Platelet CD40L mediates thrombotic and inflammatory processes in atherosclerosis

Platelets orchestrate remote tissue damage after mesenteric ischemia-reperfusion

Ischemia-reperfusion (I/R) injury is a leading cause of morbidity and mortality. A functional role for platelets in tissue damage after mesenteric I/R is largely unknown. The hypothesis that mesenteric I/R local and remote injury are platelet dependent was tested. Using a murine mesenteric I/R model, we demonstrate that platelets orchestrate remote lung tissue damage that follows mesenteric I/R injury and also contribute, albeit to a lesser degree, to local villi damage. While lung damage is delayed compared with villi damage, it increased over time and was characterized by accumulation of platelets in the pulmonary vasculature early, followed by alveolar capillaries and extravasation into the pulmonary space. Both villi and lung tissues displayed complement deposition. We demonstrate that villi and lung damage are reduced in mice made platelet deficient before I/R injury and that platelet transfusion into previously platelet-depleted mice before I/R increased both villi and lung tissue damage. Increased C3 deposition accompanied platelet sequestration in the lung, which was mostly absent in platelet-depleted mice. In contrast, C3 deposition was only minimally reduced on villi of platelet-depleted mice. Our findings position platelets alongside complement as a significant early upstream component that orchestrates remote lung tissue damage after mesenteric I/R and strongly suggest that reperfusion injury mitigating modalities should consider the contribution of platelets.

Platelets and atherogenesis: Platelet anti-aggregation activity and endothelial protection from tomatoes (Solanum lycopersicum L.)

In recent years, it has been shown that platelets are not only involved in the arterial thrombotic process, but also that they play an active role in the inflammatory process of atherogenesis from the beginning. The interaction between platelets and endothelial cells occurs in two manners: activated platelets unite with intact endothelial cells, or platelets in resting adhere to activated endothelium. In this context, inhibition of the platelet function (adhesion/aggregation) could contribute to the prevention of atherothrombosis, the leading cause of cardiovascular morbidity. This can be achieved with antiplatelet agents. However, at the public health level, the level of primary prevention, a healthy diet has also been shown to exert beneficial effects. Among those elements of a healthy diet, the consumption of tomatoes (Solanum lycopersicum L.) stands out for its effect on platelet anti-aggregation activity and endothelial protection, which may be beneficial for cardiovascular health. This article briefly discusses the involvement of platelets in atherogenesis and the possible mechanisms of action provided by tomatoes for platelet anti-aggregation activity and endothelial protection.

Oral versus vaginal combined hormonal contraceptives' effect on coagulation and inflammatory biomarkers among young adult women

In order to compare the effect of combined oral contraceptive (COC) and combined vaginal contraceptive (CVC) methods on the inflammation and procoagulation, we recruited female participants in 3 groups: control participants, COC users, and CVC users. We measured different blood biomarkers. The users of both COC and CVC had higher levels of C-reactive protein (P < .0001) and factor VII (P < .0001). However, CD40 ligand was only higher for COC users (P < .0001) and not the CVC users. Even though the levels of thrombin/antithrombin III were not higher for COC and CVC users, as compared to the controls, CVC users had higher levels as compared to COC users (P = .0327). As compared to the control group, we observed higher levels von Willebrand factor among CVC users but not the COC users. Longitudinal studies with larger sample size are needed to better assess the inflammatory and procoagulation response due to CVC use.

Platelet-associated CD40/CD154 mediates remote tissue damage after mesenteric ischemia/reperfusion injury

Several innate and adaptive immune cell types participate in ischemia/reperfusion induced tissue injury. Amongst them, platelets have received little attention as contributors in the process of tissue damage after ischemia reperfusion (I/R) injury. It is currently unknown whether platelets participate through the immunologically important molecules including, CD40 and when activated, CD154 (CD40L), in the pathogenesis of I/R injury. We hypothesized that constitutive expression of CD40 and activation-induced expression of CD154 on platelets mediate local mesenteric and remote lung tissue damage after I/R injury. Wild type (WT; C57BL/6J), CD40 and CD154 deficient mice underwent mesenteric ischemia for 30 minutes followed by reperfusion for 3 hours. WT mice subjected to mesenteric I/R injury displayed both local intestinal and remote lung damage. In contrast, there was significantly less intestinal damage and no remote lung injury in CD40 and CD154 deficient mice when compared to WT mice. Platelet-depleted WT mice transfused with platelets from CD40 or CD154 deficient mice failed to reconstitute remote lung damage. In contrast, when CD40 or CD154 deficient mice were transfused with WT platelets lung tissue damage was re-established. Together, these findings suggest that multiple mechanisms are involved in local and remote tissue injury and also identify platelet-expressed CD40 and/or CD154 as mediators of remote tissue damage.

Effector Memory T cells Are Associated With Atherosclerosis in Humans and Animal Models

BACKGROUND#ENTITYSTARTX02014;: Adaptive T-cell response is promoted during atherogenesis and results in the differentiation of naïve CD4(+)T cells to effector and/or memory cells of specialized T-cell subsets. Aim of this work was to investigate the relationship between circulating CD4(+)T-cell subsets and atherosclerosis. METHODS AND RESULTS#ENTITYSTARTX02014;: We analyzed 57 subsets of circulating CD4(+)T cells by 10-parameter/8-color polychromatic flow cytometry (markers: CD3/CD4/CD45RO/CD45RA/CCR7/CCR5/CXCR3/HLA-DR) in peripheral blood from 313 subjects derived from 2 independent cohorts. In the first cohort of subjects from a free-living population (n=183), effector memory T cells (T(EM): CD3(+)CD4(+)CD45RA(-)CD45RO(+)CCR7(-) cells) were strongly related with intima-media thickness of the common carotid artery, even after adjustment for age (r=0.27; P<0.001). Of note, a significant correlation between T(EM) and low-density lipoproteins was observed. In the second cohort (n=130), T(EM) levels were significantly increased in patients with chronic stable angina or acute myocardial infarction compared with controls. HLA-DR(+)T(EM) were the T(EM) subpopulation with the strongest association with the atherosclerotic process (r=0.37; P<0.01). Finally, in animal models of atherosclerosis, T(EM) (identified as CD4(+)CD44(+)CD62L(-)) were significantly increased in low-density lipoprotein receptor and apolipoprotein E deficient mice compared with controls and were correlated with the extent of atherosclerotic lesions in the aortic root (r=0.56; P<0.01). CONCLUSIONS#ENTITYSTARTX02014;: Circulating T(EM) cells are associated with increased atherosclerosis and coronary artery disease in humans and in animal models and could represent a key CD4(+)T-cell subset related to the atherosclerotic process. (J Am Heart Assoc. 2012;1:27-41.).

MicroRNAs in the regulation of immune cell functions--implications for atherosclerotic vascular disease

Regarded as a chronic inflammatory disease of the vessel wall, the development of atherosclerotic lesions is shaped by immune responses and their regulation. Macrophages and dendritic cells are positioned at the crossroad of innate and adaptive immune responses by sensing atherogenic danger signals and by taking up and presenting antigens. T helper cells and auto-antibodies produced by B cells, together with their cytokine responses in turn modulate atheroprogression. In addition, platelets contribute to atherosclerosis by multiple pathways. microRNAs (miRNAs) that post-transcriptionally regulate gene expression may thus critically control immune cell differentiation and functions during plaque evolution. This review summarises the role of miRNAs in regulating lipid uptake and expression of inflammatory mediators in monocytes/macrophages and dendritic cells, in lymphocyte functions with a focus on T helper cell responses, as well as in platelet biology, and the implications of altering these functions in vascular pathology and atherosclerosis. T systematically survey miRNA functions in controlling molecular mechanisms and immune responses in atherosclerosis holds potential for the development of novel miRNA-based strategies for therapies targeting inflammation and immunity in atherosclerosis.

Platelets: a critical link between inflammation and microvascular dysfunction

Inflammation is an underlying feature of a variety of human diseases. An important manifestation of this pathophysiological response is microvascular dysfunction, which includes the activation of vascular endothelial cells, and circulating leucocytes and platelets. While endothelial cells and leucocytes are widely accepted as critical players in the microvascular alterations induced by inflammation, recent attention has focused on the modulatory role of platelets, which act both as effector and target cells in inflamed microvessels. Evidence is presented to demonstrate the capacity for 'cross-talk' between platelets and other cells (endothelial cells, leucocytes) that contribute to an inflammatory response, and to illustrate the pathophysiological consequences of these interactions of platelets with other cells within the microvasculature.

