Mac-1 deficiency ameliorates pressure overloaded heart failure through inhibiting macrophage polarization and activation

Persistent pressure overload commonly leads to pathological cardiac hypertrophy and remodeling, ultimately leading to heart failure (HF). Cardiac remodeling is associated with the involvement of immune cells and the inflammatory response in pathogenesis. The macrophage-1 antigen (Mac-1) is specifically expressed on leukocytes and regulates their migration and polarization. Nonetheless, the involvement of Mac-1 in cardiac remodeling and HF caused by pressure overload has not been determined. The Mac-1-knockout (KO) and wild-type (WT) mice were subjected to transverse aortic constriction (TAC) for 6 weeks. Echocardiography and pressure-volume loop assessments were used to evaluate cardiac function, and cardiac remodeling and macrophage infiltration and polarization were estimated by histopathology and molecular techniques. The findings of our study demonstrated that Mac-1 expression was markedly increased in hearts subjected to TAC treatment. Moreover, compared with WT mice, Mac-1-KO mice exhibited dramatically ameliorated TAC-induced cardiac dysfunction, hypertrophy, fibrosis, oxidative stress and apoptosis. The potential positive impacts may be linked to the inhibition of macrophage infiltration and M1 polarization via reductions in NF-kB and STAT1 expression and upregulation of STAT6. In conclusion, this research reveals a new function of Mac-1 deficiency in reducing pathological cardiac remodeling and HF caused by pressure overload. Additionally, inhibiting Mac-1 could be a potential treatment option for patients with HF in a clinical setting.

αMI-domain of Integrin Mac-1 Binds the Cytokine Pleiotrophin Using Multiple Mechanisms

The integrin Mac-1 (αMβ2, CD11b/CD18, CR3) is an important adhesion receptor expressed on macrophages and neutrophils. Mac-1 is also the most promiscuous member of the integrin family that binds a diverse set of ligands through its αMI-domain. However, the binding mechanism of most ligands is not clear. We have determined the interaction of αMI-domain with the cytokine pleiotrophin (PTN), a cationic protein known to bind αMI-domain and induce Mac-1-mediated cell adhesion and migration. Our data show that PTN's N-terminal domain binds a unique site near the N- and C-termini of the αMI-domain using a metal-independent mechanism. However, stronger interaction is achieved when an acidic amino acid in a zwitterionic motif in PTN's C-terminal domain chelates the divalent cation in the metal ion-dependent adhesion site of the active αMI-domain. These results indicate that αMI-domain can bind ligands using multiple mechanisms, and suggest that active αMI-domain prefers acidic amino acids in zwitterionic motifs.

Dual wave of neutrophil recruitment determines the outcome of C. albicans infection

Candida albicans is a ubiquitous fungus that can cause superficial and systemic infections in humans. Neutrophils play a crucial role in controlling C. albicans infections. When C. albicans enters the bloodstream, it tends to get trapped in capillary vessels. However, the behavior of neutrophils in combating capillary-residing fungi has not been fully characterized. In this study, we used transgenic mice and whole mount imaging to investigate the growth of C. albicans and its interaction with innate immune cells in different organs. We observed that C. albicans rapidly grows hyphae within hours of infection. Following intravenous infection, we observed two waves of neutrophil recruitment, both of which significantly contributed to the elimination of the fungi. The first wave of neutrophils was induced by complement activation and could be prevented by C5aR blockade. Interestingly, we discovered that the fungicidal effect in the lungs was independent of adhesion molecules such as Mac-1, LFA-1, and ICAM-1. However, these molecules played a more significant role in the optimal killing of C. albicans in the kidney. Importantly, the initial difference in killing efficiency resulted in significantly reduced survival in knockout mice lacking these adhesion molecules. We identified a second wave of neutrophil recruitment associated with hyphal growth and tissue damage, which was independent of the aforementioned adhesion molecules. Overall, this study elucidates the dual wave of neutrophil recruitment during C. albicans infection and highlights the importance of early fungal clearance for favorable disease outcomes.

An Activation-Specific Anti-Mac-1 Designed-Ankyrin-Repeat-Protein Attenuates Colitis in Mice

(1) Background: Inflammatory bowel diseases are complex and multifactorial disorders of unknown etiology. The extravasation of activated leukocytes is a critical step in the pathogenesis of these diseases. Leukocyte integrin Mac-1 (α_Mβ₂; CD11b/CD18) is crucial for the extravasation of myeloid cells, and a novel activation-specific anti-Mac-1 Designed Ankyrin Repeat protein (DARPin F7) is a promising therapeutic agent for inflammatory diseases. In its activated conformation, Mac-1 expresses the high-affinity binding site I-domain, which the DARPin F7 selectively targets. In our study, we aimed to explore the therapeutic potential of anti-Mac-1 DARPin F7 in murine dextrane sodium sulfate (DSS)-induced colitis. (2) Methods: C57BL/6J mice received 3% DSS drinking water for five days, followed by normal drinking water for one week. The mice were treated with DARPin F7 or a control substance daily via intraperitoneal injections. Disease activity index (DAI), colon length, myeloperoxidase (MPO) activity measurements, H&E staining, and qRT-PCR were conducted after euthanizing the mice on day 12. (3) Results: Treatment with DARPin F7 resulted in less pronounced colon shortening and significantly lower histological scores. The DARPin F7-treated animals experienced substantially less disease and myeloperoxidase (MPO) activity. Animals that received DARPin F7 treatment suffered less weight loss and recovered from the weight loss more efficiently. Treatment with DARPin F7 also led to significantly reduced mRNA expression of inflammatory cytokines. (4) Conclusion: Anti-Mac-1 treatment markedly reduced disease activity and inflammatory reaction accompanying DSS-induced colitis in mice.

The complement receptor C5aR2 regulates neutrophil activation and function contributing to neutrophil-driven epidermolysis bullosa acquisita

Introduction

The function of the second receptor for the complement cleavage product C5a, C5aR2, is poorly understood and often neglected in the immunological context. Using mice with a global deficiency of C5aR2, we have previously reported an important role of this receptor in the pathogenesis of the neutrophil-driven autoimmune disease epidermolysis bullosa acquisita (EBA). Based on in vitro analyses, we hypothesized that the absence of C5aR2 specifically on neutrophils is the cause of the observed differences. Here, we report the generation of a new mouse line with a LysM-specific deficiency of C5aR2.

Methods

LysM-specific deletion of C5aR2 was achieved by crossing LysM^cre mice with tdTomato-C5ar2^fl/fl mice in which the tdTomato-C5ar2 gene is flanked by loxP sites. Passive EBA was induced by subcutaneous injection of rabbit anti-mouse collagen type VII IgG. The effects of targeted deletion of C5ar2 on C5a-induced effector functions of neutrophils were examined in in vitro assays.

