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噪声诱导的耳蜗F-肌动蛋白解聚通过ROCK2/p-ERM信号传导介导。

Noise-induced cochlear F-actin depolymerization is mediated via ROCK2/p-ERM signaling.

作者信息

Han Yu, Wang Xianren, Chen Jun, Sha Su-Hua

机构信息

Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, South Carolina, USA.

出版信息

J Neurochem. 2015 Jun;133(5):617-28. doi: 10.1111/jnc.13061. Epub 2015 Mar 2.

Abstract

Our previous work has suggested that traumatic noise activates Rho-GTPase pathways in cochlear outer hair cells (OHCs), resulting in cell death and noise-induced hearing loss (NIHL). In this study, we investigated Rho effectors, Rho-associated kinases (ROCKs), and the targets of ROCKs, the ezrin-radixin-moesin (ERM) proteins, in the regulation of the cochlear actin cytoskeleton using adult CBA/J mice under conditions of noise-induced temporary threshold shift (TTS) and permanent threshold shift (PTS) hearing loss, which result in changes to the F/G-actin ratio. The levels of cochlear ROCK2 and p-ERM decreased 1 h after either TTS- or PTS-noise exposure. In contrast, ROCK2 and p-ERM in OHCs decreased only after PTS-, not after TTS-noise exposure. Treatment with lysophosphatidic acid, an activator of the Rho pathway, resulted in significant reversal of the F/G-actin ratio changes caused by noise exposure and attenuated OHC death and NIHL. Conversely, the down-regulation of ROCK2 by pretreatment with ROCK2 siRNA reduced the expression of ROCK2 and p-ERM in OHCs, exacerbated TTS to PTS, and worsened OHC loss. Additionally, pretreatment with siRNA against radixin, an ERM protein, aggravated TTS to PTS. Our results indicate that a ROCK2-mediated ERM-phosphorylation signaling cascade modulates noise-induced hair cell loss and NIHL by targeting the cytoskeleton. We propose the following cascade following noise trauma leading to alteration of the F-actin arrangement in the outer hair cell cytoskeleton: Noise exposure reduces the levels of GTP-RhoA and subsequently diminishes levels of RhoA effector ROCK2 (Rho-associated kinase 2). Phosphorylation of ezrin-radixin-moesin (ERM) by ROCK2 normally allows ERM to cross-link actin filaments with the plasma membrane. Noise-decreased levels of ROCK results in reduction of phosphorylation of ERM that leads to depolymerization of actin filaments. Lysophosphatidic acid (LPA), an agonist of RhoA, binds to the G-protein-coupled receptor (GPCR) leading to activation of RhoA through Gα12/13 and RhoGEF. Administration of LPA rescues the noise-diminished F/G-actin ratio.

摘要

我们之前的研究表明,创伤性噪声可激活耳蜗外毛细胞(OHC)中的Rho-GTPase信号通路,导致细胞死亡和噪声性听力损失(NIHL)。在本研究中,我们使用成年CBA/J小鼠,在噪声诱导的暂时性阈移(TTS)和永久性阈移(PTS)听力损失条件下,研究了Rho效应器、Rho相关激酶(ROCKs)以及ROCKs的靶标埃兹蛋白-根蛋白-膜突蛋白(ERM)蛋白在耳蜗肌动蛋白细胞骨架调节中的作用,这些条件会导致F/G-肌动蛋白比率发生变化。TTS或PTS噪声暴露1小时后,耳蜗ROCK2和p-ERM水平降低。相比之下,OHC中的ROCK2和p-ERM仅在PTS噪声暴露后降低,而在TTS噪声暴露后未降低。用Rho信号通路激活剂溶血磷脂酸处理,可显著逆转噪声暴露引起的F/G-肌动蛋白比率变化,并减轻OHC死亡和NIHL。相反,用ROCK2 siRNA预处理下调ROCK2,可降低OHC中ROCK2和p-ERM的表达,使TTS加重至PTS,并加剧OHC损失。此外,用针对ERM蛋白根蛋白的siRNA预处理会使TTS加重至PTS。我们的结果表明,ROCK2介导的ERM磷酸化信号级联通过靶向细胞骨架调节噪声诱导的毛细胞损失和NIHL。我们提出了噪声创伤后导致外毛细胞骨架中F-肌动蛋白排列改变的以下信号级联:噪声暴露降低了GTP-RhoA的水平,随后降低了RhoA效应器ROCK2(Rho相关激酶2)的水平。ROCK2对埃兹蛋白-根蛋白-膜突蛋白(ERM)的磷酸化通常允许ERM将肌动蛋白丝与质膜交联。噪声导致的ROCK水平降低导致ERM磷酸化减少,进而导致肌动蛋白丝解聚。溶血磷脂酸(LPA)作为RhoA的激动剂,与G蛋白偶联受体(GPCR)结合,通过Gα12/13和RhoGEF激活RhoA。给予LPA可挽救噪声降低的F/G-肌动蛋白比率。

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