White hair can be caused by stem cell failure – 04/21/2023 – Equilibrium and Health

Many of the signs of aging are invisible, slow and subtle – changes in cell division ability, cardiac output and kidney function don’t exactly show up in the mirror. But gray hair is one of the most obvious clues that the body is not working the way it used to.

Our hair turns gray when the melanin-producing stem cells stop working properly. A new study with mice, but with implications for people and published on Wednesday (19) in the journal Nature, provides a clearer picture about the cellular failures that transform us into “silver foxes”.

“This is a really big step forward in understanding why we go gray,” said Mayumi Ito, study author and professor of dermatology at New York University’s Grossman School of Medicine.

Unlike embryonic stem cells, which develop into all sorts of different organs, adult stem cells have a more defined pathway. The melanocyte stem cells in our hair follicles are responsible for producing and maintaining the pigment in our hair.

Each hair follicle stores immature melanocyte stem cells. When needed, these cells travel from one part of the follicle to another, where proteins stimulate them to mature into pigment-producing cells, giving hair its hue.

Scientists assumed that gray hair was the result of that reserve of melanocyte stem cells that dried up. However, previous studies in mice have Ito and her co-author, Qi Sun, wondering whether hair could lose its pigment even when stem cells are still present.

To learn more about stem cell behavior throughout the different stages of hair growth, the researchers spent two years tracking and visualizing individual cells in the skin of mice. To their surprise, the stem cells traveled back and forth within the hair follicle, transitioning into their mature pigment-producing state and then out again.

“We were surprised,” Sun said, as seeing a group of stem cells switching between mature and young states doesn’t match existing explanations.

Over time, however, the melanocyte cells could not maintain the double act. A hair falling out and growing back affects the follicle and eventually the stem cells stop making their journey and therefore stop receiving protein signals to produce pigment. From then on, the new hair that grows does not get its dose of melanin.

The researchers explored this effect further by plucking hair from mice, simulating a faster hair growth cycle. This “forced aging” led to an accumulation of melanocyte stem cells trapped in their storage site, ceasing to produce melanin. The mice’s fur turned from dark brown to gray.

Although the study was conducted on rodents, the researchers say their findings should be relevant to how human hair gains and loses its color. What’s more, they hope the findings could be a step towards preventing or reversing the aging process.

Melissa Harris, a biologist at the University of Alabama at Birmingham who was not involved in the study, said the findings help “confirm” previous evidence she’s seen suggesting that “not all melanocyte stem cells are created equal, and even if you have some left over, they might not be useful”.

Harris said he takes the study’s findings on the “forced aging” of mouse hair “with perhaps a bit of caution,” as a plucked hair may not behave the same way as naturally aged hair. But she found the study valuable, not just because a “cure” for gray hair could be a hit with the public; insights into stem cell behavior could help researchers understand things like cancer and cell regeneration.

“I think sometimes people take hair for granted,” she said, “but in some ways it really makes it very easy for us to see the ways that aging or other disorders can affect our bodies.”