Oya Ryohei, Woo Kwang Min, Fabella Brian, Alonso R G, Bravo Paloma, Hudspeth A J
Howard Hughes Medical Institute, The Rockefeller University, New York, NY, 10065, USA.
Laboratory of Sensory Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA.
J Assoc Res Otolaryngol. 2025 Apr 16. doi: 10.1007/s10162-025-00986-1.
In the receptor organs of the inner ear, hair cells detect mechanical stimuli such as sounds and accelerations by deflection of their hair bundles. Myosin regulatory light chain (RLC) and non-muscle myosin II (NM2) are expressed at the apical surfaces of hair cells, and NM2 and the phosphorylation of RLC by myosin light chain kinase (MLCK) have earlier been shown to regulate the shapes of hair cells' apical surfaces in rodents. The aim of our study was to elucidate the function of myosin molecules on hair cell physiology.
We investigated the expression of NM2 and RLC in the bullfrog's saccule by immunostaining. Using NM2 and MLCK inhibitors, we measured the stiffness, spontaneous oscillation, and resting open probability of frog hair bundles. Six to ten saccules from pleural animals were used in each experiment. In addition, we recorded auditory brainstem responses in ten mice after transtympanic injection of an MLCK inhibitor.
We confirmed the expression of NM2A/B and MYL9 on the apical surfaces of hair cells and of NM2A and MYL12A in hair bundles. We found that NM2 and MLCK inhibitors reduce the stiffness of hair bundles from the bullfrog's saccule. Moreover, MLCK inhibition inhibits the spontaneous oscillation of hair bundles and increases the resting open probability of transduction channels. In addition, MLCK inhibition elevates hearing thresholds in mice.
We conclude that NM2 and the phosphorylation of RLC modulate the physiological function of hair cells and thereby help to set the normal operating conditions of hair bundles.
在内耳的感受器器官中，毛细胞通过其毛束的偏转来检测声音和加速度等机械刺激。肌球蛋白调节轻链（RLC）和非肌肉型肌球蛋白II（NM2）在毛细胞的顶端表面表达，并且之前已表明在啮齿动物中，NM2以及肌球蛋白轻链激酶（MLCK）对RLC的磷酸化作用可调节毛细胞顶端表面的形状。我们研究的目的是阐明肌球蛋白分子对毛细胞生理功能的作用。
我们通过免疫染色研究了牛蛙球囊斑中NM2和RLC的表达。使用NM2和MLCK抑制剂，我们测量了蛙毛束的硬度、自发振荡以及静息开放概率。每个实验使用来自6至10只动物的球囊斑。此外，我们在经鼓膜注射MLCK抑制剂后记录了10只小鼠的听觉脑干反应。
我们证实了NM2A/B和MYL9在毛细胞顶端表面以及NM2A和MYL12A在毛束中的表达。我们发现NM2和MLCK抑制剂降低了牛蛙球囊斑毛束的硬度。此外，MLCK抑制可抑制毛束的自发振荡并增加转导通道的静息开放概率。另外，MLCK抑制会提高小鼠的听力阈值。
我们得出结论，NM2和RLC的磷酸化调节毛细胞的生理功能，从而有助于设定毛束的正常工作条件。
