'Stuck' stem cells may cause hair to turn grey

The movement of stem cells within hair follicles may explain why hair pigment is lost with age.

Researchers in New York studying hair follicles in mice found that the stem cells that produce the pigment in hair move between compartments in the follicle to function. However – according to research published in Nature – with ageing, they get stuck in one compartment meaning that they are no longer exposed to the signals they need to make the pigments for hair colour. As a result, the hair turns grey or white.

'Our study adds to our basic understanding of how melanocyte stem cells work to colour hair,' said first author Dr Qi Sun from the New York University (NYU) Grossman School of Medicine. 'The newfound mechanisms raise the possibility that the same fixed positioning of melanocyte stem cells may exist in humans.'

Stem cells are specialised cells that can both self-renew and differentiate (mature) into other types of cells. Melanocyte stem cells (McSCs), which are found in the skin of mice and humans, are a specialist type of stem cell which produce the pigments that give colour to hair.

McSCs have a unique ability which allows them to move between compartments in the hair follicle where they receive different signals. This means that they toggle between a self-renewing state and a mature state where they produce the pigment that colours hair.

Researchers tracked McSC movements between compartments in the hair follicles of mice. They found that as the hair was aged through plucking and regrowth, the number of McSCs that were stuck in a compartment called the hair follicle bulge increased from 15 percent to nearly 50 percent. This meant that the cells did not receive the signals they needed to either self-renew or mature.

'These findings suggest that melanocyte stem cell motility and reversible differentiation are key to keeping hair healthy and coloured,' commented lead author Professor Mayumi Ito, also from NYU. 'It is the loss of chameleon-like function in melanocyte stem cells that may be responsible for greying and loss of hair colour.'

Dr Sun suggests that this research may lead to strategies to prevent or reverse the greying of hair by helping stuck cells move between compartments again.