Distinct Migratory Properties of M1, M2, and Resident Macrophages Are Regulated by α\u3csub\u3ed\u3c/sub\u3eβ\u3csub\u3e2\u3c/sub\u3eand α\u3csub\u3em\u3c/sub\u3eβ\u3csub\u3e2\u3c/sub\u3eIntegrin-Mediated Adhesion

Chronic inflammation is essential mechanism during the development of cardiovascular and metabolic diseases. The outcome of diseases depends on the balance between the migration/accumulation of pro-inflammatory (M1) and anti-inflammatory (M2) macrophages in damaged tissue. The mechanism of macrophage migration and subsequent accumulation is still not fully understood. Currently, the amoeboid adhesion-independent motility is considered essential for leukocyte migration in the three-dimensional environment. We challenge this hypothesis by studying the contribution of leukocyte adhesive receptors, integrins αMβ2, and αDβ2, to three-dimensional migration of M1-polarized, M2-polarized, and resident macrophages. Both integrins have a moderate expression on M2 macrophages, while αDβ2 is upregulated on M1 and αMβ2 demonstrates high expression on resident macrophages. The level of integrin expression determines its contribution to macrophage migration. Namely, intermediate expression supports macrophage migration, while a high integrin density inhibits it. Using in vitro three-dimensional migration and in vivo tracking of adoptively-transferred fluorescently-labeled macrophages during the resolution of inflammation, we found that strong adhesion of M1-activated macrophages translates to weak 3D migration, while moderate adhesion of M2-activated macrophages generates dynamic motility. Reduced migration of M1 macrophages depends on the high expression of αDβ2, since αD-deficiency decreased M1 macrophage adhesion and improved migration in fibrin matrix and peritoneal tissue. Similarly, the high expression of αMβ2 on resident macrophages prevents their amoeboid migration, which is markedly increased in αM-deficient macrophages. In contrast, αD- and αM-knockouts decrease the migration of M2 macrophages, demonstrating that moderate integrin expression supports cell motility. The results were confirmed in a diet-induced diabetes model. αD deficiency prevents the retention of inflammatory macrophages in adipose tissue and improves metabolic parameters, while αM deficiency does not affect macrophage accumulation. Summarizing, β2 integrin-mediated adhesion may inhibit amoeboid and mesenchymal macrophage migration or support mesenchymal migration in tissue, and, therefore, represents an important target to control inflammation

Pleiotrophin, a Multifunctional Cytokine and Growth Factor, Induces Leukocyte Responses Through the Integrin Mac-1

Pleiotrophin (PTN) is a multifunctional, cationic, glycosaminoglycan- binding cytokine and growth factor involved in numerous physiological and pathological processes, including tissue repair and inflammation-related diseases. PTN has been shown to promote leukocyte responses by inducing their migration and expression of inflammatory cytokines. However, the mechanisms through which PTN mediates these responses remain unclear. Here, we identified the integrin Mac-1 (αMβ2, CD11b/CD18) as the receptor mediating macrophage adhesion and migration to PTN. We also found that expression of Mac-1 on the surface of human embryonic kidney (HEK) 293 cells induced their adhesion and migration to PTN. Accordingly, PTN promoted Mac-1-dependent cell spreading and initiated intracellular signaling manifested in phosphorylation of Erk1/2. While binding to PTN, Mac-1 on Mac-1-expressing HEK293 cells appears to cooperate with cell-surface proteoglycans because both anti-Mac-1 function-blocking mAb and heparin were required to block adhesion. Moreover, biolayer interferometry andNMRindicated a direct interaction between theαMI domain, the major ligand-binding region of Mac-1, and PTN. Using peptide libraries, we found that in PTN the αMI domain bound sequences enriched in basic and hydrophobic residues, indicating thatPTNconforms to the general principle of ligandrecognition specificity of the αMI domain toward cationic proteins/ peptides. Finally, using recombinant PTN-derived fragments, we show that PTN contains two distinct Mac-1-binding sites in each of its constitutive domains. Collectively, these results identify PTN as a ligand for the integrin Mac-1 on the surface of leukocytes and suggest that this interaction may play a role in inflammatory responses

