Project description:Age-related hearing impairment (ARHI), one of the most common medical conditions, is strongly heritable, yet its genetic causes remain largely unknown. We conducted a meta-analysis of GWAS summary statistics from multiple hearing-related traits in the UK Biobank (n = up to 323,978) and identified 31 genome-wide significant risk loci for self-reported hearing difficulty (p < 5e-8), of which 30 have not been reported previously at genome-wide significance. We interpreted these loci in the context of newly generated ATAC-seq and single-cell RNA-seq from cells in the mouse cochlea. Risk-associated genes were enriched for expression in cochlear epithelial and non-epithelial cells, as well as for genes related to sensory perception and known Mendelian deafness genes, supporting their relevance to auditory function. Regions of the human genome homologous to open chromatin in sensory epithelial cells from the mouse were strongly enriched for heritable risk for hearing difficulty, even after adjusting for baseline effects of evolutionary conservation and cell-type non-specific regulatory regions. Epigenomic and statistical fine-mapping most strongly supported 50 putative risk genes. Of these, at least 45 were expressed in mouse cochlea and 15 were enriched specifically in sensory hair cells. These results reveal new risk loci and risk genes for hearing difficulty and suggest an important role for altered gene regulation in the cochlear sensory epithelium.
Project description:Purpose and Methods: Cochlear sensory hair cells (HCs) are essential for our sense of hearing. They are embedded in the organ of Corti that lacks regenerative capacity, which is a major cause of hearing loss. However, some neonatal non-sensory cells in the organ of Corti display a limited regenerative ability. We used fluorescence-activated cell sorting (FACS) to isolate different cochlear cell types from postnatal day 2 (P2) mice to assess the individual cell groups’ potential to grow organoids and to generate new HCs. Single-cell RNAseq validated the composition of the cell types in the sorted cell groups. Results and Conclusions: The greater epithelial ridge (GER), a transient tissue that only exists in the neonatal inner ear, harbored the most potent organoid-forming cells. GER-derived organoids expanded into large colonies when cultured adherently and gave rise to new hair cell marker-expressing cells in a sensory epithelia-resembling organization. The organoid forming ability of GER cells was synergistically enhanced when they were cultured at increasing density. The synergistic effect relied on direct cell-to-cell contact rather than released soluble factors.
Project description:In the mammalian auditory system, frequency discrimination depends on numerous morphological and physiological properties of the organ of Corti that gradually change along the longitudinal (tonotopic) axis of the organ. For example, the basilar membrane stiffness changes tonotopically, thus affecting the tuning properties of individual hair cells. At the molecular level, those frequency-specific characteristics are mirrored by gene expression gradients; however, the molecular mechanisms controlling tonotopic gene expression in the mouse cochlea remain elusive. Through analyzing scRNA-seq data from two developmental time points, we predicted that morphogens, rather than a timing-associated mechanism, confer spatial identity in the cochlea. Subsequently, we reconstructed the developing cochlea in 3D space from scRNA-seq data to investigate the molecular pathways mediating tonotopic information. The retinoic acid and sonic hedgehog pathways were found to form opposing tonotopic gradients, and functional interrogation using mouse cochlear explants suggested that both pathways jointly specify the tonotopic axis during development.
Project description:ARHL has been thought to result from disordered hair cell function and their loss. ARHL has a significant genetic component. We sought to determine the expression in the cochlea of genes associated with single nucleotide polymorphisms linked to ARHL. We find widespread and varying expression of genes associated with these SNPs in subtypes of cells in the cochlea identified by single-cell RNA sequencing. Genes associated with SNPs with the highest significance were preferentially expressed highly in hair cells while genes associated with SNPs with a lower significance were expressed more universally.