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martyb writes:

TReg and Jagged 1 -- together they seem to be a key to overcoming hair loss:

In experiments in mice, UC San Francisco researchers have discovered that regulatory T cells (Tregs; pronounced "tee-regs"), a type of immune cell generally associated with controlling inflammation, directly trigger stem cells in the skin to promote healthy hair growth. Without these immune cells as partners, the researchers found, the stem cells cannot regenerate hair follicles, leading to baldness.

"Our hair follicles are constantly recycling: when a hair falls out, a portion of the hair follicle has to grow back," said Michael Rosenblum, MD, PhD, an assistant professor of dermatology at UCSF and senior author on the new paper. "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."

The new study – published online May 26 in Cell – suggests that defects in Tregs could be responsible for alopecia areata, a common autoimmune disorder that causes hair loss, and could potentially play a role in other forms of baldness, including male pattern baldness, Rosenblum said. Since the same stem cells are responsible for helping heal the skin after injury, the study raises the possibility that Tregs may play a key role in wound repair as well.

More..

[...] Tregs' role in triggering hair growth did not appear related to their normal ability to tamp down tissue inflammation, the researchers found. Instead, they discovered that Tregs trigger stem cell activation directly through a common cell-cell communication system known as the Notch pathway. First, the team demonstrated that Tregs in the skin express unusually high levels of a Notch signaling protein called Jagged 1 (Jag1), 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 Jag1 protein restored Notch signaling in the stem cells and successfully activated follicle regeneration.

"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," Rosenblum said. "Now the stem cells rely on the Tregs completely to know when it's time to start regenerating."

[...] the findings may have implications for alopecia areata, an autoimmune disease that interferes with hair follicle regeneration and causes patients to lose hair in patches from their scalp, eyebrows, and faces. Alopecia is among the most common human autoimmune diseases – it's as common as rheumatoid arthritis, and more common than type 1 diabetes – but scientists have little idea what causes it.

An abstract is available: Regulatory T Cells in Skin Facilitate Epithelial Stem Cell Differentiation ( DOI: http://dx.doi.org/10.1016/j.cell.2017.05.002 ); full article is paywalled.

Finally, new hope for balding neckbeards?

Original Submission