New research suggests that gray hair may be a sign that the body is effectively protecting itself from cancer.
Triggers that cause cancer, such as ultraviolet (UV) light The study found that certain chemicals activate a natural defense pathway that leads to premature graying but also reduces the incidence of cancer.
The researchers who conducted the study traced the fate of the stem cells responsible for producing the pigment that gives hair its color. In experiments on mice, they found that these cells respond to DNA they cause damage by either stopping growing and dividing, which leads to gray hair, or by multiplying uncontrollably, eventually leading to tumor formation.
The findings were reported in October in the journal Natural Cell Biologyhighlight the importance of these types of protective mechanisms that emerge with age as protection against DNA damage and disease, the study authors say.
Gray hair protects against cancer
Healthy hair growth depends on a population of stem cells that are constantly renewed within the hair follicle. A tiny pocket inside the follicle contains reserves of melanocyte stem cells, the precursor cells that produce the pigment melanin, which gives hair its color.
“Every hair growth cycle, these melanocyte stem cells will divide and produce several mature, differentiated cells,” he said. Dot Bennettcell biologist from St George's, University of London, who was not involved in the study. “They migrate down to the bottom of the hair follicle and begin to produce pigment that goes into the hair.”
Graying occurs when these cells can no longer produce enough pigment to thoroughly color each strand.
“It's a kind of wasting called cellular senescence,” Bennett explained. “This limits the total number of divisions a cell can go through and appears to be an anti-cancer mechanism, preventing random genetic errors acquired over time from spreading uncontrollably.”
When melanocyte stem cells reach this “stemness checkpoint,” they stop dividing, meaning the follicle no longer has a source of hair color pigment. This usually occurs in old age as stem cells naturally reach this limit. However, Amy Nishimuraprofessor of age-related stem cell medicine and his colleagues at the University of Tokyo were interested in how this same mechanism operates in response to DNA damage—a key trigger for Cancer development.
In studies in mice, the team used a combination of methods to track the progress of individual melanocyte stem cells through the hair growth cycle after exposing them to a variety of harmful environmental conditions, including ionizing radiation and carcinogenic compounds. Interestingly, they found that the type of damage affected the cell's response.
The ionizing radiation caused the stem cells to differentiate and mature and ultimately activated the biochemical pathway responsible for cell aging. As a result, melanocyte stem cell reserves were rapidly depleted during the hair growth cycle, stopping the production of further mature pigment cells and leading to gray hair.
Meanwhile, by essentially shutting down cell division, this aging pathway prevented the mutated DNA from passing on to a new generation of cells, thereby reducing the likelihood of those cells forming cancerous tumors.
Exposure to chemical carcinogens such as 7,12-dimethylbenz[a]anthracene (DMBA)a tumor initiator widely used in cancer research appears to bypass this protective mechanism. Instead of turning on senescence, it turned on a competing cellular pathway.
This alternative chemical sequence blocked cell aging in mouse studies, allowing hair follicles to retain stem cell reserves and the ability to produce pigment even after DNA damage. This meant that the hair retained its color, but in the long term, uncontrolled replication of damaged DNA led to the formation of tumors and cancer, the team said in the report. statement.
These results show that the same population of stem cells can suffer different fates depending on the type of stress they are exposed to, Nishimura, the study's lead author, said in a statement. “He's redefining graying hair and melanoma. [skin cancer] not as unrelated events, but as different outcomes of stem cell responses to stress,” Nishimura added.
The next step will be to translate this understanding to human hair follicles to see if these observations in mice translate to humans, Bennett said.
This article is for informational purposes only and is not intended to provide medical advice.
