Although an experimental drug designed to treat Alzheimer’s by inhibiting an enzyme called gamma-secretase that activates a number of cellular pathways, researchers led by Albert Edge at Massachusetts Eye and Ear and Harvard Medical School have found that it may eventually play a significant part in restoring hearing loss by helping to generate new sound sensory hair in the inner ear.
Nearly 50 million people in the US alone suffer from some form of deafness, generally caused when the hair cells in the cochlea become severely damaged due to a number of factors including loud noises, infections, toxins, certain antibiotics and anti-cancer drugs, in addition to normal aging. Although hearing aids and cochlear implants can improve the symptoms somewhat, they do not actually restore hearing, because once lost, the auditory hair cells in mammals (unlike those in birds or fish) don’t regenerate.
“What you are born with is what you have throughout your whole life,” stated Edge.
However, when he and his colleagues applied the enzyme inhibitor to the cochlear of mice deafened by noise trauma, they found that it inhibited a signal generated by a protein known as “Notch” on the surface of other inner ear cells, causing them to transform into hair cells themselves, and restored 20% of the rodents’ hearing.
“This is the first demonstration of hair cell regeneration in an adult mammal, exclaimed Edge. "We're excited about these results because they are a step forward in the biology of regeneration and prove that mammalian hair cells have the capacity to regenerate," Dr. Edge said. "With more research, we may eventually be able to restore hearing in humans through regeneration as well.”