[Show abstract][Hide abstract] ABSTRACT: Recently, we reported that extracellular cyclophilin A (CyPA) is an important agonist for platelets. Whereas soluble CyPA-levels have been associated with cardiovascular risk factors, cell-bound CyPA has not been investigated yet. In this study, we analyzed for the first time platelet-bound CyPA in patients with symptomatic coronary artery disease (CAD).
blood was obtained from 388 consecutive patients: 204 with stable CAD and 184 with acute coronary syndrome (76 with unstable angina, 78 with non ST-elevation myocardial infarction (NSTEMI), and 30 with STEMI). In vitro stimulation of platelets with classical agonists revealed an enhanced expression of CyPA on the platelet surface. In patients with stable CAD, platelet-bound CyPA correlated excellently with platelet activity measured by P-selectin exposure in flow cytometry. The analysis of classical risk factors for atherosclerosis revealed that patients with hypertension and hypercholesterolemia had significantly enhanced platelet-bound CyPA, whereas diabetes and smoking were not associated with enhanced CyPA-binding to the platelet surface. In multivariate analysis, hypercholesterolemia was the only significant predictor of enhanced platelet-bound CyPA. Interestingly, in patients with acute myocardial infarction (AMI) platelet-bound CyPA was significantly decreased compared with patients with stable CAD.
Enhanced platelet-bound CyPA is associated with hypertension and hypercholesterolemia in stable CAD patients. In patients with AMI platelet-bound CyPA is significantly decreased.
[Show abstract][Hide abstract] ABSTRACT: There is emerging evidence that platelets have an important role in inflammation beyond their involvement in hemostasis. Platelets can contribute to inflammatory reactions via crosstalk both with immune cells and endothelial cells. Inflamed vessels are characterized by the presence of activated endothelial cells. These activated endothelial cells upregulate receptors necessary for leukocyte recruitment, but also for the adhesion of platelets. Subsequently, immune cells can bind to platelets through adhesion receptors presented on the platelet surface, thus supporting leukocyte recruitment to the vessel wall. There are several neurological diseases associated with vascular inflammation including multiple sclerosis (MS) and stroke. Increased markers of platelet activation could be demonstrated in patients suffering from MS compared to healthy individuals. Reports from murine models indicate that platelets may be of importance for disease progression and severity by mediating leukocyte recruitment as one potential underlying mechanism. Blocking platelet function disease severity was considerably ameliorated. Moreover, processes of tissue remodelling may be influenced by platelet derived mediators. Whether a role of platelets for vascular inflammation can be extrapolated to further neurological diseases will have to be investigated in further in depth experimental and clinical trials.
Platelets and platelet associated mechanisms may offer novel starting points to understand neurovascular diseases from a different point of view and to develop novel approaches to access the disease.
[Show abstract][Hide abstract] ABSTRACT: Cyclophilins are a group of highly conserved cytosolic enzymes that have a peptidylprolyl cis/trans isomerase activity. Cyclophilin A (CyPA) can be secreted in the extracellular space by inflammatory cells and upon cell death. The presence of CyPA in patients with nonischemic cardiomyopathy is associated with poor clinical prognosis. Here, we investigated the inhibition of extracellular CyPA in a mouse model of troponin I-induced autoimmune myocarditis using the strictly extracellular CyPA-inhibitor MM284. Since A/J mice develop severe inflammation and fibrosis after immunization with murine cardiac troponin I (mcTn I), we used this model to analyze the effects of an extracellular CyPA inhibition. As extracellular CyPA-inhibitor we used the recently described CsA-derivate MM284. In vitro studies confirmed that MM284 inhibits CyPA-induced monocytic migration and adhesion. A/J mice immunized with mcTnI were treated with MM284 or vehicle every second day. After 28 days, we found a considerable reduction of myocardial injury and fibrosis. Further analysis revealed a reduced myocardial presence of T-cells and macrophages compared to control treated animals. Whereas MMP-9 expression was reduced significantly by MM284, we observed no significant reduction of inflammatory cytokines such as IL-6 or TNFα. Extracellular CyPA plays an important role in autoimmune myocarditis for myocardial damage and fibrosis. Our data suggest a new pharmacological approach for the treatment of myocardial inflammation and reduction of cardiac fibrosis by inhibition of extracellular CyPA.
