Discovery of key protein may help prevent hearing loss

时间:2019-03-02 10:01:08166网络整理admin

By Roxanne Khamsi (Image: J of Neurosci/Ahmed et al) A protein identified in the ear may play a key role in converting sounds into nerve signals, say researchers. They speculate that regulating levels of this protein might one day help to protect against hearing loss associated with ageing. Roughly 15% of American adults report some degree of hearing loss, and the condition is more prevalent among the elderly. Affected individuals have relatively few treatment options and must often rely on battery-operated hearing aids to amplify sounds. Some people have serious hearing problems due to genetic disorders, such as type 1 Usher syndrome. Those affected by this illness are born deaf and typically also lose their sight by late adolescence. Approximately 3% to 6% of deaf US children are thought to suffer from Usher syndrome. Experts have succeeded in linking specific gene mutations to the disorder. But because the illness has multiple symptoms, they do not know for sure which proteins affected by these mutations influence hearing loss. An international team of researchers have now identified the protein protocadherin-15 – which is mutated in Usher syndrome – as a potential key player in hearing after finding it in ear tissue samples from mice and chickens. The team analysed the protein content of the samples using a technique called mass spectrometry peptide sequencing. Among other proteins in the sample, they detected protocadherin-15, which had previously been described in eye cells, but not ear cells. The genetic sequence of the protein from the animals closely matched that of protocadherin-15 in humans. Further tests, using antibody molecules that bind to protocadherin-15, revealed that the protein was concentrated on the ends of special filaments that appear to help the ear translate sound waves into nerve impulses. When a sound reaches the ear, it causes tiny hairs suspended in the fluid of the inner ear to move. Each of these hair cells holds roughly 150 to 300 even tinier branches. Movement from sound waves somehow causes membrane channels on the branches to open, allowing positively charged ions such as calcium and potassium to flow inside. This sets off an electrical impulse that travels to the brain. The filaments that contain protocadherin-15 also attach pairs of these branches together, and appear to coordinate the opening of such channels. Scientists say that loud noises can destroy these filaments and suspect that protocadherin-15 may be degraded in these conditions. The protein might also get degraded over time as a result of ageing, and perhaps to varying degrees among individuals. “Maybe there is a genetic propensity for tough ears or gentle ears,” suggests Thomas Friedman at the National Institute on Deafness and Other Communication Disorders in Bethesda, Maryland, and co-author of the study. He speculates that if protocadherin-15 proves as important as experts suspect, someday scientists may devise a genetic test to see whether certain people produce a less stable form of this protein and thus have “gentle” ears prone to hearing loss. Other members of the team hint that in the future drugs may prevent the degradation of protocadherin-15 and thereby help to preserve hearing as people age. And they add that gene therapy might one day enable those with Usher syndrome to hear. Journal reference: The Journal of Neuroscience (DOI: