Membrane-derived Microparticles Research Articles

Platelet membrane-derived microparticles may be biomarkers in patients with hepatocellular carcinoma and can promote the invasion and metastasis of hepatoma carcinoma cells.

Platelet membrane-derived microparticles (PMPs) released by apheresis platelets (APs) during storage are involved in immunomodulatory and tumor processes. However, few studies have emphasized the relationship between PMPs and hepatocellular carcinoma (HCC). Enzyme-linked immunosorbent assay (ELISA) was used to detect PMPs in the plasma of HCC patients and healthy individuals. ELISA and flow cytometry were separately applied to analyze the variation in PMPs from APs prepared after 0, 3, 5, and 7 days of storage. Transwell was used to demonstrate the effects of PMPs on the invasion and migration of HCC cells. HCC-related indicators and invasion and migration-related markers were detected in vivo. We found the amount of PMPs was significantly increased in HCC patients. There was also a significant difference in the amount of PMPs in APs with prolonged storage time. Further, the PMPs in D5 promoted the invasion and migration of HepG2 and Huh7 cells. Transcriptomics revealed striking differences in the expression of many tumor metastasis associated genes with PMPs treatment. PMPs promoted tumor growth and weight loss in HCC-bearing mice, and Western blot results showed that invasion and migration-related indicators also increase. The content of PMPs in the plasma of HCC patients increases, and it can also promote the invasion and migration of HCC.

Inhibition of Band 3 tyrosine phosphorylation: a new mechanism for treatment of sickle cell disease.

Many hypotheses have been proposed to explain how a glutamate to valine substitution in sickle haemoglobin (HbS) can cause sickle cell disease (SCD). We propose and document a new mechanism in which elevated tyrosine phosphorylation of Band 3 initiates sequelae that cause vaso-occlusion and the symptoms of SCD. In this mechanism, denaturation of HbS and release of heme generate intracellular oxidants which cause inhibition of erythrocyte tyrosine phosphatases, thus permitting constitutive tyrosine phosphorylation of Band 3. This phosphorylation in turn induces dissociation of the spectrin-actin cytoskeleton from the membrane, leading to membrane weakening, discharge of membrane-derived microparticles (which initiate the coagulation cascade) and release of cell-free HbS (which consumes nitric oxide) and activates the endothelium to express adhesion receptors). These processes promote vaso-occlusive events which cause SCD. We further show that inhibitors of Syk tyrosine kinase block Band 3 tyrosine phosphorylation, prevent release of cell-free Hb, inhibit discharge of membrane-derived microparticles, increase sickle cell deformability, reduce sickle cell adhesion to human endothelial cells, and enhance sickle cell flow through microcapillaries. In view of reports that imatinib (a Syk inhibitor) successfully treats symptoms of sickle cell disease, we suggest that Syk tyrosine kinase inhibitors warrant repurposing as potential treatments for SCD.

Role of Band 3 Tyrosine Phosphorylation in Causing the Vaso-Occlusive Events in Sickle Cell Disease

