A way to produce replacement auditory nerve cells that can restore hearing to deaf animals has been discovered by scientists in the UK.
Working with human embryonic stem cells (hESCs), Marcelo Rivolta and his colleagues at the University of Sheffield exposed the cells to two growth factors called FGF3 and FGF10 which have been linked previously to embryonic ear development.
The team showed that adding these factors triggers a proportion of the unspecialised embryonic cells to switch on a discrete set of "marker" genes called PAX2, nestin, SIX1 and GATA3.
Cells expressing these markers, they found, go on to produce two separate populations of cells, those resembling the hair cells that convert sound waves into the electrical signals in the inner ear, and a second group of cells destined to become the nerves that carry the signals from the hair cells to the brain.
Injected into the inner ears of gerbils with a form of drug-induced deafness, nerve cells produced this way were able to restore hearing in the animals, in some cases completely.
The researchers found evidence of the new nerve cells forming connections to the hearing-related parts of the animals' brainstems, accounting for the recovery.
In their paper, published this week in Nature, the Sheffield team conclude, "The ability to reinstate auditory neurone functionality paves the way for a future cell-based treatment for auditory neuropathies," which are a significant cause of deafness among adults and children.
"It may also, in combination with a cochlear implant," the team suggest, "offer a therapeutic solution to a wider range of patients that currently remain without viable treatment."