HOUSTON–(March 29, 2001) — An enzyme discovered by Baylor College of
Medicine researchers is critical to the metabolic pathway that governs
the body’s ability to burn fat and could open a door into new ways to
reduce obesity, diabetes and other fat-related human diseases.
In an article in the March 30 issue of the journal Science, Dr. Salih
Wakil described laboratory mice, whose genes were manipulated to make
them deficient in the enzyme acetyl-CoA carboxylase 2, or ACC2, as
being able to eat as much as 40 percent more than normal mice and weigh
10 to 15 percent less.
ACC1 and ACC2 are involved in producing malonyl-CoA, which is key to
the formation of fatty acids and to fat burning. Wakil, chairman of
Baylor’s department of biochemistry and molecular biology, and his
colleagues found that there are two pools of malonyl-CoA in the cell.
The one in which ACC1 is important is critical to the formation of the
long carbon chain component of fatty acids. The other pool associated
with ACC2 regulates the transfer of fatty acids to the mitochondria,
the cell’s powerhouse. Without AAC2, fat burns continuously in the
ACC2 was identified in Wakil’s laboratory in 1989 where researchers
sequenced its DNA and located it on the chromosome. To determine the
different effects of ACC1 and ACC2, Wakil and his colleagues created
two forms of "knock-out" mice. The mice that lacked ACC1 died as
embryos, demonstrating the value of fat in development.
"However, the mice genetically engineered to lack ACC2 seem very happy,
live and breed well," Wakil said. The difference was that they ate
more, weighed less and accumulated less fat than the normal animals.
Studies demonstrated that the ACC2-deficient mice had nearly
one-half the fat of the normal mice. The fatty livers of normal mice
looked pale compared to the bright red, virtually fat-free livers of
the genetically engineered animals.
In one study, the researchers gave the ACC2-deficient mice insulin,
which is produced in response to eating carbohydrates. In a normal
system, insulin stimulates production of an enzyme that activates ACC1
and ACC2, increasing the production of fatty acids and inhibiting the
burning of fat. However, in the ACC2-deficient mouse, "fat oxidation
continues in the presence of insulin," Wakil said.
"This enzyme ACC2 could be a target for generating drugs that
could regulate the burning of fat," Wakil said. "It could be important
in the regulation of obesity, treatment of diabetes and eventually even
the utilization and accumulation of fat, which could affect diseases
such as atherosclerosis."
Co-authors were Drs. Lutfi Abu-Elheiga and K.A.H. Abo-Hashema in collaboration with Martin M. Matzuk.
Baylor College Of Medicine. April 2001.