Regulation of the genetic code in megakaryocytes and platelets

Transcription factor 3 is dysregulated in megakaryocytes in myelofibrosis

Transcription factor 3 (TCF3) is a DNA transcription factor that modulates megakaryocyte development. Although abnormal TCF3 expression has been identified in a range of hematological malignancies, to date, it has not been investigated in myelofibrosis (MF). MF is a Philadelphia-negative myeloproliferative neoplasm (MPN) that can arise de novo or progress from essential thrombocythemia [ET] and polycythemia vera [PV] and where dysfunctional megakaryocytes have a role in driving the fibrotic progression. We aimed to examine whether TCF3 is dysregulated in megakaryocytes in MPN, and specifically in MF. We first assessed TCF3 protein expression in megakaryocytes using an immunohistochemical approach analyses and showed that TCF3 was reduced in MF compared with ET and PV. Further, the TCF3-negative megakaryocytes were primarily located near trabecular bone and had the typical "MF-like" morphology as described by the WHO. Genomic analysis of isolated megakaryocytes showed three mutations, all predicted to result in a loss of function, in patients with MF; none were seen in megakaryocytes isolated from ET or PV marrow samples. We then progressed to transcriptomic sequencing of platelets which showed loss of TCF3 in MF. These proteomic, genomic and transcriptomic analyses appear to indicate that TCF3 is downregulated in megakaryocytes in MF. This infers aberrations in megakaryopoiesis occur in this progressive phase of MPN. Further exploration of this pathway could provide insights into TCF3 and the evolution of fibrosis and potentially lead to new preventative therapeutic targets.

Prospective, international, multisite comparison of platelet isolation techniques for genome-wide transcriptomics: communication from the SSC of the ISTH

Genome-wide platelet transcriptomics is increasingly used to uncover new aspects of platelet biology and as a diagnostic and prognostic tool. Nevertheless, platelet isolation methods for transcriptomic studies are not standardized, introducing challenges for cross-study comparisons, data integration, and replication. In this prospective multicenter study, called "Standardizing Platelet Transcriptomics for Discovery, Diagnostics, and Therapeutics in the Thrombosis and Hemostasis Community (STRIDE)" by the International Society on Thrombosis and Haemostasis Scientific and Standardization Committees, we assessed how 3 of the most commonly used platelet isolation protocols influence metrics from next-generation bulk RNA sequencing and functional assays. Compared with washing alone, more stringent removal of leukocytes by anti-CD45 beads or PALL filters resulted in a sufficient quantity of RNA for next-generation sequencing and similar quality of RNA sequencing metrics. Importantly, stringent removal of leukocytes resulted in the lower relative expression of known leukocyte-specific genes and the higher relative expression of known platelet-specific genes. The results were consistent across enrolling sites, suggesting that the techniques are transferrable and reproducible. Moreover, all 3 isolation techniques did not influence basal platelet reactivity, but agonist-induced integrin αIIbβ3 activation is reduced by anti-CD45 bead isolation compared with washing alone. In conclusion, the isolation technique chosen influences genome-wide transcriptional and functional assays in platelets. These results should help the research community make informed choices about platelet isolation techniques in their own platelet studies.

Mitochondrial gene expression is required for platelet function and blood clotting

Platelets are anucleate blood cells that contain mitochondria and regulate blood clotting in response to injury. Mitochondria contain their own gene expression machinery that relies on nuclear-encoded factors for the biogenesis of the oxidative phosphorylation system to produce energy required for thrombosis. The autonomy of the mitochondrial gene expression machinery from the nucleus is unclear, and platelets provide a valuable model to understand its importance in anucleate cells. Here, we conditionally delete Elac2, Ptcd1, or Mtif3 in platelets, which are essential for mitochondrial gene expression at the level of RNA processing, stability, or translation, respectively. Loss of ELAC2, PTCD1, or MTIF3 leads to increased megakaryocyte ploidy, elevated circulating levels of reticulated platelets, thrombocytopenia, and consequent extended bleeding time. Impaired mitochondrial gene expression reduces agonist-induced platelet activation. Transcriptomic and proteomic analyses show that mitochondrial gene expression is required for fibrinolysis, hemostasis, and blood coagulation in response to injury.

