Auditory Nerve Degeneration and Repair

描述(申请人提供)：螺旋神经节神经元(SGN)变性会导致永久性感音神经性听力损失(SNHL)，并且是不可逆转的。外源性神经干细胞(NSCs)移植为治疗包括SNHL在内的多种神经退行性疾病提供了一种很有前途的治疗策略。然而，对各种神经退行性疾病动物模型的研究表明，神经干细胞损伤后成功移植的时间窗口很窄，神经干细胞的长期存活和功能整合有限，特别是在慢性退化的宿主环境中。尽管假设移植后NSCs的存活和适当分化需要良好的微环境，但宿主微环境究竟如何影响移植后NSCs的行为却鲜有人关注。为了解决这一差距，我们利用哇巴因诱导的急性SGN损伤的动物模型，记录了移植的NSCs在损伤后早期的听神经中的存活率显著高于损伤后的晚期。最近，我们发现急性SGN损伤诱导Sox2的表达上调，Sox2是一种转录因子，在发育和成年神经发生和神经胶质形成过程中在未分化的神经细胞中高表达。这种上调，以及损伤的成年听神经中Sox2神经胶质细胞的增殖，表明成熟的神经胶质细胞可以恢复到分化较差的表型，并重新进入细胞周期，以响应急性SGN损伤。基于这些新的发现，我们假设SGN损伤刺激静止的神经胶质细胞经历表型转化，从而产生更有利于移植的NSCs存活和分化的微环境。本项目的目标是确定 宿主微环境，主要是内源性神经胶质细胞，在调节移植的神经干细胞的存活和分化方面发挥着重要作用。我们将确定急性SGN损伤后神经胶质细胞表型变化的特征(目标1)；确定急性损伤诱导的神经胶质细胞表型变化在体外介导神经干细胞存活和分化的机制(目标2)；以及确定去分化的胶质细胞在体内影响移植的神经干细胞存活、神经元分化和形态整合的能力(目标3)。这些实验将揭示1)与SGN损伤反应中神经胶质细胞表型变化相关的关键分子因素，2)去分化神经胶质细胞促进移植神经干细胞存活的分子机制。这些数据将为神经胶质细胞生物学的基本问题提供答案，并为听觉系统中神经胶质细胞的研究建立体外和体内模型。此外，所获得的信息将对以神经胶质细胞为靶点的SNHL和其他神经退行性疾病的治疗策略的设计具有极大的公共卫生意义。

DESCRIPTION (provided by applicant): Degeneration of spiral ganglion neurons (SGNs) results in permanent sensorineural hearing loss (SNHL) and is irreversible. Transplantation of exogenous neural stem cells (NSCs) offers a promising therapeutic strategy for the treatment of a variety of neural degenerative disorders including SNHL. However, studies of various animal models of neurodegenerative diseases indicate that the time window for the successful transplantation of NSCs after injury is narrow, and that long-term survival and functional integration of NSCs is limited, particularly, in the chronically degenerated host environment. Despite the assumption that a favorable microenvironment is required for the survival and appropriate differentiation of NSCs after transplantation, little attention has been paid to exactl how the host microenvironment affects the behavior of transplanted NSCs. To address this gap, we have documented that survival of transplanted NSCs is significantly greater in the injured auditory nerve at early post-injury intervals compared to later post-injury intervals using a well-characterized animal model of ouabain-induced acute SGN injury. More recently, we have shown that acute SGN injury induces up-regulation of Sox2, a transcription factor that is highly expressed in undifferentiated neural cells during development and adult neurogenesis and gliogenesis. This up-regulation, along with the proliferation of Sox2+ glial cells in the injured adult auditory nerve, suggests that mature glial cells can revert to a less differentiated phenotype and re-enter the cell cycle in response to acute SGN injury. Based on these new findings, we hypothesize that SGN injury stimulates the quiescent glial cells to undergo a phenotypic transformation resulting in a microenvironment more conducive to the survival and differentiation of transplanted NSCs. The objective of this project is to determine the role of the host microenvironment, with a focus on endogenous glial cells, in regulating the survival and differentiation of transplanted NSCs. We will characterize phenotypic changes of glial cells in response to acute SGN injury (Aim 1); determine the mechanisms whereby acute injury-induced glial phenotypic changes mediate NSC survival and differentiation in vitro (Aim 2); and determine the ability of de-differentiated glial cells to influence the survival, neuronal differentiation and morphological integration of transplanted NSCs in vivo (Aim 3). The proposed experiments will reveal 1) the key molecular factors associated with glial cell phenotypic changes in response to SGN injury and 2) the molecular mechanisms promoting the survival of transplanted NSCs by de-differentiated glial cells. Such data will provide answers to basic questions about glial cell biology and establish in vitro and in vivo models for studies of glial cells in the auditory system. In addition, information obtained will be of great public health interest for the design of therapeutic strategies for SNHL and other neurodegenerative disorders using glial cells as targets.