Background: Sickle cell disease (SCD) derives from a mutation in sickle hemoglobin (HbS) that leads to vaso-occlusive events that eventually cause organ failure. Based on observations from multiple labs, we hypothesize that the events linking HbS denaturation to vaso-occlusion are: HbS denaturation→oxidative stress→inhibition of erythrocyte tyrosine phosphatases→enhanced tyrosine phosphorylation of band 3→dissociation of the spectrin/actin cytoskeleton from the membrane→release of membrane-derived microparticles (MPs) and discharge of cell-free HbS→induction of microthromboses and activation of the vascular endothelium→vascular occlusion. In the studies below, we document each step of this pathway and demonstrate that inhibitors of Band 3 tyrosine phosphorylation block all downstream events. Methods: Band 3 tyrosine phosphorylation, plasma MP counts, plasma cell-free Hb concentration, sickle cell deformability, sickle cell flow through micro-capillaries, and adhesion of sickle erythrocytes to activated endothelial cells are quantitated using fresh sickle blood both before and after incubation with inhibitors of Band 3 tyrosine phosphorylation. Findings: Imatinib and other Syk kinase inhibitors block Band 3 tyrosine phosphorylation, suppress release of membrane MPs, reduce discharge of cell-free HbS, improve sickle cell deformability, enhance flow of sickle cells through microcapillaries, and reduce adherence of sickle cells to heme-activated endothelium. Interpretation: Inhibition of Band 3 Tyrosine phosphorylation restores membrane integrity and thereby suppresses the downstream sequelae that lead to vaso-occlusive events in SCD. Inhibitors of Band 3 tyrosine phosphorylation may therefore constitute a novel effective therapy for SCD. Funding Statement: NIH grants R01GM24417-40 (P.S.L.), 1RF1 NS110049-01 (J.W.), R01HL133574 (U.A.G. and J.A.L.), T32HL134622 (R.A.), and NSF #1552782 (U.A.G.). Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: All sickle cell blood samples were obtained following informed consent using procedures approved by the local IRBs.

Role of platelet-derived microparticles in transfer of the chemokine receptor CXCR4 to CXCR4-negative cells.

Background: Membrane-derived microparticles (PMPs) are produced from platelets during activation, storage, and apoptosis. PMP can transfer some adhesion molecules such as CXCR4 to CXCR4-negative cells. In this study, the ability of PMPs to deliver CXCR4 molecule to CXCR4-null targets (Daudi, K562 and U937 cell line) was evaluated and the different concentrations of PMPs were examined to transfer CXCR4. Methods: In this experimental study, PMPs were prepared using serial centrifugations. After confirmation of PMP with flow cytometry, PMP concentration was evaluated using the Bradford method. CXCR4-negative cell lines (1×105 cells/ml) were cultured in RPMI1640 with 10% FBS and 1% antibiotic. PMPs in 7 different concentrations were added to cell culture plates and incubated for 1 hour at 37ºc and 5% CO2. The presence of CXCR4 on cells was analyzed by flowcytometry. Results: In this study, characterization of PMPs and cell lines were done by flow cytometry. Then, the PMPs’ ability to transfer CXCR4 to null cells (Daudi, K562 and U937 cell lines) was evaluated in 7 concentrations (10, 20, 50,125, 250, 500, 1000 μg/mL); incubation lasted for 1 hour. The best result of transferring CXCR4 by PMP was done in the concentration of 250µg/mL. Conclusion: PMPs in different concentrations can transfer CXCR4 to target cells. Also, the increase of PMPs concentration up to 250µg/mL can increase the CXCR4 presence on null cells.

Pro-Inflammatory Actions of Red Blood Cell-Derived DAMPs.

Damage-associated molecular patterns (DAMPs) or alarmins are endogenous danger signals that are derived from damaged cells and extracellular matrix degradation, capable of triggering innate immune response to promote tissue damage repair. Hemolytic or hemorrhagic episodes are often associated with inflammation, even when infectious agents are absent, suggesting that damaged red blood cells (RBCs) release DAMPs.Hemoglobin (Hb) composes 96% of the dry weight of RBCs; therefore upon hemolysis, tremendous amounts of Hb are released into the extracellular milieu. Hb oxidation occurs outside the protective environment of RBCs, leading to the formation of different Hb oxidation products and heme. Heme acts as a prototypic DAMP participating in toll-like receptor as well as intracellular nucleotide-binding oligomerization domain-like receptor signaling. Oxidized Hb forms also possess some inflammatory actions independently of their heme releasing capability. Non-Hb-derived DAMPs such as ATP, interleukin-33, heat shock protein 70, as well as RBC membrane-derived microparticles might also contribute to the innate immune response triggered by hemolysis/hemorrhage.In this chapter we will discuss the inflammatory properties of RBC-derived DAMPs with a particular focus on Hb derivatives, as well as therapeutic potential of the endogenous Hb and heme-binding proteins haptoglobin and hemopexin in the prevention of hemolysis/hemorrhage-associated inflammation.

