MECHANISMS OF CHROMATIN REMODELING PROMOTING AXON REGENERATION

摘要 缺乏强健的轴突再生是损伤后功能恢复的主要障碍 中枢神经系统(CNS)内的神经元。相比之下，外周神经元在损伤后可以再生。 外周神经元中促再生生长程序的激活依赖于 再生相关基因(RAG)，允许强健的轴突重新生长。尽管有几个基因有 由于其促进再生的影响而被确认，基于个体基因的方法产生的效果有限 轴突再生的成功，表明对单个碎屑的处理不太可能足以 刺激受损中枢神经系统中强健的远距离轴突再生。因此，理解一个多大的 受伤后可以同时激活的碎布集合可能揭示了启动 转录促进再生程序。表观遗传调控，包括染色质的修饰， 影响多个基因的组合，因此是促进神经修复的理想策略。我们的目标 是对调控染色质功能的分子事件获得新的见解 外周神经元，并确定未来治疗中枢神经系统损伤的潜在靶点 我们以前证明了轴突损伤会引起表观遗传开关，刺激再生 感觉神经元的能力。具体地说，我们发现钙波从脑内的 轴突损伤部位增加组蛋白乙酰化水平，刺激感觉再生能力 神经元。这项工作证明了轴突损伤和染色质重塑之间的联系，并表明 协调的促再生计划是由表观遗传格局的变化启动的。在我们最近的 研究发现，低氧诱导因子1α(HIF-1α)是调节轴突的重要因子 通过表观遗传和转录调控机制进行再生。我们发现HIF-1α是 在受损的感觉神经元中需要提高组蛋白乙酰化水平，以刺激前- 再生基因和促进轴突再生。在反复呼吸低氧水平的小鼠中 短期内(即急性间歇性低氧)，我们观察到HIF-1α水平升高并增强 感觉神经元中的轴突再生。然而，常氧条件下的信号通路调节 缺氧诱导因子-1α蓄积及其α调控受损神经元染色质的精确机制 仍然难以捉摸。在这里，我们建议揭示控制HIF-1α稳定性和 目的：研究损伤后神经元的活性，并确定其在受损神经元染色质重塑中的特殊作用。我们会 还要测试AIH是否能至少部分概括外周轴突损伤引起的表观遗传学变化 激活外周和中枢神经元的促再生程序。这项提议有可能 为改进以AIH为基础的人类患者治疗策略提供进一步的理论依据。 。

ABSTRACT Lack of robust axonal regeneration represents a major barrier to functional recovery following injury to neurons within the central nervous system (CNS). In contrast, peripheral neurons can regenerate after injury. Activation of a pro-regenerative growth program in peripheral neurons relies on the expression of regeneration-associated genes (RAGs) that allow for robust axonal re-growth. Although several genes have been identified for their pro-regenerative influence, individual gene based approaches have yielded limited success in axon regeneration, illustrating that manipulation of individual RAGs is unlikely to be sufficient to stimulate robust long-distance axon regeneration in the injured CNS. Therefore, understanding how a large ensemble of RAGs can be simultaneously activated after injury could reveal strategies to initiate the transcriptional pro-regenerative program. Epigenetic regulations, which include modification of the chromatin, affect combinations of multiple genes and hence represent ideal strategies to promote neural repair. Our goal is to gain new insights into the molecular events that regulate chromatin function in response to injury in peripheral neurons, and identify potential targets for future treatment of CNS injuries We previously demonstrated that axon injury elicits an epigenetic switch stimulating the regenerative competence of sensory neurons. Specifically, we discovered that calcium wave back-propagating from the site of axonal injury increases histone acetylation levels, stimulating the regenerative competence of sensory neuron. This work demonstrates a link between axon injury and chromatin remodeling and suggests that a coordinated pro-regenerative program is initiated by changes in the epigenetic landscape. In our recent studies, we identified hypoxia-inducible factor 1α (HIF-1α) as an important factor regulating axon regeneration via epigenetic as well as transcriptional regulatory mechanisms. We found that HIF-1α is required in injured sensory neurons to increase histone acetylation levels, to stimulate the expression of pro- regenerative genes and to promote axon regeneration. In mice breathing repeatedly low oxygen levels for brief periods (i.e., acute intermittent hypoxia, AIH) we observed increased levels of HIF-1α and enhanced axon regeneration in sensory neurons. However, the signaling pathways in normoxic conditions regulating HIF-1α accumulation and the precise mechanisms by which HIF-1α regulates chromatin in injured neurons remain elusive. Here we propose to uncover the molecular mechanisms controlling HIF-1α stability and activity following injury and to establish its specific roles in chromatin remodeling in injured neurons. We will also test if AIH can recapitulate at least in part the epigenetic changes elicited by peripheral axon injury and activate a pro-regenerative program in both peripheral and central neurons. This proposal has the potential to provide further rationale for the improvement of AIH-based treatment strategies for human patients. .