A new study has identified that certain stem cells located in the hair have a unique ability to move between growth compartments in hair follicles, when we are young and as we age, these cells get stuck and therefore lose their ability. to mature and maintain hair color.
The study led by researchers from the Grossman School of Medicine from new york universitywas applied to skin cells in mice and also in humans called melanocyte stem cells or McSCs.
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Hair color is controlled by McSC clusters that are non-functional but continuously multiplying within hair follicles, signaled to become mature cells that produce the protein pigments responsible for color, the researchers explained.
University work shows that McSCs are remarkably plastic. This means that during normal hair growth, these cells continually move back and forth in the maturity axis as they transit between the gaps in the developing hair follicle. It is within these compartments that McSCs are exposed to different levels of protein signals that influence maturity.
The scientists found that as hair ages, falls out, and then repeatedly grows back, an increasing number of McSCs become stuck in the stem cell compartment called the hair follicle bulge. There they remain, not maturing to the state of transit amplification, and not traveling back to their original location in the germinal compartment, where proteins, called WNTs, would have pushed them to regenerate into pigment cells.
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“Our study adds to our basic understanding of how melanocyte stem cells work to color hair,” said the study’s principal investigator, Qi Sun, PhD, a postdoctoral fellow at NYU Langone Health. “The newly discovered mechanisms raise the possibility that the same fixed positioning of melanocyte stem cells may exist in humans. If so, it presents a potential pathway to reverse or prevent aging of human hair by helping stuck cells move back between compartments of the developing hair follicle.”
Furthermore, the researchers say McSC plasticity is not present in other self-regenerating stem cells, such as those that make up the hair follicle itself, which are known to move in only one direction along a set timeline as they mature. . For example, the hair follicle cells that amplify the transit never return to their original stem cell state. This helps explain in part why hair can continue to grow even when its pigmentation fails, says Dr. Sun.
The New York University recalls that previous work by the same research team showed that WNT signaling was necessary to stimulate McSCs to mature and produce pigment. That study also showed that McSCs were trillions of times less exposed to WNT signaling in the hair follicle than in the hair germ compartment, which lies directly below the bulge.
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In the latest experiments in mice whose hair was physically aged by plucking and forced regrowth, the number of hair follicles with McSCs housed in the follicle pons increased from 15 percent before plucking to almost half after forced aging. These cells remained unable to regenerate or mature into pigment-producing melanocytes.
The researchers found that the stuck McSCs ceased their regenerative behavior as they were no longer exposed to much WNT signaling and thus their ability to produce pigment in new hair follicles, which continued to grow.
In contrast, other McSCs that continued to move back and forth between the follicle bulge and the hair germ maintained their ability to regenerate as McSCs, mature into melanocytes, and produce pigment throughout the two-year study period.
“It is the loss of chameleon function in melanocyte stem cells that may be responsible for aging and loss of hair color,” said the study’s lead investigator, It’s smellyPhD , Professor in the Ronald O. Perelman Department of Dermatology and Department of Cell Biology at NYU Langone Health.
“These findings suggest that melanocyte stem cell motility and reversible differentiation are key to maintaining healthy, colored hair,” said Dr. Ito.
Dr. Ito says the team has plans to investigate ways to restore McSCs’ motility or physically move them back to their germ compartment, where they can produce pigment.
For the study, the researchers used recent 3D intravital imaging and scRNA-seq techniques to track cells in near real time as they aged and moved within each hair follicle.
