Immediate-early intra-axonal signaling in neurodegeneration

 描述(申请人提供)：尽管阿尔茨海默病(AD)的患病率持续上升，但其发病机制仍然难以捉摸。为了延缓或防止疾病的进展，了解AD大脑中发生的最早的致病改变是很重要的。阿尔茨海默病的病理特征包括B-淀粉样斑块的沉积和过度磷酸化的tau缠结，尽管这些标志在疾病发病机制中的病理生理学相关性尚不清楚。淀粉样蛋白假说表明，低聚A？多肽--A？斑块的毒性前体--在观察到的阿尔茨海默病脑内神经退行性改变中发挥了致病作用。对AD小鼠模型大脑的研究表明，轴突暴露于Aü足以引发整个神经元的神经退化，最终导致细胞死亡。轴突内信号事件在AD发病机制中的作用被人类AD脑中的研究进一步支持，该研究表明突触功能障碍先于细胞死亡。在我们最近发表的研究中，我们在体外和体内证明，轴突应用确实通过激活转录因子4(ATF4)的局部合成和逆行运输而诱导神经变性，随后是ATF4依赖的促凋亡基因表达的变化。与这些发现一致的是，与年龄匹配的对照组相比，AD患者死后脑组织中轴突和细胞体中ATF4mRNA和蛋白的表达频率更高。我的论文项目是这项研究的有机扩展，主要集中在对Aü反应发生的最早的轴突内信号事件。我的初步数据显示，轴向应用Aü可诱导快速的钙依赖核糖体激活，抑制轴突蛋白质合成和逆行运输都足以阻断Aü诱导的ATF4向轴突的募集。这些发现让人想起脊髓损伤领域的研究，这些研究表明，轴突切断的外周神经元立即诱导钙内流，随后驻留的mRNAs快速翻译，其蛋白产物在逆行损伤信号转导到细胞核中发挥关键作用。有趣的是，我们先前研究的健康海马轴突的RNA测序实验显示，存在编码许多已知参与坐骨神经逆行损伤信号的蛋白质的mRNAs。因此，我假设，与周围神经系统受损的轴突类似，用Aü刺激的海马轴突会诱导钙依赖的逆行信号复合体的快速局部翻译，该复合体向细胞体通报外周退行性损伤。本应用程序的具体目的是评估Aü诱导的轴突内即刻-早期信号转导的作用：(I)确定控制A？诱导的即刻-早期局部蛋白质合成的机制；(Ii)展示对A？诱导的逆行信号复杂成分的快速局部合成。这些研究将为我们提供对Aü诱导的最早的轴突内致病信号的洞察，这可以提高我们对神经退行性变如何在整个大脑中退行性传播的理解。

 DESCRIPTION (provided by applicant): Though the prevalence Alzheimer's disease (AD) continues to increase, the mechanisms underlying disease pathogenesis remain to be elusive. In order to delay or prevent disease progression, it is important to understand the earliest pathogenic alterations that occur in AD brain. Characteristics of AD pathology include the deposition of ß-amyloid (Aß) plaques and hyperphosphorylated tau tangles, though the pathophysiological relevance of these hallmarks in disease pathogenesis is unclear. The amyloid hypothesis suggests that oligomeric Aß peptides, toxic precursors of Aß plaques, play a causative role in neurodegenerative alterations observed in AD brains. Studies from brains of AD mouse models suggest that axonal exposure to Aß is sufficient to trigger neurodegeneration of the entire neuron, ultimately resulting in cell death. The role of intra- axonal signaling event in AD pathogenesis is further supported by studies in human AD brains showing that synaptic dysfunction precedes cell death. In our recently published study we demonstrate in vitro and in vivo that axonal Aß application does indeed induce neurodegeneration via local synthesis and retrograde transport of activating transcription factor 4 (ATF4), which is followed by ATF4-dependent pro-apoptotic changes in gene expression. Consistent with these findings, post-mortem brain tissues from AD patients exhibited higher frequencies of ATF4 mRNA and protein in axons and cell bodies compared to age-matched controls. My dissertation project is an organic extension of this study, which is primarily focused on the earliest intra-axonal signaling events that occur in response to Aß. My preliminary data shows that axonally applied Aß induces rapid Ca2+-dependent ribosomal activation, and inhibition of axonal protein synthesis and retrograde transport are both sufficient to block Aß-induced recruitment of Atf4 to axons. These findings are reminiscent of studies from the field of spinal cord injury, which show that axotomized peripheral neurons induce an immediate Ca2+ influx followed by rapid translation of resident mRNAs whose protein products play critical roles in retrograde injury signaling to the nucleus. Interestingly, RNA sequencing experiments of healthy hippocampal axons from our previous study reveal the presence of mRNAs encoding many of the proteins known to be involved in sciatic nerve retrograde injury signaling. Therefore, I hypothesize that, similar to injured axons of the peripheral nervous system, hippocampal axons challenged with Aß induce rapid Ca2+-dependent local translation of a retrograde signaling complex that informs cell bodies of a peripheral degenerative insult. The specific aims of this application to assess the role of immediate-early intra-axonal signaling induced by Aß will be: (i) to determine the mechanisms controlling Aß-induced immediate-early local protein synthesis and (ii) to demonstrate the rapid local synthesis of retrograde signaling complex components in response to Aß. These studies will provide insight into the earliest intra-axonal pathogenic signals induce by Aß, which can improve our understanding of how neurodegeneration spreads retrogradely throughout the brain.