Discovery and characterization of a novel candidate gene for inherited hearing loss

项目总结/文摘

PROJECT SUMMARY/ABSTRACT The goal of this proposal is to characterize a novel candidate gene for inherited hearing loss using clinical, genomic, and biological tools. The approach combines clinical evaluation of informative families, genome sequencing to identify candidate genes, in vitro analysis of the consequences of candidate mutant alleles on gene and protein function, and in vivo recreation and full evaluation of the phenotype observed in CRISPR-Cas9 mice bearing the human candidate genotype. The identification of new genes for hearing loss will expand diagnostic genetic testing, yield insight into cellular and molecular mechanisms of hearing, and allow for future development of therapies targeting these mechanisms. My proposal describes the application of this approach to a consanguineous family with two children with congenital, bilateral, profound, non-syndromic hearing loss. The children are homozygous for the missense mutation ALDOC p.R149C. ALDOC encodes aldolase C, one of three aldolase isozymes (A, B, and C) that are critical for glycolysis and fructose metabolism. ALDOC is highly expressed in brain and in the sensory epithelium of the inner ear and plays a role in neurodevelopment. Mutations in its paralog, ALDOB, lead to hereditary fructose intolerance where accumulation of the substrate fructose-1-phosphate causes hepatocyte injury and cell death. Here, we propose a similar mechanism within the inner ear for ALDOC-related hearing loss and outline experimental approaches to test this hypothesis. Aim 1. To evaluate the biochemical properties of mutant ALDOC p.R149C, I first purified wild-type and mutated aldolase C from E. coli and demonstrated near complete loss of catalytic activity of the mutant protein. To further quantify this mutation’s effects, I will complete thermostability testing, Michael-Menten enzyme kinetics calculations, and also evaluate its effect on aldolase heteromers by creating and assaying an aldolase A/C hybrid set. Aim 2. To evaluate the phenotypic effects of Aldoc p.R149C, I designed a CRISPR-Cas9 mouse carrying the human mutation. Preliminary results from homozygous mice show a mild hearing loss. Next, I will thoroughly evaluate the hearing of the homozygotes, with and without fructose supplementation, by auditory brainstem response (ABR) testing and analyze cochlear explants by immunohistochemistry and scanning electron microscopy. Aim 3. To determine the cell type(s) involved in ALDOC p.R149C hearing loss, I will utilize single-cell RNA sequencing to identify differences in inner ear cell populations between wild type and Aldoc p.R149C homozygous mice. My project will provide training across auditory neuroscience, biochemistry, and genomics. It will afford ample opportunities for growth in scientific literacy and communication, experimental design and execution, and interdisciplinary collaboration. It is complemented by clinical exposure to otolaryngology and embedded in the UW MSTP, which has 50 years’ experience training physician-scientists. This integrated training plan will provide the experience and mentorship necessary to begin a successful career as a physician scientist.