Protein boost restores hearing in deaf mice

Tissue from a mouse ear--Courtesy of Corfas lab/University of Michigan

Zeroing in on a protein that's vital to providing communication between the ears and brain, scientists have restored hearing in mice that were partly deaf. The researchers say that boosting the production of this protein in humans through gene therapy may be able to one day cure people who have lost part or all of their hearing.

Investigators from the University of Michigan Medical School's Kresge Hearing Research Institute and Harvard University found that adequate levels of the protein NT3 are needed in order to form and maintain connections between hair cells and nerve cells. This type of connection, called a ribbon synapse, facilitates the rapid communication of signals back and forth across tiny gaps between the two types of cells. When these ribbon synapses are damaged by noise or aging, hearing loss can occur.

To study the role of NT3 in hearing, researchers genetically engineered mice to produce additional NT3 in cells of specific areas of the inner ear. Then, the genetically engineered mice and a group of normal mice were both exposed to noise loud enough to reduce hearing. The mice with higher levels of the NT3 protein regained their hearing ability better and more quickly than the control mice.

In a separate test, the scientists then tried boosting NT3 production in the ear's supporting cells, which form a physical base for the hearing system's hair cells in the ear that interact directly with the nerves that transmit sound signals to the brain.

The scientists activated the NT3 genes by giving the mice a dose of the drug tamoxifen, which triggered the supporting cells to make more of the protein. Before and after the mice were given tamoxifen, their hearing was checked using auditory brainstem response, or ABR--the same hearing test used on humans.

Over a period of two weeks after being exposed to the deafening noise, mice with increased levels of NT3 regained their hearing and were able to hear better than mice without the extra NT3 production.

The researchers detail the importance of NT3's role in the inner ear and the impact of increased NT3 production on hearing after a noise exposure in a study appearing in the journal eLife. The next step, the researchers say, is to identify potential drug candidates that work in the same way NT3 does.

- get the study abstract
- see the press release

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