Wednesday, February 5, 2025
2/5/2025
Project Summary One out of seven adults in the United States suffers difficulty in hearing. Most hearing loss is related to inner ear dysfunction. A prominent signature of hearing loss is damage of outer hair cells, which can result in 40-60 dB of hearing loss. Outer hair cells are known as cellular actuators that are needed for cochlear amplification. Outer hair cells are situated in the cochlear sensory epithelium called the organ of Corti. The organ of Corti is sandwiched between two collagen-fiber-rich matrices called the basilar and tectorial membranes. Traditionally, studies on cochlear amplification were focused on motion of the basilar membrane, but new evidence is suggesting that we have been seeing only one-side of the story (basal-side of the outer hair cells). Recent advancement in imaging and velocimetry techniques enables scientists to ‘see-through’ the cochlea so that they can capture organ of Corti motion beyond the basilar membrane. New observations using recent techniques are both exciting and puzzling. For example, at the apical side of the outer hair cell, vibrations are broadly tuned as compared to basilar membrane motion or neural responses. Functional consequences of the incongruence between mechanical and neural tuning are unclear. Two challenges are impeding the progress of hearing science regarding cochlear amplification. First, despite recent progress, the resolution of velocity measurement techniques is insufficient to specify individual outer hair cells. Second, in experiments with live animals, there are very limited means to control outer hair cell physiology. This project resolves those two challenges. We have developed novel in vitro methods that enable us to measure the motion of individual outer hair cells under electrically, chemically and mechanically controlled conditions. Experimental outcomes are explained and extended by our Virtual Cochlea—a set of computer models to analyze cochlear mechano-transduction. By combining these experiments and the computer models, we can ensure scientific rigor of our research while minimizing animal use. For transparency, acquired data and computer programs will be made available to public. The three aims of this proposal are designed to quantify the most needed biophysical attributes needed to address open questions regarding cochlear amplification and tuning. They are 1) the deflection of stereocilia (mechano-receptive organelle of the hair cells) due to outer hair cell motility, 2) mechanical properties of the tectorial membrane and the Deiters cell (structures in series with the outer hair cell), and 3) the operating range of stereocilia mechano-transduction (stereocilia deflection to saturate hair cell mechano-transduction). The Virtual Cochlea is validated by comparing with the measurements of three aims before testing our overarching hypothesis—the organ of Corti must be as compliant as the outer hair cells for the outer hair cells to generate power for cochlear amplification.
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