Researchers from University of California, San Francisco (UCSF; CA, USA) have discovered that, in a murine model, regulatory T cells (Tregs) directly trigger stem cells in the skin to promote healthy hair growth. Tregs are usually associated with controlling inflammation but in this instance their absence means that hair cells can’t regenerate, which can lead to baldness. The study was recently published in Cell.
“Our hair follicles are constantly recycling: when a hair falls out, a portion of the hair follicle has to grow back,” commented study senior author and assistant professor of dermatology Michael Rosenblum (UCSF). “This has been thought to be an entirely stem cell-dependent process, but it turns out Tregs are essential. If you knock out this one immune cell type, hair just doesn’t grow.”
Tregs’ importance to hair growth was first shown by researchers when using a technique for temporarily removing it from the skin of murine models. When a patch of skin was shaved they noticed that the hair didn’t grown back.
In the current research it was demonstrated that Tregs in the skin express unusually high levels of a Notch signaling protein called Jagged 1, compared to Tregs elsewhere in the body. They then showed that removing Tregs from the skin significantly reduced Notch signaling in follicle stem cells and that replacing Tregs with microscopic beads covered in Jagged 1 restored Notch signaling in the stem cells and successfully activated follicle regeneration. This discovery showed that Tregs triggers stem cell activation through the notch pathway.
“It’s as if the skin stem cells and Tregs have co-evolved, so that the Tregs not only guard the stem cells against inflammation but also take part in their regenerative work,” explained Rosenblum. “Now the stem cells rely on the Tregs completely to know when it’s time to start regenerating.”
“We think of immune cells as coming into a tissue to fight infection, while stem cells are there to regenerate the tissue after it’s damaged, but what we found here is that stem cells and immune cells have to work together to make regeneration possible,” concluded Rosenblum.
Sources: Ali N, Zirak B, Rodriguez RS et al. Regulatory T Cells in Skin Facilitate Epithelial Stem Cell Differentiation. Cell. pii: S0092-8674(17)30529-9. (2017) (Epub ahead of print); https://www.ucsf.edu/news/2017...
Written by- Adam Tarring