Deciphering the human platelet sheddome

Serum semaphorin 7A is associated with the risk of acute atherothrombotic stroke

Semaphorin 7A (Sema7A), a neural guidance cue, was recently identified to regulate atherosclerosis in mice. However, the clinical relevance of Sema7A with atherosclerotic diseases remains unknown. The aim of this study was to investigate the association between serum Sema7A and the risk of acute atherothrombotic stroke (AAS). We measured serum concentrations of Sema7A in 105 newly onset AAS cases and 105 age‐ and sex‐matched controls, showing that median Sema7A level in AAS cases was over three times of that in controls (5.86 vs 1.66 ng/mL). Adjusted for hypertension, body mass index, fasting blood glucose, total cholesterol, triglyceride, high‐density lipoprotein (HDL)‐cholesterol, low‐density lipoprotein (LDL)‐cholesterol, current smoking and alcohol consumption, multivariate logistic regression showed that higher Sema7A was independently associated with the odds of AAS (OR = 6.40, 95% CI: 2.88‐14.25). Each 1‐standard deviation increase in Sema7A was associated with a threefold higher odds of AAS (OR = 3.42, 95% CI: 1.84‐6.35). Importantly, adding Sema7A to a multivariate logistic model containing conventional cardiovascular risk factors improved the area under receiver operating characteristic curves from 0.831 to 0.891 for the association with AAS. In conclusion, elevated serum Sema7A is independently associated with the risk of AAS, suggesting that it may play a potential role in AAS.

Signaling Pathways of Receptors Involved in Platelet Activation and Shedding of These Receptors in Stored Platelets

All cells encounter various signals coming from the surrounding environment and they need to receive and respond to these signals in order to perform their functions. Cell surface receptors are responsible for signal transduction .Platelets are blood cells which perform several functions using diverse receptors. Platelet concentrate is one of the most consumed blood products. However, due to the short lifespan of the platelets and platelets damage during storage, we face shortage of platelet products. One of the damages that platelets undergo during storage is the loss of surface receptors. Since cell surface receptors are responsible for all cell functions, the loss of platelet receptors reduces the quality of platelet products. In this study, we reviewed the important receptors involved in platelet activation and their associated signaling pathways. We also looked at the platelet receptors that shed during storage and the causes of this incident. We found that GPIbα, P-selectin, CD40 and GPVI are platelet receptors that fall during platelet storage at room temperature. Considering that GPVI and GPIbα are the most important receptors which involved in platelet activation, their shedding can cause decrease in platelet activation after transfusion and decrease thrombus consistence. Shear stress and platelet contact with the container wall are among the mechanisms discussed in this process, but studies in this area have to be continued.

Human Platelet Protein Ubiquitylation and Changes following GPVI Activation

Platelet activators stimulate post-translational modification of signalling proteins to change their activity or their molecular interactions leading to signal propagation. One covalent modification is attachment of the small protein ubiquitin to lysine residues in target proteins. Modification by ubiquitin can either target proteins for degradation by the proteasome or act as a scaffold for other proteins. Pharmacological inhibition of deubiquitylases or the proteasome inhibition of platelet activation by collagen, demonstrating a role for ubiquitylation, but relatively few substrates for ubiquitin have been identified and the molecular basis of inhibition is not established. Here, we report the ubiquitome of human platelets and changes in ubiquitylated proteins following stimulation by collagen-related peptide (CRP-XL). Using platelets from six individuals over three independent experiments, we identified 1,634 ubiquitylated peptides derived from 691 proteins, revealing extensive ubiquitylation in resting platelets. Note that 925 of these peptides show an increase of more than twofold following stimulation with CRP-XL. Multiple sites of ubiquitylation were identified on several proteins including Syk, filamin and integrin heterodimer sub-units. This work reveals extensive protein ubiquitylation during activation of human platelets and opens the possibility of novel therapeutic interventions targeting the ubiquitin machinery.

Mechanisms of receptor shedding in platelets

The ability to upregulate and downregulate surface-exposed proteins and receptors is a powerful process that allows a cell to instantly respond to its microenvironment. In particular, mobile cells in the bloodstream must rapidly react to conditions where infection or inflammation are detected, and become proadhesive, phagocytic, and/or procoagulant. Platelets are one such blood cell that must rapidly acquire and manage proadhesive and procoagulant properties in order to execute their primary function in hemostasis. The regulation of platelet membrane properties is achieved via several mechanisms, one of which involves the controlled metalloproteolytic release of adhesion receptors and other proteins from the platelet surface. Proteolysis effectively lowers receptor density and reduces the reactivity of platelets, and is a mechanism to control robust platelet activation. Recent research has also established clear links between levels of platelet receptors and platelet lifespan. In this review, we will discuss the current knowledge of metalloproteolytic receptor regulation in the vasculature with emphasis on the platelet receptor system to highlight how receptor density can influence both platelet function and platelet survival.

Platelet-derived TLT-1 is a prognostic indicator in ALI/ARDS and prevents tissue damage in the lungs in a mouse model

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) affect >200 000 individuals yearly with a 40% mortality rate. Although platelets are implicated in the progression of ALI/ARDS, their exact role remains undefined. Triggering receptor expressed in myeloid cells (TREM)-like transcript 1 (TLT-1) is found on platelets, binds fibrinogen, and mediates clot formation. We hypothesized that platelets use TLT-1 to manage the progression of ALI/ARDS. Here we retrospectively measure plasma levels of soluble TLT-1 (sTLT-1) from the ARDS Network clinical trial and show that patients whose sTLT-1 levels were >1200 pg/mL had nearly twice the mortality risk as those with <1200 pg/mL (P < .001). After correcting for confounding factors such as creatinine levels, Acute Physiology And Chronic Health Evaluation III scores, age, platelet counts, and ventilation volume, sTLT-1 remains significant, suggesting that sTLT-1 is an independent prognostic factor (P < .0001). These data point to a role for TLT-1 during the progression of ALI/ARDS. We use a murine lipopolysaccharide-induced ALI model and demonstrate increased alveolar bleeding, aberrant neutrophil transmigration and accumulation associated with decreased fibrinogen deposition, and increased pulmonary tissue damage in the absence of TLT-1. The loss of TLT-1 resulted in an increased proportion of platelet-neutrophil conjugates (43.73 ± 24.75% vs 8.92 ± 2.4% in wild-type mice), which correlated with increased neutrophil death. Infusion of sTLT-1 restores normal fibrinogen deposition and reduces pulmonary hemorrhage by 40% (P ≤ .001) and tissue damage by 25% (P ≤ .001) in vivo. Our findings suggest that TLT-1 uses fibrinogen to govern the transition between inflammation and hemostasis and facilitate controlled leukocyte transmigration during the progression of ARDS.

