miR-204-5p and Platelet Function Regulation: Insight into a Mechanism Mediated by CDC42 and GPIIbIIIa.

BACKGROUND: Several platelet-derived microRNAs are associated with platelet reactivity (PR) and clinical outcome in cardiovascular patients. We previously showed an association between miR-204-5p and PR in stable cardiovascular patients, but data on functional mechanisms are lacking. AIMS: To validate miR-204-5p as a regulator of PR in platelet-like structures (PLS) derived from human megakaryocytes and to address mechanistic issues. METHODS: Human hematopoietic stem cells were differentiated into megakaryocytes, enabling the transfection of miR-204-5p and the recovery of subsequent PLS. The morphology of transfected megakaryocytes and PLS was characterized using flow cytometry and microscopy. The functional impact of miR-204-5p was assessed using a flow assay, the quantification of the activated form of the GPIIbIIIa receptor, and a fibrinogen-binding assay. Quantitative polymerase chain reaction and western blot were used to evaluate the impact of miR-204-5p on a validated target, CDC42. The impact of CDC42 modulation was investigated using a silencing strategy. RESULTS: miR-204-5p transfection induced cytoskeletal changes in megakaryocytes associated with the retracted protrusion of proPLS, but it had no impact on the number of PLS released. Functional assays showed that the PLS produced by megakaryocytes transfected with miR-204-5p were more reactive than controls. This phenotype is mediated by the regulation of GPIIbIIIa expression, a key contributor in platelet-fibrinogen interaction. Similar results were obtained after CDC42 silencing, suggesting that miR-204-5p regulates PR, at least in part, via CDC42 downregulation. CONCLUSION: We functionally validated miR-204-5p as a regulator of the PR that occurs through CDC42 downregulation and regulation of fibrinogen receptor expression.

An Ex Vivo and In Silico Study Providing Insights into the Interplay of Circulating miRNAs Level, Platelet Reactivity and Thrombin Generation: Looking beyond Traditional Pharmacogenetics.

Platelet reactivity (PR), a key pharmacodynamic (PD) component of the action of antiplatelet drugs in cardiovascular disease (CVD) patients, is highly variable. PR is associated with occurrence or recurrence of thrombotic and bleeding events, but this association is modulated by several factors. Conventional pharmacogenetics explains a minor part of this PR variability, and among determinants of PR, circulating microRNAs (miRNAs) have been the focus of attention during these last years as biomarkers to predict PR and clinical outcomes in CVD. This being said, the impact of miRNAs on platelet function and the mechanisms behind it are largely unknown. The level of a set of candidate miRNAs including miR-126-3p, miR-150-5p, miR-204-5p and miR-223-3p was quantified in plasma samples of stable CVD patients and correlated with PR as assessed by light-transmission aggregometry and in vivo thrombin generation markers. Finally, miRNA target networks were built based on genes involved in platelet function. We show that all candidate miRNAs were associated with platelet aggregation, while only miR-126-3p and miR-223-3p were positively correlated with in vivo thrombin generation markers. In silico analysis identified putative miRNA targets involved in platelet function regulation. Circulating miRNAs were associated with different aspects of platelet reactivity, including platelet aggregation and platelet-supported thrombin generation. This paves the way to a personalized antithrombotic treatment according to miRNA profile in CVD patients.

Functional Validation of microRNA-126-3p as a Platelet Reactivity Regulator Using Human Haematopoietic Stem Cells.

