“Bionic Ear” Project Finds Stem Cells for Critical Inner-Ear Sensory Hairs

Newswise — Vanity aside, you've never seen the most important hairs on your head. They line your inner ear. When trauma, antibiotics, or aging damage these sensory hair cells, you will join the roughly 10 percent of the population with significant hearing impairment. At present, there is no "Inner Ear Hair Club for Men and Women." Your best long-term hope may come from a European research initiative working under the banner of "The Bionic Ear." In a paper delivered at the American Society for Cell Biology's 43rd Annual Meeting in San Francisco, the researchers report the isolation, at least in mice, of progenitor or adult stem cells from vestibular sensory epithelia (VSE) that the researchers were able to manipulate into becoming new sensory hair cells.

Funded by the European Commission, the sensory hair-cell part of the "Bionic Ear" project is a collaboration between the CNRS lab of Eric Scarfone at the University of Montpellier and the Karolinska Institute labs of Dongguang Wei and of Mats Ulfendahl in Stockholm. The VSE is a sensitive layer cake of specialized cell types, including sensory hair-cells, nerve endings and glial cells. For many years it has been thought that sensory hair cells and their connecting neurons were irreplaceable. This idea has been washed away by growing reports of novel stem cell populations elsewhere in the brain and nervous system. These European researchers decided to search for stem cells in the inner ears of adult mice.

Researchers carefully dissected VSE patches from adult mice inner ears, and then isolated only the hair cells and their non-sensory supporting cells. These cells were cultured in dishes for several weeks. When they added two specific growth factors (EGF and FGF2) the cells proliferated rapidly and filled the petri dishes. But were these proliferating cells truly adult stem cells, with the capacity to differentiate into all the different types in the VSE? To test this possibility, researchers changed the types of growth factors added, and found that cells could differentiate into neurons and glial cells. By adding retinoic acid to the serum, they caused cells to differentiate into new sensory hair cells. The specific identities of these cell types were confirmed by immunocytochemistry to verify the presence of characteristic marker proteins, and by labeling the nuclei with BrdU to identify newly-dividing cells.

Thus, the "Bionic Ear" project now has a stem cell population that can resupply the VSE. The next step is to see if these progenitors can be triggered into becoming functional neurons or working hair cells that could replace damaged elements. That breakthrough will be music to old ears.

Regenerative Potential of Adult Mammalian Inner Ear, D. G. Wei,1 M. Blanchard,2 C. B. Johansson*,3 N. Holmström,3 J. Frisen,3 M. Ulfendahl,1 E. Scarfone 2 ; 1 Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden, 2 CNRS, Universite de Montpellier 2, Montpellier, France, 3, Department of cell and molecular biology, Karolinska Institute, Stockholm, Sweden. *CBJ present address: Stanford University School of Medicine, Stanford, CA. Funding: European Commission RTD Contract: "Bionic Ear" (QLG3-CT-2000-1343)