It is well known that chronic stress is not good for us – this is also reflected in the abundance of hair: Psychological stress can promote hair loss. A study on mice is now shedding light on the mechanisms behind this effect. The stress hormone corticosterone therefore leads to a lower division activity of the hair follicle stem cells in rodents. The experiments show that blocking the responsible signal path can also stimulate hair growth. These results can possibly be transferred to humans and at least prospects for the development of treatment options for stress-related hair loss are emerging.
Hair is getting thinner and flabby – for many people, hair loss is a stressful observation when looking in the mirror. First of all, it is important to note that hair loss can have very different causes. So predisposition, deficiency symptoms or autoimmune reactions can be the basis. However, chronic stress is also known to be a factor that can cause hair thinning. So far, however, it is unclear on which mechanisms this effect is based. In order to gain fundamental insights, the researchers working with Sekyu Choi from Harvard University in Cambridge have now carried out experiments on animals that are often used as human models: mice.
Hair roots in sight
As they explain, hair development in furry rodents is largely based on principles similar to those in humans. It is divided into three phases: growth, degeneration and rest. As the hair follicle grows, it continuously creates an elongated shaft in the hair follicle. This formation is based on the activity of hair follicle stem cells. During the degeneration phase, growth stops and the lower part of the hair follicle shrinks. In the course of the ensuing rest, the hair then falls out. Later the cycle starts all over again. It was therefore suspected that the increased hair loss during stress is due to a premature transition of the follicle into the resting phase. Specifically, stress hormones could be the masterminds.
In order to follow this trail in the mouse model, Choi and his colleagues exposed some rodents to experimental stress over the course of nine weeks and investigated the effect on hair growth. They were initially able to confirm that this treatment led to reduced hair growth in connection with increased blood levels of the stress hormone corticosterone. As they explain, corticosterone is the animal equivalent to the human stress hormone cortisol, which is produced in the adrenal gland. To confirm the role of the adrenal glands and corticosterone in the mice, the scientists removed the tissue from some test animals. It was shown that the resting phases of the hair follicles associated with the falling out were shortened in these mice. However, when the scientists artificially administered the stress hormone corticosterone to the animals, this effect disappeared. Conversely, this confirmed that the stress hormone influences the development of the hair roots.
Causes and treatment options are emerging
As the researchers explain, it suggested that the effect is based on the sensitivity of certain cells in the hair follicle to glucocorticoid. It is known that this hormone works through a glucocorticoid receptor. The researchers therefore switched off this signal receiver in a targeted manner in the different cells in the area of the hair roots of mice. It was shown that it is not the hair follicle stem cells that react directly to the hormone, but rather the cells below them – the so-called dermal papillae. Subsequent molecular genetic investigations enabled them to show what role these cells play in signal transmission. According to this, the stress hormone glucocorticoid inhibits the formation of a protein called GAS6 in the dermal papillae. This substance is in turn responsible for the stimulation of the hair follicle stem cells: GAS6 stimulates the cell division necessary for the hair growth phase.
The researchers were able to make this clear by artificially increasing the production of GAS6 in the dermal papillae of mice using genetic engineering. This stimulated hair growth in the test animals when they were exposed to chronic stress or given corticosterone. These results made it clear: The release of corticosterone in the event of chronic stress leads to an inhibition of GAS6 production in the dermal papillae. But the associated negative effect on hair growth can be eliminated through an artificial supply of GAS6.
From a human perspective, these results appear promising as possible causes and treatment options for stress-related hair loss are emerging. However, there are still some open questions to be clarified in this context, the researchers point out. Above all, it is questionable to what extent the results in mice can be transferred to humans. Because despite many similarities, there are also differences between our hair development and the processes in furry rodents. They could affect the effectiveness of approaches to reverse the stress-related inhibition of hair follicle stem cells. Extensive follow-up examinations are therefore now necessary. Nonetheless, the results are extremely promising, says the dermatologist Rui Yi of Northwestern University in Chicago in a comment on the study: “Perhaps one day it will be possible to counter the negative effects of chronic stress on our hair,” says Yi with regard to the results.