A healthy dose of a single protein makes crucial sensory cells grow anew in tissue from the ears of rat pups. The finding, reported in the June issue of Nature Neuroscience, raises the prospect that gene therapy might treat some forms of hearing loss.
Inside the ears of mammals, so-called hair cells convert sound vibrations into electrical signals that then pass down nerve fibers and to the brain. Unfortunately, hair cells grow only as an embryo develops; once they're mangled or worn out in mature animals, the cells are gone for good. That's why more than a third of adults over 64 suffer some hearing loss. For years, researchers had known that mice lacking a gene called Math1--which turns certain other genes on and off--are born without hair cells and are deaf. So neurobiologists Wei-Qiang Gao and J. Lisa Zheng from Genentech Inc. in South San Francisco set out to see if an extra dose of Math1 would make extra hair cells grow after gestation is complete.
The researchers took slices from the inner ears of newborn rats and put them in petri dishes. After opening holes in the cells' membranes by zapping them with electricity, they slipped in a specially designed stretch of DNA containing the Math1 gene. Equipped with the gene, the cells began cranking out Math1's characteristic protein, and during the next several days, the cells containing the extra gene slowly sprouted into hair cells. Indeed, electron microscope images showed that the transformed cells looked just like bone fide hair cells.
The finding is an important step toward restoring hair cells in people, says neurobiologist Donna Fekete of Purdue University in West Lafayette, Indiana. But don't expect DNA-laden eardrops to cure deafness anytime soon; there are still many uncertainties. For instance, the researchers worked with tissue from rat pups, not adult rats. "The question is," Fekete says, "will this work on older, more mature sensory organs?"