IGF-I PROTECTS NEURONS FROM GLUCOSE INDUCED CELL DEATH

糖尿病神经病变（DN）是周围神经病变的最常见原因。 神经病变在美国，但发病机制仍然未知。 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。 高血糖症被 在动物和人类研究中均涉及DN的发病机制 最近的临床试验表明， 糖尿病肾病患者应严格控制血糖，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DN。 胰岛素样生长因子I（IGF-I）可改善糖尿病患者的血糖控制。 糖尿病，并能够促进神经元的生长，发育， 神经元的再生 在正在进行的初步研究中，我们发现， 高血糖症导致大鼠DRG感觉神经元生长受损， 程序性细胞死亡（PCD）。在这两种范式中，IGF-I都是 神经保护 我们对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）作用 活化导致粘着斑下游磷酸化 参与肌动蛋白细胞骨架和神经突组织的蛋白质 IGF-IR激活磷脂酰肌醇-3激酶 PI-3 K是从PCD中拯救神经元细胞所必需的。 我们有 提出了一种新的假说来解释高血糖 神经毒性 我们推测高糖改变了IGF-IR的激活 背根神经节神经元 这导致了局灶性磷酸化的变化， 导致肌动蛋白细胞骨架破坏的粘附蛋白 并损害DGR神经突生长。 我们认为随后的细胞骨架 单独的变化或与直接葡萄糖毒性结合， DRG神经元中的PCD。 IGF-IR的激活1）通过增强细胞内的IGF-IR的表达来防止PCD。 粘着斑蛋白磷酸化和稳定细胞骨架， 和/或2）通过激活PI 3 K途径阻断PCD，这可能影响PCD 调节蛋白如bcl-2和/或死亡蛋白酶。 本提案中 我们将测试模型的每个组成部分。我们有两个目标：1。 审查 高糖对DRG神经元的影响。 在DRG神经元中， a）DRG神经元形态和神经突生长 B）IGF-IR转录、细胞表面丰度和自磷酸化 c）粘着斑蛋白和DRG细胞骨架的磷酸化 和d）DRG 2中的PCD。表征DRG神经元的IGF-IR保护 葡萄糖暴露后。 在DRG神经元中，对高糖的反应， 检查IGR-I对以下的影响：a）DRG神经元形态和神经突 生长B）IGF-IR转录，细胞表面丰度，和 c）粘着斑蛋白的磷酸化， DRG细胞骨架3. 研究IGF-IR的基础组件 从葡萄糖诱导的PCD中拯救DRG。A.确定关联 在所观察到的粘着斑蛋白的变化之间， 细胞骨架，响应于高葡萄糖的PCD途径B）检查 高糖和IGF-I对PI-3 K IGF-IR活化作用c） 确定IGF-IR激活是否通过促进 抑制细胞死亡的调节蛋白，如bcl-2 d）确定是否 高糖通过激活死亡蛋白酶促进PCD， IGF-IR激活调节这一PCD途径。 IGF-I目前 在糖尿病神经病变的临床试验中进行评价。 的 目前的建议将有助于阐明这一作用的机制， IGF-I在预防神经元形态学和PCD变化中的作用 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.