Calcium-calpain Dependent Pathways Regulate Vesiculation in Malignant Breast Cells.

Multidrug resistance in cancer (MDR) occurs when tumours become crossresistant to a range of different anticancer agents. One mechanism by which MDR can be acquired is through cell to cell communication pathways. Membrane-derived microparticles (MPs) are emerging as important signaling molecules in this process. MPs are released from most eukaryotic cells and transfer functional proteins and nucleic acids to recipient cells conferring deleterious traits within the cancer cell population including MDR, metastasis, and angiogenesis. MP formation is known to be dependent on calpain, an intracellular cysteine protease which acts to cleave the cytoskeleton underlying the plasma membrane, resulting in cellular surface blebbing Objective: To establish the role of calpain in vesiculation in malignant and non-malignant cells by 1) comparing membrane vesiculation at rest and following the release of intracellular calcium, and 2) comparing vesiculation in the presence and absence of calpain inhibitor II (ALLM). This study examines the differences in vesiculation between malignant and non-malignant cells using high-resolution Atomic Force Microscopy (AFM). HBEC, MBE-F, MCF-7, and MCF- 7/Dx cells were analysed at rest and following treatment with calcium ionophore A23187 for 18 hours. Vesiculation of calcium activated and resting malignant and non-malignant cells was also assessed after 18 hour treatment of calpain inhibitor II (ALLM). We demonstrate that malignant MCF-7 and MCF-7/Dx cells have an intrinsically higher degree of vesiculation at rest when compared to non-malignant human brain endothelial cells (HBEC) and human mammary epithelial cells (MBE-F). Cellular activation with the calcium ionophore A23187 resulted in an increase in vesiculation in all cell types. We show that calpain-mediated MP biogenesis is the dominant pathway at rest in malignant cells as vesiculation was shown to be inhibited with calpain inhibitor II (ALLM). These results suggest that differences in the biogenic pathways exist in malignant and non-malignant cells and have important implications in defining novel strategies to selectively target malignant cells for the circumvention of deleterious traits acquired through intercellular exchange of extracellular vesicles.

Neutrophil Microparticles Deliver Active Myeloperoxidase to Injured Mucosa To Inhibit Epithelial Wound Healing.

Neutrophil (PMN) infiltration of the intestinal mucosa often leads to severe epithelial injury; however, how this process occurs is unclear. This article describes a novel mechanism whereby membrane-derived microparticles released by tissue infiltrating PMNs (PMN-MPs) serve as shuttles to protect and deliver active mediators to locally modulate cellular function during inflammation. Specifically, myeloperoxidase (MPO), which is abundantly expressed in PMN azurophilic granules and is used for microbial killing, was found to be mobilized to the PMN surface and subsequently released in association with PMN-MPs upon PMN activation and binding to intestinal epithelial cells (IECs). The enzymatic activity of PMN-MP-associated MPO was enhanced compared with soluble protein, leading to potent inhibition of wound closure following PMN-MP binding to IECs. Importantly, localized microinjection of PMN-MPs into wounded colonic mucosa was sufficient to impair epithelial wound healing in vivo. PMN-MP/MPO-dependent inhibition of IEC wound healing was due to impaired IEC migration and proliferation, resulting from impeded actin dynamics, cell spreading, and cell cycle arrest. Thus, our findings provide new insight into mechanisms governing PMN-induced tissue injury and implicate PMN-MPs and MPO as important regulators of cellular function.

Deposition of microparticles by neutrophils onto inflamed epithelium: a new mechanism to disrupt epithelial intercellular adhesions and promote transepithelial migration.

