ABOUT a quarter of the people who contract Covid-19 experiences hair loss six months after the onset of symptoms, possibly due to the systemic shock caused by the ordeal of the infection and recovery. In fact, it is chronic stress has always been associated with hair loss, but the underlying mechanism linking this condition to hair follicle stem cell dysfunction is still unclear. A new study published in Nature that he highlighted (in mice) as high levels of stress hormone inhibit the stamina cells of hair follicles, slowing hair growth and causing hair loss fall.
Over the course of a person’s life, hair growth goes through three stages: growth (anagen), degeneration (catagen), and rest (telogen). During anagen, a hair follicle continually pushes out the growing hair shaft. During catagen, hair growth stops and the lower part of the hair follicle shrinks, but the hair stays in place. During the telogen, the hair remains dormant for some time, eventually falling out. Under severe stress, many hair follicles enter the telogen prematurely and the hair falls out quickly.
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The role of stem cells
The stamina cells of the hair follicle (Hfsc) are located in the suprabulbar (or bulge) region of the hair follicle. These cells play a crucial role in governing hair growth by interpreting both internal and external signals. For example, during the telogen phase, hair follicle stem cells are kept in a quiescent state and therefore do not divide. When hair growth is initiated in the next anagen phase, the Hfscs are instructed to divide and produce progenitor cells which begin to differentiate, generating several layers of hair follicles and ultimately the hair shaft.
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I study
Harvard University researchers sought to understand how stress can affect the activity of these stem cells by testing the role of the adrenal glands – which produce stress hormones and are a key endocrine organ – in regulating hair growth. . To do this, they surgically removed them from the mice. Telogen phases were much shorter in the hair follicles of these animals (which the team dubbed Adx mice) than in control mice (less than 20 days versus 60-100 days), and the follicles involved in hair growth about three times thicker.
The effect of the stress hormone
The authors were able to suppress this frequent hair growth and restore the normal hair cycle by feeding the Adx mice with corticosterone (a stress hormone normally produced by the animals’ adrenal glands). After exposing ‘normal’ mice to various mild stressors for nine weeks, the researchers observed elevated corticosterone levels accompanied by reduced hair growth, supporting the idea that corticosterone produced by the adrenal glands during chronic stress inhibits the onset of hair growth. Thus, in the absence of systemic corticosterone, Hfscs enter substantially more cycles of the regeneration cycle throughout their life. Conversely, under chronic stress, increased corticosterone levels prolong stem cell quiescence and keep hair follicles in a prolonged resting phase.
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Possible new treatment strategies
Established the link between stress and hair loss, Harvard researchers tried to understand how hair follicle stem cells detect corticosterone and found that the hormone basically prevents dermal papilla cells from secreting Gas6, a factor that researchers have shown is capable of activating the stem cells of the follicle. If these results are also confirmed in humans, Gas6 could become a possible target in strategies to reactivate the stem cells of the follicles and restart hair growth even if there are several aspects to be clarified. First, even though corticosterone is considered the rodent equivalent of human cortisol, we still don’t know if cortisol behaves in a similar way in humans. Second, the length of the hair cycle phases is different in mice and humans.
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Counteract the impact of stress
While more studies are needed, Harvard researchers have discovered a cellular and molecular mechanism that links the stress hormones produced by the adrenal glands to the activation of hair follicle stem cells by controlling Gas6 expression in the dermal papillae. Furthermore, they showed that injecting this factor into the skin can restart hair growth in mice even when the animals are experiencing chronic stress. This discovery could prove very useful given that our life is characterized by high ‘doses’ of stress and this study gives us a glimpse of the possibility that one day, it will be possible to fight at least the negative impact of chronic stress on our hair by ‘adding’ a some Gas6.
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