Hereditary hearing loss is prevalent in every population and poses significant challenges to the lives of the hearing impaired. Eighty-six distinct genetic loci (DFNB) have now been linked to recessively inherited hearing loss segregating in large families, and the mutated genes for 38 of these loci have been identified. However, understanding of the function of the genes and how they account for a hearing loss phenotype is incomplete. In vivo studies of gene function are an important step in filling this knowledge gap, and the mouse serves as an ideal mammalian model for understanding the functions of genes that are important for hearing in humans. Our long-term goal is to understand how tight junctions, including tight junction (TJ) proteins, are involved in organogenesis and function of the ear. More specifically, we wish to understand the mechanisms and pathophysiology of hearing impairment caused by mutations in the tight junction protein Tricellulin, encoded by TRIC, the causative gene for nonsyndromic deafness at the DFNB49 locus. Tricellulin in the inner ear forms unique, structurally complex and elongated tricellular tight junctions (tTJs), which are presumed to control permeability at these contact points between three cells. Our central hypothesis is that Tricellulin is critical for the formation of the epithelial barriers required for the proper functioning of the inner ear. Here we present preliminary data on the generation of two mutant mouse models TricR497X and Tricflox- ex3. Mice homozygous for the p.R497X mutation of Tric have profound hearing loss by age P30 and the hair cells in these mice start to degenerate at approximately P12. We plan to test our hypotheses by pursuing two specific aims: (1) elucidate the underlying cause of deafness in TricR497X mice and (2) determine the functions of Tricellulin in the development, maintenance and assembly of the TJ complex in the inner ear. Our experimental approach is to define the consequences of loss of Tricellulin on the inner ear morphology, ionic barrier, endocochlear potential, cytoskeletal and ultrastructural alterations. Our studies will employ state-of-the art genetic, molecular, histological and physiological techniques. The rationale for the proposed work is that it will provide an enhanced understanding of the cellular and molecular function of Tricellulin. At the completion of this project, we will have acquired knowledge about a) the mechanism of deafness caused by loss of Tricellulin function and the resulting pathophysiology and b) the more general role of Tricellulin in TJ biogenesis and barrier formation. A more complete knowledge of the genes involved in the auditory system will provide a foundation for development of potential therapeutic interventions to treat this neurosensory deficit.
Advancement in the understanding of molecular mechanisms of the inner ear is a prerequisite to developing therapeutic strategies for hearing impairment. The studies outlined in this proposal seek to understand the general function of a tight junction protein known as Tricellulin and its associated pathophysiology due to mutations of TRIC encoding this protein. Thus the proposed research is developing fundamental knowledge that will help to reduce the burden of human hearing loss.
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