Hearing loss is often irreversible because there is no way to recover the necessary sensory cells of outer and inner ear after they have been killed. But we may already be on the road to change, thanks to new research in mice.
Scientists have discovered a single master gene that can regulate whether ear hair cells into outer or inner type needed to restore hearing. This is a significant step towards being able to do this in the lab.
The master gene is called TBX2. In experiments on mice, the team found that when expressed, hair cells in the ear become inner hair cells. When blocked, the hair cells in the ear become outer hair cells. It’s an important toggle switch.
“Our discovery gives us the first clear cell switch to-make one type over the other,” said neuroscientist Jaime García Añoveros of Northwestern University in Chicago. “This will provide an unprecedented tool to-make inner or an outer hair cell. We’ve overcome a major hurdle.”
As the researchers look to translate their findings into a actual, viable cell development process, a “cocktail of genes” will be needed: the ATOH1 & GF1 genes to-make cochlear hair cells from non hair cells & TBX2 to choose an outer or inner hair cell. INSM1 also plays a role, an important transcription factor for the creation of outer hair cells.
Currently, it is possible to produce artificial hair cells under laboratory conditions, but because it cannot differentiate into inner or outer cells, there are issues with their ability to-produce hearing.
As sound waves hit ear, the outer hair cells expand & contract in response to pressure – the sound is then amplified for inner hair cells, which transmit the vibrations as signals to Brain.
Without this delicate dance of microscopic cells, hearing would not happen. The death of the outer hair cells, which develop in the embryo and do not reproduce, is the most common cause of deafness & hearing loss.
“We can now understand how to-make specifically the inner or outer hair cells and determine why latter are more likely to die & cause deafness,” explains García Añoveros.
Dead outer hair cells can-be-down to aging or repeated exposure to loud noises, as well as from certain treatments for diseases such as cancer. According to the Centers for Disease Control (CDC), about 8.5% of American adults aged 55 to 64 have disabling hearing loss.
This number rises to nearly 25% for those aged 65 to 74 and over and 50% for those aged 75 and older. This new genetic discovery offers hope that the necessary hair cells will be able to grow back that they will not be lost forever.
The team points out that the study is still in the experimental phase and there is still a long way to go before these results can be used. For us, it’s also another reminder of the incredible complexity & fascination of the human body, right down to ear hairs.
“It was like a ballet,” says García Añoveros. “The ear is a beautiful organ. There is no other organ in mammals where the cells are so precisely positioned.”
The research has been published in Nature.