When we are under chronic stress or after a long illness, our hair can turn grey. This previously mysterious phenomenon has just been explained by a new study.
After a long illness or chronic stress, hair loses its natural color and turns grey or white. This phenomenon can also occur in relatively young people. Partly due to genetic factors, hair graying is still largely an enigma for the scientific community.
A team of scientists from the University of Alabama and the National Institutes of Health (NIH) may have just solved the mystery. In a study published in the journal PLOS Biology, they explain that they found out that the immune system, and interferons, in particular, play a predominant role in hair bleaching.
The immune system
Our hair, whether black, blond, brown or red, is actually white underneath. It is colored by a pigment, melanin, which is produced by cells called melanocytes. These melanocytes are found in hair follicles. As each hair grows, it is “infused” with melanin, which gives it its color. With age, melanocytes decrease and slowly disappear, reducing the amount of pigment produced and leaving the hair grey and then white.
This phenomenon can be accelerated in case of illness or when the body undergoes a period of significant stress. When the body is invaded by a pathogen, the innate immune system is the first to respond. Also known as the non-specific immune system, it includes the cells and mechanisms that allow the body to defend itself immediately against infectious agents.
The cells that make up the innate immune system have the ability to recognize invaders and when they do, release interferons, proteins that induce other cells to act by also increasing the activity of genes that block viral replication.
Stem cell melanocyte dysfunction
The main researcher of the study, Melissa Harris, an associate in the Department of Biology at the University of Alabama, explains how they came across this surprising link between hair color and interferons when testing mice. “My lab is harnessing the power of gray 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 essential stem cells for the production of melanocytes,” he explains.
Together with his team, Prof. Harris focused on a particular gene in melanocytes, called Microphthalmia-associated transcription factor (MITF). It is this gene that tells melanocytes to produce melanin.
In rats whose fur turned gray at an early stage, researchers first noticed that their MITF production was unusually high, which probably led them to rapidly deplete their melanocyte reserves. More surprisingly, they also found that rats who produced less MITF also had gray hair.
They then suggested that MITF not only supervises melanin production in melanocytes but also controls the genes responsible for the release of interferons. Without enough MITF, the melanocytes produce too much interferon, which causes the immune system to attack the melanocytes, which no longer produce melanin.
Hope for vitiligo
For researchers, this discovery is important because it implies that the same genes regulate the pigmentation of hair, eyes, and skin, as well as the immune system. This link may help them understand some pigmentation diseases such as vitiligo, which causes bleaching of the skin and affects between 0.5 and 1% of the world’s population. Many researchers working with vitiligo have already speculated about the role of innate immunity in the etiology of vitiligo. This work is just one more step towards identifying the mechanisms that can initiate vitiligo, Professor Harris told ZME Science.
Gray hair in humans
According to another study conducted last December on 790 men under 40 years of age with coronary artery disease and 1,270 healthy men, young men with coronary artery disease are more likely to have early aging hair (50% vs. 30%) and early baldness (49% vs. 27%). Early baldness and premature aging hair would be the strongest predictors of coronary heart disease in young men before obesity.
These results 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 stated that gray hair is a warning sign of heart attack in men. “Our results suggest that graying hair indicates the biological age of patients and may be a warning sign of a heart attack,” said Dr. Samuel, adding that patients at high risk of heart disease should be carefully monitored and treated preventively, even if they show no symptoms.
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