WSUV looks at hearing cell loss

Researchers study regrowth, encourage protection against noise




Fourteen thousand cells might sound insignificant when you consider the trillions inside every human body.

But the 14,000 cells that allow you to hear are special. If you kill them, they don’t grow back.

“We get about 14,000 of these cells when we’re born, and when they’re gone, they’re gone,” said Allison Coffin, an assistant professor of neuroscience at Washington State University Vancouver. “We can’t produce new (ones).”

The cells, called ear hair cells, are in constant danger over a person’s lifetime. Loud music, especially in headphones and ear buds, can cause irreparable damage early on, as can loud movies, games and concerts.

That 137.6 decibel record that the Seahawks crowd set on Dec. 2? That was louder than standing next to a jet plane engine. Those in the crowd who weren’t wearing ear plugs most likely killed off or damaged some of their remaining 14,000 cells.

Coffin and Christine Portfors, associate professor of biological science and neuroscience at WSUV, are looking for ways to regrow the highly specialized cells and counter the effects of hearing loss — but in the meantime, and perhaps for the long haul, they also want to share the message of how important it is to protect what you have.

“The noisy world out there is celebrated on some level,” Portfors said. “And we’re not saying don’t go to movies, don’t go to a game and make lots of noise. We just want people to realize that those things, without protection, will kill your ear hair cells.”

Earplugs are all you really need to prevent a lot of the damage. That and keeping the volume to a dull roar on those headphones, the researchers said.

“If the people next to you can hear the music from your headphones, it’s too loud,” Portfors said.

That said, even with that protection, there’s a natural degrading of ear hair cells and hearing as people age. Most children and teenagers, unless their hearing has already been damaged, can hear certain sounds, like those around 17.4 khz, that older people can’t.

As we age, that range naturally gets shorter, which is something the researchers would like to improve.

“As people lose their hearing when they get older, they become more socially isolated,” Portfors said. “That’s how we communicate. There’s actually a higher likelihood of depression in people who go deaf than in people who go blind.”

The keys to unlocking the ear’s biological puzzle box may lie in two small creatures that the researchers are studying — mice and zebrafish.

It turns out some fish, including the zebrafish, can regrow those cells. So Coffin is looking at the genetics to try to understanding how the fish retained that ability and mammals, which are a later part of the evolutionary chain, lost it.

“That’s a big question,” Coffin said. “Why can’t mammals do that anymore? And how do we turn this ability back on in an orderly way?”

Other researchers have tried using stem cells to regrow the special cells, but they haven’t been very successful, Coffin said.

Zebrafish are ideal for studying genetics because, like fruit flies, they reproduce quickly, and it’s a fairly simple process to turn parts of their genetic code off and on. One thing Coffin is looking for is the portion of the gene that controls production of those ear hair cells.

But there’s another side of the equation beyond just reproducing the cells. They also have to be biologically linked into the brain correctly for them to work.

That’s especially an issue with age-related hearing loss. Beyond damaged cells, older people, especially those 65 and older, also tend to have problems differentiating sounds in noisy places. And many need a little extra processing time for sounds and speech as the brain ages, which likely has to do with how the brain is interpreting the signals it gets.

That’s where Portfors comes in.

She’s studying mice, looking at how their brains interpret sounds when they communicate with one another.

If she can understand how the signals relay through the brain of a mouse, that knowledge could help new hair cells connect into the right place in the brain so they work effectively.

“We can take these mice and test their social and communication behavior and compare that with humans,” Portfors said. “We’re really interested in how communication sounds can be detected and discriminated across different parts of the brain and its pathways.”

You could think of those cells and the brain as pins in a Lite-Brite toy, with pins as the cells and the display as the brain. If you make new cells or pins, but don’t know where to plug them into the display, you get a random bunch of lights. But if you make new cells and plug them into the right place in a pattern, you get a picture you can understand.

The hope is that her research may lead to new drugs that allow the brain to process hearing more effectively, and to ways that could prevent hearing loss in the first place.

The work that both Portfors and Coffin are doing is in the early stages, and while it could lead to some remarkable fixes for those with hearing problems, those solutions are also a long way off. In the meantime, they both want to stress how important it is to protect what you still have.

“It’s going to be many years until that technology is available,” Portfors said. “So the solution goes back to the noise problem — we live in a noisy world where we need to turn the volume down.”