1058 Examination of circadian clock gene expression in human skin explants and pharmacological modulation with small molecule compounds

The circadian clock regulates diverse physiological processes throughout the body, including in the skin. Though circadian rhythms have been monitored in various animal tissues ex-vivo, whether or not an intact and functioning circadian clock exists in human skin explants has not previously been reported. Using discarded human panniculectomy skin from 10 different individuals (both males and females, ages 17-63), we examined the epidermal mRNA expression of the clock genes ARNTL, NR1D2, PER2, and CRY1 over the course of 24 hours. Though significant inter-individual variation in expression was observed, the compiled averages revealed similarities with previously published human epidermal skin gene expression data; including higher ARTNL expression in the evening (6 PM) than at mid-day (12 PM), and higher NR1D2 expression at noon than at midnight. These results suggest that discarded surgical skin may be a useful ex-vivo model system for studying the human skin circadian clock. We further examined whether expression of known clock-control genes can be altered by pharmacological manipulation. Skin explants were topically treated with 100 μM of both the cryptochrome inhibitor KS15 and REV-ERB antagonist SR8278 and examined to determine the expression of both core clock genes and clock-controlled genes involved in canonical DNA damage responses (XPA, Wee1, and p21). Variable responses were observed among the different skin samples, with significant enhancement observed in some samples but repression seen in others. Thus, further work is needed to understand how clock-modulating compounds impact clock-regulated genes in human skin epidermis. Nonetheless, this work is the first to analyze the expression patterns of circadian genes in human skin explants and sets the stage for utilizing this model system to better understand how the clock regulates skin physiology and how the skin clock can be modulated pharmacologically.