Regulation of the perilymphatic-endolymphatic water shunt in the cochlea by membrane translocation of aquaporin-5
Regulation of the perilymphatic-endolymphatic water shunt in the cochlea by membrane translocation of aquaporin-5
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DOI：
10.1007/s00424-015-1720-6
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发表时间：
2015-12-01
影响因子：
4.5
通讯作者：
Loewenheim, H.
中科院分区：
文献类型：
--
作者：
Eckhard, A.;Dos Santos, A.;Loewenheim, H.
耳蜗内淋巴的容量稳态取决于径向和纵向内淋巴运动（LEM）。体内测量的 LEM 已在生理挑战性条件下被专门识别，例如实验诱导的外淋巴渗透压或内淋巴体积的改变。调节 LEM 以满足内淋巴容量稳态的生理要求的调节机制仍然未知。在这里，我们描述了小鼠耳蜗出生后发育过程中基于水通道蛋白（AQP）的“水分流”的形成及其通过不同触发因素的调节。耳蜗顶端外沟细胞 (OSC) 中 AQP5（顶膜）和 AQP4（基底外侧膜）的最终互补表达模式是在听力功能开始时（出生后 (p)8-p12）获得的。在体外，外淋巴液空间的高渗灌注或在耳蜗外植体中施用毒蕈碱激动剂毛果芸香碱 (p14) 诱导 AQP5 通道蛋白易位到 OSC 的顶膜中。 AQP5 膜易位被毒蕈碱拮抗剂阿托品阻断。通过 mRNA 表达、免疫标记和使用 M3R 特异性荧光配体的体外结合研究，在小鼠 OSC 中鉴定了毒蕈碱 M3 乙酰胆碱 (ACh) 受体 (M3R)。最后，水分流元件 AQP4、AQP5 和 M3R 也在人类耳蜗的 OSC 中得到了证实。耳蜗尖 OSC 中 AQP4/AQP5 水分流的调节为调节内淋巴容量稳态提供了分子基础。此外，其失调或破坏可能对与内淋巴积水相关的临床病症（例如 M,niSre 病）具有病理生理学意义。
Volume homeostasis of the cochlear endolymph depends on radial and longitudinal endolymph movements (LEMs). LEMs measured in vivo have been exclusively recognized under physiologically challenging conditions, such as experimentally induced alterations of perilymph osmolarity or endolymph volume. The regulatory mechanisms that adjust LEMs to the physiological requirements of endolymph volume homeostasis remain unknown. Here, we describe the formation of an aquaporin (AQP)-based "water shunt" during the postnatal development of the mouse cochlea and its regulation by different triggers. The final complementary expression pattern of AQP5 (apical membrane) and AQP4 (basolateral membrane) in outer sulcus cells (OSCs) of the cochlear apex is acquired at the onset of hearing function (postnatal day (p)8-p12). In vitro, hyperosmolar perfusion of the perilymphatic fluid spaces or the administration of the muscarinic agonist pilocarpine in cochlear explants (p14) induced the translocation of AQP5 channel proteins into the apical membranes of OSCs. AQP5 membrane translocation was blocked by the muscarinic antagonist atropine. The muscarinic M3 acetylcholine (ACh) receptor (M3R) was identified in murine OSCs via mRNA expression, immunolabeling, and in vitro binding studies using an M3R-specific fluorescent ligand. Finally, the water shunt elements AQP4, AQP5, and M3R were also demonstrated in OSCs of the human cochlea. The regulation of the AQP4/AQP5 water shunt in OSCs of the cochlear apex provides a molecular basis for regulated endolymphatic volume homeostasis. Moreover, its dysregulation or disruption may have pathophysiologic implications for clinical conditions related to endolymphatic hydrops, such as M,niSre's disease.