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）在内毛细胞上形成传入突触 （IHC），并将听觉信息传递给大脑。噪音损害耳蜗传入突触，即使在 音量太低，无法破坏毛细胞。噪声诱导的耳蜗“突触病”（NICS）可通过 突触的组织学检查和计数，并且也是明显的，非侵入性的，因为听觉的减少， 脑干反应（ABR）I波振幅。虽然突触病不会明显影响听觉 如果听力阈值低于正常阈值，则可能导致听力受损，例如噪声中语音性能较差或耳鸣。在 在研究预防NICS的方法的过程中，我们观察到雌性小鼠的易感性明显降低， 比男性对NICS更敏感值得注意的是，雌性易感性随发情周期阶段而变化， 易感性与孕酮（P4）水平最高（和雌激素）的发情期相关 最低）。体外实验还表明，高水平的P4促进突触的快速再生。 这些显示突触病性别差异的数据首次表明， 动情周期，并显示出保护作用的P4。为了跟进，我们的第一个目标是确定是否有一个高 类固醇性激素水平降低NICS。为此，我们将实验性地操纵P4的水平， 和雌激素。我们进一步表明，不仅P4，而且神经营养因子 CNTF因子和激活环AMP（cAMP）信号传导的试剂促进突触再生。后者 包括可以全身给药的化合物如咯利普兰。P4、CNTF和咯利普兰 代表了研究突触再生中cAMP在体内作用的优良试剂，并且还可以 成为噪音后突触再生疗法的候选疗法。然而，耳蜗突触可能会失去 它们的再生能力随着时间的推移后损坏和时间进程可能会有所不同， 促进再生的药剂。我们的第二个目标是确定这些物质，P4，CNTF， 或cAMP，并且仍然促进再生。与肽类神经营养因子的情况不同， 孕酮或cAMP促进突触再生的分子和细胞机制 保持模糊。我们的第三个目标是询问这些因子是通过基因组作用还是通过细胞质作用发挥作用 靶点或质膜受体-未来详细机制研究的必要初步步骤 信号通路和可能的转录组变化。对于cAMP，问题是cAMP- 依赖性蛋白激酶进入细胞核或保持细胞质信号，一个问题，我们成功地 关于生存信号的回答。对于孕酮，我们的初步研究表明， 核受体不参与，因此我们的重点将放在质膜孕酮受体上。

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.