Oregon scientists discover mechanism responsible for hearing

PORTLAND, Ore. (CN) — For the first time ever, scientists have identified the structure of the inner ear responsible for hearing and balance: the mechanosensory transduction complex. Indeed, this term might sound complex, but it actually represents a simple protein structure present in most animals including the roundworm, which led scientists to the discovery.

Scientists at Oregon Health & Science University hope their findings could lead to new treatments for hearing impairments that affect over 460 million people worldwide.

“This is the last sensory system in which that fundamental molecular machinery has remained unknown,” senior scientist Dr. Eric Gouaux said in a statement. “The molecular machinery that carries out this absolutely amazing process has been unresolved for decades.”

Gouaux’s team discovered the structure by isolating the process the enables the inner ear to convert vibrations into sounds. However, what led scientists to the finding the structure was identifying the similarities between the mechanosensory complex in humans and the roundworm Caenorhabditis elegans.

“What we really want to do is understand, in humans, how sound is transduced into a signal that goes to the brain, and that leads you to think that you heard something,” Gouaux said in an interview. “But it turns out that that machinery in our ears — and in the ears of pretty much every animal — the number of pieces of the machinery are very, very few.”

As illustrated by Gouaux’s study in the journal Nature, the mechanosensory transduction complex or “machine” is a symmetrical protein complex composed of three parts, and this structure allows the inner ear to convert vibrations into sound through what is known as the mechanosensory transduction process.

“They're just a crazy tiny number of these little machines that do this transduction of sound into electricity,” Gouaux said. “So, what we did was we turned to, believe it or not, a worm that responds to touch, kind of like we respond to sound, and this worm has all of the components of the machine to do this mechanical to electrical transduction.”

After five years and 60 million worms, scientists figured out how to isolate and visualize the molecular structure of these machines through cryoelectron microscopy, a process Gouaux explains as “a super complicated word for a crazy powerful microscope that allows you to see atoms.”

By visualizing the molecular structure, scientists believe they can design a molecule that fits into complex to rescue it from genetic mutations or environmental damage — both of which cause hearing loss.  

“It turns out that in our ears, there are only a few of these little machines,” Gouaux said. “And that's one of the reasons why if you damage them, you lose sensory ability and you start to become deaf.”

The question now is how scientists go about repairing hearing loss.

“Well, that's a big problem, actually,” Gouaux said, noting that until now there have been two fundamental issues: accessing the inner ear and visualizing the structure responsible for sound.

“Now that we know what it looks like, and we have a much better understanding of how it works, it offers new opportunities for coming up with strategies to fix it,” Gouaux said. “And that's one of the things that we're, of course, super excited about.”

To the worm’s credit, Gouaux added: “I think that it's just one of those examples where so-called basic science and fundamental research using an organism like a round worm can have direct impact and relevance to understanding kind of human health disease.”

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