Researchers at the Spanish National Cancer Research Centre (CNIO) have discovered an unexpected connection between macrophages and skin regeneration revealing a new way to stimulate hair follicle growth.
Turns out that macrophages are not just immune system cells, they are also responsible for activating skin stem cells and inducing hair growth, the CNIO scientists said in a December 23 PLOS Biology article entitled “Macrophages Contribute to the Cyclic Activation of Adult Hair Follicle Stem Cells.”
Their discovery sheds light on a broader issue of how to regenerate tissues and may also have implications for skin repair, inflammatory skin diseases, and cancer.
The CNIO researchers did not initially set out to investigate the relationship between hair and macrophages. In fact, the revelation emerged from an observation made by Mirna Perez-Moreno, one of the study’s authors, while working on an entirely different research project in which mice received anti-inflammatory drugs, a treatment that also reactivated hair growth. Perez-Moreno's lab began to experiment with the different types of cells involved in the body´s defense system, convinced that the explanation could reside in the existence of close communication between stem cells and immune cells.
Research showed that “skin-resident macrophages decrease in number because of apoptosis before the onset of epithelial hair follicle stem cell activation during the murine hair cycle. This process is linked to distinct gene expression, including Wnt transcription.”
By mimicking this event through the selective induction of macrophage apoptosis in early telogen, the researchers identified the involvement of macrophages in stem cell activation in vivo. Significantly, they found that the macrophage-specific pharmacological inhibition of Wnt production delays hair follicle growth and therefore perifollicular macrophages contribute to the activation of skin epithelial stem cells as an additional cue that regulates their regenerative activity.