What Fish and Birds are Helping Us Discover about Reversing Hearing Loss and Regenerating Inner Ear Hair Cells

One of the sometimes bothersome things about being a hearing care specialist

is that a lot of the circumstances we deal with that have caused our patients to lose their hearing can’t be reversed. Damage to the tiny, very sensitive hair cells of the inner ear is one of the more prevalent reasons for hearing loss. The work of these hair cells is to vibrate in response to sounds. What we think of as hearing are the translations of these vibrations into electrical energy, which is then sent to and interpreted in the brain.

These hair cell structures have to be really small and sensitive to do their jobs correctly. It is precisely because they are small and sensitive that they are also readily damaged. Aging, infections, certain medications or exposure to loud sounds (resulting in noise-induced hearing loss/NIHL) are all possible sources of damage. In humans, once these hair cells have become damaged or destroyed, they cannot be regenerated or “fixed.” As a result, hearing professionals and audiologists have to treat hearing loss technologically, using hearing aids

or cochlear implants.

Things would be a lot simpler if we humans were more like chickens and fish. In contrast to humans, some fish species and birds actually have the ability to regenerate their damaged inner ear hair cells and regain their lost hearing. Odd, but true. Zebra fish and chickens are just 2 examples of species that have the capacity to spontaneously replicate and replace their damaged inner ear hair cells, thus allowing them to fully recover from hearing loss

.

While it is important to state at the outset that the following research is in its beginning stages and that no practical benefits for humans have yet been achieved, considerable advancements in the treatment of hearing loss may come in the future from the innovative Hearing Restoration Project (HRP). This research, funded by the nonprofit Hearing Health Foundation, is currently being conducted in 14 labs in Canada and the US. What the HRP scientists are attempting to do is isolate the molecules that allow this replication and regeneration in animals, with the purpose of finding some way of stimulating similar regeneration of inner ear hair cells in humans.

The work is painstaking and challenging, because so many distinct compounds either help with replication or prevent hair cells from replicating. But their hope is that if they can identify the molecules that stimulate this regeneration process to happen in avian and fish cochlea, they can find a way to stimulate it to happen in human cochlea. Some of the HRP scientists are pursuing gene therapies as a way to stimulate such regrowth, while others are working on stem cell-based approaches.

As noted before, this work is still in its very early stages, but we join with others in wishing that it will bear fruit, and that one day we will be able to help humans reverse their hearing loss as easily as chickens do.