Axe Cardiologie, Centre de Recherche de l'Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada.
Diabetes. 2010 Apr;59(4):861-71. doi: 10.2337/db09-1238. Epub 2010 Jan 26.
The present study was undertaken to assess the contribution of inducible nitric oxide (NO) synthase (iNOS) to lipid-induced insulin resistance in vivo.
Wild-type and iNOS(-/-) mice were infused for 6 h with a 20% intralipid emulsion, during which a hyperinsulinemic-euglycemic clamp was performed.
In wild-type mice, lipid infusion led to elevated basal hepatic glucose production and marked insulin resistance as revealed by impaired suppression of liver glucose production and reduced peripheral glucose disposal (R(d)) during insulin infusion. Liver insulin resistance was associated with a robust induction of hepatic iNOS, reduced tyrosine phosphorylation of insulin receptor (IR) beta, insulin receptor substrate (IRS)-1, and IRS-2 but elevated serine phosphorylation of IRS proteins as well as decreased Akt activation. The expression of gluconeogenic enzymes Pepck and G6Pc was also increased in the liver of wild-type mice. In contrast to their wild-type counterparts, iNOS(-/-) mice were protected from lipid-induced hepatic and peripheral insulin resistance. Moreover, neither the phosphorylation of insulin signaling intermediates nor expression of gluconeogenic enzymes were altered in the lipid-infused iNOS(-/-) mice compared with their saline-infused controls. Importantly, lipid infusion induced tyrosine nitration of IRbeta, IRS-1, IRS-2, and Akt in wild-type mice but not in iNOS(-/-) animals. Furthermore, tyrosine nitration of hepatic Akt by the NO derivative peroxynitrite blunted insulin-induced Akt tyrosine phosphorylation and kinase activity.
These findings demonstrate that iNOS induction is a novel mechanism by which circulating lipids inhibit hepatic insulin action. Our results further suggest that iNOS may cause hepatic insulin resistance through tyrosine nitration of key insulin signaling proteins.
本研究旨在评估诱导型一氧化氮合酶（iNOS）在体内脂质诱导胰岛素抵抗中的作用。
给野生型和 iNOS（-/-）小鼠输注 20%脂肪乳剂 6 小时，在此期间进行高胰岛素-正常血糖钳夹。
在野生型小鼠中，脂质输注导致基础肝葡萄糖生成升高和明显的胰岛素抵抗，表现在胰岛素输注期间肝葡萄糖生成抑制受损和外周葡萄糖摄取（R(d)）减少。肝胰岛素抵抗与肝 iNOS 的强烈诱导、胰岛素受体（IR）β、胰岛素受体底物（IRS）-1 和 IRS-2 的酪氨酸磷酸化减少以及 IRS 蛋白的丝氨酸磷酸化增加以及 Akt 激活减少有关。肝内糖异生酶 Pepck 和 G6Pc 的表达也增加。与野生型小鼠相比，iNOS（-/-）小鼠对脂质诱导的肝和外周胰岛素抵抗具有保护作用。此外，与生理盐水输注的对照组相比，脂质输注并未改变 iNOS（-/-）小鼠的胰岛素信号转导中间物的磷酸化或糖异生酶的表达。重要的是，脂质输注诱导了野生型小鼠中 IRβ、IRS-1、IRS-2 和 Akt 的酪氨酸硝化，但在 iNOS（-/-）动物中没有。此外，NO 衍生物过氧亚硝酸盐对肝 Akt 的酪氨酸硝化削弱了胰岛素诱导的 Akt 酪氨酸磷酸化和激酶活性。
这些发现表明，iNOS 诱导是循环脂质抑制肝胰岛素作用的一种新机制。我们的结果进一步表明，iNOS 可能通过关键胰岛素信号蛋白的酪氨酸硝化引起肝胰岛素抵抗。
