Immune Cell-Mediated Amplification of Stem Cell Activation in Hairy Melanocytic Nevus via Osteopontin-CD44 Axis

This study investigates the role of immune cells in amplifying stem cell activation in hairy melanocytic nevus through the Osteopontin-CD44 axis. Using mouse models with melanocyte-specific mutations in oncogenes Nras or Braf, researchers observed hyperactivation of hair follicle (HF) stem cells and excessive hair growth. The study identifies Osteopontin as a key factor secreted by senescent melanocytes, which recruits Osteopontin-positive myeloid cells expressing gamma-secretase activating protein (GSAP). GSAP likely mediates the cleavage of CD44, an Osteopontin receptor, releasing its intracellular domain to regulate gene expression. This mechanism highlights the crosstalk between tissue-resident stem cells and their niche, suggesting that immune cell-derived factors enhance the effects of senescence-associated secreted phenotypes (SASP) on HF stem cells.