After a long illness or chronic stress, the hair loses its natural color and becomes gray or white. This phenomenon called canities can even occur in relatively young people. Due in part to genetic factors, it was still largely an enigma for the scientific community.
A team of researchers from the National Institutes of Health (NIH) and the University of Alabama, Birmingham, may have finally unravelled the mystery. In a study published this week in the journal PLOS Biology, they explain having discovered that the immune system, and especially interferons, played a predominant role in hair whitening.
Our hair, before being black, blond, chestnut or red, is actually naturally white. They are stained by a pigment, melanin, which is produced by cells called melanocytes. These melanocytes are positioned in the hair follicles. As each hair grows, it is “infused” with melanin, which gives it its color. As we get older, melanocytes slow down and disappear slowly, which reduces the amount of pigment produced and leaves us with gray, then white hair.
This phenomenon can be accelerated in case of illness or when the body is subjected to a period of significant stress. When the body is invaded by a pathogen, the innate immune system is the first responder. Also known as the non-specific immune system, it includes cells and mechanisms that enable the body to be defended against infectious agents immediately.
The cells that make up the innate immune system have the ability to recognize invaders and, when they do, they release interferons, proteins that induce other cells to act by increasing the activity of genes that block viral replication. .
Lead author of the study, Melissa Harris, Assistant Professor in the Department of Biology at the University of Alabama, explains how they came across this surprising link between hair color and interferons by conducting tests on mice . “My lab is harnessing the power of graying mouse models to better understand stem cells and aging. The stem cells we are studying are the melanocytic stem cells of the hair follicle, which are the stem cells that are essential for the production of melanocytes,” she explains.
With her team, Dr. Harris focused on a particular gene in melanocytes, called the melanogenesis-associated transcription factor (MITF) gene. It is this gene that tells the melanocytes to produce melanin.
In mice whose fur became gray early, the researchers first noticed that their MITF production was unusually high: which probably led them to deplete their melanocyte stores quickly. More surprisingly, they also found that mice producing less MITF also had hair that turned gray.
They then suggested that MITF not only oversees the production of melanin in melanocytes, but also controls the genes responsible for interferon release. Without enough MITF, melanocytes produce too much interferon, which then induces the immune system to attack melanocytes, which no longer produce melanin. Hence the appearance of gray hair.
For the researchers, this discovery is important, since it suggests that it is the same genes that control both the pigmentation of hair, eyes and skin, and the immune system. This connection may help to understand some diseases of pigmentation such as vitiligo, which causes discolored skin spots and affects between 0.5 and 1% of the world population. “Many researchers working on vitiligo have already speculated on the role of innate immunity in the etiology of vitiligo. These works are just another step towards the identification of mechanisms capable of initiating vitiligo”, said Dr. Harris.
According to another study conducted last December on 790 men under the age of 40 with coronary artery disease and 1270 in good health, young men with coronary artery disease more often have premature hair graying (50% vs. 30%) and early baldness (49% versus 27%). Early baldness and premature gray hair are the strongest predictors of coronary artery disease in young men, compared to obesity.
These findings go hand in hand with those of an Egyptian study presented in Malaga (Spain) at the congress of the European Society of Preventive Cardiology in April 2017 which asserted the graying hair would be a harbinger of heart attack in humans. “Our findings suggest that graying indicates patients’ biological age and could be a warning sign of heart attack,” said Dr. Samuel, adding that patients at high risk of heart disease need to be closely followed and preventive treatment, even if they have no symptoms.