BACKGROUND: Platelets are an abundant source of micro-ribonucleic acids (miRNAs) that may play a role in the regulation of platelet function. Some miRNAs, such as miR-126-3p, have been noted as potential biomarkers of platelet reactivity and the recurrence of cardiovascular events. However, the biological relevance of these associations remains uncertain, and the functional validation of candidate miRNAs on human-derived cells is lacking. OBJECTIVE: This article functionally validates miR-126-3p as a regulator of platelet reactivity in platelet-like structures (PLS) derived from human haematopoietic stem cells. MATERIALS AND METHODS: CD34+-derived megakaryocytes were transfected with miR-126-3p and differentiated in PLS. PLS reactivity was assessed using perfusion in a fibrinogen-coated flow chamber. miR-126-3p's selected gene targets were validated using quantitative polymerase chain reaction, protein quantification and a reporter gene assay. RESULTS: CD34+-derived megakaryocytes transfected with miR-126-3p generated PLS exhibiting 156% more reactivity than the control. These functional data were in line with those obtained analysing CD62P expression. Moreover, miR-126-3p transfection was associated with the down-regulation of a disintegrin and metalloproteinase-9 (ADAM9) messenger RNA (mRNA), a validated target of miR-126-3p, and of Plexin B2 (PLXNB2) mRNA and protein, an actin dynamics regulator. Silencing PLXNB2 led to similar functional results to miR-126-3p transfection. Finally, using a reporter gene assay, we validated PLXNB2 as a direct target of miR-126-3p. CONCLUSION: We functionally validated miR-126-3p as a regulator of platelet reactivity in PLS derived from human haematopoietic stem cells. Moreover, PLXNB2 was validated as a new gene target of miR-126-3p in human cells, suggesting that miR-126-3p mediates its effect on platelets, at least in part, through actin dynamics regulation.

Turbidimetry on Human Washed Platelets: The Effect of the Pannexin1-inhibitor Brilliant Blue FCF on Collagen-induced Aggregation.

Turbidimetry is a laboratory technique that is applied to measure the aggregation of platelets suspended in either plasma (platelet-rich plasma, PRP) or in buffer (washed platelets), by the use of one or a combination of agonists. The use of washed platelets separated from their plasma environment and in the absence of anticoagulants allows for studying intrinsic platelet properties. Among the large panel of agonists, arachidonic acid (AA), adenosine di-phosphate (ADP), thrombin and collagen are the most frequently used. The aggregation response is quantified by measuring the relative optical density (OD) over time of platelet suspension under continuous stirring. Platelets in homogeneous suspension limit the passage of light after the addition of an agonist, platelet shape change occurs producing a small transitory increase in OD. Following this initial activation step, platelet clots form gradually, allowing the passage of light through the suspension as a result of decreased OD. The aggregation process is ultimately expressed as a percentage, compared to the OD of platelet-poor plasma or buffer. Rigorous calibration is thus essential at the beginning of each experiment. As a general rule: calibration to 0% is set by measuring the OD of a non-stimulated platelet suspension while measuring the OD of the suspension medium containing no platelets represents a value of 100%. Platelet aggregation is generally visualized as a real-time aggregation curve. Turbidimetry is one of the most commonly used laboratory techniques for the investigation of platelet function and is considered as the historical gold standard and used for the development of new pharmaceutical agents aimed at inhibiting platelet aggregation. Here, we describe detailed protocols for 1) preparation of human washed platelets and 2) turbidimetric analysis of collagen-induced aggregation of human washed platelets pretreated with the food dye Brilliant Blue FCF that was recently identified as an inhibitor of Pannexin1 (Panx1) channels.

New molecular insights into modulation of platelet reactivity in aspirin-treated patients using a network-based approach.

Platelet reactivity (PR) is variable between individuals and modulates clinical outcome in cardiovascular (CV) patients treated with antiplatelet drugs. Although several data point to a genetic control of platelet reactivity, the genes contributing to the modulation of this phenotype are not clearly identified. Integration of data derived from high-throughput technologies may yield novel insights into the molecular mechanisms that govern platelet reactivity. The aim of this study is to identify candidate genes modulating platelet reactivity in aspirin-treated CV patients using an integrative network-based approach. Patients with extreme high (n = 6) or low PR (n = 6) were selected and data derived from quantitative proteomic of platelets and platelet sub-cellular fractions, as well as from transcriptomic analysis were integrated with a network biology approach. Two modules within the network containing 123 and 182 genes were identified. We then specifically assessed the level of miRNAs in these two groups of patients. Among the 12 miRNAs differentially expressed, 2 (miR-135a-5p and miR-204-5p) correlated with PR. The predicted targets of these miRNAs were mapped onto the network, allowing the identification of seven overlapping genes (THBS1, CDC42, CORO1C, SPTBN1, TPM3, GTPBP2, and MAPRE2), suggesting a synergistic effect of these two miRNAs on these predicted targets. Integration of several omics data sets allowed the identification of 2 candidate miRNAs and 7 candidate genes regulating platelet reactivity in aspirin-treated CV patients.