Increased GPIbα shedding from platelets treated with immune thrombocytopenia plasma

Immune thrombocytopenia (ITP) is a heterogeneous autoimmune disease, characterized by accelerated platelet destruction/clearance or decreased platelet production. ADAM17-mediated platelet receptor GPIbα extracellular domain shedding has been shown to be involved in platelet clearance. Whether GPIbα shedding participates in the pathogenesis of ITP remains poorly understood. This study aims to investigate the role of GPIbα shedding in the development of ITP via incubating normal platelets with ITP plasma to mimic ITP in vivo environment. Plasma was isolated from ITP patients or healthy control and incubated with platelets in vitro followed by measuring GPIbα expression by flow cytometry and western blot, ADAM17 expression by western blot, ROS generation and platelet activation by flow cytometry. Compared with control plasma, ITP plasma-treated platelet displayed significantly reduced GPIbα surface expression, increased ADAM17 expression and ROS generation. However, metalloproteinase inhibitor GM6001 blocked the ITP-plasma-induced decrease in GPIbα surface expression, increase in ADAM17 expression and platelet activation. In addition, inhibitors of NADPH oxidase or mitochondria respiration significantly inhibited ROS generation from ITP plasma-treated platelets. Moreover, ROS inhibition or blocking FcγRIIa attenuated the decrease in GPIbα surface expression, platelet activation and ROS generation (for blocking FcγRIIa) in ITP plasma-treated platelets. In conclusion, ITP plasma induces platelet receptor GPIbα extracellular domain shedding, suggesting that it might participate in the pathogenesis of ITP and targeting it might be a novel approach for treating ITP.

The Platelet Releasate is Altered in Human Pregnancy

PURPOSE

Healthy pregnancy is characterized by an increase in platelet activation and a decrease in the number of circulating platelets with gestation. Despite this recognized importance, proteomic studies investigating platelets in healthy pregnancy have not been performed. As platelet cargo can be altered in different conditions, it is hypothesized that platelets may store a relevant and bespoke collection of molecules during pregnancy.

EXPERIMENTAL DESIGN

Comparative label-free quantitative proteomic profiling of platelet releasates (PRs) is performed from 18 healthy pregnant and 13 non-pregnant women using an MS/MS approach.

RESULTS

Of the 723 proteins identified, 69 PR proteins are found to be differentially released from platelets in pregnancy, including proteins only expressed during pregnancy such as pregnancy-specific glycoproteins and human placental lactogen. Moreover, the population of exosomal vesicles present in the PR is also modified in pregnancy. Receiver operating characteristic analysis shows the predictive ability of 11 PR proteins to distinctly classify pregnant and nonpregnant women with an area under the curve of 0.876, a sensitivity of 88.9%, and a specificity of 84.6%.

CONCLUSIONS AND CLINICAL RELEVANCE

Taken together this demonstrates that platelets and their released cargo are 'educated' in physiologic stressful conditions such as pregnancy and may represent a promising platform to study pregnancy complications.

Calcific tendinopathy of the shoulder: clinical perspectives into the mechanisms, pathogenesis, and treatment

Calcific tendinopathy (CT) of the shoulder is a common, painful condition characterized by the presence of calcium deposits in the rotator cuff tendons. Current theories indicate that CT may be the result of a cell-mediated process in which, after a stage of calcium deposition, calcifications are spontaneously resorbed. However, in a minority of cases, this self-healing process is somehow disrupted, resulting in symptoms. Recent literature shows an emerging role of biological and genetic factors underlying CT. This new evidence could supplement the classic mechanical theory of rotator cuff tendinopathy complicated by calcium precipitation, and it may also explain why the majority of the therapies currently in use are only able to provide partially satisfactory outcomes. This review aims to summarize the current knowledge about the pathological processes underlying CT of the shoulder and thereby justify the quest for advanced biological treatments of this condition when it becomes symptomatic.

Platelet toll-like receptors are crucial sensors of infectious danger moieties

In addition to their haemostatic role and function in the repair of damaged vascular epithelium, platelets play a defensive role in innate immunity, having the capacity to produce and secrete various anti-infectious factors, as well as cytokines, chemokines and related products, to interact with other immune cells to modulate immune responses to pathogens. Thus, it is now widely acknowledged that platelets participate in inflammatory processes and infection resolution, most notably by expressing and using receptors to bind infectious pathogen moieties and contributing to pathogen clearance. The ability of platelets to sense external danger signals relates to the expression of certain innate immunity receptors, such as toll-like receptors (TLRs), and the activation of efficient cell signalling machinery. TLR engagement triggers platelet response, which results in adapted degranulation according to: the type of TLR engaged, the nature of the ligand and the milieu; together, the TLR-mediated event and other signalling events may be followed by aggregation. Platelets thus use complex tools to mediate a whole range of functions upon sensing danger. By linking the inflammatory and haemostatic platelet response to infection, TLRs play a central role. The extent of the inflammatory response to pathogen clearance is still a debatable issue and is discussed in this short review.

Extracellular Vesicles as Biomarkers in Cardiovascular Disease; Chances and Risks

The field of extracellular vesicles (EV) is rapidly expanding, also within cardiovascular diseases. Besides their exciting roles in cell-to-cell communication, EV have the potential to serve as excellent biomarkers, since their counts, content, and origin might provide useful information about the pathophysiology of cardiovascular disorders. Various studies have already indicated associations of EV counts and content with cardiovascular diseases. However, EV research is complicated by several factors, most notably the small size of EV. In this review, the advantages and drawbacks of EV-related methods and applications as biomarkers are highlighted.

Platelet Releasate Proteome Profiling Reveals a Core Set of Proteins with Low Variance between Healthy Adults

Upon activation, platelets release a powerful cocktail of soluble and vesicular signals, collectively termed the "platelet releasate" (PR). Although several studies have used qualitative/quantitative proteomic approaches to characterize PR; with debated content and significant inter-individual variability reported, confident, and reliable insights have been hindered. Using label-free quantitative (LFQ)-proteomics analysis, a reproducible, quantifiable investigation of the 1U mL^-1 thrombin-induced PR from 32 healthy adults was conducted. MS proteomics data are available via ProteomeXchange, identifier PXD009310. Of the 894 proteins identified, 277 proteins were quantified across all donors and form a "core" PR. Bioinformatics and further LFQ-proteomic analysis revealed that the majority (84%) of "core" PR proteins overlapped with the protein composition of human platelet-derived exosomes. Vesicles in the exosomal-size range were confirmed in healthy-human PR and reduced numbers of similar-sized vesicles were observed in the PR of a mouse model of gray platelet syndrome, known to be deficient in platelet alpha-granules. Lastly, the variability of proteins in the PR was assessed, and reproducible secretion levels were found across all 32 healthy donors. Taken together, the PR contains valuable soluble and vesicular cargo and has low-population variance among healthy adults, rendering it a potentially useful platform for diagnostic fingerprinting of platelet-related disease.

