Gray hair may be a sign of a protective process in the body, not just a sign of aging. A new study in mice shows that damaged stem cells that produce hair pigment can take two different paths - either disappear and lead to graying, or continue to divide and create the conditions for melanoma.
At the center of the work are melanocyte stem cells. They are found in hair follicles and serve as a reserve for the formation of melanocytes - the cells that give color to hair and skin. Under normal conditions, these cells are cyclically activated to maintain pigmentation during hair growth.
When a damaged cell “retires”
Every day, DNA in cells can be damaged by ultraviolet radiation, chemicals, and processes related to cellular metabolism. In some of these damages, especially double-stranded DNA breaks, melanocyte stem cells undergo a process called senogenesis.
This means that they irreversibly transform into mature pigment cells and leave the stem cell reserve. When the supply is gradually depleted, new hairs lose their pigment and begin to turn gray. According to the study description, this mechanism can limit the accumulation of cells with dangerous genetic changes.
“Every gray hair is a small victory of self-sacrifice“, writes Justin Stebbing, professor of biomedical sciences at Anglia Ruskin University“.The other way leads to melanoma
Experiments show that not all damage triggers the protective response. When exposed to carcinogenic chemicals and ultraviolet radiation, damaged stem cells sometimes bypass senogenesis. Signals from surrounding tissue can encourage them to self-renew and continue dividing, despite carrying genetic damage.
This creates an environment in which cells that give rise to melanoma - a form of skin cancer - can emerge. The published study describes these two outcomes as opposing fates of the same stem cell population: one leads to graying, while the other can promote tumor development.
This does not mean that gray hair itself protects against cancer. Rather, graying may be a side effect of a process by which the body eliminates risky cells. When this control is bypassed by certain carcinogens and signals in the tissue, the damaged cells can survive.
Results not yet proven in humans
The bulk of the data was obtained in mice. It is not yet known whether human melanocyte stem cells respond in the same way, as there are biological differences between species and human genetics and lifestyle are more complex.
The findings could guide future research on aging, DNA damage, and melanoma development. However, for now, they do not provide grounds for accepting hair graying as an indicator of lower or higher individual cancer risk.
Source: Independent