Summary: Researchers at Kyoto University in Japan recently discovered a way to solve a problem facing the scientific community in transplanting stem cells. Stem cells are thought to hold the potential to restore damaged hair cells in the cochlea that contribute to both hearing loss and tinnitus in many patients. However, in past experiments, transplantation of stem cells into the damaged areas has produced only varying results, and a challenging problem that prevents successful stem cell transplantation is to avoid stem cell deaths. Stem cells often die due to failure to bypass the glial scar, a hallmark of neural damage that is thought to act as a barrier for cell transplantation. The scientists at Kyoto University discovered that applying new stem cells to the surface of the glial scar rather than underneath it helps their survival. They reported that the survived stem cells were able to grow from the damaged segment of the auditory nerve, which then travel from the cochlea to the brainstem, the part of the brain which controls flow of messages between the brain and the rest of the body – in this case, the ear - and eventually restored remarkable auditory function. They discovered that auditory function was better restored with the new, surface transplantation method in comparison to previous direct transplantation.

Key Outcomes: This study suggests that surface stem cell transplant may become a powerful way to repair damage and restore lost function of auditory pathways.

Relevance to tinnitus/hyperacusis: The current scientific models of tinnitus and possibly hyperacusis indicate that impairments in the connection between external sound and the central nervous system are necessary for the onset of phantom sounds (tinnitus) or intolerance to sounds (hyperacusis). As is commonly the case with tinnitus, these impairments may be consequent to noise-induced damage to hair cells in the cochlea, or possibly damage directly to the auditory nerve that carries information about sound from the ear to the central nervous system. Thus, perhaps restoring normal functioning of these connections, as this new stem cell transplantation method in part seems to do, could mitigate or even in some cases eliminate tinnitus. The improved connections between the ear and the brain could also readjust the abnormally enhanced gain in the brain, thus lessening the symptoms of hyperacusis.

Study authors: Sekiya T, Holley MC, Hashido K, Ono K, Shimomura K, Horie RT, Hamaguchi K, Yoshida A, Sakamoto T, Ito J. Proceeds of the National Academy of Science.

http://www.ncbi.nlm.nih.gov/pubmed/26080415

ATA Summary completed by Ted Turesky, ATA Board of Directors and Jinsheng Zhang, Ph.D., Chair, ATA Scientific Advisory Committee