Elucidation of Under-Investigated Biological Mechanisms of Age-Related Hearing Loss

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ABSTRACT This proposal will establish a proof-of-concept relating autophagy and age-related hearing loss (ARHL); which is a highly-prevalent communication and neurosensory disorder of our expanding aging population, affecting hundreds of millions worldwide, and costing billions of dollars annually for management and interventions. Clinical interventions are particularly challenging in many ways, because the mechanisms of ARHL are not clear. This proposal is highly innovative because it aims to carry out translational research for new breakthrough strategies, based upon links between age-related autophagy changes in the auditory system and the progression of ARHL. In ongoing experiments, we have found age-related accumulations of autophagy markers such as LC3 and p62 in the mammalian cochlea. Our in vivo turnover experiments showed that an autophagic flux stress may exist in autolysosomal formation steps. We also found that inhibition of autophagy flux decreased the membrane expressions of Na,K-ATPase (NKA) and sodium potassium chloride cotransporter (NKCC1) in the SV-cell line (SV-K1). These are the two key ion channels that maintain the endocochlear potential (EP) for normal hearing. Given our new findings, we hypothesis that aging may affect sensory, neural and metabolic aspects of the cochlea through age-related autophagic stress. Therefore, we propose to carry out step-by-step cellular mechanism studies to yield a comprehensive view of the role of autophagy in the aged cochlea. The aims of this proposal are threefold: First, we are going to determine whether autophagy stress is a general feature of hearing loss. Several autophagy inhibitors will be used to treat young adult CBA/CaJ mice and their hearing abilities and biomarker changes will be measured. Second, the functional roles of autophagy flux stress in the cochlea, including age-related apoptosis and SV-related ion channel activity will be investigated. Third, we will identify target step(s) in autophagic flux on which aging exerts influences in the cochlea, and explore original, feasible ways for future interventions for ARHL. This project is expected to provide novel insights into unknown areas of the biological mechanisms of ARHL, and resolve many of the mysteries that will not only fuel a better understanding of cochlear aging process, but will facilitate the development of more sophisticated and effective prevention and treatment options for ARHL.