Mouse model of UVB-induced hyperpigmentation and SF treatment.

For topical SF treatment, 6-month-old WT and Nrf2^–/– C57BL/6 male mice were exposed to 80 mJ/cm² UVB (range 290–315 nm) using a Philips TL Broadband UVB lamp (TL 20W/12 RS SLV/25, Philips) in ventilated cabinets equipped with UVB lamps once daily 5 times a week for 4 weeks. For the next 4 weeks of UVB treatment, just prior to the UVB treatment, mice were anesthetized (2% isoflurane), and SF (1 μM; LKT Laboratories Inc.) was topically applied to the right ear (UVB+SF), while the left ear received either vehicle oil (jojoba oil, MP Biomedical LLC) (UVB+Oil) or no topical treatment (UVB). For the topical SF preventative treatment, 6-week-old WT, Nrf2^–/–, or K14-Cre-ER^T2IL-6Rα^fl/fl (previously treated with tamoxifen [1 mM] i.p. daily for 5 days) C57BL/6 male mice were exposed to 80 mJ/cm² UVB daily 5 times a week for 4 weeks and, in the anesthetized mice just prior to UVB exposure, topical SF was applied to the right ear (UVB+SF), while the left ear received either vehicle oil (jojoba oil, MP Biomedical LLC) (UVB+Oil) or no topical treatment (UVB). In all experiments, an additional Un control group of age-matched male mice that received no UVB treatment and no topical treatment was included.