Don't stress when the going gets tough - you'll go gray!

According to the latest research the gray hairs which appear as we age are really signs of stress.

A study by Japanese researchers has revealed that a certain kind of stress damages the hair - they say "genotoxic stress" damages DNA by depleting the melanocyte stem cells (MSCs) within hair follicles that are responsible for making the pigment-producing cells.

The team say instead of dying off, when the going gets tough, those precious stem cells differentiate, forming fully mature melanocytes themselves and anything which limits the stress might stop the graying from happening.

The researchers say 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 and a single cell in mammals can encounter approximately 100,000 DNA damaging events each day.

As a result cells have devised elaborate ways to repair damaged DNA and prevent the lesions from being passed on to their daughter cells - once stem cells are damaged irreversibly, the damaged stem cells need to be eliminated to maintain the quality of the stem cell pools and the researchers found that excessive genotoxic stress triggers differentiation of melanocyte stem cells which may be a more sophisticated way to get rid of those cells than stimulating their death.

The team led by Emi Nishimura of Tokyo Medical and Dental University had earlier traced the loss of hair color to the gradual dying off of the stem cells that maintain a continuous supply of new melanocytes, giving hair its youthful color - they say those specialized stem cells are not only lost, they also turn into fully committed pigment cells and in the wrong place.

In their new research in mice they found that irreparable DNA damage, as caused by ionizing radiation, is responsible and the "caretaker gene" known as ATM (ataxia telangiectasia mutated) serves as a so-called stemness checkpoint, protecting against MSCs differentiation.

The researchers say this is why people with Ataxia-telangiectasia, an aging syndrome caused by a mutation in the ATM gene, go gray prematurely.

The researchers say this supports the theory that genome instability is a significant factor underlying aging in general and the "stem cell aging hypothesis," which suggests that DNA damage to long-lived stem cells can be a major cause for the symptoms that come with age.

The researchers say in addition to the aging-associated stem cell depletion typically seen in melanocyte stem cells, qualitative and quantitative changes to other body stem cells have been reported in blood stem cells, cardiac muscle, and skeletal muscle and stresses on stem cell pools and genome maintenance failures have also been implicated in the decline of tissue renewal capacity and the accelerated appearance of aging-related characteristics.

They say their study has revealed that hair graying, the most obvious aging phenotype, can be caused by the genomic damage response through stem cell differentiation, which suggests that physiological hair graying can be triggered by the accumulation of unavoidable DNA damage and DNA-damage response associated with aging through MSC differentiation.

The report is published in the June 12th issue of Cell, a Cell Press publication.