How does stress affect mice?

Mice stressed to lose their hair. A new study shows that these rodents lose their coat under stress, because of a hormone that disrupts their hair growth. She may be a new source of hope for humans who are losing their hair.

The study, published Wednesday in Nature, is the first to show how stress can lead to hair loss, and suggests a way to stop them. Hair growth follows three phases: anagen, catagen and telogen, respectively for the growth of the hair, its stopping and finally its fall (which corresponds to the rest of the capillary gland). The researchers, led by Professor Ya-Chieh Hsu of Harvard University, wondered if the hormones produced under stress had an effect on these phases.

In humans, stress induces the production of cortisone, the equivalent of which in mice is the corticosterone, produced by the adrenal gland. To gauge the role of corticosterone, researchers have removed the adrenal gland from a group of mice, called ADX, then compared their hair growth to that of a control group.

How to prevent falling in mice?

ADX mice, without an adrenal gland, had a shorter telogen (resting) phase, and their hairs grew faster and longer during the anagen phase. They also went through the three growth phases much more quickly, at a rate of 10 times over 16 months, compared to only three times for the mice in the control group.

The study also examined the effects of an increase in corticosterone levels in mice, obtained through the administration of this hormone or by subjecting the rodent to external stresses. In both cases, the mice underwent a longer resting phase of their hair growth than the normal phase.

Researchers found that corticosterone interferes with the production of a protein, Gas6, essential for hair growth. They checked that they could counteract the effect of corticosterone by injecting the Gas6 protein into the skin of mice.

A solution for humans?

Unfortunately, this finding is far from being a cure for human hair loss, warned Professor Hsu. “Our discovery is just the first important step, and more work will be needed before finding an application in humans, “he told AFP. Even if he” would be interesting to see if Gas6 can stimulate growth hair in general, “he added.

There is also important differences between mice and humans in this area, explained Rui Yi, professor of pathology and dermatology at Northwestern University, cited in Nature. “Even though corticosterone is considered to be the rodent equivalent of human cortisone, we don’t know if cortisone works the same in humans,” he wrote.

Hair growth cycles also differ between the two species. Most of a mouse’s hair is usually found in a resting state, while this is the case for only 10% of human hair.

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