By Margarita Nahapetyan
Grey hair is a sign of age, without any doubt, but the real cause of the hair color change is stress, report Japanese scientists in a paper. The study also says that if individuals experienced less stress in their lives, they could keep their natural color much longer.
According to the principal author of the study, Emi Nishimura, of Kanazawa University in Japan, stress, in fact, damages DNA and depletes the melanocyte stem cells within hair follicles that are responsible for the production of the pigment-producing cells. In its turn, the depletion results in irreversible graying of hair. The findings could help explain why people with Ataxia telangiectasia, a rare, neurodegenerative syndrome which is caused by a mutation in the ATM gene, go grey prematurely. But the good news is that limiting the amount of strain people usually find themselves under, can stop grey hair from growing - or at least slow the progress.
"The DNA in cells is under constant attack by exogenously- and endogenously-arising DNA-damaging agents such as mutagenic chemicals, ultraviolet light and ionizing radiation," said Emi Nishimura. "It is estimated that a single cell in mammals can encounter approximately 100,000 DNA damaging events on a daily basis," the expert added.
Consequently, Nishimura explained, cells have elaborate ways to repair damaged DNA and prevent the damage from being passed on to their daughter cells. Once stem cells are damaged completely, they need to be taken out in order to maintain the quality of the stem cell pools, researchers explained. "We found that excessive genotoxic stress triggers differentiation of melanocyte stem cells," Nishimura said, and also added that differentiation might be a more sophisticated way and a better solution to get rid of those cells rather than stimulating their death.
In previous studies, Nishimura and her colleagues have examined and traced the loss of hair color to the gradual death of the stem cells that provide a constant supply of new melanocytes, therefore giving hair the opportunity to maintain its youthful color. Those specialized stem cells are not only getting lost, but they also transform into fully committed different pigment cells and in the wrong place.
In the new study, the investigators were able to demonstrate in mice that irreparable DNA damage, as caused by ionizing radiation, is the one responsible for symptoms of aging, with gray hair being the most visible one. But they also plan to find out whether a stem-cell quality control mechanism that keeps defective stem cells from replicating might also protect against cancer. The study looked only at stem cells in hair follicles, and only in mice. Further experiments could explore whether stem cell differentiation is a common quality control mechanism that animals, including humans, use to prevent damaged cells from causing disease.
The findings are being reported in the June 12 issue of the journal Cell.