Macrophages Contribute to the Cyclic Activation of Adult Hair Follicle Stem Cells

The study demonstrated that skin-resident macrophages played a role in the activation of hair follicle stem cells during the murine hair cycle by undergoing apoptosis before stem cell activation. This process was associated with changes in gene expression, including Wnt transcription. By inducing macrophage apoptosis in early telogen, researchers identified macrophages as contributors to stem cell activation in vivo. Additionally, inhibiting macrophage-specific Wnt production delayed hair follicle growth, suggesting that perifollicular macrophages provided a novel regulatory cue for the regenerative activity of skin epithelial stem cells. These findings had potential implications for skin repair, inflammatory skin diseases, and cancer.