DNAJC14 Ameliorates Inner Ear Degeneration in the DFNB4 Mouse Model

Abstract

The His723Arg (H723R) mutation in SLC26A4, encoding pendrin, is the most prevalent mutation in East Asia, resulting in DFNB4, an autosomal recessive type of genetic hearing loss. Although the main pathological mechanism of H723R was identified as a protein-folding defect in pendrin, there is still no curative treatment for associated hearing loss. Here, we show that H723R-pendrin expression and activity are rescued by activation of the chaperonin DNAJC14. In vitro, DNAJC14 was activated via Japanese encephalitis virus (JEV) inoculation, and toxin-attenuated JEV rescued the surface expression and anion exchange activity of H723R-pendrin. Human H723Rpendrin transgenic mice (hH723R Tg) were established in a mouse slc26a4 knockout background, in which only hH723Rpendrin was expressed in the inner ear (Pax2-Cre dependent) to mimic human DFNB4 pathology. Crossing hH723R Tg with DNAJC14-overexpressing mice resulted in reduced cochlear hydrops and more preserved outer hair cells in the cochlea compared to those in hH723R Tg mice. Furthermore, the stria vascularis and spiral ligament were thicker and KCNJ10 expression was increased with DNAJC14 overexpression; however, hearing function and enlarged endolymphatic hydrops were not recovered. These results indicate that DNAJC14 overexpression ameliorates the cochlear degeneration caused by misfolded pendrin and might be a potential therapeutic target for DFNB4.

Toward the Pathogenicity of the SLC26A4 p.C565Y Variant Using a Genetically Driven Mouse Model

“…Similarly, different SLC26A4 variants are associated with different phenotypic severities in animal models. To date, several mouse models were generated, including knock-out Slc26a4 −/− mice [ 13 ], Slc26a4 loop/loop mice with the p.S408F variant [ 14 ], Slc26a4 919-2A>G9/919-2A>G mice with the c.919-2 A>G variant [ 15 ], Slc26a4 H723R/H723R mice with the p.H723R variant [ 16 ], Slc26a4 L236P/L236P mice with the p.L236P variant [ 17 ], conditional knock-outs Tg[E]; Tg[R]; Slc26a4 Δ/Δ mice [ 18 ], and hH723R Tg mice with the p.H723R mutation in the context of the human pendrin protein [ 19 ] ( Table 1 ). Slc26a4 −/− , Slc26a4 loop/loop , hH723R, and Slc26a4 919-2A>G9/919-2A>G mice exhibited congenital profound SNHI, which represents the most severe symptom in the phenotypic spectrum, whereas Slc26a4 H723R/H723R mice exhibited normal hearing, representing the least severe symptom in the phenotypic spectrum.…”

“…For instance, the amino acid sequence of the pendrin C terminus (i.e., amino acids 508–780) shares only 86% identity between mice and humans ( (accessed on 18 August 2020), which might explain the inconsistent pathogenicity of p.C565Y between mice and humans. To address this, humanized transgenic mice generated with mutant human cDNA sequences could provide a solution, as this approach can better recapitulate clinical phenotypes in humans [ 19 , 39 ]. Third, even for transgenic mice with positive phenotypes, there are still valid discrepancies in the audiovestibular features that are reported between mice and humans.…”

“…In addition to cell-line models, transgenic mice were also demonstrated to be a powerful tool for investigating the pathogenic mechanisms of SLC26A4 variants [ 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. However, previously established mouse models with different SLC26A4 variants were reported to have diverse auditory phenotypes, ranging from normal to profound hearing loss, none of which perfectly recapitulated the clinical phenotypes in patients.…”

Effect of Cochlear Implantation on Hearing Fluctuation in Patients with Biallelic <b><i>SLC26A4</i></b> Variants

“…Moreover, the enlargement of cochlear lumens due to reduced fluid absorption by the endolymphatic sac causes an increase in the diffusional distance of epithelial cells and disrupts cell-to-cell signaling between gap junctions in early postnatal development. Reduced KCNJ10 channel expression (sensitive to reactive oxygen species [ROS], located in the intermediate cell of stria vascularis, and releasing K + into the intrastrial space) compromises DOI: 10.1159/000508858 endocochlear potential stability [Choi et al, 2020]. Normally, ROS is generated when marginal cells secrete K + to endolymphatic space and attenuates KCNJ10 channel expression.…”

Insights into phenotypic differences between humans and mice with p.T721M and other C-terminal variants of the SLC26A4 gene

“…The pathogenesis of SNHI in patients with DFNB4 and PS has been partially elucidated in various mouse models. Several mouse models have been generated, including knock-out Slc26a4 -/- mice 7 , Slc26a4 loop/loop mice with the p.S408F variant 8 , Slc26a4 919-2A > G9/919-2A > G mice with the c.919–2 A > G variant 9 , Slc26a4 H723R/H723R mice with the p.H723R variant 10 , Slc26a4 L236P/L236P mice with the p.L236P variant 11 , Slc26a4 C565Y/C565Y mice with p.C565Y variant 12 , conditional knock-out Tg[E]; Tg[R]; Slc26a4 Δ/Δ mice 13 , and humanized hH723R Tg mice with the p.H723R variant in the human SLC26A4 sequence 14 . None of these models recapitulated SNHI phenotypes in humans.…”