Research in the US revealed that switching off a single gene can regrow important inner-ear cells in mice, suggesting that a similar approach might be useful for repairing hearing damage in people.

Age-related deafness, which affects one in three people by the age of 70, is generally caused by the loss of many of the 50,000 hair cells that line the cochlea of the inner ear.

The cells form a ribbon of vibration sensors which pick up sound waves and trigger nerve impulses that travel to the auditory cortex of the brain, but they are easily damaged by noise, infection or toxins.

As mammals are born with all the hair cells they will ever have, and they do not regenerate when they die, the steady cell loss that accompanies ageing causes irreversible deafness.

Researchers at Massachusetts General Hospital in Boston, however, have shown that knocking out a gene in mice can kick-start the regeneration of hair cells in the inner ear, raising the prospect of regrowing replacements that could reverse deafness.

The results, which are published today in the journal Science, indicate that similar genetic triggers could be used to regenerate other types of cell that do not normally regrow after injury, particularly neurons for treating degenerative brain conditions or paralysis.

Zheng-Yi Chen, who led the study, said: “These findings give us a potential strategy for hair cell regeneration, which could have enormous implications for the treatment of hearing and balance disorders.

“It also shows that cells that have been considered incapable of regeneration — like most nerve cells — can reproduce under the right conditions.”

He focused on a gene known as retinoblastoma, or Rb1, after colleagues at Tufts University in Boston developed mice in which the gene was knocked out. The mice ran round in circles, indicating that something was awry in the inner ear, which also controls balance. The scientists found that mice without the Rb1 gene grew more hair cells in the inner ear than usual, and these cells continued to grow in adult animals.

The results suggest that the Rb1 gene acts as a permanent brake on hair cell regeneration, and that switching it off could be used to regrow the cells. This indicates that drugs that turn off Rb1 in the inner ear could be used to treat certain forms of deafness.

More research is needed before this approach can be tried in patients. In particular, it will be necessary to control hair cell regrowth, as unchecked regeneration would be likely to cause fresh hearing or balance disorders, or even tumours.

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