Two sides of omentum
Tissue that surrounds the abdominal organs—the omentum and its overlying layer of mesothelium—could provide a promising source of stem or progenitor cells for heart repair therapies.
The omentum is fatty tissue that connects the stomach to the intestines. It is covered by mesothelium, which provides the tissue’s vasculature and which has remarkable regenerative potential.
Surgeons have used the omentum for many years as a sort of natural “bandage” to promote healing of surgical incisions and injuries, says David Bader, Ph.D, professor of Medicine and Cell & Developmental Biology at Vanderbilt, whose group first reported the angiogenic properties of mesothelium in the abdomen in 2005.
Bader is currently examining the mechanism behind the omentum’s healing properties and trying to determine if its mesothelial covering contains a source of stem or progenitor cells that could be used for regenerative therapies.
“It is very easy to turn these (mesothelial) cells into cells that make blood vessels,” Bader says. “They like to make stuff like blood vessels, smooth muscle, endothelium”—a capacity that would be very useful in heart repair.
During embryonic development, the mesothelium provides progenitor cells for the development of several organs.
“The adult structure has the capacity to do produce these cells when stimulated,” says Bader. “I don’t know that the naturally-occurring process would be reparative, but we have found a way to ‘wake up’ that embryonic potential.”
Omentum is not without its dark side, however.
Central obesity, the accumulation of intra-abdominal fat, is a well known risk factor for cardiovascular disease. There is some evidence that removal of the omentum during gastric bypass surgery reduces that risk.
Omentum is not a neutral tissue. It is rich in macrophages, a type of white blood cell that produces inflammatory factors called “adipokines,” says Alfonso Torquati, M.D., assistant professor of Surgery in the Vanderbilt Center for Surgical Weight Loss.
Some adipokines are protective, while others can damage the endothelium, the inner lining of blood vessels.
In 2007 Torquati and his colleagues began a look at the effect in obese patients with diabetes of gastric bypass surgery on sub-clinical atherosclerosis (thickening of the wall of the carotid arteries as detected by ultrasound) and on levels of levels of inflammatory factors in the blood.
“Our theory is that with gastric bypass surgery, we induce a reduction of the ‘bad’ adipokines—TNF-alpha, IL-6—and we increase the ‘good’ adipokines like adiponectin,” Torquati says.