A goal of the cochlear physiology laboratory is to understand how sound induced vibration of the tissues in the inner ear results in loss of sensory function and cell pathology. A number of important questions are captured within the scope of the two Aims. Broadly stated they are 1) to learn the mechanisms of the pathophysiology of the sound stimulated lateral wall and 2) to find out how the metabolic load and hypoxia induced by loud sound impacts mitochondria morphology and the redox state of organ of Corti hair cells. Under the first point there are three specific questions about lateral blood flow and stress. We will determine whether there is a local cochlear flow that correlates with the sound tonotopic stimulation and shows the "real time" metabolic and vascular state of the lateral wall. That metabolic state, we believe, is a functional hypoxia that induces breach of the vascular blood/labyrinth barrier. We study the hypoxia initiated signaling pathway to alter adherens junction proteins of the endothelial cells. We then determine, using molecular biological methods, if hypoxia also initiates lateral wall fibrocyte inflammation. The mutant mouse model (Chd23 mutant or salsa) is employed as a way of inducing altered transduction current, which is a drive for lateral wall metabolism and, possibly, capillary reactivity. Standard techniques are clearly insufficient for answering these questions, so new and innovative methodology will be used. We developed the Optical Micro- Angiography method for the study of lateral wall cochlear blood flow. We also adopt super-resolution imaging of the adherens junction fluorescent labeled proteins to determine how altered junction and cytoskeleton open the trans-cellular permeability gap. The cochlear outer hair cells are subjects of the second question where, in separate experiments using salsa mice and pharmacologic agents, we determine the sub- cellular sources of reactive oxygen species in outer hair cells? We then investigate, using the salsa mouse, if the physical forces of sound (apart from metabolic stress) can produce oxidative stress. Finally, since stress and metabolism directly influence mitochondria population, we study whether OHC mitochondria can dynamically adapt their number under sound stimulation. A GPF- mitochondria transgenic mouse will be used to study the sound altered population of mitochondria in the process called biogenesis.
Normal hearing depends upon a robust blood supply to the cochlea, while defects in the cochlea's vascular system contribute to hearing loss from loud sounds, age and certain diseases. Within the cochlea, the capillaries of the vascular area called the stria vascularis are damaged and become leaky with loud sound. That sound also damages and kills the sensory cells of the organ of Corti. This proposal will learn how loud sound causes hearing loss by studying its physical and metabolic impact to the vascular and sensory cells.
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