Stem cells can be coaxed into becoming the hair cells deep inside the ears that are destroyed in hearing loss, U.S. researchers reported on Thursday.
The experiment, done with two types of stem cells, raises the possibility of treating many types of deafness and hearing loss, the team reported in the journal Cell.
While they have so far succeeded only in mice, they are hopeful of transforming human cells.
Dr. Kazuo Oshima of Stanford University in California and colleagues used two types of master cells to create the mouse hair cells — embryonic stem cells and a similar type of cells called induced pluripotent stem cells, or iPS cells, which are ordinary cells re-programed to act like stem cells.
Both came from mice, and the next step is to try the experiment using human cells.
Hearing loss is an enormous problem — the National Institute on Deafness and Other Communication Disorders estimates that 15 percent of Americans between 20 and 69, or 26 million people, have high frequency hearing loss caused by noise.
Antibiotics and genetic disorders can also damage the hair cells in the middle ear needed for normal hearing.
Sounds are carried via a series of complex structures to the ear's inner cochlea, which is filled with fluid that ripples. Hair cells covered with bristles called stereocilia "ride the wave" and as they bend channels open, creating an electrical signal that can be carried to the brain.
Once damaged, these cells cannot be replaced.
Oshima's team believes regrowing these cells could serve several purposes.
"What we are thinking is to get human iPS cells from hearing loss patients and just try to re-make the disorder in the petri dish," Oshima said in a telephone interview.
This could be used to screen drugs that might cause the cells to regenerate, or to activate hibernating stem cells in the ear, he said.
It may also be possible to grow the cells and inject them into the ear, but no one has developed a technique for doing this, Oshima said.
"There are still so many hurdles to overcome," he said.
Oshima and colleagues used embryonic stem cells from mice and a type of cell called a fibroblast cell for their experiment.
They tried various factors — proteins and chemicals — to nurture the cells and nudge them into becoming hair cells.
"We knew it was really working when we saw them in the electron microscope," Stanford's Stefan Heller said in a statement. "They really looked like they were more or less taken out of the ear."
The next step is to try using human iPS cells, said Oshima, but it has not worked so far.
"This gives us real hope that there might be some kind of therapy for regenerating hair cells," said David Corey, a professor of neurobiology at Harvard University in Massachusetts who was not involved in the study.
"It could take a decade or more, but it's a possibility."