Regulation of human skin pigmentation in situ by repetitive UV exposure: molecular characterization of responses to UVA and/or UVB

Abstract

UV radiation is a major environmental factor that affects pigmentation in human skin and can eventually result in various types of UV-induced skin cancers. The effects of various wavelengths of UV on melanocytes and other types of skin cells in culture have been studied, but little is known about gene expression patterns in situ following in situ exposure of human skin to different types of UV (UVA and/or UVB). Paracrine factors expressed by keratinocytes and/or fibroblasts that affect skin pigmentation might be regulated differently by UV, as might their corresponding receptors expressed on melanocytes. To test the hypothesis that different mechanisms are involved in the pigmentary responses of the skin to different types of UV, we used immunohistochemical and whole human genome microarray analyses to characterize human skin in situ to examine how melanocyte-specific proteins and paracrine melanogenic factors are regulated by repetitive exposure to different types of UV compared with unexposed skin as a control. The results show that gene expression patterns induced by UVA or UVB are distinct-UVB eliciting dramatic increases in a large number of genes involved in pigmentation as well as in other cellular functions, whereas UVA had little or no effect on these. The expression patterns characterize the distinct responses of the skin to UVA or UVB, and identify several potential previously unidentified factors involved in UV-induced responses of human skin.

Figure 1

Tanning responses and Fontana-Masson staining of skin following exposure to UV. A) Photograph of the back of subject 2 showing representative tans elicited by repetitive exposure to SSR (upper right), UVA (bottom left) or UVB (bottom right); unirradiated skin is used as the control (top left). B) Representative specimens stained for melanin content by Fontana Masson staining (subject 2); numbers represent quantitation (mean ± SEM) of melanin density in 10 different images each from 2 biopsies from each of the 4 areas on each of the 6 subjects (n=12 specimens, 120 images for each area). * = p <0.05. Bar = 50 μm.

Figure 2

Immunohistochemistry of melanocyte-specific proteins encoded by UV-regulated genes. Pmel17, TYR, DCT and MITF were identified by staining with α PEP13h, α PEP7h, α PEP8 and Ab3, respectively, using Texas red. All specimens were from subject 2 and all are at the same magnification (200X); insets show regions depicted by the dashed boxes at 600X magnification. Numbers represent quantitation (mean ± SEM) of staining density in 6 different images each from 1 biopsy from each of the 4 areas on each of the 6 subjects (n=6 specimens, 36 images for each area). * = p <0.05. Bar = 50 μm.

Figure 3

Immunohistochemistry of paracrine melanogenic factors and their receptors in human skin exposed to SSR, UVA or UVB. KIT, FGFR1, EDNRB, ET1, GM-CSF and DKK3 were identified by staining with specific antibodies as listed in SI Materials and Methods and Texas red as the chromogen. Melanocytes are identified in the sections by staining with MART1 (green) and nuclei are stained with DAPI (blue). All specimens were from subject 2, and all are at the same magnification (200X); insets show regions depicted by the dashed boxes at 600X magnification. Numbers represent quantitation (mean ± SEM) of staining density in 6 different images each from 1 biopsy from each of the 4 areas on each of the 6 subjects (n=6 specimens, 36 images for each area). * = p <0.05; ** = p <0.01. Bar = 50 μm.

Figure 4

Immunohistochemistry of factors encoded by UV-regulated genes. Localization of IGFBP7, TRIM63, SLC7A11 and MPLP using specific antibodies as listed in SI Materials and Methods and Texas red as the chromogen. Melanocytes were identified in the sections by co-staining with MART1 (green) and nuclei are stained with DAPI (blue). All specimens were from subject 8, and all are at the same magnification (200X); insets show regions depicted by the dashed boxes at 600X magnification. Bar = 50 μm.