Inflammation is a beneficial host response to foreign challenges or tissue injury that leads ultimately to the restoration of tissue structure and function. Leukocyte migration to sites of injury or infection is a defining step of inflammatory responses. In the mammalian cochlea, however, leukocyte migration into the auditory organ must be prevented as it may abolish the endocochlear potential by disrupting the tight-junction barrier at the organ of Corti luminal border (anatomically defined as the reticular lamina), leading to apoptosis of sensorimotor outer hair cells and irreversible, profound deafness. Thus, leukocytes are never found in the organ of Corti except in cases of extreme, irreversible cochlear damage. The mechanism used by the cochlea to prevent leukocyte migration is still unknown. The current gold standard clinical strategy to protect the organ of Corti against inflammatory damage is the local delivery of glucocorticoids. However, the mechanism by which glucocorticoids confer this protection is also unknown. The goal of this proposal is to fill these gaps in our knowledge, a crucial step in our quest to understand the regulation of inflammatory responses in the mammalian cochlea. Our preliminary studies provide strong support to the following hypotheses: 1) Annexin A1 (ANXA1), a pivotal regulator of many aspects of the innate and adaptive immune systems, have a major role in preventing leukocyte migration into the OC and facilitating the resolution phase of the inflammatory response; 2) glucocorticoids stimulate guinea pig Hensen cells to release ANXA1 via a myosin IIC-driven mechanism; and 3) Hensen cells store ANXA1 inside the prominent lipid droplets filling their cytoplasm. Thus, we propose to use the guinea pig as an in vivo model, an auditory cell line as an in vitro model, and a combination of non-overlapping techniques and methodological approaches to test these hypotheses by addressing the following Specific Aims: 1) Demonstrate that ANXA1 released by Hensen cells prevents leukocyte migration, 2) Elucidate the mechanism/s involved in the intracellular transport and release of ANXA1, and 3) Identify and characterize the mechanism/s involved in the storage and release of ANXA1 by Hensen cell lipid droplets.
Inflammatory responses in the cochlea, triggered by virus, noise, or ototoxic agents, can result in mild to profound hearing loss. The current gold standard clinical strategy to protect the auditory organ against inflammatory damage is the local delivery of glucocorticoids. However, the mechanism by which glucocorticoids confer this protection is still unknown. We are confident that by accomplishing the aims of the present proposal we will be able to provide critical insights about the mechanisms associated with inflammatory and anti-inflammatory responses in the cochlea, as well as identify new molecular targets for prevention and treatment of sudden sensorineural hearing loss.
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