Dose and time effects of solar-simulated ultraviolet radiation on the in vivo human skin transcriptome

Abstract

Background: Terrestrial ultraviolet (UV) radiation causes erythema, oxidative stress, DNA mutations and skin cancer. Skin can adapt to these adverse effects by DNA repair, apoptosis, keratinization and tanning.

Objectives: To investigate the transcriptional response to fluorescent solar-simulated radiation (FSSR) in sun-sensitive human skin in vivo.

Methods: Seven healthy male volunteers were exposed to 0, 3 and 6 standard erythemal doses (SED). Skin biopsies were taken at 6 h and 24 h after exposure. Gene and microRNA expression were quantified with next generation sequencing. A set of candidate genes was validated by quantitative polymerase chain reaction (qPCR); and wavelength dependence was examined in other volunteers through microarrays.

Results: The number of differentially expressed genes increased with FSSR dose and decreased between 6 and 24 h. Six hours after 6 SED, 4071 genes were differentially expressed, but only 16 genes were affected at 24 h after 3 SED. Genes for apoptosis and keratinization were prominent at 6 h, whereas inflammation and immunoregulation genes were predominant at 24 h. Validation by qPCR confirmed the altered expression of nine genes detected under all conditions; genes related to DNA repair and apoptosis; immunity and inflammation; pigmentation; and vitamin D synthesis. In general, candidate genes also responded to UVA1 (340-400 nm) and/or UVB (300 nm), but with variations in wavelength dependence and peak expression time. Only four microRNAs were differentially expressed by FSSR.

Conclusions: The UV radiation doses of this acute study are readily achieved daily during holidays in the sun, suggesting that the skin transcriptional profile of 'typical' holiday makers is markedly deregulated. What's already known about this topic? The skin's transcriptional profile underpins its adverse (i.e. inflammation) and adaptive molecular, cellular and clinical responses (i.e. tanning, hyperkeratosis) to solar ultraviolet radiation. Few studies have assessed microRNA and gene expression in vivo in humans, and there is a lack of information on dose, time and waveband effects. What does this study add? Acute doses of fluorescent solar-simulated radiation (FSSR), of similar magnitude to those received daily in holiday situations, markedly altered the skin's transcriptional profiles. The number of differentially expressed genes was FSSR-dose-dependent, reached a peak at 6 h and returned to baseline at 24 h. The initial transcriptional response involved apoptosis and keratinization, followed by inflammation and immune modulation. In these conditions, microRNA expression was less affected than gene expression.

Figure 1

Volcano plots of gene expression in skin after fluorescent solar‐simulated radiation exposure (different doses and time points). Plots show effect size log₂ fold change (Log2FC) vs. –log10(P‐value). (a) and (b) show dose effects at time 6 h; and (c) and (d) dose effects at 24 h. Genes that reached 5% false discovery rate are in red. The number of differently expressed genes is higher at the higher dose [6 standard erythemal doses (SED)] and earlier time after exposure (6 h). The change in their expression levels is also more pronounced at the higher dose (6 SED) and earlier time (6 h). All plots show rather symmetric patterns. However, at 6 SED, the number of upregulated genes is slightly increased and their Log2FC slightly stronger.

Figure 2

Venn diagram of genes detected at 5% false discovery rate in skin after fluorescent solar‐simulated radiation exposure (different doses and time points). Overlap of differently expressed genes under different models: different time (6 h and 24 h) and different dose [3 standard erythemal doses (SED) and 6 SED].

Figure 3

Comparison of the effect size of candidate genes after exposure to fluorescent solar‐simulated radiation (FSSR), ultraviolet (UV)A1 and UVB. (a) Genes detected under all conditions of FSSR exposure: AEN,BYSL,CDKAL1,ELP4,EPHB1,GRIP1,NOLC1,PRKCB,SLC24A3. (b) DNA repair and apoptosis genes: POLH. (c) Immunity and inflammation genes: CD83,IL1A,IL20,IL6,TNF. (d) Pigmentation genes. (d1) Tyrosinase complex: DCT,TYR,TYRP1; (d2) tyrosinase complex regulation (reg.): OCA2,PMEL;SCL24A5; (d3) melanin synthesis regulation: ASIP,ATRN; (d4) melanosome transport (trans.): LYST; (d5) melanoblast (melanobl.) migration (migr.) and differentiation (diff.): EDN3,EDNRB,KIT; (d6) transcription factor: MITF; (d7) other: FGFR2. (e) vitamin D genes: CYP2R1. y‐axis represents log₂ fold change (Log2FC), scale adapted to each gene; x‐axis represents different exposure conditions: different wavelength [FSSR, UVA1 (340–400 nm) or UVB (300 nm)], dose [3 standard erythemal doses (SED), 6 SED or 1 minimal erythemal dose (MED) (~2 SED, ranging from 1·6 to 2·6 SED)], time after exposure (6 h or 24 h). For FSSR, Log2FC (^–∆∆Ct) obtained in the quantitative polymerase chain reaction experiment are shown. *P < 0·05 compared with unexposed samples (0 SED); **P < 2·8E‐04 compared with unexposed samples (0 SED).

Figure 4

Volcano plots of microRNA (miRNA) expression in skin after fluorescent solar‐simulated radiation (FSSR) exposure (different doses and time points). Plots show effect size log₂ fold change (Log2FC) vs. –log10(P‐value). (a) and (b) show dose effects at time 6 h; and (c) and (d) dose effects at 24 h. Only four miRNAs survived multiple testing correction (shown in red). All plots show symmetric patterns. The size of the effects of FSSR on miRNA expression was smaller than on gene expression.

Figure 5

microRNA (miRNA) expression in skin after fluorescent solar‐simulated radiation (FSSR) exposure (different doses and time points). Normalized miRNA expression levels and mean standard error (y‐axis) by FSRR dose (x‐axis) and time (6 h in black and 24 h in red). (a) hsa‐miR‐223‐3p [6 h–0 standard erythemal doses (SED) vs. 6 h–6 SED: P = 1·17E‐06] and (b) hsa‐miR‐146b‐5p (6 h–0 SED vs. 6 h–6 SED: P = 1·71E‐05); (c) hsa‐miR‐142‐5p (24 h 0 SED vs. 24 h 3 SED: P = 1·08E‐04) and (d) hsa‐miR‐204‐5p (24 h 0 SED vs. 24 h 3 SED: P = 9·52E‐05).