Miyoshi Takushi, Yamaguchi Taro, Ogita Kiyokazu, Tanaka Yasuko, Ishibashi Ken-Ichi, Ito Hiroaki, Kobayashi Taisuke, Nakagawa Takayuki, Ito Juichi, Omori Koichi, Yamamoto Norio
Department of Otolaryngology, Head and Neck Surgery, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Kyoto, Japan.
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, Neyagawa, 572-0074, Osaka, Japan.
J Assoc Res Otolaryngol. 2017 Apr;18(2):247-261. doi: 10.1007/s10162-016-0607-3. Epub 2016 Dec 21.
Aquaporins (AQPs) are a family of small membrane proteins that transport water molecules across the plasma membrane along the osmotic gradient. Mammals express 13 subtypes of AQPs, including the recently reported "subcellular AQPs", AQP11 and 12. Each organ expresses specific subsets of AQP subtypes, and in the inner ear, AQPs are essential for the establishment and maintenance of two distinct fluids, endolymph and perilymph. To evaluate the contribution of AQPs during the establishment of inner ear function, we used quantitative reverse transcription polymerase chain reaction to quantify the expression levels of all known AQPs during the entire development and maturation of the inner ear. Using systematic and longitudinal quantification, we found that AQP11 was majorly and constantly expressed in the inner ear, and that the expression levels of several AQPs follow characteristic longitudinal patterns: increasing (Aqp0, 1, and 9), decreasing (Aqp6, 8, and 12), and peak of expression on E18 (Aqp2, 5, and 7). In particular, the expression level of Aqp9 increased by 70-fold during P3-P21. We also performed in situ hybridization of Aqp11, and determined the unique localization of Aqp11 in the outer hair cells. Immunohistochemistry of AQP9 revealed its localization in the supporting cells inside the organ of Corti, and in the root cells. The emergence of AQP9 expression in these cells was during P3-P21, which was coincident with the marked increase of its expression level. Combining these quantification and localization data, we discuss the possible contributions of these AQPs to inner ear function.
水通道蛋白（AQPs）是一类小的膜蛋白家族，可沿渗透梯度将水分子转运过质膜。哺乳动物表达13种AQP亚型，包括最近报道的“亚细胞AQPs”，即AQP11和AQP12。每个器官表达特定的AQP亚型子集，在内耳中，AQPs对于两种不同液体——内淋巴和外淋巴的建立和维持至关重要。为了评估AQPs在内耳功能建立过程中的作用，我们使用定量逆转录聚合酶链反应来量化内耳整个发育和成熟过程中所有已知AQPs的表达水平。通过系统的纵向定量分析，我们发现AQP11在内耳中主要且持续表达，并且几种AQPs的表达水平呈现出特征性的纵向模式：增加（Aqp0、1和9）、减少（Aqp6、8和12）以及在E18时表达峰值（Aqp2、5和7）。特别是，Aqp9在P3 - P21期间表达水平增加了70倍。我们还进行了Aqp11的原位杂交，并确定了Aqp11在外毛细胞中的独特定位。AQP9的免疫组织化学显示其定位于柯蒂氏器内的支持细胞以及根细胞中。这些细胞中AQP9表达的出现是在P3 - P21期间，这与其表达水平的显著增加相一致。结合这些定量和定位数据，我们讨论了这些AQPs对内耳功能的可能贡献。
