Link between ‘stuck’ stem cells to graying hair

June 02, 2023 | Histopathology

During aging, stem cells that have the ability to move between growth compartments in hair follicles get stuck. This leads to losing the ability to mature and maintain hair color, suggests a new study by the NYU Langone Health and NYU Grossman School of Medicine research team.

The researchers focused on the skin cells of mice and melanocyte stem cells (McSCs) from humans, using 3D-intravital-imaging and scRNA-seq techniques in tracking cells real time as they aged and moved within each hair follicle. In their experiment, mice hair was physically aged by plucking and forced regrowth. There was an increase of the number of hair follicles with McSCs lodged in the follicle bulge, from 15 percent before plucking to nearly a half after forced aging.

Hair color is determined by whether McSCs within hair follicles get the signal to become mature cells. They found that the McSCs are plastic or that they vacillate on the maturity axis as they transfer between compartments of a developing hair follicle where it gets varying levels of exposure to protein signals that influence maturity. This meant that depending on their location, the McSCs transform from their primitive stem cell state to the next stage of maturation.

The more the hair ages, sheds, and regenerates, a growing number of McSCs get stuck in the hair follicle bulge where they remain and do not mature. These McSCs cannot go back to their original location in the germ compartment where WNT proteins prod them to become pigment cells. Thus, it is the loss of chameleon-like function in melanocytes that leads to the loss of hair color.

These findings illustrate a potential pathway for reversing or preventing the graying of hair in humans by melanocyte stem cell motility and reversible differentiation.