umans are born with around 15,000 hair cells — think tiny, sound-sensing fibers — in each ear.
The cells can’t regenerate, though. Over time, loud noises, certain medications, and chemotherapy can kill them off and cause hearing loss. But scientists working with a mouse model and a donated cochlea have found a possible way to regenerate hair cells.
Here’s what biomedical engineer Jeff Karp of Brigham and Women’s Hospital said about the work, published in Cell Reports.
How do hair cells work?
The hair cells aren’t actually hair. They’re actually cells that have these cilia that move and what happens is that they’re able to detect sound. The hair cell converts that sound to an electrical signal, which connects to a neuron, which then signals sound to the brain. The hair cells are in the inner ear, which is also where the cochlea is. The cochlea is like a spiral. You have high frequency when you first enter, and it spirals until you get to low frequencies. That’s why when people have hearing loss, it affects the high frequencies first, because it’s closest.
Where did you turn to study hair cell regeneration?
We started in the intestine because it’s the most regenerative tissue in the human body. The entire lining of the intestine regenerates every four or five days. In the lining of the intestine, there’s a stem cell that’s really the workhorse making all the cell types in the epithelium. We spent some time trying to understand that biology and developing drug combinations that could target that cell to expand the numbers of the cells and control the differentiation.
How did that translate to cells in the ear?
We started looking to see there were similar regenerative cells in the body, and found these progenitor cells that are the precursor of hair cells. We took the molecules we used in the intestine and used them in inner ear and it worked. We were able to proliferate progenitor cells. Those progenitors could form hair cells, which were bona fide, functional hair cells. We did this in very young mice and adult mice. We also had a patient who had a tumor near the cochlea and we tested it on those cochlear cells, which expanded too.