Cause of grey hair may be 'stuck' stem cells, study finds

Scientists believe they may have uncovered why our hair turns grey as we age, citing the inability of pigment-making stem cells to mature.

The study, published in the journal Nature, could provide a basis for reversing the greying process.

It found that 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 team led by researchers from NYU Grossman School of Medicine in the US focused on cells in the skin of mice and also found in humans called melanocyte stem cells, or McSCs.

Hair color is controlled by whether nonfunctional but continually multiplying pools of McSCs within hair follicles get the signal to become mature cells that make the protein pigments responsible for color.

The study showed that McSCs are remarkably plastic. This means that during normal hair growth, such cells continually move back and forth on the maturity axis as they transit between compartments of the developing hair follicle.

It is inside these compartments where McSCs are exposed to different levels of maturity-influencing protein signals.

The researchers found that 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.

They noted 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. These cells do not mature into the transit-amplifying state, and do not travel back to their original location in the germ compartment, where proteins would have prodded them to regenerate into pigment cells.

”Our study adds to our basic understanding of how melanocyte stem cells work to color hair,” said study lead investigator Qi Sun, a postdoctoral fellow at NYU Langone Health.

”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 graying of human hair by helping jammed cells to move again between developing hair follicle compartments,” Sun said.

Researchers say McSC plasticity is not present in other self-regenerating stem cells, such as those making up the hair follicle itself, which are known to move in only one direction along an established timeline as they mature.

For example, transit-amplifying hair follicle cells never revert to their original stem cell state. This helps explain in part why hair can keep growing even while its pigmentation fails, said Sun.

”It is the loss of chameleon-like function in melanocyte stem cells that may be responsible for graying and loss of hair colour,” said study senior investigator Mayumi Ito, a professor at NYU Langone Health.

”These findings suggest that melanocyte stem cell motility and reversible differentiation are key to keeping hair healthy and colored,” Ito added.