Irreversible Hearing Loss May One Day Not Be So Permanent: Promising Research Into Inner Ear Hair Cell Regeneration
As hearing professionals, one of the sometimes frustrating things we encounter in our practice is that the conditions that have caused hearing loss in our patients can’t be reversed. For example, one of the most common causes of hearing loss is damage to the miniature, sensitive hair cells that line the inner ear and vibrate in response to sound. What we think of as hearing are the translations of these vibrations into electrical impulses which are sent to and interpreted in the brain.
The fact is that, the same sensitivity of these hair cells that allows them to react to sounds and translate them into electrical impulses that our brains perceive as hearing also makes them fragile, and vulnerable to damage. The hair cells of the inner ear can sustain damage from exposure to loud noises (causing noise-induced hearing loss, or NIHL), by certain drugs, by infections, and by aging. The hair cells in human ears cannot be regenerated or “fixed” after they have become damaged or destroyed. Instead, hearing professionals and audiologists must use technologies such as hearing aids or cochlear implants to compensate for hearing loss that is essentially irreversible.
This would not be true if humans were more like chickens and fish. In contrast to humans, some fish species and birds have the ability to regenerate their damaged inner ear hair cells and recover their lost hearing. Strange, but true. Zebra fish and chickens are just two examples of species that have the capacity to automatically replicate and replace their damaged inner ear hair cells, thus permitting them to fully recover from hearing loss
While it is crucial to state at the outset that the following research is in its early stages and that no practical benefits for humans have yet been achieved, considerable breakthroughs in the treatment of hearing loss may come in the future as the result of the groundbreaking Hearing Restoration Project (HRP). This research, financed by the nonprofit Hearing Health Foundation, is presently taking place at 14 labs in Canada and the United States. Researchers included in the HRP are working to isolate the molecules that allow the inner ear hair cells in some animals to replicate themselves, with the eventual goal of finding some way to enable human hair cells to do the same thing.
This work is painstaking and demanding. Researchers need to sift through the many compounds active in the regeneration process – some of which facilitate replication while others impede it. By pinpointing which of the molecules regulate this process in avian or fish cochlea, the researchers are hoping to establish which compounds stimulate hair cell growth. The HRP researchers are taking a divide and conquer approach to attain their joint goal. While some labs pursue gene therapies others focus on approaches using stem cells.
Although this research is still in the early stages, our team wishes them swift success so that their results can be extended to humans. Absolutely nothing would be more thrilling than to be able to offer our hearing loss patients a true cure.