As we go through life, our cells face many types of stress that can damage their DNA. These stressors come from both inside the body and the outside environment.
Scientists know that DNA damage plays a role in aging and cancer, but the exact connection—especially how this affects stem cells and long-term tissue health—has been unclear.
A new study from The University of Tokyo is now helping to explain this mystery. Researchers looked closely at a type of stem cell called melanocyte stem cells, or McSCs. These cells are responsible for creating pigment in our skin and hair.
They live in hair follicles and help renew color in our hair each time it grows back.
In their study, which was published in the journal Nature Cell Biology, scientists used advanced methods to watch these cells over time in live mice.
They wanted to see how these cells react when their DNA is damaged.
They found something surprising. When McSCs experience a serious type of DNA damage—called a double-strand break—the cells go through a process called “senescence-coupled differentiation” or “seno-differentiation.”
This means the cells stop dividing and mature fully. Once they do this, they can’t go back to being stem cells. As a result, they disappear from the hair follicle, which causes hair to turn gray. This is controlled by a well-known safety switch in cells, the p53–p21 pathway.
So graying hair may not just be a sign of getting older—it could be a sign that the body is protecting itself. By forcing damaged stem cells to mature and go away, the body may be removing cells that could otherwise turn dangerous.
However, the study also showed a darker side. When the researchers exposed McSCs to certain cancer-causing substances like ultraviolet light or a chemical called DMBA, the stem cells didn’t go through seno-differentiation. Even though they had damaged DNA, these cells kept dividing and even expanded in number.
This was partly due to a signal called KIT ligand, which comes from nearby skin cells and tells the McSCs to keep renewing themselves. Because the stem cells weren’t removed, they had a higher chance of becoming cancerous, potentially leading to melanoma, a dangerous form of skin cancer.
Lead researcher Professor Emi Nishimura explains that these findings show stem cells can go down two very different paths depending on the type of stress and signals from their surroundings.
In some cases, stress causes the stem cells to shut down and disappear—leading to gray hair. In other cases, stress leads them to keep growing in risky ways—possibly starting cancer.
This research does not mean that having gray hair will stop you from getting cancer. Instead, it suggests that graying is a kind of natural safety mechanism. When this mechanism fails or is bypassed, it may increase the chances of cancer.
The study gives us a new way to understand how aging and cancer are connected. It shows that sometimes aging signs like gray hair may actually be the body’s way of staying safe. Removing damaged stem cells through a natural process—like senolysis—might protect us in the long run.
If you care about cancer, please read studies about a new method to treat cancer effectively, and this low-dose, four-drug combo may block cancer spread.
For more information about cancer prevention, please see recent studies about nutrient in fish that can be a poison for cancer, and results showing this daily vitamin is critical to cancer prevention.
The study is published in Nature Cell Biology.
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