Interaction Between the Integrin Mac-1 and Signal Regulatory Protein α (SIRPα) Mediates Fusion in Heterologous Cells

Published under exclusive license by The American Society for Biochemistry and Molecular Biology, Inc. Macrophage fusion leading to the formation of multinucleated giant cells is a hallmark of chronic inflammation. Several membrane proteins have been implicated in mediating cell- cell attachment during fusion, but their binding partners remain unknown. Recently, we demonstrated that interleukin-4 (IL-4)- induced fusion of mouse macrophages depends on the integrin macrophage antigen 1 (Mac-1). Surprisingly, the genetic deficiency of intercellular adhesion molecule 1 (ICAM-1), an established ligand of Mac-1, did not impair macrophage fusion, suggesting the involvement of other counter-receptors. Here, using various approaches, including signal regulatory protein α (SIRPα) knockdown, recombinant proteins, adhesion and fusion assays, biolayer interferometry, and peptide libraries, we show that SIRPα, which, similar to ICAM-1, belongs to the Ig superfamily and has previously been implicated in cell fusion, interacts with Mac-1. The following results support the conclusion that SIRPα is a ligand of Mac-1: (a) recombinant ectodomain of SIRPα supports adhesion of Mac-1-expressing cells; (b) Mac-1-SIRPα interaction is mediated through the ligand-binding αMI-domain of Mac-1; (c) recognition of SIRPα by the αMIdomain conforms to general principles governing binding of Mac-1 to many of its ligands; (d) SIRPα reportedly binds CD47; however, anti-CD47 function-blocking mAb produced only a limited inhibition of macrophage adhesion to SIRPα; and (e) co-culturing of SIRPα- and Mac-1-expressing HEK293 cells resulted in the formation of multinucleated cells. Taken together, these results identify SIRPα as a counter-receptor for Mac-1 and suggest that the Mac-1-SIRPα interaction may be involved in macrophage fusion

Inhibition of Integrin α\u3csub\u3ed\u3c/sub\u3eβ\u3csub\u3e2\u3c/sub\u3e-Mediated Macrophage Adhesion to End Product of Docosahexaenoic Acid (DHA) Oxidation Prevents Macrophage Accumulation During Inflammation

A critical step in the development of chronic inflammatory diseases is the accumulation of proinflammatory macrophages in the extracellular matrix (ECM) of peripheral tissues. The adhesion receptor integrin αDβ2 promotes the development of atherosclerosis and diabetes by supporting macrophage retention in inflamed tissue. We recently found that the end product of docosahexaenoic acid (DHA) oxidation, 2-(ω-carboxyethyl)- pyrrole (CEP), serves as a ligand forαDβ2.CEPadduct withECM is generated during inflammation-mediated lipid peroxidation. The goal of this project was to identify a specific inhibitor for αDβ2-CEP interaction that can prevent macrophage accumulation. Using a specially designed peptide library, Biacore-detected protein-protein interaction, and adhesion of integrin-transfected HEK 293 cells, we identified a sequence (called P5 peptide) that significantly and specifically inhibited αD-CEP binding. In the model of thioglycollate-induced peritoneal inflammation, the injection of cyclic P5 peptide reduced 3-fold the macrophage accumulation in WT mice but had no effect in αD-deficient mice. The tracking of adoptively transferred, fluorescently labeled WT and αD-/- monocytes in the model of peritoneal inflammation and in vitro two-dimensional and three-dimensional migration assays demonstrated thatP5peptide does not affectmonocytetransendothelial migration or macrophage efflux from the peritoneal cavity but regulates macrophage migration through the ECM. Moreover, the injection ofP5peptide intoWTmiceona high-fat diet prevents macrophage accumulation in adipose tissue in anαDβ2-dependent manner.Takentogether, these resultsdemonstratetheimportance of αDβ2-mediated macrophage adhesion for the accumulation of infiltrating macrophages in the inflamed ECM and propose P5 peptide as a potential inhibitor of atherogenesis and diabetes