TNF superfamily in inflammatory disease: translating basic insights

The tumor necrosis factor (TNF) and TNF receptor superfamilies (TNFSF and TNFRSF) consist of approximately 50 membrane and soluble proteins that can modulate cellular function. Most of these molecules are expressed by or can target cells of the immune system, and they have a wide range of actions including promoting cellular differentiation, survival, and production of inflammatory cytokines and chemokines. Emerging data show that TNFSF ligand-receptor signaling pathways are active in inflammatory and autoimmune disease. Furthermore, several genetic polymorphisms in TNFSF and TNFRSF associate with susceptibility to developing disease. Here, we examine recent data regarding the potential of these molecules as targets for therapy of autoimmune and inflammatory disease.

Platelet soluble CD40L and matrix metalloproteinase 9 activity are proinflammatory mediators in Behçet disease patients

Platelets are the major source of plasma-soluble CD40L (sCD40L), an important inflammatory mediator. This study explored the impact of platelet-derived sCD40L on Behçet disease (BD), an autoinflammatory vasculitis. We also searched for influences by platelet matrix metalloproteinases (MMP) -2 and MMP-9, implicated in several inflammatory diseases, on CD40L shedding from platelet membrane. Platelet activation were studied by flow cytometry and aggregometry, surface expression of CD40L and platelet-leukocyte aggregates by flow cytometry, sCD40L by ELISA, cellular CD40L and CD40 levels by Western blot and MMPs activity by gelatin zymography. The effect of sCD40L on MMP9 expression was studied in cultured MEG-01 cells. Plasma and platelet-released sCD40L levels were higher in BD patients. No differences in platelet activation and in platelet-leukocyte aggregates formation were observed between BD patients and controls. Plasma and platelet MMP-9 levels were increased in BD patients, whereas there was no difference in platelet MMP-2 activity. Since a correlation between plasma sCD40L and platelet MMP-9 activity was observed, we studied the influence of sCD40L on MMP-9 levels in the megakaryoblastic cell line MEG-01. Treatment of MEG-01 cells with recombinant sCD40L increased MMP-9 but did not change MMP-2 levels. In conclusion, sCD40L release from platelets was mediated by MMP-9, and MMP-9 expression was in turn upregulated by sCD40L in the MEG-01 cell line. We conclude that platelets and megakaryocytes might participate in a positive feedback loop occurring between sCD40L and MMP-9 which would contribute to the proinflammatory state observed in BD.

Atherosclerosis: current pathogenesis and therapeutic options

Coronary artery disease (CAD) arising from atherosclerosis is a leading cause of death and morbidity worldwide. The underlying pathogenesis involves an imbalanced lipid metabolism and a maladaptive immune response entailing a chronic inflammation of the arterial wall. The disturbed equilibrium of lipid accumulation, immune responses and their clearance is shaped by leukocyte trafficking and homeostasis governed by chemokines and their receptors. New pro- and anti-inflammatory pathways linking lipid and inflammation biology have been discovered, and genetic profiling studies have unveiled variations involved in human CAD. The growing understanding of the inflammatory processes and mediators has uncovered an intriguing diversity of targetable mechanisms that can be exploited to complement lipid-lowering therapies. Here we aim to systematically survey recently identified molecular mechanisms, translational developments and clinical strategies for targeting lipid-related inflammation in atherosclerosis and CAD.

Chemokines: established and novel targets in atherosclerosis

In their role as small chemotactic cytokines, chemokines are crucial mediators and regulators of leukocyte trafficking during immune surveillance and inflammation. Their involvement in the development and progression of inflammatory diseases has been subject of intense investigation. Concordantly, the chemokine system has been explored in search for therapeutic targets to prevent or treat inflammatory disorders, such as atherosclerosis. Targeting the chemokine system offers various entry points for a causative treatment of this widespread and chronic illness. Although this approach has encountered some setbacks, several innovative compounds are currently in an advanced stage of development. In this review, the current standing of this dynamic field is highlighted and the potential advantages and drawbacks of particular strategies are discussed.

