Molecules in the Ear that Convert Sound into Brain Signals

For scientists who study the genetics of hearing and deafness, finding the exact genetic machinery in the inner ear that responds to sound waves and converts them into electrical impulses, the language of the brain, has been something of a holy grail.

Now this quest has come to fruition. Scientists at The Scripps Research Institute (TSRI) in La Jolla, CA, have identified a critical component of this ear-to-brain conversion - a protein called TMHS. This protein is a component of the so-called mechanotransduction channels in the ear, which convert the signals from mechanical sound waves into electrical impulses transmitted to the nervous system.

''Scientists have been trying for decades to identify the proteins that form mechanotransduction channels,'' said Ulrich Mueller, PhD, a professor in the department of cell biology and director of the Dorris Neuroscience Center at TSRI who led the new study, described in the 7 December 2012 issue of the journal Cell.

Not only have the scientists finally found a key protein in this process, but the work also suggests a promising new approach toward gene therapy. In the laboratory, the scientists were able to place functional TMHS into the sensory cells for sound perception of newborn deaf mice, restoring their function. ''In some forms of human deafness, there may be a way to stick these genes back in and fix the cells after birth,'' said Mueller.

TMHS appears to be the direct link between the spring-like mechanism in the inner ear that responds to sound and the machinery that shoots electrical signals to the brain. When the protein is missing in mice, these signals are not sent to their brains and they cannot perceive sound.

Specific genetic forms of this protein have previously been found in people with common inherited forms of deafness, and this discovery would seem to be the first explanation for how these genetic variations account for hearing loss.