In a new study, scientists were able to restore partial hearing to deaf gerbils by implanting human embryonic stem cells in their ears. The breakthrough offers hope that one day a similar treatment may be developed to cure hearing loss in humans.
One cause of hearing loss is auditory neuropathy, the impairment of auditory neurons that normally transmit sound signals from the ear to the brain. Researchers at the University of Sheffield in the UK sought to restore hearing in 18 gerbils whose auditory nerves had been experimentally damaged, by replacing the nerves with new ones derived from human embryonic stem cells.
The undifferentiated embryonic stem cells were first subject to chemicals to induce them into becoming auditory neurons. These new auditory neurons were then placed into the gerbils’ ears. Ten weeks later, many of the transplanted cells had grown fibers that reached the brainstem where several relay centers necessary for hearing are found. To see if those fibers helped the gerbils to hear, the researchers played sounds to the gerbils of increasing volume, and used electrodes to determine what volume was needed to evoke brain activity. The gerbils showed improved hearing ten weeks after receiving the stem cells, with a 46 percent increase in sensitivity. The improvement, however, was far from consistent. A third responded exceptionally well, with some regaining 90 percent of their hearing, while another third showed almost no recovery at all.
What would a 46 percent improvement mean for the hearing impaired human? Dr. Marcelo Rivolta, who led the study, told the BBC, “It would mean going from being so deaf that you wouldn’t be able to hear a lorry or truck in the street to the point where you would be able to hear a conversation.”