In mice, the fight-or-flight response overactivates the cells, causing a drop in their numbers, which leads to loss of hair color.
by ASHLEY YEAGER
Stress definitely does turn hair gray—in mice, at least.
Researchers have found that stress triggers the fight-or-flight response, which damages the cells that ultimately give skin and hair its color and leads to the cells’ depletion. In experiments, dark-furred mice that were stressed turned white in just days, the team reported yesterday (January 22) in Nature.
Folklore has long suggested that stress could strip the color from even the richest reds, blondes, and browns, but how it happens has been a mystery. “It was satisfying to question a popular assumption . . . [and] to identify the mechanisms that now open up new areas of work,” Ya-Chieh Hsu, a stem cell biologist at Harvard University and a coauthor of the study, tells Science News.
In their study, Hsu and her colleagues injected a compound related to capsaicin—an ingredient in chili peppers that gives them their heat—into mice to stress the animals. Five days later, the mice’s fur lost its color. The team thought the immune system might be killing the pigment-producing cells, but experiments showed that wasn’t happening. The stress hormone cortisol wasn’t involved in the loss of color either.
Instead, the team found, the color loss was related to the way stress affects the mice’s sympathetic nervous system, which is responsible for the fight-or-flight response. Stress triggered the fight-or-flight response, which caused a release of norepinephrine, a neurotransmitter that aids muscle contraction, including contraction of the heart. Norepinephrine, the researchers show, also caused stem cells in hair follicles to rapidly convert to pigment-producing cells called melanocytes, which regularly die. In the stressed mice, all of the stem cells differentiated into melanocytes, depleting the pool of stem cells completely within five days. That ultimately left no melanocytes to give the mice’s fur its color. The team tested the mechanism in cultures of human melanocyte stem cells and found a similar result.
“I was amazed by how dramatic this change is,” Mayumi Ito, a biologist at the New York University School of Medicine who was not involved in the study, tells The New York Times. She studies graying of aging mice. In her animals the color change is gradual because the depletion of melanocytes is much slower.
“Melanocyte stem cells are also lost during aging,” Hsu tells Reuters. “An interesting hypothesis could be that stress is an accelerated aging process. But we don’t know if that is true yet. We are interested in finding out the link.”