Hearing is one of the senses that is most impacted by aging. Progressive loss of hearing in humans occurs because the hair cells of the auditory system, which are instrumental to convert acoustic waves into perceptible sound, do not regenerate. Once a hair cell is lost, it cannot grow back. Hence, progressive hearing loss is one of the most common consequences of aging.
Hopefully, the groundbreaking work of a team of scientists at the Massachusetts Institute of Technology (MIT) could help change this reality. They are developing a drug-based treatment that stimulates the regeneration of new hair cells to restore hearing function.
Humans are born with the greatest amount of hair cells they'll ever have at any point in their life - 12 to 15 thousand per ear. As people age, this number drops to 3,000 - 4,000 hair cells per ear.
Hair cells are formed from the surrounding supporting cells. This is how the hair cells of some animals, unlike humans, regenerate. Based on the same principle, and using their previous experience at successfully generating new cells in the intestinal lining by stimulating the associated stem cells, the MIT scientists are now trying to enable the regeneration of hair cells in the auditory system. They have achieved positive results testing with cochlea cell samples from mice.
Through molecular exposure, they were able to control two signaling pathways — Wnt and Notch — to stimulate progenitor cell multiplication. These cells were then exposed to another set of molecules, which successfully stimulated them to differentiate into new hair cells. A treatment based on this technique could enable not only the regeneration of hair cells but also the growth of a custom-sized quantity of new hair cells (which could restore young-like hearing function in old people).
Scientists note that an actual treatment based on this technique would be even simpler given that the molecules and signaling pathways in the cochlea itself could trigger proper cell proliferation on their own. In theory, a single drug injection in the middle ear would be enough to cure deafness. This treatment looks so simple and promising that some members of the research team have already started a company called Frequency Therapeutics dedicated to develop an effective solution for humans. They plan to trial the method in humans within 18 months. According to the researchers Jeffrey Karp and Will McLean, another great benefit of this method is that it allows researchers to grow a large pool of cells for experimental and medical purposes.