The tiny hair cells in your inner ear are responsible detecting for sound; when these are damaged, either by genetic disorders, loud sounds or old age they can lead to hearing difficulty and even deafness.
Now, in a series of experiments on mice, researchers based at the Salk Institute and the University of Sheffield have identified a protein that can be delivered to these cells via gene therapy in order to trigger their growth. Though they are as yet unable to restore hearing.
“Our discovery shows that hair cell function can be restored in certain cells,” said co-author Uri Manor, assistant research professor and director of the Waitt Advanced Biophotonics Core at Salk.
“I was born with severe to profound hearing loss and feel it would be a wonderful gift to be able to provide people with the option to have hearing.”
Deafness that occurs in children before they are able to speak is commonly due to genetic factors. One such factor can lead to the sensory hair cells known as stereocilia that enable us to hear being underdeveloped, resulting in deafness.
Stereocilia hair cells are found throughout the cochlea, the spiral tube-like structure found within our inner ear. Low-frequency-sensing regions of the cochlea have longer stereocilia while high-frequency-sensing regions have shorter stereocilia.
When sounds enter the ear, they cause fluid within the cochlea to vibrate, which in turn causes the stereocilia to vibrate. These then send signals to neurons, which ultimately pass on information about the sounds that we are hearing to the brain.
In a previous study, Manor found that EPS8 was involved in determining the length of hair cell stereocilia. Without it, the growth of the hairs is stunted, and they remain very short.
In another previous study, co-author Prof Walter Marcotti, of the University of Sheffield, also discovered the link between EPS8 and stereocilia development.
For this latest study, the two teamed up to design an experiment to see if adding EPS8 to stereocilia hair cells could trigger their regrowth and improve hearing in mice.
They used a common gene therapy technique to deliver the protein to the hair cells via a virus. They then investigated the effects using detailed imaging techniques.
The team found that EPS8 increased the length of the stereocilia and restored their function in low-frequency cells- although not enough to restore the mice's hearing.
However, they also found that the cells seemed to lose their ability to regenerate as they aged.
“EPS8 is a protein with many different functions, and we still have a lot more to uncover about it,” said Manor.
“I am committed to continuing to study hearing loss and am optimistic that our work can help lead to gene therapies that restore hearing.”
The team now plan to investigate the action of EPS8 further, with the hope of extending the age range over which it is effective.
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