Cellular and molecular mechanisms of gp120 neurotoxicity

描述(由申请人提供)： 轴突损伤见于人类免疫缺陷病毒1型(HIV)相关性痴呆(HAD)患者。缺乏HIV直接感染神经元的书面证据，促使研究揭示HIV介导的轴突损伤的可能机制。然而，神经元最初损伤的性质和位置尚不清楚，尤其是这一过程是始于轴突本身还是始于神经元细胞体。多项独立研究表明，病毒包膜蛋白gp120促进神经元退化。Gp120的神经毒性作用是通过趋化因子受体实现的。初步证据表明，趋化因子受体CXCR4促进T嗜性gp120内吞进入神经元。Gp120的内吞作用之后，轴突通过微管运输。与积累gp120的神经元相比，没有内化gp120的神经元的轴突长度和存活率明显更大。此外，即使在细胞因子存在的情况下，阻断轴突运输的药物也对gp120具有神经保护作用，这表明gp120的毒性效应可能不一定需要炎症反应。最重要的是，gp120的内吞和转运先于突触简化和caspase-3激活，从而导致神经细胞死亡，这表明gp120的蓄积和轴突转运是其毒性的关键。这些数据导致了一个新的具有挑战性的假设，即gp120与CXCR4受体结合启动了一系列事件，从而触发了直接的轴突毒性。然而，人们对这种效应的细胞和分子机制知之甚少。内化的gp120可以通过影响轴突蛋白或损害神经元生存和维持所必需的重要分子的轴突运输而导致轴突损伤和神经元凋亡。该项目计划的实验将检查gp120是否影响选定的轴突运输调节蛋白，或微管相关蛋白，如Tau，或其他细胞骨架蛋白，当受损时，促进退行性变的“回死”模式。这些实验将伴随着对内小体或其他细胞器内gp120免疫反应性的组织学分析，以及促炎细胞因子的生化分析。Gp120诱导迅速的轴突/树突状变性的能力提出了一种假设，即即使在没有其他内源性神经毒素或其他病理生理侮辱的情况下，gp120也足以启动不可逆转的神经退化过程。如果得到证实，我们关于gp120通过内化并运输到神经元胞体来损伤神经元的假设将导致这一领域的重大发现。总体而言，我们希望提供新的重要数据，帮助设计针对艾滋病毒引起的突触简化的辅助疗法。

DESCRIPTION (provided by applicant): Axonal injury is seen in subjects with Human Immunodeficiency Virus type 1 (HIV) associated dementia (HAD). The lack of documented evidence of direct infection of neurons by HIV has prompted studies to reveal possible mechanisms for HIV-mediated axonal damage. However, the nature and the site of initial injury to the neuron are unknown; in particular it is unclear if the process starts in the axons itself or in the neuronal cell body. Several lines of independent investigations have shown that the viral envelope protein gp120 promotes neuronal degeneration. The neurotoxic effect of gp120 occurs through chemokine receptors. Preliminary evidence has shown that the chemokine receptor CXCR4 promotes endocytosis of T-tropic gp120 into neurons. Endocytosis of gp120 is followed by axonal transport through microtubules. The length of axons and survival rate of neurons that do not internalize gp120 is significantly greater when compared to those accumulating gp120. Moreover, agents that block axonal transport are neuroprotective against gp120 even in the presence of cytokines, suggesting that the toxic effect of gp120 may not necessarily require an inflammatory response. Most importantly, gp120 endocytosis and transport precede synaptic simplification and caspase-3 activation and therefore neuronal cell death, suggesting that accumulation and axonal transport of gp120 are crucial to its toxicity. These data lead to a new challenging hypothesis that gp120 binding to CXCR4 receptor initiates a series of events that triggers direct axonal toxicity. However, little is known about the cellular and molecular mechanisms of this effect. Internalized gp120 could cause axonal damage and neuronal apoptosis by affecting axonal proteins or impairing the axonal transport of important molecules that are necessary for neuronal survival and maintenance. The experiments planned in this project will examine whether gp120 affects selected regulatory kinases of axonal transport, or microtubule-associated protein such as Tau, or other cytoskeleton proteins that when impaired, promote the "dying-back" pattern of degeneration. These experiments will be accompanied by histological analysis of gp120 immunoreactivity within endosomes or other cellular organelles, as well as by biochemical analyses of pro-inflammatory cytokines. The ability of gp120 to induce a rapid axonal/dendritic degeneration raises the hypothesis that this protein is sufficient to initiate an irreversible neurodegenerative process even in the absence of other endogenous neurotoxins or other patho-physiological insults. If proven, our hypothesis that gp120 injures neurons by being internalized and transported to their cell bodies will lead to a major discovery in this field. Overall, we expect to provide new significant data that help in the design of adjunct therapies against synaptic simplifications caused by HIV.