As we grow older, many of us notice the gradual appearance of grey hairs. Although we attribute it to the natural ageing process, the underlying cause of this change in hair colour has remained a mystery.
However, a new study conducted by researchers at NYU Grossman School of Medicine suggests that certain stem cells getting “stuck” may be the reason behind the greying of hair as people age.
Stem cells, which have the unique ability to develop into various cell types, play a crucial role in the growth of hair follicles. In particular, melanocyte stem cells (McSCs) are responsible for producing protein pigments that give hair its colour.
These McSCs continuously move between different compartments in hair follicles, undergoing various stages of maturation.
As hair grows, sheds and regrows over time, more and more McSCs become lodged in a stem cell compartment called the hair follicle bulge. Instead of maturing and returning to their original location, these stuck McSCs fail to regenerate into pigment-producing cells, leading to the greying of hair.
“Our study adds to our basic understanding of how melanocyte stem cells work to colour hair,” says study lead investigator Qi Sun, a postdoctoral fellow at NYU Langone Health in New York.
“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.”
In experiments conducted on mice, researchers observed that the number of hair follicles with stuck McSCs increased significantly after the hair was physically aged by plucking and forced regrowth.
These trapped McSCs remained incapable of regenerating or maturing into pigment-producing melanocytes, according to the study published in Nature.
The researchers discovered that the stuck McSCs stopped regenerating due to the lack of exposure to signals that would have otherwise allowed them to produce pigment in new hair follicles.
Meanwhile, other McSCs that continued to move between the follicle bulge and hair germ retained their ability to regenerate, mature into melanocytes and produce pigment over the 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,” says study senior investigator Mayumi Ito, a professor in the Ronald O. Perelman Department of Dermatology and the Department of Cell Biology at NYU Langone Health.
Future research will focus on finding ways to restore the movement of McSCs, or to physically move them back to their germ compartment where they can produce pigment. If successful, these findings could potentially lead to ways of reversing or preventing grey hair in humans.
