Scientists studying hair follicles in mice may have finally discovered a mechanism behind how and why hair turns gray.
At a basic level, we already know that hair turns gray when specialized pigment-producing cells called melanocytes are in short supply. But still not how and why this happens, or if there is a way to prevent it. A new study now adds a few more details by challenging previous ideas about how melanocytes develop. Melanocytes are derived from melanocyte stem cells (McSCs) in the hair follicle, and it is on these stem cells that the latest research is focused. It appears that as we age, these precursor pigment-producing cells “get stuck” in a region called the follicle swelling and stop developing into melanocytes in sufficient numbers to fill the growing strand of hair with color. In tests on mice, after a forced aging process, the number of hair follicles with McSCs deposited in the follicle bulge increased from 15% to nearly half. These cells were no longer regenerating or maturing into cells that could produce pigment and instead remained stuck as McSCs. “Our study adds to our basic understanding of how melanocyte stem cells work to color hair,” says New York University dermatologist Qi Sun. “The new mechanisms raise the possibility that the same fixed positioning of melanocyte stem cells could exist in humans.” “If so, it represents a potential pathway to reverse or prevent graying in human hair by helping blocked cells move between compartments of the developing hair follicle again.” Researchers have found that McSCs, unlike other types of stem cells, can go from a pure stem cell state to what is known as the Transit Amplified (TA) state – a sort of intermediate state between a stem cell and a complete melanocyte cell. This TA state appears to be important for the health of the McSC and continued hair color production, but the team found that being able to switch into TA mode depends on signals from specific locations, from which cells are cut. out when follicular swellings are blocked.
The stem cells that color hair need to be in a specific region to be activated to develop into pigment. All of this has yet to be observed in human hair follicles, of course, but it’s possible the same mechanisms are at play in our own hair. Further down the line, this research may even offer a way to treat hair to make sure it doesn’t lose its color. “These results identify a new model whereby dedifferentiation is integral to maintaining stem cell homeostasis and suggest that modulation of McSC mobility may represent a novel approach for hair graying prevention,” write the researchers in their article published . In other words, MSSCs can move to change state in ways that other stem cells do not, and it appears that this mobility and plasticity is crucial for the continued production of melanin by melanocytes. Hair follicle stem cells are not required to transition into follicle cells. So while melanocytes generation stops, the follicle itself can continue to push out new hair growth, the researchers say. This partly explains why our hair can continue to grow even as it loses its color, researchers say. It is worth noting that there are other mechanisms at play here as well, not everything down to MsSCs: we also know from previous studies that genetics and stress levels are also involved in hair graying with age. “It is the loss of chameleon function in melanocyte stem cells that may be responsible for the graying and loss of color in hair,” says dermatologist Mayumi Ito, of New York University. “These findings suggest that melanocyte stem cell motility and reversible differentiation are critical for maintaining healthy, colored hair.”