Results

We confirm the successful deletion of C5aR2 at both the genetic and protein levels in neutrophils. The mice appeared healthy and the expression of C5aR1 in bone marrow and blood neutrophils was not negatively affected by LysM-specific deletion of C5aR2. Using the antibody transfer mouse model of EBA, we found that the absence of C5aR2 in LysM-positive cells resulted in an overall amelioration of disease progression, similar to what we had previously found in mice with global deficiency of C5aR2. Neutrophils lacking C5aR2 showed decreased activation after C5a stimulation and increased expression of the inhibitory Fcγ receptor FcγRIIb.

Discussion

Overall, with the data presented here, we confirm and extend our previous findings and show that C5aR2 in neutrophils regulates their activation and function in response to C5a by potentially affecting the expression of Fcγ receptors and CD11b. Thus, C5aR2 regulates the finely tuned interaction network between immune complexes, Fcγ receptors, CD11b, and C5aR1 that is important for neutrophil recruitment and sustained activation. This underscores the importance of C5aR2 in the pathogenesis of neutrophil-mediated autoimmune diseases.

THE CIS ASSOCIATION OF CD47 WITH INTEGRIN Mac-1 REGULATES MACROPHAGE RESPONSES BY STABILIZING THE EXTENDED INTEGRIN CONFORMATION

CD47 is a ubiquitously expressed cell surface integrin-associated protein. Recently, we have demonstrated that integrin Mac-1 (α_Mβ₂, CD11b/CD18, CR3), the major adhesion receptor on the surface of myeloid cells, can be coprecipitated with CD47. However, the molecular basis for the CD47-Mac-1 interaction and its functional consequences remain unclear. Here, we demonstrated that CD47 regulates macrophage functions directly interacting with Mac-1. In particular, adhesion, spreading, migration, phagocytosis, and fusion of CD47-deficient macrophages were significantly decreased. We validated the functional link between CD47 and Mac-1 by co-immunoprecipitation analysis using various Mac-1-expressing cells. In HEK293 cells expressing individual α_M and β₂ integrin subunits, CD47 was found to bind both subunits. Interestingly, a higher amount of CD47 was recovered with the free β₂ subunit than in the complex with the whole integrin. Furthermore, activating Mac-1-expressing HEK293 cells with PMA, Mn²⁺_, and activating antibody MEM48 increased the amount of CD47 in complex with Mac-1, suggesting CD47 has a greater affinity for the extended integrin conformation. Notably, on the surface of cells lacking CD47, fewer Mac-1 molecules could convert into an extended conformation in response to activation. Additionally, we identified the binding site in CD47 for Mac-1 in its constituent IgV domain. The complementary binding sites for CD47 in Mac-1 were localized in integrin epidermal growth factor-like domains 3 and 4 of the β₂ and calf-1 and calf-2 domains of the α subunits. These results indicate that Mac-1 forms a lateral complex with CD47, which regulates essential macrophage functions by stabilizing the extended integrin conformation.

Monocyte-Derived miRNA-1914-5p Attenuates IL-1β-Induced Monocyte Adhesion and Transmigration

Atherosclerosis can lead to cardiovascular and cerebrovascular diseases. Atherosclerotic plaque formation is promoted by the accumulation of inflammatory cells. Therefore, modulating monocyte recruitment represents a potential therapeutic strategy. In an inflammatory state, the expression of adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) is upregulated in endothelial cells. We previously reported that miR-1914-5p in endothelial cells suppresses interleukin (IL)-1β-induced ICAM-1 expression and monocyte adhesion to endothelial cells. However, whether monocyte miR-1914-5p affects monocyte recruitment is unclear. In this study, IL-1β decreased miR-1914-5p expression in a human monocyte cell line. Moreover, miR-1914-5p inhibition enhanced adhesion to endothelial cells with the upregulation of macrophage-1 antigen (Mac-1), a counter-ligand to ICAM-1. Transmigration through the endothelial layer was also promoted with the upregulation of monocyte chemotactic protein-1 (MCP-1). Furthermore, a miR-1914-5p mimic suppressed IL-1β-induced monocyte adhesion and transmigration in monocytes with Mac-1 and MCP-1 downregulation. Further investigation of miR-1914-5p in monocytes could lead to the development of novel diagnostic markers and therapeutic strategies for atherosclerosis.

Spatiotemporal characteristics of P-selectin-induced β2 integrin activation of human neutrophils under flow

Activation of integrins is crucial for recruitment of flowing leukocytes to inflammatory or injured vascular sites, but their spatiotemporal characteristics are incompletely understood. We discovered that β2-integrin activation over the entire surface of neutrophils on immobilized P-selectin occurred via mitogen-activated protein kinase (MAPK) or non-MAPK signaling with a minute-level timescale in a force-dependent manner. In flow, MAPK signaling required intracellular Ca2+ release to activate integrin within 2 min. Integrin activation via non-MAPK signaling occurred first locally in the vicinity of ligated P-selectin glycoprotein ligand-1 (PSGL-1) within sub-seconds, and then over the entire cell surface within 1 min in an extracellular Ca2+ influx-dependent manner. The transition from a local (but rapid) to global (but slow) activation mode was triggered by ligating the freshly activated integrin. Lipid rafts, moesin, actin, and talin were involved in non-MAPK signaling. Fluid loads had a slight effect on local integrin activation with a second-level timescale, but served as enhancers of global integrin activation.

GPR55 Antagonist CID16020046 Protects against Atherosclerosis Development in Mice by Inhibiting Monocyte Adhesion and Mac-1 Expression

GPR55 recognizes several lipid molecules such as lysophosphatidylinositol. GPR55 expression was reported in human monocytes. However, its role in monocyte adhesion and atherosclerosis development has not been studied. The role of GPR55 in monocyte adhesion and atherosclerosis development was investigated in human THP-1 monocytes and ApoE^-/- mice using O-1602 (a potent agonist of GPR55) and CID16020046 (a specific GPR55 antagonist). O-1602 treatment significantly increased monocyte adhesion to human umbilical vein endothelial cells, and the O-1602-induced adhesion was inhibited by treatment with CID16020046. O-1602 induced the expression of Mac-1 adhesion molecules, whereas CID16020046 inhibited this induction. Analysis of the promoter region of Mac-1 elucidated the binding sites of AP-1 and NF-κB between nucleotides -750 and -503 as GPR55 responsive elements. O-1602 induction of Mac-1 was found to be dependent on the signaling components of GPR55, that is, Gq protein, Ca²⁺, CaMKK, and PI3K. In Apo^-/- mice, administration of CID16020046 ameliorated high-fat diet-induced atherosclerosis development. These results suggest that high-fat diet-induced GPR55 activation leads to the adhesion of monocytes to endothelial cells via induction of Mac-1, and CID16020046 blockage of GPR55 could suppress monocyte adhesion to vascular endothelial cells through suppression of Mac-1 expression, leading to protection against the development of atherosclerosis.

