Reduce,
recycle and rebuild is as important to the most basic
component of the human body, the cell, as it is to the
environment. And a University of Florida study shows
just how much the body benefits when it “goes green,”
at least if you’re a rat: Cutting calories helps
rodents live longer by boosting cells’ ability to
recycle damaged parts so they can maintain efficient
energy production.
“Caloric restriction is a way to extend life in
animals. If you give them less food, the stress of
this healthy habit actually makes them live longer,”
said Christiaan Leeuwenburgh, chief of the division of
biology of aging in UF’s Institute on Aging.
Understanding how the process works at the cellular
level in rodents could help scientists develop drugs
that mimic the process in humans, Leeuwenburgh added.
How does it work? During the aging process, free
radicals – highly reactive byproducts of our cells’
respiration – wreak havoc on our cellular machinery.
Mitochondria, the tiny power plants that keep a cell
functioning, are especially vulnerable to this type of
damage. The effects can be disastrous – if
malfunctioning mitochondria aren’t removed, they begin
to spew out suicidal proteins that prompt the entire
cell to die. Cell death, on a whole-body scale, is
what aging is all about.
Fortunately, younger cells are adept at reducing,
recycling and rebuilding. In this process, damaged
mitochondria are quickly swallowed up and degraded.
The broken down pieces are then recycled and used to
build new mitochondria. However, older cells are less
adept at this process, so damaged mitochondria tend to
accumulate and contribute to aging.
“Cell survival is dependent upon the ability of the
cell to reduce and recycle by a mechanism called
autophagy,” said William Dunn Jr., a professor of
anatomy and cell biology in UF’s College of Medicine
and senior author of the study, which was published
online this month in the journal Rejuvenation
Research. “When a cell is under stress, autophagy is
turned on to clean up the cell by removing damaged
cellular components, while recycling building blocks
necessary to rebuild the cell. It’s there to protect
the cell. But in aged cells, they’re basically not
able to adjust to stress as well.”
UF scientists studied 22 young and old rats,
comparing those allowed to eat freely with those fed a
low-calorie, nutritious diet. The stress of a
low-calorie diet was enough to boost cellular cleaning
in the hearts of older rats by 120 percent over levels
seen in rats that were allowed to eat what they
wanted. The diet had little or no effect on younger
rats.
“Autophagy is a housekeeping mechanism that keeps
cells free of damaged and thereby detrimental
mitochondria and other toxic materials while recycling
their building blocks - nutrients needed by the cell,”
said Stephanie Wohlgemuth, a lecturer in UF’s
department of aging and geriatrics and the study’s
lead author. “So if that process is maintained with
age — or even increased — that can only be
beneficial.”
To determine how dietary restriction boosted cells’
ability to reduce the toxic trash, the scientists
studied how the amount of certain proteins changed
with the rats’ age and diet. They found that some
proteins responsible for degrading the damaged parts
of the cell by autophagy were more abundant in older,
calorie-restricted rats.
Boosting autophagy is especially important in the
heart, a vital organ packed with mitochondria,
Wohlgemuth said. Swift disposal of damaged cellular
components is essential to maintaining an abundance of
healthy heart cells as we age.
“Cardiac cells have lost the capability to divide
readily to replace dying cells. So the maintenance of
the cells’ survival mechanisms is crucial for the
heart,” Wohlgemuth said.
Now that some of these proteins have been
identified, UF researchers say the next step is to
figure out how the proteins can be activated without
inflicting dietary stress.
“What if we bypass the caloric restriction and find
a way of increasing autophagy?” asked Dunn. “That is,
instead of starving yourself you can find another way
of enhancing autophagy that will allow the enhanced
removal of various damaged organelles that accumulate
in aged cells.”
