Hepatic Insulin Action: Role of the Pentose Cycle

肝胰岛素作用：戊糖循环的作用。胰岛素刺激PI 3-激酶导致磷脂酰肌醇-3，4，5三磷酸（PIP 3）形成增加，其对葡萄糖-6-磷酸酶（G6 β）活性具有直接抑制作用，以及通过Akt活化和GSK-3抑制引发信号传导效应物链的活化，其刺激糖酵解、糖原储存和戊糖磷酸途径（PPP）通量，并抑制糖原异生。 磷酸己糖池和磷酸丙糖池之间底物通量的控制已被认为是胰岛素调节HGP的关键机制。 磷酸己糖库和磷酸丙糖库通过磷酸戊糖途径（PPP）的氧化和非氧化分支处于平衡状态。 我们的13 C质量同位素分布分析（MIDA）通量实验表明，胰岛素对PI 3-K的刺激通过PI 3-K对G6 β的抑制协调糖酵解/促生途径和磷酸戊糖途径（PPP）之间的通量。 胰岛素可以通过PPP的非氧化分支或经由葡萄糖-6-磷酸脱氢酶（G6 PDH）的氧化分支上调通量，提高木酮糖-5-磷酸（X5 P）水平，其可以刺激糖酵解。 G6 PDH也是NADPH的主要来源，NADPH使细胞质保持还原状态。研究表明，当肝细胞质氧化程度更高时，HGP就会增加。 假设：胰岛素刺激的PI 3-K刺激PPP流量，PPP流量的刺激增强胰岛素的作用。假设检验的具体目的：定量PI 3-K及其信号传导效应物/调节物Akt、MMAC（一种磷脂酰肌醇3-磷酸酶）和GSK-3（通过腺病毒介导的过表达）以及选定的PI 3-K信号传导抑制剂对磷酸己糖和磷酸丙糖池之间通量的作用和作用。 在原代大鼠肝细胞培养物中，使用质量同位素异构体分析，使用特定的13 C标记底物来确定进出G-6-P合并液的通量。 这些研究可以确定肝脏胰岛素作用缺陷发生的区域，以及可以指导基于肝脏的基因治疗的区域。

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.