MECHANISMS OF CHROMATIN REMODELING PROMOTING AXON REGENERATION

摘要 缺乏强有力的轴突再生代表了损伤后功能恢复的主要障碍， 中枢神经系统（CNS）内的神经元。相反，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），允许强大的轴突再生。虽然有几个基因 由于它们的促再生影响而被鉴定，基于个体基因的方法产生了有限的 轴突再生成功，说明单个RAG的操作不太可能足以 刺激受损中枢神经系统的长距离轴突再生。因此，了解一个大的 RAGs的集合可以在损伤后同时激活，这可能揭示了启动 转录促再生程序。表观遗传调节，包括染色质的修饰， 影响多个基因的组合，因此代表了促进神经修复的理想策略。我们的目标 是获得新的见解的分子事件，调节染色质功能，以响应损伤， 外周神经元，并确定未来治疗CNS损伤的潜在靶点 我们先前证明轴突损伤激活了一个表观遗传开关， 感觉神经元的能力。具体地说，我们发现钙波反向传播从 轴突损伤的部位增加组蛋白乙酰化水平，刺激感觉神经元的再生能力。 neuron.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， 协调的亲再生程序是由表观遗传景观的变化启动的。在我们最近 研究发现，缺氧诱导因子1α（hypoxia-inducible factor 1α，HIF-1α）是一种重要的轴突调节因子， 再生通过表观遗传以及转录调控机制。我们发现HIF-1α是 在受损的感觉神经元中需要增加组蛋白乙酰化水平，刺激前 再生基因和促进轴突再生。在小鼠中反复呼吸低氧水平， 短时间段（即，急性间歇性缺氧（AIH），我们观察到HIF-1α水平升高， 感觉神经元的轴突再生。然而，在常氧条件下， 缺氧诱导因子-1 α在损伤神经元中的积累及其调节染色质的确切机制 仍然难以捉摸在这里，我们提出揭示控制HIF-1α稳定性的分子机制， 活性损伤后，并建立其在受损神经元染色质重塑的具体作用。我们将 还测试AIH是否可以至少部分重现外周轴突损伤引起的表观遗传变化， 激活周围和中枢神经元的促再生程序。该提案有可能 为改善人类患者的基于AIH的治疗策略提供了进一步的理论基础。 .

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. .