London: When Ya-Chieh Hsu, professor of stem cell and regenerative biology at Harvard University and the Harvard Stem Cell Institute, wanted to figure out exactly what makes hair turn grey, she started with an obvious, albeit anecdotal, culprit: stress.
There are well-known historical examples of the connection between stress and hair greying Marie Antoinette’s coif reportedly blanched after she was captured during the French Revolution and studies have even linked stress in animals to greying hair. But for the first time, Hsu and her colleagues figured out the biological reason why stress saps the pigment out of hair.
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In a study published in Nature, Hsu and her team report that the process starts with the sympathetic nervous system, which orchestrates all of the critical body processes that we never have to think about—our heart rate, our breathing, as well as things like digesting food and fighting off germs.
It is also responsible for the fight-or-flight response—the auto-pilot behavior system that helps us to recognize and respond to threats before we really have time to think about and process them. The sympathetic nervous system is intimately linked to our stress response, so in that respect, it’s not entirely surprising it might have something to do with greying hair.
But the sympathetic nervous system’s response to stress is generally one of last resort, activated only in a dire emergency when other systems are too slow or have failed. It’s not called into action when you’re behind on a project at work, for example, or are anxious about making an upcoming public presentation.
Because of the energy required to turn on the fight-or-flight response, it wouldn’t make sense to rely on it for those situations. For those non-emergency stressors, there are other processes at work.
And that’s where Hsu focused her attention at first. She suspected that if stress were indeed turning hair grey, then it was probably working through something like the immune system, which might be releasing cells to attack color-producing cells in the hair follicle; or by triggering the release of stress hormones like cortisol from the adrenal glands.
But neither seemed to be the case. She chemically induced stress in mice by injecting them with a compound called resiniferatoxin, which boosted the animals’ stress hormone levels; this method provided a reliable way of inducing the stress response over other strategies that the team explored, including using restraints, tilting the animals’ cages, wetting their bedding and changing their lighting conditions.
Mice lacking immune cells and mice without adrenal glands both continued to show premature greying after getting these stress-mimicking injections. ( read more at time )