April 20, 2023: Your hair has stem cells near the roots, and they are important in turning your hair brown, black, or another natural color. But these cells need to move to a different part of the follicle and change to produce hair color. When these special stem cells get “stuck” and can no longer do their job, gray hair appears in their place, new research reveals.
Called melanocyte stem cells (McSCs), these cells need to mature into melanocytes, or pigment cells. They can last for years, but they die before other nearby cells, such as hair follicle stem cells. This difference may explain why people go gray but still grow their hair.
A new finding is that these cells can move within the hair follicle without losing their “stalk.” Similar to recycling, they start out as “undifferentiated” stem cells, move on and mature to perform their hair coloring functions, and then revert back to more primitive stem cells.
The traditional belief was that stem cells remained primitive, matured when necessary, and then died. It is now believed to be more of a cycle.
“Melanocyte stem cells were thought to be maintained in an undifferentiated state, rather than repeating differentiation and dedifferentiation,” said lead investigator Mayumi Ito, PhD, a professor in the Ronald O Department of Dermatology and Department of Cell Biology. Perelman. at NYU Langone Health in New York City.
The process involves different compartments in the hair follicle: the germinal area is where stem cells regenerate, the follicle bulge is where they get stuck. A different environment at each location dictates how they change. This “chameleon” property surprised the researchers.
Now that researchers have figured out how gray hair can start, the next step will be to find a way to stop it.
“Our study suggests that moving melanocytes to a suitable location within the hair follicle may help prevent gray hair,” Ito said.
Research has been done in mice to date, as reported online April 19 in the newspaper Nature. But the findings could translate to humans.
“Because the structure of the hair follicle is similar between mice and humans, we speculate that human melanocytes may also demonstrate plasticity.” [or ability to change] during hair regrowth,” Ito said.
A hint of melanoma?
The study could also have implications for melanoma. Melanomas are cancers that develop from the same pigment cells, melanocytes. Unlike other tumors, they can self-renew. This “plasticity,” or ability to change easily, makes melanomas difficult to remove and the most serious form of skin cancer.
“Our study suggests that normal melanocytes are very plastic and can reverse a state of differentiation. Melanoma cells are known to be very plastic,” Ito said. “We believe that this characteristic of melanoma may be related to the high plasticity of the original melanocytes.”
The finding that melanocyte stem cells “are more plastic than previously thought…certainly has implications in melanoma,” said Melissa Harris, PhD, associate professor in the Department of Biology at the University of Alabama at Birmingham.
creepy detail
Hair follicles are tiny, so advanced technology was needed to conduct the research. Ito and his colleagues used 3D intravital imaging and single-cell RNA sequencing, for example.
This level of precision allows them to track stem cells in near real time as they age and move within each hair follicle.
“This paper uses a good mix of classical and modern techniques to help answer a question that many in the field of pigmentation biology have long suspected. Not all quiescent melanocyte stem cells are the same,” Harris said. (She was the lead author of a Study January 2021 proposing a combined treatment to reverse stem cell loss and hair aging).
Questions without answer
“The only question not answered in this article is how to reverse the dysfunction of ‘stuck’ melanocyte stem cells in the hair bulge,” Harris said. “There are numerous human clinical case studies showing drug-induced hair repigmentation, and perhaps these cases are examples of dysfunctional melanocyte stem cells ‘unstuck’.”
“The concept highlighted in this article is that melanocyte stem cells are ‘stranded’ and do not receive the correct signal to adequately amplify and migrate to provide pigment to the hair shaft,” said Paradi Mirmirani, MD, a dermatologist who specializes in the care of people with hair disorders and is a faculty member of the American Academy of Dermatology.
It could be challenging to provide stem cells with the correct signals to keep them mobile and mature, “but the first step is always to understand the basic underlying mechanism,” said Mirmirani, who practices in Vallejo, CA. “It would be interesting to see if other factors such as smoking, stress and others influence melanocyte stem cells in the same way.”
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