The Arrector Pili Muscle: The Bridge Between the Follicular Stem Cell Niche and the Interfollicular Epidermis

The study investigated the arrector pili muscle (APM) and its connection to hair follicle function and hair loss, particularly in androgenetic alopecia (AGA). Using phalloidin staining, the researchers visualized the APM's anatomy and found it to have a complex "C"-shaped structure with extensive branching, which is shared between follicles within a follicular unit. In 8 patients with AGA, the APM's attachment to the bulge, a stem cell niche, was either lost or miniaturized, suggesting its importance in maintaining follicular integrity. The study suggests that the APM plays a role in hair follicle morphogenesis, renewal, and possibly in wound healing by activating bulge stem cells. The authors recommend further research to explore the APM's molecular composition and its role in hair loss and wound healing.