Sebe Joy Y, Cho Soyoun, Sheets Lavinia, Rutherford Mark A, von Gersdorff Henrique, Raible David W
Departments of Biology and Biological Structure, University of Washington, Seattle, Washington 98195-7420,
Center for Sensory Neuroscience, Boys Town National Research Hospital, Omaha, Nebraska 68131.
J Neurosci. 2017 Jun 21;37(25):6162-6175. doi: 10.1523/JNEUROSCI.3644-16.2017. Epub 2017 May 24.
We report functional and structural evidence for GluA2-lacking Ca-permeable AMPARs (CP-AMPARs) at the mature hair cell ribbon synapse. By using the methodological advantages of three species (of either sex), we demonstrate that CP-AMPARs are present at the hair cell synapse in an evolutionarily conserved manner. Via a combination of electrophysiological and Ca imaging approaches in the larval zebrafish, we show that hair cell stimulation leads to robust Ca influx into afferent terminals. Prolonged application of AMPA caused loss of afferent terminal responsiveness, whereas blocking CP-AMPARs protects terminals from excitotoxic swelling. Immunohistochemical analysis of AMPAR subunits in mature rat cochlea show regions within synapses lacking the GluA2 subunit. Paired recordings from adult bullfrog auditory synapses demonstrate that CP-AMPARs mediate a major component of glutamatergic transmission. Together, our results support the importance of CP-AMPARs in mediating transmission at the hair cell ribbon synapse. Further, excess Ca entry via CP-AMPARs may underlie afferent terminal damage following excitotoxic challenge, suggesting that limiting Ca levels in the afferent terminal may protect against cochlear synaptopathy associated with hearing loss. A single incidence of noise overexposure causes damage at the hair cell synapse that later leads to neurodegeneration and exacerbates age-related hearing loss. A first step toward understanding cochlear neurodegeneration is to identify the cause of initial excitotoxic damage to the postsynaptic neuron. Using a combination of immunohistochemical, electrophysiological, and Ca imaging approaches in evolutionarily divergent species, we demonstrate that Ca-permeable AMPARs (CP-AMPARs) mediate glutamatergic transmission at the adult auditory hair cell synapse. Overexcitation of the terminal causes Ca accumulation and swelling that can be prevented by blocking CP-AMPARs. We demonstrate that CP-AMPARs mediate transmission at this first-order sensory synapse and that limiting Ca accumulation in the terminal may protect against hearing loss.
我们报告了在成熟毛细胞带状突触处存在缺乏GluA2的钙通透性AMPA受体（CP-AMPARs）的功能和结构证据。通过利用三个物种（无论性别）的方法学优势，我们证明CP-AMPARs以进化保守的方式存在于毛细胞突触处。通过结合幼体斑马鱼的电生理和钙成像方法，我们表明毛细胞刺激会导致大量钙流入传入终末。长时间应用AMPA会导致传入终末反应性丧失，而阻断CP-AMPARs可保护终末免受兴奋性毒性肿胀。对成熟大鼠耳蜗中AMPA受体亚基的免疫组织化学分析显示突触内存在缺乏GluA2亚基的区域。对成年牛蛙听觉突触的配对记录表明，CP-AMPARs介导了谷氨酸能传递的主要成分。总之，我们的结果支持CP-AMPARs在介导毛细胞带状突触传递中的重要性。此外，通过CP-AMPARs的过量钙内流可能是兴奋性毒性刺激后传入终末损伤的基础，这表明限制传入终末中的钙水平可能预防与听力损失相关的耳蜗突触病变。单次噪声过度暴露事件会在毛细胞突触处造成损伤，随后导致神经退行性变并加剧与年龄相关的听力损失。理解耳蜗神经退行性变的第一步是确定突触后神经元初始兴奋性毒性损伤的原因。通过在进化上不同的物种中结合使用免疫组织化学、电生理和钙成像方法，我们证明钙通透性AMPA受体（CP-AMPARs）介导成年听觉毛细胞突触处的谷氨酸能传递。终末的过度兴奋会导致钙积累和肿胀，而阻断CP-AMPARs可以预防这种情况。我们证明CP-AMPARs介导了这个一级感觉突触的传递，并且限制终末中的钙积累可能预防听力损失。
