Stefano Conte

Activating stimuli induce platelet microRNA modulation and proteome reorganisation

Platelets carry megakaryocyte-derived mRNAs whose translation efficiency before and during activation is not known, although this can greatly affect platelet functions, both under basal conditions and in response to physiological and pathological stimuli, such as those involved in acute coronary syndromes. Aim of the present study was to determine whether changes in microRNA (miRNA) expression occur in response to activating stimuli and whether this affects activity and composition of platelet transcriptome and proteome. Purified platelet-rich plasmas from healthy volunteers were collected and activated with ADP, collagen, or thrombin receptor activating peptide. Transcriptome analysis by RNA-Seq revealed that platelet transcriptome remained largely unaffected within the first 2 hours of stimulation. In contrast, quantitative proteomics showed that almost half of > 700 proteins quantified were modulated under the same conditions. Global miRNA analysis indicated that reorganisation of platelet proteome occurring during activation reflected changes in mature miRNA expression, which therefore, appears to be the main driver of the observed discrepancy between transcriptome and proteome changes. Platelet functions significantly affected by modulated miRNAs include, among others, the integrin/cytoskeletal, coagulation and inflammatory-immune response pathways. These results demonstrate a significant reprogramming of the platelet miRNome during activation, with consequent significant changes in platelet proteome and provide for the first time substantial evidence that fine-tuning of resident mRNA translation by miRNAs is a key event in platelet pathophysiology.

The complex puzzle underlying the pathophysiology of acute coronary syndromes: from molecular basis to clinical manifestations

Acute coronary syndromes (ACS) still represent a major cause of death in Western countries; in the vast majority of cases, coronary atherosclerosis represents the common pathological lesion to all forms of ACS. It is currently believed that plaque complication (rupture, fissuration, and so on), with the consequent superimposed thrombosis, is a key factor ultimately leading to the clinical occurrence of ACS. Over the last two decades, our understanding of the basic mechanisms involved in the pathophysiology of ACS has progressed significantly and the crucial role of inflammation in this phenomenon is now widely recognized. The sequence of events is represented by plaque complication (i.e., rupture, fissuration or erosion), exposure of tissue factor and other prothrombotic substances, such as von Willebrand factor and collagen, to the blood flow, activation of platelets and of the coagulation cascade and thrombus formation within the coronary artery. However, not all complicated plaques cause the clinical occurrence of ACS and similar complicated plaques may cause different clinical manifestations. A complex interaction between different factors, such as arterial vessel wall substrates, degree of inflammation of the culprit lesion, local rheological characteristics of blood flow, as well as factors present in the circulating blood, will determine the severity (complete vs incomplete occlusion) and the persistence of coronary blood flow cessation, which, in turn, will be largely responsible for the clinical picture. Targeting tissue factor, the key player in the activation of the coagulation cascade, may represent an important therapeutic strategy to prevent the clinical manifestation of ACS.

The adipokine apelin-13 induces expression of prothrombotic tissue factor

Adipocytes are cells able to produce and secrete several active substances (adipokines) with direct effects on vascular cells. Apelin, one of the most recently identified adipokines has been studied in cardiovascular system physiology in regard to vessel vasodilation and myocardial contraction, but it has not yet completely characterised for its pathophysiological role in cardiovascular disease and especially in acute coronary syndromes (ACS). Several studies have indicated that tissue factor (TF) plays a pivotal role in the pathophysiology of ACS by triggering the formation of intracoronary thrombi following endothelial injury. This study investigates the effects of apelin 12 and apelin 13 on TF in human umbilical endothelial cells (HUVECs) and monocytes. Cells were stimulated with increasing concentrations of apelin 12 or apelin 13 and then processed to evaluate TF-mRNA levels by real-time PCR as well as TF expression/activity by FACS analysis and pro-coagulant activity. Finally, a potential molecular pathway involved in modulating this phenomenon was investigated. We demonstrate that apelin 13 but not apelin 12 induces transcription of mRNA for TF. In addition, we show that this adipokine promotes surface expression of TF that is functionally active. Apelin 13 effects on TF appear modulated by the activation of the G-protein-transcription factor nuclear factor (NF)-κB axis since G-protein inhibitors suppressed NF-κB mediated TF expression. Data of the present study, although in vitro, indicate that apelin-13, induces a procoagulant phenotype in HUVECs and monocytes by promoting TF expression. These observations support the hypothesis that this adipokine might play a relevant role as an active partaker in athero-thrombotic disease.

