By Will Dunham
WASHINGTON
(Reuters) - A common hormone-based mechanism seems to regulate
the aging process in a variety of organisms, scientists said on
Thursday in a finding that raises the possibility that hormonal
therapy could add decades to the human life span.
Three studies
appearing in the journal Science show that the insulin-signaling
pathway, already known to regulate aging in roundworms, serves
the same function in fruit flies and the simple life form yeast.
Scientists
studying fruit flies at Brown University in Providence, Rhode
Island, and University College London found that manipulating
genes relating to insulin-like hormones greatly extended the insects'
life span. Some of the flies lived up to 85 percent longer than
usual. But the longer-living flies all were dwarfs.
Similar work
by University of Southern California experts produced up to a
three-fold increase in yeast life span.
Insulin controls
blood sugar levels in humans, and defects in the insulin system
result in diabetes.
``What's exciting
about these findings is that they suggest that there is a genetic
system common to all animals that regulates aging,'' said David
Gems of University College London. ''If we just could tap into
the mammalian version of that system, it might be possible to
retard or even reverse human aging -- at least, in principle.''
Marc Tatar,
who led the Brown team, said insulin-like compounds control aging
in flies, worms and probably humans either by retarding growth
or by activating specific endocrine tissue to release other hormones.
``We can uncover
the basic science of aging using flies and worms, and then it's
not far fetched to think that's what's happening in us, too,''
Tatar added. He noted that the neuro-circuitry in human brains
is similar to that of flies.
Tatar said
no one knows which brain signals or external environmental signals
turn on the human aging mechanism.
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He said the
findings hint at the possibility in the future of employing a
type of hormonal treatment to extend the life span of people.
``I can see it,'' Tatar said.
``I think
it might be possible to modulate the key hormones -- growth hormone,
thyroid hormone, insulin growth factor,'' Tatar added. ``And if
we can modulate those in a healthy range -- maintain our health
but toward a level that can permit us to slow aging -- I think
it's possible to do it.''
He said experiments
involving mice suggested that about 40 healthy years could be
added to the human life span.
Tatar's team
isolated in fruit flies a gene with function in the brain called
an insulin-like receptor (InR). The gene is analogous to those
in species throughout the animal kingdom.
InR in flies
responds to a form of insulin. As a result, brain cells tell a
thyroid- or pituitary-like system to release a second hormone,
called juvenile hormone. This compound circulates in the body,
unleashing a chain of other events that trigger reproduction and
rapid aging, the scientists said.
The Brown
researchers bred fruit flies with mutant InR in a bid to suppress
the release of juvenile hormone and arrest the aging process.
The experiment yielded dwarf females with life spans extended
by up to 85 percent. Dwarf males also were produced, but they
were frail and most died within 20 days.
Worm Research
Earlier research
on roundworms found that defects in two genes, called daf-2 and
age-1, doubled and even tripled worm life span. Humans possess
genes very similar to daf-2 and age-1 that generate part of a
hormone response system that is sensitive to insulin and its hormonal
cousin insulin-like growth factor I (IGF-I). IGF-I controls growth,
and defects in the IGF system cause dwarfism.
University
College London researchers bred mutant fruit flies with defects
in the fly equivalents of daf-2 (InR) and age-1 genes, as well
as a third insulin-related gene, called chico. It turned out that
both chico and InR regulated aging, the said. In fact, the female
chico mutant flies lived up to 48 percent longer than normal but
were dwarfs.
The researchers
said IGF-I levels may affect the rate of aging in mammals, including
people, meaning less IGF-I causes longer life. Gems said that
in theory, a drug that would manipulate IGF-specific signaling
in the brain could extend the human life span. He said that after
10 to 20 years of experiments, scientists might have an idea of
how to apply the results to people without involving dwarfism.
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