Researchers Find that Sex Matters When it Comes to Stem Cells

By Corey Binnsnew, Live Science, June 9, 2007

A new study has found that the regeneration of tissue is enhanced when stem cells from the muscles from female mice are used as opposed to male mice.

The development of stem cell treatments for many conditions and diseases could be affected by this new discovery.

After almost exclusively using stem cells from female mice without giving it a second thought, scientists who had been conducting numerous studies with the cells made the interesting connection. They decided to investigate if there was any disparity between male and female cells and designed an experiment based on this premise.

Capable of developing into any type of cell in the body, embryonic stem cells are versatile. But more limited in what they can become, muscle stem cells are more specialized and instead of coming from an embryo, they are derived from adult tissue.

According to the U.S. Centers for Disease Control and Prevention, out of 3,500 to 5,000 young boys in the United States, at least one is affected by Duchene muscular dystrophy. Using mice that had been engineered to have a similar disease, researchers injected stem cells from healthy mice into those that were sick.

In humans, the muscle's cell structure collapses because the disease involves the deficiency of a crucial protein called dystrophin.

“Their muscle breaks down and is replaced by fat,” said study co-author Bridget Deasy of the University of Pittsburgh School of Medicine.

As fat takes the place of muscle tissue in the diaphragm and heart, patients typically die from cardiac or respiratory problems.

Few boys live past the age of 25. Most are wheelchair bound by their early teens, and first diagnosed by the time they are five years old.

Cell transplantation is one of the potential treatment options that scientists are presently researching.

The researchers measured the cells’ capability to redevelop muscle fibers that contained dystrophin after injecting the mice with the stem cells. They found that the female cells created many more fibers than male cells. The full published work can be read in the April 9th issue of Cell Biology.

“Regardless of the sex of the host, the implantation of female stem cells led to significantly better skeletal muscle regeneration,” said the study’s senior author Johnny Huard, also of the University of Pittsburgh School of Medicine.

The cells' stress response seems to be responsible for the sex-related differences. Causing the male cells to either stop expanding or allowing them to differentiate, free radicals expose themselves to the new cells as the tissue becomes inflamed when they are transplanted.

“When you differentiate, you’re done,” Deasy told LiveScience. “That’s the end of the line for a stem cell.”

Deasy and her colleagues believe the differences will hold true in other stem cells, including those from humans even though they are not quite sure what is behind the sex-related differences.

“I think when people start looking for it, they’ll find it,” Deasy said. “They’ll be a difference.”