In what could facilitate the development of novel treatment strategies for hair growth in humans, researchers have found that immune cells involved in wound healing can induce hair growth by surrounding and activating skin stem cells.
“We have discovered that macrophages — cells whose main function is traditionally attributed to fight infections and wound repair — are also involved in the activation of hair follicle stem cells in non-inflamed skin,” said Mirna Perez-Moreno from the Spanish National Cancer Research Centre (CNIO).
Although this study was carried out in mice, the researchers believe their discovery may lead to new treatment for hair growth in humans.
The researchers found that mice started to regrow hair when they were given anti-inflammatory drugs.
They observed that when skin cells are dormant, a fraction of macrophages die naturally due to a normal process called apoptosis.
But the dying and surviving cells activated nearby stem cells and hair began to grow again.
Macrophages secrete a number of factors including a class of signalling molecules called Wnts.
Importantly, when the researchers treated macrophages with a Wnt inhibitor drug, the activation of hair growth was delayed, demonstrating a role for Wnts from macrophages in promoting hair growth.
The discovery that immune cells called macrophages activate skin stem cells could also influence technologies with potential applications in tissue regeneration, ageing, and cancer, the researchers noted.
The study appeared in the journal PLOS Biology.
Castellana D, Paus R, Perez-Moreno M. Macrophages Contribute to the Cyclic Activation of Adult Hair Follicle Stem Cells. PLoS Biol. 2014 Dec 23;12(12):e1002002. doi: 10.1371/journal.pbio.1002002. eCollection 2014 Dec.