Long-lasting molecular changes in human skin after repetitive in situ UV irradiation

Abstract

It is known that UV modulates the expression of paracrine factors that regulate melanocyte function in the skin. We investigated the consequences of repetitive UV exposure of human skin in biopsies of 10 subjects with phototypes 2-3.5 taken 1-4 years later. The expression of melanogenic factors (TYR, MART1, MITF), growth factors/receptors (SCF/KIT, bFGF/FGFR1, ET1/EDNRB, HGF, GM-CSF), adhesion molecules (beta-catenin, E-cadherin, N-cadherin), cell cycle proteins (PCNA, cyclins D1, E2) as well as Bcl-2, DKK1, and DKK3, were analyzed by immunohistochemistry. Most of those markers showed no detectable changes at > or = 1 year after the repetitive UV irradiation. Although increased expression of EDNRB protein was detected in 3 of 10 UV-irradiated subjects, there was no detectable change in the expression of ET1 protein or in EDNRB mRNA levels. In summary, only the expression of TYR, MART1, and/or EDNRB, and only in some subjects, was elevated at > or = 1 year after UV irradiation. Thus the long-term effects of repetitive UV irradiation on human skin did not lead to significant changes in skin morphology and there is considerable subject-to-subject variation in responses. The possibility that changes in the expression and function of EDNRB triggers downstream activation of abnormal melanocyte proliferation and differentiation deserves further investigation.

Figure 1

A) Histologically, no morphological changes were detectable in the UV-irradiated skin specimens (left) and the unirradiated controls (right); specimens from B6 are shown as an example. B) Inter-individual differences in skin morphology and melanin content were seen (subjects B2 and B6 are shown as examples, top and bottom, respectively).

Figure 2

Residual increased pigmentation was visible in only 1 subject (T50, photo at 520 d after exposure) after the repetitive Sunlamp-irradiation (in medium and high exposure areas). Subject T47 is shown as an example where no residual pigmentation was observed (photo taken at 427 d after exposure).

Figure 3

Significant increases were noted in melanin content in the skin of 4 of 10 subjects following UV-irradiation, while differences in the density of MART1-positive cells were seen in 2 of 10 subjects, in the density of TYR-positive cells in 4 of 10 subjects, but no differences were seen in the density of MITF-positive cells (B6 is shown as an example for all 4 markers) bars = 50 μm.

Figure 4

Staining intensity ranged from weak to moderate, but overall there were no marked differences in the expression of SCF, KIT, bFGF, FGFR1, ET1 or GM-CSF between UV-irradiated and unirradiated control specimens (B6 is shown as an example for all 6 markers) bars = 50 μm.

Figure 5

A) Differences in EDNRB expression were noted in 2 of 6 subjects (T35 and T47, top and middle, respectively) in the Sunlamp-irradiated group and in 1 of 4 subjects (B6, bottom) in the SS-irradiated group; B) Three different specimens on the melanoma tissue array were positive for EDNRB expression; C) Tissue-in situ hybridization for EDNRB mRNA showing basal expression but no differences between UV-irradiated and unirradiated control specimens (subject T35 shown as an example) bars = 50 μm.

Figure 6

Examples of staining patterns in UV-irradiated specimens (right) and in unirradiated controls (left). ß-Catenin (subject B6), E-cadherin (subject B6), PCNA (subject B1), PCNA (subject B6, double-stained for TYR in red on far right), Bcl-2 (subject T47) and DKK3 (subject B2) bars = 50 μm.