New Clues May Explain Why Hair Turns Gray

Communication between hair follicles and melanocyte stem cells, mediated by Wnt signaling (already known to control many biological processes) can dictate hair pigmentation, according to a new study.

Researchers at the New York University (NYU) Langone Medical Center (NY, USA) used genetic mouse models to examine how hair follicle stem cells and melanocyte stem cells (McSCs) work together to generate hair growth and produce hair color. The researchers found that McSCs intimately interact with epithelial stem cells (EpSCs) in the hair follicle bulge and secondary hair germ (sHG). Together, they undergo activation and differentiation to regenerate pigmented hair; the researchers identified Wnt signaling as a key pathway that couples the behavior of EpSCs and McSCs at the onset of hair follicle regeneration within the sHG.

The researchers also showed the depletion (or inhibition or abnormal) Wnt signaling in hair follicle stem cells not only inhibits hair regrowth, but also prevents melanocytes stem cell activation required for producing hair color; in fact, the lack of Wnt activation in melanocyte stem cells leads to depigmented or gray hair. The study raises the possibility that Wnt signaling is a key pathway for the regulation of melanocyte stem cells, affecting melanocyte behavior associated with hair regeneration. This insight could provide further understanding of diseases in which melanocytes are either appropriately lost--such as hair graying--or undergo uncontrolled cell growth as in melanoma. The study was published in the June 11, 2011, issue of the journal Cell.

"We have known for decades that hair follicle stem cells and pigment-producing melanocycte cells collaborate to produce colored hair, but the underlying reasons were unknown," said lead author Assistant Professor Mayumi Ito, PhD. "We discovered Wnt signaling is essential for coordinated actions of these two stem cell lineages and critical for hair pigmentation."

Hair color is the pigmentation of hair follicles due to two types of melanin, eumelanin and pheomelanin. Generally, if more melanin is present, the color of the hair is darker; if less melanin is present, the hair is lighter. Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of more than one color. Gray or white hair is not actually a true grey or white pigment; in fact, it is clear due to lack of pigmentation and melanin. The clear hairs appear as gray or white because of the way light reflects from the hairs.

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New York University (NYU) Langone Medical Center