Is stress really responsible for our grey hair?

Allie MONTGOMERY

We all know what comes with age, those stubborn gray hairs. But it's not only age that causes those gray hairs to pop out. They are actually signs of stress, however, it is only stress on the cellular level. Genotoxic stress-which is categorized by anything that damages our DNA-sets off a chain of events in which specialized cells that are known as melanocyte stem cells (MSCs) become damaged and ultimately result in a malfunction within the cells that are responsible for our hair colour.

The scientists discovered that the type of genotoxic stress that causes damage to our DNA depletes the MSCs in the hair follicles that make the pigment-producing melanocytes. When they are exposed to the stress, these MSCs differentiate into melanocytes themselves, rather than just dying off.

Therefore, the researchers said that anything we can do to limit the genotoxic stress may also help stop the graying from taking place.

Emi Nishimura, from the Tokyo Medical and Dental University, said, "The DNA in cells in under constant attack by exogenously and endogenously arising DNA-damaging agents such as mutagenic chemicals, ultraviolet light, and ionizing radiation.

It is estimated that a single cell in mammals can encounter approximately 100,000 DNA damaging events per day." However, these particular cells have sophisticated ways to repair the damaged DNA and help prevent the damage from being passed on to their daughter cells.

Nishimura explained, "Once stem cells are damaged irreversibly, the damaged stem cells need to be eliminated to maintain the quality of the stem cell pools. We found that excessive genotoxic stress triggers differentiation of melanocyte stem cells." She also added that the differentiation might be a more sophisticate way to help eliminate those cells all together instead of fostering their death.

Previously, Nishimura's team of researchers traced the loss of hair colour to the gradual loss of the stem cells that are used to maintain a continuous supply of new melanocytes, which is gives our hair its youthful, vibrant colour.

It turns out that the specialized stem cells are not only lost, they also differentiate into fully committed pigment cells that are not in the right place. The current study, which was conducted using mice, found that the irreparable DNA damage, in this case that was caused by ionizing radiation, is responsible. Also, the researchers found that the "caretaker gene" also known as ATM (ataxia telangiectasia) serves as a stemness checkpoint that helps protect against the differentiation of MSCs. This is why the people that suffer from

Ataxia-telangiectasia, which is an aging syndrome that is caused by an ATM gene mutation, will prematurely gray.

The recent study supports the idea that genome instability plays a significant role in aging.

It also supports the "stem cell aging hypothesis," which states that the DNA damage to long-lived stem cells can be a major driver for many of the conditions that develop as we age.

In addition to the stem cell depletion that is associated with aging typically seen in MSCs, qualitative and quantitative alterations to the blood stem cells, skeletal muscle and cardiac muscle have also been reported.

Genome maintenance failures and the stresses on stem cell pools are also thought to be responsible for the decline of the tissue renewal capacity and the accelerated appearance of aging-related characteristics, such as the graying of hair.

The team wrote, "In this study, we discovered 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."

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