discovery of a link between the immune system and hair growth

Alopecia is usually treated with glucocorticoids, steroid hormones that are able to inhibit the immune response in the skin. A team from the Salk Institute has discovered that these hormones not only play the role of immunosuppressants, but also have a regenerative effect involving specific immune cells.

Alopecia: when the immune system derails

Alopecia is an autoimmune disease characterized by accelerated hair loss. In case of alopecia areata (also called alopecia areata), the immune system mistakenly attacks the hair follicles – causing more or less extensive hair loss. Ye Zheng, an associate professor at the NOMIS Center for Immunobiology and Microbial Pathogenesis, and his collaborators were interested in the role of regulatory T cells (Treg) and glucocorticoid hormones in autoimmune diseases. In particular, they looked closely at the function of these immune components in multiple sclerosis, Crohn’s disease and asthma.

Also read: Immunology: The immune system helps keep the line

Treg cells are very important for the maintenance of homeostasis. Their role is to inhibit the activity of autoimmune lymphocytes, which attack healthy cells in the body. They are therefore essential for the maintenance of immune tolerance. ” For a long time, regulatory T cells have been studied for how to reduce immune overreactions in autoimmune diseases. says Zheng.

Although both Treg cells and glucocorticoids have an immunosuppressive effect, the researchers found that they did not play a significant role in any of the autoimmune diseases considered. They then sat down to study environments where Treg cells express particularly high levels of glucocorticoid receptors, such as skin tissue.

Communication between Treg cells and stem cells

Maintaining tissue homeostasis depends on communication between stem cells and support cells from the same niche, researchers in Natural immunology. Treg cells appear as an essential component in the stem cell niche to support their differentiation. However, it was unclear how Treg cells sense dynamic signals in this tissue microenvironment and communicate with stem cells.

Also read: Do men naturally have shorter hair than women?

To better understand this mode of communication, the researchers first used the mouse hair follicles. They shaved the backs of normal mice and other mice whose Treg cells lacked glucocorticoid receptors. After two weeks, the latter showed almost no signs of regrowth, while the hairs of the normal mice had grown completely out again.

Left: After hair loss, skin cells (blue) from a normal mouse activate the hair follicle stem cells (magenta). Right: Mouse cells that lack glucocorticoid receptors in their Treg cells cannot activate the hair follicle stem cells. Conclusion: these receptors are essential in the treatment of alopecia.

These results confirm that there must be some form of communication between Treg cells and the hair follicle stem cells to enable hair regeneration. Following this experiment on mice, the researchers examined the behavior of Treg cells and glucocorticoid receptors in skin tissue samples. They found that glucocorticoids “direct” Treg cells to activate the hair follicle stem cells, leading to hair growth.

A messenger that stimulates the formation of new hair follicles

Further analyzes confirmed that this pathway was completely independent of the ability of Treg cells to maintain immune balance: ablation of the glucocorticoid receptor in Treg cells blocks hair regeneration without affecting immune homeostasis.

Also read: Regenerates the brain: stem cells restore lost neuronal connections

This communication between Treg cells and stem cells depends on a mechanism by which glucocorticoid receptors induce the production of the TGF beta 3 protein (a transforming growth factor, involved in cell differentiation) in Treg cells. This protein then activates the stem cells of the hair follicle to differentiate into new hair follicles.

We have now identified the upstream hormone signal and the downstream growth factor that actually promote hair growth and regeneration, independent of immune response suppression. says Zheng. In other words, researchers have uncovered a possible way to manipulate Treg cells to support tissue regeneration.

Normally, Treg cells do not produce TGF beta 3. When scientists investigated this, they found that this phenomenon also occurs in damaged muscle and heart tissue – just as hair removal simulated skin tissue damage in this study. The team now plans to study other injury models and isolate Treg cells from damaged tissue to monitor levels of TGF beta 3 and other growth factors.

Leave a Comment