Keratinocyte Stem Cells but Not Melanocyte Stem Cells Are the Primary Target for Radiation-Induced Hair Graying

The study by Hitomi Aoki and colleagues from 2013 demonstrated that keratinocyte stem cells (KSCs) are the primary target for ionizing radiation (IR)-induced hair graying, not melanocyte stem cells (MSCs). The research, which involved experiments on mice, showed that while both KSCs and MSCs were affected by IR, the effects on KSCs were more detrimental, leading to a temporary reduction in their colony-forming activity and a delayed hair cycle. In contrast, MSCs retained their self-renewal and differentiation potentials even after high doses of IR. The study also found that irradiated KSCs suppressed the colony formation of MSCs in vitro and that pigmented hairs were not reconstituted in vivo in the presence of irradiated KSCs. This suggests that the niche activity for MSCs is specifically compromised by KSCs following IR exposure. Additionally, the study indicated that the loss of functional niche molecules in KSCs, such as Kitl, may be responsible for the graying, and that exogenously expressed Kitl in skin keratinocytes can prevent radiation-induced hair graying.