Reprogramming megakaryocytes to engineer platelets as delivery vehicles

We developed a method for the efficient generation of engineered platelets that can be filled with any recombinant therapeutic protein during the differentiation process by reprogramming megakaryocytes, the progenitor cells of platelets. To demonstrate the versatility of this approach, we loaded cytoplasmic and secreted proteins that can be delivered as active enzymes to recipient cells, be released upon platelet activation, or be continuously secreted by platelets over time.

Role of microRNAs and their downstream target transcription factors in zebrafish thrombopoiesis

Previous studies have shown that human platelets and megakaryocytes carry microRNAs suggesting their role in platelet function and megakaryocyte development, respectively. However, a comprehensive study on the microRNAs and their targets has not been undertaken. Zebrafish thrombocytes could be used as a model to study their role in megakaryocyte maturation and platelet function because thrombocytes have both megakaryocyte features and platelet properties. In our laboratory, we identified 15 microRNAs in thrombocytes using single-cell RNA sequencing. We knocked down each of these 15 microRNAs by the piggyback method and found knockdown of three microRNAs, mir-7148, let-7b, and mir-223 in adult zebrafish led to an increase in the percentage of thrombocytes. Functional thrombocyte analysis using plate tilt assay showed no modulatory effect of the three microRNAs on thrombocyte aggregation/agglutination. We also found enhanced thrombosis using arterial laser thrombosis assay in a group of zebrafish larvae after mir-7148, let-7b, and mir-223 knockdowns. These results suggested mir-7148, let-7b, and mir-223 are repressors for thrombocyte production. We then explored miRWalk database for let-7b downstream targets and then selected those that are expressed in thrombocytes, and from this list based on their role in differentiation selected 14 genes, rorca, tgif1, rfx1a, deaf1, zbtb18, mafba, cebpa, spi1a, spi1b, fhl3b, ikzf1, irf5, irf8, and lbx1b that encode transcriptional regulators. The qRT-PCR analysis of expression levels of the above genes following let-7b knockdown showed changes in the expression of 13 targets. We then studied the effect of the 13 targets on thrombocyte production and identified 5 genes, irf5, tgif1, irf8, cebpa, and rorca that showed thrombocytosis and one gene, ikzf1 that showed thrombocytopenia. Furthermore, we tested whether mir-223 regulates any of the above 13 transcription factors after mir-223 knockdown using qRT-PCR. Six of the 13 genes showed similar gene expression as observed with let-7b knockdown and 7 genes showed opposing results. Thus, our results suggested a possible regulatory network in common with both let-7b and mir-223. We also identified that tgif1, cebpa, ikzf1, irf5, irf8, and ikzf1 play a role in thrombopoiesis. Since the ikzf1 gene showed a differential expression profile in let-7b and mir-223 knockdowns but resulted in thrombocytopenia in ikzf1 knockdown in both adults and larvae we also studied an ikzf1 mutant and showed the mutant had thrombocytopenia. Taken together, these studies showed that thrombopoiesis is controlled by a network of transcription regulators that are regulated by multiple microRNAs in both positive and negative manner resulting in overall inhibition of thrombopoiesis.

Tumor educated platelet: the novel BioSource for cancer detection

Platelets, involved in the whole process of tumorigenesis and development, constantly absorb and enrich tumor-specific substances in the circulation during their life span, thus called "Tumor Educated Platelets" (TEPs). The alterations of platelet mRNA profiles have been identified as tumor markers due to the regulatory mechanism of post-transcriptional splicing. Small nuclear RNAs (SnRNAs), the important spliceosome components in platelets, dominate platelet RNA splicing and regulate the splicing intensity of pre-mRNA. Endogenous variation at the snRNA levels leads to widespread differences in alternative splicing, thereby driving the development and progression of neoplastic diseases. This review systematically expounds the bidirectional tumor-platelets interactions, especially the tumor induced alternative splicing in TEP, and further explores whether molecules related to alternative splicing such as snRNAs can serve as novel biomarkers for cancer diagnostics.

