Why are white hair pulling out more and more? Nature: Stem cells are stuck

Why does human hair gradually turn gray with age? Is there a basis for the common saying that “white hair is plucked more and more”? Recently, a study led by a research team led by New York University Grossman School of Medicine revealed the underlying mechanism behind these natural phenomena: hair whitening or due to melanocytes being “stuck”. The research paper was published online April 19 in the journal Nature.

Hair follicle melanocytes (McSCs) are directly involved in the production of melanocytes, which are key to hair color. Researchers believe that hair whitening is because melanocytes are “stuck” at a specific location of the hair follicle, so they cannot move to the correct position and receive relevant molecular signals of “mature differentiation”, and can no longer differentiate into melanocytes.

The study proposes that, unlike the unidirectional, sequential differentiation of other adult stem cells, mouse melanocytes have the ability to “wander” in hair follicles – the researchers tracked the cells in real time through 3D in vivo imaging technology and single-cell RNA sequencing technology and found that most McSCs are mobile, they translocate back and forth between different compartments of the hair follicles, and repeatedly differentiate and “dedifferentiate” (that is, return to an undifferentiated state) in the process, showing a unique mechanism of reversible change.

However, the years change and the hair follicles gradually age. As the hair grows and falls out over and over again, more and more McSCs get stuck in a special area called follicular carina. The researchers reasoned that in this particular region, McSCs were unable to receive signals from maturely differentiated molecules, and they were also unable to move to a region where they could mature. Over time, the hair continues to grow, but gradually does not get enough melanin, which causes the green silk to gradually turn gray.

To test this inference, the research team plucked out the hair of the experimental mice again and again over a two-year period, and finally bred pepper-and-salt (black and white) mice — almost in line with the oft-called “more and more white hair”. The researchers said that hair plucking is to accelerate the speed of hair regrowth and aging of hair follicles in mice. Live-cell imaging and genetic sequencing showed that the proportion of McSCs in the areas of aging follicle carina increased from 10% to 50% compared to young follicles that had not been plucked.

After repeated hair plucking, the mice gradually turned salt-and-pepper. Image source: paper with pictures

The research team said that the unique mechanism of change and maturation of melanocytes may be one of the reasons for their premature “failure” compared to other adult stem cells. At the same time, the researchers also believe that the discovery of this mechanism also shows that people have the opportunity to intervene and prevent the phenomenon of “white juvenile heads” by regulating the migration of McSCs.

However, the research team affirmed that melanocytes are not the only factors that determine hair growth and color, and some research views believe that many factors such as sun exposure, hormones, stress, genetics, and medication also play an important role. (Source: China Science News Zhao Guangli)

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