When you see large amounts of hair daily in your comb or brush, you may become distressed. Androgenetic alopecia or male pattern baldness is the primary cause of hair loss in men. In male pattern baldness, hair follicles shrink until no more hairs are produced. A new study is giving hope to men with androgenetic alopecia. Researchers were surprised to find that the shrunken follicles of a balding scalp contain just as many live stem cells as normal hair follicles. Cells, derived from these stem cells, called progenitor cells, however, were severely reduced in the bald hair follicles. These results suggest that if the stem cells within hair follicles of balding scalps can be awakened or activated to produce progenitor cells, hair loss can be reversed.
Hair Growth Cycle
Hair grows out from the hair follicles in repeated cycles. Each cycle is made up of distinct stages: the anagen, catagen, and telogen phase. The anagen phase is the active or growing phase; it can last for two to six years. About 85 percent of all hairs are in this phase at any one time. When the anagen phase ends, the catagen or transitional phase begins and lasts about one to three weeks. During the catagen phase, the hair follicle shrinks and the lower part is destroyed. The resting or telogen phase follows the catagen phase and lasts for one to four months. During this period, the hair does not grow, but stays attached to the follicle. About 10 to 15 percent of scalp hairs are in this phase at any one time. At the end of the telogen phase, the hair is shed and hair follicles go back to the anagen or growth phase and a new hair is produced. In men with androgenetic alopecia, more and more hair follicles fail to reenter the anagen phase.
Stem Cells
When a hair follicle produces a new pair, the stem cells within the follicle start to divide and generate progenitor cells. Progenitor cells produce the new hair. Researchers at the University of Pennsylvania, School of Medicine, used scalp samples from men undergoing hair transplants and analyzed the stem cells in hair follicles from bald scalp regions and normal scalp regions.
Surprisingly, the numbers of stem cells in both bald and normal scalp were similar. However, bald follicles had greatly reduced numbers of progenitor cells. The researchers confirmed that progenitor cells could grow hair in a nude mouse model. They injected mouse progenitor cells into the skin of nude mice. These mice are immunodeficient and are characterized by lack of hair growth. The mouse progenitor cell successfully formed hair follicles in these mice. The researchers write, “These results suggest that loss of progenitor cells, but not stem cells, contribute to male pattern baldness” (Garza, L.A. et al.).
Implications
Although androgens, testosterone and dihydrotestosterone, play a role in male pattern baldness, little is known about the cellular basis for androgenetic alopecia. This study shows that the absence or reduction of hair follicle progenitor cells or the inability of hair follicle stem cells to produce progenitor cells is the cause of male pattern baldness. The good news is that the hair follicles of balding men are alive and well. Now new strategies to activate these stem cells can be explored. Although the researchers have not looked at the scalps of women with androgenetic alopecia, a similar situation may exist.
