Many of the conditions that cause hearing loss in our patients can’t be reversed which is quite frustrating for our hearing professionals. Damage to the very tiny, sensitive hair cells of the inner ear is among the more common reasons for hearing loss. The work of these hair cells is to vibrate in response to sound waves. These vibrations are translated by the brain into what we call hearing.
The sensitivity of these tiny hair cells enables them to vibrate in such a manner, and thus enables us to hear, but their very sensitivity makes them extremely fragile, and at risk of damage. The hair cells of the inner ear can sustain damage from exposure to loud sounds (causing noise-induced hearing loss, or NIHL), by specific drugs, by infections, and by aging. The hair cells in human ears can’t be regenerated or “fixed” once they are damaged or destroyed. Since we cannot reverse the damage, hearing professionals and audiologists look to technology instead. We make up for hearing loss due to inner ear hair cell damage with hearing aids and cochlear implants.
If humans were more like chickens or fish, we’d have other options. That may sound like an odd statement, however it is true, because – unlike humans – some birds and fish can regenerate the hair cells in their inner ears, thereby regaining their hearing after it is lost. To name 2 such species, zebra fish and chickens have been shown to have the capacity to spontaneously replicate and replace inner ear hair cells that have become damaged, thereby regaining their full functional hearing.
While it is vital to point out at the outset that the following research is in its beginning stages and that no practical benefits for humans have yet been achieved, significant breakthroughs in the treatment of hearing loss may come in the future from the groundbreaking Hearing Restoration Project (HRP). Financed by a nonprofit organization called the Hearing Health Foundation, this research is presently being conducted in 14 unique labs in Canada and the US.Working to identify the compounds that allow the replication and regeneration in some animals, HRP researchers hope to find some way to enable human inner ear hair cells to do the same.
The work is painstaking and difficult, because so many different molecules either help with replication or hinder inner ear 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 enable it to happen in human cochlea. The HRP scientists are taking a divide and conquer approach to achieve their joint goal. While some labs pursue gene therapies others work on approaches using stem cells.
As noted before, this work is still in its very early stages, but we join with others in hoping that it will bear fruit, and that one day we will be able to help humans cure their hearing loss as easily as chickens do.