THURSDAY, Jan. 13, 2005 (HealthDayNews) -- Not only have Harvard researchers discovered the gene that keeps ear hair cells from regenerating in mice, but they've also found a way to block the gene's action, which allowed hair cells to regenerate and function.
These discoveries could lead one day to treatments that would restore many types of human hearing loss.
"We have shown that the hair cell is capable of reproducing and regenerating under the right conditions," said study author Zheng-Yi Chen, an assistant professor of neurology at Massachusetts General Hospital and Harvard Medical School, both in Boston. "Since most of deafness is caused by the loss of hair cells, we hope in the future that we will be able to regenerate ear hair cells in humans."
Dr. Anil K. Lalwani, chairman of otolaryngology at New York University Medical Center, said the study was "amazing" and that the researchers had "potentially learned the on-off switch that determines how hair cells divide or don't divide, which has critical implications for hearing, the hearing sciences and for patients with hearing loss."
Results of the study appear in the Jan. 13 online issue of Science.
Chen said the researchers began their search by looking to see which genes were activated in the ear during the mouse life cycle. They found one, called the retinoblastoma protein.
Chen said this protein is very complicated and seems to perform different functions in different parts of the body. In the eye, for example, this protein is responsible for tumors and in some parts of the body it helps cells to continue dividing, according to Chen. In the ear, however, it appears the retinoblastoma protein is responsible for stopping the proliferation of hair cells.
When Chen and his colleagues studied mice bred to be missing this gene, they found these mice had more hair cells than control mice did.
They also studied mature hair cells from mice in culture, and found that when the action of the retinoblastoma gene was blocked, the hair cells were able to regenerate.
"Those cells were still dividing and differentiating. Those cells are functioning and performing the same way as normal hair cells. We know these are the real hair cells because they connect with neurons," Chen said.
Lalwani said: "The vast majority of hearing loss, whether age-, noise- or toxicity-related, is due to the loss of hair cells. The neurons often stay in place, so if hair cells regenerate, they could use the neurons already in the cochlea. These findings are pretty exciting, and could have quick implications."
Chen said the next step is to create a deaf mouse and then use the new findings to reproduce hair cells.
"We will see if those newly generated hair cells can help the mice recover their hearing, and if that can be achieved in the mouse model, then there's a very good chance it will work in humans, too," Chen said.
Lalwani said there likely wouldn't be much concern over side effects from manipulating this gene, because it would be applied just in the ear and would be used short-term.
"One could envision a directed delivery to the cochlea through a minor surgical procedure," he said. And, once the hair cells had replenished, there would be no need to continue blocking the action of the gene, he added.
More information
To learn more about hearing loss that can occur as you age, visit the National Institute on Deafness and Other Communication Disorders.
