Cell survival and cell death in the auditory nerve

描述(申请人提供)：螺旋神经节神经元(SGN)是将听觉信息从耳蜗内毛细胞(IHC)传递到中枢神经系统的初级传入神经元。虽然已知SGN的退变是由于损伤和年龄的增加而发生的，但对活体内这种病理基础的细胞或分子事件的序列知之甚少。核因子-KB(NFKB)是一种转录因子，在包括神经元在内的多种细胞类型中都能调节细胞的凋亡。NFKB还与细胞内钙调节有关，其功能障碍是神经元兴奋性毒性和细胞凋亡的重要因素。本项目的目的是确定核因子kB在急性损伤后SGN存活中的作用。将野生型和NFKB基因敲除小鼠作为动物模型。这些基因敲除的小鼠表现出随年龄增长的渐进性听力损失，这与SGN的加速退化密切相关。此外，这种基因敲除中SGN放射状树突的病理学表明，在IHC突触的传入树突中存在过度的兴奋毒性。基于这些观察结果，我们推测NFKB在保护SGN急性损伤后免于变性中具有抗凋亡作用，其潜在机制是NFKB活性有助于维持SGN内的钙稳态，从而减少兴奋性毒性效应。这些假说将通过两个具体目标进行检验。第一个目标将确定在体内激活NFKB是否能保护SGN在急性噪声和哇巴因暴露下免于退化。噪声和哇巴因暴露允许对SGN变性背后的兴奋性毒性和细胞凋亡过程进行不同的评估。第二个目标将确定在这些急性损伤后，是否需要NF-KB活性来维持SGN中的钙稳态。这些实验使用了电生理学、组织病理学和免疫荧光技术，以及使用了凝胶迁移率改变分析(EMSA)和实时逆转录聚合酶链式反应(RT-PCR)。这些研究结果将有助于更好地了解SGN变性的细胞和分子机制，并将有助于开发新的方法来预防和治疗人类感音神经性听力损失。

DESCRIPTION (provided by applicant): Spiral ganglion neurons (SGNs) are the primary afferent neurons that carry auditory information from the inner hair cells (IHCs) of the cochlea to the central nervous system. Although degeneration of SGNs is known to occur in response to injury and with age, little is known about the sequence of cellular or molecular events underlying this pathology in vivo. Nuclear factor - KB (NF KB) is a transcription factor that is known to regulate apoptosis in response to insults in many cell types, including neurons. NF KB is also associated with intracellular Ca2+ regulation, the dysfunction of which is an important factor in neuronal excitotoxicity and apoptosis. The goal of this project is to determine the role of NF KB in the survival of SGNs following acute insults. Wild type and NF KB knockout mice will be used as animal models. These knockout mice show a progressive hearing loss with age that is closely correlated with accelerated degeneration of SGNs. Moreover, the pathology of the SGN radial dendrites in this knockout suggests that excessive excitotoxicity is present in the afferent dendrites at IHC synapses. Based on these observations, we hypothesize that NF KB plays an anti-apoptotic role in the protection of SGNs from degeneration after acute injury, and that the underlying mechanism of this protection is that NF KB activity helps maintain Ca2+ homeostasis in SGNs to reduce excitotoxic effects. These hypotheses will be tested with two specific aims. The first aim will determine whether activation of NF KB in vivo protects SGNs from degeneration in response to acute noise and ouabain exposures. The noise and ouabain exposures allow differing assessments of the processes of excitotoxicity and apoptosis underlying SGN degeneration. The second aim will determine whether NF KB activity is required to maintain Ca2+ homeostasis in SGNs after these acute insults. These experiments employ electrophysiological, histopathological and immunofluorescence techniques, along with those using electrophoretic mobility shift assay (EMSA) and real-time reverse transcription polymerase chain reaction (RT-PCR). The results of these studies will lead to a better understanding of the cellular and molecular mechanisms of SGN degeneration and will contribute to the development of novel approaches to the prevention and treatment of sensorineural hearing loss in humans.