Utilizing genetic tools in mice, researchers at Johns Hopkins Medicine state they have actually identified a pair of proteins that exactly control when sound-detecting cells, called hair cells, are born in the mammalian inner ear. The proteins, explained in a report released June 12 in eLife, might hold a crucial to future treatments to restore hearing in people with irreparable deafness.
" Scientists in our field have actually long been searching for the molecular signals that set off the formation of the hair cells that sense and send noise," states Angelika Doetzlhofer, Ph.D., associate professor of neuroscience at the Johns Hopkins University School of Medicine. "These hair cells are a major player in hearing loss, and knowing more about how they develop will help us find out methods to replace hair cells that are damaged."
In order for mammals to hear, sound vibrations travel through a hollow, snail shell-looking structure called the cochlea. Lining the inside of the cochlea are two types of sound-detecting cells, inner and external hair cells, which communicate sound details to the brain.
An estimated 90% of genetic hearing loss is brought on by issues with hair cells or damage to the auditory nerves that connect the hair cells to the brain. Deafness due to direct exposure to loud noises or particular viral infections occurs from damage to hair cells. Unlike their counterparts in other mammals and birds, human hair cells can not regenerate. So, as soon as hair cells are harmed, hearing loss is most likely permanent.
Scientists have actually known that the primary step in hair cell birth starts at the outermost part of the spiraled cochlea. Here, precursor cells begin changing into hair cells. Then, like sports fans performing "the wave" in an arena, precursor cells along the spiral shape of the cochlea become hair cells along a wave of transformation that stops when it reaches the inner part of the cochlea. Knowing where hair cells start their development, Doetzlhofer and her group entered search of molecular cues that were in the ideal location and at the correct time along the cochlear spiral.
Of the proteins the researchers examined, the pattern of two proteins, Activin A and follistatin, stuck out from the rest. Along the spiral course of the cochlea, levels of Activin A increased where precursor cells were becoming hair cells. Follistatin, however, appeared to have the opposite behavior of Activin A. Its levels were low in the outermost part of the cochlea when precursor cells were first starting to change into hair cells and high at the innermost part of the cochlea's spiral where precursor cells had not yet started their conversion. Activin A seemed to relocate a wave inward, while follistatin relocated a wave outside.
" In nature, we understood that Activin A and follistatin operate in opposite methods to regulate cells," says Doetzlhofer. "And so, it seems, based upon our findings like in the ear, the two proteins perform a stabilizing act upon precursor cells to manage the orderly development of hair cells along the cochlear spiral."