Mac-1 Receptor Clustering Initiates Production of Pro-Inflammatory, Antibacterial Extracellular Vesicles From Neutrophils

Depending on the prevailing environmental conditions, neutrophilic granulocytes release extracellular vesicles (EV) which have either anti-inflammatory effects on other neutrophils or pro-inflammatory and antibacterial effects. In the present study we investigated the molecular mechanisms underlying the biogenesis of functionally heterogenic EVs. We show that selective stimulation of Mac-1 integrin (complement receptor 3) by specific ligands initiates the generation of EVs which are able to impair bacterial growth and to induce the secretion of the pro-inflammatory cytokine IL-8 (aEV). However, direct Mac-1 stimulation results in aEV release only if neutrophils were activated on ligand coated surfaces whereas soluble ligands are ineffective. Using total internal reflection fluorescence (TIRF) microcopy, an increased clustering of Mac-1 molecules could be visualized in neutrophils added to C3bi coated surfaces; moreover antibody induced cluster formation triggers aEV release as well. Mac-1 induced production of aEV apparently necessitates a strong calcium signal as it fully depends on the presence of extracellular calcium. However, initiation of a strong calcium signal by an ionophore only results the generation of EV devoid of any antibacterial or pro-inflammatory effect. Our results thus demonstrate that stimulation and clustering of Mac-1 is necessary and sufficient for initiation of aEV biogenesis. In contrast, an intracellular calcium signal is necessary but by itself not sufficient for the production of antibacterial and pro-inflammatory EVs.

Monocyte Dysfunction Detected by the Designed Ankyrin Repeat Protein F7 Predicts Mortality in Patients Receiving Veno-Arterial Extracorporeal Membrane Oxygenation

Background: Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is used for critically ill patients requiring hemodynamic support but has been shown to induce an inflammatory response syndrome potentially leading to severe complications and poor outcome. Monocytes are comprised of different subsets and play a central role in the innate immune system. The unique small binding proteins, Designed Ankyrin Repeat Protein “F7” and single chain variable fragment “MAN-1,” specifically detect the activated conformation of the leukocyte integrin Mac-1 enabling the highly sensitive detection of monocyte activation status. The aim of this study was to characterize monocyte function and heterogeneity and their association with outcome in VA-ECMO patients.

Methods: VA-ECMO patients were recruited from the ICUs of the University Hospital in Freiburg, Germany. Blood was sampled on day 0 and day 3 after VA-ECMO placement, after VA-ECMO explantation and from healthy controls. Monocyte subset distribution, baseline activation and stimulability were analyzed by flow cytometry using the unique small binding proteins F7 and MAN-1 and the conventional activation markers CD163, CD86, CD69, and CX3CR1. Furthermore, expression of monocyte activation markers in survivors and non-survivors on day 0 was compared. Simple logistic regression was conducted to determine the association of monocyte activation markers with mortality.

Results: Twenty two patients on VA-ECMO and 15 healthy controls were recruited. Eleven patients survived until discharge from the ICU. Compared to controls, baseline monocyte activation was significantly increased, whereas stimulability was decreased. The percentage of classical monocytes increased after explantation, while the percentage of intermediate monocytes decreased. Total, classical, and intermediate monocyte counts were significantly elevated compared to controls. On day 0, baseline binding of F7 was significantly lower in non-survivors than survivors. The area under the ROC curve associated with mortality on day 0 was 0.802 (p = 0.02).

Conclusions: Distribution of monocyte subsets changes during VA-ECMO and absolute classical and intermediate monocyte counts are significantly elevated compared to controls. Monocytes from VA-ECMO patients showed signs of dysfunction. Monocyte dysfunction, as determined by the unique tool F7, could be valuable for predicting mortality in patients receiving VA-ECMO and may be used as a novel biomarker guiding early clinical decision making in the future.

MD Simulations on a Well-Built Docking Model Reveal Fine Mechanical Stability and Force-Dependent Dissociation of Mac-1/GPIbα Complex

Interaction of leukocyte integrin macrophage-1 antigen (Mac-1) to platelet glycoprotein Ibα (GPIbα) is critical for platelet-leukocyte crosstalk in hemostasis and inflammatory responses to vessel injuries under hemodynamic environments. The mechano-regulation and its molecular basis for binding of Mac-1 to GPIbα remain unclear, mainly coming from the lack of crystal structure of the Mac-1/GPIbα complex. We herein built a Mac-1/GPIbα complex model through a novel computer strategy, which included a flexible molecular docking and system equilibrium followed by a "force-ramp + snapback" molecular dynamics (MD) simulation. With this model, a series of "ramp-clamp" steered molecular dynamics (SMD) simulations were performed to examine the GPIbα-Mac-1 interaction under various loads. The results demonstrated that the complex was mechano-stable for both the high rupture force (>250 pN) at a pulling velocity of 3 Å/ns and the conformational conservation under various constant tensile forces (≤75 pN); a catch-slip bond transition was predicted through the dissociation probability, examined with single molecular AFM measurements, reflected by the interaction energy and the interface H-bond number, and related to the force-induced allostery of the complex; besides the mutation-identified residues D222 and R218, the residues were also dominant in the binding of Mac-1 to GPIbα. This study recommended a valid computer strategy for building a likely wild-type docking model of a complex, provided a novel insight into the mechanical regulation mechanism and its molecular basis for the interaction of Mac-1 with GPIbα, and would be helpful for understanding the platelet-leukocyte interaction in hemostasis and inflammatory responses under mechano-microenvironments.

Double-stranded RNA-induced dopaminergic neuronal loss in the substantia nigra in the presence of Mac1 receptor

BACKGROUND

The underlying mechanism of viral infection as a risk factor for Parkinson's disease (PD), the second most common neurodegenerative disease, remains unclear.

OBJECTIVE

We used Mac-1^-/- and gp91^phox-/- transgene animal models to investigate the mechanisms by which poly I:C, a mimic of virus double-stranded RNA, induces PD neurodegeneration.

METHOD

Poly I:C was stereotaxically injected into the substantia nigra (SN) of wild-type (WT), Mac-1-knockout (Mac-1^-/-) and gp91 ^phox-knockout (gp91 ^phox-/-) mice (10 μg/μl), and nigral dopaminergic neurodegeneration, α-synuclein accumulation and neuroinflammation were evaluated.

RESULT

Dopaminergic neurons in the nigra and striatum were markedly reduced in WT mice after administration of poly I:C together with abundant microglial activation in the SN, and the expression of α-synuclein was also elevated. However, these pathological changes were greatly dampened in Mac-1^-/- and gp91 ^phox-/- mice.

CONCLUSIONS

Our findings demonstrated that viral infection could result in the activation of microglia as well as NADPH oxidase, which may lead to neuron loss and the development of Parkinson's-like symptoms. Mac-1 is a key receptor during this process.

