Study links an accumulation of stranded stem cells to hair turning gray

Now, where is the cure? 😊 However, this is a highly complicated process!

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

the new 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.

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.

The 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, 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. ..."

From the abstract:

"For unknow reasons, the melanocyte stem cell (McSC) system fails earlier than other adult stem cell populations, which leads to hair greying in most humans and mice. Current dogma states that McSCs are reserved in an undifferentiated state in the hair follicle niche, physically segregated from differentiated progeny that migrate away following cues of regenerative stimuli. Here we show that most McSCs toggle between transit-amplifying and stem cell states for both self-renewal and generation of mature progeny, a mechanism fundamentally distinct from those of other self-renewing systems. Live imaging and single-cell RNA sequencing revealed that McSCs are mobile, translocating between hair follicle stem cell and transit-amplifying compartments where they reversibly enter distinct differentiation states governed by local microenvironmental cues (for example, WNT). Long-term lineage tracing demonstrated that the McSC system is maintained by reverted McSCs rather than by reserved stem cells inherently exempt from reversible changes. During ageing, there is accumulation of stranded McSCs that do not contribute to the regeneration of melanocyte progeny. These results identify a new model whereby dedifferentiation is integral to homeostatic stem cell maintenance and suggest that modulating McSC mobility may represent a new approach for the prevention of hair greying."

Study links 'stuck' stem cells to hair turning gray (Secondary source) 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 color, a new study shows.

Study Links ‘Stuck’ Stem Cells to Hair Turning Gray (Primary source) 

Dedifferentiation maintains melanocyte stem cells in a dynamic niche (open access)

Hair-coloring stem cells (at left, in pink) need to be in the hair germ compartment in order to be activated (at right) to develop into pigment.