An updated guide to hair follicle stem cell markers and changes in their expression with aging

The availability of identification markers is a major expectation in the field of stem and progenitor cell biology, whether to decipher the hierarchy of these cellular compartments or to isolate these cells for use in tissue reconstruction and regeneration approaches. Epithelial hair follicle stem cells (HFSCs) constitute a well-established model of multipotent tissue stem cells. Knowledge of relevant HFSC phenotypes is crucial for their identification and manipulation for therapeutics, including hair regeneration in patients with alopecia and skin engineering after injury. In this review, we provide a detailed review of murine and human HFSC markers, drawing upon traditional studies that identify classic HFSC markers and highlighting single-cell RNA-sequencing studies that have greatly expanded our knowledge of HFSCs. Recently defined HFSC subsets with distinct marker expression, microRNAs that qualify as cycle-specific HFSC markers, and HFSC marker changes with aging are all discussed.