USC researchers reversed the hearing damage of the mice activating a regenerative capacity they have as infants and think it could help reverse permanent hearing loss in humans as well.
Permanent hearing loss is a common side effect of aging: it affects over 60% of people reaching retirement age.
Reversing hearing loss could improve the lives of tens of millions of people, enabling them to live independently and longer.
The special "gift" of hearing
The inner ear contains two types of sensory cells. There are "hair cells," which are hair-like and receive sound vibrations, and there are also support cells, which play a role in the structure and function of the inner ear.
Hair cells are very delicate. They can be damaged, up to the point of hearing loss, by loud noises, infections, certain medications and aging in general. The death of a single hair cell can heavily affect hearing and when a hair cell is gone, it's gone forever.
Or so we've always thought.
Restoration of hearing in mice
For about a week after birth, mice can reverse any damage to the ear and hearing by turning the supporting cells into cells ciliated. A process called "transdifferentiation".
In a new study, USC researchers determined that a molecule called H3K4me1 is the key to this regenerative capacity. It keeps the genes for hair cells "primed" within the supporting cells, like the players on the bench, ready to take the field.
If their hair cells are damaged, neighboring supporting cells transform and replace them. After a week of birth, however, mice lose this molecule and the ability to repair hearing loss.
The researchers gave the mice a drug that extended the presence of H3K4me1, and with it the regeneration capacity of hair cells.
From mice to men
Given the success of the tests in mice, the researchers suspect that humans could also reverse hearing loss through transdifferentiation.
Unlike mice, which have this "superpower" one week after birth, we lose this ability before we are even born.
Of course, if the team's hypothesis is right, it could trigger the growth of new hair cells in our ears and restore hearing ability. But how?
“Our study increases the possibility of using therapeutic drugs, gene editing or other strategies. We could make epigenetic changes that exploit the latent regenerative capacity of inner ear cells to restore hearing, "he said. Neil Segil, USC researcher.
Beyond the sound
Segil also speculated that someday this technique could also be used to regenerate other parts of the body.
"Similar epigenetic modifications may also prove useful in other non-regenerating tissues, such as the retina, kidneys, lungs and heart."