Influence of ionizing irradiation on tissue-resident stem cells

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Introduction: It remains unclear how ionizing radiation damages healthy skin and hair follicles in a short and long term.Methods: C57BL/J6 mouse (8 weeks old) were distributed to three groups (control: CTR,10Gy once irradiation: 10Gy×1, 5Gy twice irradiations: 5Gy×2). After hair epilation, the groin area was radiated. At 0, 1, 2, and 4 weeks, 3, 6 months after irradiation, the skin samples were evaluated histologically and macroscopically.Results: At 1, 2, and 4 weeks, the epidermis was thicker in 10Gy×1 than CTR and 5Gy×2,without increasing the layer number of epidermal keratinocytes. The number of capillaries in dermis was fewer in 5Gy×2 and 10Gy×1 than CTR at 1 and 2 weeks. At 4 weeks, the the dermis was thicker in CTR than 5Gy×2 and 10Gy×1. At 6 months, the subcutaneous fat tissue was thinner in 5Gy×2 than 10Gy and CTR. At 3 and 6 months, capillaries in groin fat of5Gy×2 and 10Gy×1 appeared to be fewer than thoes of CTR and the size of adipocytes became smaller in 5Gy×2. Many of hair shafts disappeared at 1 week, followed by gradual regrow of hairs by 3 months. The number and size of hair remained decreased in 5Gy×2 and 10Gy×1 than CTR at 6 months when hairs were restored and the gray hairs were macroscopically observed.Discussions/Conclusions: In short term (1 to 4 weeks), the number of hair follicles andcapillaries decreased and the dermis became thinner because of acute radiation injury. In long term (3 to 6 months), tissue damage was generally more severe in 5Gy×2 than 10Gy×1. These data provide clinical insights for minimizing short and long term radiation injuryand revitalizing the radiated ischemic and fibrous tissue.