Gerbils regain hearing thanks to stem cell therapy

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(CBS News) Scientists have restored hearing in gerbils using a stem cell therapy that may hold promise for deaf humans.

Using human embryonic stem cells, researchers at the University of Sheffield were able to implant immature nerve cells into gerbils, which then regenerated and were able to improve hearing ability in the animals. The study was published on Sept. 12 in Nature.

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According to a Nature News article on the study, more than 275 million people have moderate-to-profound hearing loss, many of whom have it caused by a disruption in communication between the inner ear and brain. Senior study author Dr. Marcelo Rivolta, a stem cell researcher at the University of Sheffield told HealthDay that about 80 to 90 percent of deafness is due to problems with cells in the inner ear.

There are two types of inner ear cells. Hair cells translate vibrations into electrical signals that are transmitted via the auditory nerve to the brain. Problems with these cells are typically fixed via cochlear implant, a small device which can bypass the hair cells and directly send signals to intact auditory nerves. Neurons make up the auditory nerve, and when these are damaged, doctors have little to no treatment options available.

It's important to note that the type of deafness that the gerbils had affected only neurons, making it very rare. The Associated Press points out that type of deafness only affects between less than 1 percent to 15 percent of patients. Furthermore, the treatment won't work in all the patients with that disorder.

But, because so many disorders have to do with inner ear cell problems, the research is promising and may have future human applications.

Researchers in the study took embryonic stem cells, which can develop into any other kind of cell in the body, and grew them into a test tube that had molecules that are available when the fetus develops ears, known as fibroblast growth factors (FGFs). Some stem cells developed characteristics similar to hair cells and others turned into cells that looked like neurons.

Then the neuron-like cells, which were called otic neural progenitors (ONPs), were transplanted into the ears of gerbils that had been given ouabain, a chemical that damages the neurons in the auditory nerves but not the hair cells.

Ten weeks later, the cells had grown and some connected to the brain stem. The gerbils on average had a 46 percent overall improvement in hearing, with many of the animals registering brain activity at much fainter sounds after the transplant.

Dr. John Goddard, a neurologist at the House Clinic in Los Angeles, told HealthDay that the study was exciting because it showed stem cells helped nerve cells regrow, but added that it will take some time before it's determined if it is an appropriate treatment for human deafness. Stefan Heller, a stem-cell researcher at Stanford University in California, told Nature News it could take as long as 15 years before it is ready.

"It is clearly of interest for a lot of people because the potential is dramatic," Goddard said. "The specific article sheds additional light that there is some potential there for regrowth, or regeneration, of sensory cells. But this is going to take many years."

Prof Dave Moore, the director of the Medical Research Council's Institute of Hearing Research in Nottingham, U.K., explained to the BBC that despite the "major development," part of the difficulty with deaf patients is accessing the part of the inner ear where the problems are.

"It's extremely tiny and very difficult to get to and that will be a really formidable undertaking," he said.

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