专四晨读美文：Exercise and Longevity

Exercise and Longevity
ONE sure giveaway of quack medicine is the claim
that a product can treat any ailment.
There are, sadly, no panaceas.
But some things come close, and exercise is one of them.
As doctors never tire of reminding people,
exercise protects against a host of illnesses,
from heart attacks and dementia to diabetes and infection.
Dr Levine and her team were testing a theory
that exercise works its magic,
at least in part, by promoting autophagy.
This process, whose name is derived
from the Greek for "self-eating",
is a mechanism by which surplus,
worn-out or malformed proteins and other cellular components
are broken up for scrap and recycled.
To carry out the test,
Dr Levine turned to those stalwarts of medical research,
genetically modified mice.
Her first batch of rodents were tweaked
so that their autophagosomes-
structures that form around components
which have been marked for recycling-glowed green.
After these mice had spent half an hour on a treadmill,
she found that the number of autophagosomes in their muscles
had increased, and it went on increasing
until they had been running for 80 minutes.
To find out what, if anything,
this exercise-boosted autophagy was doing for mice,
the team engineered a second strain
that was unable to respond this way.
Exercise, in other words,
failed to stimulate their recycling mechanism.
When this second group of modified mice
were tested alongside ordinary ones,
they showed less endurance
and had less ability to take up sugar from their bloodstreams.
There were longer-term effects, too.
In mice, as in people, regular exercise helps prevent diabetes.
But when the team fed their second group of modified mice
a diet designed to induce diabetes,
they found that exercise gave no protection at all.
Dr Levine and her team reckon their results suggest
that manipulating autophagy
may offer a new approach to treating diabetes.
And their research is also suggestive in other ways.
Autophagy is a hot topic in medicine,
as biologists have come to realise
that it helps protect the body from all kinds of ailments.