23 March 2011

Two genes, two types of protein and two types of hearing loss

Research has shown how hearing loss differs depending on which proteins are lost.

Researchers at the University of Minnesota Medical School have gained an insight into how different types of age-related hearing loss may occur in humans.

The researchers studied how two very closely related genes contribute to hearing functions in mice. Mutations in the same genes are associated with deafness in humans. They discovered two key cellular processes that are required to maintain auditory function.

The genes contain proteins called beta-actin and gamma-actin. In humans, deafness-causing mutations have been linked to both proteins. Beta-actin and gamma-actin comprise the primary structural elements of stereocilia (the hair-like fibres in the inner ear), which convert mechanical sound energy into the nerve signals that allow humans to hear.

The two proteins are 99% identical; however, their slight differences have been exactly preserved through evolution from birds to mammals, suggesting that each protein may have important and distinct functions. The researchers, James Ervasti and Ben Perrin, both  Ph. Ds, tested the idea that two closely linked proteins have separate, but important, roles in hearing by disabling each gene in mouse auditory hair cells.

Two different types of hearing loss

They found that beta-actin and gamma-actin do have different maintenance functions that together keep the hair-like fibres - that allow mice to hear - healthy. Both mice with disabled genes had normal hearing at young ages, but developed specific types of progressive hearing loss and stereocilia pathology that differed depending on which protein was lost.

"These separate maintenance pathways are likely important for maintaining auditory function during aging and may contribute to future understanding of common forms of age-related hearing loss in humans," one of the authors, Ben Perrin, Ph. D., said.

The discovery may eventually help physicians develop drugs to combat progressive hearing loss in the future.


www.sciencedaily.com and PLoS Genetics.

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