Scientists have made a major breakthrough in the pursuit of a cure for deafness, by restoring the hearing of deaf gerbils using human stem cells.
The technique, which is the first to use stem cells to treat deafness, could one day benefit hundreds of thousands of sufferers in the UK.
Researchers from the University of Sheffield were able to turn human embryonic stem cells into ear cells, which were then transplanted into the inner ear of gerbils that had been made deaf. On average the deaf gerbils’ hearing improved by 46 per cent , which in a human would mean the difference between not hearing a lorry passing by, and being able to conduct a conversation at an indoor volume, the researchers said.
The gerbils, which were used because of the close similarity between their hearing range and that of humans, underwent chemically-induced damage to one ear. Around 50,000 inner ear nerve cells were then implanted via a small incision behind the ear and a hole drilled into the base of the cochlea. Although recovery rates varied, on average the gerbils’ hearing substantially improved and in some was almost totally restored.
The technique could be used to cure a form of deafness known as auditory neuropathy, characterised by damage to the cochlear nerve, which links the inner ear to the brain. The improvement to the gerbils’ hearing was measured by a technique known as auditory brainstem evoked responses (ABR), which measures the electrical signals given off by the brain when it receives a sound stimulation.
As many as 15 per cent of hearing problems are understood to be associated with the auditory neuropathy, which is usually genetic but can also be exacerbated by environmental factors such as noise exposure and jaundice at birth. In the UK as many as one in six have hearing problems, while around three million people are profoundly deaf. The researchers estimate that 300,000 of them could benefit from stem cell treatment in the future.
“This is an important step forward,” said Dr Marcelo Rivolta, who lead the study. “We now have a method to produce human cochlear sensory cells that we could use to develop new drugs and treatments, and to study the function of genes. And more importantly, we have the proof-of-concept that human stem cells could be used to repair the damaged ear.”
Scientists were able to produce both inner ear hair cells and nerve cells, or neurons, from stem cells by mimicking the chemical signals given off when the body produces these cells in the embryonic stage. Damage to both types of cell can cause deafness but scientists were only able to implant neurons into the gerbils’ ears. Future research will analyse whether a full cochlear implant will be possible to restore the hearing of those with damage to inner ear hair cells – which act as the links between the cochlear nerve and the brain.
The researchers said that, although they could not be “one hundred per cent certain” that cells would react in the same way when implanted into human rather than gerbil ears, the ultimate aim of the study was to trial the technique as a medical treatment.
“The final aim is to take this to a clinical application,” said Dr Rivolta. “Deafness affects millions of people and the social impact on people’s lives is huge. This is just the first stage of the story.”