The pathogenesis of common Gjb2 mutations associated with human hereditary deafness in mice

Abstract

Mutations in GJB2 (Gap junction protein beta 2) are the most common genetic cause of non-syndromic hereditary deafness in humans, especially the 35delG and 235delC mutations. Owing to the homozygous lethality of Gjb2 mutations in mice, there are currently no perfect mouse models carrying Gjb2 mutations derived from patients for mimicking human hereditary deafness and for unveiling the pathogenesis of the disease. Here, we successfully constructed heterozygous Gjb2+/35delG and Gjb2+/235delC mutant mice through advanced androgenic haploid embryonic stem cell (AG-haESC)-mediated semi-cloning technology, and these mice showed normal hearing at postnatal day (P) 28. A homozygous mutant mouse model, Gjb235delG/35delG, was then generated using enhanced tetraploid embryo complementation, demonstrating that GJB2 plays an indispensable role in mouse placenta development. These mice exhibited profound hearing loss similar to human patients at P14, i.e., soon after the onset of hearing. Mechanistic analyses showed that Gjb2 35delG disrupts the function and formation of intercellular gap junction channels of the cochlea rather than affecting the survival and function of hair cells. Collectively, our study provides ideal mouse models for understanding the pathogenic mechanism of DFNB1A-related hereditary deafness and opens up a new avenue for investigating the treatment of this disease.

A murine model for the del(GJB6-D13S1830) deletion recapitulating the phenotype of human DFNB1 hearing impairment: generation and functional and histopathological study

“…In addition to these KOs, a knock-in (KI) model was constructed to investigate the effects of the highly frequent c.35delG truncating GJB2 mutation (Table 2 ). This KI mouse was made viable by performing enhanced tetraploid embryo complementation, a complex process with low success rate (just 1.78% of reconstituted embryos survived into adulthood) [ 28 ]. In contrast, our Dfnb1 em274 model keeps the structure of Gjb2 intact, but abolishes its expression almost completely, leading to a nearly absent Cx26 staining in the organ of Corti, spiral limbus and lateral wall (including stria vascularis) in HOM mice.…”

“…The phenotype of the c.35delG KI is similar to that of the Dfnb1 em274 mouse, with an immature sensory epithelium without tunnel of Corti, surviving IHC, mostly intact OHC and profound hearing loss (slightly lower ABR thresholds at 80 dB SPL) across all frequencies. Intriguingly, cochlear Cx30 expression in the c.35delG KI was reported as downregulated all throughout the cochlea from P14 onward [ 28 ], a co-regulation between Cx26 and Cx30 first described by Ortolano et al [ 33 ]. It is tempting to speculate that the difference in the severity of the hearing loss between c.35delG KI and Dfnb1 em274 models, albeit small (ABR thresholds at 80 dB SPL versus > 90 dB SPL), is due to differences in the cochlear levels of Cx30 (downregulated versus abolished).…”