MAPK-interacting kinase 1 regulates platelet production, activation, and thrombosis

The MAPK-interacting kinase (Mnk) family includes Mnk1 and Mnk2, which are phosphorylated and activated in response to extracellular stimuli. Mnk1 contributes to cellular responses by regulating messenger RNA (mRNA) translation, and mRNA translation influences platelet production and function. However, the role of Mnk1 in megakaryocytes and platelets has not previously been studied. The present study investigated Mnk1 in megakaryocytes and platelets using both pharmacological and genetic approaches. We demonstrate that Mnk1, but not Mnk2, is expressed and active in human and murine megakaryocytes and platelets. Stimulating human and murine megakaryocytes and platelets induced Mnk1 activation and phosphorylation of eIF4E, a downstream target of activated Mnk1 that triggers mRNA translation. Mnk1 inhibition or deletion significantly diminished protein synthesis in megakaryocytes as measured by polysome profiling and [35S]-methionine incorporation assays. Depletion of Mnk1 also reduced megakaryocyte ploidy and proplatelet forming megakaryocytes in vitro and resulted in thrombocytopenia. However, Mnk1 deletion did not affect the half-life of circulating platelets. Platelets from Mnk1 knockout mice exhibited reduced platelet aggregation, α granule secretion, and integrin αIIbβ3 activation. Ribosomal footprint sequencing indicated that Mnk1 regulates the translation of Pla2g4a mRNA (which encodes cPLA2) in megakaryocytes. Consistent with this, Mnk1 ablation reduced cPLA2 activity and thromboxane generation in platelets and megakaryocytes. In vivo, Mnk1 ablation protected against platelet-dependent thromboembolism. These results provide previously unrecognized evidence that Mnk1 regulates mRNA translation and cellular activation in platelets and megakaryocytes, endomitosis and thrombopoiesis, and thrombosis.

Human Platelets Contain, Translate, and Secrete Azurocidin; A Novel Effect on Hemostasis

Platelets play a significant role in hemostasis and perform essential immune functions, evidenced by the extensive repertoire of antimicrobial molecules. Currently, there is no clear description of the presence of azurocidin in human platelets. Azurocidin is a 37 kDa cationic protein abundant in neutrophils, with microbicidal, opsonizing, and vascular permeability-inducing activity. Therefore, this work aimed to characterize the content, secretion, translation, and functions of azurocidin in platelets. Our results show the presence of azurocidin mRNA and protein in α-granules of platelet and megakaryoblasts, and stimulation with thrombin, ADP, and LPS leads to the secretion of free azurocidin as well as within extracellular vesicles. In addition, platelets can translate azurocidin in a basal or thrombin-induced manner. Finally, we found that the addition of low concentrations of azurocidin prevents platelet aggregation and activation. In conclusion, we demonstrate that platelets contain, secrete, and translate azurocidin, and this protein may have important implications for hemostasis.

Transcriptional landscape of circulating platelets from patients with COVID-19 reveals key subnetworks and regulators underlying SARS-CoV-2 infection: implications for immunothrombosis

Background

Thrombosis and coagulopathy are pervasive pathological features of coronavirus disease 2019 (COVID-19), and thrombotic complications are a sign of severe COVID-19 disease and are associated with multiple organ failure and increased mortality. Platelets are essential cells that regulate hemostasis, thrombus formation and inflammation; however, the mechanism underlying the interaction between platelets and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains unclear.

Results

The present study performed RNA sequencing on the RNA isolated from platelets obtained from 10 COVID-19 patients and eight healthy donors, and discovered that SARS-CoV-2 not only significantly altered the coding and non-coding transcriptional landscape, but also altered the function of the platelets, promoted thrombus formation and affected energy metabolism of platelets. Integrative network biology analysis identified four key subnetworks and 16 risk regulators underlying SARS-CoV-2 infection, involved in coronavirus disease-COVID-19, platelet activation and immune response pathways. Furthermore, four risk genes (upstream binding transcription factor, RNA polymerase II, I and III subunit L, Y-box binding protein 1 and yippee like 2) were found to be associated with COVID-19 severity. Finally, a significant alteration in the von Willebrand factor/glycoprotein Ib-IX-V axis was revealed to be strongly associated with platelet aggregation and immunothrombosis.

