Good News: Scientists Discovered New Hair Growth Mechanism

Faulty Immune Cells May Play Role in Alopecia, Other Forms of Baldness

Good News: Scientists Discovered New Hair Growth Mechanism
In a highly magnified cross section of mouse skin, fluorescent Tregs (red) are seen clustered around hair follicles and hairs (green). Credit: Rosenblum lab/UCSF

Scientists at the UC San Francisco have recently discovered that regulatory T cells (Tregs) linked with inflammation control, directly trigger stem cells in the skin to promote healthy hair growth. Through these immune cells partners, the stem cells produce hair follicles, leads to hair growth.

If there are defects in Tregs, it may cause alopecia areata. Alopecia areata is a common autoimmune disorder that causes hair loss, and could potentially lead to baldness.

Michael Rosenblum, an assistant professor of dermatology at UCSF said, “Our hair follicles are constantly recycling: when a hair falls out, the whole hair follicle has to grow back. 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.”

“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.”

“Generally, Tregs lies in the body’s lymph nodes and mimics as peacekeepers and diplomats. They inform immune system difference between friend and foe. When Tregs don’t function properly, we may develop allergies to harmless substances like peanut protein or cat dander, or suffer from autoimmune disorders in which the immune system turns on the body’s own tissues.”

Sometimes Tregs live permanently in other tissues, where they evolved with local metabolic functions and normal anti-inflammatory role. In the skin, Tregs help establishes immune tolerance to healthy skin microbes in newborn mice. They also secrete molecules that help with wound healing into adulthood.

Scientists actually wanted to better understand the role of these resident immune cells in skin health. To do so, they developed a technique for temporarily removing Tregs from the skin. For that purpose, they shaved patches of hair from the mice to observe affections on skin.

Rosenblum said, “We quickly noticed that the shaved patches of hair never grew back, and we thought, ‘Hmm, now that’s interesting. We realized we had to delve into this further.”

After conducting few experiments, the evidence suggests that Tregs play a role in triggering regeneration of hair follicles.

Tregs have a close relationship with the stem cells that reside within hair follicles and allow them to regenerate. They trigger stem cell activation directly through a common cell-cell communication system known as the Notch pathway.

Rosenblum said, “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. 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. It 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.”

“What we found here is that stem cells and immune cells have to work together to make regeneration possible.”