Ultraviolet A(1) radiation induces nitric oxide synthase-2 expression in human skin endothelial cells in the absence of proinflammatory cytokines

Skin exposure to ultraviolet radiation from sunlight causes erythema and ed ema formation as well as inflammatory responses. As some of these ultraviol et-induced effects are potentially mediated by nitric oxide synthases, we e xamined the role of cytokines and ultraviolet A, radiation (340-400 nm) on the expression of the nitric oxide synthase-2 in endothelia of normal human skin biopsies during short-term organ culture as well as expression and ac tivity of the nitric oxide synthase-2 in in vitro cell cultures of human de rmal endothelial cells. Both, cytokine challenge (interleukin-1 beta + tumo r necrosis factor-alpha + interferon-gamma) but also ultraviolet A, exposur e (50 J per cm(2)) in the absence of cytokines led to the expression of nit ric oxide synthase-2 in human skin organ cultures as shown by immunohistoch emistry. Moreover, exposing human dermal endothelial cell cultures to proin flammatory cytokines but also to ultraviolet A, radiation (6-24 J per cm(2) ) in the absence of cytokines resulted in significant nitric oxide synthase -2 mRNA and protein expression as well as enzyme activity. Ultraviolet A, i rradiation of cytokine activated cells led to further increases in nitric o xide synthase-2 mRNA, protein expression, and enzyme activity. Moreover, a reporter gene assay using a human nitric oxide synthase-2 promoter construc t provide evidence that ultraviolet A,, in the absence of cytokines, induce s nitric oxide synthase-2 expression and activity, as previously shown for cytokines. Thus, the results presented here demonstrate for the first time that in dermal endothelia of human skin ultraviolet A, radiation alone repr esents a proinflammatory stimulus sufficient to initiate nitric oxide synth ase-2 expression as well as activity comparable with the respective respons e seen in the presence of proinflammatory cytokines.