The sound-detecting hair cells of the inner ear can be grown in the lab from embryonic stem cells, US scientists have shown. The work raises another possible alternative to cochlear implants for treating deafness.
Hair cells convert sound waves into electrical signals that go to the brain. In mammals including humans, these cells die off with age. The result is irreversible hearing loss.
Stefan Heller's team at the Massachusetts Eye and Ear Infirmary in Boston generated the hair cells by exposing mouse embryonic stem cells - which are capable of turning into any type of cell - to the chemical factors that a normal hair cell would encounter.
To see if these lab-grown cells would make themselves at home in a developing ear, Heller transplanted partially developed cells into chicken embryos. The cells continued to develop, behaving just like the hair cells the chicken already had.
However, while the cells look normal, Heller does not yet know if the lab-grown hair cells will function like the cells that developed in an animal. His next step is to see if cell transplants can restore hearing in hard-of-hearing mice.
One encouraging sign is that the stem cells formed connections with neurons in the same petri dish, a crucial characteristic of hair cells in an animal.
Another group has shown that gene therapy can turn other inner ear cells into hair cells (New Scientist print edition, 7 June 2003).
The advantage of using embryonic stem cells is that great numbers of hair cells could be grown says Yehoash Raphael, a hair cell expert at the University of Michigan Medical Center. However, unlike gene therapy, there could be problems with immune system rejection of transplanted cells.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.2334503100)
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