Innate Immunity to Spiral Ganglion Neuron Degeneration

项目总结 螺旋神经节神经元是耳蜗区的初级传入神经元，发挥着重要的生理功能。 通过将听觉信息从机械感觉毛细胞传输到大脑并在恢复过程中进行听力 耳聋患者通过人工耳蜗术获得的听力。然而，暴露在创伤性和/或长期噪音中 导致不同类型的SGN及其与毛细胞的突触联系的退化和随后的丢失 程度，导致听觉信息退化，并阻碍人工耳蜗术或 未来的毛细胞或突触再生策略。这种SGN变性的原因尚不清楚。至 提示新疗法的开发为了保存或再生功能性SGN，了解 损伤耳蜗区SGN变性和存活的生物学机制。我们最近确认了 在表达趋化因子CX3CL1配体的SGN和先天的 巨噬细胞和单核细胞(表达同源CX3CR1受体)等免疫细胞是关键 神经保护信号，促进SGN存活和损伤耳蜗突触修复。在这里，我们寻求 研究Fractalkine信号转导神经保护的细胞和分子机制 小鼠耳蜗声损伤分级后的变化。具体来说，AIM 1将确定CX3CR1的确切角色- SGN存活或退变过程中蜗居巨噬细胞和血源性巨噬细胞的表达 噪音创伤。利用命运图区分和选择性耗尽耳蜗居留和招募 巨噬细胞，我们将检验表达CX3CR1的招募巨噬细胞促进SGN存活的假设 在噪音创伤后。目的2将确定CX3CR1是否调节噪声创伤后的巨噬细胞反应 使得CX3CR1缺失导致促炎细胞因子的产生增加且持续 以及对SGN生存不利的反应性氧化因子。效应促炎和抗炎细胞因子， 在完整的耳蜗和巨噬细胞中均可检测到活性氧和氮的存在。 在噪声损伤后，可能存在Fractalkine信号转导和CX3CR1缺失。目标3将考察两者之间的关系 人类CX3CR1基因多态性与噪声性听力损失大约25%-30%的人携带两个单一的 CX3CR1基因座(hCX3CR1-I249/M280)显示结合缺陷的核苷酸多态(SNP) CX3CL1配体与巨噬细胞趋化功能的丧失使用一种新的人性化小鼠模型 表达上述人类CX3CR1 SNPs，我们将检验巨噬细胞调节失调的假设 这些变异体中CX3CR1信号受损导致的反应加速突触和神经元的丢失 噪音创伤后听力恶化。总之，这些研究将从根本上检验新的假说。 认为先天免疫系统、巨噬细胞和分裂因子信号的特定成分是至关重要的 神经保护性免疫治疗的靶点，以促进损伤耳蜗中的突触修复和SGN存活。

PROJECT SUMMARY Spiral ganglion neurons (SGNs), the primary afferent neurons in the cochlea, play vital functions in normal hearing by transmitting auditory information from the mechanosensory hair cells to the brain, and in restoration of hearing via cochlear implants in deaf individuals. However, exposure to traumatic and/or prolonged noise causes degeneration and subsequent loss of SGNs and their synaptic connections with hair cells in varied degrees, leading to degradation of auditory information, and impeding the performance of cochlear implants or future hair cell or synapse regeneration strategies. The reasons for such SGN degeneration remain unclear. To inform the development of novel therapies to preserve or regrow functional SGNs, it is critical to understand the biological mechanisms of SGN degeneration and survival in the injured cochlea. We have recently identified fractalkine signaling (CX3CL1-CX3CR1) between SGNs (which express chemokine CX3CL1 ligand) and innate- immune cells such as macrophages and monocytes (which express cognate CX3CR1 receptor) as a key neuroprotective signaling that promotes SGN survival and synapse repair in the injured cochlea. Here, we seek to examine the cellular and molecular mechanisms by which fractalkine signaling mediates neuroprotection in mouse cochleae following graded noise trauma. Specifically, Aim 1 will determine the precise roles of CX3CR1- expressing cochlear resident and blood-derived recruited macrophages in SGN survival or degeneration after noise trauma. Using fate mapping to distinguish and selectively deplete cochlear resident and recruited macrophages, we will test the hypothesis that CX3CR1-expressing recruited macrophages promote SGN survival after noise trauma. Aim 2 will determine whether CX3CR1 regulates macrophage responses after noise trauma such that absence of CX3CR1 results in an increased and sustained production of pro-inflammatory cytokines and reactive oxidative factors that is detrimental for SGN viability. Effector pro- and anti-inflammatory cytokines, and reactive oxygen and nitrogen species will be detected in both cochleae and macrophages with intact fractalkine signaling and those that lack CX3CR1 after noise trauma. Aim 3 will examine the relationship between human CX3CR1 polymorphisms and noise-induced hearing loss. Approximately 25-30% humans carry two single nucleotide polymorphisms (SNPs) in the CX3CR1 locus (hCX3CR1-I249/M280) that show defective binding to CX3CL1 ligand and loss of chemotactic function in macrophages. Using a novel humanized mouse model expressing the aforementioned human CX3CR1 SNPs, we will test the hypothesis that dysregulated macrophage responses due to impaired CX3CR1 signaling in these variants accelerates synapse and neuron loss and worsens hearing following noise trauma. Together, these studies will test fundamentally new hypotheses proposing specific elements of the innate immune system, macrophages and fractalkine signaling as critical targets for neuroprotective immunotherapies to promote synapse repair and SGN survival in an injured cochlea.