April 21, 2024

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Nature big discovery: Why did hairs become gray?

Nature big discovery: Why did hairs become gray?


Nature big discovery: Why did hairs become gray?

Hair conditions such as gray hair and hair loss are one of the most common conditions encountered by humans, and hair graying is usually a gradual process that begins in middle age.

Melanocyte stem cell (McSC) tissue responsible for hair pigmentation is thought to be similar to hair follicle stem cell (HFSC) tissue.

McSC is located in the bulge region (bulge) and hair matrix (HG) region of the telogen hair follicle (HF) , where McSC is surrounded by hair follicle epithelial stem cells (bulge cells) and progenitor cells (hair matrix cells) , forming the McSC niche .


At the onset of anagen, McSC regenerates differentiated melanocytes that migrate down into the hair bulb, where they produce melanin for the hair. In most mammals, as well as humans, McSCs are depleted earlier than HFSCs, which leads to hair graying during aging. Why McSCs are depleted earlier remains unclear.


On April 19, 2023, the team of Professor Mayumi Ito of New York University Grossman School of Medicine published a research paper entitled: Dedifferentiation maintains melanocyte stem cells in a dynamic niche in Nature .


The study identified the reason for hair graying with age. Melanocyte stem cells (McSCs) have the ability to move back and forth between hair follicle growth areas, and as aging progresses, these stem cells become “trapped”, As a result, the ability to maintain hair color is lost, which in turn leads to graying of the hair. The research opens up a potential new way to prevent or reverse graying.


Nature big discovery: Why did hairs become gray?



Melanocyte stem cells (McSC) in hair follicles can continuously proliferate and differentiate. When they receive sufficient signal stimulation, they will differentiate from a stem cell state into mature melanocytes, thereby producing protein pigments and controlling hair color.


In this latest study, the research team used 3D in vivo imaging and single-cell RNA sequencing ( scRNA-seq ) technology to track and observe McSCs in individual hair follicles of mice for a long time.

They found that during normal hair growth, McSCs develop Various regions of the hair follicle in the brain are constantly moving back and forth, and in these different regions, the McSCs are exposed to signals that affect stem cell maturation differently.

That said, the team found that McSCs switch between their most primitive stem cell state and their mature state depending on where they are located in the hair follicle .


As hair ages, falls out, and then grows out repeatedly, more and more McSCs become trapped in stem cells called the bulge of the follicle, where the McSCs are left without further maturation and differentiation, and do not return to them At their initial location in the hair matrix, WNT proteins stimulate the maturation and differentiation of McSCs into melanocytes.

In the hair follicle bulge region, McSCs were exposed to trillions of times less WNT signaling than in the hair matrix region, which prevented McSCs trapped here from maturing and producing melanin.


Nature big discovery: Why did hairs become gray?Melanocyte stem cells (red), which determine hair color, need to be activated in the hair follicle hair matrix (right) to produce melanin


Other stem cells with self-regenerating abilities, such as hair follicle stem cells, do not have the plasticity of McSCs, and they only move in one direction along the established time axis when they mature.

This also partly explains why hair continues to grow even when pigmentation fails (hair turns gray) .


In this latest study, the research team also promoted hair aging by plucking mice and forcing hair regeneration.

The results showed that the number of McSCs in the bulge area of ​​hair follicles increased from 15% to 50% before plucking, but These cells cannot regenerate or mature into melanocytes, which produce melanin.

In contrast, other McSCs that continued to move back and forth between the follicle’s bulge and the hair matrix remained capable of regenerating, maturing into melanocytes, and producing melanin.


Nature big discovery: Why did hairs become gray?



Dr. Sun Qi , the first author of the paper , said that this research deepens our basic understanding of how melanocyte stem cells (McSC) affect hair color, and it also suggests a potential method – by helping trapped McSC to develop Removal of hair follicles in hair to reverse gray hair or prevent graying of human hair.


Mayumi Ito , the corresponding author of the paper , said that the loss of function of melanocyte stem cells (McSC) may be the cause of hair graying.

These findings suggest that McSC motility and reversible differentiation are key to maintaining hair health and color.


It is reported that the research team plans to further explore ways to restore the ability of McSC to move, or physically move McSC back to the hair matrix area of ​​​​the hair follicle, so that they can produce melanin there.








Paper link :

Nature big discovery: Why did hairs become gray?

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