Platelet biology in regenerative medicine of skeletal muscle

Platelet-based applications such as platelet-rich plasma (PRP) and platelet releasate have gained unprecedented attention in regenerative medicine across a variety of tissues as of late. The rationale behind utilizing PRP originates in the delivery of key cytokines and growth factors from α-granules to the targeted area, which in turn act as cell cycle regulators and promote the healing process across a variety of tissues. The aim of the present review is to assimilate current experimental evidence on the role of platelets as biomaterials in tissue regeneration, particularly in skeletal muscle, by integrating findings from human, animal and cell studies. This review is composed of 3 parts: firstly, we review key aspects of platelet biology that precede the preparation and use of platelet-related applications for tissue regeneration. Secondly, we critically discuss relevant evidence on platelet-mediated regeneration in skeletal muscle focusing on findings from (i) clinical trials, (ii) experimental animal studies and (iii) cell culture studies; and thirdly, we discuss the application of platelets in the regeneration of several other tissues including tendon, bone, liver, vessels and nerve. Finally, we review key technical variations in platelet preparation that may account for the large discrepancy in outcomes from different studies. This review provides an up-to-date reference tool for biomedical and clinical scientists involved in platelet-mediated tissue regenerative applications.

Platelet proteomics: from discovery to diagnosis

INTRODUCTION

Platelets are the smallest cells within the circulating blood with key roles in physiological hemostasis and pathological thrombosis regulated by the onset of activating/inhibiting processes via receptor responses and signaling cascades. Areas covered: Proteomics as well as genomic approaches have been fundamental in identifying and quantifying potential targets for future diagnostic strategies in the prevention of bleeding and thrombosis, and uncovering the complexity of platelet functions in health and disease. In this article, we provide a critical overview on current functional tests used in diagnostics and the future perspectives for platelet proteomics in clinical applications. Expert commentary: Proteomics represents a valuable tool for the identification of patients with diverse platelet associated defects. In-depth validation of identified biomarkers, e.g. receptors, signaling proteins, post-translational modifications, in large cohorts is decisive for translation into routine clinical diagnostics.

Emerging Concepts in Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disease defined by low platelet counts which presents with an increased bleeding risk. Several genetic risk factors (e.g., polymorphisms in immunity-related genes) predispose to ITP. Autoantibodies and cytotoxic CD8⁺ T cells (Tc) mediate the anti-platelet response leading to thrombocytopenia. Both effector arms enhance platelet clearance through phagocytosis by splenic macrophages or dendritic cells and by induction of apoptosis. Meanwhile, platelet production is inhibited by CD8⁺ Tc targeting megakaryocytes in the bone marrow. CD4⁺ T helper cells are important for B cell differentiation into autoantibody secreting plasma cells. Regulatory Tc are essential to secure immune tolerance, and reduced levels have been implicated in the development of ITP. Both Fcγ-receptor-dependent and -independent pathways are involved in the etiology of ITP. In this review, we present a simplified model for the pathogenesis of ITP, in which exposure of platelet surface antigens and a loss of tolerance are required for development of chronic anti-platelet responses. We also suggest that infections may comprise an important trigger for the development of auto-immunity against platelets in ITP. Post-translational modification of autoantigens has been firmly implicated in the development of autoimmune disorders like rheumatoid arthritis and type 1 diabetes. Based on these findings, we propose that post-translational modifications of platelet antigens may also contribute to the pathogenesis of ITP.

Initiation and Propagation of Vascular Calcification Is Regulated by a Concert of Platelet- and Smooth Muscle Cell-Derived Extracellular Vesicles

The ageing population continues to suffer from its primary killer, cardiovascular disease (CVD). Despite recent advances in interventional medicinal and surgical therapies towards the end of the 20th century, the epidemic of cardiovascular disease has not been halted. Yet, rather than receding globally, the burden of CVD has risen to become a top cause of morbidity and mortality worldwide. Most CVD arises from thrombotic rupture of an atherosclerotic plaque, the pathologic thickening of coronary and carotid artery segments and subsequent distal ischemia in heart or brain. In fact, one-fifth of deaths are directly attributable to thrombotic rupture of a vulnerable plaque. Atherosclerotic lesion formation is caused by a concert of interactions between circulating leukocytes and platelets, interacting with the endothelial barrier, signalling into the arterial wall by the release of cytokines and extracellular vesicles (EVs). Both platelet- and cell-derived EVs represent a novel mechanism of cellular communication, particularly by the transport and transfer of cargo and by reprogramming of the recipient cell. These interactions result in phenotypic switching of vascular smooth muscle cells (VSMCs) causing migration and proliferation, and subsequent secretion of EVs. Loss of VSMCs attracts perivascular Mesenchymal Stem Cells (MSCs) from the adventitia, which are a source of VSMCs and contribute to repair after vascular injury. However, continuous stress stimuli eventually switch phenotype of cells into osteochondrogenic VSMCs facilitating vascular calcification. Although Virchow’s triad is over 100 years old, it is a reality that is accurate today. It can be briefly summarised as changes in the composition of blood (platelet EVs), alterations in the vessel wall (VSMC phenotypic switching, MSC infiltration and EV release) and disruption of blood flow (atherothrombosis). In this paper, we review the latest relevant advances in the identification of extracellular vesicle pathways as well as VSMCs and pericyte/MSC phenotypic switching, underlying vascular calcification.

Vascular Semaphorin 7A Upregulation by Disturbed Flow Promotes Atherosclerosis Through Endothelial β1 Integrin

OBJECTIVE

Accumulating evidence suggests a role of semaphorins in vascular homeostasis. Here, we investigate the role of Sema7A (semaphorin 7A) in atherosclerosis and its underlying mechanism.

APPROACH AND RESULTS

Using genetically engineered Sema7A^-/-ApoE^-/- mice, we showed that deletion of Sema7A attenuates atherosclerotic plaque formation primarily in the aorta of ApoE^-/- mice on a high-fat diet. A higher level of Sema7A in the atheroprone lesser curvature suggests a correlation of Sema7A with disturbed flow. This notion is supported by elevated Sema7A expression in human umbilical venous endothelial cells either subjected to oscillatory shear stress or treated with the PKA (protein kinase A)/CREB (cAMP response element-binding protein) inhibitor H89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide·2HCl hydrate). Further studies using the partial carotid artery ligation model showed that disturbed flow in the left carotid artery of Sema7A^+/+ApoE^-/- mice promoted the expression of endothelial Sema7A and cell adhesion molecules, leukocyte adhesion, and plaque formation, whereas such changes were attenuated in Sema7A^-/-ApoE^-/- mice. Further studies showed that blockage of β1 integrin, a known Sema7A receptor, or inhibition of FAK (focal adhesion kinase), MEK1/2 (mitogen-activated protein kinase kinase 1/2), or NF-κB (nuclear factor-κB) significantly reduced the expression of cell adhesion molecules and THP-1 (human acute monocytic leukemia cell line) monocyte adhesion in Sema7A-overexpressing human umbilical venous endothelial cells. Studies using chimeric mice suggest that vascular, most likely endothelial, Sema7A plays a major role in atherogenesis.

CONCLUSIONS

Our findings indicate a significant role of Sema7A in atherosclerosis by mediating endothelial dysfunction in a β1 integrin-dependent manner.

