Download Stem Cells Restore Hearing in Deaf Gerbils

Angela Aldous
Bio 1615
Stem Cells Restore Hearing in Deaf Gerbils
Deafness can have any number of causes. One form of deafness is
caused by damage to tiny hair-like neurons in the ear called spiral ganglion
neurons (SGNs). This is called auditory neuropathy. The SGNs communicate
signals from the ear to the brain. While cochlear implants are able to improve
hearing in some patients, there is no current treatment for auditory neuropathy.
A group of researchers at the University of Sheffield in the UK decided to study
the effect of stem cell therapy on this form of deafness1. The group hypothesized
that if they implant specialized human embryonic stem cells into a damaged
gerbil ear, the cells will grow into new SGNs and restore hearing in the gerbils.
Embryonic stem cells have the ability to transform into different cell types
and also to replicate indefinitely. Scientists use the plasticity of the stem cells in
order to generate specific cells for testing. In this case, the research group
started their experiment by collecting human embryonic stem cells and
differentiating them for development into auditory nerve cells. In order to create
cells destined to be ear cells (otic progenitors), the researchers treated the stem
cells with fibroblast growth factors (FGF). These specific growth factors (FGF3
and FGF10) are molecules that stimulate the cells to develop as otic progenitors.
They created cell colonies that had the potential to become two different types of
ear cells—hair cells or neurons. The group was more interested in obtaining the
colony that could become neurons. The researchers applied a poison (ouabain)
to the ears of gerbils, significantly damaging the SGNs and leaving the rest of the
ear untouched. The researchers tested the hearing of the gerbils through a
Angela Aldous
Bio 1615
method called Auditory Brainstem Response (ABR). They assessed the activity
in the brain to determine the response to noise. The auditory response of the
gerbils measured at around 20 decibels before the treatment. After the
application of ouabain, the gerbils had little response at 80 decibels and were
effectively deaf. The researchers then transplanted the differentiated neuron
cells into the ears of some of the gerbils. The researchers tested the auditory
response of both the experimental and control groups of the gerbils over a period
of ten weeks.
Within a couple of weeks, the gerbils with the transplanted cells began
growing new neurons that connected to the brain stem. As they tested the
auditory response of the gerbils, the control group exhibited minimal
improvement over time. The experimental gerbils started showing improvement
after a few weeks. 10 weeks after transplantation, they exhibited an average of a
46% improvement in their auditory response.
The improved hearing in the transplanted gerbils supports the hypothesis
of implanted stem cells restoring damaged SGNs. The experiment demonstrates
the use of embryonic stem cells to repair sensory functions. The particular type
of hearing loss in the gerbils is rare, but it does show the ability of the stem cells
to regenerate as SGNs. While additional research and testing needs to be done,
this could lead to treatment for those patients with auditory neuropathy in the
future.
1
Chen W, Jongkamonwiwat N, Abbas L, Eshtan SJ, Johnson SL, Kuhn S, Milo M, Thurlow JK, Andrews PW, Marcotti W,
Moore HD, Rivolta MN. “Restoration of auditory evoked responses by human ES-cell-derived otic progenitors.” Nature.
2012 Sep 12. doi: 10.1038/nature11415.