Grey hair may be protecting us from cancer

 
Another article from New Scientist documenting the slow decline of that journal into a typical supermarket rag [Grey hair may be protecting us from cancer ].

GREY hair may be unwelcome, but the processes that produce it are now better understood and could be protecting us from cancer.

First off, I want to make it clear that many of us with grey hair do not find it "unwelcome" in spite of societal pressures to make us feel embarrassed.

Second, here's the actual paper and abstract [doi:10.1016/j.cell.2009.03.037].

Inomata, K., Aoto, T., Binh, N.T., Okamoto, N., Tanimura, S., Wakayama, T., Iseki, S., Hara, E., Masunaga, T., Shimizu, H., and Nishimura, E.K. (2009) Genotoxic Stress Abrogates Renewal of Melanocyte Stem Cells by Triggering Their Differentiation. Cell 137: 1088-1099.

Somatic stem cell depletion due to the accumulation of DNA damage has been implicated in the appearance of aging-related phenotypes. Hair graying, a typical sign of aging in mammals, is caused by the incomplete maintenance of melanocyte stem cells (MSCs) with age. Here, we report that irreparable DNA damage, as caused by ionizing radiation, abrogates renewal of MSCs in mice. Surprisingly, the DNA-damage response triggers MSC differentiation into mature melanocytes in the niche, rather than inducing their apoptosis or senescence. The resulting MSC depletion leads to irreversible hair graying. Furthermore, deficiency of Ataxia-telangiectasia mutated (ATM), a central transducer kinase of the DNA-damage response, sensitizes MSCs to ectopic differentiation, demonstrating that the kinase protects MSCs from their premature differentiation by functioning as a “stemness checkpoint” to maintain the stem cell quality and quantity.

The idea is that DNA damage causes stem cells to differentiate into melanocytes that eventually die. Since there are fewer stem cells there will be fewer melanocytes produced over time and hair becomes grey. The fact that damaged stem cells undergo terminal differentiation instead of remaining as stem cells means that they are probably less likely to serve as the progenitors of a cancerous cell line.

Whether this has any real effect on protecting us from cancer is an open question. I doubt it very much but it's an easy hypothesis to test. Is it true that people with grey hair develop fewer cancers than people of the same age with darker hair?

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