LAUSR

Purpose or Objective The highly proliferative hair follicles are sensitive to radiation and hair loss (alopecia) often develops. We found, local prostaglandin E2 (PGE2) pretreatment could reduce hair loss from radiation injury by preventing entry into catagen (regression phase) and telogen (resting phase) (Figure 1a). Whether and how anagen hair follicles attempt to repair themselves in response to ionizing radiation (IR) under PGE2 local treatment has not been characterized. In this work, we try to investigate the proceeding regenerative process in hair follicle cells following radiation injury under prostaglandin treatment. Material and Methods The dorsal hair of female C57BL/6 mice on postnatal day 32 when hair follicles were in the early full anagen (growth phase) was carefully shaved. Single dose of 8.5Gy was given from dorsal side 2 hours after dmPGE2 (A stabilized derivative of prostaglandin E2,16,16-dimethyl-PGE2) locally injected. Skin specimen was harvested at multiple time points after radiation exposure. H&E staining, Immunohistochemical analysis and double staining with hair follicle cell markers were used to monitor the dynamics of cell differentiation at different time points. The fluorescence ubiquitination cell cycle indicator (FUCCI) system, which can easily determine G1 and/or S/G2/M phases of the cell cycle through analyzes living cells in a spatio-temporal manner using a dual color scheme of orange and green, is used for evaluating cell cycle condition. Results Severe dystrophic change of anagen hair follicles were observed after 8.5Gy radiation injury. We found anagen hair follicles were able to initiate spatially and temporally repair activities to restore their structure under PGE2 pretreatment after radiation injury. The hair follicle bulge stem cells were not activated during the repair process. (Figure 1b) Continuous BrdU pulse labeling after PGE2 local pretreatment revealed that the proliferation of hair follicle bulb matrix cells (hair follicle transit amplifying cells (TACs) ) was transiently halted) (Figure 2a). Immunostaining of cell cycle marker of cyclin D showed decrease level after PGE2 pretreatment. (Figure 2b). These suggested PGE2 might reduce the radiosensitivity of TACs through cell cycle G1 phase arrest. We further took advantage of the fluorescence ubiquitination cell cycle indicator (FUCCI) system and confirmed the process.