Endothelial-transcytosed myeloperoxidase activates endothelial nitric oxide synthase via a phospholipase C-dependent calcium signaling pathway

During vascular inflammation, the leukocyte-derived enzyme myeloperoxidase (MPO) is transcytosed across endothelium and into sub-endothelial extracellular matrix, where it promotes endothelial dysfunction by catalytically consuming nitric oxide (NO) produced NO synthase (eNOS). In presence of chloride ions hydrogen peroxide (H2O2), MPO forms oxidant hypochlorous acid (HOCl). Here we examined short-term implications HOCl endothelial-transcytosed for eNOS activity. Incubation with cultured aortic cells (ECs) resulted in its transport sub-endothelium. Exposure MPO-containing ECs to low micromolar concentrations H2O2 yielded enhanced rates consumption that correlated formation increased The MPO-dependent activation occurred despite reduced cellular uptake substrate l-arginine, which involved a decrease maximal activity (Vmax), but not affinity (Km), major l-arginine transporter, cationic amino transporter-1. Activation exposed rapid elevation cytosolic calcium phosphorylation at Ser-1179 de-phosphorylation Thr-497. These signaling events were attenuated intracellular chelation, removal inhibition phospholipase C. This study shows stimulation activates promoting C-dependent altered may constitute compensatory response aimed maintaining production face MPO-catalyzed oxidative stress.