A novel Variant in GAS2 Is Associated with Non-Syndromic Autosomal Dominant Hearing Impairment in a Chinese Family

Abstract

Abstract Mutation in the GAS2 gene, encoding growth arrest-specific protein 2 (GAS2), causes the disorganization and destabilization of microtubule bundles in supporting cells of the cochlear duct, leading to hearing loss in vivo. The expression and function of GAS2 in cochlear duct is confirmed. However, the molecular mechanism of GAS2 mutant resulting in hearing loss is still unknown. Whole exome sequencing (WES) was employed to identify pathogenic variants. The reverse transcription-PCR was used to show the retention of GAS2 intron 6. The wild-type GAS2 and the truncated GAS2 (mimicking GAS2 variant) were constructed. The protein expression level and cellular localization of GAS2 were checked by Western blots and immunofluorescence staining. The cell apoptosis was assayed by Cell Counting Kit-8 and The DeadEnd™ Fluorometric TUNEL System. We identify a novel heterozygous variant in GAS2 (c.616-2A > G) as the only candidate mutation segregating with late-onset and progressive NSHL in a large dominant family by WES. The mutation causes the retention of intron 6 in mature mRNA and a C-terminally truncated protein (named as GAS2mu) due to an in-frame stop codon (TGA) at c.615 + 109–111 in intron 6. Mechanically, GAS2mu enhances its degradation by ubiquitin-proteasome and displays disorganized microtubule bundles. Additionally, GAS2mu further promotes cell apoptosis by upregulating the ratio of Bcl-xS/Bcl-xL, instead of p53-dependent as wild-type, indicating that GAS2mu acts as a toxic molecule to aggravate cell apoptosis. Our findings demonstrate that the novel variant of GAS2 promotes its protein degradation, microtubule disorganization and cell apoptosis, leading to hearing loss in variant carriers. This study expands the spectrum of GAS2 variants and elucidates the underlying pathogenic mechanisms, which provides a foundation for future investigation of new therapeutic strategies to prevent GAS2-associated progressive hearing loss.