Researchers supported by the National Institute on Deafness and Other Communication Disorders (NIDCD) have come one step closer to understanding how hair cells regenerate, a finding that could lead to new treatments for restoring hearing. In the January 13 issue of Science magazine, scientists at the Massachusetts General Hospital in Boston, MA report that they could cause hair cells to regrow by removing a single gene in mice.

Regeneration of hair cells is important because hair cells are the key links in the chain of signals that makes hearing possible. Hair cells are found in the cochlea, part of the inner ear that sends the electrical signal of sound to the brain. Vibrations from the eardrum and bones of the middle ear are relayed to the cochlea, where they stimulate the hair cells. This energy is converted to electrical signals that are carried by nerves to the brain and interpreted as sound.

In the current study, the researchers isolated a gene that was activated in the ear during the mouse life cycle. The gene, Rb1, encodes for the retinoblastoma protein, which has various functions throughout the body, including acting as a molecular switch to stop the growth of hair cells. Mice that were bred to be missing the retinoblastoma gene were found to have more hair cells than control mice. Mature hair cells grown in culture dishes also were able to regenerate when the retinoblastoma gene was deleted.

Dr. James Battey, director of NIDCD has called this discovery "a very important first step toward learning" how to restore hearing in human patients. Hearing loss is one of the most common conditions affecting older adults.

Most deafness occurs because hair cells are damaged either by disease, injury or aging. Humans are born with about 50,000 inner ear hair cells, but the number gradually declines over time. Once these cells are lost, they cannot be restored.

Although the studies were done in mice, the mouse ear structure is very similar to that of humans. The next step will be to develop methods to reversibly block the Rb1 gene in inner ear hair cells to see if hair cells regenerate and hearing can be restored.