With about 48 million Americans suffering from hearing loss, scientists have been working for years on ways to provide treatment, and we recently learned that there may be hope on the horizon. Researchers have found that the effects of hearing loss can be mitigated by stimulating the growth of cochlear hair.
THE COCHLEAR HAIR CELLS
Every person is born with approximately 15,000 sensory hair cells in each inner ear. These hair cells are responsible for detecting sound waves from the surroundings and converting them into signals that the brain can interpret. This is how humans are able to hear and distinguish music, speech, and ambient noises, among other sounds. Over time, these cells deteriorate due to many factors, including exposure to noise. However, these hair cells do not grow back, meaning that any damage the hairs suffer is permanent.
With every cell that dies, an individual’s sense of hearing diminishes. Consequently, the longer a person lives, the more exposure the ear gets to risk factors and the more the cochlear hair cells die, which is why many senior citizens seem to have trouble hearing. The new study of hearing loss treatment focuses on regenerating about 2,000 more hair cells. This research is the work of Boston researchers, including Jeffrey Karp, of Brigham and Women’s Hospital, Massachusetts Eye and Ear’s otolaryngology professor, Albert Edge and a research team from MIT.
THE SCIENCE OF IT
The basis of the research into hair regeneration stemmed from the question of why it is possible for animals to grow back their hair cells but not humans. They turned to the intestines, which carry the most regenerative tissues in the human biological system. The cells in the lining of the intestines can grow back every four days. In 2013, the research team discovered that by exposing immature intestinal cells to particular molecules, they could grow them back and differentiate them. What they did was to separate the part of the intestinal cells that was responsible for the rapid regrowth and use it to create the molecules that could control the process. It was during this experiment that the researchers realized that the support cells in the cochlea shared some similarities with the intestinal cells and in theory, the same approach could trigger regeneration.
To test the ability of cochlear hair cells to regrow, they used a lab-grown inner ear from a mouse. They applied the same molecules that stimulate rapid multiplication of hair cells and had great success. These molecules work on the Wnt pathway, but they had to use other molecules to trigger the Notch pathway to ensure that regeneration does not happen too fast. The team got about 2,000 immature hair cells that turned into mature cells after differentiation. Compared to previous experiments that have been used to stimulate regeneration, this approach produces 60 times more progenitor cells.
A patient would need an injection in the middle ear to administer the drugs that trigger regrowth and from there, they would travel to the cochlea. Injections into the middle ear are not uncommon especially when treating ear infections with antibiotics. For this reason, if successful, this treatment will just be a standard outpatient procedure. The team of Boston researchers has formed Frequency Therapeutics, a company that is working on delivering the treatment option for clinical use. In a matter of months, it is expected that the team will begin its clinical trials on humans. The scientists working on this treatment options anticipate that it will pave the way for other experts in the field of hearing loss to pursue other techniques.
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