Neutrophil [polymorphonuclear leukocyte (PMN)] transepithelial migration (TEM) is a hallmark of inflammatory mucosal disorders. PMN TEM is associated with epithelial injury; however, mechanisms involved in this process are not well defined. The current work describes a new mechanism whereby deposition of PMN membrane-derived microparticles (PMN-MPs) onto intestinal epithelial cells (IECs) during TEM leads to loss of epithelial cadherins, thus promoting epithelial injury and increased PMN recruitment. PMN-MPs secreted by activated PMNs during TEM displayed a high level of enzymatically active matrix metalloproteinase 9 (MMP-9), and were capable of mediating potent effects on IEC integrity. Isolated PMN-MPs efficiently bound to IEC monolayers and induced cleavage of desmoglein-2 (DSG-2) but not E-cadherin, leading to disruption of IEC intercellular adhesions. Furthermore, PMN-MP binding to intestinal epithelium in vitro in transwell assays and in vivo in ligated intestinal loop preparations facilitated increases in PMN TEM. These effects were MMP-9 dependent and were reversed in the presence of specific pharmacological inhibitors. Finally, we demonstrated that IEC Dsg-2 serves as a barrier for migrating PMNs, and its removal by PMN-MP-associated MMP-9 facilitates PMN trafficking across epithelial layers. Our findings thus implicate PMN-MPs in PMN-mediated inflammation and epithelial damage, as observed in inflammatory disorders of mucosal surfaces.-Butin-Israeli, V., Houser, M. C., Feng, M., Thorp, E. B., Nusrat, A., Parkos, C. A, Sumagin, R. Deposition of microparticles by neutrophils onto inflamed epithelium: a new mechanism to disrupt epithelial intercellular adhesions and promote transepithelial migration.

Low ascites levels of cell membrane-derived microparticles indicate worse short-term prognosis in patients with decompensated cirrhosis

Low ascites levels of cell membrane-derived microparticles indicate worse short-term prognosis in patients with decompensated cirrhosis

The Gas6-Axl Protein Interaction Mediates Endothelial Uptake of Platelet Microparticles

Upon activation, platelets release plasma membrane-derived microparticles (PMPs) exposing phosphatidylserine on their surface. The functions and clearance mechanism of these microparticles are incompletely understood. As they are pro-coagulant and potentially pro-inflammatory, rapid clearance from the circulation is essential for prevention of thrombotic diseases. The tyrosine kinase receptors Tyro3, Axl, and Mer (TAMs) and their ligands protein S and Gas6 are involved in the uptake of phosphatidylserine-exposing apoptotic cells in macrophages and dendritic cells. Both TAMs and their ligands are expressed in the vasculature, the functional significance of which is poorly understood. In this study, we investigated how vascular TAMs and their ligands may mediate endothelial uptake of PMPs. PMPs, generated from purified human platelets, were isolated by ultracentrifugation and labeled with biotin or PKH67. The uptake of labeled microparticles in the presence of protein S and Gas6 in human aortic endothelial cells and human umbilical vein endothelial cells was monitored by flow cytometry, Western blotting, and confocal/electron microscopy. We found that both endothelial cell types can phagocytose PMPs, and by using TAM-blocking antibodies or siRNA knockdown of individual TAMs, we show that the uptake is mediated by endothelial Axl and Gas6. As circulating PMP levels were not altered in Gas6(-/-) mice compared with Gas6(+/+) mice, we hypothesize that the Gas6-mediated uptake is not a means to clear the bulk of circulating PMPs but may serve to locally phagocytose PMPs generated at sites of platelet activation and as a way to effect endothelial responses.

Phospholipid Binding Protein C Inhibitor (PCI) Is Present on Microparticles Generated In Vitro and In Vivo.

