A deafness mechanism of digenic Cx26 (GJB2) and Cx30 (GJB6) mutations: Reduction of endocochlear potential by impairment of heterogeneous gap junctional function in the cochlear lateral wall

Abstract

Digenic Connexin26 (Cx26, GJB2) and Cx30 (GJB6) heterozygous mutations are the second most frequent cause of recessive deafness in humans. However, the underlying deafness mechanism remains unclear. In this study, we created different double Cx26 and Cx30 heterozygous (Cx26+/−/Cx30+/−) mouse models to investigate the underlying pathological changes and deafness mechanism. We found that double Cx26+/−/Cx30+/− heterozygous mice had hearing loss. Endocochlear potential (EP), which is a driving force for hair cells producing auditory receptor current, was reduced. However, unlike Cx26 homozygous knockout (Cx26−/−) mice, the cochlea in Cx26+/−/Cx30+/− mice displayed normal development and had no apparent hair cell degeneration. Gap junctions (GJs) in the cochlea form two independent networks: the epithelial cell GJ network in the organ of Corti and the connective tissue GJ network in the cochlear lateral wall. We further found that double heterozygous deletion of Cx26 and Cx30 in the epithelial cells did not reduce EP and had normal hearing, suggesting that Cx26+/−/Cx30+/− may mainly impair gap junctional functions in the cochlear lateral wall and lead to EP reduction and hearing loss. Most of Cx26 and Cx30 in the cochlear lateral wall co-expressed in the same gap junctional plaques. Moreover, sole Cx26+/− or Cx30+/− heterozygous mice had no hearing loss. These data further suggest that digenic Cx26 and Cx30 mutations may impair heterozygous coupling of Cx26 and Cx30 in the cochlear lateral wall to reduce EP, thereby leading to hearing loss.

Analyses of del(GJB6‐D13S1830) and del(GJB6‐D13S1834) deletions in a large cohort with hearing loss: Caveats to interpretation of molecular test results in multiplex families

“…Homozygous deletion of GJB6 , although rare, was found in one proband and another relative of a proband in our study which results in severe to profound HL, similar to the mouse model (Chen et al, ; Marziano, Casalotti, Portelli, Becker, & Forge, ; Mei et al, ). Unlike in humans, the GJB2/GJB6 double heterozygous mice also show decreased endocochlear potential but have moderate HL (Mei et al, ; Teubner et al, ).…”

Single Cell and Single Nucleus RNA-Seq Reveal Cellular Heterogeneity and Homeostatic Regulatory Networks in Adult Mouse Stria Vascularis

“…The contribution of neurocristopathies to hearing loss is a developing area of research (Hao et al, 2014;Locher et al, 2015;Shibata et al, 2016;Ritter and Martin, 2019). Another example of hearing loss where multiple cell types may be affected includes Connexin 26 and 30 encoded by Gjb2 and Gjb6, respectively, which appear to be expressed in intermediate and basal cells and, to a lesser extent, marginal cells ( Figure 10) (Lang et al, 2007;Nickel and Forge, 2008;Liu et al, 2009;Mei et al, 2017). These data reveal expression of a subset of human deafness genes in SV cell types and define potential opportunities for further investigation into the function of these genes in the SV.…”

Single cell and single nucleus RNA-Seq reveal cellular heterogeneity and homeostatic regulatory networks in adult mouse stria vascularis

“…The contribution of neurocristopathies to hearing loss is a developing area of research (Hao et al, 2014;Locher et al, 2015;Ritter & Martin, 2019;Shibata et al, 2016). Another example of hearing loss where multiple cell types may be affected includes Connexin 26 and 30 encoded by Gjb2 and Gjb6, respectively, which appear to be expressed in intermediate and basal cells and, to a lesser extent, marginal cells ( Figure 10) (W. Liu, Boström, Kinnefors, & Rask-Andersen, 2009;Mei et al, 2017). These data reveal expression of a subset of human deafness genes in SV cell types and define potential opportunities for further investigation into the function of these genes in the SV.…”

“…Mutations in Gjb2 and Gjb6 followed by digenic mutations in these genes are among the most common causes of nonsyndromic autosomal recessive sensorineural hearing loss (SNHL) in many populations across the world (Mei et al, 2017;Nickel & Forge, 2008). Mei and colleagues demonstrate that the loss of Gjb2 and Gjb6 in the stria vascularis and lateral wall result in a loss of EP and hearing loss while the loss of Gjb2 and Gjb6 in cochlear supporting cells does not (Mei et al, 2017). These data identify the loss of these genes in the SV as principal drivers of hearing loss in digenic Gjb2 and Gjb6 mutations.…”