RIAM-VASP Module Relays Integrin Complement Receptors in Outside-In Signaling Driving Particle Engulfment

The phagocytic integrins and complement receptors α_Mβ₂/CR3 and α_Xβ₂/CR4 are classically associated with the phagocytosis of iC3b-opsonized particles. The activation of this receptor is dependent on signals derived from other receptors (inside-out signaling) with the crucial involvement of the Rap1-RIAM-Talin-1 pathway. Here, we analyze the implication of RIAM and its binding partner VASP in the signaling events occurring downstream of β₂ integrins (outside-in) during complement-mediated phagocytosis. To this end, we used HL-60 promyelocytic cell lines deficient in RIAM or VASP or overexpressing EGFP-tagged VASP to determine VASP dynamics at phagocytic cups. Our results indicate that RIAM-deficient HL-60 cells presented impaired particle internalization and altered integrin downstream signaling during complement-dependent phagocytosis. Similarly, VASP deficiency completely blocked phagocytosis, while VASP overexpression increased the random movement of phagocytic particles at the cell surface, with reduced internalization. Moreover, the recruitment of VASP to particle contact sites, amount of pSer157-VASP and formation of actin-rich phagocytic cups were dependent on RIAM expression. Our results suggested that RIAM worked as a relay for integrin complement receptors in outside-in signaling, coordinating integrin activation and cytoskeletal rearrangements via its interaction with VASP.

Phagocytic Integrins: Activation and Signaling

Phagocytic integrins are endowed with the ability to engulf and dispose of particles of different natures. Evolutionarily conserved from worms to humans, they are involved in pathogen elimination and apoptotic and tumoral cell clearance. Research in the field of integrin-mediated phagocytosis has shed light on the molecular events controlling integrin activation and their effector functions. However, there are still some aspects of the regulation of the phagocytic process that need to be clarified. Here, we have revised the molecular events controlling phagocytic integrin activation and the downstream signaling driving particle engulfment, and we have focused particularly on α_Mβ₂/CR3, α_Xβ₂/CR4, and a brief mention of α_Vβ₅/α_Vβ₃integrins.

CD147 is a Novel Interaction Partner of Integrin αMβ2 Mediating Leukocyte and Platelet Adhesion

Surface receptor-mediated adhesion is a fundamental step in the recruitment of leukocytes and platelets, as well as platelet-leukocyte interactions. The surface receptor CD147 is crucially involved in host defense against self-derived and invading targets, as well as in thrombosis. In the current study, we describe the previously unknown interaction of CD147 with integrin αMβ2 (Mac-1) in this context. Using binding assays, we were able to show a stable interaction of CD147 with Mac-1 in vitro. Leukocytes from Mac-1^-/- and CD147^+/- mice showed a markedly reduced static adhesion to CD147- and Mac-1-coated surfaces, respectively, compared to wild-type mice. Similarly, we observed reduced rolling and adhesion of monocytes under flow conditions when cells were pre-treated with antibodies against Mac-1 or CD147. Additionally, as assessed by antibody inhibition experiments, CD147 mediated the dynamic adhesion of platelets to Mac-1-coated surfaces. The interaction of CD147 with Mac-1 is a previously undescribed mechanism facilitating the adhesion of leukocytes and platelets.

Repurposed Drugs That Block the Gonococcus-Complement Receptor 3 Interaction Can Prevent and Cure Gonococcal Infection of Primary Human Cervical Epithelial Cells

Novel therapies that avert the problem of Neisseria gonorrhoeae with acquired antibiotic resistance are urgently needed. Gonococcal infection of the human cervix is initiated by an interaction between a galactose modification made to its surface appendages, pili, and the I-domain region of (host) complement receptor 3 (CR3). By targeting this crucial gonococcal–I-domain interaction, it may be possible to prevent cervical infection in females. To this end, we identified the I-domain galactose-binding epitope of CR3 and characterized its galactose lectin activity. Moreover, we identified two drugs, carbamazepine and methyldopa, as effective host-targeted therapies for gonorrhea treatment. At doses below those currently used for their respective existing indications, both carbamazepine and methyldopa were more effective than ceftriaxone in curing cervical infection ex vivo. This host-targeted approach would not be subject to N. gonorrhoeae drug resistance mechanisms. Thus, our data suggest a long-term solution to the growing problem of multidrug-resistant N. gonorrhoeae infections.

In the absence of a vaccine, multidrug-resistant Neisseria gonorrhoeae has emerged as a major human health threat, and new approaches to treat gonorrhea are urgently needed. N. gonorrhoeae pili are posttranslationally modified by a glycan that terminates in a galactose. The terminal galactose is critical for initial contact with the human cervical mucosa via an interaction with the I-domain of complement receptor 3 (CR3). We have now identified the I-domain galactose-binding epitope and characterized its galactose-specific lectin activity. Using surface plasmon resonance and cellular infection assays, we found that a peptide mimic of this galactose-binding region competitively inhibited the N. gonorrhoeae-CR3 interaction. A compound library was screened for potential drugs that could similarly prohibit the N. gonorrhoeae-CR3 interaction and be repurposed as novel host-targeted therapeutics for multidrug-resistant gonococcal infections in women. Two drugs, methyldopa and carbamazepine, prevented and cured cervical cell infection by multidrug-resistant gonococci by blocking the gonococcal-CR3 I-domain interaction.

Effects of sinomenine in LPS-associated diseases are related to inhibition of LBP, Mac-1, and L-selectin levels

The aim of the research was to investigate the anti-endotoxin and anti-inflammatory effects of Sinomenine, an agent commonly found in Chinese herbal medicines. Endotoxin (i.e., 1 mg lipopolysaccharide (LPS)/kg)) was administered via intraperitoneal (IP) injection to piglets in high-, middle-, and low-dose sinomenine groups. Piglets were then treated with 1, 5 or 10 mg/kg sinomenine, intramuscularly (i.m.), 3 hr after LPS. Vehicle was administered, as above, to drug control group piglets followed 3 hr later by 10 mg/kg sinomenine i.m.. LPS control group piglets were challenged with 1 mg/kg LPS IP, followed by vehicle i.m., and naïve control piglets were treated with normal saline IP, followed by normal saline i.m., as above. Temperatures were measured, and blood samples were collected from the precaval veins of piglets at 12, 24, and 48 hr post-LPS or vehicle injection. Clinical signs were recorded, and index levels were analyzed via ELISA. Sinomenine was found to reduce the incidence and severity of LPS-induced toxicities, including body temperature elevation, cell adhesion, and systemic inflammation. These data suggest that sinomenine may be effective for regulating inflammatory responses and has the potential for use as an anti-endotoxin therapy.

Circulating Factors and Ultrasono-findings are Linked to Previous Atherosclerotic Burden and Recurrent Risk

Abstract: Background:

In the progression of atherosclerosis, platelet activation and the interaction of platelets with leukocytes play a crucial role in arterial thrombus formation and are associated with the pathophysiology of carotid and cerebrovascular disease (CVD), including ischemic stroke. With aged participants, we evaluated and followed up the change in circulating factor and platelet-leukocyte aggregate levels in participants with or without CVD history. This study investigated whether circulating factor changes and ultrasonographic characteristics link to CVD risk and other relating long-term outcomes.