Platelet dysfunction in vascular pathologies and how can it be treated

Cardiovascular diseases are one of the leading causes of morbidity and mortality in industrialized countries, and although many processes play a role in the development of vascular disease, thrombosis is the primary event that precipitates stroke and acute coronary syndromes. The blood platelets are of significant importance in medicine. These cells are involved in many physiological processes, particularly haemostasis through their ability to aggregate and form clots in response to activation. In addition, these dynamic cells display activities that extend beyond thrombosis, including an important role in initiating and sustaining vascular inflammation. The expansion of knowledge from basic and clinical research has highlighted the critical position of platelets in several inflammatory diseases such as arthritis and atherosclerosis. Platelets are emerging as important mediators of inflammation and provide important signals to mediate phenotype of other blood and vascular cells. The important role of platelets in arterial thrombosis and the onset of acute myocardial infarction after atherosclerotic plaque rupture make inhibition of platelet aggregation a critical step in preventing thrombotic events associated with stroke, heart attack, and peripheral arterial thrombosis. However, the use of platelet inhibitors for thrombosis prevention must seek a delicate balance between inhibiting platelet activation and an associated increased bleeding risk. The aim of this review is to up-date the knowledge on platelets physiology and dysfunction in pathologies, such as diabetes mellitus, hypercholesterolemia, and hypertension, emphasizing the link between platelets and the inflammation-related atherosclerosis. The review evaluates the opportunities offered by the novel platelet inhibitors to efficiently alleviate the thrombotic events.

The role of CD40/CD40 ligand interactions in bone marrow granulopoiesis

The CD40 ligand (CD40L) and CD40 are two molecules belonging to the TNF/TNF receptor superfamily, and their role in adaptive immune system has widely been explored. However, the wide range of expression of these molecules on hematopoietic as well as nonhematopoietic cells has revealed multiple functions of the CD40/CD40L interactions on different cell types and processes such as granulopoiesis. CD40 triggering on stromal cells has been documented to enhance the expression of granulopoiesis growth factors such as granulocyte-colony-stimulating factor (G-CSF) and granulocyte/monocyte-colony-stimulating factor (GM-CSF), and upon disruption of the CD40/CD40L-signaling pathway, as in the case of X-linked hyperimmunoglobulin M (IgM) syndrome (XHIGM), it can lead to neutropenia. In chronic idiopathic neutropenia (CIN) of adults, however, under the influence of an inflammatory microenvironment, CD40L plays a role in granulocytic progenitor cell depletion, providing thus a pathogenetic cause of CIN.

Platelets in atherosclerosis

Beyond obvious functions in haemostasis and thrombosis, platelets are considered to be essential in proinflammatory surroundings such as atherosclerosis, allergy, rheumatoid arthritis and even cancer. In atherosclerosis, platelets facilitate the recruitment of inflammatory cells towards the lesion sites and release a plethora of inflammatory mediators, thereby enriching and boosting the inflammatory milieu. Platelets do so by interacting with endothelial cells, circulating leukocytes (monocytes, neutrophils, dendritic cells, T-cells) and progenitor cells. This cross-talk enforces leukocyte activation, adhesion and transmigration. Furthermore, platelets are known to function in innate host defense through the release of antimicrobial peptides and the expression of pattern recognition receptors. In severe sepsis, platelets are able to trigger the formation of neutrophil extracellular traps (NETs), which bind and clear pathogens. The present antiplatelet therapies that target key pathways of platelet activation and aggregation therefore hold the potential to modulate platelet-derived immune functions by reducing cellular interactions of platelets with other immune components and by reducing the secretion of inflammatory proteins into the milieu. The objective of this review is to update and discuss the current perceptions of the platelet immune constituents and their prospect as therapeutic targets in an atherosclerotic setting.

Platelet activation in chronic cocaine users: effect of short term abstinence

Cocaine abuse increases the risk of cardiac and cerebrovascular events, such as myocardial infarction and ischemic stroke. The underlying mechanisms leading to these complications are not fully understood although intravascular thrombus formation has been observed. The aim of this study was to investigate the existence of platelet activation and the effect of short-term abstinence in chronic cocaine consumers. We studied 23 cocaine dependent individuals (aged 20-54 years) who met DSM-IV criteria for cocaine dependence and 20 controls. Samples were obtained at baseline, within 72 h of last drug exposure and after 4 weeks of controlled abstinence. Monocyte-platelet aggregates (MPA) were measured by flow cytometry. Plasma levels of soluble CD40L (sCD40L), Neutrophil-Activating Peptide-2 (NAP-2) and regulated on activation normal T cells expressed and secreted (RANTES) were determined by ELISA. Levels of MPA, sCD40L, NAP-2 and RANTES were significantly higher (all p < 0.05) in cocaine addicts compared to controls at baseline. All the parameters returned to values similar to the control group after 4-weeks' abstinence. Levels of sCD40L and RANTES were associated with an index of intensity of drug consumption (p < 0.02). Our results demonstrate that cocaine use induces platelet activation which is a prominent finding after recent consumption. The persistence over time of this condition may contribute not only to acute thrombotic complications but also to the development of early-onset atherosclerotic process observed in cocaine abusers.