PLoS ONE 04/2015; 10(4):e0124606. DOI:10.1371/journal.pone.0124606 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Platelets contribute to processes beyond thrombus formation and may play a so far underestimated role as an immune cell in various circumstances. This review outlines immune functions of platelets in host defense, but also how they may contribute to mechanisms of infectious diseases. A particular emphasis is placed on the interaction of platelets with other immune cells. Furthermore, this article outlines the features of atherosclerosis as an inflammatory vascular disease highlighting the role of platelet crosstalk with cellular and soluble factors involved in atheroprogression. Understanding, how platelets influence these processes of vascular remodeling will shed light on their role for tissue homeostasis beyond intravascular thrombosis. Finally, translational implications of platelet-mediated inflammation in atherosclerosis are discussed.
Frontiers in Immunology 03/2015; 6:98. DOI:10.3389/fimmu.2015.00098
[Show abstract][Hide abstract] ABSTRACT: Atherosclerosis and its late sequels are still the number one cause of death in western societies. Platelets are a driving force not only during the genesis of atherosclerosis, but especially in its late stages, as evidenced by complications such as arterial thrombosis, myocardial infarction, and ischemic stroke. Atherosclerosis is increasingly recognized as an inflammatory disease, influenced by various immune mechanisms. The complement system is part of our innate immune system, and its diverse roles in atherosclerosis have become evident over the past years. In this review we identify points of intersection between platelets and the complement system and discuss their relevance for atherosclerosis. Specifically, we will focus on roles for platelets in the onset as well as progression of the disease, a possible dual role for complement in the genesis and development of atherosclerosis, and review emerging literature revealing previously unrecognized cross-talk between platelets and the complement system and discuss its possible impact for atherosclerosis. Finally, we identify limitations of current research approaches and discuss perspectives of complement modulation in the control of the disease.
Frontiers in Physiology 03/2015; 6:49. DOI:10.3389/fphys.2015.00049 · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Surface expression of stromal cell-derived factor-1 (SDF-1, CXCL12) on platelets is enhanced during ischaemic events and plays an important role in peripheral homing of stem cells and myocardial repair mechanisms. SDF-1 effects are mediated through CXCR4 and CXCR7. Both CXCR4 and CXCR7 are surface expressed on human platelets and to a higher degree in patients with coronary artery disease (CAD) when compared with healthy controls. In this study, we investigated the prognostic role of platelet CXCR4- and CXCR7 surface expression in patients with symptomatic CAD.
In a cohort study, platelet surface expression of CXCR4 and CXCR7 was measured by flow cytometry in 284 patients with symptomatic CAD at the time of percutaneous coronary intervention (PCI). The primary combined endpoint was defined as all-cause death and/or MI during 12 month follow-up. Secondary endpoints were defined as the single events of all-cause death and myocardial infarction (MI). We found significant differences of CXCR4 values in patients who developed a combined endpoint compared to event-free patients (mean MFI 3.17 vs. 3.44, 95% CI 0.09 - 0.45) and in patients who subsequently died (mean MFI 3.10 vs. 3.42, 95% CI 0.09 - 0.56). In multivariate Cox regression analysis lower platelet CXCR4 levels were independently and significantly associated with all cause mortality (HR 0.24, 95% CI 0.07 - 0.87) and the primary combined endpoint of all-cause death and/or MI (HR 0.30, 95% CI 0.13 - 0.72).
These findings highlight a potential prognostic value of platelet expression CXCR4 on clinical outcomes in patients with CAD. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Journal of Thrombosis and Haemostasis 02/2015; 13(5). DOI:10.1111/jth.12870 · 5.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objective:
Inhibition of components of the complement system or of its receptors has been postulated as a concept for primary and secondary prevention in atherosclerosis and was applied in clinical trials. Although the anaphylatoxin-receptors C3aR and C5aR are commonly associated with inflammatory cells, in vitro studies suggested their expression also on platelets.
