Salk scientists discovered an unexpected molecular target of a common treatment for alopecia. The findings, published in Nature Immunology, describe how immune cells called ‘regulatory T cells’ interact with skin cells using a hormone as a messenger to generate new hair follicles and hair growth.
The scientists didn’t begin by studying hair loss. They initially researched the roles of regulatory T cells and glucocorticoid hormones in autoimmune diseases. They first investigated how these immune components functioned in multiple sclerosis, Crohn’s disease, and asthma.
They found that glucocorticoids and regulatory T cells did not function together to play a significant role in any of these conditions. So, they thought they’d have more luck looking at environments where regulatory T cells expressed particularly high levels of glucocorticoid receptors, such as in skin tissue. The scientists induced hair loss in normal mice and mice lacking glucocorticoid receptors in their regulatory T cells. There was a noticeable difference between the mice—the normal mice grew back their hair, but the mice without glucocorticoid receptors barely could. The findings suggest that communication must occur between regulatory T cells and hair follicle stem cells to allow for hair regeneration.
The scientists then investigated how the regulatory T cells and glucocorticoid receptors behaved in skin tissue samples, finding that glucocorticoids instruct the regulatory T cells to activate hair follicle stem cells, which leads to hair growth. This crosstalk between the T cells and the stem cells is based on the receptors inducing the production of a protein TGF-beta3. TGF-beta3 then activates the hair follicle stem cells to differentiate into new hair follicles, promoting hair growth.
The study revealed that regulatory T cells and glucocorticoid hormones are not just immunosuppressants but also have a regenerative function.