It has been said that aging is a “privilege denied to many,” and gray hair often accompanies that privilege. Gray hair can also be caused by stress, but scientists may be closer to finding out exactly why even the most colorful hair turns gray with age. A study published April 19 in the journal Nature discovered that certain stem cells have a unique ability to move between growth compartments in hair follicles, but get stuck and lose their ability to mature and maintain hair color as people age.
[Related: We finally know why stress turns your hair white.]
Melanocyte stem cells (McSC) in hair follicles are responsible for producing and maintaining pigment in our hair. Each hair follicle stores immature melanocyte stem cells, and when needed, the cells travel from one part of the follicle to another. When they reach other parts of the follicle, the proteins convert them into more mature pigment-producing cells and give the hair its hue. Within the compartments of these follicles, McSCs are exposed to different levels of protein signals that influence maturity as a person ages.
According to the study, McSC cells from mice, as hair ages, falls out, and then repeatedly grows back, more McSCs get stuck in a stem cell compartment called the hair follicle bulge. While there, they lie still, unable to mature or move between the compartments of the follicles. Nor do they travel back to their original location where WNT proteins would have pushed them to regenerate into pigment cells.
“Our study adds to our basic understanding of how melanocyte stem cells work to dye hair,” study co-author and New York University computer engineer Qi Sun said in a statement. “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.”
To learn more about how stem cells behave during different phases of hair growth, the team tracked down and imaged individual cells in mouse fur. The stem cells actually traveled back and forth within the hair follicle and even transitioned into their mature pigment-producing state and then out again as they moved.
As time passed, the McSCs were unable to continue this process, and a hair that falls out and grows back takes its toll on the follicle. Eventually, the stem cells stopped making this journey through the follicle and stopped receiving protein signals to produce pigment. From then on, any new hair growth does not get the melanin needed to produce hair color.
[Related: Alopecia patients finally have an FDA-approved hair-loss treatment.]
To further explore this effect, the ream plucked hair from mice to stimulate a faster growth cycle. The experiment led to an accumulation of McSCs stuck in storage that were no longer producing melanin, and the fur changed from dark brown to a distinguished salt-and-pepper color.
“It is the loss of chameleon function in melanocyte stem cells that may be responsible for aging and loss of hair color,” co-author and NYU pharmacologist and cell biologist Mayumi Ito said in a statement. “These findings suggest that melanocyte stem cell motility and reversible differentiation are key to maintaining healthy, colored hair.
Some next steps for the team include investigating how to restore motility in these stem cells so they can return to the pigment-producing compartments. Until then, consider joining the “gray revolution” of people embracing that beautiful gray hair.