Background: Hearing impairment is frequently caused by the loss of hair cells in the cochlea of the inner ear. Hair cells, named for the hairlike projections on the top surface of the cell, play a vital role in detecting sound. When sound waves enter the cochlea, they produce corresponding waves in the fluid beneath the hair cells. The wave motion drives the hair cells into an overlying membrane. The "hairs" on the tips of the cells bend, setting off a signaling cascade within the cells. These signals are ultimately carried to the brain by the auditory nerve and interpreted as sound. Many factors can cause individuals to lose hair cells, including normal aging, excessive noise exposure, infections, and treatment with certain antibiotics. After hair cells die, the nerve cells that take the sound message to the brain (spiral ganglion neurons) may also die. Scientists are searching for ways to regenerate or prevent the death of hair cells and spinal ganglion neurons.

Advances: Two groups of NIDCD-funded scientists have now used a viral expression strategy (gene therapy) to prevent death of hair cells and spiral ganglion cells in animals. The first group used a virus to deliver protective antioxidants to hair cells in the cochlea. The treatment was able to prevent antibiotics from destroying hair cells. The second group expressed a protein, called brain derived neurotrophic factor (BDNF), in spiral ganglion cells. This strategy was able to inhibit the death of spiral ganglion neurons after the death of their corresponding hair cells.

Implications: If this observation can be repeated in humans, scientists may be able to prevent or delay hair cell and spiral ganglion cell degeneration resulting in preservation of hearing.

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