Molecular Dissection of the Axonal Injury Response for Regeneration and Neuroprotection

神经元之间的轴突连接对于它们的正常功能是必不可少的。中断这些连接 从脊髓损伤到青光眼到化疗引起的神经病变等侮辱都是经常发生的 让人虚弱。虽然轴突再生的内在能力为三叉神经节的恢复提供了希望，但它在 中枢神经系统与损伤引起的神经变性一起，经常导致永久性的缺陷。我们实验室的目标是 了解神经元对轴突损伤的反应，目的是调节这种反应以改善轴突 再生和神经元存活。在目前的提案中，我们利用了我们最近发现的一种 意想不到的轴突损伤反应的第二分支，这一途径也与正常记忆有关 形成和神经退行性疾病。了解这一途径的影响，称为 综合应激反应(ISR)对三叉神经节和中枢神经系统轴突损伤易处理模型修复和存活的影响 可能会促进目前正在探索的针对各种情况的基于ISR的疗法。此前，我们和其他人 已经证明轴突再生和神经退行性变都依赖于 轴突损伤反应称为双亮氨酸拉链酶(DLK)。损伤诱导的DLK激活导致 一种多方面的转录反应，主要通过启动众所周知的MAPK(MAPK) 信号级联。出乎意料的是，我们最近发现DLK也是参与的必要条件和充分条件 ISR。DLK反应的MAPK和ISR分支如何相互作用来定义不同的细胞凋亡 中枢神经和三叉神经节受损神经元的再生命运？我们为解决这个问题所作的持续努力 已经聚集在ISR的一个主要下游效应因子--激活转录因子4上 (ATF4)，作为一种潜在的再生和凋亡调节因子。我们的初步证据表明 ATF4可能对CNS和PNS的再生潜能有不同程度的影响。与此同时，我们发现 抑制ISR减少了中枢神经系统模型中的神经变性，尽管目前尚不清楚这是否会导致 从减少的ATF4或从ISR的其他方面。了解ATF4在ISR和ISR中的角色 对于更广泛的DLK反应，我们建议将体外方法与体内CNS和PNS损伤模型相结合。 首先，为了了解ISR抑制对神经保护的作用，我们将确定ATF4对基因的特定贡献 体内中枢神经系统的表达变化和神经元丢失。其次，我们将测试ISR和ISR在体内的作用 ATF4在周围神经损伤和视神经损伤后轴突再生中的作用 与部分克服中枢神经系统再生故障的手法相结合。第三，发现 ATF4调节轴突再生的机制，我们将测试ATF4与其 在我们建立的体外模型中，假定的结合伙伴、上游介体和下游靶标。这些 研究将揭示DLK反应的ISR-ATF4轴在决定轴突再生和 神经退行性变，告知这些靶点在轴突病变和其他情况下的治疗潜力。

The axonal connections between neurons are essential for their proper function. Disruption of these connections in insults ranging from spinal cord injury to glaucoma to chemotherapy-induced neuropathy are frequently debilitating. Whereas intrinsic capacity for axon regeneration offers hope for recovery in the PNS, its failure in the CNS, along with injury-induced neurodegeneration, frequently results in permanent deficits. Our lab aims to understand how neurons respond to axon injuries, with the goal of modulating this response for improved axon regeneration and neuronal survival. In the current proposal, we capitalize on our recent discovery of an unexpected second branch of the axonal injury response, a pathway that is also implicated in normal memory formation and in neurodegenerative diseases. Understanding the impact of this pathway, known as the Integrated Stress Response (ISR), on repair and survival in the tractable models of PNS and CNS axonal injury may facilitate ISR-based therapies currently being explored for a variety of conditions. Previously, we and others have demonstrated that both axon regeneration and neurodegeneration depend on a master regulator of the axonal injury response known as the Dual Leucine-zipper Kinase (DLK). Injury-induced DLK activation leads to a multifaceted transcriptional response, primarily through the initiation of a well-known MAP kinase (MAPK) signaling cascade. Unexpectedly, we recently discovered that DLK is also necessary and sufficient to engage the ISR. How do the MAPK and ISR branches of the DLK response interact to define the differential apoptotic and regenerative fates of injured neurons in the CNS and PNS? Our ongoing efforts to address this question have converged on one of the principal downstream effectors of the ISR, the Activating Transcription Factor 4 (ATF4), as a potential regulator of both regeneration and apoptosis. Our preliminary evidence suggests that ATF4 may differentially impact regenerative potential in the CNS and PNS. In parallel, we have found that inhibition of the ISR reduces neurodegeneration in a CNS model, though it is not yet known whether this results from reduced ATF4 or from other aspects of the ISR. To understand the role of ATF4 within the ISR and within the broader DLK response, we propose to combine in vitro approaches with in vivo CNS and PNS injury models. First, to understand neuroprotection by ISR inhibition, we will determine the specific contribution of ATF4 to gene expression changes and neuronal loss in the CNS in vivo. Secondly, we will test the in vivo roles of the ISR and ATF4 in axon regeneration following peripheral nerve injury and following optic nerve injury, the latter in combination with manipulations that partially overcome CNS regenerative failure. Thirdly, to discover mechanisms by which ATF4 regulates axon regeneration, we will test the genetic interactions of ATF4 with its putative binding partners, upstream mediators, and downstream targets in our established in vitro model. These studies will expose the roles of the ISR-ATF4 axis of the DLK response in determining axon regeneration and neurodegeneration, informing the therapeutic potential of these targets in axonopathies and other conditions.