Stem Cells May Provide Cure for Deafness

Have you ever passed by someone listening to their iPod so loud that you could recognize the song playing? That person is probably doing irreparable damage to their hearing. Continuous or repeated exposure to loud noises can damage the small sensory cells in the inner ear, called hair cells, which convert sound energy into electrical signals that travel to the brain. Once damaged, hair cells cannot grow back and there is no treatment—no medication, no surgery, not even a hearing aid, that can fully correct a person’s hearing once it is damaged by noise. But thanks to pioneering stem cell research, a cure for deafness could be in the foreseeable future.

Researchers, led by Dr. Marcelo N. Rivolta of the University of Sheffield, have been able to successfully grow early versions of the sensory hair cells and neurons essential for hearing in the laboratory using stem cells taken from the inner ear of discarded 9-11 week-old human fetuses. “The potential is very exciting. This is a very important step forward. The hair cells and neurons that give us the ability to hear are only produced during the embryonic stage of development,” said Rivolta. “Once they are damaged or lost, they do not regenerate. There is a clear need for a therapy that can regenerate or replace them.”

“These cells would help us to develop the technologies needed to deliver them into damaged tissues, such as the cochlea, in order to restore the different cell types,” Rivolta said. “In the long term we all hope they may offer a route to restoring hearing for patients.”

Though a treatment for deafness could still be a decade away, the cells could be used more immediately to investigate the causes of deafness and to test new drugs. “We have now an experimental system to study genes and drugs in a human context,” said Rivolta. “The next step in our research is to explore how these cells react when grafted into animal models.”

Rivolta’s research parallels work on the eye by another group of British-based scientists, who plan to use stem cells to treat age-related macular degeneration, a common cause of blindness, in clinical tests starting in 2010 or 2011.

“This research is incredibly promising and opens up exciting possibilities by bringing us closer to restoring hearing in the future,” said Dr. Ralph Holme, director of biomedical research at the Royal National Institute for Deaf and Hard of Hearing People, which helped fund the study. “There are currently no treatments to restore permanent hearing loss so this has the potential to make a difference to millions of deaf people.” About 500 million people worldwide and 28 million Americans are hearing impaired.

Given their unique regenerative abilities, stem cells offer exciting possibilities for cures to such diseases as Parkinson’s, diabetes, heart disease, cancer and multiple sclerosis. Scientists are already using stem cells in the laboratory to screen new drugs and to develop model systems to study normal growth and identify the causes of birth defects.

Details of the research were published in the journal Stem Cells and are due to be presented at a major stem cell conference in Oxford next week.