Deaf gerbils have recovered their hearing after human stem cells were
injected into their ears.
"It's a proof of concept,
and it's important because for the first time we've shown stem cells can be
used to repair the ear," says Marcelo Rivolta of the University of
Sheffield, UK, and head of the team that treated the gerbils.
Spiral ganglion neurons in the
ear convert mechanical sound vibrations into electrical signals that the brain
interprets as sound.
When these neurons get damaged or
die they can't be replaced. This results in a form of deafness called auditory
neuropathy, which affects about a tenth of deaf people, possibly as many as
300,000 in the UK alone, says Rivolta.
Cochlear implants can correct the
main form of deafness, which occurs when the cochlea loses hair cells that
register sound by bending. But neurons can't be substituted except through an
expensive, risky and invasive procedure to implant an electrode directly into
the brain.
Now, Rivolta and his colleagues
hope to develop much simpler treatments based on the so-called otic neural
progenitor stem cells they made in the lab from human embryonic stem cells, the
cells in embryos that can turn into all types of bodily tissues.
Restoring ganglion neurons
Rivolta's team injected about
50,000 of the otic neural progenitor cells into single ears of 18 gerbils. The
animals' spiral ganglion neurons had been deliberately destroyed with a drug
called ouabain, leaving them completely deaf. The stem cells were injected into
the cochlea through a tiny, drilled hole.
Post mortems showed that the stem
cells turned into specialised spiral ganglion neurons in the ear.
Within 10 weeks, about two-thirds
of the animals had recovered some hearing. On average, the animals recovered
about 46 per cent of their hearing, as measured by their ability to respond to
sounds of varying volume.
"In people, this would mean
going from only being able to hear a loud truck on the street to being able to
hold a conversation," says Rivolta. However, he adds that considerably
more work in animals is needed to refine the procedure – it will be years
before it can be tested in people.
The team also produced cells
similar to the hair cells that are damaged in the majority of deaf people, but
Rivolta says much more work is needed to turn these into fully functional hair
cells. "If we could replace hair cells, that would enable us to treat 80
to 90 per cent of all deaf people," he says.
Journal reference: Nature, DOI:
10.1038/nature.11415
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