Corwin’s research aims to reverse hearing
Take a chicken to a loud
rock concert and chances are the chicken will understand the lyrics
about as well as you will. But about 10 days later, while you
are suffering from irreparable hearing loss, the chicken will
begin to recover its hearing.
Is this weird? Sure. Most non-mammals — birds, amphibians,
fish — can regenerate the hearing and balance cells of the
inner ear throughout their lives. But mammals, including humans,
stop growing these cells while still in the womb, and will never
again grow new ones.
Unless Jeff Corwin has anything to say about it.
Corwin, a U.Va. professor of otolaryngology
is looking for ways to replace damaged hearing and balance cells
of the inner ear. All of his work is conducted in the lab on the
sensory cells of mouse, rat, and chicken specimens, but the work
should translate to humans.
“We hope that eventually our research
will improve the quality of life for people who suffer from hearing
loss and the balance disorders that currently are considered irreversible,”
he said. “The work may lead to the development of effective
More than 20 million Americans have persistent hearing loss, the
result of the loss of sensory cells. Many older people have balance
problems that also can result from losing balance cells in the
began his career at Cornell University as a biologist. He later
focused his studies on the inner ear detectors of sharks, skates
and rays at the University of Hawaii and the University of California-San
Diego, where he earned a Ph. D. in neurosciences.
He was fascinated to discover that sharks’ inner ears, which
were once considered primitive, actually had far more sensory
cells than the human inner ear because they were able to add new
hearing and balance cells throughout life. A juvenile shark has
about 20,000 cells, while an adult eventually generates 240,000.
Human ears have about 16,000 hearing cells at birth, and the number
declines with age.
“I became interested in trying to figure out whether regenerative
replacement could lead to recovery from cell loss,” Corwin
said. “I wrote a proposal to NIH to look for regeneration
and for ways to eventually stimulate replacement of damaged hearing
and balance cells in mammals.”
Corwin got the NIH funding, which has continued for 21 years.
He and his colleagues are getting closer to finding ways to stimulate
the regeneration of neurosensory cells and to preventing their
The hearing and balance cells of the inner ear are microscopic
and hair-like in structure. These sensory cells pick up the vibrations
of sound, and encode them as signals for the brain. Balance hair
cells also help us maintain balance by allowing our nervous systems
to rapidly and automatically reposition our eyes to compensate
for the motion of our head and stabilize our visual world as we
Corwin said we lose these cells throughout our lives as a normal
part of aging. We also can lose cells when exposed to loud noises,
infections and some medicines, such as certain antibiotics.
“Hearing loss and balance problems increase as people age,”
Half of all people over 70 have significant hearing loss and many
elderly people injure themselves from falls that may be related
to balance problems and loss of inner ear cells.
“There are profound psychological effects from loss of hearing,”
he said. “It can affect a person’s ability to interact
socially, although for people who are deaf from birth, the situation
is quite different.”
Corwin and his team conduct their research on cells in tissue
with colleagues at U.Va. and elsewhere they are using stem cells
to look for ways to specifically grow hearing and balance cells.
“We’ve been able to stimulate growth of mammalian
ear cells in culture,” Corwin said. “But we need to
understand a spectrum of molecular signals so we can control cell
replacement in the ear.”
Jason Meyers, Themis Karaoli, Dawn Davies, Mark Ranck and Victoria
Chiou in Corwin’s group are determining what causes hearing
and balance cells to stop growing in mammals. Understanding what
causes the halt is important to learning how to restart the process
and stimulate healing where there is damage.
Because stem cells have to specialize to become hearing and balance
cells, Corwin’s work draws on results from cancer research
and developmental biology. By understanding the molecular signals
that turn on or off the development of particular cells, scientists
could apply that knowledge to better understanding how normal
and cancerous cells proliferate.
Catharine Cowan, Jason Meyers, and Stefanie McCormack in Corwin’s
team use time-lapse micro-imaging of cell replacement and growth,
capturing images of the cells in culture every few minutes for
days. Then they can “turn the direction of time backwards”
by running the images in reverse for an action narrative that
visually tells how the replacement cells arose.
“If we could someday regenerate cells in the human ear,
we could see dramatic improvements for people with hearing damage,”
Corwin said. “This area of research may be one of the first
places where regenerative medicine could work.”