| HHIssues@aol.com 2005-10-06, 10:26 pm |
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source: [HOH-LD-News] Volume 25 Issue 1
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- Article 2: The Origins of Regenerated Hair Cells - Part 1
by Cheryl Heppner
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Editor: The 2005 SHHH Convention's 12th Annual Research
Symposium was on the Origins of Regenerated Hair Cells. Those
who are following this research know that scientists are making
substantial progress towards the day when they'll be able to
regrow hair cells in humans; they also know that day is stills a
ways off.
Here's Cheryl's report on this very interesting symposium. If
you'd like to share this article, please be sure to credit NVRC.
(See credit at the end of the article.)
This is Part 1 of 2 parts.
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Dr. Jeffrey T. Corwin
Department of Neuroscience, university of Virginia
- The number of hair cells in both the inner and outer ear
declines as we age.
- Early research on fruit flies led to further research. In the
1970s Dr. Corwin was in the Central Pacific -- Enewetak Atoll --
studying how sharks could hear and locate sounds. In 1974 he
found that a juvenile shark had 20,000 hair cells but a mature
adult had 240,000 hair cells. In humans, nerve deafness is
permanent and we don't regenerate hair cells.
- Sharks, bony fish and amphibians get new hair cells from cells
that are regenerated when supporting cells divide.
- Doug Cotanche at the university of Hawaii did key research on
hair cell regeneration. He was studying birds for technical
reasons, and it was accidental that he exposed birds to loud
sounds, then got them to sit for 10 days. He found that one
preserved its cells immediately, and that stimulated interest.
The newly regenerated hair and support cells contained new DNA.
- A laser was used to focus inside a hair cell nucleus, and a
pulse was given to shoot and kill them. Time-lapse photography
showed that support cells nearby divided and reproduced.
- In non-mammals, hair cell regeneration goes in stages. The
support cells lose their specialty, divide and become two cells.
The offspring can specialize as either a supporting cell or hair
cell. The default fate is to become a hair cell unless the cell
is inhibited from adapting that fate. Replacement hair cells
form synapses and restore hearing and balance function.
- One graduate student liked to tell others that if they were at
a rock concert, and stood next to a speaker for a certain amount
of time with a chicken, the chicken's hair cells would grow back
in 10 days but human hearing loss would be permanent. We're
trying to become more like chickens.
- Can mammals regenerate hair cells? Tissue from a 52-year-old
patient that would normally be discarded was brought back to the
lab. They wanted to see if it had the machinery to regenerate.
The result was encouraging. Replicated DNA showed new cells
could form in hair cell organs in mature human ears.
- It showed the machinery can occur in older mammals, with
hundreds of cells in a human. But in a bird you would have seen
tens of thousands of hair cells.
- The question then becomes: Can we enhance the occurrence of
cell divisions in mammal ears through supporting cells and wake
up the regeneration machinery in the ear? Or as some scientists
like to say, "a way to step on the gas pedal."
- In tissue culture we can now strongly enhance the
proliferation of supporting cells in the mammalian ear with two
drugs --forskolin and a biotech drug rhGGF2.
- So what are the limits of regeneration? One is the age of the
animal. In examining tissue of a newborn, during the first
couple of weeks of life, supporting cells were found to be
becoming quiescent.
- Microsurgical cuts were made, and these excision wounds healed
rapidly in ears from embryonic mammals.
- Persistent hearing and balance losses are all too common and
result in the loss of one type of cell. That just one type of
cell is responsible is very important to pharmaceutical and
biotech companies. Whether it is a bird or fish, all lose
hearing for the same reason.
- Animal models for damage that results in hearing and balance
loss are truly representative of humans.
- Supporting cells are the source of the cells that specialize
as hair replacement cells.
- What is reasonable to expect from research in regeneration?
We could get a major breakthrough at any time. Often
breakthroughs are just an accident when scientists are looking
for something else. Research is moving faster and faster. Most
people in research are optimists.
- Steps needed for hair cell regeneration:
1. Induce cell production
2. Suspend quiescence
3. Induce differentiation (specialization of new cells as
replacement hair cells)
Q: Why did mammals lose the ability to regenerate hair cells?
A: There's no clear reason why it would be an advantage to lose
hair cells. What's unique about our hair cells is that they
have a single-file line, very structured. At no place else in
the body do cells line up in such order. We don't know any
reason why evolution would have caused that.
Q: We don't have a Nancy Reagan to support this research, and
the deaf community opposes it. What should be done?
A: It's completely different for people born deaf than those
who develop hearing and lose it. That point needs to get
across. We now have only about 1/3 of the funding needed for
this level of research and the proposed federal budget cuts this
amount. Only about 2/3 of the work underway will continue to be
funded if that amount is not increased.
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(c)2005 by Northern Virginia Resource Center for Deaf and Hard
of Hearing Persons (NVRC), www.nvrc.org. When sharing this
information, please ensure credit is given to NVRC.
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