Focusing on plasma glycoprotein VI

New methods for analysing both platelet and plasma forms of the platelet-specific collagen receptor, glycoprotein VI (GPVI) in experimental models or human clinical samples, and the development of the first therapeutic compounds based on dimeric soluble GPVI-Fc or anti-GPVI antibody-based constructs, coincide with increased understanding of the potential pathophysiological role of GPVI ligand binding and shedding. Platelet GPVI not only mediates platelet activation at the site of vascular injury where collagen is exposed, but is also implicated in the pathogenesis of other diseases, such as atherosclerosis and coagulopathy, rheumatoid arthritis and tumour metastasis. Here, we describe some of the critical mechanisms for generating soluble GPVI from platelets, and future avenues for exploiting this unique platelet-specific receptor for diagnosis and/or disease prevention.

Platelet-mediated shedding of NKG2D ligands impairs NK cell immune-surveillance of tumor cells

Platelets promote metastasis, among others by coating cancer cells traveling through the blood, which results in protection from NK cell immune-surveillance. The underlying mechanisms, however, remain to be fully elucidated. Here we report that platelet-coating reduces surface expression of NKG2D ligands, in particular MICA and MICB, on tumor cells, which was mirrored by enhanced release of their soluble ectodomains. Similar results were obtained upon exposure of tumor cells to platelet-releasate and can be attributed to the sheddases ADAM10 and ADAM17 that are detectable on the platelet surface and in releasate following activation and at higher levels on platelets of patients with metastasized lung cancer compared with healthy controls. Platelet-mediated NKG2DL-shedding in turn resulted in impaired "induced self" recognition by NK cells as revealed by diminished NKG2D-dependent lysis of tumor cells. Our results indicate that platelet-mediated NKG2DL-shedding may be involved in immune-evasion of (metastasizing) tumor cells from NK cell reactivity.

A review of platelet secretion assays for the diagnosis of inherited platelet secretion disorders

Measurement of platelet granule release to detect inherited platelet secretion disorders (IPSDs) is essential for the evaluation of patients with abnormal bleeding and is necessary to distinguish which granule sub-types are affected and whether there is abnormal granule bio-synthesis or secretion. The radioactive serotonin incorporation and release assay, described before 1970, is still considered the “gold standard” test to assess platelet δ-granule release, although is unsuitable for clinical diagnostic laboratories. Luciferin-based assays, such as lumiaggregometry, are the most widely performed alternatives, although these methods do not distinguish defects in δ-granule biosyn-thesis from defects in secretion. Platelet α-granule release is commonly evaluated using flow cytometry by measuring surface exposure of P-selectin after platelet activation. However, this assay has poor sensitivity for some α-granule disorders. Only few studies have been published with more recently developed assays and no critical reviews on these methods are available. In this review, we describe the rationale for developing robust and accurate laboratory tests of platelet granule release and describe the characteristics of the currently available tests. We identify an unmet need for further systematic evaluation of new assays and for standardisation of methodologies for clinical diagnostic laboratories.

Suppression of tumor-derived Semaphorin 7A and genetic ablation of host-derived Semaphorin 7A impairs tumor progression in a murine model of advanced breast carcinoma

Solid tumors can generate a plethora of neurogenesis-related molecules that enhance their growth and metastasis. Among them, we have identified axonal guidance molecule Semaphorin 7A (SEMA7A) in breast cancer. The goal of this study was to determine the therapeutic effect of suppressing SEMA7A levels in the 4T1 murine model of advanced breast carcinoma. We used anti-SEMA7A short hairpin RNA (shRNA) to gene silence SEMA7A in 4T1 mammary tumor cells. When implanted into the mammary fat pads of syngeneic mice, SEMA7A shRNA-expressing 4T1 tumors exhibited decreased growth rates, deferred metastasis and reduced mortality. In vitro, SEMA7A shRNA-expressing 4T1 cells had weakened proliferative, migratory and invasive abilities, and decreased levels of mesenchymal factors. Atomic force microscopy studies showed that SEMA7A shRNA-expressing 4T1 cells had an increase in cell stiffness that corresponded with their decreased malignant potential. Genetic ablation of host-derived SEMA7A further enhanced the antitumor effects of SEMA7A shRNA gene silencing in 4T1 cells. Our preclinical findings demonstrate a critical role for SEMA7A in mediating mammary tumor progression.

Monitoring storage induced changes in the platelet proteome employing label free quantitative mass spectrometry

Shelf life of platelet concentrates is limited to 5-7 days due to loss of platelet function during storage, commonly referred to as the platelet storage lesion (PSL). To get more insight into the development of the PSL, we used label free quantitative mass spectrometry to identify changes in the platelet proteome during storage. In total 2501 proteins were accurately quantified in 3 biological replicates on at least 1 of the 7 different time-points analyzed. Significant changes in levels of 21 proteins were observed over time. Gene ontology enrichment analysis of these proteins revealed that the majority of this set was involved in platelet degranulation, secretion and regulated exocytosis. Twelve of these proteins have been shown to reside in α-granules. Upon prolonged storage (13-16 days) elevated levels of α-2-macroglobulin, glycogenin and Ig μ chain C region were identified. Taken together this study identifies novel markers for monitoring of the PSL that may potentially also be used for the detection of "young" and "old" platelets in the circulation.

SheddomeDB: the ectodomain shedding database for membrane-bound shed markers

BACKGROUND

A number of membrane-anchored proteins are known to be released from cell surface via ectodomain shedding. The cleavage and release of membrane proteins has been shown to modulate various cellular processes and disease pathologies. Numerous studies revealed that cell membrane molecules of diverse functional groups are subjected to proteolytic cleavage, and the released soluble form of proteins may modulate various signaling processes. Therefore, in addition to the secreted protein markers that undergo secretion through the secretory pathway, the shed membrane proteins may comprise an additional resource of noninvasive and accessible biomarkers. In this context, identifying the membrane-bound proteins that will be shed has become important in the discovery of clinically noninvasive biomarkers. Nevertheless, a data repository for biological and clinical researchers to review the shedding information, which is experimentally validated, for membrane-bound protein shed markers is still lacking.

RESULTS

In this study, the database SheddomeDB was developed to integrate publicly available data of the shed membrane proteins. A comprehensive literature survey was performed to collect the membrane proteins that were verified to be cleaved or released in the supernatant by immunological-based validation experiments. From 436 studies on shedding, 401 validated shed membrane proteins were included, among which 199 shed membrane proteins have not been annotated or validated yet by existing cleavage databases. SheddomeDB attempted to provide a comprehensive shedding report, including the regulation of shedding machinery and the related function or diseases involved in the shedding events. In addition, our published tool ShedP was embedded into SheddomeDB to support researchers for predicting the shedding event on unknown or unrecorded membrane proteins.

CONCLUSIONS

To the best of our knowledge, SheddomeDB is the first database for the identification of experimentally validated shed membrane proteins and currently may provide the most number of membrane proteins for reviewing the shedding information. The database included membrane-bound shed markers associated with numerous cellular processes and diseases, and some of these markers are potential novel markers because they are not annotated or validated yet in other databases. SheddomeDB may provide a useful resource for discovering membrane-bound shed markers. The interactive web of SheddomeDB is publicly available at http://bal.ym.edu.tw/SheddomeDB/ .

