107 Follicular Slow Cycling Stem Cells are Directed to Cell Death by Plucking, Followed by Regeneration in the Reconstructed Bulge Region

M. Ito, and K. Kizawa. Basic Research Laboratory, Kanebo Ltd., Odawara, Japan

Hair follicle stem cells reside in the bulge region that marks the lowest end of the permanent portion of the follicle. The bulge region is considered to be an excellent compartment for protection of follicular stem cells. However, after plucking clubs for anagen induction, we previously found that most cells in the bulge region experienced massive cell death1. To clarify whether follicular stem cells, defined by their slow cycling nature, are directed to cell death by plucking, we determined the precise location of slow cycling stem cells in plucked follicles. Neonatal mice were injected subcutaneously with 5-bromo-2-deoxyuridine (BrdU) (50µg/g body weight) twice daily for 3 days from the third day after birth. Consistent with other reports, in 8 to 10-week old mice slowly cycling stem cells that retain BrdU label were found to reside in the bulge area. After plucking telogen follicle clubs, the sections were subjected to a TUNEL reaction as well as immunohistochemistry for BrdU. We found that most of the follicular epithelial cells labeled with BrdU were positive for TUNEL staining at 4.5 hours after plucking, showing that follicular stem cells were directed to cell death. Nevertheless, the disrupted bulge regions were restored by 48 hours after plucking, and hair follicle regeneration was accomplished without delay. To know whether the repopulated bulge cells acquired a slow cycling nature, we attempted to characterize the label retaining property of the reconstructed bulge region. Eight-week-old mice received an intraperitoneal injection with BrdU during bulge reconstruction. Most of the epidermal cells, including repopulated bulge cells, were labeled with BrdU within 3 days. By 22 days after plucking, BrdU labels were exclusively retained in the bulge area of the telogen follicles. These results indicated that slow cycling cells are repopulated and form the functional stem cell compartment. We concluded that plucking is a useful means of inducing experimental cell death in follicular stem cells. Furthermore, subsequent reconstruction of the bulge region involves the renewal of follicular slow cycling stem cells. 1. M Ito, K Kizawa J Invest Dermatol 114:854, 2000 (abstr.)