Protein C inhibitor is a secreted, non-specific serine protease inhibitor with broad protease reactivity. It binds glycosaminoglycans and anionic phospholipids, which can modulate its activity. Anionic phospholipids, such as phosphatidylserine are normally localized to the inner leaflet of the plasma membrane, but are exposed on activated and apoptotic cells and on plasma membrane-derived microparticles. In this report we show by flow cytometry that microparticles derived from cultured cells and activated platelets incorporated protein C inhibitor during membrane blebbing. Moreover, protein C inhibitor is present in/on microparticles circulating in normal human plasma as judged from Western blots, ELISAs, flow cytometry, and mass spectrometry. These plasma microparticles are mainly derived from megakaryocytes. They seem to be saturated with protein C inhibitor, since they do not bind added fluorescence-labeled protein C inhibitor. Heparin partially removed microparticle-bound protein C inhibitor, supporting our assumption that protein C inhibitor is bound via phospholipids. To assess the biological role of microparticle-bound protein C inhibitor we performed protease inhibition assays and co-precipitated putative binding partners on microparticles with anti-protein C inhibitor IgG. As judged from amidolytic assays microparticle-bound protein C inhibitor did not inhibit activated protein C or thrombin, nor did microparticles modulate the activity of exogenous protein C inhibitor. Among the proteins co-precipitating with protein C inhibitor, complement factors, especially complement factor 3, were most striking. Taken together, our data do not support a major role of microparticle-associated protein C inhibitor in coagulation, but rather suggest an interaction with proteins of the complement system present on these phospholipid vesicles.

Flow cytometric assessment of circulating platelet and erythrocytes microparticles in young thalassemia major patients: relation to pulmonary hypertension and aortic wall stiffness

Heart disease is the leading cause of mortality and morbidity in β-thalassemia major (β-TM). Aggregability of abnormal red cells and membrane-derived microparticles (MPs) stemming from activated platelets and erythrocytes are responsible for thrombotic risk. We measured platelet and erythrocyte MPs (PMPs and ErMPs) in 60 young β-TM patients compared with 40 age- and sex-matched healthy controls and assessed their relation to clinicopathological characteristics and aortic elastic properties. Patients were studied stressing on transfusion history, splenectomy, thrombotic events, chelation therapy, hematological and coagulation profiles, flow cytometric measurement of PMPs (CD41b(+) ) and ErMPs (glycophorin A(+) ) as well as echocardiographic assessment of aortic elastic properties. Aortic stiffness index and pulmonary artery pressure were significantly higher, whereas aortic strain and distensibility were lower in TM patients than controls (P < 0.001). Both PMPs and ErMPs were significantly elevated in TM patients compared with controls, particularly patients with risk of pulmonary hypertension, history of thrombosis, splenectomy or serum ferritin >2500 μg/L (P < 0.001). Compliant patients on chelation therapy had lower MPs levels than non-compliant patients (P < 0.001). PMPs and ErMPs were positively correlated to markers of hemolysis, serum ferritin, D-dimer, vWF Ag, and aortic stiffness, whereas negatively correlated to hemoglobin level and aortic distensibility (P < 0.05). We suggest that increased MPs may be implicated in vascular dysfunction, pulmonary hypertension risk, and aortic wall stiffness observed in thalassemia patients. Their quantification could provide utility for early detection of cardiovascular abnormalities and monitoring the biological efficacy of chelation therapy.

Platelet-Derived Microvesicles: Multitalented Participants in Intercellular Communication

Platelets can release a heterogeneous pool of vesicles which include plasma membrane-derived microparticles (PMPs) and multivesicular body-derived exosomes. As both vesicle types are generated upon activation and their distinction is complicated due to an overlap in their molecular properties and sizes, they are best discussed as an entity, the platelet-derived microvesicles (PMVs). PMPs can be formed through several induction pathways, which determine their different molecular profiles and facilitate tailor-made participation in intercellular communication. This dynamic variability may lie behind the multifaceted and sometimes very different observations of the PMPs in physiological and pathological settings. Currently, little is known of platelet-derived exosomes. In all, PMVs not only participate in several homeostatic multicellular processes, such as hemostasis, maintenance of vascular health, and immunity, but they also play a role in thrombotic and inflammatory diseases and cancer progression. In the past few years, the number of original articles and reviews on microvesicles has dramatically increased, but the data simultaneously raise further questions, the answers to which depend on forthcoming analytical improvements. In this article, the differential activation pathways and the molecular and functional properties of PMVs are reviewed in context with their sometimes paradoxical role in health and in disease. Also, the methodological issues of PMV detection and analysis are discussed in the light of recent advances within the field.

