Immunity and melanocytes

Gray hair is rooted in the immune system

Daria Zagorskaya, Vesti

Melanocytic stem cells, which are present in the hair follicles, play a key role in the coloring of our hair. During the growth of a new hair, they are the source of melanocytes – cells that produce the hair-coloring pigment melanin. That is, it depends on the activity of these cells whether a person will be blond, brunette or brown-haired. At the same time, in organisms devoid of such stem cells, the hair has a color from light gray to white.

Melissa Harris from the University of Alabama and her colleagues studied the genetic basis of hair graying in mice. According to the researchers, this work seemed to them quite simple. After all, they only needed to track factors that disrupt the normal function of melanocytic stem cells.

But during experiments with mice, scientists noticed a rather unexpected relationship between gray hair, MITF protein and the work of the immune system.

In melanocytes, the MITF transcription factor triggers the conversion of the amino acid tyrosine into the pigment melanin. But in addition to this, the protein performs a number of other functions. For example, it controls the reaction of signaling molecules – interferons, which are produced after the detection of pathogenic microorganisms or viruses and trigger defense mechanisms in neighboring cells.

Harris' team created a line of mice in which melanocyte progenitor cells produced very little MITF. As they expected, the fur of these animals acquired a light gray color very early.

But the most interesting thing was that the genetically modified rodents also activated genes involved in the immune response.

In addition, in experiments with mice predisposed to early gray hair, artificial stimulation of the innate immune system also caused an increase in the number of gray hairs. The results of the study and the conclusions of the authors were presented in an article published in the journal PLOS Biology (A direct link between MITF, innate immunity, and hair graying).

"Our discovery suggests that genes that control the presence of pigment in hair and skin are also involved in the regulation of innate immunity," study co–author William Pavan from the National Human Genome Research Institute says in a press release. "These results can improve our understanding of the processes of hair color change, as well as shed light on problems such as vitiligo, when innate immunity is involved."

Now scientists want to check whether the discovered mechanism can be the cause of premature gray hair, which often occurs due to diseases and stress. It is likely that a combination of genetic predisposition and frequent viral infections negatively affect the progenitor cells of melanocytes and lead to graying.

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