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Stem cell therapy for hearing loss?
SHEFFIELD, U.K.—Researchers at the University of Sheffield recently reported that they have found a way to turn human stem cells into ones that behave like sensory hair cells—also known as auditory neurons—which could theoretically be surgically inserted into the ear to restore lost hearing.
The research, funded by the Royal National Institute for Deaf People (RNID) and Deafness Research UK, has also resulted in a peer-reviewed journal article to be published in the May issue of Stem Cells, as well as a presentation on April 6 at the UK National Stem Cell Network annual science conference in Oxford, U.K.
"The potential of stem cells is very exciting. We have now an experimental system to study genes and drugs in a human context," notes one of the lead researchers, Dr. Marcelo Rivolta, a senior research fellow at the University of Sheffield. "Moreover, these cells would help us to develop the technologies needed to deliver them into damaged tissues, such as the cochlea, in order to restore the different cell types. This should facilitate the development of a stem cell treatment for deafness."
Currently, there is no way to repair hair cells, which are the cells that detect sound. Once they have been damaged, the resulting hearing loss is permanent. In addition to those people who have lost hearing due to damage to the hair cells, therapies potentially arising out of this research might also help some people born with inherited hearing problems, the researchers speculate.
An analysis of the research by the United Kingdom's National Health Service (NHS) notes that the Sheffield team's work has indeed shown that embryonic stem cells can be isolated from tissue from part of the human fetal inner ear and can then be grown in the laboratory so that they develop into cells with hair cell and nerve cell-like characteristics.
"However, the hair cells were not fully developed, and did not show the typical hair-like projections from their surfaces," the NHS points out. "As such, further experiments will need to investigate whether these cells can become fully functional cells."
This is not a fact lost on the researchers, for whom this is the next step planned in their research. And so far, they have only tried inserting the auditory cells into animal models. Regardless, though, they believe their findings are something about which to be excited.
"Stem cell therapy for hearing loss is still some years away, but this research is incredibly promising and opens up exciting possibilities by bringing us closer to restoring hearing in the future," says Dr. Ralph Holme, director of biomedical research at RNID.
Looking to the larger issue of stem cell research, Vivienne Michael, chief executive of Deafness Research UK, says, "This study highlights the importance of stem cell research. In addition to the future potential for restoring hearing with stem cell therapy, the recent research success means that we may now have better ways to test the efficacy and toxicity of new drugs on auditory cells."
To carry out this early phase of their research, the team obtained cochlear tissue from human fetuses aged nine to 11 weeks, which were retrieved from terminated pregnancies, having previously obtained ethical approval and informed consent to use this tissue. The researchers dissolved pieces of the cochlear tissue to release the individual cells so they could grow them with various chemicals that have previously supported the growth of stem cells.
The researchers identified stem cells by looking at the genes that were switched on in these cells and examining what proteins were being produced, with an eye toward those that typically express genes called SOX2 and OCT4. Once the researchers confirmed that they had isolated stem cells, they investigated how long they could keep the cells alive in the laboratory, and whether the cells had the ability to develop into the sensory hair cells and nerve cells found in the ear. The cells continued to divide in vitro for seven to eight months, after which time they could live for another four to five months, but would no longer divide. This timeframe is similar to what researchers have seen in other non-embryonic stem cell populations, such as bone marrow.