Researchers at the NYU Grossman School of Medicine have made a significant discovery regarding the aging process and gray hair. They have found that specific stem cells possess a unique ability to migrate within hair follicles, potentially preserving the original pigment in strands.
The study revealed that as hair ages, sheds, and regrows, an increasing number of these stem cells become trapped in a compartment called the hair follicle bulge. Instead of returning to their original location in the compartment, where proteins aid in their regeneration into pigment cells, they remain stuck, causing the hairs to lose their color.
The researchers conducted their study on physically aged mice hairs and observed the accumulation of trapped stem cells with aging. They also noted that these cells were unable to regenerate or mature into pigment-producing hairs.
This breakthrough research offers hope for maintaining healthy and colored hair well into old age. By focusing on melanocyte stem cells (McSCs) found in the skin of mice, which are also present in humans, the study provides insights into the control of hair color.
Hair color is determined by non-functional pools of McSCs within hair follicles, which continuously multiply. These cells require specific signals to transform into mature cells responsible for producing protein pigments.
The NYU study, published in Nature, discovered that McSCs are adaptable or “plastic.” During normal hair growth, they move back and forth on the maturity axis while transitioning between compartments within the developing hair follicle.
Within these compartments, the McSCs are exposed to varying levels of protein signals that influence their maturation. These signals transform the cells from their primitive stem cell state to the next stage of maturation.
The scientists found that an increasing number of McSCs become trapped in the bulge. Once trapped, they fail to mature into the transit state necessary to return to their original location in the germ compartment. In this compartment, proteins can facilitate their regeneration into pigment cells.
Unlike other self-regenerating stem cells that move in a single direction along a predetermined timeline as they mature, McSCs exhibit adaptability. This characteristic explains why hair can continue to grow despite the loss of pigmentation in aging hair follicles.
These findings offer valuable insights into the mechanisms underlying hair pigmentation and may pave the way for future strategies to maintain hair health and color in the later stages of life.
“Our study adds to our basic understanding of how melanocyte stem cells work to color hair,” said the study’s lead investigator, Dr Qi Sun. He is a postdoctoral fellow at NYU Langone Health. “The newfound mechanisms raise 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.”
Earlier work that was done by scientists at NYU displayed that “WNT signaling was needed to stimulate the McSCs to mature and produce pigment”. According to this previous study, it was observed that McSCs in the hair follicle bulge were significantly less exposed to WNT signaling compared to the hair germ compartment, which is located directly below the bulge.
In the recent experiments conducted by the NYU team, they artificially aged mice’s hair by plucking them out and inducing regrowth. As a result, the percentage of hair follicles containing McSCs in the follicle bulge increased from 15 percent before plucking to nearly half after the process.
However, these McSCs remained unable to regenerate or mature into pigment-producing melanocytes. It was discovered that these trapped McSCs had lost their regenerative behavior due to insufficient exposure to WNT protein signaling. Consequently, they were incapable of producing pigment in the newly growing hair follicles.
On the other hand, the McSCs that continued to migrate between the follicle bulge and hair germ retained their ability to regenerate as McSCs, mature into melanocytes, and produce pigment throughout the entire two-year study period.
“It is the loss of chameleon-like function in melanocyte stem cells that may be responsible for graying and loss of hair color,” added Dr Mayumi Ito. He is a Langone Health professor.
“These findings suggest that melanocyte stem cell motility and reversible differentiation are key to keeping hair healthy and colored.”
The team’s current focus is to explore strategies for restoring the motility of McSCs or relocating them to their germ compartment. By doing so, they aim to enable the production of pigment, effectively preventing the graying of hair.