Myeloperoxidase attracts neutrophils by physical forces

Abstract

Recruitment of polymorphonuclear neutrophils (PMNs) remains a paramount prerequisite in innate immune defense and a critical cofounder in inflammatory vascular disease. Neutrophil recruitment comprises a cascade of concerted events allowing for capture, adhesion and extravasation of the leukocyte. Whereas PMN rolling, binding, and diapedesis are well characterized, receptor-mediated processes, mechanisms attenuating the electrostatic repulsion between the negatively charged glycocalyx of leukocyte and endothelium remain poorly understood. We provide evidence for myeloperoxidase (MPO), an abundant PMN-derived heme protein, facilitating PMN recruitment by its positive surface charge. In vitro, MPO evoked highly directed PMN motility, which was solely dependent on electrostatic interactions with the leukocyte's surface. In vivo, PMN recruitment was shown to be MPOdependent in a model of hepatic ischemia and reperfusion, upon intraportal delivery of MPO and in the cremaster muscle exposed to local inflammation or to intraarterial MPO application. Given MPO's affinity to both the endothelial and the leukocyte's surface, MPO evolves as a mediator of PMN recruitment because of its positive surface charge. This electrostatic MPO effect not only displays a so far unrecognized, catalysis-independent function of the enzyme, but also highlights a principal mechanism of PMN attraction driven by physical forces. (Blood. 2011; 117(4):1350-1358) IntroductionRecruitment of polymorphonuclear neutrophils (PMNs) is considered a hallmark in host defense. 1 With vessel-and tissue-infiltrating PMNs also being mechanistically linked to a broad range of vascular inflammatory diseases including coronary artery disease, heart failure and ischemia/reperfusion injury, the pathophysiologic significance of PMN motility reaches far beyond innate immunity. [2][3][4] So far, PMN migration is primarily viewed to be energydependent and cytoskeleton-dependent with G-protein coupled receptors and integrins initiating and orchestrating signaling pathways obligatory for neutrophil adhesion, spreading, diapedesis and chemotactic agitation. [5][6][7] On activation, PMN releases myeloperoxidase (MPO), an abundant heme protein in PMN with potent bactericidal and vascular-inflammatory properties. The enzyme accumulates along the endothelium and in the subendothelial space, 8 where it binds to anionic glycocalyx residues such as heparan sulfate glycosaminoglycans. Given the affinity of MPO to both PMN and endothelial cells, we evaluated whether MPO affects PMN locomotion and recruitment. Methods Isolation of PMNPeripheral blood was drawn from healthy human volunteers and heparinized, and isolation of PMN was performed as previously described. 9 In brief, after sedimentation in dextran solution (45 mg/mL), the supernatant was placed over Histopaque 1077 (Sigma-Aldrich) for density gradient centrifugation. Remaining red blood cells were eliminated by hypotonic lysis and the pellet was resuspended in Hanks balanced salt solution (HBSS; Invitrogen) containing 0...

Demyelinating Diseases: Myeloperoxidase as an Imaging Biomarker and Therapeutic Target

“…MPO appears to be involved in positive feedback regulation of inflammation, as observed in both published literature (43)(44)(45)(46)(47) and our study. Indeed, investigators in a recent study found that MPO can bring together endothelial and leukocyte membranes via electrostatic forces (44), potentially acting as a positive feedback for cell recruitment.…”

“…Indeed, investigators in a recent study found that MPO can bring together endothelial and leukocyte membranes via electrostatic forces (44), potentially acting as a positive feedback for cell recruitment. This is consistent with our observation of decreased inflammatory cell infiltration of the brain after MPO inhibition.…”

MPO and neutrophils: a magnetic attraction

“…Klinke et al demonstrate that the proinflammatory actions of MPO may extend to promotion of leukocyte recruitment. 5 MPO is shown to invoke directional neutrophil movement in in vitro chemotaxis experiments, independent of its enzymatic activity and intracellular processes in neutrophils such as phosphatidylinositol 3-kinase activity and actin polymerization. Most interestingly, even fixed/dead neutrophils were attracted toward MPO, as were negatively charged beads.…”

“…In this issue, Klinke et al demonstrate that the highly cationic MPO molecule is able to attract leukocytes via its electrostatic characteristics. 5 MPO is a heme-containing peroxidase highly expressed by polymorphonuclear neutrophils. Its major function is generation of hypochlorous acid as part of the neutrophil's antimicrobial armory.…”

Neutrophils Amplify Autoimmune Central Nervous System Infiltrates by Maturing Local APCs

“…First, we investigated the contribution of neutrophil-related enzymes such as MPO or ELANE for EAE development. MPO is involved in the regulation of endothelial barrier permeability (21) and the transmigration of neutrophils to inflamed sites (22). ELANE, together with proteinase 3, has been described to generate a proinflammatory environment by degrading anti-inflammatory progranulin, thereby producing proinflammatory granulin peptides (23).…”