IGF-I PROTECTS NEURONS FROM GLUCOSE INDUCED CELL DEATH

糖尿病神经病变是外周血管病变最常见的原因 神经病在美国，但其发病机制仍不清楚。 虽然糖尿病可以影响所有的外周神经元，但感觉神经元 最常见的影响，可能是因为背根神经节(DRG) 神经元位于血-神经屏障之外。高血糖一直是 在动物和人类研究中都与糖尿病肾病的发病机制有关 而最近的临床试验表明，糖尿病的进展有所减缓 糖尿病肾病患者需仔细控制血糖，并加强胰岛素治疗。 然而，即使良好的血糖控制也不能预防或逆转糖尿病肾病。 胰岛素样生长因子I(IGF-I)可改善糖尿病患者的血糖控制 并能够促进神经元的生长、发育和 神经元的再生。在正在进行的初步研究中，我们发现 高血糖导致大鼠背根神经节感觉神经元生长受损 程序性细胞死亡(PCD)。在这两个范例中，IGF-I是 具有神经保护作用。IGF-I神经保护作用的初步研究 揭示1)IGF-I通过I型IGF受体(IGF-IR)发挥作用 激活导致焦点黏附的下游磷酸化 参与肌动蛋白细胞骨架和轴突组织的蛋白质 3)磷脂酰肌醇-3激酶的IGF-IR激活 (PI-3K)对于挽救PCD中的神经细胞是必不可少的。我们有 提出了一种新的假说来解释高血糖偶联 神经毒性。我们推测高糖改变了IGF-IR的激活 在背根节神经元中。这导致了聚焦蛋白磷酸化的变化。 导致肌动蛋白细胞骨架破坏的黏附蛋白 并损害DGR轴突生长。我们相信随后的细胞骨架 单独或与直接的葡萄糖毒性一起引起的变化 背根神经节神经元中的PCD。IGF-IR 1)的激活通过促进 粘着斑蛋白的磷酸化和稳定细胞骨架， 和/或2)通过激活PI 3K通路阻断PCD，这可能影响PCD 调控蛋白如bcl-2和/或死亡蛋白。在本建议书中 我们将测试模型的每个组件。我们有两个目标：1.考试 高糖对背根神经节神经元的影响在DRG神经元中，作为反应 对于高糖，观察：a)背根神经节神经元形态和轴突生长 B)IGF-IR转录、细胞表面丰度和自磷酸化 C)粘着斑蛋白和背根神经节细胞骨架的磷酸化 和d)背根神经节中的PCD 2.表征背根节神经元的IGF-IR保护 在接触了葡萄糖之后。在DRG神经元中，对高糖的反应， 观察IGR-I对：a)背根神经节神经元形态和突起的影响 生长b)IGF-IR转录、细胞表面丰度和 粘着斑蛋白的自动磷酸化c)磷酸化 DRG细胞骨架3.研究IGF-IR的潜在成分 从葡萄糖诱导的PCD中抢救DRG。A)确定关联 在观察到的粘着斑蛋白的变化之间， 细胞骨架，一种PCD反应高糖的途径b)检查 高糖和IGF-I对PI-3K细胞IGF-IR活化的影响 探讨IGF-IR激活是否通过促进细胞外基质的表达来预防PCD 抑制细胞死亡的调节蛋白，如bcl2d)决定了 高糖通过激活死亡蛋白水解酶促进PCD及其作用 IGF-IR激活在调节这一PCD途径中的作用。IGF-I目前 在糖尿病神经病变的临床试验中进行评估。这个 目前的提案将有助于阐明这一角色的潜在机制 胰岛素样生长因子-I预防脑缺血后神经元形态改变及PCD的作用 糖尿病神经病变。

Diabetic neuropathy (DN) is the most common cause of peripheral neuropathy in the United States, yet the pathogenesis remains unknown. Although diabetes can affect all peripheral neurons, sensory neurons are most commonly affected, possibly because dorsal root ganglion (DRG) neurons reside outside the blood-nerve barrier. Hyperglycemia has been implicated in both animal and human studies in the pathogenesis of DN and recent clinical trials have shown a reduction in the progression of DN with careful control of blood glucose an intensive insulin therapy. However even excellent glycemic control fails to prevent or reverse DN. Insulin-alike growth factor I (IGF-I) can improve glycemic control in diabetes and is able to promote neuronal growth, development, and regeneration of neurons. In ongoing preliminary studies, we find that hyperglycemia leads to impaired rat DRG sensory neuronal growth and programmed cell death (PCD). In both paradigms, IGF-I is neuroprotective. Our initial investigations of IGF-I neuroprotection reveal that 1) IGF-I acts trough the type I IGF receptor (IGF-IR activation results in downstream phosphorylation of focal adhesion proteins involved in organization of the actin cytoskeleton and neurite formative, and 3) IGF-IR activation of phosphatidylinositol-3 kinase (PI-3K) is essential for rescue of neuronal cells from PCD. We have developed a novel hypothesis to explain hyperglycemic coupled neurotoxicity. We speculate that high glucose alters IGF-IR activation in DRG neurons. This result in changes in the phosphorylation of focal adhesion proteins which results in disruption of the actin cytoskeleton and impairs DGR neurite growth. We believe subsequent cytoskeletal changes alone, or in conjunction with direct glucose toxicity, induce PCD in DRG neurons. Activation of IGF-IR 1) prevents PCD by enhancing focal adhesion protein phosphorylation and stabilizing the cytoskeleton, and/or 2) blocks PCD by activating PI 3K pathways, which may effect PCD regulatory proteins like bcl-2 and/or death proteases. In this proposal we will test each component of the model. We have 2 aims: 1. Examine the effect of high glucose on DRG neurons. In DRG neurons, in response to high glucose, examine: a) DRG neuronal morphology and neurite growth b) IGF-IR transcription, cell surface abundance, and autophosphorylation c) Phosphorylation of focal adhesion proteins and the DRG cytoskeleton and d) PCD in DRG 2. Characterize IGF-IR protection of DRG neurons following glucose exposure. In DRG neuron, in response to high glucose, examine the effect of IGR-I on: a) DRG neuronal morphology and neurite growth b) IGF-IR transcription, cell surface abundance, and autophosphorylation c) Phosphorylation of focal adhesion proteins and the DRG cytoskeleton 3. Investigate the components underlying IGF-IR rescue of DRG from glucose-induced PCD. a) Determine the association between the observed changes in focal adhesion proteins, the cytoskeleton, an PCD pathways in response to high glucose b) Examine the effect of high glucose and IGF-I on IGF-IR activation of PI-3K c) Ascertain if IGF-IR activation prevents PCD by promoting expression of regulatory proteins that suppress cell death, like bcl-2 d) Determine if high glucose promotes PCD by activation of death proteases, and the role of IGF-IR activation in modulating this PCD pathway. IGF-I is currently undergoing evaluation in clinical trails of diabetic neuropathy. The current proposal will help elucidate the mechanisms underlying the role of IGF-I in preventing changes in neuronal morphology and PCD in diabetic neuropathy.