The nematode worm Caenorhabditis
elegans, often used as a research model, turned out to provide
evidence that a form of molecular garbage is associated with the aging
process, researchers say. (Image Courtesy NASA)
(Click image to enlarge)
New studies have provided evidence for a theory that garbage is a key cause of aging and death.
This doesn’t mean we are all fated to be buried in an avalanche of
overflowing landfill junk. The “garbage” referred to in this theory is
trash that, over a lifetime, gradually clogs up our cells.
This “garbage-accumulation theory” has gotten fresh support from
scientists who experimented with cells whose internal garbage-removal
systems were blocked.
Several theories of why we get old are under consideration by
scientists, another popular one being that DNA damage accumulates over
a lifetime and kills us.
Some of the
theories overlap, and many researchers believe more than one could be
correct; so the statement that one theory has gotten new support
doesn’t necessarily disprove other theories or invalidate past research.
But the findings could shed light on a key aspect of the aging problem, and help suggest possible future anti-aging therapies,
according to Yuri Stroikin of Linköping University, Linköping, Sweden, and
colleagues. The team conducted one recent study that they said supported the
garbage accumulation theory.
The theory holds that aging is the result of years of accumulated
damage to molecules important for our bodies’ functioning. The
molecules suffer damage largely as a result of power-generating
structures in each cell called mitochondria, which—not unlike man-made
produce harmful chemicals in addition to life-sustaining energy.
These chemicals, called free radicals, can wreak havoc on DNA and other
vital molecular structures inside the cell. Cells are not helpless in
the face of this damage; they have DNA-repair mechanisms as well as
systems for sweeping out the damaged material to make room for
But these sweeping systems don’t operate with perfect efficiency. The
result is an accumulation of damaged molecules that are under-efficient
or altogether worthless—molecular “garbage.”
According to the garbage-accumulation theory, this refuse builds up
until it starts seriously getting in the way of cellular business, if
not actively doing harm on its own. Eventually it reaches “a critical
level incompatible” with life, Stroikin’s team wrote in a paper
published in the January issue of the research journal
In the paper, Stroikin and his research team described experiments
they had done on cells treated with a chemical that blocks their
internal garbage-removal system, called autophagy. This treatment led
to an accumulation of “garbage” and sharply raised the chances that any
given cell would die as time progressed, the researchers found.
However, the treatment wasn’t harmful to cells that were given space to
constantly reproduce by division, the team found. This was also
consistent with the theory, they added, because it holds that one way
cells can evade death by garbage is by continuously dividing.
Cell division staves off the onslaught of trash by distributing the
debris evenly between the two daughter cells, halving each cell’s
But an organism’s cells don’t divide forever. After an animal reaches
adulthood, cell division slows down. This is when the problem begins,
according to the garbage-accumulation theory.
“Our results indicate that biological ‘garbage’ is, indeed, deleterious
for cells and ﬁnally kills them if accumulates in large enough
quantities,” Stroikin and colleagues wrote. A weakness of the study, he
acknowledged, is that individual cells are only a model of the aging
process, not the real process itself.
An important component of biological garbage is a thought to be a
substance called lipofuscin, a brownish pigment left over from the
body’s breakdown and cleanup of damaged blood cells. Being a
plastic-like material, lipofuscin is hard for the body to break down.
Lipofuscin builds up inside the heart of the body’s garbage-disposal
system itself: tiny sacs of digestive enzymes in each cell called
lysosomes, which are in effect cellular garbage bags.
In a more recent study, scientists found that quicker lipofuscin accumulation was associated with shorter lifespans in
roundworms, creatures often used as a research model for basic
molecular life processes.
Thus the buildup specifically characterizes “a physiologically aged
state rather than simply marking chronological time,” the researchers,
with Rutgers University in Piscataway, N.J., wrote in a paper
describing their findings. The paper appeared in the June issue of the
Stroikin and colleagues wrote that “accumulation of such biological
‘garbage’ seems to upset normal cellular functions, resulting in
decreased adaptability and ﬁnally in cell death. Cell division is
apparently a natural anti-ageing mechanism.”
Strokin and his team suggested that the garbage-accumulation theory
also fits with the fact that one of the few scientifically
well-established ways to delay aging is by nearly going on a
near-starvation diet. This “caloric restriction” extends lifespans by
roughly 35 percent to 65 percent in mice, a 1986 study found.
The prolonged fasting characteristic of caloric-restriction diets leads
to an increase in autophagy, the garbage removal process. This is
consistent with the garbage accumulation theory, because it predicts
better garbage removal would increase lifespans, Stroikin and
colleagues pointed out.
That caloric restriction would boost autophagy makes sense because
autophagy, seen from another point of view, is also a process in which
the body consumes its own tissues in order to feed itself in the
absence of other food. The word autophagy literally means self-eating.
These considerations may provide fodder for possible anti-aging therapies in the future, Stroikin and colleagues
added; one strategy might be seeking out treatments that stimulate these
Aubrey de Grey of the University of Cambridge, U.K., has proposed that
one solution might be to insert genes into the body that produce
enzymes that degrade lipofuscin. Certain bacteria and fungi possess
such genes. The strategy is “radical and challenging,” Stroikin and
colleagues suggested, but it might work.
June 18, 2005
Source: World Science