A reverse signaling pathway downstream of Sema4A controls cell migration via Scrib

Semaphorins comprise a large family of ligands that regulate key cellular functions through their receptors, plexins. In this study, we show that the transmembrane semaphorin 4A (Sema4A) can also function as a receptor, rather than a ligand, and transduce signals triggered by the binding of Plexin-B1 through reverse signaling. Functionally, reverse Sema4A signaling regulates the migration of various cancer cells as well as dendritic cells. By combining mass spectrometry analysis with small interfering RNA screening, we identify the polarity protein Scrib as a downstream effector of Sema4A. We further show that binding of Plexin-B1 to Sema4A promotes the interaction of Sema4A with Scrib, thereby removing Scrib from its complex with the Rac/Cdc42 exchange factor βPIX and decreasing the activity of the small guanosine triphosphatase Rac1 and Cdc42. Our data unravel a role for Plexin-B1 as a ligand and Sema4A as a receptor and characterize a reverse signaling pathway downstream of Sema4A, which controls cell migration.

Taking the stock of granule cargo: Platelet releasate proteomics

Human platelets are key players in a multitude of physiological and pathological processes. Upon activation they release cargo from different types of granules as well as microparticles in an apparently well-regulated and orchestrated manner. The resulting specific platelet releasates create microenvironments of biologically active compounds and proteins during platelet aggregation and thrombus formation, allowing efficient delivery of growth factors and immune modulators to their sites of effect and enhancing the coagulative response in a positive feedback loop. Thus, platelet releasates play a central role in the regulation of platelet homeostasis and heterotypic cell interaction. Additionally, it recently emerged that both the qualitative and quantitative composition of the releasate as well as release dynamics may be stimulus dependent and therefore more complex than expected. Mass spectrometry-based proteomics is an important asset for studying platelet releasates in vitro, as it allows not only (i) identifying released proteins, but moreover (ii) determining their quantities and the dynamics of release as well as (iii) differentially comparing releasates across a variety of conditions. Though owing to the high sensitivity and comprehensiveness of modern proteomic techniques, a thorough experimental design and a standardized and robust sample preparation are essential to obtain highly confident and reliable insights into platelet biology and pathology. Here, we review releasate proteome studies and crucial sample preparation strategies to summarize possible achievements of state-of-the-art technologies and furthermore discuss potential pitfalls and limitations. We provide a future perspective of platelet releasate proteomics including targeted analyses, post-translational modifications and multi-omics approaches that should be adopted by platelet releasate researchers due to their tremendous depth and comprehensiveness.

Basic mechanisms of platelet receptor shedding

Proteolytic shedding of the extracellular ectodomain of platelet receptors provides a key mechanism for irreversible loss of ligand-binding capacity, and for regulating platelet function in health and disease. Platelets derived from megakaryocytes are small anucleate cells in peripheral blood, with the ability to rapidly adhere, become activated, and secrete an array of procoagulant and proinflammatory factors at sites of vascular injury or disease, and to form a platelet aggregate (thrombus) which is not only critical in normal hemostasis and wound healing, but in atherothrombotic diseases including myocardial infarction and ischemic stroke. Basic mechanisms of receptor shedding on platelets have important distinctions from how receptors on other cell types might be shed, in that shedding is rapidly initiated (within seconds to minutes) and occurs under altered shear conditions encountered in flowing blood or experimentally ex vivo. This review will consider the key components of platelet receptor shedding, that is, the receptor with relevant cleavage site, the (metallo)proteinase or sheddase and how its activity is regulated, and the range of known regulatory factors that control platelet receptor shedding including receptor-associated molecules such as calmodulin, factors controlling sheddase surface expression and activity, and other elements such as shear stress, plasma membrane properties, cellular activation status or age. Understanding these basic mechanisms of platelet receptor shedding is significant in terms of utilizing receptor surface expression or soluble proteolytic fragments as platelet-specific biomarkers and/or ultimately therapeutic targeting of these mechanisms to control platelet reactivity and function.

Is Autoimmune Thrombocytopenia Itself the Primary Disease in the Presence of Second Diseases Data from a Long-Term Observation

BACKGROUND

Dependent on the absence or presence of associated diseases, autoimmune thrombocytopenia (ITP) can be classified as primary or secondary form. The manifestation of the associated diseases is not temporally defined and may occur during observation. Thus the question which disease is the primary one remains unanswered.

METHODS

All 386 patients included in this study were treated by a single primary physician between 1996 and 2015 at the Charité Berlin and met current ITP criteria. Medical records and investigations were reviewed to assess diseases associated with ITP.

RESULTS

Initially, the vast majority of patients presented with primary ITP (isolated disease). Based on our findings, ITP was found to be associated with other abnormalities in most cases. These abnormalities included: positive direct antiglobulin test in 49 of 386 tested patients (13%), affections of the thyroid gland in 41 of 386 tested patients (11%), infections in 30 (8%), solid malignancies in 20 (5%) and hematological malignancies in 10 patients (3%), as well as many other miscellaneous diseases. Moreover, of 160 patients who did not receive prior intravenous immunoglobulin treatment, 40 (25%) showed antibody deficiency.

CONCLUSION

In conclusion, the incidence of 'true' ITP as a primary disease is less common than has yet been suggested. Additionally, there is evidence that ITP itself predispose affected subjects toward development of other diseases.

Regulation of platelet membrane protein shedding in health and disease

Extracellular proteolysis of platelet plasma membrane proteins is an event that ensues platelet activation. Shedding of surface receptors such as glycoprotein (GP) Ibα, GPV and GPVI as well as externalized proteins P-selectin and CD40L releases soluble ectodomain fragments that are subsequently detectable in plasma. This results in the irreversible functional downregulation of platelet receptor-mediated adhesive interactions and the generation of biologically active fragments. In this review, we describe molecular insights into the regulation of platelet receptor and ligand shedding in health and disease. The scope of this review is specially focused on GPIbα, GPV, GPVI, P-selectin and CD40L where we: (1) describe the basic physiological regulation of expression and shedding of these proteins in hemostasis illustrate alterations in receptor expression during (2) apoptosis and (3) ex vivo storage relevant for blood banking purposes; (4) discuss considerations to be made when analyzing and interpreting shedding of platelet membrane proteins and finally; (5) collate clinical evidence that quantify these platelet proteins during disease.