Methods and results:
Expression levels of C3aR and C5aR were measured by flow cytometry in a collective of 302 patients with documented coronary artery disease (CAD) including patients with stable CAD (n = 152), unstable angina (n = 54), acute myocardial infarction (AMI; Non-ST elevation myocardial infarction, n = 70, ST elevation MI, n = 26) or healthy controls (n = 21). Patients with stable CAD, unstable angina or AMI had significantly higher expression of C5aR on platelets in comparison to healthy controls (MFI 14.68 (5.2), 14.56 (5.18) and 13.34 (4.52) versus 10.68 (3.1)); p < 0.001). In contrast, the expression of C3aR on platelets was significantly enhanced in patients with stable and unstable CAD but not in patients with AMI compared to controls. While there was a strong correlation between the soluble ligands of these receptors C3a and C5a, we observed only a weak correlation with their receptors on platelets. Similarly, agonist induced aggregation (MEA, ADP, and TRAP) showed only a weak correlation with the expression level of anaphylatoxin - receptors on platelets. Of note, the expression of both anaphylatoxin-receptors on platelets strongly correlated with platelet activation as assessed with the surface activation marker P-selectin (r = 0.47, p > 0.001 for C3aR, r = 0.76 for C5aR, p < 0.001). Likewise, we observed a positive correlation of C3aR with other molecules associated with platelet activation such as SDF-1.
In summary, we observed a positive correlation between the expression of anaphylatoxin-receptors C3aR and C5aR with platelet activation in patients with CAD. Further investigations are needed to study the clinical and mechanistic relevance of these findings.
[Show abstract][Hide abstract] ABSTRACT: Inflammation in the central nervous system (CNS) and disruption of its immune privilege are major contributors to the pathogenesis of multiple sclerosis (MS) and of its rodent counterpart, experimental autoimmune encephalomyelitis (EAE). We have previously identified developmental endothelial locus-1 (Del-1) as an endogenous anti-inflammatory factor, which inhibits integrin-dependent leukocyte adhesion. Here we show that Del-1 contributes to the immune privilege status of the CNS. Intriguingly, Del-1 expression decreased in chronic-active MS lesions and in the inflamed CNS in the course of EAE. Del-1-deficiency was associated with increased EAE severity, accompanied by increased demyelination and axonal loss. As compared with control mice, Del-1(-/-) mice displayed enhanced disruption of the blood-brain barrier and increased infiltration of neutrophil granulocytes in the spinal cord in the course of EAE, accompanied by elevated levels of inflammatory cytokines, including interleukin-17 (IL-17). The augmented levels of IL-17 in Del-1-deficiency derived predominantly from infiltrated CD8(+) T cells. Increased EAE severity and neutrophil infiltration because of Del-1-deficiency was reversed in mice lacking both Del-1 and IL-17 receptor, indicating a crucial role for the IL-17/neutrophil inflammatory axis in EAE pathogenesis in Del-1(-/-) mice. Strikingly, systemic administration of Del-1-Fc ameliorated clinical relapse in relapsing-remitting EAE. Therefore, Del-1 is an endogenous homeostatic factor in the CNS protecting from neuroinflammation and demyelination. Our findings provide mechanistic underpinnings for the previous implication of Del-1 as a candidate MS susceptibility gene and suggest that Del-1-centered therapeutic approaches may be beneficial in neuroinflammatory and demyelinating disorders.Molecular Psychiatry advance online publication, 11 November 2014; doi:10.1038/mp.2014.146.
