Hearing Loss –
Researchers study method to regenerate Inner Ear Damage
April 28th, 2006
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Researchers from
Massachusetts General Hospital continue studies on hearing loss and
found that gene knockout affects different areas of the inner ear. The
researcher’s goal is to be able to regenerate the inner ear’s hair cells
that are responsible for converting sound into nerve impulses that is
then transmitted to the brain.
The current
research study is being reported in the upcoming issue of Proceeding of
the National Academy of Sciences and will also be published online as
well. The researchers focused on the suppression of retinoblastoma (Rb)
protein. They discovered that changing the protein had different
effects in the inner ear.
"In these first
studies of the role of the Rb protein in the ears of postnatal mice, we
have confirmed that – under the right conditions – mature hair cells can
go through the cell cycle and produce new, functioning hair cells. But
we've also confirmed that you need to block Rb reversibly and at an
early stage of development, otherwise the hair cells will die," said
Zheng-Yi Chen, DPhil, of the MGH Neurology Service who is the study's
senior author.
The hair cells are
very sensitive and can be damaged by loud noise, infections and toxins.
If damage occurs to the hair cells they die and cause hearing loss of
the inner ear.
In their first
study they used the Rb protein was blocked from being made in mice to
simulate hearing impairment. These genetically altered mice treated
with Rb protein had more hair cells compared to the normal mice at the
same embryonic developmental stage. The modified mice did not survive
past birth. They hair cells looked normal and they looked like they
were actively regenerating.
The current study
the researchers developed a new strain of inner ear Rb knockout mice
which some survived up to 6 months after birth. The Rb-negative
auditory hair cells in the born mice showed hair cells that were
dividing and growing. They found that the hair cells did not develop
properly and they eventually died with the mice becoming deaf around 3
months after being born.
The researchers
found that vestibular hair cells grew and matured in a normal manor even
as the Rb-knockout mice aged. In the adult Rb-knockout mice some mice
had vestibular function that allowed for them to have a sense of
balance.
"We've shown that
vestibular hair cell regeneration may be achieved and may be less of an
obstacle than auditory cell regeneration," Chen says. "Now we need to
find ways to create a similar system in the auditory cells, and this new
model will help us better understand the mechanisms behind functional
hair cell regeneration. Our next step will be developing a transient,
reversible block of Rb function to assess its role in both types of hair
cell." Chen is an assistant professor of Neurology of Harvard Medical
School.
Nicole Wilson
Best Syndication
Ear Nose and Throat Books
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