GREY hair may be unwelcome, but the processes that produce it are now better understood and could be protecting us from cancer.
Cells called melanocytes produce the pigments that colour hair and their numbers are kept topped up by stem cells. Hair goes grey when the number of stem cells in hair follicles declines. Now Emi Nishimura of Tokyo Medical and Dental University in Japan and colleagues have found what causes this decline in mice.
When the researchers exposed mice to radiation and chemicals that harmDNA, damaged stem cells transformed permanently into melanocytes. This ultimately led to fewer melanocytes, as it meant there were fewer stem cells capable of topping up the melanocyte pool. The mice also went grey (Cell, vol 137, p 1088). Nishimura's team proposes that the same process leads to the reduction in stem cells in the follicles of older people, especially as DNA damage accumulates as we age.
David Fisher, a cancer researcher at Harvard Medical School, suggests such processes may help protect us from cancer, by discouraging the proliferation of stem cells with damaged DNA, which could pass on mutations. "One likely beneficial effect is the removal of potentially dangerous cells that may contain pre-cancerous capabilities," he says.