Fig. 6.

Light enhances hedgehog signaling in HFSCs to promote anagen entry. (A) Pulse BrdU labeling under daily 2 J/cm² blue light stimulation. Cell proliferation of HFSCs was first observed in secondary hair germs on day 3 (yellow arrowheads) and then in the bulge area on day 5 (white arrowheads). In the nonirradiated control group, no cell proliferation was observed in the HFSC compartment. Similar results were observed in all HFs examined (n = 30). (Scale bar, 50 μm.) BG, bulge; DP, dermal papilla; SHG, secondary hair germ. (B) Analysis of gene expression 1 d after initiation of light stimulation by RNA-sequencing. The top five signaling pathways enhanced by light stimulation are shown here. P values are shown on the right. (C) Gene expression in HFSCs determined by quantitative PCR 1 d after initiation of light stimulation. Expression of Gli1 and Gli2 was up-regulated in bulge and secondary hair germ SCs after light irradiation. In the interfollicular epidermis, expression of Gli1 and Gli2 was not significantly increased. *P < 0.05, control vs. light-treated group (n = 3). (D and E) Effect of hedgehog pathway inhibitor. (D) Topical cyclopamine inhibited light-triggered anagen entry. *P < 0.05 (n = 10). (E) Pulse BrdU labeling under cyclopamine treatment. Cyclopamine inhibited light-triggered HFSC activation. Similar results were observed in all HFs examined (n = 30). (Scale bar, 50 μm.)