Scientists have partially restored the hearing of deaf gerbils with injections of nerve cells created from human embryonic stem cells. The procedure may be a first step towards treating deaf people by replacing damaged nerve cells in the inner ear.
The research team from the University of Sheffield took human embryonic stem cells, which can grow into many different tissue types, and transformed them with chemical growth factors into both early stage auditory neurons and sensory hair cells found in the cochlea - the spiral tube that forms part of the inner ear. Together, these cells convert sounds from the outside world into electrical signals.
The animals were first given a drug in one ear that caused deafness by damaging the auditory nerves. The team then cut an incision behind the ear, drilled a small hole in the temporal bone to get into the cochlea, and injected about 50,000 of the early-stage auditory neurons.
After 10 weeks, the 18 animals that received the cell implants had regained on average 46% of their hearing ability, measured by the volume of sound to which they responded. A control group of eight gerbils that received no treatment remained profoundly deaf.
The animals' hearing was also tested by using electrodes to pick up brain signals triggered by sound.
The scientists tried the auditory neurons on gerbils because they have a hearing range close to that of humans.
In the future
Stem cell biologist Marcelo Rivolta who led the research team said it would be several years before the nerve cells could be trialled in humans.
"We have the proof of concept that we can use human embryonic stem cells to repair the damaged ear. More work needs to be done, but now we know it's possible," said Marcelo Rivolta.
The study has been published in the journal Nature.
Sources: www.guardian.co.uk and www.nature.com