Deafness is primarily caused by the loss of sensory hair cells in the ear and their associated auditory neurons. Basically, the connection between the inner ear and the brain is breached. Cochlear implants offer a partial solution to the loss of hair cells, but no treatment has been able to help with sensory neuron loss.
So a team led by Marcelo Rivolta of the University of Sheffield attempted to repair the auditory nerve using human embryonic stem cells.
- They generated precursors of ear cells – or ‘otic progenitor cells’ -- by inducing the differentiation of human embryonic stem cells, which have the potential to become many different cell types.
- These otic progenitors can then differentiate into cells with the same properties as the hair cells and auditory neurons – the functional cells involved in the hearing process.
- They transplanted the progenitor cells into chemically damaged gerbil ears.
- Ten weeks after the procedure, some of the transplanted cells had grown projections that formed connections to the brain, Nature explains, restoring auditory responses in the brainstem.
Many of the gerbils could hear much fainter sounds after transplantation, with an overall improvement in hearing of 46%. This is the first proof that stem cells can reconnect the inner ear to the brain and successfully restore hearing in animals.
"In people, this would mean going from only being able to hear a loud truck on the street to being able to hold a conversation," Rivolta says. (Though, it will be years before it can be tested in people.)
Pictured: otic neurons repopulating the cochlea of deaf gerbils. Human cells are green, red marks maturing neurons, and yellow cells are neurons of human origin.
The stem-cell treatment could eventually be combined with cochlear implants to give more deaf patients the ability to hear.
The number of people who might benefit from a stem-cell-driven increase in auditory neurons remains unclear, but stem cells could broaden the reach of existing therapies, Nature explains. And since functioning auditory neurons are necessary for cochlear implants to work, stem cells open a candidate pool that haven’t been helped yet.
The work was published in Nature yesterday.
Image: Marcelo Rivolta / University of Sheffield