Why does hair go grey? Study links ‘stuck’ stem cells to lack of pigment in hair

Following news of a breakthrough in the mechanisms behind hair greying, Cosmetics Business rounds up its edit of anti-greying active ingredients

Repeated shed and growth leads to melanocyte stem cells becoming stuck in the hair follicle bulge

Grey hair is a hallmark of ageing, but one that is increasingly being embraced.

Recent years have witnessed stars like Andie MacDowell and Sarah Jessica Parker celebrating the changing colour of their hair.

Meanwhile, brands developed specifically for the needs of silver strands, like White Hot Hair, Arey and Silvina London are attracting attention.

In November, for example, Arey closed a funding round of US$4.15m – more than double that of its original $2m target.
But what causes hair to go grey?

New research from NYU Grossman School of Medicine, published in the journal Nature on 19 April, suggests the process is linked to ‘stuck’ stem cells.

The study looked at melanocyte stem cells, found in the skin of mice but also humans.

Hair colour, the scientists said, is controlled by whether non-functional but continually multiplying pools of these stem cells within hair follicles get the signal to become mature cells which make the protein pigments responsible for colour.

The study showed that melanocyte stem cells are remarkably plastic; this means that during normal hair growth, such cells continually move back and forth on the maturity axis as they transit between compartments of the developing hair follicle.

It is inside these compartments where the cells are exposed to different levels of maturity-influencing protein signals.

The research team found that the cells transform between their most primitive stem state and the next stage of their maturation (the transit-amplifying state) depending on their location.

As hair ages, sheds and repeatedly grows back, increasing numbers of melanocyte stem cells get stuck in the stem cell compartment called the hair follicle bulge.

They remain in the hair follicle bulge, do not mature into the transit-amplifying state and do not travel back to their original location in the germ compartment, where Wnt proteins (signalling molecules) would have encouraged them to regenerate into pigment cells.

“Our study adds to our basic understanding of how melanocyte stem cells work to colour hair,” said the study’s lead investigator, Qi Sun, a postdoctoral fellow at NYU Langone Health.

“The newfound mechanisms raise the possibility that the same fixed positioning of melanocyte stem cells may exist in humans.

“If so, it presents a potential pathway for reversing or preventing the greying of human hair by helping jammed cells to move again between developing hair follicle compartments.”

Such plasticity is not present in other self-regenerating stem cells, such as those making up the hair follicle itself.

This, said the researchers, helps explain, in part, why hair can keep growing even while its pigmentation fails.

The study also found that stuck melanocyte stem cells ceased their regenerative behaviour as they were no longer exposed to much Wnt signalling.

In contrast, melanocyte stem cells that continued to move back and forth between the follicle bulge and hair germ retained their ability to regenerate as melanocyte stem cells, mature into melanocytes and produce pigment over the entire study period of two years.

“It is the loss of chameleon-like function in melanocyte stem cells that may be responsible for greying and loss of hair colour,” said study senior investigator Mayumi Ito, a professor in the Ronald O. Perelman Department of Dermatology and Department of Cell Biology at NYU Langone Health.

“These findings suggest that melanocyte stem cell motility and reversible differentiation are key to keeping hair healthy and coloured,” said Ito.
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In good news for those consumers not ready to embrace their greys, the team plans to investigate means of restoring the motility of melanocyte stem cells, or of physically moving them back to their germ compartment, where they can produce pigment.

from Cosmetics Business