Materials and Methods:

Two hundred fifteen participants who enrolled in the study were divided into two groups with CVD and without CVD history. We evaluated and analyzed the correlation between ultrasonography-based morphological characteristics and circulating factor-based functional changes in both groups.

Results:

There was no difference in p-selectin level between both groups. However, activated monocyte and platelet-monocyte aggregate levels were higher in patients with previous CVD than without previous CVD. Circulating factor and ultrasonographical characteristics were correlated in the group with CVD, whereas these factors were not correlated in the group without CVD.

Conclusion:

We found that circulating blood factor levels showed a different tendency in participants with and without CVD history. The results depict that atherosclerotic severity might depend on the history of CVD and progression of atherosclerosis. We suggest that the circulating factor levels, atherosclerotic severity, and history of CVD are considered in the observation of pathologic progression to manage the development of CVD risks and CVD relating outcomes.

The pattern-recognition molecule mindin binds integrin Mac-1 to promote macrophage phagocytosis via Syk activation and NF-κB p65 translocation

Mindin has a broad spectrum of roles in the innate immune system, including in macrophage migration, antigen phagocytosis and cytokine production. Mindin functions as a pattern‐recognition molecule for microbial pathogens. However, the underlying mechanisms of mindin‐mediated phagocytosis and its exact membrane receptors are not well established. Herein, we generated mindin‐deficient mice using the CRISPR‐Cas9 system and show that peritoneal macrophages from mindin‐deficient mice were severely defective in their ability to phagocytize E  coli. Phagocytosis was enhanced when E  coli or fluorescent particles were pre‐incubated with mindin, indicating that mindin binds directly to bacteria or non‐pathogen particles and promotes phagocytosis. We defined that ¹³¹I‐labelled mindin binds with integrin Mac‐1 (CD11b/CD18), the F‐spondin (FS)‐fragment of mindin binds with the α_M‐I domain of Mac‐1 and that mindin serves as a novel ligand of Mac‐1. Blockade of the α_M‐I domain of Mac‐1 using either a neutralizing antibody or si‐Mac‐1 efficiently blocked mindin‐induced phagocytosis. Furthermore, mindin activated the Syk and MAPK signalling pathways and promoted NF‐κB entry into the nucleus. Our data indicate that mindin binds with the integrin Mac‐1 to promote macrophage phagocytosis through Syk activation and NF‐κB p65 translocation, suggesting that the mindin/Mac‐1 axis plays a critical role during innate immune responses.

Regulation of immune cell signaling by activated protein C

Innate immune cells are an essential part of the host defense response, promoting inflammation through release of proinflammatory cytokines or formation of neutrophil extracellular traps. While these processes are important for defense against infectious agents or injury, aberrant activation potentiates pathologic inflammatory disease. Thus, understanding regulatory mechanisms that limit neutrophil extracellular traps formation and cytokine release is of therapeutic interest for targeting pathologic diseases. Activated protein C is an endogenous serine protease with anticoagulant activity as well as anti-inflammatory and cytoprotective functions, the latter of which are mediated through binding cell surface receptors and inducing intracellular signaling. In this review, we discuss certain leukocyte functions, namely neutrophil extracellular traps formation and cytokine release, and the inhibition of these processes by activated protein C.

Leukocyte integrin Mac-1 (CD11b/CD18, αMβ2, CR3) acts as a functional receptor for platelet factor 4

Platelet factor 4 (PF4) is one of the most abundant cationic proteins secreted from α-granules of activated platelets. Based on its structure, PF4 was assigned to the CXC family of chemokines and has been shown to have numerous effects on myeloid leukocytes. However, the receptor for PF4 remains unknown. Here, we demonstrate that PF4 induces leukocyte responses through the integrin Mac-1 (α_Mβ₂, CD11b/CD18). Human neutrophils, monocytes, U937 monocytic and HEK293 cells expressing Mac-1 strongly adhered to immobilized PF4 in a concentration-dependent manner. The cell adhesion was partially blocked by anti-Mac-1 mAb and inhibition was enhanced when anti-Mac-1 antibodies were combined with glycosaminoglycans, suggesting that cell-surface proteoglycans act cooperatively with Mac-1. PF4 also induced Mac-1-dependent migration of human neutrophils and murine WT, but not Mac-1-deficient macrophages. Coating of Escherichia coli bacteria or latex beads with PF4 enhanced their phagocytosis by macrophages by ∼4-fold, and this process was blocked by different Mac-1 antagonists. Furthermore, PF4 potentiated phagocytosis by WT, but not Mac-1-deficient macrophages. As determined by biolayer interferometry, PF4 directly bound the α_MI-domain, the major ligand-binding region of Mac-1, and this interaction was governed by a K_d of 1.3 ± 0.2 μm Using the PF4-derived peptide library, synthetic peptides duplicating the α_MI-domain recognition sequences and recombinant mutant PF4 fragments, the binding sites for α_MI-domain were identified in the PF4 segments Cys¹²-Ser²⁶ and Ala⁵⁷-Ser⁷⁰ These results identify PF4 as a ligand for the integrin Mac-1 and suggest that many immune-modulating effects previously ascribed to PF4 are mediated through its interaction with Mac-1.

Microglial-mediated PDGF-CC activation increases cerebrovascular permeability during ischemic stroke

Treatment of acute ischemic stroke with the thrombolytic tissue plasminogen activator (tPA) can significantly improve neurological outcomes; however, thrombolytic therapy is associated with an increased risk of intra-cerebral hemorrhage (ICH). Previously, we demonstrated that during stroke tPA acting on the parenchymal side of the neurovascular unit (NVU) can increase blood–brain barrier (BBB) permeability and ICH through activation of latent platelet-derived growth factor-CC (PDGF-CC) and signaling by the PDGF receptor-α (PDGFRα). However, in vitro, activation of PDGF-CC by tPA is very inefficient and the mechanism of PDGF-CC activation in the NVU is not known. Here, we show that the integrin Mac-1, expressed on brain microglia/macrophages (denoted microglia throughout), acts together with the endocytic receptor LRP1 in the NVU to promote tPA-mediated activation of PDGF-CC. Mac-1-deficient mice (Mac-1^−/−) are protected from tPA-induced BBB permeability but not from permeability induced by intracerebroventricular injection of active PDGF-CC. Immunofluorescence analysis demonstrates that Mac-1, LRP1, and the PDGFRα all localize to the NVU of arterioles, and following middle cerebral artery occlusion (MCAO) Mac-1^−/− mice show significantly less PDGFRα phosphorylation, BBB permeability, and infarct volume compared to wild-type mice. Bone-marrow transplantation studies indicate that resident CD11b⁺ cells, but not bone-marrow-derived leukocytes, mediate the early activation of PDGF-CC by tPA after MCAO. Finally, using a model of thrombotic stroke with late thrombolysis, we show that wild-type mice have an increased incidence of spontaneous ICH following thrombolysis with tPA 5 h after MCAO, whereas Mac-1^−/− mice are resistant to the development of ICH even with late tPA treatment. Together, these results indicate that Mac-1 and LRP1 act as co-factors for the activation of PDGF-CC by tPA in the NVU, and suggest a novel mechanism for tightly regulating PDGFRα signaling in the NVU and controlling BBB permeability.

