Researchers use gene therapy to grow new hair cells in mammals

June 5, 2003

Researchers supported by the NIDCD have used gene therapy to grow new hair cells, small sensory cells in the inner ear that play an important role in hearing, in adult guinea pigs. The findings, which mark the first time that hair cells have been regenerated in adult mammals, could one day lead to new treatments for people with deafness or hearing loss. The study is published in the June 1 issue of the Journal of Neuroscience.

Hair cells, so called because of tiny hairlike projections jutting from the top of the cell in bundles, reside in the cochlea, a snail-shaped, fluid-filled organ in the inner ear. When a sound occurs, vibrations originating from the eardrum set cochlear fluid into motion, which, in turn, causes a membrane underlying the hair cells to vibrate and the hair bundles to bend. This bending action creates an electrical signal that travels to the brain by way of the auditory nerve, enabling a person to hear. Noise, disease, trauma, medications, and hereditary factors can damage or destroy hair cells, preventing the electrical signal from being generated and causing hearing loss to occur. Because hair cells stop growing early in development and cannot be renewed or repaired, hearing loss of this type is considered permanent. Until now, only birds and reptiles were found capable of regenerating hair cells.

Using a virus as a vehicle, researchers at the University of Michigan inserted a gene that is normally expressed in embryonic hair cells but not expressed in non-sensory cells--named Math1--into non-sensory epithelial cells lining the cochlea of the adult guinea pig. After 30 to 60 days, the researchers discovered hair cells growing in parts of the cochlea where hair cells are typically not found. What's more, they found nerve fibers growing toward the newly formed hair cells, indicating that the hair cells are somehow communicating with auditory neurons. Researchers next plan to determine if the regenerated hair cells function and are able to transmit sound signals to auditory neurons. They will also examine whether the procedure works for aging and deaf guinea pigs.

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