Loss of ARHGEF6 Causes Hair Cell Stereocilia Deficits and Hearing Loss in Mice.

Changsheng Zhu ,Xiaoqian Yan,Qingqing He,Yuan Zhang,Zhengrong Xu,Yanfei Wang,Xia Gao,Cheng Cheng,Waqas Muhammad,Wei Xiong,Shasha Zhang,Zhigang Xu,Chenjie Yu,Buwei Shao,Weijie Zhu,Renjie Chai,Xiaoyun Qian,Shuang Liu,Zhong Zhang,Ling Lü

doi:10.3389/fnmol.2018.00362

Abstract

ARHGEF6 belongs to the family of guanine nucleotide exchange factors (GEFs) for Rho GTPases, and it specifically activates Rho GTPases CDC42 and RAC1. Arhgef6 is the X-linked intellectual disability gene also known as XLID46, and clinical features of patients carrying Arhgef6 mutations include intellectual disability and, in some cases, sensorineural hearing loss. Rho GTPases act as molecular switches in many cellular processes. Their activities are regulated by binding or hydrolysis of GTP, which is facilitated by GEFs and GTPase-activating proteins, respectively. RAC1 and CDC42 have been shown to play important roles in hair cell (HC) stereocilia development. However, the role of ARHGEF6 in inner ear development and hearing function has not yet been investigated. Here, we found that ARHGEF6 is expressed in mouse cochlear HCs, including the HC stereocilia. We established Arhgef6 knockdown mice using the clustered regularly interspaced short palindromic repeat-associated Cas9 nuclease (CRISPR-Cas9) genome editing technique. We showed that ARHGEF6 was indispensable for the maintenance of outer hair cell (OHC) stereocilia, and loss of ARHGEF6 in mice caused HC stereocilia deficits that eventually led to progressive HC loss and hearing loss. However, the loss of ARHGEF6 did not affect the synapse density and did not affect the mechanoelectrical transduction currents in OHCs at postnatal day 3. At the molecular level, the levels of active CDC42 and RAC1 were dramatically decreased in the Arhgef6 knockdown mice, suggesting that ARHGEF6 regulates stereocilia maintenance through RAC1/CDC42.

Highlights

Sensorineural hearing loss (SNHL) is the most prevalent sensory defect and affects millions of individuals all over the world (Smith et al, 2005)
We report that ARHGEF6 is expressed in auditory hair cells (HCs) in the mouse cochlea and that loss of ARHGEF6 causes HC stereocilia deficits and progressive HC loss, which eventually leads to hearing loss
At P7, Arhgef6 isoform1 and Arhgef6 were higher expressed in vestibule and basilar membrane (BM) than in spiral ganglion neurons (SGNs), but the expression of Arhgef6 isoform2 was almost undetectable in vestibule, SGN and BM (Figure 1F)

Summary

Introduction

Sensorineural hearing loss (SNHL) is the most prevalent sensory defect and affects millions of individuals all over the world (Smith et al, 2005). A reciprocal X/21 translocation that breaks the Arhgef transcription at exon 10–11 was shown to be responsible for the severe intellectual disability, mild dysmorphic features, and SNHL in a male patient (Kutsche et al, 2000). The IVS1-11T→C mutation in the first intron of Arhgef was found to cause nonspecific mental retardation IDX46 in a large Dutch family (Yntema et al, 1998). This mutation causes skipping of exon 2 and produces a protein presumably lacking 28 amino acids (Kutsche et al, 2000)

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