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 and NMR indicated a direct interaction between the α_MI domain, the major ligand-binding region of Mac-1, and PTN. Using peptide libraries, we found that in PTN the α_MI domain bound sequences enriched in basic and hydrophobic residues, indicating that PTN conforms to the general principle of ligand-recognition specificity of the α_MI 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.

The balance between Treg and TH17 cells: CD11b and interleukin-6

One of the gold standards for animal models of rheumatoid arthritis is the murine collagen-induced arthritis model. Native type II collagen together with CFA is injected into susceptible mouse strains. Unfortunately, only mice with H-2^q or H-2^r MHC haplotypes are susceptible, making the widely used C57BL/6 mouse strain, which carries the H-2^b haplotype, resistant against the disease. In this issue of the European Journal of Immunology, Stevanin et al. [Eur. J. Immunol. 2017. 47: 637-645] now convincingly show that although WT C57BL/6 mice are resistant to collagen-induced arthritis, mice with a homozygous deletion of CD11b on the same genetic background are fully susceptible in this important animal model of rheumatoid arthritis. They clearly demonstrate that the injection of type II collagen together with CFA leads to early onset of the disease with high incidence and with sustained severity. The authors further characterize this disease with an increase of leukocyte infiltration and enhanced TH₁₇ differentiation.

CD40L and Its Receptors in Atherothrombosis-An Update

CD40L (CD154), a member of the tumor necrosis factor superfamily, is a co-stimulatory molecule that was first discovered on activated T cells. Beyond its fundamental role in adaptive immunity-ligation of CD40L to its receptor CD40 is a prerequisite for B cell activation and antibody production-evidence from more than two decades has expanded our understanding of CD40L as a powerful modulator of inflammatory pathways. Although inhibition of CD40L with neutralizing antibodies has induced life-threatening side effects in clinical trials, the discovery of cell-specific effects and novel receptors with distinct functional consequences has opened a new path for therapies that specifically target detrimental properties of CD40L. Here, we carefully evaluate the signaling network of CD40L by gene enrichment analysis and its cell-specific expression, and thoroughly discuss its role in cardiovascular pathologies with a specific emphasis on atherosclerotic and thrombotic disease.

Activated protein C inhibits neutrophil extracellular trap formation in vitro and activation in vivo

Activated protein C (APC) is a multifunctional serine protease with anticoagulant, cytoprotective, and anti-inflammatory activities. In addition to the cytoprotective effects of APC on endothelial cells, podocytes, and neurons, APC cleaves and detoxifies extracellular histones, a major component of neutrophil extracellular traps (NETs). NETs promote pathogen clearance but also can lead to thrombosis; the pathways that negatively regulate NETosis are largely unknown. Thus, we studied whether APC is capable of directly inhibiting NETosis via receptor-mediated cell signaling mechanisms. Here, by quantifying extracellular DNA or myeloperoxidase, we demonstrate that APC binds human leukocytes and prevents activated platelet supernatant or phorbol 12-myristate 13-acetate (PMA) from inducing NETosis. Of note, APC proteolytic activity was required for inhibiting NETosis. Moreover, antibodies against the neutrophil receptors endothelial protein C receptor (EPCR), protease-activated receptor 3 (PAR3), and macrophage-1 antigen (Mac-1) blocked APC inhibition of NETosis. Select mutations in the Gla and protease domains of recombinant APC caused a loss of NETosis. Interestingly, pretreatment of neutrophils with APC prior to induction of NETosis inhibited platelet adhesion to NETs. Lastly, in a nonhuman primate model of Escherichia coli-induced sepsis, pretreatment of animals with APC abrogated release of myeloperoxidase from neutrophils, a marker of neutrophil activation. These findings suggest that the anti-inflammatory function of APC at therapeutic concentrations may include the inhibition of NETosis in an EPCR-, PAR3-, and Mac-1-dependent manner, providing additional mechanistic insight into the diverse functions of neutrophils and APC in disease states including sepsis.

MFG-E8-derived peptide attenuates adhesion and migration of immune cells to endothelial cells

Milk fat globule-epidermal growth factor-factor 8 (MFG-E8) plays an immunomodulatory role in inflammatory diseases. MFG-E8-derived short peptide (MSP68) greatly reduces neutrophil infiltration and injury in the lung during sepsis. In this study, we examined the effect of MSP68 on chemotaxis of various immune cells and its regulatory mechanism. Bone marrow-derived neutrophils (BMDNs) from C57BL/6 mice, human monocyte THP-1 cell line, and human T lymphocyte Jurkat cell line were used for adhesion and migration assays using a Transwell method in the presence of MSP68. Treatment with MSP68 significantly inhibited the BMDN and THP-1 cell but not Jurkat cell adhesion on the TNF-α-stimulated pulmonary artery endothelial cell (PAEC) monolayer dose-dependently. MSP68 also significantly reduced BMDN adhesion on VCAM-1-coated wells dose dependently. Surface plasmon resonance (SPR) analysis revealed that MSP68 efficiently recognized integrin α₄β₁ (receptor for VCAM-1) at the dissociation constant (K_D) of 1.53 × 10^-7 M. These findings implicate that MSP68 prevents neutrophil adhesion to the activated endothelial cells by interfering with the binding between integrin α₄β₁ on neutrophils and VCAM-1 on endothelial cells. Moreover, MSP68 significantly attenuated the migration of BMDN and THP-1 cells but not Jurkat cells to their chemoattractants. Pretreatment with MSP68 inhibited the transmigration of BMDNs across the PAECs toward chemoattractants, fMLP, MIP-2, and complement fragment 5a (C5a) dose-dependently. Finally, we identified that the activation of p38 MAPK in BMDNs by fMLP was inhibited by MSP68. Thus, MSP68 attenuates extravasation of immune cells through the endothelial cell lining into inflamed tissue, implicating MSP68 to be a novel, therapeutic agent for inflammatory diseases caused by excessive immune cell infiltration.