Pregnancy-associated plasma protein-A promotes TF procoagulant activity in human endothelial cells by Akt–NF-κB axis

Pregnancy-associated plasma protein-A (PAPP-A) is a metalloproteinase with a controversial role in pathophysiology of cardiovascular disease. It seems involved in progression of atherosclerosis and is widely represented in atherosclerotic plaque. PAPP-A plasma levels are elevated in patients with acute coronary syndromes (ACS), thus it has been suggested that it might be a prognostic marker for developing major cardiovascular events. However, the pathophysiological link(s) between PAPP-A and ACS are still unknown. Several studies have indicated that tissue factor (TF) plays a pivotal role in the pathophysiology of ACS by triggering the formation of intracoronary thrombi following endothelial injury. This study investigates whether PAPP-A, at concentrations measurable in ACS patients, might induce TF expression in human endothelial cells in culture (HUVEC). In HUVEC, PAPP-A induced TF-mRNA transcription as demonstrated by real time PCR and expression of functionally active TF as demonstrated by FACS analysis and pro-coagulant activity assay. PAPP-A induced TF expression through the activation of Akt/NF-κB axis, as demonstrated by luciferase assay and by suppression of TF-mRNA transcription as well as of TF expression/activity by Akt and NF-κB inhibitors. These data indicate that PAPP-A promotes TF expression in human endothelial cells and support the hypothesis that this proteinase, besides being involved in progression of atherosclerosis, does not represent an independent risk factor for adverse cardiovascular events, but it rather might play an “active” role in the pathophysiology of ACS as an effector molecule able to induce a pro-thrombotic phenotype in endothelial cells.

Expression of functional tissue factor in activated T-lymphocytes in vitro and in vivo: A possible contribution of immunity to thrombosis?

OBJECTIVE T-lymphocyte activation plays an important role in the pathophysiology of acute coronary syndromes (ACS). Plaques from ACS patients show a selective oligoclonal expansion of T-cells, indicating a specific, antigen-driven recruitment of T-lymphocytes within the unstable lesions. At present, however, it is not known whether T-cells may contribute directly to thrombosis by expressing functional tissue factor (TF). Accordingly, the aim of the present study was to investigate whether T-cells are able to express functional TF in their activated status. METHODS In vitro, CD3(+)-cells, isolated from buffy coats, were stimulated with anti-CD3/CD28 beads, IL-6, TNF-α, IL-17, INF-γ or PMA/ionomycin. Following stimulation, TF expression on cell-surface, at gene and protein levels, as well as its procoagulant activity in whole cells and microparticles was measured. In vivo, TF expression was evaluated in CD3(+)-cells isolated from the aorta and the coronary sinus of ACS-NSTEMI and stable coronary artery disease (SCAD) patients. The presence of CD3(+)-TF(+)cells was also evaluated by immunohistochemistry in thrombi aspirated from ACS-STEMI patients. RESULTS PMA/ionomycin and IL-17 plus INF-γ stimulation resulted in a significant TF increase at gene and protein levels as well as at cell-surface expression. This was accompanied by a parallel increase in FXa generation, both in whole cells and in microparticles, indicating that the induced membrane-bound TF was active. Furthermore, transcardiac TF gradient was significantly higher in CD3(+)-cells obtained from ACS-patients compared to SCAD-patients. Interestingly, thrombi from ACS-STEMI patients resulted enriched in CD3(+)-cells, most of them expressing TF. CONCLUSIONS Our data demonstrate that activated T-lymphocytes in vitro express functional TF on their membranes, suggesting a direct pathophysiological role of these cells in the thrombotic process; this hypothesis is further supported by the observations in vivo that CD3(+)-cells from coronary circulation of ACS-NSTEMI patients show increased TF levels and that coronary thrombi from ACS-STEMI patients are enriched in CD3(+)-cells expressing TF.

Pregnancy-Associated Plasma Protein-A and its Role in Cardiovascular Disease. Biology, Experimental/Clinical Evidences and Potential Therapeutic Approaches

Pregnancy-Associated Plasma Protein-A (PAPP-A) is a zinc-binding metalloproteinase protein produced by placental syncytio-trophoblasts and secreted into the maternal circulation where its concentration progressively increases until term. In recent years, PAPP-A has been studied for its potential involvement in cardiovascular (CV) disease. However, all those studies did not provide a clear view to identify the pathophysiological links between PAPP-A plasma levels and the occurrence of CV events. In this review, starting from a complete description of PAPP-A structure and biology, we present an updated overview of experimental as well as clinical evidence on the role of this metalloproteinase in CV disease. Finally, we discuss possible therapeutic approaches to antagonize its potential detrimental CV effects.

