Concert goers, loud music listeners, and basically anyone constantly around loud sounds may have something to look forward to in the near-to-far future. Researchers from the University of Virginia are looking into how humans who experience hearing loss may one day be able to regenerate the cells responsible for picking up sounds, similar to the way salamanders regrow their tails.
According to the National Institute on Deafness and Other Communication Disorders (NIDCD), which funded the research, almost 17 percent of U.S. adults have some degree of hearing loss. While the ability to hear diminishes with age — 47 percent of adults over 75 can’t hear properly — about 15 percent of children have low-frequency or high-frequency hearing loss of at least 16 decibels in one or both ears, the American Speech-Language-Hearing Association reports. But the promise of hearing might be most profound for the two to three children of every thousand who are born deaf.
By looking in the ears of chickens, which are able to regrow specialized hair cells in the cochlea — a small spiral structure within the inner ear — the researchers were able to get some insight into how humans might also be able to regenerate these cells. These cells are tuned to specific pitches due, in part, to where they’re located on the cochlea, as well as the amount and length of hair-like protrusions, called stereocilia, that are on them. “When you hear different sounds, not every single hair cell on the cochlea is responding, only the ones that are sensitive to specific sound frequencies,” Dr. Benjamin Thiede, lead author of the study, said in a press release.
Studying the chicken cells in lab dishes, Thiede and his team observed how two molecules, Bmp7 and retinoic acid, help new cells develop these specific properties. They found that Bmp7 begins the process of patterning the cells, after which retinoic acid helps the cell’s tiny hairs grow to a certain length. The key finding in their tests emerged, however, when they added more retinoic acid to the cells, and found that the bundles of hair grew longer, which meant they were more likely to capture low-pitched sounds. Conversely, inhibiting retinoic acid function resulted in shorter bundles, which are more likely to pick up high-pitched sounds.
“So the question is, are developmental signals like Bmp7 and retinoic acid involved in reestablishing the pattern of hair cells and restoring hearing to the regenerating cochlea?” Thiede said in the release. “If we look at the mammalian system, which can’t regenerate, are these signals lost? … Does the mammal turn off these important signals once development is completed, so they’re not reactivated for regeneration?”
Thiede’s research is the latest in a growing line of hearing loss-related studies. One from February also looked at regenerating these cells in the cochlea, although with the help of supporting cells in the ear. The researchers had already known that very small quantities of cells are able to regenerate, but by inhibiting a signaling pathway among cells in the ear, it could push more of the cells to differentiate into the specialized hair cells.
It’s obvious that these studies are still in their beginning phases, as hearing loss, along with blindness, are some of the more complex human disabilities to correct. Nevertheless, technology to help people hear is out there, and it’s more usable than ever.
Source: Thiede B, Mann Z, Kelley M, et al. A gradient of Bmp7 specifies the tonotopic axis in the developing inner ear. Nature Communications. 2014.