Erythrocytes and Platelets May Contribute to Hypercoagulability In Nephrotic Syndrome Through Enhanced Phosphatidylserine Exposure and Microparticles Release

Abstract 36 Background.Nephrotic syndrome (NS) is frequently accompanied by thromboembolic complications such as renal vein thrombosis, deep vein thrombosis and pulmonary embolism. However, the cause of the hypercoagulable state in NS patients is not understood. In contrast to quiescent cells, membrane-derived microparticles have exposed phosphatidylserine which may support procoagulant enzyme complexes in thrombosis. Objectives.The aim of this work was to measure the type and quantity of MPs that expose PS in NS patients, and to evaluate the associated procoagulant activity (PCA). Methods.The subjects with membranous nephropathy (MN) or minimal change nephrotic syndrome (MCNS) were compared to healthy controls. Flow cytometry and confocal microscopy was used to evaluate microparticles. PCA was determined by clotting time and purified coagulation complex assays. Results.We found that the number of lactadherin+ MPs was significantly higher in each NS group MCNS (3230 ± 536)/MN (4642 ± 697) than that in the controls (1748 ± 239), furthermore, MPs in MN patients are significantly higher than ones in MCNS (P < 0.05; Table 1), which mostly derived from RBC and platelet membranes. The percentage of lactadherin+ RBCs was also significantly increased in each NS group, MN (9.7 ± 3.2%)/MCNS (5.1 ± 2.4%) patients compared to the controls (0.5 ± 0.2%). In addition, the mean percentage of lactadherin+ RBCs in MN showed significantly higher than that in MCNS (P < 0.05). In both NS groups, the percentage of lactadherin+ platelets was significantly higher than that in healthy control subjects (4.1 ± 1.1%) (P < 0.05 for both). Furthermore, patients in MN (11.5 ± 3.1%) also had significantly increased lactadherin+ platelets than in MCNS (7.3 ± 2.3%) (P < 0.05). By confocal laser-scanning microscope, nearly no staining by Alexa Fluro 488-lactadherin could be detected on RBCs or platelets membranes in healthy subjects, whereas a light green fluorescence on RBC and platelet with lactadherin accompanying vesiculation were observed in NS patients. PCA of RBCs/platelets from healthy individuals and NS patients was assessed by recalcification time assays, intrinsic, extrinsic FXa and prothrombinase assays. MPs shedding and PS exposure of RBCs/platelets were highly procoagulant in NS patients and blockade of PS with lactadherin inhibited over 90% of PCA. However, an anti-TF antibody had no significant inhibition effect (Figure 1). [Display omitted] Table 1MPs numbers per microliter of plasma in MCNS, MN and controls.ControlsMCNSMNTotal lactadherin+ MPs (/μl)1748 (1341–2014)3230* (2484–3819)4642*,# (3499–5496)Lactadherin+ CD41a+1237 (944–1450)2363* (1888–2587)3470*,# (2587–4144)Lactadherin+ CD235a+23 (16–32)174* (138–205)335*,# (262–410)Lactadherin+ CD142+2.6 (0–4.2)2.7 (0–4.9)2.6 (0–6.8)Corrected for the number of events with isotype controls,*P < 0.05 versus controls.#P < 0.05 versus MCNS. Conclusions.This is the first study to show that loss of RBCs/platelets membrane phospholipid asymmetry with increased PS exposure and MPs release may contribute to the hypercoagulable state of NS patients. The extent of PS exposure on cells and MPs may be a marker of thromboembolic risk in these patients. Disclosures:No relevant conflicts of interest to declare.

