Dancing hair cells fine-tune hearing

23 May 2008

A new study by scientists at St Jude’s Children’s Research Hospital in Tennessee sheds light on the way cells in the inner ear enable finely-tuned hearing.

Inner hair cells simply convey sound signals towards the brain, while outer hair cells (OHCs) actively amplify the signal under the control of feedback from higher brain centres. This function is reduced or lost completely when OHCs become damaged, for example in age-related hearing loss.

One theory of how the amplification could work involves a protein called prestin, which is found in the cell wall of OHCs. Prestin changes its shape – or ‘dances’ – when electrically stimulated, and this is thought to mechanically increase vibration of the membrane on which the cells sit. Previous studies have looked at mice that lack the gene for prestin and found that without it, the amplification does not take place. However, OHCs that lack prestin have an abnormal structure, meaning that this, rather than the lack of prestin, may be responsible.

Now Jian Zuo, in collaboration with Peter Dallos at Northwestern University in Chicago, and David He at Creighton University in Omaha, has shown that no amplification occurs in mice with a genetically altered version of prestin. This mutated prestin allows the cell to remain structurally intact even though it doesn’t dance. The results, published in the journal Neuron, show that prestin in its natural form is vital for the amplification. Studying prestin may help scientists better understand the mechanisms of hearing loss. “For example, an overdose of aspirin causes a high-frequency hearing loss by inhibiting prestin’s function,” Zuo says, adding “and two mutations that have been detected in the prestin gene in humans are reported to be associated with deafness.”