The Interaction of Integrin α IIb β 3 with Fibrin Occurs through Multiple Binding Sites in the α IIb β-Propeller Domain

The currently available antithrombotic agents target the interaction of platelet integrin αIIbβ3 (GPIIb-IIIa) with fibrinogen during platelet aggregation. Platelets also bind fibrin formed early during thrombus growth. It was proposed that inhibition of platelet-fibrin interactions may be a necessary and important property of αIIbβ3 antagonists; however, the mechanisms by which αIIbβ3 binds fibrin are uncertain. We have previously identified the γ370–381 sequence (P3) in the γC domain of fibrinogen as the fibrin-specific binding site for αIIbβ3 involved in platelet adhesion and platelet-mediated fibrin clot retraction. In the present study, we have demonstrated that P3 can bind to several discontinuous segments within the αIIb β-propeller domain of αIIbβ3 enriched with negatively charged and aromatic residues. By screening peptide libraries spanning the sequence of the αIIb β-propeller, several sequences were identified as candidate contact sites for P3. Synthetic peptides duplicating these segments inhibited platelet adhesion and clot retraction but not platelet aggregation, supporting the role of these regions in fibrin recognition. Mutant αIIbβ3 receptors in which residues identified as critical for P3 binding were substituted for homologous residues in the I-less integrin αMβ2 exhibited reduced cell adhesion and clot retraction. These residues are different from those that are involved in the coordination of the fibrinogen γ404–411 sequence and from auxiliary sites implicated in binding of soluble fibrinogen. These results map the binding of fibrin to multiple sites in the αIIb β-propeller and further indicate that recognition specificity of αIIbβ3 for fibrin differs from that for soluble fibrinogen

Regulation of Monoamine Oxidase A (MAO-A) Expression, Activity, and Function in IL-13–Stimulated Monocytes and A549 Lung Carcinoma Cells

Monoamine oxidase A (MAO-A) is a mitochondrial flavoen-zyme implicated in the pathogenesis of atherosclerosis and inflammation and also in many neurological disorders. MAO-A also has been reported as a potential therapeutic target in prostate cancer. However, the regulatory mechanisms controlling cytokine-induced MAO-A expression in immune or cancer cells remain to be identified. Here, we show that MAO-A expression is co-induced with 15-lipoxygenase (15-LO) in interleukin 13 (IL-13)-activated primary human monocytes and A549 nonsmall cell lung carcinoma cells. We present evidence that MAO-A gene expression and activity are regulated by signal transducer and activator of transcription 1, 3, and 6 (STAT1, STAT3, and STAT6), early growth response 1 (EGR1), and cAMP-responsive element– binding protein (CREB), the same transcription factors that control IL-13– dependent 15-LO expression. We further established that in both primary monocytes and in A549 cells, IL-13–stimulated MAO-A expression, activity, and function are directly governed by 15-LO. In contrast, IL-13– driven expression and activity of MAO-A was 15-LO–independent in U937 promonocytic cells. Furthermore, we demonstrate that the 15-LO– dependent transcriptional regulation of MAO-A in response to IL-13 stimulation in monocytes and in A549 cells is mediated by peroxisome proliferator–activated receptor (PPAR) and that signal transducer and activator of transcription 6 (STAT6) plays a crucial role in facilitating the transcriptional activity of PPAR. We further report that the IL-13–STAT6 – 15-LO–PPAR axis is critical for MAO-A expression, activity, and function, including migration and reactive oxygen species generation. Altogether, these results have major implications for the resolution of inflammation and indicat

The Role of Integrin αDβ2 in Macrophage Migration.