Circulating endothelial progenitor cells, microparticles and vascular disease

Circulating endothelial progenitor cells, microparticles and vascular disease

Increased levels of procoagulant tissue factor-bearing microparticles within the occluded coronary artery of patients with ST-segment elevation myocardial infarction: Role of endothelial damage and leukocyte activation

Objective During myocardial infarction, platelet activation and endothelial apoptosis are responsible for the release of procoagulant membrane-derived microparticles (MPs) in the bloodstream. Few data are available on the potential role played by MPs in coronary atherothrombosis. In the present study, we investigated the levels and cellular origins of MPs within the occluded coronary artery of patients with ST-segment elevation myocardial infarction (STEMI) treated by primary angioplasty (PCI). Methods A total of 12 patients with STEMI treated by primary PCI within 24 h of symptom onset were included in this study. MPs procoagulant activity and cellular origin were characterized within the occluded coronary artery before PCI (C 0), after restoration of the epicardial blood flow (C 1), and in blood collected from the femoral artery (F). Results Levels of leukocyte-derived CD11a + MPs, endothelial-derived CD105 + MPs, and tissue factor (TF)-bearing MPs were significantly higher within the occluded coronary artery than in peripheral blood samples. Restoration of the epicardial blood flow led to a significant reduction of procoagulant CD11a + and CD105 + MPs by 30% and 42%, respectively ( p < 0.05). Conclusions Elevation of procoagulant MPs within the occluded coronary artery of patients with STEMI suggests their pathophysiological role in coronary atherothrombosis.

Receptor Swapping

The signals that a cell receives from its environment can be altered if cells acquire new receptors on their cell surface. In fact, cells appear to be able to acquire receptors that they themselves are not programmed to express through incorporation of membrane-derived microparticles released from other cells. In particular, during inflammatory responses, platelet-derived microparticles (PMPs) are released that can transfer molecules to cells in the blood vessel walls or to cells in the blood, like neutrophils. Salanova et al. discovered that the integrin glycoprotein IIb/IIIa (GPIIb/IIIa), which recognizes various adhesion proteins and thus contributes to platelet aggregation, can be transferred in PMPs to circulating neutrophils. After treatment of whole human blood with adenosine diphosphate to activate platelets, the authors used flow cytometry and fluorescence microscopy to show that neutrophils, which originally showed little evidence of GPIIb/IIIa on their cell surface, acquired small patches on the cell surface that contained the integrin. These receptors appeared to be transferred by PMPs, because they were also present when PMPs were isolated and then applied to purified neutrophils. Neutrophils activate the transcription factor NF-κB when they receive integrin signals together with stimulation by cytokines. Salanova et al . observed that neutrophils treated with the cytokine GM-CSF (granulocyte-macrophage colony-stimulating factor) that had also acquired GPIIb/IIIa from PMPs activated NF-κB in response to antibodies that stimulated GPIIb/IIIa or the native integrin CD18. Blocking activation of either one of the integrins inhibited activation of NF-κB. Similarly treated cells that didn’t acquire PMPs did not activate NF-κB in response to activation of either integrin. Fluorescence microscopy indicated that the two integrins were localized together on the cell surface of the neutrophils. Thus, transferred GPIIb/IIIa appears to act together with native integrins of the neutrophil. Inflammation is thought to contribute to the deleterious effects of vascular injury, and inhibition of such responses may be of therapeutic value. In this regard, Salanova et al . showed that inhibitors of GPIIb/IIIa already in use clinically to limit platelet aggregation prevented activation of NF-κB in neutrophils that had acquired GPIIb/IIIa and were exposed to GM-CSF and fibronectin (an integrin ligand). B. Salanova, M. Choi, S. Rolle, M. Wellner, F. C. Luft, R. Kettritz, β2-integrins and acquired glycoprotein IIb/IIIa (GPIIb/IIIa) receptors cooperate in NF-κB activation of human neutrophils. J. Biol Chem. 282 , 27960-27969 (2007). [Abstract] [Full Text]

