUCOSE OBESE MICE
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DOI：
10.1152/ajpendo.1995.268.4.e604
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发表时间：
1995-04-01
影响因子：
5.1
通讯作者：
LEMARCHANDBRUSTEL, Y
中科院分区：
文献类型：
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作者：
HEYDRICK, SJ;GAUTIER, N;LEMARCHANDBRUSTEL, Y
在体内和体外研究了年轻(8wk)和老年(30wk)金-硫代葡萄糖肥胖小鼠比目鱼肌和脂肪细胞中磷脂酰肌醇3-激酶(PIK)的激活。从肌肉葡萄糖转运和糖原合成评估的胰岛素抵抗在年轻和老年肥胖小鼠中都存在。年轻肥胖小鼠的脂肪细胞脂肪合成和肌肉糖酵解或葡萄糖氧化没有缺陷，但后来变得有抵抗力。在与50 NM胰岛素孵育后，幼年和老年动物的肌肉抗磷酸酪氨酸免疫沉淀PIK活性都被刺激了5到10倍。在年轻和老年肥胖小鼠的肌肉中，这种反应分别受损了56%和75%。在年轻肥胖小鼠的肌肉中，胰岛素对受体酪氨酸激酶活性的刺激仅轻微降低，而胰岛素受体底物1(IRS-1)的酪氨酸磷酸化被钝化。因此，在体内和体外都存在的肌肉中改变的PIK刺激，其特征是PIK活性与IRS-1的关联性降低，似乎是由于IRS-1酪氨酸磷酸化减少所致。在从瘦小鼠分离的脂肪细胞中，抗磷酸酪氨酸免疫沉淀的PIK在与胰岛素孵育10分钟内增加了25倍。这种刺激在年轻和老年肥胖小鼠中都发生了明显的变化，而脂肪生成只有在老年肥胖动物中是胰岛素抵抗的。在幼年肥胖小鼠的脂肪细胞中，胰岛素对胰岛素受体p亚基pp60和外源性底物的磷酸化的刺激作用是正常的，而IRS-1酪氨酸的磷酸化明显受到抑制。在老年肥胖小鼠的脂肪细胞中，所有蛋白质的酪氨酸磷酸化都发生了变化。与体外实验结果不同的是，体内脂肪垫中胰岛素刺激的PIK活性仅在老年肥胖动物中受到抑制。这些结果表明，PIK水平的胰岛素抵抗在肌肉和脂肪组织中很早就发生了，此时肌肉中的葡萄糖运输和代谢变化中等，甚至脂肪细胞中没有。我们的结果表明，PIK激活缺陷可能参与了这两种组织胰岛素抵抗的建立，而IRS-1磷酸化水平的改变似乎在胰岛素抵抗中起着关键作用。
The activation of phosphatidylinositol 3-kinase (PIK) was studied in vivo and in vitro in soleus muscle and adipocytes from young (8 wk) and old (30 wk) gold thioglucose obese mice. Insulin resistance assessed from muscle glucose transport and glycogen synthesis was present both in young and old obese mice. Adipocyte lipid synthesis and muscle glycolysis or glucose oxidation are not defective in young obese mice but become resistant later on. After incubation with 50 nM insulin, muscle antiphosphotyrosine-immunoprecipitable PIK activity was stimulated 5- to 10-fold in both young and old animals. This response was impaired by 56 and 75% in muscles from young and old obese mice, respectively. Insulin stimulation of receptor tyrosine kinase activity was only slightly decreased in muscle of young obese mice, whereas insulin receptor substrate 1 (IRS-1) tyrosine phosphorylation was blunted. The altered PIK stimulation in muscle, which is present both in vivo and in vitro, is thus characterized by a reduced association of PIK activity with IRS-1 and appears to result from a diminished IRS-1 tyrosine phosphorylation. In adipocytes isolated from lean mice, antiphosphotyrosine-immunoprecipitable PIK increased 25-fold within 10 min of incubation with insulin. This stimulation was markedly altered both in young and old obese mice, whereas lipogenesis was insulin resistant only in old obese animals. In adipocytes from young obese mice, insulin's stimulatory effect on the phosphorylation of insulin receptor p-subunit, pp60, and an exogenous substrate was normal, whereas IRS-1 tyrosine phosphorylation was markedly depressed. In adipocytes from old obese mice, the tyrosine phosphorylation of all proteins was altered. Different from the in vitro results, the insulin stimulation of PIK activity in fat pads in vivo was depressed only in old obese animals. Those results show that insulin resistance at the level of PIK occurs very early both in muscle and adipose tissue at a time when alterations in glucose transport and metabolism are moderate in muscle or even absent in adipocytes. Our results suggest that the defect in PIK activation could participate in the establishment of insulin resistance in both tissues and that alterations at the level of IRS-1 phosphorylation seem to play a key role in insulin resistance.