Structural Basis of Outer Hair Cell FunctionAbstract The last two decades witnessed a huge increase in our understanding of outer hair cell (OHC) structure andfunction. We know, for example, that cochlear amplification is associated with OHC fast motility, which isdriven by forces generated in the plasma membrane by conformational changes in thousands of copies of theintegral-membrane protein prestin. We know that these forces are harnessed and oriented parallel to theOHC's major axis by the cortical cytoskeleton, a two-dimensional anisotropic network of actin filaments cross-linked by spectrin that underlies the entire OHC lateral plasma membrane, and we know that that is possiblebecause the plasma membrane is linked to cytoskeletal actin filaments by thousands of structural 'pillars'. Westill don't know, however, the nature of these pillars. We don't know how they work, or whether they haveany role in the regulation of the prestin-generated force. We don't know either the molecular mechanisms thatcontrol OHC length and motility by regulating cytoskeletal organization and its pillar-mediated connection to theplasma membrane. The goal of this proposal is to fill these gaps in our knowledge of OHC's structure andfunction, a crucial step in our quest to understand cochlear function, malfunctions that involve changes in OHCshape, and protective mechanisms in response to over stimulation, by addressing the following Specific Aims:1) Demonstrate that proteins GLUT5, Dematin and Adducin are major components of OHC pillars, 2)Determine the role of actin polymerization and depolymerization induced by profilin- and cofilin-mediatedsignals in the regulation of OHC length and motility, and 3) Determine the role of the RhoA/ROCK-PKCpathway in the modulation of OHC length and motility.
Structural and/or functional damage of the organ of Corti is the major cause of sensori-neural hearing loss afflicting millions of people around the world. The exquisitearchitecture of the organ of Corti is uniquely adapted to support an enormous range ofinput sound pressures; and outer hair cells (OHCs) are unique in having their bodylength directly influencing important aspects of the micromechanics of this organ. Forexample; minute changes in OHC length can dynamically adjust the operating point ofthe mechano-sensory apparatus hosted in the cell stereocilia and/or the local resonanceof the basilar membrane. Changes in OHC length; known as ''OHC motility''; are thoughtto be essential for cochlear amplification. Despite their importance; many gaps exist inour knowledge of the structure and function of OHCs. Filling these gaps would be animportant step towards a better understanding of cochlear function; malfunctions thatinvolve changes in OHC shape; and protective mechanisms activated in response tooverstimulation. We are confident that accomplishing the aims of the present proposalwill provide essential information about the structure of OHCs and the role of thecytoskeleton in the regulation of OHC length and motility; as well as critical insights intothe basic mechanisms of both normal human hearing and deafness.
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