The IU group, led by Eri Hashino, Ph.D., was able to transform, in the laboratory, stem cells taken from adult bone marrow into cells with many of the characteristics of sensory nerve cells -- neurons -- found in the ear. The results suggest that these adult stem cells could be used to treat deaf patients in the future, said Dr. Hashino, an associate professor and Ruth C. Holton Scholar in the Department of Otolaryngology -- Head and Neck Surgery.
The cells used in the research are called marrow stromal cells -- a type of stem cell from which fat, bone and cartilage normally develop.
"We were interested in marrow stromal cells because of their potential for use in autologous cell-based therapy," said Dr. Hashino, referring to cell transplantation in which a patient's own cells are used in treatment. The cells can be collected easily and kept alive in the laboratory until needed, she said.
Other researchers had previously shown that the marrow stromal cells could be induced to transform into neuronal cells, but it wasn't clear whether, or how, the cells could be further transformed into useful specialized neurons.
In a two-step process, Dr. Hashino and her colleagues first cultivated mouse marrow stromal cells with chemicals known to encourage stems cells to change into primitive neurons. The bone marrow cells took the shape and other characteristics of neurons. Next, they exposed the cells to two molecules that are secreted from nearby tissues of the ear during embryonic development. The two molecules -- known as Sonic hedgehog and retinoic acid -- together caused the marrow stromal cells to further develop into cells with many of the characteristics of auditory neurons, such as the presence of specific genes and proteins.
Dr. Hashino said she and her colleagues are beginning new experiments to test the feasibility of marrow stromal cell transplantation to stimulate the growth of the nerve cells that are often missing from the inner ears of patients with profound hearing loss.
"Sonic hedgehog and retinoic acid are molecules found in embryonic tissues, but not in adult tissues," said Dr. Hashino. "This suggests that treating marrow-derived stem cells with these molecules before transplantation might greatly enhance the possibility that the process would result in development of specific sensory neurons."
The research was published March 18 in the online early edition of the Proceedings of the National Academy of Sciences, and is scheduled to appear in the print edition of the journal March 29.