Characterisation of the influences of aspirin-acetylation and glycation on human plasma proteins.

The competition effect between aspirin-mediated acetylation and protein glycation has been a matter of concern for decades. However, the exact interactions between these two post-translational modifications are still not well understood. Several efforts have been made to explain how aspirin prevents glycation, but the influence of prior protein glycation on the action of aspirin has never been investigated. This study involved qualitative and quantitative analyses to: 1) identify acetylated and glycated proteins; 2) quantify rates of acetylation and glycation; and 3) elucidate the common modification sites. Human plasma was incubated with 30mM glucose and then 500µM aspirin. A label-free mass spectrometry approach indicated an increase in the acetylation level after this sequential glucose-then-aspirin incubation; these results were also confirmed by Western blot. Interestingly, for several proteins, decreases in glycation levels were evidenced after aspirin incubation. The common modification sites, where both acetylation and glycation took place, were also identified. The influence that glycation and acetylation processes have on each other could reflect conformational changes induced by glucose and aspirin. In future studies, in order to better understand the interactions between these two PTMs, we intend to apply this strategy to other blood compartments and to diabetic patients. BIOLOGICAL SIGNIFICANCE: Non-enzymatic glycation represents an early stage in the development of the long-lasting complications that are associated with diabetes. Aspirin has been shown to prevent this process in a few reference proteins, but how the two post-translational modifications (PTMs) of aspirin-mediated acetylation and protein glycation interact with each other remains poorly investigated. This study used a label-free quantitative proteomic approach to characterise the extent of aspirin-induced acetylation and protein glycation in human plasma. The results clearly supported a mutual influence between these PTMs, which lead us to propose a potential model based on structural conformational changes.

Characterization of the platelet granule proteome: evidence of the presence of MHC1 in alpha-granules.

In the present study, we performed an extensive qualitative characterization of the platelet granule proteome using subcellular fractionation followed by mass spectrometry analysis and functional annotation. Eight-hundred-and-twenty-seven proteins were identified, most of them being associated to granules and to the granule's secretory machinery. Functional pathway analysis revealed 30 pathways, including the major histocompatibility complex class 1 (MHC I) presenting antigen pathway. This pathway was of particular interest for its potential interrelation between platelets and the immune system. Key proteins belonging to this metabolic route such as ß-2-microglobulin, 26S protease regulatory subunit 10B from the proteasome and proteins 1 and 2 of the transporter associated with antigen processing were shown to co-localize with von Willebrand factor in resting platelets and to be located on the plasma membrane when platelets were activated. Key proteins of the MHC1 antigen-presenting pathway are located in platelet alpha-granules. These results suggest a possible functional role of platelet granules in platelet-related immune modulation. BIOLOGICAL SIGNIFICANCE: In this study, we described the largest dataset related to platelet granule proteins. We performed a functional pathway analysis that evidenced several expected granule-related pathways. We also highlighted the "Antigen processing and presentation" pathway that has drawn our attention. Using immunofluorescence technique, we confirmed the presence of several key proteins for antigen presentation in platelet granules. This study suggests a putative functional role of MHC1 and platelet granules in the immune modulation.

Antiplatelet drug response status does not predict recurrent ischemic events in stable cardiovascular patients: results of the Antiplatelet Drug Resistances and Ischemic Events study.

