[ad_1]
When faced with incredible stress, people sometimes lose their hair at the handle, but scientists are not sure exactly why. Now, a new study in mice offers a clue: stress hormones can put hair growth on hold.
Follicles, the specialized organs that make hair germinate, go through the “growing” and “resting” stages, where the follicle first actively produces new hair and then goes dormant. In mouse, chronically elevated levels of stress the hormone corticosterone – similar to the human hormone cortisol – keeps follicles at rest longer than usual, according to new study published March 31 in the journal Nature. This response prevents the hair follicles from entering the growth phase, during which the stem cells in the follicle produce new hair.
Specifically, corticosterone stops hair growth by connecting to a receptor on cells that lie under the base of each follicle and release chemicals to regulate the hair cycle. Once plugged in, corticosterone blocks the production of a protein called GAS6; without GAS6, hair follicle stem cells cannot activate to start growing hair.
Related: 5 ways your cells deal with stress
“So instead of directly regulating stem cells, chronic stress affects the expression of stem cell activation signals,” said lead author Ya-Chieh Hsu, associate professor of stem cells and regenerative biology at Harvard University, in an email.
This chain reaction can occur slightly differently in human hair follicles, but the mechanism can be very similar, as rodent corticosterone and human cortisol belong to the same. hormone family and interact with the same type of receptors, she says. “In humans, resting hair can fall out more easily than resting hair. [the growth phase], “which could explain how stress leads to hair loss, Note Hsu.
“If the finding can be translated in humans, they must show that cortisol can push growing hair follicles into the resting phase,” said Rui Yi, professor in the departments of pathology and dermatology at Northwestern University. Feinberg School of Medicine in Chicago. , who did not participate in the study.
If the mechanism identified in mice also applies to humans, “in principle,” treatments could potentially be developed to prevent stress-induced hair loss, Yi told Live Science. But before embarking on new treatments, scientists will need to sort out the differences between the mouse model and humans, he said.
As for the mice, “scientifically, it’s a really complete story”; the authors traced every link in the chain reaction that led to changes in hair growth, Yi said.
In the study, Hsu and his colleagues first blocked stress production of hormones in a group of mice by removing the adrenal glands of animals – a endocrine organ that produces stress hormones. The hair follicles from these mice entered the growth phase about three times more often than the unmodified control mice. In addition, their resting phase was considerably shortened, lasting less than 20 days, compared to the 60 to 100 days usual in normal mice.
The study authors found that if they fed the modified mice with corticosterone, their hair follicle cycle returned to the rate of normal mice. This hinted that the hormone had somehow suppressed the exuberant growth of their hair. The authors tested this idea in normal mice by exposing them to mild stressors intermittently for nine weeks and found that as the corticosterone levels in stressed animals increased, their normal hair growth decreased.
Seeing this link between hormone levels and hair growth, the authors focused on the hair follicle itself, to see if corticosterone directly interacts with the stem cells inside. The hormone plugs into the so-called “glucocorticoid receptor,” so the authors selectively suppressed this receptor in different cells involved in hair growth and then applied corticosterone to the mice.
Removal of the stem cell receptor from the hair follicles made no difference; the hormone further retarded hair growth. However, when the team removed the receptor from neighboring skin papilla cells, hair growth proceeded as usual, with no prolonged resting phase. So whatever the cause of the halt in hair growth, it must act on the skin papillae, the authors thought.
The team later found that normal dermal papillary cells stopped producing GAS6 when exposed to corticosterone. They also found that GAS6 typically connects to and activates hair follicle stem cells, which in turn stimulates hair growth. But without the protein, the hair follicles remain at rest. Likewise, injecting GAS6 directly into a mouse the skin can trigger hair growth even if the animal is stressed and has high levels of corticosterone, the team found.
It’s possible, in theory, that GAS6 or a very similar protein could also trigger hair growth in stressed humans, Yi said. But first there are several big questions that must be answered.
On the one hand, while corticosterone and cortisol are chemically similar, we don’t know that they play the exact same role in rodent and human hair cycles, Yi said. In addition, the cycles of rodents and human hair take place on very different timeframes. As mice mature, the resting stage of their hair follicles gets longer and longer, he said. And by the time a mouse is around 1.5 years old, the majority of its hair follicles are resting most of the time, which means its hair has stopped growing.
“You never see a mice going to the hairdresser,” Yi said.
In comparison, about 90% of adult human hair follicles may be in the growing stage at some point, Yi wrote in an independent commentary on the study, also published March 31 in Nature. Since the mouse study only showed how stress hormones can prolong the state of rest and prevent the onset of growth, it will be interesting to see if cortisol can not only prolong the state of rest in man, but also force the actively growing hair to return to the state of rest. , Said Yi.
And finally, while the hair typically falls out during the resting state, it is not clear exactly why the dormant hair falls off the scalp, Yi said. So besides preventing hair growth, maybe stress releases hair from its place, he said. But that’s another mechanism to explore.
While many questions remain unanswered, the mouse study suggests potential solutions for stress-induced hair loss that may one day be explored in humans. “I can imagine that manipulations related to the GAS6 pathways could have potential, if the results are confirmed in humans in the future,” Hsu said. The mouse study represents a “critical first step” towards the development of these treatments, she said.
Originally posted on Live Science.
[ad_2]
Source link