Determinants of age-induced hearing loss and reversal strategies

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Abstract Age-related hearing loss (ARHL) or presbycusis is the most prevalent sensory deficit and with the increase in life expectancy, it is predicted to have vast impact in the well-being of our society. Indeed, audition and communication is the essence of our human interactions. The overall framework for this programmatic proposal is that a comprehensive understanding of ARHL is only possible through studies of not only the vulnerable synaptic and neural structures of the inner ear, but also examination of the neural plasticity that occurs in response to changes at the neurites of spiral ganglion neurons. We have brought together expert individuals from genetics to cell biology and physiology (Tempel, Yamoah, Ricci, and Gratton). These investigators have already worked together in a highly synergistic and productive manner. There are three projects (P) served by three Cores (Administrative, Mouse Genetics and Structural Analysis Cores) to test the Central Hypothesis that the aging auditory sensory epithelia undergo structural changes that allow the high K+ endolymph to leak into the perilymph, triggering HC and SGN depolarization, increased intracellular Ca2+ ([Ca2+]i) and subsequent “silent” synaptic and neuronal degeneration (P2, P3). We predict that structural changes are mediated by weakening tight junctions (TJs) in the aging cochlear sensory epithelium (P1, Core C). Genetic manipulation of Claudin 9 and Occludin, two identified TJ proteins in the sensory epithelium, that show robust reduction in expression levels, will be used as prototypes together with three additional ARHL models to test our hypothesis (P1-3, Cores B-C). We propose that neural and synaptic alterations at the periphery (P2, P3) will mediate cellular changes that confer long-lasting alterations auditory system. The proposed studies will reveal critical neural and synaptic mechanisms of ARHL. New therapeutic targets for the treatment of ARHL will be assessed, tested and proposed, thus, transforming and shifting the prevailing paradigm to mechanistic and translational platforms.