By David H. Kirkwood
BOSTON—When scientists finally discover a cure for sensorineural hearing loss, the key that unlocks the door for them will probably be some mechanism to stimulate the regeneration of sensory hair cells in the human cochlea.
The toll that age, noise, ototoxic medicines, and infections take on these hair cells is the most common cause of hearing loss in humans. Thus, spurring the growth of new hair cells to replace those destroyed over a lifetime of wear and tear has long been the Holy Grail sought by researchers in this area.
In some species of birds, amphibians, and fish, when hair cells die, new ones arise spontaneously to take their place and maintain these creatures’ hearing. However, in man and other mammals, when hair cells die, new ones do not take over the job, and so the resulting hearing loss is irreversible. That’s why for decades scientists have been searching for some mechanism that will make the human auditory system work more like that of birds.
ARTICLE IN NEURON REPORTS BREAKTHROUGH
Recently, researchers from Massachusetts Eye and Ear Infirmary, Harvard Medical School, and Keio University School of Medicine in Japan took a major stride forward in this quest. Writing in the January 10 issue of the journal Neuron the scientists demonstrated that they had achieved something unprecedented: They were able to stimulate resident cells to become new hair cells in an adult mouse ear, resulting in partial recovery of hearing in ears damaged by noise trauma.
This is the first demonstration of hair cell regeneration in an adult mammal. The finding holds great potential for treatments that may someday reverse deafness in humans.
In their experiment, the researchers applied a drug to the cochlea of deaf mice. The drug they used had been shown to inhibit an enzyme called gamma-secretase. When applied to the cochlea, the drug inhibited a signal generated by a protein called Notch on the surface of cells that surround hair cells.
Scientists had previously learned that Notch signaling caused supporting cells, a type of stem cells naturally found in the ear, not to develop into hair cells. The team from Harvard, and Mass Eye and Ear, and Keio wanted to find out if turning off the Notch signal would allow hair cells to develop in the mice used in their study.
That is precisely what did happen. After being treated with the drug, supporting cells turned into new hair cells. Replacing the damaged hair cells with new ones improved hearing in the mice, and the improved hearing could be traced to the areas in which supporting cells had become new hair cells.
In an interview with the press office at Massachusetts Eye and Ear, Albert Edge, PhD, the senior author, said, “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.” He added, “With more research, we think that regeneration of hair cells opens the door to potential therapeutic applications in deafness.”
This sounds fantastic.. How soon will they be able to test it on humans, and how does one sign up for the test?
I too would like to know the answer to Garret’s question. What is the estimated time period when human trails will begin leading to clinical applications?
With hearing loss and severe tinnitus caused by exposure to loud noise, TMJ surgery and who knows what else, I would love to be involved in clinical trials. As A musician for over 40 years , I had developed a highly trained level of pitch and tone control which has now become highly compromised,. It has become increasing difficult to hear various frequencies, much less discerning accurate pitch . I am frightened by the possibility of progressing to even more severe, if not total, hearing loss and living with the ever increasing ringing.
Indeed, it is depressing going into the specialist only to be told “there’s NOTHING” we can do.
It is through the awesome efforts of people dedicated to helping the millions of people who suffer with hearing loss and nerve damage that we may find solutions. I thank the researchers, lab techs, scientists , doctors and others for their efforts and am excited at the possibilities. Sign me up.
Dana LeBlanc and a number of other readers asked the same questions: When may this way of restoring hair cells be available for use in people and how can they sign up for trials? I posed those questions to Mary Leach, a spokesperson for Massachusetts Eye and Ear Infirmary, where the research was conducted.
Here is her reply:
Dr. Edge’s work is in the very preliminary stages. We cannot anticipate how long it will be before the research moves into clinical trials. We are not keeping a list of willing subjects. However, we do promise to get the word out when we have any hearing-related advances, including in Dr. Edge’s area, by way of our hearing research interest group email list. If someone wishes to be added to the hearing research interest group list, he or she may email [email protected].
Hope this helps. – Mary