The CD40-CD40L system in cardiovascular disease

The CD40-CD40L system is a pathway which is associated with both prothrombotic and proinflammatory effects. CD40 and its ligand were first discovered on the surface of activated T cells, but its presence on B cells, antigen-presenting cells, mast cells, and finally platelets, is evident. The soluble form of CD40L (sCD40L) is derived mainly from activated platelets and contributes to the pathophysiology of atherosclerosis and atherothrombosis. Indeed, sCD40L has autocrine, paracrine, and endocrine activities, and it enhances platelet activation, aggregation, and platelet-leucocyte conjugation that may lead to atherothrombosis. It has even been suggested that sCD40L may play a pathogenic role in triggering acute coronary syndromes. Conversely, blockade of this pathway with anti-CD40L antibodies may prevent or delay the progression of atherosclerosis. Concentrations of sCD40L also predict risk of future cardiovascular disease in healthy women and clinical outcomes in patients with acute coronary syndromes. However, there are controversial and uncertain points over the application of this biomarker to clinical cardiology. In this review, we provide an overview of potential implications of CD40-CD40L signalling and sCD40L as a biomarker in patients with atherosclerotic vascular diseases.

Platelets and the innate immune system: mechanisms of bacterial-induced platelet activation

It has become clear that platelets are not simply cell fragments that plug the leak in a damaged blood vessel; they are, in fact, also key components in the innate immune system, which is supported by the presence of Toll-like receptors (TLRs) on platelets. As the cells that respond first to a site of injury, they are well placed to direct the immune response to deal with any resulting exposure to pathogens. The response is triggered by bacteria binding to platelets, which usually triggers platelet activation and the secretion of antimicrobial peptides. The main platelet receptors that mediate these interactions are glycoprotein (GP)IIb-IIIa, GPIbα, FcγRIIa, complement receptors, and TLRs. This process may involve direct interactions between bacterial proteins and the receptors, or can be mediated by plasma proteins such as fibrinogen, von Willebrand factor, complement, and IgG. Here, we review the variety of interactions between platelets and bacteria, and look at the potential for inhibiting these interactions in diseases such as infective endocarditis and sepsis.

CD40 ligand: a neo-inflammatory molecule in vascular diseases

CD40 Ligand (CD40L), a member of the TNF family, was initially thought to be solely implicated in thymus-dependent humoral responses. However, work by several groups showed that CD40L plays a more global role in various systems. Recent evidence has outlined an important role for CD40L in the physiopathology of the vascular system. Indeed, by interacting with its principal receptor, CD40, or with the recently identified receptors, namely αIIbβ3, α5β1, and Mac-1 integrins, CD40L displayed many biological functions in different types of vascular cells. In addition, the CD40L system was demonstrated a major player in the pathology of vascular diseases, such as atherosclerosis and restenosis. This review outlines the expression pattern and the functional properties of CD40L and its receptors at different cellular levels in the vascular system. In addition, we thoroughly describe evidence showing the implication of CD40L interactions in atherosclerosis, restenosis, and their associated clinical complications.

Intravital imaging of phagocyte recruitment

Extravasation of neutrophils and monocytes is a hallmark event in acute and chronic inflammation. Owing to recent improvements in optical imaging techniques, the classical leukocyte extravasation cascade has been refined with intermediate steps being added. Further studies have shown tissue specific leukocyte recruitment patterns, thus allowing for more selective targeting. Here we focus on recent advances in intravital imaging of leukocyte recruitment by means of optical imaging techniques and emphasise the translation thereof into tissue-specific recruitment to the lungs, the liver and large arteries.

Platelet CD40L at the interface of adaptive immunity

Initiated by the finding that platelets express functional CD40 ligand (CD40L, CD154), many new roles for platelets have been discovered in unanticipated areas, including the immune response. When current literature is considered as a whole, the picture that is emerging begins to show that platelets are able to significantly affect, for better or worse, the overall health and condition of the mammalian host. Animal models have made significant contributions to our expanding knowledge of platelet function, much of which is anticipated to be clinically relevant. While still mostly circumstantial, the evidence supports a critical role for CD40L in many normal and disease processes.