6533b7d5fe1ef96bd1263e9a

RESEARCH PRODUCT

Ultraviolet A1 radiation induces nitric oxide synthase-2 expression in human skin endothelial cells in the absence of proinflammatory cytokines.

subject

description

Skin exposure to ultraviolet radiation from sunlight causes erythema and edema formation as well as inflammatory responses. As some of these ultraviolet-induced effects are potentially mediated by nitric oxide synthases, we examined the role of cytokines and ultraviolet A 1 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 activity of the nitric oxide synthase-2 in in vitro cell cultures of human dermal endothelial cells. Both, cytokine challenge (interleukin-1β + tumor necrosis factor-α + interferon-γ) but also ultraviolet A 1 exposure (50 J per cm 2 ) in the absence of cytokines led to the expression of nitric oxide synthase-2 in human skin organ cultures as shown by immunohistochemistry. Moreover, exposing human dermal endothelial cell cultures to proinflammatory cytokines but also to ultraviolet A 1 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 1 irradiation of cytokine activated cells led to further increases in nitric oxide synthase-2 mRNA, protein expression, and enzyme activity. Moreover, a reporter gene assay using a human nitric oxide synthase-2 promoter construct provide evidence that ultraviolet A 1 , in the absence of cytokines, induces 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 1 radiation alone represents a proinflammatory stimulus sufficient to initiate nitric oxide synthase-2 expression as well as activity comparable with the respective response seen in the presence of proinflammatory cytokines.