A ٺƵ Health System study raises hope of some day reversing the hearing loss that results from the death of thousands of minute hair cells that line the inner ear. Without these hair cells, the ear cannot pick up the vibrations from sound—vibrations that are key to hearing.
The new study, published in The Proceedings of the National Academy of Sciences, showed that stem cells from the lateral ventricle area of the brain can be coaxed into replicating the sound-sensing function.
“The eventual goal is to microsurgically take the appropriate brain cells in a human patient and transfer them into that patient’s inner ear,” said the study’s senior author, Ebenezer Yamoah, a professor of anesthesiology and pain medicine in the School of Medicine. “Our study indicates these particular brain cells may be just what we have been looking for.”
The research came out of the Center for Neuroscience. Yamoah works there with postdoctoral researcher Dongguang Wei, the study’s lead author; assistant adjunct professor Liping Nie; and Professor Edward Jones, the center’s director. Postdoc Snezana Levic, formerly of the center, also contributed.
Hair-cell death—typically caused by aging or excessive exposure to loud noise—is a primary cause of hearing impairment. Nonfunctioning hair cells lead to the loss of spiral ganglia neurons, which turn hair-cell vibrations into the electrical signals that the brain uses for hearing.
According to the National Institute on Deafness and Other Communication Disorders, some 17 percent of American adults, or about 36 million people, report some degree of hearing loss. That number is expected to increase over the next 20 years as millions of baby boomers reach retirement age.
In its search for stem cells that could possibly replace inner-ear hair cells and spiral ganglia neurons, the ٺƵ team focused on a layer of brain cells with hairlike projections called cilia and which share a developmental history with inner-ear hair cells.
The researchers saw that the potential replacement cells (in the ependymal layer of the lateral ventricle) naturally expressed myosin 7A, a protein known to be essential to the structural integrity of inner-ear hair cells. The team knew from previous research that cells from an adjacent layer, the subventricular zone, contain neural stem cells and are capable of differentiating into spiral ganglia neurons.
The researchers experimented to determine whether cells from the brain’s lateral ventricle area were good candidates for production of both the inner-ear hair cells and spiral ganglia neurons, and whether the two cell types could communicate as if they were normal inner-ear hair and nerve cells.
“We are now conducting research to see whether the replacement cells work in animal models,” Yamoah said. “We want to see if these transplanted cells can really work as sensory cells in the inner ear.”
Charles Casey is a senior public information officer for the ٺƵ Health System.
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Dave Jones, Dateline, 530-752-6556, dljones@ucdavis.edu