University scientists have made breakthrough progress over the past several years in regenerating lost hair cells. Don’t let the name fool you though; this research won’t help cure baldness – but it will bring new hope to people suffering from hearing loss.

Angela Cesere
A microscopic view of damaged inner ear of a deaf person, completely barren of any hair cells. (Courtesy of Yehoash Raphael)
Angela Cesere
A microscopic view of auditory hair cells in a healthy inner ear. (Courtesy of Yehoash Raphael)

Nearly 10 percent of the population in America suffers from hearing loss, said Yehoash Raphael, a University professor of otolaryngology – the study of the ears, nose and throat.

One of the causes of hearing loss is the lack of hair cells in the ear. These hair-like cells A– while containing structures called stereocilia that resemble tiny hairs – don’t have actual hair. They are in fact specialized auditory cells that sense sound waves and transmit the signal to the brain

Using previous research to guide them and deaf guinea pigs as their subjects, Raphael and his associates have succeeded in restoring populations of hair cells in the ears of these animals

One of the first steps to developing a way to restore hair cell populations was for Raphael and his research team to examine the development of hair cells in certain animals.

In order for a cell to become a hair cell, it needs to express a gene called ATOH1. The cells that do not express ATOH1 become nonsensory hair cells.

Raphael’s research centers on the insertion of the ATOH1 gene into the non-sensory cells, turning them into hair cells in mammals.

In the 1980s, other research teams discovered that birds were able to regenerate lost hair cells, countering the previous belief that this process was impossible. The discovery motivated Raphael and his team to further research this discovery.

Raphael later determined that the new hair cells in the birds were being generated from the nonsensory cells in the traumatized bird ear. This process of change is called trans-differentiation.

But unlike birds, this does not occur spontaneously in mammals. To accomplish trans-differentiation in a mammal, Raphael and his associates needed to develop a surgical technique and vehicle to introduce the ATOH1 into the cells of a deaf mammal.

Raphael’s team did this by inserting the ATOH1 gene in a virus that resembles the cold virus, but modified it to be nonreplicating and less recognizable to the immune system.

Then they surgically introduced the gene-containing virus into the ears of deaf guinea pigs. After two months, the animals were examined and new hair cells were found in the ears.

“The hair cells weren’t perfect, their hearing wasn’t perfect, but it is an improvement. And that is better than nothing at all,” Raphael said.

“We need to work out the details to make this clinically applicable, but this is not a trivial task and will take a lot of work.”

Some of the research still left to perform includes applying the technique to different causes of hearing loss, determining if the newly regenerated cells can survive for long periods of time, whether or not long-term hearing loss can be treated in the same manner and understanding how this induced change in cell identity occurs.

The research has other implications outside of alleviating hearing loss. These hair cells are also a vital part of a person’s sense of balance, Raphael said. The hair cells in the ear help to sense movement in the inner ear and transmit that information to the brain in order to help the person balance.

Raphael emphasized the importance of his hair-cell research – older people are more prone to losing their balance and falling, resulting in broken bones that may never recover. There also aren’t any medical aids, like hearing aids, that will help a dysfunctional balance system.

In the future, Raphael hopes that treatment can be done through a pill instead of surgery, which would be more cost -effective and eliminate potential side effects.

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