The many faces of Mac-1 in autoimmune disease

Mac-1 (CD11b/CD18) is a β2 integrin classically regarded as a pro-inflammatory molecule because of its ability to promote phagocyte cytotoxic functions and enhance the function of several effector molecules such as FcγR, uPAR, and CD14. Nevertheless, recent reports have revealed that Mac-1 also plays significant immunoregulatory roles, and genetic variants in ITGAM, the gene that encodes CD11b, confer risk for the autoimmune disease systemic lupus erythematosus (SLE). This has renewed interest in the physiological roles of this integrin and raised new questions on how its seemingly opposing biological functions may be regulated. Here, we provide an overview of the CD18 integrins and how their activation may be regulated as this may shed light on how the opposing roles of Mac-1 may be elicited. We then discuss studies that exemplify Mac-1's pro-inflammatory versus regulatory roles particularly in the context of IgG immune complex-mediated inflammation. This includes a detailed examination of molecular mechanisms that could explain the risk-conferring effect of rs1143679, a single nucleotide non-synonymous Mac-1 polymorphism associated with SLE.

Effect of pioglitazone on neuropathic pain and spinal expression of TLR-4 and cytokines

The molecular mechanisms underlying neuropathic pain have yet to be elucidated. The present study aimed to examine the modulation of neuroimmune activation in the spinal cord by the synthetic peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist, pioglitazone (Pio), in a rat model of neuropathic pain induced by chronic constriction injury (CCI). Rats were randomly assigned into four groups: Sham surgery with vehicle, chronic constriction injury with vehicle or Pio (10 mg/kg), and chronic constriction injury with Pio and a PPAR-γ antagonist GW9662 (2 mg/kg). Pio or vehicle was administered 1 h prior to the surgery and continued daily until day 7 post-surgery. Paw pressure threshold was measured prior to surgery and on days 0, 1, 3 and 7 post-surgery. Microglia activation markers macrophage antigen complex-1, the mRNA expression levels of tumor necrosis factor α and interleukin-1β, and the mRNA expression levels of toll like receptor (TLR-4) in the lumbar spinal cord were determined. Administration of Pio resulted in the prominent attenuation of mechanical hyperalgesia. In addition, Pio was able to significantly inhibit neuroimmune activation characterized by glial activation, the production of cytokines and expression levels of TLR-4. Concurrent administration of a PPAR-γ antagonist, GW9662, reversed the effects of Pio. The antihyperalgesic effect of administration of Pio in rats receiving CCI may, in part, be attributed to the inhibition of neuroimmune activation associated with the sustaining of neuropathic pain.

PKC-δ activation in neutrophils promotes fungal clearance

The C-type lectin receptor dectin-1 and the integrin Mac-1 have key roles in controlling fungal infection. Here, we demonstrate that dectin-1- and Mac-1-induced activation of protein kinase Cδ in neutrophils, independent of the Card9 adaptor, is required for reactive oxygen species production and for intracellular killing upon Candida albicans uptake. Protein kinase Cδ was also required for zymosan-induced cytokine generation in neutrophils. In macrophages, protein kinase Cδ deficiency prevented fungi-induced reactive oxygen species generation but had no effect on activation of TGF-β-activated kinase-1, an effector of Card9, or nuclear factor κB activation, nor did it affect phagolysosomal maturation, autophagy, or intracellular C. albicans killing. In vivo, protein kinase Cδ-deficient mice were highly susceptible to C. albicans and Aspergillus fumigatus infection, which was partially rescued with adoptively transferred wild-type neutrophils. Thus, protein kinase Cδ activation downstream of dectin-1 and Mac-1 has an important role in neutrophil, but not macrophage, functions required for host defense against fungal pathogens.

Identification of Human Cathelicidin Peptide LL-37 as a Ligand for Macrophage Integrin αMβ2 (Mac-1, CD11b/CD18) that Promotes Phagocytosis by Opsonizing Bacteria

LL-37, a cationic antimicrobial peptide, has numerous immune-modulating effects. However, the identity of a receptor(s) mediating the responses in immune cells remains uncertain. We have recently demonstrated that LL-37 interacts with the α_MI-domain of integrin α_Mβ₂ (Mac-1), a major receptor on the surface of myeloid cells, and induces a migratory response in Mac-1-expressing monocyte/macrophages as well as activation of Mac-1 on neutrophils. Here, we show that LL-37 and its C-terminal derivative supported strong adhesion of various Mac-1-expressing cells, including HEK293 cells stably transfected with Mac-1, human U937 monocytic cells and murine IC-21 macrophages. The cell adhesion to LL-37 was partially inhibited by specific Mac-1 antagonists, including mAb against the α_M integrin subunit and neutrophil inhibitory factor, and completely blocked when anti-Mac-1 antibodies were combined with heparin, suggesting that cell surface heparan sulfate proteoglycans act cooperatively with integrin Mac-1. Coating both Gram-negative and Gram-positive bacteria with LL-37 significantly potentiated their phagocytosis by macrophages, and this process was blocked by a combination of anti-Mac-1 mAb and heparin. Furthermore, phagocytosis by wild-type murine peritoneal macrophages of LL-37-coated latex beads, a model of foreign surfaces, was several fold higher than that of untreated beads. By contrast, LL-37 failed to augment phagocytosis of beads by Mac-1-deficient macrophages. These results identify LL-37 as a novel ligand for integrin Mac-1 and demonstrate that the interaction between Mac-1 on macrophages and bacteria-bound LL-37 promotes phagocytosis.

Peptides against Mac-1 do not sufficiently target leukemia or lymphoma in vivo

BACKGROUND

β2 Integrins (cluster of differentiation-18, CD18) are expressed only by leukocytes and serve as cell surface receptors, being involved both in inside-out and outside-in signalling, and in cell movement. Therefore, they are interesting targets for therapeutic intervention. Phage display-derived inhibitory peptides against αMβ2 integrins (macrophage-1 antigen, Mac-1) have been found to be effective in preventing leukocyte movement in vitro and in vivo but little is known regarding their ability to target leukaemia and lymphoma in vivo.

MATERIALS AND METHODS

Athymic nude mice were inoculated with human THP-1 acute monocytic leukemia (AML-M5 variant), U937 diffuse histiocytic lymphoma, and OCI-AML-3 acute-myeloidic leukemia cells, and then treated with Mac-1-inhibiting peptides ADGACILWMDDGWCGAAG (DDGW) or CPCLLGCC fused with green fluorescent protein (LLG-GFP).

RESULTS

Mac-1-inhibiting DDGW peptide had no effect on leukemia and lymphoma burden in mice, and LLG-GFP fusion did not home to leukemia cells in vivo.

CONCLUSION

Although peptides against Mac-1 are promising drugs and diagnostic tools based on earlier experiments in inflammation they exhibit compromised biological avidity as a therapeutic and diagnostic means for leukaemia and lymphoma.

