Regenerative Ear Proteins Could Someday Restore Hearing

Kim Cyprian/Guardian

Researchers from UCSD and the National Institutes of Health have discovered a protein that could help treat hearing impairments.

The protein, called Sox2, is critical in the formation of spinal ganglion neurons — the auditory neurons mammals use to hear.

The leading cause of acquired hearing impairment in the ear is either the loss of hair cells in the inner ear or spiral ganglion neurons.

Dr. Alain Dabdoub, an assistant professor of surgery at UCSD, helped conduct a two-year study using the Sox2 protein to create these spiral ganglion neurons in the ear tissue of mice. The study was recently published in the Jan. 13 issue of The Journal of Neuroscience.

Researchers removed developing ear tissue from mouse embryos and studied the effects of injecting the cells with the Sox2 protein.

They used immunohistochemistry — a procedure that stains proteins using visual markers such as fluorescent dye — to differentiate the Sox2 protein, then introduced the protein to the ear cells through infection (a process known as electroporation).

According to Dabdoub, within two days of mixing the cochlear and Sox2 proteins together, the cells that were injected with the Sox2 gene developed into neurons and survived for up to two weeks. In contrast, cells that were not injected with the Sox2 gene did not become neurons.

“Utilizing genetics, we showed that Sox2 is necessary for the formation of spiral ganglion neurons, as these neurons are absent in Sox2 mutant mice — revealing a novel role for Sox2 in ear development,” Dabdoub said.

Currently, the most common therapies for hearing loss are hearing aids — which essentially increase hair-cell stimulation — or cochlear implants that act as an electronic substitute for the hair cells.

In both forms of treatment, normal spiral ganglion neurons must be intact for the treatment to be effective. For this reason, this discovery that Sox2 proteins create new nerves is promising for future advancements in hearing restoration.

The study, which initially began at the National Institute on Deafness and Other Communication Disorders, is being carried out in Dr. Dabdoub’s laboratory in the UCSD School of Medicine, Division of Otolaryngology.

“This induction has significant implications for clinical research related to cochlear implants,” he said. “The ability to replace damaged or lost neurons with new cells through gene therapy would provide a substantial benefit to those suffering from hearing impairment.”

Readers can contact Kelly Kim at [email protected].