Abstract
Vascular inflammation is associated with increased arterial O2●–/H2O2 that affect vascular tone and disease. We reported previously that in inflammation, vascular endothelial cells express indoleamine 2,3-dioxygenase 1 (IDO1, a heme-containing enzyme that oxidizes Trp to N-formyl-kynurenine) and that IDO1-mediated metabolism of Trp regulates vascular tone and blood pressure (Nat Med 16:279). Here we show that in the presence of H2O2 purified IDO1 forms singlet oxygen (1O2), as assessed by the conversion of specific probes to their endoperoxides, and light emission at 1270 nm. 1O2 formed by isolated IDO1/H2O2 stereospecifically converts Trp to a tricyclic hydroperoxide (cis-WOOH) that decays to N-formyl-kynurenine. Formation of cis-WOOH is via an oxidative dioxygenase reaction, distinct from the known reductive dioxygenase and peroxidase activities of IDO1. In vitro, cis-WOOH but not trans-WOOH oxidizes protein kinase G1α (PKG1α) to a dimer in a reaction dependent on Cys42. Similarly, exposure of endothelium-denuded arteries to cis-WOOH dimerizes PKG1α. Such cis-WOOH-induced PKG1α dimerization is associated with arterial relaxation, whereas arteries from “redox dead” PKG1α-C42S knock-in mice are refractory to relaxation by cis-WOOH. Moreover, Trp-induced relaxation of IDO1-expressing and endothelium-intact arteries depends on PKG1α-Cys42 as corresponding segments from PKG1α-C42S knock-in mice do not relax, and it is attenuated by pretreatment with PEG-catalase. Together, our data indicate that in ‘inflamed arteries’, endothelial IDO1/H2O2 generate light (i.e., 1O2) in a dark reaction. This results in formation of a tricyclic Trp-derived hydroperoxide that signals relaxation via oxidative activation of PKG1α in vascular smooth muscle cells.
Published Version
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