New evidence points more to a cycle wherein undifferentiated stem cells mature to perform their hair-coloring duties and then transform back to their primitive form. To accomplish this, they need to stay on the move.
When these special stem cells get “stuck” in the follicle, gray hair is the result, according to a new study reported online in Nature.
The regeneration cycle of melanocyte stem cells (McSCs) to melanocytes and back again can last for years. However, McSCs die sooner than do other cells nearby, such as hair follicle stem cells. This difference can explain why people go gray but still grow hair.
“It was thought that melanocyte stem cells are maintained in an undifferentiated state, instead of repeating differentiation and de-differentiation,” said the study’s senior investigator Mayumi Ito, PhD, professor in the departments of dermatology and cell biology at NYU Langone Health, New York.
The process involves different compartments in the hair follicle – the germ area is where the stem cells regenerate; the follicle bulge is where they get stuck. A different microenvironment in each location dictates how they change. This “chameleon-like” property surprised researchers.
Now that investigators figured out how gray hair might get started, a next step will be to search for a way to stop it.
The research has been performed in mice to date but 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 the plasticity during hair regeneration,” Dr. Ito told this news organization.
Future findings could also lead to new therapies. “Our study suggests that moving melanocytes to a proper location within the hair follicle may help prevent gray hair,” Dr. Ito said.
Given the known effects of ultraviolet B (UVB) radiation on melanocytes, Dr. Ito and colleagues wanted to see what effect it might have on this cycle. So in the study, they exposed hair follicles of mice to UVB radiation and report it speeds up the process for McSCs to transform to color-producing melanocytes. They found that these McSCs can regenerate or change back to undifferentiated stem cells, so UVB radiation does not interrupt the process.
A melanoma clue?
The study also could have implications for melanoma. Unlike other tumors, melanocytes that cause cancer can self-renew even from a fully differentiated, pigmented form, the researchers note.
This makes melanomas more difficult to eliminate.
“Our study suggests normal melanocytes are very plastic and can reverse a differentiation state. Melanoma cells are known to be very plastic,” Dr. Ito said. “We consider this feature of melanoma may be related to the high plasticity of original melanocytes.”
The finding that melanocyte stem cells “are more plastic than maybe previously given credit for … certainly has implications in melanoma,” agreed Melissa Harris, PhD, associate professor, department of biology at the University of Alabama, Birmingham, when asked to comment on the study.