Platelets are versatile cells: New discoveries in hemostasis, thrombosis, immune responses, tumor metastasis and beyond

Platelets are small anucleate blood cells generated from megakaryocytes in the bone marrow and cleared in the reticuloendothelial system. At the site of vascular injury, platelet adhesion, activation and aggregation constitute the first wave of hemostasis. Blood coagulation, which is initiated by the intrinsic or extrinsic coagulation cascades, is the second wave of hemostasis. Activated platelets can also provide negatively-charged surfaces that harbor coagulation factors and markedly potentiate cell-based thrombin generation. Recently, deposition of plasma fibronectin, and likely other plasma proteins, onto the injured vessel wall has been identified as a new "protein wave of hemostasis" that may occur even earlier than the first wave of hemostasis, platelet accumulation. Although no experimental evidence currently exists, it is conceivable that platelets may also contribute to this protein wave of hemostasis by releasing their granule fibronectin and other proteins that may facilitate fibronectin self- and non-self-assembly on the vessel wall. Thus, platelets may contribute to all three waves of hemostasis and are central players in this critical physiological process to prevent bleeding. Low platelet counts in blood caused by enhanced platelet clearance and/or impaired platelet production are usually associated with hemorrhage. Auto- and allo-immune thrombocytopenias such as idiopathic thrombocytopenic purpura and fetal and neonatal alloimmune thrombocytopenia may cause life-threatening bleeding such as intracranial hemorrhage. When triggered under pathological conditions such as rupture of an atherosclerotic plaque, excessive platelet activation and aggregation may result in thrombosis and vessel occlusion. This may lead to myocardial infarction or ischemic stroke, the major causes of mortality and morbidity worldwide. Platelets are also involved in deep vein thrombosis and thromboembolism, another leading cause of mortality. Although fibrinogen has been documented for more than half a century as essential for platelet aggregation, recent studies demonstrated that fibrinogen-independent platelet aggregation occurs in both gene deficient animals and human patients under physiological and pathological conditions (non-anti-coagulated blood). This indicates that other unidentified platelet ligands may play important roles in thrombosis and might be novel antithrombotic targets. In addition to their critical roles in hemostasis and thrombosis, emerging evidence indicates that platelets are versatile cells involved in many other pathophysiological processes such as innate and adaptive immune responses, atherosclerosis, angiogenesis, lymphatic vessel development, liver regeneration and tumor metastasis. This review summarizes the current knowledge of platelet biology, highlights recent advances in the understanding of platelet production and clearance, molecular and cellular events of thrombosis and hemostasis, and introduces the emerging roles of platelets in the immune system, vascular biology and tumorigenesis. The clinical implications of these basic science and translational research findings will also be discussed.

Proteolytic Cleavage Governs Interleukin-11 Trans-signaling

Interleukin (IL)-11 has been shown to be a crucial factor for intestinal tumorigenesis, lung carcinomas, and asthma. IL-11 is thought to exclusively mediate its biological functions through cell-type-specific expression of the membrane-bound IL-11 receptor (IL-11R). Here, we show that the metalloprotease ADAM10, but not ADAM17, can release the IL-11R ectodomain. Chimeric proteins of the IL-11R and the IL-6 receptor (IL-6R) revealed that a small juxtamembrane portion is responsible for this substrate specificity of ADAM17. Furthermore, we show that the serine proteases neutrophil elastase and proteinase 3 can also cleave the IL-11R. The resulting soluble IL-11R (sIL-11R) is biologically active and binds IL-11 to activate cells. This IL-11 trans-signaling pathway can be inhibited specifically by the anti-inflammatory therapeutic compound sgp130Fc. In conclusion, proteolysis of the IL-11R represents a molecular switch that controls the IL-11 trans-signaling pathway and widens the number of cells that can be activated by IL-11.

Inhibition of angiogenesis by platelets in systemic sclerosis patients

INTRODUCTION

Systemic sclerosis (SSc) is a chronic autoimmune disease characterized by microvascular damage, inflammation, and fibrosis. It has become increasingly evident that platelets, beyond regulating hemostasis, are important in inflammation and innate immunity. Platelets may be an important source of proinflammatory and profibrotic cytokines in the vascular microenvironment. In this study, we sought to assess the contribution of platelet-derived factors in patients with SSc to the angiogenesis of human dermal microvascular endothelial cells (DMVECs) in a tubule formation assay and to characterize the secretion of profibrotic and proinflammatory cytokines in these platelets.

METHODS

We analyzed platelets obtained from 30 patients with SSc and 12 healthy control subjects. Angiogenesis was evaluated in vitro with a DMVEC tubule formation assay on Matrigel and platelet-derived angiogenic factors such as vascular endothelial growth factor (VEGF), 165b isoform (VEGF165b), and cytokine secretion was evaluated. Platelet serotonin content was also determined.

RESULTS

When DMVECs were incubated with SSc platelet releasates, tubule formation was significantly inhibited (p < 0.01, t test), and higher expression of endothelin-1 in these cells was observed compared with control subjects (p < 0.05, Mann-Whitney U test). In SSc platelet releasates, VEGF165b was significantly higher (p < 0.05, t test), and the VEGF165b/VEGF ratio was increased compared with that of control subjects. Higher secretion of transforming growth factor β (p < 0.01, t test) and CD40L (p < 0.01, t test) was observed compared with control subjects. Also, intraplatelet serotonin levels were lower in platelets obtained from patients with diffuse SSc compared with patients with limited SSc and control subjects (p < 0.05, t test).

CONCLUSIONS

Our findings suggest that antiangiogenic factors such as VEGF165b, together with proinflammatory and profibrotic factors secreted by platelets, can contribute to the progression of peripheral microvascular damage, defective vascular repair, and fibrosis in patients with SSc.

Qualitative and quantitative modifications of von Willebrand factor in patients with essential thrombocythemia and controlled platelet count

BACKGROUND

Essential thrombocythemia (ET) is characterized by increased platelets and prevalent thrombosis. An acquired von Willebrand factor (VWF) disease has been hypothesized and inconsistently associated with extreme thrombocytosis or rare bleeding in ET. Whether VWF is modified in ET patients with controlled platelet count remains unclear.

OBJECTIVES

We studied different VWF- and platelet-associated parameters in ET patients treated according to current recommendations.

PATIENTS/METHODS

Sixty-nine ET patients (M = 29; median age, 62 [48-70] years; platelets, 432 [337-620] × 10(3)  μL(-1) ), 69 matched controls and 10 subjects with reactive thrombocytosis (RT) were studied. VWF:antigen (Ag), activity (act), electrophoretic patterns, VWF:propeptide, plasma glycocalycin (GC), glycoproteinV (GpV), ADAMTS-13, elastase, C-reactive protein and serum thromboxane (TX)B2 were measured.

RESULTS

In ET patients, VWF:Ag was increased by 31 ± 13% vs. controls (P < 0.01), without dependence of blood groups, while VWF:act was reduced by 21 ± 12% vs. controls and by 50 ± 24% vs. RT (P < 0.01). The VWF:act/VWF:Ag ratios in ET were reduced by 35 ± 17% vs. controls and RT patients (P < 0.001) and significantly associated with: immature or total platelet counts, GC, GpV and TXB2 . In multivariable analysis, only GC inversely predicted ET patients' VWF:act/VWF:Ag ratios (β = -0.42, P = 0.01). By electrophoresis analyses, high-molecular-weight VWF multimers were variably reduced with atypical cleavage bands in ET only. VWF:propeptide, ADAMTS-13 and elastase levels were normal in ET patients. Platelet-associated ADAM-10 and ADAM-17 hydrolyzed VWFm in vitro, showing patterns similar to those in ET samples.

