Scientists from Harvard Medical School (HMS) and the Massachusetts General Hospital have managed to restore partial hearing and balance in mice. The new model overcomes a long-standing barrier to accessing hair cells, the delicate sensors in the inner ear that capture sound and head movement and convert them to neural signals for hearing and balance. These cells have been notoriously difficult to treat with previous gene-delivery techniques.

The team’s findings, published in the February issue of Molecular Therapy, show that the treatment leads to notable gains in hearing and allows mice that normally would be completely deaf to hear the equivalent of a loud conversation.  On their quest to restore hearing through gene therapy, scientists have long sought ways to improve gene delivery into hair cells. Previous approaches were only marginally effective as they reached one set of hair cells, but another critical subset remained largely impenetrable.

“To treat most forms of hearing loss, we need to find a delivery mechanism that works for all types of hair cells,” said neuro-biologist David Corey, co-senior investigator on the study at HMS. To achieve that, the researchers used the common adeno-associated virus (AAV). The virus has already been used as a gene-delivery vehicle for retinal disorders but thus far has proven much less efficient in penetrating hair cells. To super-charge AAV as a gene carrier into the inner ear, the team used a form of the virus wrapped in protective bubbles called exosomes.

A month after treatment, nine of 12 mice had some level of hearing restored and could be startled by a loud clap, a standard behavioral test for hearing. Four could hear sounds of 70 to 80 decibel intensity, the rough equivalent of conversation in a loud restaurant.

For more details, visit Harvard Gazette or this link:

New Gene-Delivery Therapy Restores Partial Hearing, Balance in Deaf Mice