Working with mouse cells, researchers have developed a drug treatment that could reverse hearing loss. Though still in its early stages, if the treatment proves viable for humans, it could help combat one of the leading causes of hearing loss, which affects an estimated 48 million Americans.
The treatment stimulated the regeneration of hair cells in the inner ear; these cells detect soundwaves and translate them into nerve signals, allowing us to hear. We're born with about 15,000 hair cells per ear, and when they're damaged—from exposure to noise, from the use of some antibiotics or chemotherapy, or simply from aging—they don't naturally regrow. Dead cells mean diminished hearing ability.
Researchers at MIT, Brigham and Women's Hospital, and Massachusetts Eye and Ear set out to see whether the cells could be regrown. Previous work had shown that immature cells found in the intestinal lining could be exposed to certain molecules, turning them into different kinds of cells. Noticing that the cells of the inner ear (the cochlea) express some of the same surface proteins, the team began exploring whether a similar approach could work in the ear.
Using cells from a mouse cochlea, they created a large pool of immature progenitor cells. These stem cells, when exposed to the right molecules, matured into hair cells. That approach produced about 60 times more mature hair cells than the earlier best technique. It also worked in a mouse cochlea removed from the body. There it required no more drug stimulation, because once in the cochlea, the progenitor cells were naturally exposed to signals that caused them to become hair cells.
That's an important finding. "We only need to promote the proliferation of these supporting cells, and then the natural signaling cascade that exists in the body will drive a portion of those cells to become hair cells," Jeffrey Karp, a senior author on the paper published in the February 21 issue of Cell Reports, told MIT News.
That means the treatment could be very easy to administer in humans, with a simple injection into the middle ear. The drugs would then diffuse through a membrane into the inner ear—the same technique is used to treat ear infections. Researchers also believe the approach could work with other kinds of cells, including intestinal cells that are involved in insulin regulation.
Some of the team have already started a company and licensed the technology, hoping to have human testing started within 18 months. If they're successful, the kind of age-related, degenerative hearing loss that affects so many may turn out to not be so permanent after all.