SCF/c‐kit signaling is required for cyclic regeneration of the hair pigmentation unit

ABSTRACT Hair graying, an age‐associated process of unknown etiology, is characterized by a reduced number and activity of hair follicle (HF) melanocytes. Stem cell factor (SCF) and its receptor c‐kit are impor¬tant for melanocyte survival during development, and mutations in these genes result in unpigmented hairs. Here we show that during cyclic HF regeneration in C57BL/6 mice, proliferating, differentiating, and mel¬anin‐producing melanocytes express c‐kit, whereas pre¬sumptive melanocyte precursors do not. SCF overex¬pression in HF epithelium significantly increases the number and proliferative activity of melanocytes. Dur¬ing the induced hair cycle in C57BL/6 mice, adminis¬tration of anti‐c‐kit antibody dose‐dependently de¬creases hair pigmentation and leads to partially depigmented (gray) or fully depigmented (white) hairs, associated with significant decreases in melanocyte proliferation and differentiation, as determined by immunostaining and confocal microscopy. However, in the next hair cycle, the previously treated animals grow fully pigmented hairs with the normal number and distribution of melanocytes. This suggests that melanocyte stem cells are not dependent on SCF/c‐kit and when appropriately stimulated can generate melanogenically active melanocytes. Therefore, the blockade of c‐kit signaling offers a fully reversible model for hair depigmentation, which might be used for the studies of hair pigmentation disorders.—Botchkareva, N. V., Khlgatian, M., Longley, B. J., Botchkarev, V. A., and Gilchrest, B. A. SCF/c‐kit signaling is required for cyclic regeneration of the hair pigmentation unit. FASEB J. 15, 645‐658 (2001)