A good dose of a single protein makes the crucial sensory cells grow again in the tissues of the ears of baby rats. The discovery, published in the June issue of Nature Neuroscience raises the prospect that gene therapy could treat some forms of hearing loss.
Inside the ears of mammals, said cells hair converting sound vibrations to electrical signals which then pass down the nerve fibers and brain. Unfortunately, the hair cells only grow as an embryo develops; once they are mutilated or worn in adult animals, cells are gone for good. That's why more than one third of adults over 64 suffer from hearing loss. For years, researchers had known that mice lacking a gene called Math1 - that turns some other genes on and off - are born without hair cells and are deaf. While neurobiologists Wei-Qiang Gao and Lisa J. Zheng Genentech Inc. in South San Francisco set out to see if an additional dose of Math1 would make the extra hair cells develop after pregnancy is over.
researchers took slices of the inner ear of newborn rats and put them in Petri dishes. After opening holes in cell membranes by zapping them with electricity, they slipped in a specially designed stretch of DNA containing Math1 gene. Equipped with the gene, the cells began to turn the crank on Math1 characteristic protein, and in the coming days, the cells containing the added gene germinated slowly into hair cells. Indeed, the electron microscope images showed that the transformed cells resembling bone fide hair cells.
The finding is an important step towards the restoration of hair cells in people, said neurobiologist Donna Fekete of Purdue University in West Lafayette, Indiana. But do not expect DNA eardrops charged to cure deafness anytime soon; there are still many uncertainties. For example, the researchers worked with tissue from young rats, not adult rats. "The question is," Fekete says, "it will work on older sensory organs, more mature?"
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