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Ultraviolet A
Radiation Favors Expression and Substrate Supply for the Inducible Nitric
Oxide Synthase in Normal Human Skin
Schnorr, Oliver 1,
Bruch-Gerharz, Daniela2, Suschek, Christoph1
and Kolb-Bachofen, Victoria1
Research Group Immunobiology, Heinrich-Heine-University of Duesseldorf,
P.O. Box 101007, D-40001 Duesseldorf, Germany1
Department of Dermatology, Heinrich-Heine-University of Duesseldorf, P.O.
Box 101007, D-40001 Duesseldorf, Germany2
Abstract-
Expression of the inducible nitric oxide synthase (iNOS) is found in
keratinocytes and in the dermal vasculature of psoriatic skin, but is
also found to represent a normal time-limited response after UV-irradiation.
Thus, this response may represent a regulating signal of local dermal
functions during inflammatory reactions following various environmental
challenges. The enzyme activity of iNOS will be modulated by arginase-1
(inducible isoform, Arg-1) and arginase-2 (constitutive isoform, Arg-2),
as these enzymes compete for the common substrate L-arginine. In addition,
iNOS activity will also dependent on substrate supply via the cationic
amino acid transporters CAT-1 (constitutively expressed in all cells)
and CAT-2B (inducible isoform). In search for determining the in vivo
enzyme activity of the iNOS in human skin after UVA-irradiation, we
used short-term organ culture of skin biopsies obtained from mamma reduction.
Specimen were UVA-irradiated and/or cytokine-challenged and the expression
of iNOS-specific mRNA as well as mRNA specific for Arg-1, Arg-2, CAT-1
and CAT-2B was. We find that UVA-radiation leads to the induction of
iNOS mRNA expression in the skin specimens also. This induction is paralleled
by a increase in CAT-1 and the inducible CAT-2B mRNA, which we find
constitutively expressed in human skin. Expression of the mitochondrial,
constitutively expressed Arg-2 mRNA was not effected. In contrast, inducible-type
Arg-1, which we also find constitutively expressed in skin, was strongly
reduced by UVA. When iNOS mRNA expression was induced by cytokine-challenge,
similar increases in CAT-1 and CAT-2 mRNA formation with significant
decrease in Arg-1 mRNA expression was seen. UVA irradiation of cytokine-activated
specimens further increased these effects significantly. The data presented
here now indicate, that UVA leads to increases in the substrate supply
via augmented transport and reduces substrate competition by reducing
Arg-1 expression. These data all argue in favor of increased iNOS activity
following UVA exposure. Moreover, the new finding of constitutive expression
of both, CAT-2B and Arg-1 in normal, untreated skin specimen renders
keratinocytes comparable to hepatocytes as far as the expression patterns
for these two proteins appear similar in the two epithelia.
Keywords: inducible
nitric oxide synthase, arginase-1, cationic amino acid transporter,
UVA
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