Patches of hair may be gone in many men, but the stem cells that make hair are still there. This unexpected finding is raising hopes of a cure for baldness.
By comparing bald and hairy patches in scalp samples from 54 men undergoing restoration treatments, George Cotsarelis at the University of Pennsylvania School of Medicine in Philadelphia and colleagues discovered that although both had similar numbers of stem cells, most of those in the bald patches fail to develop to the next stage.
In samples from the same individuals, stem cells that had matured into so-called “progenitor cells” were 10 to 100 times as abundant on hairy patches as on bald ones, suggesting they are the key to hair growth.
If a way can be found to reawaken the stem cells, it could provide a shortcut to new hair for millions of men with male-pattern baldness.
“The fact that [the stem cells] are there at all is pretty exciting, and lowers the bar for treatment,” says Cotsarelis. “I’m generally very pessimistic about the prospects for treatment, so we were surprised to find such a large and normal complement of stem cells in the bald patches.”
Now the team is investigating why some of the stem cells become dormant while others remain active. “It could be the lack of a stimulus, or too much of an inhibitor on different parts of the scalp,” says Cotsarelis. “We’re working on that now, and have some leads, but this is a very early step in development of a treatment.”
Encouragingly, the team reports in the same paper that mouse progenitor cells were capable of regenerating entire hair follicles. This suggests that the same might be possible in people, if progenitor cells can be made from reawakened stem cells.
In earlier experiments, Cotsarelis also showed that in mice, transplanted follicular stem cells were able to regenerate hair.
One possibility would be to take stem cells from balding men, multiply these into progenitor cells, and then return them to the scalp. Another is to find a chemical signal that reawakens the stem cells, so it could simply be rubbed onto the bald areas of the scalp.
Cotsarelis says that although the finding is in men, it may be also be applicable to women. “Some 30 per cent of women have some degree of female-pattern hair loss by the age of 50,” he says.