Stem Cells Getting Stuck may be the Reason for Grey Hair

A new study suggests stem cells present between hair follicles may get stuck as hair ages and lose their ability to mature and maintain hair color.

Melanocyte stem cells moving back and forth as they transit between compartments of the developing hair follicles might not be able to travel back to their original location as the hair ages, which could be the reason behind grey hair.

This finding is according to new research led by NYU Grossman School of Medicine that focused on cells in the skin of mice and found in humans called melanocyte stem cells, or McSCs. The findings of the study are published in the journal Nature.

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

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‘Stem cells having a unique ability to undergo a transition between growth compartments in hair follicles, may lose the ability to move with age, resulting in grey hair.’

The new study showed that McSCs are remarkably plastic. This means that during normal hair growth, such cells are continually 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.

Specifically, 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.

They found that as the hair 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.

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This newfound mechanism raises 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.

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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.

The study had also shown that McSCs were many trillions of times less exposed to WNT signaling in the hair follicle bulge than in the hair germ compartment, which is situated directly below the bulge.

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The stuck McSCs ceased their regenerative behavior as they were no longer exposed to much WNT signaling and hence their ability to produce pigment in new hair follicles, which continued to grow.

By contrast, other McSCs that continued to move back and forth between the follicle bulge and hair germ retained their ability to regenerate as McSCs, mature into melanocytes, and produce pigment over the entire study period of two years.

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It is the loss of chameleon-like function in melanocyte stem cells that may be responsible for graying and loss of hair color. These findings suggest that melanocyte stem cell motility and reversible differentiation are key to keeping hair healthy and colored.

The research has plans to investigate means of restoring the motility of McSCs or of physically moving them back to their germ compartment, where they can produce pigment.

Source-Eurekalert