There may be new hope for people who have lost some of their hearing due to exposure to loud noises, or simply due to aging. Scientists from the University of Michigan and Harvard University have restored hearing in mice, by getting them to create more of a protein within their ears.

When sound waves enter our ears, they cause sensory receptors known as hair cells to vibrate. Each hair cell is in turn linked to a corresponding nerve cell via a ribbon synapse. When those synapses are functioning properly, they allow the vibrations of the hair cells to be relayed to the nerve cells, and then interpreted by the brain as sound. As the ribbon synapses break down, however, our hearing likewise deteriorates.

This microscope image of tissue from a normal mouse ear shows how ribbon synapses (red) form the connections between the hair cells of the inner ear (blue) and the tips of nerve cells (green)

In the Michigan/Harvard research, mice were first subjected to loud noises, causing them to lose some of their hearing via damage to their synapses. A group of those animals was then treated with a technique known as conditional gene recombination, in which drugs are used to activate genes in selected cells. In this case, the cells were in their inner ears, and they were triggered to produce more than the normal amount of NT3 (Neurotrophin-3) – this is a protein which plays a vital role in the production and maintenance of ribbon synapses.

After two weeks, the treated mice were found to have recovered much more of their hearing than an untreated control group.

Lead scientist Dr. Gabriel Corfas is now hoping to develop treatments for humans, in which drugs could be used to serve the same role as NT3. Getting the body to actually produce more NT3 (as was done with the mice) is another approach that could be taken, although Corfas claims that using pharmaceuticals to take its place would likely be simpler.

In either case, it will likely be at least several more years before a treatment is forthcoming. At this point, it's also not known whether it could be used to reverse complete hearing loss.

A paper on the research was recently published in the journal eLife.

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