Grey hair is a natural occurrence that happens as people age. But have you ever wondered why hair turns grey? A new study published in the journal Nature found that certain stem cells, called melanocyte stem cells (McSCs), are responsible for hair color. The study, led by researchers from NYU Grossman School of Medicine, found that McSCs can get stuck in the stem cell compartment of the hair follicle, leading to hair turning grey.
However, by restoring these stem cells to their original location, it may be possible to reverse or prevent the greying of human hair.
Plasticity of McSCs
McSCs have the unique ability to move between growth compartments in hair follicles. During normal hair growth, these cells continually move back and forth on the maturity axis as they transit between compartments of the developing hair follicle (plasticity). It is inside these compartments where McSCs are exposed to different levels of ageing protein signals. The research team found that McSCs transform between their most primitive stem cell state and the next stage of their maturation, the transit-amplifying state, depending on their location.
Why Hair Grows Grey
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, do not mature into the transit-amplifying state, and do not travel back to their original location in the germ compartment, where WNT proteins would have prodded them to regenerate into pigment cells. This results in hair turning grey.
Loss of McSC Plasticity
Researchers found that McSC plasticity is not present in other self-regenerating stem cells, such as those making up the hair follicle itself. These cells are known to move in only one direction along an established timeline as they mature. The loss of chameleon-like function in melanocyte stem cells may be responsible for greying and loss of hair color.
Moving cells back
The team plans to investigate means of physically moving them back to their germ compartment (motility), where they can produce pigment. “These findings suggest that melanocyte stem cell motility and reversible differentiation are key to keeping hair healthy and colored,” said Dr. Mayumi Ito, a professor in the Ronald O. Perelman Department of Dermatology and Department of Cell Biology at NYU Langone Health.
This study adds to our basic understanding of how melanocyte stem cells work to color hair.
The newfound mechanisms raise the possibility that the same fixed positioning of melanocyte stem cells may exist in humans. If so, it presents a potential pathway for reversing or preventing the greying of human hair by helping jammed cells to move again between developing hair follicle compartments.