Regulation of insulin signaling and sensitivity by the xenobiotic metabolizing enzyme NQO1

代谢综合征包括一组心血管危险因素，包括肥胖、高血压、血糖、 不耐受和血脂异常，其基础病理学与胰岛素抵抗有关。我们已经证明， 外源性代谢酶NQO 1对胰岛素敏感性和防止饮食诱导的疾病至关重要。 使用NQO 1转基因小鼠增加NQO 1表达可保护小鼠免受负性生化和 高脂饮食的生理作用，并赋予增加的胰岛素敏感性。NQO 1的药理学抑制 使用基于选择性机制的抑制剂导致小鼠胰岛素敏感性严重受损。NQO1 基因敲除动物是胰岛素不敏感的，导致糖尿病样表型， 与人类代谢综合征表型相关。我们的数据表明，NQO 1是激活 通过使其与蛋白质复合物TORC 2的胰岛素诱导型相互作用允许AKT丝氨酸 磷酸化和充分利用葡萄糖。胰岛素给药导致NQO 1快速显著增加 胰岛素受体的酪氨酸磷酸化和突变分析表明，磷酸化导致主要的 NQO 1功能的变化。构象依赖性抗体和电泳也表明， NQO 1构象的变化是由于吡啶核苷酸氧化还原比的改变或胰岛素的加入。 基于NQO 1的细胞功能，我们将测试所观察到的3种生物学上合理的机制。 NQO 1在胰岛素信号传导和代谢综合征表型保护中的作用。1)NQO 1调节 通过蛋白质支架的胰岛素依赖性信号传导。我们将检验一个假设，即观察到的NQO 1效应 对胰岛素敏感性的影响受到NQO 1构象变化的调节， 核苷酸水平或通过胰岛素受体磷酸化NQO 1，促进AKT的最佳结合 和Rictor和下游胰岛素信号传导; 2）NQO 1产生NAD+以获得最佳SIRT活性。脱乙酰 通过SIRTs在胰岛素信号传导中至关重要，NQO 1可以快速产生高水平的NAD+，以获得最佳的sirtuin 活性; 3）关键代谢调节剂的稳定。关键的代谢调节因子PGC 1 α被保护， NQO 1的蛋白酶体降解。PGC 1 α和AMPK均影响线粒体氧化磷酸化， 生物合成和防止代谢综合征。因此，我们将确定NQO 1是否影响代谢 通过调节PGC 1 α和AMPK水平来治疗综合征。 我们的工作假设是，NQO 1在胰岛素敏感性和保护代谢中起着关键作用。 综合征表型，但关键的问题，仍然有待回答的是机制（S）的基础上， NQO 1的好处

Metabolic syndrome comprises a group of cardiovascular risk factors including obesity, high blood pressure, glucose intolerance and dyslipidemia whose underlying pathology is related to insulin resistance. We have shown that the xenobiotic-metabolizing enzyme NQO1 is critical to insulin sensitivity and protection from diet-induced morbidities. Increasing NQO1 expression using NQO1 transgenic mice protects against the negative biochemical and physiological effects of a high fat diet and confers increased insulin sensitivity. Pharmacological inhibition of NQO1 using selective mechanism-based inhibitors led to a severe impairment in insulin sensitivity in mice. NQO1 knockout animals are insulin-insensitive resulting in a diabetes-like phenotype and a null NQO1 polymorphism is associated with metabolic syndrome phenotypes in humans. Our data shows that NQO1 is required for activation of AKT by enabling its insulin-inducible interaction with the protein complex TORC 2 allowing AKT serine phosphorylation and full glucose utilization. Insulin administration led to a rapid and marked increase in NQO1 tyrosine phosphorylation by the insulin receptor and mutational analysis suggests that phosphorylation leads to major changes in NQO1 functionality. Conformation-dependent antibodies and electrophoresis also indicated marked changes in NQO1 conformation as a result of either altered pyridine nucleotide redox ratios or addition of insulin. Based on the cellular functions of NQO1, we will test 3 biologically plausible mechanisms underlying the observed role of NQO1 in insulin signaling and protection against metabolic syndrome phenotypes. 1) NQO1 modulates insulin-dependent signaling by protein scaffolding. We will test the hypothesis that the observed effects of NQO1 on insulin sensitivity are modulated by a change in NQO1 conformation induced either by alterations in pyridine nucleotide levels or by phosphorylation of NQO1 by the insulin receptor, facilitating optimal association of AKT and Rictor and downstream insulin signaling; 2) NQO1 generates NAD+ for optimal SIRT activity. Deacetylation via SIRTs is critical in insulin signaling and NQO1 can rapidly generate high levels of NAD+ for optimal sirtuin activity; 3) Stabilization of critical metabolic regulators. The key metabolic regulator PGC1α is protected against proteasomal degradation by NQO1. Both PGC1α and AMPK influence mitochondrial oxidative phosphorylation and biogenesis and protect against metabolic syndrome. We will therefore define whether NQO1 influences metabolic syndrome by modulation of PGC1α and AMPK levels. Our working hypothesis is that NQO1 plays a critical role in insulin sensitivity and protection against metabolic syndrome phenotypes but the critical question that remains to be answered is the mechanism(s) underlying the beneficial effects of NQO1.