Greying hair may be more than a sign of age: it may reflect a cellular defence, scientists at the Institute of Medical Science at the University of Tokyo suggest. Their study in mice is published in the journal Nature Cell Biology. Dhaka Tribune reported it, citing The Telegraph and ScienceDaily.
Hair colour comes from melanocyte stem cells. Deep in the hair follicle, these cells produce pigment cells called melanocytes as needed, waking with the cycle of hair growth and shedding and then resting again. Their DNA can be damaged by ultraviolet light, chemicals or the body's normal metabolism.
The researchers found that when the damage is serious, such as breaks in both strands of DNA, the stem cell quickly turns itself into a mature pigment cell and never returns to being a stem cell, a process they call "seno-differentiation". The pool of pigment-making cells shrinks and hair turns grey or white: a potentially risky cell steps aside before it can become dangerous.
Not every kind of damage leads the same way. When the team exposed mouse melanocyte stem cells to carcinogenic chemicals and ultraviolet light, signals from surrounding tissue sometimes pushed damaged stem cells to divide again; they survived with damaged DNA, which can raise the risk of melanoma, a skin cancer. The scientists call these opposing outcomes "antagonistic fates".
The study does not claim that grey hair protects against cancer. Most key experiments were in mice, whose biology differs from ours, and human genes, lifestyle and environment may also affect the process, so more research is needed to establish how greying relates to melanoma risk in people, the report says.
Photo: attributed to Rembrandt / Wikimedia Commons (public domain)
Source: Dhaka Tribune
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