Stem cells play an important role in explaining male pattern balding, University of Pennsylvania researchers have found.
Using cell samples from men undergoing hair transplants, a team led by George Cotsarelis compared follicles from bald scalp and non-bald scalp, and found that bald areas had the same number of stem cells as normal scalp in the same person.
However, they did find that another, more mature cell type called a progenitor cell was markedly depleted in the follicles of bald scalp.
The researchers surmised that balding might arise from a problem with stem-cell activation rather than the numbers of stem cells in follicles. In male pattern balding, hair follicles actually shrink; they don't disappear.
"We asked: 'Are stem cells depleted in bald scalp?' We were surprised to find the number of stem cells was the same in the bald part of the scalp compared with other places, but did find a difference in the abundance of a specific type of cell, thought to be a progenitor cell. This implies that there is a problem in the activation of stem cells converting to progenitor cells in bald scalp," said Cotsarelis.
In 2007, the Cotsarelis lab found that hair follicles in adult mice regenerate by re-awakening genes once active only in developing embryos. The team determined that wound healing in a mouse model created an "embryonic window" of opportunity to manipulate the number of new hair follicles that form.
The findings were published in the journal Clinical Investigation.