Evaluation of hair follicle stem cells in radiation damage.

Radiation-induced hair loss is a clinically important, but under-researched topic. We reported that radiation-induced hair follicle dystrophy was characterized by morphological similarities to dystrophic catagen induced by chemotherapy. The extent of this hair follicle damage occurred in a radiation dose-dependent manner. However, the effect of irradiation on stem cells still remains unknown in radiation-induced hair follicle damage. In this study, a portion of the dorsal skin from 7-week-old male BALB/c mice, harboring uniform telogen phase hair follicles, was depilated to induce the anagen phase of the hair growth cycle. Then these mice received total body irradiation (TBI) with gamma-rays, at doses in the range of 4 to 16 Gy, 6 days after depilation. Under these conditions, hair could grow after irradiation at 4 Gy, but not at more than 6 Gy. In contrast, hair could be regenerated when mice were depilated 1 h after irradiation at 6 Gy. K15 positive stem cells drastically decreased in anagen hair follicles after irradiation. On the other hand, K15 positive stem cells remained the same in telogen hair follicles even after irradiation at all tested doses. However post-irradiation plucking - that is, anagen phase induction - dramatically diminished the number of K15 positive stem cells in those hair follicles. In contrast, post-irradiation plucking did trigger hair follicles differentiation. These findings suggest that hair follicle stem cells are relatively resistant to radiation. However, irradiation may inhibit the capability for self-renewal of stem cells, resulting in a decrease or depletion of stem cells in their differentiation. Therefore, anagen hair follicles are more sensitive to radiation than telogen hair follicles.日本研究皮膚科学会第35回年次学術大会・総