Brain Cells Coaxed to Mimic Hair Cells

Editor: Here's more progress on the quest regenerate cochlear hair cells. The folks at UC Davis have been able to coax brain cells to mimic hair cells! Here's the press release.

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March 2009

Finding lays groundwork for developing hearing-loss treatments

Deafness caused by the death of the thousands of minute hair cells that line the inner ear and vibrate to create the sense of hearing may be reversible using stem cells from another part of the brain that can be coaxed into replicating the sound-sensing functions needed for hearing, according to research now being done by UC Davis Health System scientists.

In a recently published study, UC Davis scientists showed that stem cells taken from the lateral ventricle area of the brain can be successfully transformed, or differentiated, so that they function like the hair-covered sensory cells of the inner ear that are responsible for transmitting sounds to the brain. The findings raise the hope of some day reversing what was once considered incurable hearing loss.

"The eventual goal is to micro-surgically take the appropriate brain cells in a human patient and transfer them into that patient's inner ear," said Ebenezer Yamoah, a professor of anesthesiology and pain medicine at the UC Davis School of Medicine and the senior author of the study. "Our study indicates these particular brain cells may be just what we have been looking for."

According to the National Institute on Deafness and Other Communication Disorders, approximately 17 percent of American adults, about 36 million people, report some degree of hearing loss. That number is expected to increase during the next 20 years as millions of baby boomers reach retirement age and begin to suffer age-related hearing loss.

The death of the hair cells - typically caused by aging or excessive exposure to loud noise - is a primary cause of hearing impairment. Hair cells that no longer function lead to the loss of the spiral ganglia neurons, which are the neuron that turn hair-cell vibrations into the electrical signals interpreted by the brain as sound.

In its search for stem cells that could possibly replace both types of inner-ear cells, the UC Davis research team focused on a particular layer of brain cells called the ependymal layer of the lateral ventricle. These cells have hair-like projections called cilia and share a common developmental history with inner-ear hair cells. The researchers noticed that these cells naturally expressed myosin 7A, a protein known to be essential to the structural integrity of inner-ear hair cells. They also knew from previous research that cells from an adjacent layer, called the subventricular zone, had been shown to contain neural stem cells and are capable of differentiating into spiral ganglia neurons.

The researchers performed a series of experiments to determine whether cells from the lateral ventricle section brain were good candidates for production of both the inner ear hair cells and the neurons and whether the two cells can communicate in the same way normal inner-ear hair and nerve cells do.

"The experiments provide the first evidence that cells from the brain can undergo a functional switch and replace inner-ear hair and sensory cells that no longer work," said Yamoah. "We are now conducting research to see whether the replacement cells work in animal models. We want to see if these transplanted cells can really work as sensory cells in the inner ear."

The UC Davis study, published in the December 30, 2008 issue of The Proceedings of the National Academy of Sciences, was funded by grants from the National Institutes of Health, California Institute for Regenerative Medicine, and a Judy and David Wachs Grant in Auditory Science from the National Organization of Hearing Research.

Other members of the research team included lead author Dongguang Wei and colleagues Snezana Levic, Liping Nie and Edward Jones of UC Davis, Wei-qiang Gao, of Genentech, Inc. and Christine Petit of Institut Pasteur in Paris.