Conclusions

The transcriptional landscape and the identification of critical subnetworks and risk genes of platelets provided novel insights into the molecular mechanisms of immunothrombosis in COVID-19 progression, which may pave the way for the development of novel therapeutic strategies for preventing COVID-19-associated thrombosis and improving the clinical outcome of COVID-19 patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00750-5.

Toward platelet transcriptomics in cancer diagnosis, prognosis and therapy

Widespread adoption of next-generation techniques such as RNA-sequencing (RNA-seq) has enabled research examining the transcriptome of anucleate blood platelets in health and disease, thus revealing a rich platelet transcriptomic signature that is reprogrammed in response to disease. Platelet signatures not only capture information from parent megakaryocytes and progenitor hematopoietic stem cells but also the bone marrow microenvironment, and underlying disease states. In cancer, the substantive body of research in patients with solid tumours has identified distinct signatures in 'tumour-educated platelets', reflecting influences of the tumour, stroma and vasculature on splicing, sequestration of tumour-derived RNAs, and potentially cytokine and microvesicle influences on megakaryocytes. More recently, platelet RNA expression has emerged as a highly sensitive approach to profiling chronic progressive haematologic malignancies, where the combination of large data cohorts and machine-learning algorithms enables precise feature selection and potential prognostication. Despite these advances, however, our ability to translate platelet transcriptomics toward clinical diagnostic and prognostic efforts remains limited. In this Perspective, we present a few actionable steps for our basic, translational and clinical research communities in advancing the utility of the platelet transcriptome as a highly sensitive biomarker in cancer and collectively enable efforts toward clinical translation and patient benefit.

Thrombosis and hemorrhage in myeloproliferative neoplasms: The platelet perspective

Classical myeloproliferative neoplasm (MPN), also known as BCR-ABL-negative MPN, is a clonal disease characterized by abnormal expansion of hematopoietic stem cells. It has been demonstrated that MPN patients are more susceptible to thrombotic events compared to the general population. Therefore, researchers have been exploring the treatment for MPN thrombosis. However, antithrombotic therapies have brought another concern for the clinical management of MPN because they may cause bleeding events. When thrombosis and bleeding, two seemingly contradictory complications, occur in MPN patients at the same time, they will lead to more serious consequences. Therefore, it is a major challenge to achieving the best antithrombotic effect and minimizing bleeding events simultaneously. To date, there has yet been a perfect strategy to meet this challenge and therefore a new treatment method needs to be established. In this article, we describe the mechanism of thrombosis and bleeding events in MPN from the perspective of platelets for the first time. Based on the double-sided role of platelets in MPN, optimal antithrombotic treatment strategies that can simultaneously control thrombosis and bleeding at the same time may be formulated by adjusting the administration time and dosage of antiplatelet drugs. We argue that more attention should be paid to the critical role of platelets in MPN thrombosis and MPN bleeding in the future, so as to better manage adverse vascular events in MPN.

Bioinformatics analysis of tumor-educated platelet microRNAs in patients with hepatocellular carcinoma

Background: Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies that seriously threaten global health. The primary reason for its grim prognosis is the lack of sensitive tools for early diagnosis. The purpose of the present study was to apply bioinformatics analysis to explore tumor-educated platelet (TEP) microRNA (miRNA) expression and its potential diagnostic utility in HCC.

Methods: Twenty-five HCC patients and 25 healthy controls were included. RNA sequencing was utilized to screen miRNA alterations in platelets derived from HCC patients (n=5) and controls (n=5). Gene set enrichment analysis was performed to analyze the targeted mRNAs of differentially expressed miRNAs by using the Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, aiming at main functions and pathways, respectively. We then verified the selected platelet miRNAs in another cohort by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) amplification.

Results: A total of 250 differentially expressed miRNAs were identified, among which 111 were down-regulated and 139 were up-regulated. The functional enrichment analysis of differentially expressed miRNAs suggested that their target genes were involved primarily in pathways related to HCC. Expression levels of miR-495-3p and miR-1293 were further validated by qRT-PCR, which yielded results consistent with the sequencing analysis. The area under the receiver operating characteristic (ROC) curve of miR-495-3p and miR-1293 as diagnostic tests for HCC were 0.76 and 0.78, respectively.

