story to find out more.
The smaller fat cells
from normal-weight mice (top) have fewer macrophages (the dark-bordered areas)
than fat cells from obese mice (bottom). Macrophages mop up dead fat cells and,
in doing so, can emit inflammatory chemicals. Click images for more
information about them.
Dying Fat Cells Call for Molecular Rescue
By Rosalie Marion
Bliss March 3, 2006
Scientists have known that immune cells are responsible for most of
the inflammatory chemicals that are released within fat tissue--but they
haven't known why. Now a study published by Agricultural Research Service-funded
scientists shows that white blood cells, called macrophages, appear to rush to
dead fat cells to mop them up, the same way they surround a splinter lodged in
The study, authored by physician
Greenberg, cell biologist Martin Obin and colleagues, was published in the
Journal of Lipid Research. Both
scientists are with the
Metabolism Laboratory at the
Mayer USDA Human Nutrition Research Center on Aging at Tufts University in
The researchers found that as people gain weight, fat cells gradually
enlarge and eventually break down and die. When obesity continues over a period
of time, a cycle occurs in which new fat cells form to store the added fat,
then peak in size and finally die. The study showed that more than 90 percent
of the macrophages in the fatty tissue of obese mice and humans are located
around these dead fat cells. In addition, as the fat cells get bigger, the
prevalence of macrophages increases proportionally.
Because fat doesn't dissolve in the blood, the authors theorize that
the immune system is essentially sequestering the dead fat cells and gorging on
the leftover lipids and cellular debris. During that process, the macrophages
could emit potentially dangerous amounts of inflammatory chemicals.
In a scenario of molecular rescue gone awry, the new findings may
explain how enlarged fat cells, as found in obesity, promote obesity-related
complications such as insulin resistance, diabetes or heart disease.
about this research in the March 2006 issue of Agricultural Research
ARS is the U.S. Department of
Agriculture's chief scientific research agency.