Impaired surface expression and conductance of the KCNQ4 channel lead to sensorineural hearing loss

Abstract

KCNQ4, a voltage-gated potassium channel, plays an important role in maintaining cochlear ion homoeostasis and regulating hair cell membrane potential, both essential for normal auditory function. Mutations in the KCNQ4 gene lead to DFNA2, a subtype of autosomal dominant non-syndromic deafness that is characterized by progressive sensorineural hearing loss across all frequencies. Despite recent advances in the identification of pathogenic KCNQ4 mutations, the molecular aetiology of DFNA2 remains unknown. We report here that decreased cell surface expression and impaired conductance of the KCNQ4 channel are two mechanisms underlying hearing loss in DFNA2. In HEK293T cells, a dramatic decrease in cell surface expression was detected by immunofluorescent microscopy and confirmed by Western blot for the pathogenic KCNQ4 mutants L274H, W276S, L281S, G285C, G285S, G296S and G321S, while their overall cellular levels remained normal. In addition, none of these mutations affected tetrameric assembly of KCNQ4 channels. Consistent with these results, all mutants showed strong dominant-negative effects on the wild-type (WT) channel function. Most importantly, overexpression of HSP90β, a key component of the molecular chaperone network that controls the KCNQ4 biogenesis, significantly increased cell surface expression of the KCNQ4 mutants L281S, G296S and G321S. KCNQ4 surface expression was restored or considerably improved in HEK293T cells mimicking the heterozygous condition of these mutations in DFNA2 patients. Finally, our electrophysiological studies demonstrated that these mutations directly compromise the conductance of the KCNQ4 channel, since no significant change in KCNQ4 current was observed after KCNQ4 surface expression was restored or improved.

Key Genes and Pathways Associated With Inner Ear Malformation in SOX10 p.R109W Mutation Pigs

“…Consequently, the Wnt/β-catenin signaling pathway activity was impaired, leading to compromised cochlear morphogenesis (Figure 11 ). In addition, mutations in KCNQ4 (Gao et al, 2013 ; Wang et al, 2014 ) and STRC (Francey et al, 2012 ) can induce sensorineural deafness, but this has not been found with PAX6.…”

A recurrent mutation in KCNQ4 in Korean families with nonsyndromic hearing loss and rescue of the channel activity by KCNQ activators

“…Mutations in KCNQ genes cause inherited diseases, as follows: (a) Mutations of KCNQ1 cause heart diseases, including long QT syndrome; (b) those of KCNQ2 or KCNQ3 cause benign neonatal seizures; and (c) mutations of KCNQ4 result in ADNSHL (DFNA2) (Brown, ; Maljevic et al., ). DFNA2 is characterized by progressive sensorineural hearing loss at all frequencies (Gao, Yechikov, Vazquez, Chen, & Nie, ; Kubisch et al., ). As the molecular basis of these diseases is reduction of Kv7 potassium channel activity, resulting from mutations, small compounds that activate these channels, so‐called “channel openers,” have been developed as a strategy for treatment of these conditions (Wulff, Castle, & Pardo, ).…”

Whole-exome sequencing identifies two novel mutations in KCNQ4 in individuals with nonsyndromic hearing loss

“…Missense mutations at the K + ion selectivity filter with the GYG signature sequence (p.Gly285Cys, p.Gly285Ser) or pore-helix domain (p.Leu274His, p.Trp276Ser) showed complete loss of ion conduction and decreased surface expression. Thus, these mutants exhibit strong dominant-negative effects to WT protein, and their impaired conductance was not rescued by co-assembly with conducting WT subunits 4 , 5 , 18 , 21 , 31 . In the YUHL35 family, the novel KCNQ4 missense mutation at the K + channel pore forming region (p.Asp266Tyr) produced non-conducting homotetrameric KCNQ4 channels and decreased the sensitivity to KCNQ channel openers, but did not affect membrane trafficking or the formation of heteromultimeric channels with WT subunits.…”

“…KCNQ4 (MIM 600101, Kv7.4) is a voltage-gated potassium channel that plays essential roles in maintaining ion homeostasis and regulating hair cell membrane potential 4 . KCNQ4 mutations cause deafness nonsyndromic autosomal dominant 2 (DFNA2), which is characterized by progressive sensorineural hearing loss at all frequencies 4 , 5 . Kcnq4 −/− mice exhibit degeneration of outer hair cells and progressive hearing loss 6 .…”