Like fine china and crystal, which tend to be used sparingly, stem cells divide infrequently.
It was thought they did so to protect themselves from unnecessary wear and tear. But now new research from Rockefeller University has unveiled the protein that puts the brakes on stem cell division and shows that stem cells may not need such guarded protection to maintain their potency.
This research, to be published in the January 25 issue of Cell, raises questions about what stem cells need in order to maintain their ability to regenerate tissue. It may also be key in developing new treatments for thinning hair.
The impetus for the work began five years ago when Elaine Fuchs, head of the Laboratory of Mammalian Cell Biology and Development, and several researchers in her lab discovered that the protein NFATc1 was one of only a few that are highly expressed within the stem cell compartment of the hair follicle. Clinical research, meanwhile, showed that a particular immunosuppressant that inhibits NFATc1, a drug called cyclosporine A, has a rather unsightly side effect: excessive hair growth.
Fuchs and Valerie Horsley, a postdoc in her lab, realized that there was a connection between the drug?s side effect and the abundance of NFATc1 within the hair follicle?s stem cell compartment ? the bulge. The mice they treated with the drug grew fur at a much faster rate than mice they did not treat. The researchers then showed that this excessive hair growth was due to increased stem cell activity within the bulge, a process that cranked up the production of hair. Specifically, the hair cycle shifted gears from its resting phase, when stem cells slumber, to its growth phase, when stem cells proliferate.
To maintain their multipotent properties, though, it appears that these stem cells hardly needed much ?rest? at all. These findings came as a surprise to the researchers, who, like their colleagues, had believed that stem cells proliferating infrequently protected them from depletion or mutations that would lead to hair loss. ?It seems like the resting phase isn?t as necessary as was once thought,? says Horsley. ?Even though these stem cells are highly proliferative, they still maintain their stem cell character.?
Using genetically engineered mice bred by colleagues at Harvard Medical School, Horsley and Fuchs then further explored what happens when skin stem cells lack NFATc1. They found that these mice looked exactly like the hairy mice that were treated with cyclosporine A: The loss of NFATc1 didn?t stop the hair cycle, but rather shortened the resting phase and prompted precocious entry to the growth state.