Protection and restoration of cochlear synapses from noise-induced synaptopathy in male and female mice

大多数螺旋神经节神经元(SGN)在听觉感觉细胞(内毛细胞)上进行传入突触 (IHC)，并将听觉信息传递到大脑。噪声对耳蜗区传入突触的损害 音量太低，不足以摧毁毛细胞。噪声诱导的耳蜗病(NICS)可通过 突触的组织学检查和计数，也是明显的，非侵入性，如听力下降 脑干反应(ABR)波I波幅。虽然突触不会明显地影响听觉 在达到阈值的情况下，它可能会导致听力障碍，如在噪声中的语音表现较差或耳鸣。在 在研究预防NICS的方法过程中，我们观察到雌性小鼠对NICS的易感性明显降低 对于NICS来说，男性的比例更高。值得注意的是，雌性的感受性随发情周期的不同而不同，最低 易感性与孕酮(P4)水平最高的发情期(和雌激素)相关 最低)。体外实验还表明，高水平的P4促进突触的快速再生。 这些显示突触的性别差异的数据首次表明，敏感度通过 对发情周期和P4表现出保护作用。为了跟进，我们的第一个目标是确定一个高 类固醇性激素水平确实会减少NICS。为此，我们将实验性地操纵P4的水平 雄性和雌性小鼠体内的雌激素。我们进一步证明，不仅是P4，而且还有神经营养 CNTF因子和激活环磷酸腺苷(CAMP)信号的物质促进突触再生。后者 包括可以全身给药的化合物，如罗利普兰。P4、CNTF和罗利普兰 是研究体内cAMP在突触再生中作用的优秀试剂，也可能 成为噪声后突触再生治疗的候选疗法。然而，耳蜗性突触可能会丢失 它们在损伤后随着时间的推移而再生的能力和时间过程可能在不同的 促进再生的助剂。我们的第二个目标将确定这些试剂，P4，CNTF， 或cAMP，可能会被实施，但仍能促进再生。与多肽神经营养因子不同的是， 孕酮或cAMP促进突触再生的分子和细胞机制(S) 仍然默默无闻。我们的第三个目标是问这些因子是通过基因组作用还是通过细胞质发挥作用 靶标或质膜受体--未来详细机制研究的必要准备步骤 信号通路和可能涉及的转录组变化。对于坎普来说，问题是坎普是否- 依赖的蛋白激酶进入细胞核或保持细胞质信号，这是我们成功的一个问题 关于生存信号之前已经回答过了。对于黄体酮，我们的初步研究表明 由于不涉及核受体，因此我们的重点将放在质膜孕激素受体上。

Most spiral ganglion neurons (SGNs) make afferent synapses on the auditory sensory cells, the inner hair cells (IHCs), and convey auditory information to the brain. Noise damages cochlear afferent synapses even at sound levels too low to destroy hair cells. Noise-induced cochlear “synaptopathy” (NICS) is detectable by histological examination and counting of synapses and is also evident, noninvasively, as reduced auditory brainstem response (ABR) wave I amplitude. While synaptopathy does not detectably affect auditory thresholds, it may cause hearing impairments such as poorer speech-in-noise performance or tinnitus. In the course of investigating means to prevent NICS, we observed that female mice are significantly less susceptible than are males to NICS. Remarkably, female susceptibility varies with estrous cycle phase, with lowest susceptibility correlated with the estrous phase at which progesterone (P4) levels are highest (and estrogen lowest). In vitro experiments additionally show that a high level of P4 promotes rapid regeneration of synapses. These data showing sex differences in synaptopathy are the first to show that susceptibility varies through the estrous cycle and to show a protective role for P4. To follow up, our first aim is to determine whether a high level of steroid sex hormone does reduce NICS. To that end, we will experimentally manipulate levels of P4 and estrogen in male and female mice. We have further shown that, not only P4 but also the neurotrophic factor CNTF and agents that activate cyclic AMP (cAMP) signaling promote synaptic regeneration. The latter include compounds, such as rolipram, that can be administered systemically. P4, CNTF, and rolipram represent excellent reagents for investigating the role in vivo of cAMP in synapse regeneration and may also be candidate therapeutics for post-noise synapse regeneration therapy. However, cochlear synapses may lose their capacity for regeneration with time after damage and the timecourse may differ among the different agents promoting regeneration. Our second aim will determine how long after noise these agents, P4, CNTF, or cAMP, may be administered and still promote regeneration. Unlike the case for peptide neurotrophic factors, the molecular and cellular mechanism(s) by which progesterone or cAMP promote synapse regeneration remain obscure. Our third aim asks whether these factors function via genomic actions or via cytoplasmic targets or plasma membrane receptors – a necessary preliminary step for future detailed mechanistic studies of signaling pathways and possible transcriptome changes involved. For cAMP, the question is whether cAMP- dependent protein kinase enters the nucleus or remains a cytoplasmic signal, a question we successfully answered previously with respect to survival signaling. For progesterone, our preliminary studies suggest that a nuclear receptor is not involved so our focus will be on plasma membrane progesterone receptors.