Investigation For Molecular Mechanism Of Insulin Resistance In Transgenic Mice Expressing A Mutant Shp2

为了阐明SHP-2的作用，我们制造了转基因（Tg）小鼠，表达缺乏PTPase结构域（DPTP）的显性负突变体。通过Southern blot检测鉴定的2株Tg小鼠，转基因产物在骨骼肌、肝脏和脂肪组织中表达，胰岛素诱导的胰岛素受体底物（IRS） 1与内源性SHP-2的关联被抑制，证实DPTP具有显性负性。腹腔内葡萄糖负荷试验显示Tg小鼠血糖水平升高。空腹4小时后，Tg小鼠的血浆胰岛素水平比血糖水平高3倍。通过持续的葡萄糖、胰岛素和生长抑素输注来估计胰岛素敏感性，稳态血糖水平较高，表明存在胰岛素抵抗。此外，我们观察到胰岛素刺激的肌肉和脂肪细胞的葡萄糖摄取在胰岛素的生理浓度存在的损害。此外，在肌肉和肝脏中，胰岛素对IRS-1酪氨酸磷酸化和磷脂酰肌醇3-激酶和Akt激酶活性的刺激减弱。这些结果表明，过表达显性负突变体抑制内源性SHP-2功能可能导致糖代谢胰岛素敏感性受损，因此SHP-2可能在靶组织中调节胰岛素信号传导，这些Tg小鼠是研究胰岛素抵抗分子机制的独特模型。

To elucidate roles of SHP-2, we generated transgenic (Tg) mice expressing a dominant negative mutant lacking PTPase domain (DPTP). On examining 2 lines of Tg mice identified by Southern blot, the transgene product was expressed in skeletal muscle liver and adipose tissues and insulin-induced association of insulin receptor substrate (IRS) 1 with endogenous SHP-2 was inhibited, confirming that DPTP has a dominant negative property. The intraperitoneal glucose loading test demonstrated an increase in blood glucose levels in Tg mice. Plasma insulin levels in Tg mice after 4 h fasting were 3 times greater with comparable blood glucose levels. To estimate insulin sensitivity by a constant glucose, insulin and somatostatin infusion, steady state blood glucose levels were higher, suggesting the presence of insulin resistance. Furthermore we observed the impairment of insulin-stimulated glucose uptake in muscle and adipocytes in the presence of physiological concentrations of insulin. Moreover, tyrosine-phosphorylation of IRS-1 and stimulation of phosphatidylinositol 3-kinase and Akt kinase activities by insulin were attenuated in muscle and liver. These results indicate that the inhibition of endogenous SHP-2 function by the overexpression of a dominant negative mutant may lead to impaired insulin sensitivity of glucose metabolism and thus SHP-2 may function to modulate insulin signaling in target tissues and these Tg mice are a unique model to investigate molecular mechanism for insulin resistance.