Certain stem cells have a unique ability to move between growth compartments in hair follicles, but get stuck as people age and so lose their ability to mature and maintain hair colour, a release says. The new work (Nature) focused on cells in the skin of mice and also found in humans called melanocyte stem cells (McSCs).
During normal hair growth, the melanocyte stem cells continually move back and forth on the maturity axis as they transit between compartments of the developing hair follicle. McSCs transform between their most primitive stem cell state and the next stage of their maturation, the transit-amplifying state, and depending on their location. The NYU Grossman School of Medicine researchers found that as hair ages, sheds, and then repeatedly grows back, increasing numbers of McSCs get stuck in the stem cell compartment called the hair follicle bulge.
There they remain and do not mature into the transit-amplifying state. This helps explain in part why hair can keep growing even while its pigmentation fails. The stuck McSCs ceased their regenerative behaviour as they were no longer exposed to WNT signalling, which stimulates the McSCs to mature and produce pigment in new hair follicles that continued to grow.
