If a few too many AC/DC concerts have you now turning up the volume on hearing aids instead of headphones, a new stem cell study in mice is reason for hope.
A team led by Stefan Heller of Stanford University set out to elucidate basic principles of how the inner ear detects sound. But they also created batches of cells that can potentially replace damaged ones in the ear. Their findings are published in the May 14 issue of Cell.
“We basically looked at how nature makes the inner ear, and what is known about the developmental processes involved, and then we just mimicked them in a test tube,” Heller said.
The inner ear contains tiny hair cells that deform when sound waves hit them. Little is known about how these cells transform acoustic waves into neural signals that we interpret as sound, Heller said.
Hearing has remained mysterious compared to other sensory modalities, such as vision, because the inner ear is less accessible and there are relatively few hair cells. Like certain eye cells, hair cells generally don’t regenerate once they die. Therapies using stem cells, or cells derived from embryos that can turn into myriad cell types, can potentially restore normal hearing.
Heller’s team treated cells taken from mouse embryos with various signaling molecules that coaxed them into becoming cells that looked and functioned like normal hair cells. The team used a scanning electron microscope, which forms high-resolution images by bombarding items with electrons. The images revealed that cells of varying height linked together and formed bundles. When the bundles were mechanically stimulated with a slender piece of glass, the cells generated electrical currents that resemble those produced by young hair cells.
For patients who lose hair cells because of common causes, such as noise damage, toxic compounds or aging, there’s a good possibility that regenerating these cells would be an alternative to using cochlear implants, said Albert Edge, a scientist at Harvard University who investigates ways to replace damaged cells in the inner ear. “If it really works well, it could be a cure rather than a treatment,” he said.
The method of creating hair cells in a dish will also allow scientists to discover molecules that enable hearing. And it will offer a way to screen for drugs that spur the growth of new hair cells.
But there’s still a long way to go. “Just because you have these cells in a dish, it doesn’t mean that squirting them into the ear is going to make them work,” Edge said.
To restore hearing, researchers still have to figure out how to produce millions of hair cells, prevent stem cells from forming tumors, and translate the work to human cells. “I’m very cautious about saying this will lead to a cure for deafness that is around the corner,” Heller said. A cure is at least a decade away, he said.
Until then, the best compromise might be to sit in the back row.
Image: flickr/matthijs
