Scientists believe they have discovered the protein responsible for converting sound into an electrical response the brain can understand and act upon.
"This is certainly one of the Holy Grails in the hearing world," said Peter Gillespie, a professor at Oregon Health & Sciences University in Portland. "Everyone is excited, but there is still a lot that needs to be done to prove that this is the right protein."
The finding of TRPA1 marks the end of a 25-year search, said lead investigator Jeffrey Holt, an assistant professor at the University of Virginia. He presented his findings this week at the Society for Neuroscience annual meeting in Washington, D.C.
About 16,000 hair cells lining the inner ear are responsible for registering sound and head movements and turning them into electrical signals.
Holt and colleagues discovered that hair cells develop late in the first trimester, and set out to find the genes that activate this development. That's when they found TRPA1. In the laboratory, they shut down TRPA1 and were able to stop hair cells from performing their job. The cells were no longer sensitive to sound.
They unraveled the structure of the protein and found that it looks like a doughnut. In the absence of sound, the hole in the doughnut stays closed. When sound strikes the hair cells, the hole pops open and lets in calcium and potassium, positively charged ions that result in an electrical signal.
Now, investigators are hoping to study patients with hearing loss to see if the TRPA1 gene is damaged, and/or whether the protein it makes is abnormal. They also discovered that a second protein called myosin amplifies sound in the inner ear. Myosin is critical in hearing a range of sounds.
Holt hopes these discoveries will lead to new ways to prevent or treat human deafness. One in 1,000 children is born deaf. They are now working on gene therapy to deliver into the inner ear the genes that make TRPA1 and myosin.
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