If you have been wondering if pandemic hairfall is real, rest assured that it is. Harvard University researchers have identified the biological mechanism by which chronic stress impairs hair follicle stem cells, confirming long-standing observations that stress might lead to hair loss.
In a study on mice published in Nature, the researchers found that a major stress hormone puts hair follicle stem cells into an extended resting phase, without regenerating the follicle or the hair. The researchers identified the specific cell type and molecule responsible for relaying the stress signal to the stem cells, and showed that this pathway can be potentially targeted to restore hair growth, writes Jassica Lau in The Harvard Gazette.
“My lab is interested in understanding how stress affects stem cell biology and tissue biology, spurred in part by the fact that everyone has a story to share about what happens to their skin and hair when they are stressed. I realized that as a skin stem cell biologist, I could not provide a satisfying answer regarding if stress indeed has an impact — and more importantly, if yes, what are the mechanisms,” said Ya-Chieh Hsu, the Alvin and Esta Star Associate Professor of Stem Cell and Regenerative Biology at Harvard and senior author of the study. “The skin offers a tractable and accessible system to study this important problem in depth, and in this work, we found that stress does actually delay stem-cell activation and fundamentally changes how frequently hair follicle stem cells regenerate tissues.”
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The researchers studied a mouse model of chronic stress and found that hair follicle stem cells stayed in a resting phase for a very long time without regenerating tissues. A major stress hormone produced by the adrenal glands, corticosterone, was upregulated by chronic stress; giving mice corticosterone reproduced the stress effect on the stem cells. The equivalent hormone in humans is cortisol, which is also upregulated under stress and is often referred to as the “stress hormone.”
“This result suggests that elevated stress hormones indeed have a negative effect on hair follicle stem cells,” Hsu said. “But the real surprise came when we took out the source of the stress hormones.” Under normal conditions, hair follicle regeneration slows over time— the resting phase becomes longer as the animals age. But when the researchers removed the stress hormones, the stem cells’ resting phase became extremely short and the mice constantly entered the growth phase to regenerate hair follicles throughout their life, even when they were old.