Hair Follicle Stem Cells Maintain the Differentiation Refractory Niche for Co-Occupant Melanocyte Stem Cells by Regulating Retinoid Metabolic Process

The study demonstrated that hair follicle stem cells (HFSCs) play a crucial role in maintaining a differentiation-refractory niche for melanocyte stem cells (McSCs) by regulating retinoid metabolic processes. Specifically, the deletion of the Notch pathway co-factor RBP-J in mouse HFSCs led to premature differentiation of adjacent McSCs during hair regeneration. This was linked to elevated expression of retinoic acid (RA) metabolic genes, which increased RA levels in the niche, sensitizing McSCs to differentiation signals. The research highlighted that HFSCs are the source of KIT-ligand, which normally rises at the start of hair regeneration, and that RA mediates the cross-talk between HFSCs and McSCs, ensuring a stable niche environment.