When a man's hair vanishes, it would be logical to assume his scalp has suffered a loss of those versatile stem cells that regenerate hair, blood and other body parts.
Not so, says new research from the University of Pennsylvania. Bald men have just as many stem cells in their hair follicles as any magnificently tressed Samson. The cells may just need to be woken up.
It is not clear yet how to do this, but the researchers say their findings, published online last week in the Journal of Clinical Investigation, give them hope that male baldness is reversible.
"The stem cells are still present, which to me was quite surprising," said senior author George Cotsarelis, chairman of the dermatology department at Penn's medical school. "We should be able to figure out a way of stimulating them."
The estimated 35 million balding men in the United States can now opt for hair transplants or rely on Rogaine or Propecia, drugs that help primarily in maintaining existing hair but don't stimulate new growth.
In the new research, the stem cells in question are the adult variety, not the more versatile embryonic stem cells that have stirred controversy.
Still, many scientists think these adult cells are a promising area of study, holding potential to regenerate certain organs or heal wounds without scars. And what better laboratory to study them than the scalp, where hair stem cells are accessible and plentiful?
"Many of us think we can gain clues about how to regenerate other organs by understanding how to regenerate the hair," says Stanford University dermatologist Anthony Oro, who was not involved with the new research.
For the new study, Cotsarelis, Luis A. Garza, the paper's lead author, and colleagues studied scalp samples left from men who had hair transplants. Bald scalp was found to have just as many stem cells as scalp with hair.
Where the scalp samples differed, however, was in their levels of two other kinds of so-called progenitor cells that appear to be descendants of follicle stem cells. Samples of bald scalp contained one-tenth as many of these progenitor cells, on average, when compared to "haired" scalp.
Progenitor cells are created by the division of stem cells; the progenitors then divide further to produce hair and other kinds of cells. So in bald men, stem cells seem to have slowed way down in dividing to form progenitor cells, and the answer may be simply to reactivate this process, researchers wrote.
To further test their theory, the scientists transplanted progenitor cells from one mouse to another, where the cells led to the creation of new hair follicles. This experiment could not be done in people because such donor cells would be rejected; the mice that received donated cells were immunodeficient.
Another possible solution for baldness would be to remove some of a person's hair-generating cells, grow them outside the body, and reimplant them, the authors said.