CONCLUSIONS

In ET patients with controlled platelet counts, the VWF:act/VWF:Ag ratio is decreased and predicted by GC, a product of platelet activation. ADAM-10 and/or ADAM-17 might be involved. In vivo platelet activation, which characterizes ET, might contribute to disease-specific VWF alterations.

ABO Blood Group as a Model for Platelet Glycan Modification in Arterial Thrombosis

ABO blood groups have long been associated with cardiovascular disease, thrombosis, and acute coronary syndromes. Many studies over the years have shown type O blood group to be associated with lower risk of cardiovascular disease than non-type O blood groups. However, the mechanisms underlying this association remain unclear. Although ABO blood group is associated with variations in concentrations of circulating von Willebrand Factor and other endothelial cell adhesion molecules, ABO antigens are also present on several platelet surface glycoproteins and glycosphingolipids. As we highlight in this platelet-centric review, these glycomic modifications may affect platelet function in arterial thrombosis. More broadly, improving our understanding of the role of platelet glycan modifications in acute coronary syndromes may inform future diagnostics and therapeutics for cardiovascular diseases.

Proteomic signatures of antiplatelet drugs: new approaches to exploring drug effects

Antiplatelet agents represent the mainstay of acute coronary syndrome (ACS) therapy to prevent ischemic events and to improve safety in patients undergoing percutaneous coronary intervention. However, despite the availability of several drugs and the use of dual antiplatelet therapy, the pharmacological response is highly variable with a subset of patients continuing to experience recurrent thrombotic events, revealing a wide variability in platelet response to antiplatelet drugs. Several factors may explain this, including genetic variation and environmental factors. Here we look at the application of proteomic analysis, an approach that provides an integrated readout of these diverse influences.

Platelets and infections - complex interactions with bacteria

Platelets can be considered sentinels of vascular system due to their high number in the circulation and to the range of functional immunoreceptors they express. Platelets express a wide range of potential bacterial receptors, including complement receptors, FcγRII, Toll-like receptors but also integrins conventionally described in the hemostatic response, such as GPIIb-IIIa or GPIb. Bacteria bind these receptors either directly, or indirectly via fibrinogen, fibronectin, the first complement C1q, the von Willebrand Factor, etc. The fate of platelet-bound bacteria is questioned. Several studies reported the ability of activated platelets to internalize bacteria such as Staphylococcus aureus or Porphyromonas gingivalis, though there is no clue on what happens thereafter. Are they sheltered from the immune system in the cytoplasm of platelets or are they lysed? Indeed, while the presence of phagolysosome has not been demonstrated in platelets, they contain antimicrobial peptides that were shown to be efficient on S. aureus. Besides, the fact that bacteria can bind to platelets via receptors involved in hemostasis suggests that they may induce aggregation; this has indeed been described for Streptococcus sanguinis, S. epidermidis, or C. pneumoniae. On the other hand, platelets are able to display an inflammatory response to an infectious triggering. We, and others, have shown that platelet release soluble immunomodulatory factors upon stimulation by bacterial components. Moreover, interactions between bacteria and platelets are not limited to only these two partners. Indeed, platelets are also essential for the formation of neutrophil extracellular traps by neutrophils, resulting in bacterial clearance by trapping bacteria and concentrating antibacterial factors but in enhancing thrombosis. In conclusion, the platelet-bacteria interplay is a complex game; its fine analysis is complicated by the fact that the inflammatory component adds to the aggregation response.

Are Platelets Cells? And if Yes, are They Immune Cells?

Small fragments circulating in the blood were formally identified by the end of the nineteenth century, and it was suggested that they assisted coagulation via interactions with vessel endothelia. Wright, at the beginning of the twentieth century, identified their bone-marrow origin. For long, platelets have been considered sticky assistants of hemostasis and pollutants of blood or tissue samples; they were just cell fragments. As such, however, they were acknowledged as immunizing (to specific HPA and HLA markers): the platelet’s dark face. The enlightened face showed that besides hemostasis, platelets contained factors involved in healing. As early as 1930s, platelets entered the arsenal of medicines were transfused, and were soon manipulated to become a kind of glue to repair damaged tissues. Some gladly categorized platelets as cells but they were certainly not fully licensed as such for cell physiologists. Actually, platelets possess almost every characteristic of cells, apart from being capable of organizing their genes: they have neither a nucleus nor genes. This view prevailed until it became evident that platelets play a role in homeostasis and interact with cells other than with vascular endothelial cells; then began the era of physiological and also pathological inflammation. Platelets have now entered the field of immunity as inflammatory cells. Does assistance to immune cells itself suffice to license a cell as an “immune cell”? Platelets prove capable of sensing different types of signals and organizing an appropriate response. Many cells can do that. However, platelets can use a complete signalosome (apart from the last transcription step, though it is likely that this step can be circumvented by retrotranscribing RNA messages). The question has also arisen as to whether platelets can present antigen via their abundantly expressed MHC class I molecules. In combination, these properties argue in favor of allowing platelets the title of immune cells.

Establishment of immunoassay for platelet-derived soluble glycoprotein VI, a novel platelet marker

Soluble Glycoprotein VI (GPVI) is an attractive marker for disorders marked by platelet activation, such as thrombotic microangiopathy, myocardial infarction, and stroke. Several groups have already developed an immunoassay for soluble GPVI; however, there are several discrepancies between the groups' assays. In this study, we prepared the two types of recombinant soluble GPVI, the monomeric form GPVI (GPVI-His) and the dimeric form of GPVI (GPVI-Fc), moreover, we generated four anti-GPVI antibodies, F1232-7-1 (7S1), F1232-10-2 (10S2), F1232-19-1 (19D1), and F1232-21-1 (21D1). The former 2 antibodies (7S1 and 10S2) had a high affinity for both GPVI-His and GPVI-Fc, while the latter 2 antibodies (19D1 and 21D1) showed a high affinity for GPVI-Fc but low affinity for GPVI-His. All of the antibodies comparably recognized surface GPVI on resting platelets. Furthermore, we established two immunoassays for soluble GPVI, 7S1/10S2-HRP and 19D1/21D1-HRP (capture antibody/detection antibody). 7S1/10S2-HRP showed equivalent reactivity with GPVI-His and GPVI-Fc, whereas 19D1/21D1-HRP had high affinity for GPVI-Fc but low reactivity with GPVI-His. In terms of reactivity with platelet-derived soluble GPVI, 7S1/10S2-HRP demonstrated sensitive detection whereas 19D1/21D1-HRP was nonreactive. Taken together, 7S1/10S2-HRP is a suitable candidate for a reliable soluble GPVI immunoassay as it has a high affinity for monomeric GPVI.

