Stem Cells Replace Damaged Nerve Cells In Inner Ear

Connie K. Ho for — Your Universe Online

A group of researchers from the United Kingdom who worked with deaf gerbils were recently able to give the animals the ability to hear again. The study is the first of its kind to replace damaged nerve cells with stem cells.

The study, published recently in the journal Nature, discovered that hearing can improve when nerves were placed in the ear of the gerbils. Gerbils were the focus of the study as they have a hearing range similar to that of humans. The researchers believe that, even with these new findings, it will still be difficult to treat humans who have a hearing disability.

“The research is tremendously encouraging and gives us real hope that it will be possible to fix the actual cause of some types of hearing loss in the future,” remarked Ralph Holme, head of biomedical research for the charity Action on Hearing Loss, in an article by the BBC. “For the millions of people for whom hearing loss is eroding their quality of life, this can’t come soon enough.”

According to the BBC, activities like listening to the radio or chatting with a friend require a change of sounds waves in the air to electrical signals; these messages are sent to the brain to be deciphered and occur with the help of tiny hairs in the inner ear. With one in 10 people who have extensive hearing loss have nerve cells that are damaged, scientists from the University of Sheffield worked to replace the spiral ganglion neurons with new nerve cells.

“It is a big moment, it really is a major development,” mentioned David Moore, the director of the Medical Research Council´s Institute of Hearing Research, in the BBC article. “The biggest issue is actually getting into the part of the inner ear where they’ll do some good. It’s extremely tiny and very difficult to get to and that will be a really formidable undertaking.”

The researchers targeted deafness related to neurons of the auditory nerve, as opposed to deafness from damaged hair cells that can be overcome by cochlear implants.

“We have concentrated on trying to fix the problem at the neuronal level. The cochlear implant is a device that functionally replaces the hair cell — it takes sound and transforms it into an electrical signal,” noted Dr. Marcelo Rivolta, a researcher at the University of Sheffield, in a U.S. News article. “But for the cochlear implant to work, you have to have a good connection to the brain.”

In the study, the stem cells were taken from a human embryo to be cultured in a test tube. The researchers then added a mix of chemicals to the stem cells, changing them into cells that were like the spiral ganglion neurons and injected into the inner ears of 18 gerbils that were deafened with a drug that damaged their auditory nerves. The group of investigators measured the improvement in hearing by tracking the brainwaves. The study took place over a ten-week period, with the gerbils demonstrating an average improvement of 45 percent in hearing range. Some gerbils had much success, with hearing improving up to 90 percent, while a little under a third of the gerbils did not have any response to the treatment.

“It would mean going from being so deaf that you wouldn’t be able to hear a lorry or truck in the street to the point where you would be able to hear a conversation,” remarked Rivolta in an article by the BBC. “It is not a complete cure, they will not be able to hear a whisper, but they would certainly be able to maintain a conversation in a room.”

The researchers are excited about the findings of the study.

“These results should stimulate further research into the development of a cell-based therapy for deafness,” wrote the researchers in the report.

Other scientists are excited about the possibility of working with stems cells to reproduce stem cells for the inner ear.

“It is clearly of interest for a lot of people because the potential is dramatic,” Dr. John Goddard, a neurotologist at the House Clinic, told U.S. News. “The specific article sheds additional light that there is some potential there for regrowth, or regeneration, of sensory cells. But this is going to take many years.”

Furthermore, organizations focused on hearing impairment believe that the results of the study could be a step forward for the deaf community in terms of fixing hearing loss in the future.

“For the millions of people for whom hearing loss is eroding their quality of life, this can’t come soon enough,” remarked Holme of Action on Hearing Loss, which assisted in funding the study, in a Reuter´s article.

However, according to The Telegraph, the team of investigators believes that mores studies need to be done to identify whether the benefits of the treatments are safe for humans and can last long-term.

“Stem cells have been used in animal models of deafness before, mostly the mouse, with different results, but none have shown functional recovery. What we have shown here is functional recovery using human stem cells, which is unique,” explained Rivolta in The Telegraph article. “It is difficult to say when we might be able to treat patients. We are hoping in a few years, but first we need to understand more about the biology of the system and whether it is sustainable in time and safe.”

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