Using hereditary tools in mice, researchers at Johns Hopkins Medicine say they have determined a pair of proteins that exactly manage when sound-detecting cells, called hair cells, are born in the mammalian inner ear. The proteins, explained in a report published June 12 in eLife, may hold an essential to future treatments to restore hearing in individuals with permanent deafness.
" Scientists in our field have actually long been looking for the molecular signals that activate the formation of the hair cells that pick up and transfer sound," says Angelika Doetzlhofer, Ph.D., associate teacher of neuroscience at the Johns Hopkins University School of Medicine. "These hair cells are a significant player in hearing loss, and understanding more about how they establish will assist us determine methods to change 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 within the cochlea are two kinds of sound-detecting cells, inner and external hair cells, which communicate sound information to the brain.
An estimated 90% of genetic hearing loss is triggered by problems with hair cells or damage to the auditory nerves that link the hair cells to the brain. Deafness due to exposure to loud noises or certain viral infections develops from damage to hair cells. Unlike their counterparts in other mammals and birds, human hair cells can not regrow. So, when hair cells are damaged, hearing loss is likely permanent.
Researchers have actually understood that the primary step in hair cell birth begins at the outer part of the spiraled cochlea. Here, precursor cells start changing into hair cells. Then, like sports fans carrying out "the wave" in an arena, precursor cells along the spiral shape of the cochlea turn into hair cells along a wave of improvement that stops when it reaches the inner part of the cochlea. Knowing where hair cells start their advancement, Doetzlhofer and her team went in search of molecular cues that remained in the best location and at the ideal time along the cochlear spiral.
Of the proteins the researchers analyzed, the pattern of two proteins, Activin A and follistatin, stood apart 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 very first starting to change into hair cells and high at the innermost part of the cochlea's spiral where precursor cells hadn't yet started their conversion. Activin A seemed to relocate a wave inward, while follistatin moved in a wave outside.
" In nature, we understood that Activin A and follistatin work in opposite methods to control cells," states Doetzlhofer. "And so, it appears, based on our findings like in the ear, the two proteins perform a balancing act on precursor cells to manage the organized formation of hair cells along the cochlear spiral."