Genetic Research May Help Restore Lost Hearing
Embryonic Stem Cells May Regrow Hair Cells
May 20, 2009 Elizabeth Linehan
According to the National Institutes for Health (NIH), more than 90 percent of hearing loss is due to destruction of hair cells or auditory nerve cells. Up until recently, scientists thought these cells could never regenerate. But now those assumptions may be proven wrong.
Hair Cells are Essential to Hearing
Animals – mammals, fish, amphibians and birds alike – hear by way of stereocilia, also known as hair cells. They line the cochlea in the inner ear and turn sound wave vibrations into electrical impulses. Those impulses travel through the auditory nerve to the hearing center of the brain where they are interpreted as sound. Without the hair cells, there are no impulses and thus no hearing.
For whatever reason, fish, birds and amphibians can regrow damaged or destroyed hair cells. But mammals cannot. Once lost, these cells were thought to be gone forever.
Gene Therapy Shows Promise
So far as research has shown, when a hair cell develops, the surrounding cells will not also become hair cells. Instead, they are chemically signaled to become supporting cells. The question became, can a supporting cell be convinced to change and become a hair cell in hopes of restoring lost hearing?
In their 2007 study “Hair Cell Regeneration and Hearing Loss” (NIH, 2007) the NIH experimented first with mice, destroying hair cells in the inner ear causing deafness in the mice. Without interference from the scientists, the mice’s supporting cells “migrated to the hair cell region and began growing hair bundles on their surfaces.” Still, hearing was not restored.
In a later landmark study, another experiment was performed using guinea pigs. This time, gene therapy developed in previous studies was used, causing the supporting cells again to migrate, but this time partially restoring the hearing to the guinea pigs. “This was the first demonstration of gene therapy that improved hearing in formerly deaf animals.”
Auditory Nerve Cells Grown in Petri Dishes
Subsequent studies at NIH have shown promise using mouse embryonic stem cells injected into developing deaf mouse embryos. In the laboratory such cells were shown to grow auditory hair cells in Petri dishes. Experiments are being performed to see if they will do the same in live subjects, and whether such growth will grow healthy hair cells in the mice and restore hearing.
The NIH state three hoped for outcomes of these studies:
- Predicting hearing loss by learning about the genes that cause deafness, enabling scientists to determine a person’s risk of developing hearing loss.
- Treatment – another option, if not necessarily a cure for hearing loss
- Pre-emptive treatment- to minimize long term damage after trauma or illness damage or destroy hair cells.
While it’s still early in the process, studies involving hair cells show promise in many areas that may preserve or restore hearing to those who have lost or are at risk of losing theirs.
This article is part of a series on Hearing and Hearing Loss.
Source: Fact Sheet – Hair Generation and Hearing Loss (NIH, 2007)
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