Emerging targets of biologic therapies for rheumatoid arthritis

Advances in molecular biology and the clinical success of strategies that target tumor necrosis factor (TNF) have led to further research into the pathophysiology of human rheumatoid arthritis. Several novel therapeutic targets have emerged from these efforts, including not only molecules that regulate TNF (e.g. TNF-alpha converting enzyme), the complex cytokine network (e.g. interleukin [IL]-6, IL-15, IL-17) and several adipokines, but also targets that originate from cellular and subcellular components of the disease. Strategies that aim at cellular targets include antibodies to CD20 or BLyS (also known as TNF ligand family member 13b), which deplete or inhibit B cells, as well as approaches that interfere with membrane-derived microparticles. Components of subcellular pathways, which are predominantly upstream of the central regulator of transcription nuclear factor kappaB, have also been studied. Of these, strategies that target mitogen-activated protein kinases have a leading role and are on the verge of clinical use; approaches that target specific molecules such as Janus kinases, signal transducer and activator of transcription proteins, and suppressor of cytokine signaling proteins also seem to show promise and might have a clinical application in the future.

Activated platelet‐derived microparticles in thalassaemia

Thromboembolic complications have been documented in thalassaemia patients. The aggregability of abnormal red blood cells and the high level of membrane-derived microparticles (MPs) stemming from blood cells are thought to be responsible for the associated thrombotic risk. We investigated the number of MPs, their cellular origin and their procoagulant properties in beta-thalassaemia. Fresh whole blood was simultaneously stained for annexin V, cellular antigens and the known density beads. The procoagulant properties of these phosphatidylserine (PS)-bearing MPs were also measured by assessing the platelet factor-3-like activity in the blood. Flow cytometric results showed that splenectomised beta-thalassaemia/HbE patients had significantly higher levels of PS-bearing MPs than non-splenectomised beta-thalassaemia/HbE patients and normal individuals (P < 0.0001). There was a good correlation between PS-bearing MPs and PS-bearing platelets, reflecting the existence of chronic platelet activation in beta-thalassaemia/HbE patients (r(s) = 0.511, P < 0.001). The cellular origin of PS-bearing MPs showed mostly activated-platelet origin with adhesion (CD41a/CD62P/CD36). Moreover, the platelet procoagulant activity was higher in splenectomised beta-thalassaemia/HbE patients when compared with non-splenectomised (P < 0.05) and normal individuals (P < 0.01), and the amount correlated with PS-bearing MPs (rs = 0.560, P < 0.001). These findings suggest that MPs originate from activated platelets with a potential to aggravate thrombotic events when the numbers are excessive, as is commonly seen in splenectomised beta-thalassaemia/HbE patients.

Novel Role of Toll-Like Receptor 3 in Hepatitis C-Associated Glomerulonephritis

Hepatitis C virus (HCV) infection is frequently complicated by glomerulonephritis with immune complexes containing viral RNA. We examined the potential influence of Toll-like receptors (TLRs), specifically TLR3 recognition of viral dsRNA exemplified by polyriboinosinic:polyribocytidylic acid [poly(I:C) RNA]. Normal human kidney stained positive for TLR3 on mesangial cells (MCs), vascular smooth muscle cells, and collecting duct epithelium. Cultured MCs have low TLR3 mRNA levels with predominant intracellular protein localization, which was increased by tumor necrosis factor-alpha, interleukin (IL)-1beta, interferon (IFN)-gamma, and the TLR3 ligand poly(I:C) RNA. Poly(I:C) RNA stimulation of MCs increased mRNA and protein synthesis of IL-6, IL-1beta, M-CSF, IL-8/CXCL8, RANTES/CCL5, MCP-1/CCL2, and ICAM-I; it also increased anti-proliferative and proapoptotic effects, the latter of which was decreased by inhibiting caspase-8. In microdissected glomeruli of normal and non-HCV membranoproliferative glomerulonephritis biopsies, TLR3 mRNA expression was low. In contrast TLR3 mRNA expression was significantly increased in hepatitis C-positive glomerulonephritis and was associated with enhanced mRNA for RANTES/CCL5 and MCP-1/CCL2. We hypothesize that immune complexes containing viral RNA activate mesangial TLR3 during HCV infection, thereby contributing to chemokine/cytokine release and effecting proliferation and apoptosis. Thus, TLR3 expression on renal cells, and especially MCs, may establish a link between viral infections and glomerular diseases.