[Show abstract][Hide abstract] ABSTRACT: The Bcl-2 proteins Bax and Bak can permeabilize the outer mitochondrial membrane and commit cells to apoptosis. Pro-survival Bcl-2 proteins control Bax by constant retrotranslocation into the cytosol of healthy cells. The stabilization of cytosolic Bax raises the question whether the functionally redundant but largely mitochondrial Bak shares this level of regulation. Here we report that Bak is retrotranslocated from the mitochondria by pro-survival Bcl-2 proteins. Bak is present in the cytosol of human cells and tissues, but low shuttling rates cause predominant mitochondrial Bak localization. Interchanging the membrane anchors of Bax and Bak reverses their subcellular localization compared to the wild-type proteins. Strikingly, the reduction of Bax shuttling to the level of Bak retrotranslocation results in full Bax toxicity even in absence of apoptosis induction. Thus, fast Bax retrotranslocation is required to protect cells from commitment to programmed death.
The EMBO Journal 11/2014; 34(1). DOI:10.15252/embj.201488806 · 10.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Targeted contrast-enhanced ultrasound (CEU) using microbubble agents is a promising non-invasive imaging technique to evaluate atherosclerotic lesions. In this study, we decipher the diagnostic and therapeutic potential of targeted-CEU with soluble glycoprotein (GP)-VI in vivo. Microbubbles were conjugated with the recombinant fusion protein GPVI-Fc (MBGPVI) that binds with high affinity to atherosclerotic lesions. MBGPVI or control microbubbles (MBC) were intravenously administered into ApoE(-/-) or wild type mice and binding of the microbubbles to the vessel wall was visualized by high-resolution CEU. CEU molecular imaging signals of MBGPVI were substantially enhanced in the aortic arch and in the truncus brachiocephalicus in ApoE(-/-) as compared to wild type mice. High-frequency ultrasound (HFU)-guided disruption of MBGPVI enhanced accumulation of GPVI in the atherosclerotic lesions, which may interfere with atheroprogression. Thus, we establish targeted-CEU with soluble GPVI as a novel non-invasive molecular imaging method for atherosclerosis. Further, HFU-guided disruption of GPVI-targeted microbubbles is an innovate therapeutic approach that potentially prevents progression of atherosclerotic disease.
[Show abstract][Hide abstract] ABSTRACT: Rationale:
Macrophage migration inhibitory factor (MIF) is released on platelet activation. Circulating MIF could potentially regulate platelets and thereby platelet-mediated inflammatory and regenerative mechanisms. However, the effect of MIF on platelets is unknown.
The present study evaluated MIF in regulating platelet survival and thrombotic potential.
Methods and results:
MIF interacted with CXCR4-CXCR7 on platelets, defining CXCR7 as a hitherto unrecognized receptor for MIF on platelets. MIF internalized CXCR4, but unlike CXCL12 (SDF-1α), it did not phosphorylate Erk1/2 after CXCR4 ligation because of the lack of CD74 and failed in subsequent CXCR7 externalization. MIF did not alter the activation status of platelets. However, MIF rescued platelets from activation and BH3 mimetic ABT-737-induced apoptosis in vitro via CXCR7 and enhanced circulating platelet survival when administered in vivo. The antiapoptotic effect of MIF was absent in Cxcr7(-/-) murine embryonic cells but pronounced in CXCR7-transfected Madin-Darby canine kidney cells. This prosurvival effect was attributed to the MIF-CXCR7-initiated PI3K-Akt pathway. MIF induced CXCR7-Akt-dependent phosphorylation of BCL-2 antagonist of cell death (BAD) both in vitro and in vivo. Consequentially, MIF failed to rescue Akt(-/-) platelets from thrombin-induced apoptosis when challenged ex vivo, also in prolonging platelet survival and in inducing BAD phosphorylation among Akt(-/-) mice in vivo. MIF reduced thrombus formation under arterial flow conditions in vitro and retarded thrombotic occlusion after FeCl3-induced arterial injury in vivo, an effect mediated through CXCR7.
MIF interaction with CXCR7 modulates platelet survival and thrombotic potential both in vitro and in vivo and thus could regulate thrombosis and inflammation.
Circulation Research 09/2014; 115(11). DOI:10.1161/CIRCRESAHA.115.305171 · 11.02 Impact Factor