Cloned Cows Cells Stay Young
by LAURAN NEERGAARD, AP Medical Writer
WASHINGTON, April 27, 2000 (AP) - Massachusetts scientists have cloned
six cows that show none of the worrisome premature aging reported for
Dolly the sheep. In fact, the cows' cells seem to have a surprisingly
prolonged youth, a new study shows.
The finding is important because it could erase doubts about trying to
use cloned cells to fight diseases, doubts raised when scientists
discovered Dolly's cells appeared older than she was.
But the cloned cows - the oldest turned a year old this week, while the
others are 7 months old - have cells that appear as young as the cells
of newborn calves, researchers with the biotechnology company Advanced
Cell Technologies report in Friday's edition of the journal Science.
Unlike Dolly, the cows were cloned from cells nearing the end of their
lifespan. If even very old cells can have their "aging clock"
essentially rewound, then scientists might one day be able to clone
customized replacement tissues for patients suffering diabetes,
PARKINSON'S or other diseases, say experts on cellular aging.
Does it also mean the cloned cows could live longer than normal? Maybe,
says Advanced Cell Technologies' chief scientist, Dr. Robert Lanza.
"There's a chance these could be the longest-lived cows on the planet."
But no one will know that for years, cautioned Thoru Pederson, a
cellular biologist at the University of Massachusetts Medical School.
After all, cows typically live 20 years, and there's more to aging than
the cellular characteristic the company is investigating.
"It's important not to overdramatize this as a 'fountain of youth'
thing," stressed one of the nation's leading experts on cellular aging,
Jerry Shay of the University of Texas Southwestern Medical Center.
Instead, Shay says, the study provides "the first very dramatic proof"
that people's very old cells could one day be rejuvenated for tissue
engineering.
Cells can divide only a certain number of times before they die - about
70 times for human cells; around 60 times for cows.
All chromosomes have protective tips called telomeres that prevent a
cell's genetic code from fraying during this cellular division. But each
time the cell divides, the telomere gets a little shorter. It eventually
becomes too short to protect the chromosome, so the cell can no longer
divide and eventually dies.
Dolly was the first large animal to be cloned from genetic material
extracted from an adult cell. She seems healthy. But last year,
scientists discovered her telomeres were too short - while she was just
3, her genetic material was aging at the rate of the 6-year-old sheep
from which she was cloned. Not only did that suggest Dolly could age and
sicken prematurely, it meant any cloned cells one day developed as
medical treatments might be too old to last in the body and fight
disease.
Now Advanced Cell Technologies has discovered the opposite effect: Its
six new cloned cows have telomeres significantly longer than regular
cows the same age - in other words, the cells look far younger than
expected.
When cloned cow cells were put in a lab dish, they divided more than 90
times before dying, the researchers report in Science.
And the company just had four new calves born last month that had
telomeres "longer than any I've ever seen," Lanza added.
Why? Nobody knows.
The cow cloning process is done a little differently than Dolly was
cloned. The sheep was cloned from a cell that temporarily stopped
dividing, not a terribly old cell. In contrast, Lanza let cow cells
divide in a dish for several months until they were at the very end of
their lifespan, a period called senescence. He cloned only the oldest of
these old cells, ones with incredibly short telomeres.
One theory: Putting super-old genetic material into an egg - the next
step in cloning - may prompt the egg to overreact and ensure it produces
an embryo with extra-long telomeres, Shay said.
"This is good news, "said Huber Warner, associate director of the
National Institute on Aging. "This says telomeres can be repaired."
Copyright © 2000 The Associated Press.
--
Judith Richards, London, Ontario, Canada
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