Abstract Integrin αDβ2 (CD11d/CD18), the most recently discovered member of the β2 sub-family of adhesion receptors, is strongly upregulated on macrophage foam cells which underscores its potential role in atherosclerosis. However, the contribution of αDβ2 to monocyte/macrophage adhesive reactions and the significance of its overexpression on these cells remain unknown. Recently we characterized αDβ2 as a multiligand receptor capable of binding many extracellular matrix proteins with the recognition specificity overlapping that of the major myeloid-specific integrin αMβ2 (Mac-1). We hypothesized that the αDβ2 ability to bind numerous ligands in the extracellular matrix and its capacity to be upregulated to high density on the surface of macrophages may modulate cell adhesiveness and, thus, affect migration. To evaluate the role of αDβ2 in migration, we generated model and natural cells expressing different densities of αDβ2 and tested their migration to different extracellular matrix proteins. In vitro studies demonstrated that αDβ2 expressed at low densities, either on the surface of HEK293 cells or the mouse macrophage cell line IC-21, supported migration which was partially inhibited by anti-αD function-blocking antibodies. Furthermore, β1 and β3 integrins expressed on HEK293 cells and IC-21 macrophages, respectively, contributed to migration because anti-β1 and anti-β3 antibodies inhibited migration. Increased expression of αDβ2 on the surface of HEK293 cells and its upregulation by PMA on IC-21 macrophages resulted in the inhibition of cell migration. Ligation of αDβ2 with anti-αD antibodies restored β1- and β3-driven cell migration by means of removing restraints imposed by the excess of the αDβ2-ligand adhesive bonds. To test the possibility that progressive upregulation of αDβ2 can block macrophage migration in vivo, we assessed the effect of anti-αD function blocking antibodies using the thioglycollate-induced peritonitis model. More than 4-fold upregulation of αDβ2 was detected on macrophages in 72 h after thioglycollate stimulation and, similar to in vitro studies, the numbers of migration macrophages increased in the presence of anti-αD antibodies. These results demonstrate that the density of αDβ2 can modulate cell migration and suggest that low levels of αDβ2 can contribute to monocyte migration while αDβ2 upregulation on differentiated macrophages might facilitate their retention at the site of inflammation.</jats:p

Biological and Pathophysiological Roles of End-Products of DHA Oxidation

© 2016 Elsevier B.V. Background Polyunsaturated fatty acids (PUFA) are known to be present and/or enriched in vegetable and fish oils. Among fatty acids, n-3 PUFA are generally considered to be protective in inflammation-related diseases. The guidelines for substituting saturated fatty acids for PUFAs have been highly publicized for decades by numerous health organizations. Recently, however, the beneficial properties of n-3 PUFA are questioned by detailed analyses of multiple randomized controlled clinical trials. The reported heterogeneity of results is likely due not only to differential effects of PUFAs on various pathological processes in humans, but also to the wide spectrum of PUFA\u27s derived products generated in vivo. Scope of review The goal of this review is to discuss the studies focused on well-defined end-products of PUFAs oxidation, their generation, presence in various pathological and physiological conditions, their biological activities and known receptors. Carboxyethylpyrrole (CEP), a DHA-derived oxidized product, is especially emphasized due to recent data demonstrating its pathophysiological significance in many inflammation-associated diseases, including atherosclerosis, hyperlipidemia, thrombosis, macular degeneration, and tumor progression. Major conclusions CEP is a product of radical-based oxidation of PUFA that forms adducts with proteins and lipids in blood and tissues, generating new powerful ligands for TLRs and scavenger receptors. The interaction of CEP with these receptors affects inflammatory response, angiogenesis, and wound healing. General significance The detailed understanding of CEP–mediated cellular responses may provide a basis for the development of novel therapeutic strategies and dietary recommendations