Going grey may help remove damaged cells linked to cancer, study finds

Grey hair is one of the most visible signs of ageing. But new research suggests that greying may also be linked to a cellular process that removes damaged cells and may help protect against melanoma, a type of skin cancer.

A new study in mice has found a connection between hair greying and the way melanocyte stem cells respond to DNA damage. These cells, found in hair follicles, produce melanocytes, the pigment-producing cells responsible for hair and skin colour, reports the Independent.

Normally, melanocyte stem cells repeatedly produce new pigment-producing cells as part of the hair-growth cycle, helping maintain hair colour.

But cells are constantly exposed to factors that can damage their DNA, including ultraviolet radiation, chemicals and normal processes inside the body. Serious DNA damage can contribute to ageing and cancer.

The study focused on what happens when melanocyte stem cells suffer a particularly severe form of DNA damage known as a double-strand break.

Researchers found that, in response to this type of damage, some of the stem cells undergo a process called "seno-differentiation".

The cells irreversibly mature into pigment-producing cells and are then depleted from the stem-cell pool. As the supply of melanocyte stem cells falls, hair can gradually lose its colour and turn grey.

The researchers suggest that this process may act as a protective mechanism by removing damaged stem cells that could otherwise accumulate genetic changes and potentially contribute to cancer.

The findings, however, suggest that not all types of DNA damage trigger the same response.

Cancer link

In experiments on mice, researchers exposed melanocyte stem cells to carcinogens and ultraviolet B radiation. Under these conditions, some damaged stem cells bypassed seno-differentiation and continued to renew themselves and divide.

The researchers found that signals from surrounding tissue could support this continued self-renewal, allowing damaged stem cells to persist and creating conditions that may contribute to melanoma development.

The study identified signalling involving KIT ligand and arachidonic acid metabolism as part of this process.

The findings suggest that the fate of melanocyte stem cells depends on both the type of DNA damage they suffer and signals from their surrounding environment.

Under some forms of stress, damaged stem cells are effectively removed from the stem-cell population, contributing to hair greying. Under certain carcinogenic conditions, however, they can escape this process and continue multiplying.

Scientists describe these as "antagonistic fates" -- the same population of stem cells can follow two very different paths depending on the type of stress and the signals in their surrounding environment.

The findings do not mean that grey hair itself protects people from cancer. Rather, greying may be a visible consequence of a cellular process that removes potentially dangerous stem cells. The researchers' findings specifically concern melanoma and should not be interpreted as evidence that grey hair lowers a person's overall cancer risk.

The research may also provide clues about the relationship between ageing and cancer. As the body ages, changes in stem cells and their surrounding environment may influence whether damaged cells are eliminated or continue to grow.

However, the study's findings cannot yet be directly applied to humans. The research was conducted in mice, and further work is needed to determine whether human melanocyte stem cells respond to DNA damage in the same way.

Even so, the findings could help scientists better understand how ageing and cancer are connected. Further research into the signals that determine whether damaged stem cells are eliminated or continue dividing could eventually point to new approaches to cancer prevention or treatment.