School of Medicine scientists have discovered biological mechanisms that appear to play a role in the regeneration of cells in the inner ear.

Over a lifetime, these cells often are damaged or die due to oxidative stress, excessive noise exposure or toxic drugs. The accumulated loss can significantly compromise hearing. Nearly one in four people ages 65-74, and half who are 75 or older, are candidates for hearing aids because of disabling hearing loss.

The discoveries could lead to new ways of evaluating, in animal models, experimental drug treatments intended to prevent hearing loss or restore hearing, and might even lead to methods for regenerating vital cells that have been lost, said Stefan Heller, PhD, professor of otolaryngology.

A paper describing the findings, as well as new methods to quickly link changes in cell function during development to molecular changes within cells, was published June 9 in Cell Reports. Heller is the senior author of the paper. Postdoctoral scholars Jöerg Waldhaus, PhD, and Robert Durruthy-Durruthy, PhD, share the lead authorship.

Sound waves striking the eardrum cause vibrations that are transmitted through tiny bones in the middle ear to fluid within the snail-shell-shaped cochlea of the inner ear. Specialized cochlear cells in a region called the organ of Corti use hairlike sensors to detect the vibrations in cochlear fluid and then trigger nerve signals that are sent to the brain.

“Compared to other senses, we know very little about how hearing works,” Heller said. “The cells are rare. We have to crack open a bone to get to them. They perish quickly, so we must work fast.” There are 120 million retinal cells in a mouse eye, Heller said, but only 3,200 hair cells in a mouse ear.

By using new techniques to rapidly and deeply probe individual cells, Heller’s team has begun to close the knowledge gap.

Molecular mysteries

Many of the biophysical properties of hair cells are understood. Different hair cells along the cochlear spiral are tuned to respond to distinct ranges of sound frequency based on differences in their electrical properties. Frequency is encoded by the place and the properties of the cells’ locations in the cochlea. This understanding has led to the development of cochlear implants to restore hearing in deaf people.