Stress seen to act on nerve cells; have permanent effect on hair graying
Acute stress has been known to impact the body long-term –a new discovery made at Harvard University, Massachusetts, US, has shown how stress can activate nerves that are part of the fight-or-flight response, which eventually damages pigment-regenerating stem cells in hair follicles.
Accounting for a whole-body response, the scientists’ first theory was that stress would cause an immune attack on pigment-producing cells; the theory went out the window when mice lacking immune cells still lost colour in their coat. After a lengthy and systematic elimination process, the sympathetic nervous system provided an answer: stress causes sympathetic nerves to release the chemical norepinephrine, which gets taken up by nearby pigment-regenerating stem cells in each hair follicle on the skin.Now, certain stem cells act as a reservoir of pigment-producing cells; some of the stem cells convert into pigment-producing cells that color the hair. The norepinephrine induces an over-active state – the stem cells all convert into pigment-producing cells and prematurely deplete the reservoir.
“This detrimental impact of stress was beyond what I imagined,” said Associate Professor Ya-Chieh Hsu, at Harvard’s Department of Stem Cell and Regenerative Biology. “After just a few days, all of the pigment-regenerating stem cells were lost. Once they’re gone, you can’t regenerate pigment anymore. The damage is permanent.”
The findings highlights the negative side effects of an otherwise protective evolutionary response, but can explain how neurons interact with stem cells on a cellular/molecular level to link stress with hair graying, which later translates to the more obvious organs and tissues. It could guide new studies that seek to modify or block the damaging effects of stress.
Hsu commented, “Understanding how our tissues change under stress is critical towards eventual treatment that can stop or revert the detrimental impact of stress.”
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