Nobiletin inhibits oxidized-LDL mediated expression of Tissue Factor in human endothelial cells through inhibition of NF-κB

INTRODUCTION Flavonoids are nutrients usually included in human diet with several significant biological activities. Nobiletin is a flavonoid that, besides having anti‐inflammatory and anti‐tumoral activity, seems to exert protective effects on cardiovascular system. Several studies investigated nobiletin as a natural drug to antagonize the atherosclerotic disease. On the contrary, literature about its potential role in modulating the main acute complication of atherosclerosis, thrombosis, is still scanty. Several studies have indicated that Tissue Factor (TF) plays a pivotal role in the pathophysiology of cardiovascular thrombotic events by triggering the formation of intracoronary thrombi. Oxidized‐LDL have an important role in promoting athero‐thrombotic events. This study investigates whether nobiletin might exert protective cardiovascular effects by preventing the oxidized‐LDL mediated expression of TF in human endothelial cells in vitro. Moreover, we have studied whether the nobiletin effects might be modulated by the inhibition of the NF‐&kgr;B pathway. METHODS AND RESULTS In HUVEC, ox‐LDL induced TF‐mRNA transcription as demonstrated by real time PCR and expression of functionally active TF as demonstrated by Western‐blot, FACS analysis and pro‐coagulant activity assay. Nobiletin prevented these ox‐LDL‐mediated effects by exerting antioxidant effects, finally leading to inhibition of the transcription factor NF‐&kgr;B. CONCLUSIONS These data suggest that nobiletin might be a potential antithrombotic agent of dietary origin. This flavonoid, through its antioxidant proprieties, might potentially exert an antithrombotic activity by inhibiting TF expression/activity in a cell population never investigated before in this context and that is normally represented in vessel wall such as endothelial cells.

Colchicine reduces platelet aggregation by modulating cytoskeleton rearrangement via inhibition of cofilin and LIM domain kinase 1

INTRODUCTION Platelets activation/aggregation with subsequent thrombus formation is the main event in the pathophysiology of acute coronary syndrome. Once activated, platelets show an extensive cytoskeleton rearrangement that leads to recruitment of additional platelets to finally cause haemostatic plug formation. Thus, the cytoskeleton plays a pivotal role in this phenomenon. Colchicine (COLC) is an anti-inflammatory drug proven to reduce major cardiovascular events in patients with coronary artery disease. The molecular mechanisms by which COLC exerts these protective effects remain partially still unknown. Since COLC causes disruption of tubulin, a component of cell cytoskeleton, we investigated whether this drug might interfere with platelet aggregation by acting on cytoskeleton rearrangement. METHODS AND RESULTS Platelets isolated from healthy volunteers were activated with Adenosine Diphosphate (ADP, 20 μM) Collagen (COLL, 60 μg/ml) and Thrombin Activating Receptor Peptide (TRAP 25 μM) with/without COLC 10 μM pretreatment. After stimulus, aggregation was measured by light aggregometry overtime. Microtubules structure was assessed by immunohistochemistry and key proteins involved in regulation of actin-filament assembly and contractility such as Myosin Phosphatase Targeting subunit (MYPT), LIM domain kinase 1(LIMK1) and cofilin were evaluated by Western Blot analysis. Colchicine pretreatment significantly blunted ADP/COLL/TRAP-induced platelet aggregation (up to 40%). COLC effects appeared mediated by microtubules depolymerization and cytoskeleton disarrangement associated to inactivation of MYPT and LIMK1 that finally interfered with cofilin activity. CONCLUSIONS Our data indicate that colchicine exerts anti-platelet effects in vitro via inhibition of key proteins involved in cytoskeleton rearrangement, suggesting that its beneficial cardiovascular properties may be due, at least in part, to an inhibitory effect of platelet activity.

COLCHICINE EXERTS ANTITHROMBOTIC PROPERTIES IN OXLDL-TREATED ENDOTHELIAL CELLS VIA INHIBITION OF TISSUE FACTOR EXPRESSION AND ACTIVITY

Background: Tissue factor (TF) exposure is the key trigger of thrombus formation. Oxidized low-density lipoproteins (oxLDL) induce TF in endothelial cells (ECs), suggesting that oxLDL may act locally promoting thrombosis in atherosclerotic lesions. Colchicine (COL) is an anti-inflammatory agent that