Cells known as melanocytes make up melanin and give our hair its color. Special stem cells then add melanocytes to new follicles when our hair falls out. When these stem cells stop working, our hair loses its pigment. It is this process and its relationship with our immune system's defenses that scientists at the National Institutes of Health (NIH) and the University of Alabama, Birmingham, (UAB) set out to investigate - in mice.
Our immune system is constantly defending us against viruses and bacteria, prompting cells under attack to produce signaling molecules called interferons. Interferons tell other cells to turn on the gene expression that prevents viruses from replicating, and trigger immune effector cells that protect the body.
For their paper, published in the journal PLOS Biology, the authors studied how the immune system’s response to attacks affects the MITF protein, which helps melanocytes to function. They found that when MITF loses control of the interferon response in melanocyte stem cells, the hair can turn gray. What's more, mice genetically predisposed to developing gray hair had this response even when the immune response was turned on artificially. Further research is now needed to understand what caused these reactions and also to see if these effects occur in the human body too.
The scientists hope their research will offer new insights into diseases that affect pigmentation, including vitiligo, a condition that destroys pigment cells in the skin.
Melissa Harris, lead author of the study and an assistant professor in UAB's Biology Department, said in a statement, "Genomic tools allow us to assess how all of the genes within our genome change their expression under different conditions, and sometimes they change in ways that we don't anticipate.
"We are interested in genes that affect how our stem cells are maintained over time. We like to study gray hair because it's an easy read-out of melanocyte stem cell dysfunction," Harris added.
William Pavan, chief of the Genetic Disease Research Branch at the NIH's National Human Genome Research Institute and co-author of the study, said in a statement, "This new discovery suggests that genes that control pigment in hair and skin also work to control the innate immune system.
"These results may enhance our understanding of hair graying. More importantly, discovering this connection will help us understand pigmentation diseases with innate immune system involvement like vitiligo," he said.
The research follows a 2016 study by academics at University College London (UCL) that, for the first time, linked the gene called IRF4 to going gray.
The lead author, Kaustubh Adhikari of UCL's Cell and Developmental Biology Department, said in a statement at the time, “We already know several genes involved in balding and hair color, but this is the first time a gene for graying has been identified in humans, as well as other genes influencing hair shape and density.”
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