Shinkawa Chikako, Ito Tsukasa, Hozumi Yasukazu, Chiba Makoto, Matsui Hirooki, Goto Kaoru, Kakehata Seiji
Department of Otolaryngology, Head and Neck Surgery, Yamagata University Faculty of Medicine, 2-2-2 Iida-Nishi, Yamagata-shi, Yamagata, 990-9585, Japan.
Department of Cell Biology and Morphology, Akita University Graduate School of Medicine, Akita, 010-8543, Japan.
Histochem Cell Biol. 2019 Jun;151(6):461-474. doi: 10.1007/s00418-019-01781-9. Epub 2019 Apr 8.
Cochlear hair cells are essential for the mechanotransduction of hearing. Sensorineural hearing loss can be irreversible because hair cells have a minimal ability to repair or regenerate themselves once damaged. In order to develop therapeutic interventions to prevent hair cell loss, it is necessary to understand the signaling pathway operating in cochlear hair cells and its alteration upon damage. Diacylglycerol kinase (DGK) regulates intracellular signal transduction through phosphorylation of lipidic second messenger diacylglycerol. We have previously reported characteristic expression and localization patterns of DGKs in various organs under pathophysiological conditions. Nevertheless, little is known about morphological and functional aspects of this enzyme family in the cochlea. First RT-PCR analysis reveals predominant mRNA expression of DGKα, DGKε and DGKζ. Immunohistochemical analysis shows that DGKζ localizes to the nuclei of inner hair cells (IHCs), outer hair cells (OHCs), supporting cells and spiral ganglion neurons in guinea pig cochlea under normal conditions. It is well known that loud noise exposure induces cochlear damage, thereby resulting in hair cell loss. In particular, OHCs are highly vulnerable to noise exposure than IHCs. We found that after 1 week of noise exposure DGKζ translocates from the nucleus to the cytoplasm in damage-sensitive OHCs and gradually disappears thereafter. In sharp contrast, DGKζ remains to the nucleus in damage-resistant IHCs. These results suggest that DGKζ cytoplasmic translocation is well correlated with cellular damage under noise-exposure stress conditions and is involved in delayed cell death in cochlear outer hair cells.
耳蜗毛细胞对于听力的机械转导至关重要。感音神经性听力损失可能是不可逆的，因为毛细胞一旦受损，其自我修复或再生的能力极小。为了开发预防毛细胞损失的治疗干预措施，有必要了解耳蜗毛细胞中运行的信号通路及其在损伤时的改变。二酰基甘油激酶（DGK）通过脂质第二信使二酰基甘油的磷酸化来调节细胞内信号转导。我们之前已经报道了病理生理条件下DGK在各个器官中的特征性表达和定位模式。然而，关于该酶家族在耳蜗中的形态和功能方面知之甚少。首次逆转录聚合酶链反应（RT-PCR）分析显示DGKα、DGKε和DGKζ的mRNA表达占主导。免疫组织化学分析表明，在正常条件下，DGKζ定位于豚鼠耳蜗内毛细胞（IHC）、外毛细胞（OHC）、支持细胞和螺旋神经节神经元的细胞核中。众所周知，强噪声暴露会导致耳蜗损伤，从而导致毛细胞损失。特别是，OHC比IHC更容易受到噪声暴露的影响。我们发现，噪声暴露1周后，DGKζ在对损伤敏感的OHC中从细胞核转移到细胞质，此后逐渐消失。与之形成鲜明对比的是，DGKζ在抗损伤的IHC中仍留在细胞核中。这些结果表明，在噪声暴露应激条件下，DGKζ的细胞质转位与细胞损伤密切相关，并参与耳蜗外毛细胞的延迟性细胞死亡。
