Hepatic Insulin Action: Role of the Pentose Cycle

肝脏胰岛素作用：戊糖循环的作用。胰岛素对PI3-Kinase的刺激导致磷脂酰肌醇-3，4，5-三磷酸(PIP3)生成增加，对葡萄糖-6-磷酸酶(G6Pase)活性有直接抑制作用，并通过Akt激活和GSK-3抑制启动信号效应链的激活，刺激糖酵解、糖原储存和戊糖磷酸途径(PPP)通量，并抑制糖异生。控制六糖磷酸和三糖磷酸之间的底物流量被认为是胰岛素调节HGP的关键机制。己糖和磷酸三糖通过磷酸戊糖途径(PPP)的氧化和非氧化分支处于平衡状态。我们的13C质量同位素分布分析(MIDA)通量实验表明，胰岛素对PI3-K的刺激通过PI3-K抑制G6Pase来协调糖酵解/糖异生途径和磷酸戊糖途径(PPP)之间的通量。胰岛素可以通过PPP的非氧化肢体或通过葡萄糖-6-磷酸脱氢酶(G6PDH)的氧化肢体上调通量，提高木糖-5-磷酸(X5P)的水平，从而刺激糖酵解。G6PDH也是NADPH的主要来源，NADPH使细胞质处于还原状态。研究表明，当肝脏细胞质被更多地氧化时，HGP就会增加。假设：胰岛素刺激的PI3-K刺激PPP通量，刺激PPP通量增强胰岛素的作用。假设检验的具体目的：量化PI3-K及其信号效应/调节剂Akt、MMAC、磷脂酰肌醇3-磷酸酶和GSK-3通过腺病毒介导的过度表达和选定的PI3-K信号抑制剂的作用和对己糖磷酸和三糖磷酸盐池之间的通量的作用。特定的13C标记底物将用于在原代大鼠肝细胞培养中使用质量同位素分析来确定进出G-6-P池的通量。这些研究可能确定肝脏胰岛素作用发生缺陷的领域，以及基于肝脏的基因治疗可以指导的领域。

Hepatic insulin action: Role of the pentose cycle. Insulin stimulation of PI3-Kinase results in an increase in phosphatidylinositol-3,4,5 tri-phosphate (PIP3) formation, which has direct inhibitory effects on glucose-6-phosphatase (G6Pase) activity, as well as initiating the activation of a signaling effector chain, via Akt activation and GSK-3 inhibition, that stimulates glycolysis, glycogen storage, and pentose phosphate pathway (PPP) flux, and inhibits gluconeogenesis. The control of substrate flux between the hexose phosphate pool and the triose phosphate pool has been recognized as the key mechanism for insulin's regulation of HGP. The hexose phosphate pool and the triose phosphate pool are in equilibrium through the oxidative and non-oxidative branches of the pentose phosphate pathway (PPP). Our 13C mass isotopomer distribution analysis (MIDA) flux experiments indicate that insulin's stimulation of PI3-K coordinates flux between the glycolytic/gluconeogenic pathways and the pentose phosphate pathway (PPP) via PI3-K's inhibition of G6Pase. Insulin can upregulate flux through the non-oxidative limb of the PPP, or the oxidative limb via glucose-6-phosphate dehydrogenase (G6PDH), raising xylulose-5-phosphate (X5P) levels, which can stimulate glycolysis. G6PDH is also the principal source of NADPH, which keeps the cytoplasm in a reduced state. Studies suggest that when the liver cytoplasm is more oxidized, HGP is increased. Hypothesis: Insulin-stimulated PI3-K stimulates PPP flux, and the stimulation of PPP flux enhances the function of insulin action. Specific aims for hypothesis testing: To quantitate the roles, and actions on the flux between the hexose phosphate and the triose phosphate pools, of PI3-K and its signaling effectors/modulators Akt, MMAC, a phosphatidylinositol 3- phosphatase, and GSK-3, via adenoviral mediated overexpression, and selected inhibitors of PI3-K signaling. Specific 13C labeled substrates will be used to determine flux passing to and from the G-6-P pool using mass isotopomer analysis in primary rat hepatocyte culture. These studies may identify areas where defects in hepatic insulin action occur, and where hepatic-based gene therapies can be directed.