BACKGROUND: The biological response to antiplatelet drugs has repeatedly been shown to predict the recurrence of major adverse cardiovascular events (MACEs). However, most studies involved coronary artery disease patients with recent vessel injury shortly after the initiation of antiplatelet therapy. Data on stable cardiovascular patients are scarce, and the added predictive value of specific assays (the vasodilator phosphoprotein assay for the clopidogrel response and serum thromboxane B2 for the aspirin response) and aggregation-based assays relative to common predictors has rarely been addressed. METHODS AND RESULTS: Stable cardiovascular outpatients participating in the Antiplatelet Drug Resistances and Ischemic Events (ADRIE) study (n=771) were tested twice, at 2 separate visits, with specific and aggregation-based assays. Follow-up lasted 3 years, and <1% of patients were lost to follow-up. MACEs were adjudicated by an independent committee. Multivariate survival analyses included relevant variables identified in univariate analysis and platelet function test results. The C-index was used to express the prognostic value of various multivariate models. MACEs, the primary end point, occurred in 16% of patients. Hypertension, smoking, older age, and elevated low-density lipoprotein cholesterol were predictive of MACE recurrence, with a C-index of 0.63 (P<0.001). Neither the specific nor the aggregation-based assays added significant predictive value for the primary end point. CONCLUSIONS: Biological antiplatelet drug responsiveness, measured with specific or aggregation-based assays, has no incremental predictive value over common cardiovascular risk factors for MACE recurrence in stable cardiovascular outpatients. These results do not support platelet function testing for MACE risk evaluation in stable cardiovascular patients. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00501423.

Platelet proteomics.

Platelets are small cell fragments, produced by megakaryocytes, in the bone marrow. They play an important role in hemostasis and diverse thrombotic disorders. They are therefore primary targets of antithrombotic therapies. They are implicated in several pathophysiological pathways, such as inflammation or wound repair. In blood circulation, platelets are activated by several pathways including subendothelial matrix and thrombin, triggering the formation of the platelet plug. Studying their proteome is a powerful approach to understand their biology and function. However, particular attention must be paid to different experimental parameters, such as platelet quality and purity. Several technologies are involved during the platelet proteome processing, yielding information on protein identification, characterization, localization, and quantification. Recent technical improvements in proteomics combined with inter-disciplinary strategies, such as metabolomic, transcriptomics, and bioinformatics, will help to understand platelets biological mechanisms. Therefore, a comprehensive analysis of the platelet proteome under different environmental conditions may contribute to elucidate complex processes relevant to platelet function regarding bleeding disorders or platelet hyperreactivity and identify new targets for antiplatelet therapy.

Connexin 37 limits thrombus propensity by downregulating platelet reactivity.

BACKGROUND: Formation of platelet plug initiates hemostasis after vascular injury and triggers thrombosis in ischemic disease. However, the mechanisms leading to the formation of a stable thrombus are poorly understood. Connexins comprise a family of proteins that form gap junctions enabling intercellular coordination of tissue activity, a process termed gap junctional intercellular communication. METHODS AND RESULTS: In the present study, we show that megakaryocytes and platelets express connexin 37 (Cx37). Deletion of the Cx37 gene in mice shortens bleeding time and increases thrombus propensity. Aggregation is increased in murine Cx37(-/-) platelets or in murine Cx37(+/+) and human platelets treated with gap junction blockers. Intracellular microinjection of neurobiotin, a Cx37-permeant tracer, revealed gap junctional intercellular communication in platelet aggregates, which was impaired in Cx37(-/-) platelets and in human platelets exposed to gap junction blockers. Finally, healthy subjects homozygous for Cx37-1019C, a prognostic marker for atherosclerosis, display increased platelet responses compared with subjects carrying the Cx37-1019T allele. Expression of these polymorphic channels in communication-deficient cells revealed a decreased permeability of Cx37-1019C channels for neurobiotin. CONCLUSIONS: We propose that the establishment of gap junctional communication between Cx37-expressing platelets provides a mechanism to limit thrombus propensity. To our knowledge, these data provide the first evidence incriminating gap junctions in the pathogenesis of thrombosis.