Regulation of hepatic gene expression and metabolism by FoxO proteins

项目总结/摘要 肝脏产生过多的葡萄糖在糖尿病的发展中起着核心作用。 糖尿病，其中胰岛素调节肝葡萄糖产生（HGP）的能力受损。 FoxO转录因子是胰岛素的主要靶点，在介导胰岛素依赖性高血糖和胰岛素抵抗中起重要作用。 胰岛素对肝脏葡萄糖和脂质代谢多方面的影响，包括 糖酵解和脂肪生成。然而，FoxO的机制 蛋白质以综合方式发挥这些不同的作用仍然知之甚少。 在我们之前的资助期间，我们发现a）FoxO蛋白也发挥重要作用， 通过调节脂肪代谢对肝内脂肪分解和脂肪酸氧化的影响 三酰甘油脂肪酶（ATGL），它介导的第一步脂解，及其抑制剂， G 0/S1开关2基因（G 0 S2），和B）ATGL依赖性脂解在介导 FoxO蛋白在肝脏中的不同作用，包括对促生、糖酵解和 脂肪生成基因表达和代谢。这些研究还表明，ATGL依赖性 FoxO 1对糖酵解和促细胞凋亡基因的影响需要脂解作用来介导 表达，并计划在小鼠模型和分离的肝细胞中进行额外的研究， 更好地了解介导脂质代谢和脂质代谢之间这种新联系的具体机制， 通过胰岛素/FoxO途径进行葡萄糖调节。 此外，使用肝脏特异性胰岛素受体（IR）敲除（LIRKO）和IR/FoxO 1 在双基因敲除（LIRFKO）小鼠中，我们还发现破坏肝脏中的FoxO 1就足够了， 恢复胰岛素维持葡萄糖稳态和抑制HGP的能力（基于 正常血糖高胰岛素钳夹研究）。这些 结果表明，（a）抑制FoxO 1对直接（肝脏）和间接效应都至关重要 （B）胰岛素的肝外效应足以 维持正常的全身和肝脏葡萄糖代谢时，肝脏FoxO 1活性， 被打乱了基于这些发现，利用转基因和基因敲除小鼠的其他研究 模型，细胞培养和胰岛素钳夹技术计划确定是否ATGL- 依赖性脂解作用在FoxO 1介导肝葡萄糖的作用中也起着关键作用 在肝胰岛素抵抗的背景下，是否靶向ATGL及其代谢， 下游效应物可提供治疗糖尿病的有效策略， 肝脏胰岛素抵抗患者。

Project Summary/Abstract Excessive production of glucose by the liver plays a central role in the development of diabetes, where the ability of insulin to regulate hepatic glucose production (HGP) is impaired. FoxO transcription factors are major targets of insulin and play an important role in mediating effects of insulin on multiple aspects of glucose and lipid metabolism in the liver, including gluconeogenesis, glycolysis and lipogenesis. However, the mechanisms by which FoxO proteins exert these diverse effects in an integrated fashion remain poorly understood. During our previous funding period, we found that a) FoxO proteins also exert important effects on intrahepatic lipolysis and fatty acid oxidation via the regulation of adipose triacylglycerol lipase (ATGL), which mediates the first step in lipolysis, and its inhibitor, the G0/S1 switch 2 gene (G0S2), and b) ATGL-dependent lipolysis plays a critical role in mediating diverse effects of FoxO proteins in the liver, including effects on gluconeogenic, glycolytic and lipogenic gene expression and metabolism. These studies also indicate that ATGL-dependent lipolysis is required to mediate effects of FoxO1 on glycolytic and gluconeogenic gene expression, and additional studies are planned in mouse models and isolated hepatocytes to better understand specific mechanisms mediating this novel link between lipid metabolism and glucoregulation by the insulin/FoxO pathway. In addition, using liver-specific insulin receptor (IR) knockout (LIRKO) and IR/FoxO1 double knockout (LIRFKO) mice, we also found that disrupting FoxO1 in the liver was sufficient to restore the ability of insulin to maintain glucose homeostasis and suppress HGP (based on euglycemic hyperinsulinemic clamp studies) in mice lacking the hepatic insulin receptor. These results indicate that (a) inhibition of FoxO1 is critical for both direct (hepatic) and indirect effects of insulin on HGP and glucose utilization, and (b) extrahepatic effects of insulin are sufficient to maintain normal whole-body and hepatic glucose metabolism when liver FoxO1 activity is disrupted. Based on these findings, additional studies utilizing transgenic and knockout mouse models, cell culture and insulin clamp techniques are planned to determine whether ATGL- dependent lipolysis also plays a critical role in mediating effects of FoxO1 on hepatic glucose metabolism in the setting of hepatic insulin resistance, and whether targeting ATGL and its downstream effectors may provide an effective strategy for treatment of diabetes mellitus in patients with hepatic insulin resistance.