Interaction between sensory and supporting cells in the organ of Corti: basis for sensitivity and frequency selectivity of mammalian cochlea.

我们的主要目标是研究单个细胞和耳蜗Corti器官（OC）复杂感觉上皮细胞的其他元素之间的相互作用，决定了哺乳动物听觉的灵敏度和频率选择性。了解这种相互作用对于未来开发成功的听力损失治疗方法至关重要，特别是那些涉及恢复受损或替换死亡的感觉毛细胞（HC）的治疗方法。当暴露在强烈的声音、耳毒性、疾病、年龄和遗传疾病中时，HC会死亡。据世界卫生组织统计，世界人口的5%患有不可恢复的听力损失。OC中的HC在死亡时不会被替换。随后的听力取决于剩余的，通常是低频的，HC。为什么非哺乳类脊椎动物的HC被取代，而不是哺乳动物耳蜗中的HC，目前还不清楚。我们认为这是一个机制的结果，通过该机制，HC被调谐到声学频率。非哺乳类脊椎动物的HC频率调谐通常是由于固有的电和机械共振，并且每个HC被提供替代HC来源的支持细胞（SC）环包围。哺乳动物耳蜗中的HC依赖于机械调谐的外部来源：基底膜（BM），其构成螺旋形的非细胞带，具有从耳蜗的顶点到基部逐渐增加的刚度，并且紧密地附接到OC。BM振动使HC感觉毛束偏转。对于延伸OC长度的三排感觉-运动外HC（OHC），所产生的受体电位驱动将能量反馈到BM的运动力。这些力将BM振动提升到接近OHC的频率位置，这些振动被传递到感觉内毛细胞（IHC）的行。为了与BM相互作用，每个OHC被限制在一个复杂的、灵活的、充满液体的笼子里，笼子里有专门的、相互连接的、包括柱细胞（PC）和Deiter细胞（DC）的SC。提出了笼以优化OHC与耳蜗分区的其他元件（包括BM）之间的能量交换和控制。已经表明，它们的复杂性使得哺乳动物SC不能作为HC替代的来源。然而，最近，我们已经表明，SC可以在出生后的各个阶段转化为HC，但仍然不成熟，可能是由于缺乏与周围SC的相互作用，这就是为什么理解这种相互作用对于听力恢复至关重要。为此，我们将系统地修饰和删除小鼠OHC、PC、DC和BM中的特定蛋白，并建立年龄相关性和先天性听力损失的小鼠模型。对于在OHC和SC中表达通道视紫红质的小鼠，我们可以用闪光刺激并可逆地改变耳蜗的机械特性。通过建模，基于体内和体外声学，机械和电学测量，我们可以开发和测试OHC及其SC笼之间相互作用的功能意义的理解，从而充分利用现在可用的令人兴奋的再生可能性所需的详细理解。通过缝隙连接相互连接，缝隙连接被认为在耳蜗和/或细胞间信号传导中的流体稳态中起作用。缝隙连接是由特殊的蛋白质（连接蛋白）介导的。大多数遗传性听力障碍，包括年龄相关性听力损失（ARHL）与连接26（Cx 26）和Cx 30的缺陷或缺乏表达有关。连接DC和PC的Cx 26和Cx 30最近被认为与OC内的力传递有关。我们希望发现他们是如何做到这一点的，以及特定的Cx 30突变如何挽救患有严重ARHL的小鼠品系的听力损失。

Our prime objective is to study interaction between individual cells and other elements of the complex sensory epithelium of the organ of Corti (OC) of the cochlea that determines the exquisite sensitivity and frequency selectivity of mammalian audition. Understanding this interaction is essential for future development of successful treatments for hearing loss, especially those involving recovery of damaged, or replacement of dead, sensory hair cells (HCs). HCs die when damaged by exposure to intense sounds, ototoxicity, disease, age, and genetic disorders. According to WHO, 5% of the world population suffer from irrecoverable hearing loss. HCs in the OC are not replaced when they die. Subsequent hearing depends on remaining, usually low frequency, HCs. Why HCs of non-mammalian vertebrates are replaced, but not those in the mammalian cochlea, is not known. We suggest it is a consequence of the mechanism, by which HCs are tuned to acoustic frequencies. HC frequency tuning of non-mammalian vertebrates is due usually to intrinsic electrical and mechanical resonances and each HC is surrounded by a ring of supporting cells (SC)s that provide a source of replacement HCs. HCs in the mammalian cochlea rely on an extrinsic source of mechanical tuning: the basilar membrane (BM), which constitutes a spiralling acellular ribbon with graded stiffness increasing from apex to the base of the cochlea and is intimately attached to the OC. BM vibrations deflect the HC sensory hair bundles. For the three rows of sensory-motor outer HCs (OHCs) extending the length of the OC, the resultant receptor potentials drive motile forces that feedback energy to the BM. The forces boost BM vibrations close to the frequency place of the OHC, which are transmitted to the row of sensory inner hair cells (IHCs). Resultant deflections of IHC hair bundles generate voltages that control transmitter release and flow of afferent signals in the auditory nerve.To interact with the BM, each OHC is restrained in a complex, flexible, fluid filled cage of specialized, interconnected, SCs comprising pillar cells (PCs) and Deiter's cells (DCs). The cage is proposed to optimize exchange and control of energy between OHCs and other elements of the cochlear partition, including the BM. It has been suggested that their complexity renders mammalian SCs unavailable as sources for HC replacement. Recently, however, we have shown that SCs can be converted into HCs at various postnatal stages, but remain immature, possibly due to lack of interaction with surrounding SCs, which is why it is essential to understand this interaction for restoration of hearing. To this end, we will systematically modify and delete specific proteins in OHCs, PCs, DCs and BM in mice and produce mouse models of age-related and congenital hearing loss. With mice that express channel rhodopsins in OHCs and SCs, we can excite and reversibly change the mechanical properties of the cochlea with light flashes. Through modelling, based on in vivo and in vitro acoustical, mechanical, and electrical measurements, our understanding of the functional significance of interaction between OHCs and their SC cages can be developed and tested, leading to the detailed understanding necessary to fully exploit the exciting regenerative possibilities now becoming available.SCs, but not HCs, are interconnected by gap junctions that are thought to play a role in fluid homeostasis in the cochlea and/or intercellular signalling. Gap junctions are mediated by special proteins (connexins). The majority of hereditary hearing disorders, including age-related hearing-loss (ARHL) are associated with defects in, or lack of expression of, connexions 26 (Cx26) and Cx30. Cx26 and Cx30, which interconnect DCs and PCs, have been recently implicated in the transmission of forces within the OC. We wish to discover how they might do this and how a specific Cx30 mutation can rescue hearing loss in a mouse strain with severe ARHL.