A study conducted by scientists at the University of Tokyo found that gray hair is not only a sign of aging, but can also be a reflection a defense reaction of the body against genetic damage that promotes the development of cancer.
The research, published in the journal Natural cell biology, focused on the behavior of melanocyte stem cells, which are responsible for producing melanin, which gives color to hair and skin. Under normal conditions, these cells are activated in each hair cycle, dividing and producing mature melanocytes that pigment the hair.
Over the years, this ability weakens and the hair loses color. The novelty of the study was to show that this process does not always respond only to the wear and tear of time, but also to a biological control system that protects the organism.
The researchers observed this Certain types of DNA damage in mice, such as those caused by ionizing radiation, activate a defense pathway that forces these stem cells to irreversibly mature. This pathway leads to their depletion, preventing further division and leaving the follicle without a source of pigment. The visible result was the appearance of gray hair, But the invisible effect was the key: by stopping cell division, the organism reduces the risk of dangerous mutations are transmitted and lead to tumors.
“It is a type of exhaustion called cellular aging. “It is a limit to the total number of cell divisions a cell can undergo, and it appears to be an anti-cancer mechanism designed to prevent genetic errors acquired randomly over time from spreading uncontrollably,” he explained. Dot Bennettcell biologist City of St George’s, University of Londonwho did not take part in the study.
The experimental work was carried out on mice, where the professor’s team worked Emi Nishimura and the teacher assistant Yasuaki Mohri has been using cell tracking and genetic analysis techniques for several years. The goal was to track the fate of individual stem cells after they were exposed to different types of environmental stress. The results showed that not all DNA damage triggers the same response. Some attacks push cells toward senescence, while others block this natural brake.
When melanocyte stem cells suffer double breaks in their DNA, a process called sinusoidal differentiation is activated. This mechanism mediated by the p53-p21 signaling pathway forces cells to mature and lose their ability to self-renew. When this cell reserve disappears, the hair turns gray. From the body’s perspective, this loss serves a protective function by eliminating potentially harmful cells before they can become cancerous.
The study showed a disturbing contrast when the genetic damage came from specific causes chemical carcinogens or des ultraviolet B radiation. In these cases the senescence mechanism was not activated. In contrast, the stem cells retained their ability to divide and produce pigments, allowing the hair to retain its color.
In the long term, this apparent aesthetic advantage had an impact biological costs: The replication of damaged DNA promoted the clonal expansion of altered cells and increased the risk of cancer, such as melanoma.
According to the researchers The cellular environment plays a crucial role. Signals from the hair follicle niche, such as the KIT ligand present in the surrounding skin, influence the stem cells’ decision. When these signals block the senescence pathway, damaged cells are not eliminated and remain in the tissue, creating a scenario that favors malignant transformation.
“The same population of stem cells can take opposite paths, exhaust or expand“Depending on the type of damage and the signs of the environment,” said Emi Nishimura, lead author of the study, quoted by the University of Tokyo itself. The researcher claimed that this finding forces us to rethink Relationship between age and cancertwo processes that have been studied as separate phenomena for decades.
From this perspective, gray hair is no longer a mere cosmetic sign, but a visible indication of profound cellular defense mechanisms. This is what the work suggests Faced with certain attacks, the organism prioritizes genetic safety over preserving functions such as pigmentation. Gray hair then appears as a biological price for a strategy that protects tissue from tumor development.
The study authors emphasized that this phenomenon does not mean that people with gray hair are protected from cancer. The graying reflects the activation of a mechanism. no absolute guarantee. However, it suggests so The body has control systems that, when functioning correctly, limit the proliferation of damaged cells. The problem arises when these pathways become blocked or fail, either due to environmental factors or abnormal signals from the cellular environment.
The connection between Aging, selective cell destruction and cancer It manifested itself at the molecular level. The research identified biochemical pathways that tip the balance between the elimination of dangerous cells and their disorderly proliferation. In this delicate balance, processes such as senolysis, which promotes the controlled elimination of aged or damaged cells, appear as a central component of the body’s defenses.
Scientists have spent eight years reconstructing this map of cellular decisions. They used animal models to simulate both normal aging and exposure to carcinogens. The results showed that sinusoidal differentiation functions as natural brake against genetic damagewhile its blockage opens the door for the accumulation of mutations and the development of tumors.
From a broader perspective, the study offers a new way to understand aging. It is far from being a purely degenerative process; adaptive responses which are aimed at preserving the integrity of the organism. Gray hair appears in this context as external manifestation of an internal decision: Sacrifice secondary functions to avoid more serious consequences.
The next step, according to experts, is this Apply these observations to human hair. Although the basic mechanisms are conserved in mammals, how these pathways function in humans and what environmental or genetic factors influence their activation remain to be confirmed. Understanding these differences is key to evaluating potential clinical applications.
In the long term, the findings open the door new prevention and treatment strategies. If scientists can modulate the signals that drive stem cells toward senescence or expansion, therapies could be developed that boost protective mechanisms without affecting essential tissue functions. In the area skin cancer, This knowledge could be particularly relevant.
The study first invites us to look at gray hair with different eyes. What was interpreted for years as an inescapable symbol of aging could also be the visible trace of it microscopic fight in which the organism tries to protect itself.
In this tension between wear and defense, gray hairs appear as a reminder that the Aging does not always mean losssometimes also reflects silent cell survival strategies.
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