Conclusion: TEP miRNAs such as miR-495-3p and miR-1293 were differentially expressed in HCC patients, and may be involved in the pathophysiology of HCC.

Platelets Contribution to Thrombin Generation in Philadelphia-Negative Myeloproliferative Neoplasms: The "Circulating Wound" Model

Current cytoreductive and antithrombotic strategies in MPNs are mostly based on cell counts and on patient's demographic and clinical history. Despite the numerous studies conducted on platelet function and on the role of plasma factors, an accurate and reliable method to dynamically quantify the hypercoagulability states of these conditions is not yet part of clinical practice. Starting from our experience, and after having sifted through the literature, we propose an in-depth narrative report on the contribution of the clonal platelets of MPNs-rich in tissue factor (TF)-in promoting a perpetual procoagulant mechanism. The whole process results in an unbalanced generation of thrombin and is self-maintained by Protease Activated Receptors (PARs). We chose to define this model as a "circulating wound", as it indisputably links the coagulation, inflammation, and fibrotic progression of the disease, in analogy with what happens in some solid tumours. The platelet contribution to thrombin generation results in triggering a vicious circle supported by the PARs/TGF-beta axis. PAR antagonists could therefore be a good option for target therapy, both to contain the risk of vascular events and to slow the progression of the disease towards end-stage forms. Both the new and old strategies, however, will require tools capable of measuring procoagulant or prohaemorrhagic states in a more extensive and dynamic way to favour a less empirical management of MPNs and their potential clinical complications.

Liquid Biopsy in Glioblastoma Management: From Current Research to Future Perspectives

Glioblastoma (GBM) is the most common primary tumor of the central nervous system. Arising from neuroepithelial glial cells, GBM is characterized by invasive behavior, extensive angiogenesis, and genetic heterogeneity that contributes to poor prognosis and treatment failure. Currently, there are several molecular biomarkers available to aid in diagnosis, prognosis, and predicting treatment outcomes; however, all require the biopsy of tumor tissue. Nevertheless, a tissue sample from a single location has its own limitations, including the risk related to the procedure and the difficulty of obtaining longitudinal samples to monitor treatment response and to fully capture the intratumoral heterogeneity of GBM. To date, there are no biomarkers in blood or cerebrospinal fluid for detection, follow-up, or prognostication of GBM. Liquid biopsy offers an attractive and minimally invasive solution to support different stages of GBM management, assess the molecular biology of the tumor, identify early recurrence and longitudinal genomic evolution, predict both prognosis and potential resistance to chemotherapy or radiotherapy, and allow patient selection for targeted therapies. The aim of this review is to describe the current knowledge regarding the application of liquid biopsy in glioblastoma, highlighting both benefits and obstacles to translation into clinical care. IMPLICATIONS FOR PRACTICE: To translate liquid biopsy into clinical practice, further prospective studies are required with larger cohorts to increase specificity and sensitivity. With the ever-growing interest in RNA nanotechnology, microRNAs may have a therapeutic role in brain tumors.

The heterogeneity of megakaryocytes and platelets and implications for ex vivo platelet generation

Platelets, the chief effector of hemostasis, are small anucleate blood cells generated from megakaryocytes (MKs), and the defects in platelet production or function lead to a variety of bleeding complications. Emerging evidence indicates that MKs and platelets are much more diverse than previously appreciated and involved in many physiological and pathological processes besides hemostasis, such as innate and adaptive immune responses, angiogenesis, and tumor metastasis, while the ontogenic variations in MK and platelet function have also become a focus in the field. However, whether MKs and platelets fulfill these distinct functions by utilizing distinct subpopulations remains poorly understood. New studies aimed at deciphering the MK transcriptome at the single‐cell level have provided some key insights into the functional heterogeneity of MKs. In this review, we will discuss some of the recent discoveries of functional and developmental heterogeneity of MKs and its potential link to the heterogeneity of platelets. We will also discuss the implications of these findings while focusing on the ex vivo generation of platelets from human pluripotent stem cells. The improved understanding of the heterogeneity underlying human MK development and platelet production should open new avenues for future platelet regeneration and clinical treatment of related diseases.

