Ultraviolet radiation (UVR) reaching the skin is a carcinogen, inducing immunosuppression and DNA mutations, 1 and the wavelengths of ultraviolet light B (UVB) represent a biologically very active part of it. 2 The chromophores transduct the electromagnetic energy of UVB into neural, chemical, and hormonal signals to produce rapid (neural) or slow (humoral or immune) responses at the local and systemic levels. 3,4 Skin irradiated by UVB can activate both the central and local hypothalamic-pituitary-adrenal (HPA) axis to turn on homeostatic responses and deactivate local and systemic damage. 4,5 Locally UVB irradiation of the skin leads to activation of pro-opiomelanocortin (POMC) and corticotropin-releasing hormone (CRH) in epidermal and dermal skin, produces cutaneous POMC peptides and activates the corresponding receptors that are important regulators on the pigmentary and the inflammatory reactions. 6-8 In addition, keratinocytes stimulated by UVB can, as a rapid effect, secrete, for example, Summary Background: Recent findings suggest that circadian time regulates cellular functions in the skin and may affect protection against ultraviolet radiation (UVR). It is not known, however, whether UVR through skin directly affects the expression of circadian genes. We investigated the effect of ultraviolet B (UVB) exposure on cryptochrome circadian clock 1 (CRY1), cryptochrome circadian clock 2 (CRY2), and circadian associated repressor of transcription (CIART) genes.Methods: Healthy volunteers (n = 12) were exposed to narrow-band UVB radiation of four standard erythemal dose (SED). Epidermal/dermal and subcutaneous adipose tissue samples were obtained by punch biopsies from irradiated and non-irradiated skin 10 cm away from the irradiated site 24 hours after UVB exposure. Gene expression of CRY1, CRY2, and CIART was measured using RT-PCR (TaqMan).
Results: Ultraviolet B radiation affected mRNA expression in the epidermal/dermal skin and in the subcutaneous adipose tissue. It down-regulated expression of CRY2 gene in the epidermal/dermal skin, whereas it up-regulated expression of CRY1 and CIART genes in the subcutaneous adipose tissue.
Conclusion:We showed for the first time that UVB radiation affects expression of circadian genes in the subcutaneous adipose tissue. Further studies are warranted to understand the mechanisms in detail.