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Studying hearing, researchers create functional hair cells

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Stanford researchers recently created the first ever hair cells in culture. Hair cells, the mechanical receptor neurons located within the ear, pick up sound waves in air and transmit the signals to the brain — what we call hearing.

Stefan Heller, professor of otolaryngology and chief author of the study, and his colleagues were able to program mouse-induced pluripotent stem cells into hair cells outside of the animal. Previously, any hair cells used in research had to be harvested from living animals.

With this new technique, Heller and many other researchers can produce enough hair cells to do further research on hearing.

“That was the main goal — creating a bucket full of cells,” Heller said.

The research has been in the works for many years, with some stumbling stones along the way. Heller was previously able to create cells with all the same markers of real hair cells, but without their functionality. These cells, however, respond to mechanical stimulation the same way as undifferentiated hair cells.

“We found that if you mimic airborne sound . . . the cells respond,” said Anthony Ricci, professor of otolaryngology. Ricci was a co-author of the study and did the biophysics work, recording electrical stimulation from the cells.

Now that Heller’s lab has found a way to produce the cells, Heller said he first wants to look into how individual hair cell types develop. Hair cells in different parts of the ear have different molecular markers and electrical patterns. He is interested in developmental biology and therefore intends to pursue work on these immature hair cells’ differentiation.

Ricci said further research could reveal more about trace proteins involved in the hearing process.

“This may help us to identify proteins specific to hair cells previously out of our reach,” Ricci said. “By making a lot of cells, it will help us identify novel proteins. The channel responsible for mechanosensation [has] yet to be identified because there are so few [cells].”

From a clinical perspective, hair cells are the ones lost by the deaf and those with hearing loss. These cells have potential significance for therapies in the long run, researchers say.

Heller said these stem cells could be possibly be transplanted to restore hearing in the ear. However, the researchers would first need to purify the cells and translate the findings to human cells. The cells also could be used to test drugs meant to work to restore hearing in vitro.

“We can use the ‘ear in a test tube’ as a kind of assay for future drug screens,” Heller said.

Though the findings published in the journal Cell show promise, both Heller and Ricci noted the early stage of their work and the fact that it currently has no clinical significance.

The findings are on the track for long-run clinical significance, however, Ricci said. In the meantime, there are existing therapies for the deaf, including cochlear implants, Heller said.

“I think that’s the direction,” Ricci said, referring to the clinical applications. “But it’s a very slow, tedious process and that’s very far off.”

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