models such as worms, flies, and mice that would not be
Macaca mulatta
possible in humans. They also can better isolate the variable
BIOLOGY OF AGING: RESEARCH TODAY FOR A HEALTHIER TOMORROW 9
they want to investigate because animal studies
biological pathway. Sometimes it does not.
are conducted in tightly controlled environ-
Part of the reason might be that while mice,
ments. The animals typically have a very struc-
for example, have only a slightly larger number
tured daily regimen with limited exposure to
of genes than worms, and the genes in mice
pollutants, stressors, or other elements that
and worms serve similar functions, the activ-
could otherwise affect lifespan and health span. ity of mouse genes is different and somewhat Different types of studies use different
more complex than that of worms. As a result,
animal models. Animal models with a short
a genetic intervention that increases a worm’s
lifespan take less time and fewer resources
lifespan by fourfold might have a significantly
to study from birth to death and to test inter-
less impressive effect on a mouse’s lifespan.
ventions that might affect the aging process.
For similar reasons, an intervention might be
Scientists might favor a fruit fly when studying
promising in mice, but that does not mean it
a possible genetic target for an intervention to
will work the same way or at all in humans.
increase longevity, for example, because their
Studies in animal models closer to
average lifespan is only 30 days. This allows
humans, such as monkeys or other nonhuman
researchers to measure the effects in about a
primates, can be key to understanding how
month. The roundworm’s 2- to 3-week lifespan
basic discoveries might apply to humans.
makes it another ideal model for identifying and They are essential for pre-clinical studies, studying genes that might affect longevity. In a
an intermediary step between research in
landmark study, NIA-funded researchers found
animal models like mice and clinical studies
that reducing the activity of a set of genes, called in humans. Studies in nonhuman primates, for daf, increased roundworm lifespan by three- or
example, have demonstrated to NIA researchers
even fourfold. Daf genes are involved in the
how normal age-related changes in the heart
roundworm’s ability to enter a type of hiberna-
influence risk of heart disease. They have also
tion stage, called diapause, to survive periods of
been important for testing interventions to
food scarcity. This research would not have been lower risks of heart disease, such as drugs to as feasible if conducted using an animal model
decrease blood vessel stiffness.
with an average lifespan of 10 or 20 years.
So, if something works to slow aging in
After scientists establish a possible inter-
mice, worms, fruit flies, or monkeys, does
vention in one animal model, they then apply
that mean it will definitely work for you?
the intervention to increasingly complex
The answer is no. Certainly, data from animal
organisms. They might work their way up
studies provide critical insights to the aging
from worms or flies to mice and then to larger
process and can form the basis for testing
mammals, such as nonhuman primates. At each potential interventions. But direct testing in step, researchers carefully study if the interven-humans is essential before an intervention
tion has the same effect on the comparable
can be considered safe and effective.
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