Platelet transfusion - the new immunology of an old therapy

Platelet transfusion has been a vital therapeutic approach in patients with hematologic malignancies for close to half a century. Randomized trials show that prophylactic platelet transfusions mitigate bleeding in patients with acute myeloid leukemia. However, even with prophylactic transfusions, as many as 75% of patients, experience hemorrhage. While platelet transfusion efficacy is modest, questions and concerns have arisen about the risks of platelet transfusion therapy. The acknowledged serious risks of platelet transfusion include viral transmission, bacterial sepsis, and acute lung injury. Less serious adverse effects include allergic and non-hemolytic febrile reactions. Rare hemolytic reactions have occurred due to a common policy of transfusing without regard to ABO type. In the last decade or so, new concerns have arisen; platelet-derived lipids are implicated in transfusion-related acute lung injury after transfusion. With the recognition that platelets are immune cells came the discoveries that supernatant IL-6, IL-27 sCD40L, and OX40L are closely linked to febrile reactions and sCD40L with acute lung injury. Platelet transfusions are pro-inflammatory, and may be pro-thrombotic. Anti-A and anti-B can bind to incompatible recipient or donor platelets and soluble antigens, impair hemostasis and thus increase bleeding. Finally, stored platelet supernatants contain biological mediators such as VEGF and TGF-β1 that may compromise the host versus tumor response. This is particularly of concern in patients receiving many platelet transfusions, as for acute leukemia. New evidence suggests that removing stored supernatant will improve clinical outcomes. This new view of platelets as pro-inflammatory and immunomodulatory agents suggests that innovative approaches to improving platelet storage and pre-transfusion manipulations to reduce toxicity could substantially improve the efficacy and safety of this long-employed therapy.

Primary haemostasis: newer insights

At the same time as biophysical and omics approaches are drilling deeper into the molecular details of platelets and other blood cells, as well as their receptors and mechanisms of regulation, there is also an increasing awareness of the functional overlap between human vascular systems. Together, these studies are redefining the intricate networks linking haemostasis and thrombosis with inflammation, infectious disease, cancer/metastasis and other vascular pathophysiology. The focus of this state-of-the-art review is some of the newer advances relevant to primary haemostasis. Of particular interest, platelet-specific primary adhesion-signalling receptors and associated activation pathways control platelet function in flowing blood and provide molecular links to other systems. Platelet glycoprotein (GP)Ibα of the GPIb-IX-V complex and GPVI not only initiate platelet aggregation and thrombus formation by primary interactions with von Willebrand factor and collagen, respectively, but are also involved in coagulation, leucocyte engagement, bacterial or viral interactions, and are relevant as potential risk markers in a range of human diseases. Understanding these systems in unprecedented detail promises significant advances in evaluation of individual risk, in new diagnostic or therapeutic possibilities and in monitoring the response to drugs or other treatment.

Tumor necrosis factor-alpha-converting enzyme activities and tumor-associated macrophages in breast cancer

The role of the tumor microenvironment especially of tumor-associated macrophages (TAMs) in the progression and metastatic spread of breast cancer is well established. TAMs have primarily a M2 (wound-healing) phenotype with minimal cytotoxic activities. The mechanisms by which tumor cells influence TAMs to display a pro-tumor phenotype are still debated although the key roles of immunomodulatory cytokines released by tumor cells, including colony-stimulating factor 1, tumor necrosis factor (TNF) and soluble TNF receptors 1/2, soluble vascular cell adhesion molecule 1, soluble interleukin 6 receptor and amphiregulin, have been demonstrated. Importantly, these factors are released through ectodomain shedding by the activities of the tumor necrosis factor-alpha-converting enzyme (TACE/ADAM17). The role of TACE activation leading to autocrine effects on tumor progression has been extensively studied. In contrast, limited information is available on the role of tumor cell TACE activities on TAMs in breast cancer. TACE inhibitors, currently in clinical trials, will certainly affect TAMs and subsequently treatment outcomes based on the substrates it releases. Furthermore, whether targeting a subset of the molecules shed by TACE, specifically those leading to TAMs with altered functions and phenotype, holds greater therapeutic promises than past clinical trials of TACE antagonists' remains to be determined. Here, the potential roles of TACE ectodomain shedding in the breast tumor microenvironment are reviewed with a focus on the release of tumor-derived immunomodulatory factors shed by TACE that directs TAM phenotypes and functions.

Semaphorin7A: branching beyond axonal guidance and into immunity

Semaphorins are a family of proteins that were originally described for their role in axonal guidance. Studies now show that semaphorins encompass many physiological functions outside of the nervous system, including immune responses. Semaphorin7A (SEMA7A) belongs to the "immune" semaphorin group and has been shown to play a crucial role in regulating immune responses. In this review, we discuss the structure and function of SEMA7A as well as its role in innate and adaptive immunity [corrected].We further describe SEMA7A's involvement in inflammatory disease and its emergent role in cancer.

Emerging Roles for Platelets in Inflammation and Disease

Platelets and their interaction with cells of the immune system contribute through a variety of molecular mechanisms to support hemostasis and inflammation. These simple yet essential cells exert their effects in lymphocytes, monocytes, and neutrophils, both recruiting and modulating their function after activation. Emerging evidence is starting to define the mechanisms that allow platelets to also play pivotal roles in host defense. For example, platelet cell-surface expression of toll-like receptors allows platelets to direct neutrophil activation toward extracellular trap formation and facilitate the elimination of blood pathogens. In addition to these well-known receptors, two of the most recently discovered platelet receptors, C-type lectin receptor 2 (CLEC-2), and TREM-like transcript-1 (TLT-1), have been shown to modulate hemostatic and inflammation-related roles in platelets. This review will discuss the evolution of our understanding of platelet functions from hemostasis to inflammation, and highlight novel mechanisms that platelets use to mediate hemostasis under inflammatory pressure.

A computerized prediction model of hazardous inflammatory platelet transfusion outcomes

BACKGROUND

Platelet component (PC) transfusion leads occasionally to inflammatory hazards. Certain BRMs that are secreted by the platelets themselves during storage may have some responsibility.

METHODOLOGY/PRINCIPAL FINDINGS

First, we identified non-stochastic arrangements of platelet-secreted BRMs in platelet components that led to acute transfusion reactions (ATRs). These data provide formal clinical evidence that platelets generate secretion profiles under both sterile activation and pathological conditions. We next aimed to predict the risk of hazardous outcomes by establishing statistical models based on the associations of BRMs within the incriminated platelet components and using decision trees. We investigated a large (n = 65) series of ATRs after platelet component transfusions reported through a very homogenous system at one university hospital. Herein, we used a combination of clinical observations, ex vivo and in vitro investigations, and mathematical modeling systems. We calculated the statistical association of a large variety (n = 17) of cytokines, chemokines, and physiologically likely factors with acute inflammatory potential in patients presenting with severe hazards. We then generated an accident prediction model that proved to be dependent on the level (amount) of a given cytokine-like platelet product within the indicated component, e.g., soluble CD40-ligand (>289.5 pg/109 platelets), or the presence of another secreted factor (IL-13, >0). We further modeled the risk of the patient presenting either a febrile non-hemolytic transfusion reaction or an atypical allergic transfusion reaction, depending on the amount of the chemokine MIP-1α (<20.4 or >20.4 pg/109 platelets, respectively).

CONCLUSIONS/SIGNIFICANCE

This allows the modeling of a policy of risk prevention for severe inflammatory outcomes in PC transfusion.