Good news! deafness caused by aging could be reversed.

Presbycusis or Age-related hearing loss is the gradual loss of hearing in both ears. It’s one of the most common problems linked to aging.

One in 3 adults over age 65 has hearing loss, a study shows. Most commonly, hearing loss arises from slight changes in the inner ear as we age. Not only that, but this condition can also develop gradually as a result of changes in the middle ear. Scientists say Complex changes along the nerve pathways from the ear to the brain can also cause hearing loss.

Hearing loss was irreversible because scientists have not been able to reprogram existing cells to develop into the outer and inner ear sensory cells once they die.

 

But now, things changed. Researchers at Northwestern Medicine —- a non-profit healthcare system affiliated with the Northwestern University Feinberg School of Medicine, Chicago —- have discovered a single master gene that programs ear hair cells into either outer or inner ones. Scientists overcame a crucial problem that obstructed the development of these cells to restore hearing, according to their study report published in Nature.

“Our finding gives us the first clear cell switch to make one type versus the other. It will provide a previously unavailable tool to make an inner or outer hair cell. We have overcome a major hurdle,” said Jaime Garcia-Anoveros, lead study author, professor of anesthesia, neurology, and neuroscience.

Center for Disease Control(CDC) estimates, In the US, about 8.5 percent of adults aged 55 to 64 have disabling hearing loss. That increases to nearly 25 percent of those aged 65 to 74 and 50 percent of those who are 75 and older.

inner ear hair cells
Inner ear hair cells

Now, researchers are able to develop an artificial hair cell. It does not differentiate into an inner or outer cell. Although, it’ll provide different essential functions to produce hearing cells. This discovery is a giant step toward developing hearing cells.

The death of outer hair cells made by the Cochlea —- a hollow, spiral-shaped bone found in the inner ear that plays a key role in the sense of hearing and process of auditory transduction —- is most often the cause of deafness and hearing loss. The low-level sound that enters the Cochlea is amplified by these outer hair cells. This sound amplification is powered by the movement of their hair bundles, or by an electrically driven motility of their cell bodies.

In response to the pressure of sound waves entering the Cochlea, these outer hair cells expand and contract and amplify sound for the inner hair cells. Then inner cells transmit the amplified sound to the neurons to create the sounds we hear. These cells develop in the embryo and do not reproduce.

 

“It’s like a ballet,” Garcia-Anoveros explains “The outers crouch and jump and lift the inners further into the ear. “The ear is a beautiful organ. There is no other organ in a mammal where the cells are so precisely positioned. (I mean, with micrometric precision). Otherwise, hearing doesn’t occur.”

According to Scientific American, the master gene switches are proteins, called gene activators, that bind to specific regions of DNA, or genes. Master Gene Switch initiates a series of steps that control everything from cell growth and development to seeding disease

TBX2, the master gene switch Northwestern scientists discovered can program the ear hair cells. The report says, When the gene is expressed, the cell becomes an inner hair cell and when the gene is blocked, the cell becomes an outer hair cell. “The ability to produce one of these cells will require a gene cocktail,” Garcia-Anoveros said. The ATOH1 and GF1 genes are important to make a cochlear hair cell from a non-hair cell. Then the TBX2 would be turned on or off to produce the needed inner or outer cell.

 

The goal of researchers was to reprogram supporting cells, which are arranged in the form of lattices among the hair cells and provide them with structural support, into outer or inner hair cells.

“We can now figure out how to make specifically inner or outer hair cells and identify why the later are more prone to dying and cause deafness,” Garcia-Anoveros said.

The study was funded by the National Institute of Deafness and other Communications Disorders grants R01 DC015903 and R01 DC019834 of the National Institutes of Health.

 

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