Located in the spiraled cochlea, the hearing portion of the inner ear, the hair cells transform the mechanical vibrations that enter the ear in the form of sound waves into chemical signals, which they then direct to the brain. Ping Chen, PhD, assistant professor of cell biology at Emory University School of Medicine, and her colleagues found that the development of cochlea and hair cells is dependent on a genetic pathway called the PCP (planar cell polarity) pathway.
Although some species, including birds, are capable of re-growing hair cells, mammals lack the ability to naturally regenerate hair cells. Thus individuals born with improperly developed hair cells, or those who lose them through trauma, disease, environmental factors or aging, cannot regain their hearing. Reports from the National Institutes of Health (NIH) indicate that severe hearing impairment affects 28 million Americans. That number includes the approximately 4,000 Americans each year who suffer from sudden deafness, and the roughly 12,000 children born each year with difficulty hearing.
Scientists have been optimistic that by discovering the genes involved in development of the ear they could learn the molecular and genetic basis for some forms of deafness and offer promises for future efforts in hearing restoration. For the past two decades they have understood that the unique asymmetrical shape of hair cells was an essential part of their proper function. However, it was not clear which genes were involved in the development of this polarized shape within the cochlea. By using mouse models, Dr. Chen and her research team discovered that the PCP pathway is involved in shaping the cochlea and the sensory hair cells. Mutations within this genetic pathway impact the shape of the cochlea and the polarity of the sensory hair cells that are essential for hearing.
"This basic molecular pathway is involved in regulating many other aspects of embryonic development in addition to the formation of the polarized structure of the auditory sensory organ," says Dr. Chen. "Finding out which processes are involved in the formation of these polarized cells is an essential, fundamental issue for both developmental and cell biologists."
Other authors of the study included Jianbo Wang and Anthony Wynshaw-Boris from the University of California San Diego School of Medicine, Sharayne Mark, Xiaohui Zhang, Dong Qian, Seung-Jong Yoo, Kristen Radde-Gallwitz, Yanping Zhang, Xi Lin from Emory University School of Medicine, and Andres Collazo from House Ear Institute.
The research was funded by the NIH and the Woodruff Foundation.