A proteomic approach for the elucidation of the specificity of ectodomain shedding

Ectodomain shedding (shedding) is a posttranslational modification mechanism, which liberates extracellular domains of membrane proteins through juxtamembrane processing. Because shedding alters cell characteristics in a rapid and irreversible manner, it must be strictly regulated. However, the regulatory mechanisms of shedding in response to environmental changes remain obscure. To evaluate the regulatory mechanisms of endogenous shedding, we previously developed a proteomic screening system to identify shedding targets. This system revealed a comprehensive picture of membrane proteins shed under defined conditions. In this study, we have improved the screening system to compare the shedding patterns in a mouse macrophage cell line treated with two different shedding inducers, lipopolysaccharide (LPS) and 12-O-tetradecanoylphorbol 13-acetate (TPA). We show here that LPS simultaneously activates the shedding of multiple membrane proteins. We further show that TPA specifically activates the shedding of αM/β2 integrin (Mac-1), which was not shed upon LPS-stimulation of macrophages. These results clearly demonstrate that the regulation of endogenous membrane protein shedding is both stimulus- and substrate-specific.

BIOLOGICAL SIGNIFICANCE

The shedding targets reported to date play pivotal roles in a variety of biological phenomena, including the immunological response, cell growth, cell adhesion and cell movement. In addition, several disease-related membrane proteins are shedding targets. Thus, understanding the regulation of shedding is important for the elucidation of pathogenesis and the development of therapeutic strategies. We submit that a comprehensive characterization of endogenous shedding is indispensable for understanding the regulatory mechanisms of shedding, and thus have developed a proteomic screening system to identify shedding targets. In this study, using our screening system, we demonstrate that different extracellular stimuli activate different types of shedding, even in a single cell. Our results prove that this proteomic approach is quite effective for the elucidation of the regulatory mechanisms of shedding.

Expression and cell distribution of receptor for advanced glycation end-products in the rat cortex following experimental subarachnoid hemorrhage

Convincing evidence indicates that inflammation contributes to the adverse prognosis of subarachnoid hemorrhage (SAH). Some pro-inflammatory molecules such as high mobility group protein 1, S100 family of proteins, β-amyloid peptide, and macrophage antigen complex 1 have been involved in the damaging inflammation process following SAH. The receptor for advanced glycation end-products (RAGE) is a transmembrane receptor that senses these molecules and plays central role in inflammatory processes. This study aimed to determine the expression and cell distribution of RAGE in the brain cortex after SAH. Male Sprague-Dawley rats were randomly divided into sham group and SAH groups at 6 h, 12 h and on day 1, day 2 and day 3 (n=6 for each subgroup). SAH groups suffered experimental SAH by injection of 0.3 ml autologous blood into the prechiasmatic cistern. RAGE expression was measured by Western blot, real-time PCR, immunohistochemistry and immunofluorescence. Nuclear expression of p65 protein, the major subunit of nuclear factor kappa B, was also detected. Our data demonstrated that the expression levels of RAGE and nuclear p65 protein were both markedly increased after SAH. Moreover, there was a significant positive correlation between the expression of RAGE and that of p65 protein. Double immunofluorescence staining showed that RAGE was expressed by neuron and microglia rather than astrocyte after SAH. These results suggest that RAGE may be directly involved in the inflammatory response after SAH, and there might be important implications for further studies using specific RAGE antagonists to decrease inflammation-mediated brain injury following SAH.

Reprint of Neutrophil cell surface receptors and their intracellular signal transduction pathways

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca(2+) signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.

Neutrophil cell surface receptors and their intracellular signal transduction pathways

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca^2 + signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.

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Neutrophils are crucial players in innate and adaptive immunity.

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Neutrophils also participate in autoimmune and inflammatory diseases.

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Various neutrophil receptors recognize pathogens and the inflammatory environment.

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The various cell surface receptors trigger diverse intracellular signaling.

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Neutrophil receptors and signaling are potential targets in inflammatory diseases.

Modulation of Neutrophil Apoptosis and the Resolution of Inflammation through β2 Integrins

Precise control of the neutrophil death program provides a balance between their defense functions and safe clearance, whereas impaired regulation of neutrophil death is thought to contribute to a wide range of inflammatory pathologies. Apoptosis is essential for neutrophil functional shutdown, removal of emigrated neutrophils, and timely resolution of inflammation. Neutrophils receive survival and pro-apoptosis cues from the inflammatory microenvironment and integrate these signals through surface receptors and common downstream mechanisms. Among these receptors are the leukocyte-specific membrane receptors β2 integrins that are best known for regulating adhesion and phagocytosis. Accumulating evidence indicate that outside-in signaling through the β2 integrin Mac-1 can generate contrasting cues in neutrophils, leading to promotion of their survival or apoptosis. Binding of Mac-1 to its ligands ICAM-1, fibrinogen, or the azurophilic granule enzyme myeloperoxidase suppresses apoptosis, whereas Mac-1-mediated phagocytosis of bacteria evokes apoptotic cell death. Mac-1 signaling is also target for the anti-inflammatory, pro-resolving mediators, including lipoxin A4, aspirin-triggered lipoxin A4, and resolvin E1. This review focuses on molecular mechanisms underlying Mac-1 regulation of neutrophil apoptosis and highlights recent advances how hierarchy of survival and pro-apoptosis signals can be harnessed to facilitate neutrophil apoptosis and the resolution of inflammation.

Expression and significance of ICAM-1 and its counter receptors LFA-1 and Mac-1 in experimental acute pancreatitis of rats

AIM: To investigate the role of intercellular adhesion molecule-1 (ICAM-1) and its counter receptors LFA-1 and Mac-1 in acute pancreatitis (AP).

METHODS: SD rats were allocated to AP group and control group randomly (25 rats each). AP was induced by infusion of 5% chenodeoxycholic acid into the pancreatic duct, followed by ligation of pancreatic duct. The rats were sacrificed at 1, 3, 6, 12 and 24 h after induction of pancreatitis. Five rats were sacrificed at one time point in the two groups before the blood and specimens from pancreas and lung were obtained. Serum amylase and ascitic fluid were measured at each time point. Expression of ICAM-1 at different time points was assessed by immunohistochemistry in pancreas and lung, and the expression of LAF-1 and Mac-1 on neutrophils at different time points was detected by flow cytometer.

RESULTS: Induction of AP was confirmed by the serum levels of amylase and histological studies. The expression of ICAM-1 in pancreas increased significantly than that in the control group at all time points (P < 0.05 or P < 0.01), as well as the expression in lung except at 1 h. The expression of LFA-1 and Mac-1 on neutrophil in blood increased significantly in AP group than that in control group at several time points (P < 0.05 or P < 0.01). The amount of ascitic fluid and serum amylase level of AP group increased significantly than that of control group at all time points (P < 0.05 or P < 0.01). Parallel to these results, a significant neutrophil infiltration was found in pancreas and lung tissues of AP group rats.

CONCLUSION: Our findings suggest the important role for ICAM-1, LFA-1 and Mac-1 in mediating the development of AP from a local disease to a systemic illness. Upregulation of ICAM-1, LFA-1, Mac-1 and subsequent leukocyte infiltration appear to be significant events of pancreatic and pulmonary injuries in AP.