Have you ever stopped to notice how some people get gray hair too early? In large cities like São Paulo, it is common to see young adults in their 20s, 30s with several light strands on their heads. Sometimes, after a stressful period in our lives, we may come across gray hair that we didn’t used to have recently.
This is because not only age or genetics influence how quickly our hair loses its color: stress can also give us a white head. But how?
Researchers from the Ribeirão Preto School of Medicine (FMRP), University of São Paulo (USP) investigated how the hair whitening process works through acute stress.
“It has long been said that stress causes hair to turn white. But, to date, this claim had no scientific basis. We proved in this study that the phenomenon does occur and we identified the mechanisms involved. In addition, we found a way to interrupt the process of bleaching due to stress ”, reveals Thiago Mattar Cunha, a member of CRID, to Agência Fapesp.
The research was conducted in partnership with Harvard University, under the coordination of Professor of Regenerative Biology Ya-Chieh Hsu. The results have just been published in the international scientific journal Nature.
Mattar Cunha explains how the discovery came about. “We were doing a study on pain in mice of the Black-C57 strain, whose coat is black.” After applying a toxin for weeks that induced a sensation of intense pain in the animal, an unexpected change was obtained: “a doctoral student observed that the animals had completely white hairs”.
The experiment was repeated a few times, until the USP group became convinced that the whitening of the wires had indeed been caused by the application of the substance.
The scientist explained that the sympathetic nervous system has an intimate relationship with stress. This division of the autonomic nervous system – composed of innervations that run alongside the spinal cord – controls the body’s responses to situations of imminent danger.
Through a surge of adrenaline and cortisol, the nervous system makes the heart beat faster, blood pressure rises, breathing accelerates and pupils dilate, among other effects.
“After injecting the toxin into the mice, we treated the animals with an antihypertensive agent capable of inhibiting neurotransmission. We observed that the capillary whitening process was blocked by the treatment ”, points out Thiago Mattar Cunha.
In another experiment, neurotransmission was interrupted by surgical removal of rodent’s sympathetic fibers. In this case too, hair depigmentation did not occur in the weeks following the procedure for inducing pain.
During a period as a visiting professor at the American university, Thiago Mattar Cunha discovered that a group from Harvard had made discoveries similar to Brazilian research.
At that point, the researchers already knew that the stress associated with pain, in some way, caused the mice to “ripen” early in the melanocytic stem cells existing within the hair bulb. They are responsible for the generation of cells that produce melanin (melanocytes), a pigment that colors the hair.
“When we are young, these cells are in an undifferentiated state, like all stem cells. As we get older, they gradually differentiate and, when the process is complete, they stop producing melanocytes. We have shown that an intense sympathetic activation makes the differentiation process progress much faster. In other words, in our model, pain accelerated the aging of melanocytic stem cells ”, explains the scientist.
“The damaging impact of the stress we discovered is beyond what I expected,” says professor Ya-Chieh Hsu, the group’s coordinator at Harvard, to Agência Fapesp. “After just a few days, all melanocytic stem cells were lost. The damage is permanent ”, adds the teacher.
Blocking the process
According to the researchers, the discovery calls attention to negative side effects of a protective evolutionary response. “Acute stress, particularly the fight or flight response, has traditionally been seen as beneficial to an animal’s survival. But in this case, the acute stress caused the permanent depletion of stem cells ”, emphasizes to Agência Fapesp Bing Zhang, postdoctoral fellow in the laboratory of Hsu and first author of the article.
When the researchers repeated the procedure to induce pain and, at the same time, treated the animals with an inhibitor of the enzyme CDK, they observed that the process of differentiation of the melanocytic stem cell was prevented, as well as the whitening of hair.
“This data indicates that the CDK enzyme participates in the process and can, therefore, be a therapeutic target in the future. If this target is ever going to be used in the clinic, it is still early to know, but it is worth exploring better ”, says the researcher.