Small hairs inside the ear that recognize sounds have been regenerated to reverse deafness for the first time, according to a new study in the journal Neuron.
A group of researchers from Massachusetts Eye and Ear Harvard Medical School have shown that hair cells can be regenerated by a using a drug to provoke cells that live inside the ear to become new hair cells. This brings about partial hearing recovery in mice with previously damaged ears.
This discovery holds great promise for future use in possibly reversing deafness in humans.
Senior author, Dr. Albert Edge, of Harvard Medical School and Mass. Eye and Ear explains:
“Hair cells are the primary receptor cells for sound and are responsible for the sense of hearing. We show that hair cells can be generated in a damaged cochlea and that hair cell replacement leads to an improvement in hearing.”
Hearing loss is a public health issue that affects nearly 50 million people just in the U.S. The most common condition is known as sensorineural hearing loss which is created by the loss of sensory hair cells in the cochlea.
In 2008 a report stated that the incidence of hearing loss in adults in the U.S. is higher than originally documented. The researchers recommended that screening begin in young adulthood.
Hearing loss can be the result of the following circumstances:
- certain antibiotics and anti-cancer drugs
- noise exposure
In order to hear, sound waves must be changed into electrical signals which the brain can interpret. The initial step of this activity happens inside the inner ear where vibrations move little hairs – the movement produces an electrical signal.
Hearing loss is normally caused by damage to these hairs. There are no known treatments to completely bring back hearing. However, there are hearing aids and cochlear implants that can reduce the symptoms slightly.
Hearing loss can never be reversed completely because auditory hair cells in mammals do not regenerate once they are gone, unlike those of birds or fish. The findings from this study could be a stepping stone for treatment that could bring back hearing after loss of hair cells.
During the experiment, the investigators used a drug that generates hair cells when combined with stem cells outside of the ear. They administered this drug to the cochlea of deaf mice.
The drug was aimed at cells which normally give support to individual hairs. It then changed the path of the cells by changing which genes were being used in the cells, to alter them into hair cells.
Dr. Edge explained:
“The missing hair cells had been replaced by new hair cells after the drug treatment, and analysis of their location allowed us to correlate the improvement in hearing to the areas where the hair cells were replaced.”
The results of this study demonstrate the first hair cell regeneration in an adult mammal. The researchers are excited about the outcomes and their future implications in the possible treatment of deafness in humans.
Written by Kelly Fitzgerald