The Molecular Aspects of Disturbed Platelet Activation through ADP/P2Y12 Pathway in Multiple Sclerosis

Epidemiological studies confirm a high risk of ischemic events in secondary-progressive multiple sclerosis (SP MS) patients, directly associated with an increased level of pro-thrombotic activity of platelets. Our work aimed to verify potential molecular abnormalities of the platelet P2Y₁₂ receptor expression and functionality as a cause of an increased risk of thromboembolism observed in the course of MS. We have demonstrated an enhanced platelet reactivity in response to adenosine diphosphate (ADP) in SP MS relative to controls. We have also shown an increased mRNA expression for the P2RY12 gene in both platelets and megakaryocytes, as well as enhanced density of these receptors on the platelet surface. We postulate that one of the reasons for the elevated risk of ischemic events observed in MS may be a genetically or phenotypically reinforced expression of the platelet P2Y₁₂ receptor. In order to analyze the effect of the PAR1 (protease activated receptor type 1) signaling pathway on the expression level of P2Y₁₂, we also analyzed the correlation parameters between P2Y₁₂ expression and the markers of platelet activation in MS induced by selective PAR1 agonist (thrombin receptor activating peptide-6, TRAP-6). Identifying the molecular base responsible for the enlarged pro-thrombotic activity of platelets in SP MS could contribute to the implementation of prevention and targeted treatment, reducing the development of cardiovascular disorders in the course of the disease.

Alterations in platelet behavior after major trauma: adaptive or maladaptive?

Platelets are damage sentinels of the intravascular compartment, initiating and coordinating the primary response to tissue injury. Severe trauma and hemorrhage induce profound alterations in platelet behavior. During the acute post-injury phase, platelets develop a state of impaired ex vivo agonist responsiveness independent of platelet count, associated with systemic coagulopathy and mortality risk. In patients surviving the initial insult, platelets become hyper-responsive, associated with increased risk of thrombotic events. Beyond coagulation, platelets constitute part of a sterile inflammatory response to injury: both directly through release of immunomodulatory molecules, and indirectly through modifying behavior of innate leukocytes. Both procoagulant and proinflammatory aspects have implications for secondary organ injury and multiple-organ dysfunction syndromes. This review details our current understanding of adaptive and maladaptive alterations in platelet biology induced by severe trauma, mechanisms underlying these alterations, potential platelet-focused therapies, and existing knowledge gaps and their research implications.

The Role of Platelet Cell Surface P-Selectin for the Direct Platelet-Tumor Cell Contact During Metastasis Formation in Human Tumors

Mammalian platelets, devoid of nuclei, are the smallest cells in the blood stream. They are essential for hemostasis, but also transmit cell signals that are necessary for regenerative and generative processes such as inflammation, immunity and tissue repair. In particular, in malignancies they are also associated with cell proliferation, angiogenesis, and epithelial-mesenchymal transition. Platelets promote metastasis and resistance to anti-tumor treatment. However, fundamental principles of the interaction between them and target cells within tumors are complex and still quite obscure. When injected into animals or circulating in the blood of cancer patients, cancer cells ligate platelets in a timely manner closely related to platelet activation either by direct contact or by cell-derived substances or microvesicles. In this context, a large number of different surface molecules and transduction mechanisms have been identified, although the results are sometimes species-specific and not always valid to humans. In this mini-review, we briefly summarize the current knowledge on the role of the direct and indirect platelet-tumor interaction for single steps of the metastatic cascade and specifically focus on the functional role of P-selectin.

Soluble factors differ in platelets derived from separate niches: a pilot study comparing the secretome of peripheral blood and bone marrow platelets

BACKGROUND AIMS

Platelet-rich plasma (PRP) and bone marrow aspirate are commonly used in orthobiologics for their anti-inflammatory, anabolic/regenerative and immunomodulatory characteristics via platelet degranulation and cell secretions. Although platelets are derived from megakaryocytes in the bone marrow, no attention has been paid to the potential benefits of bone marrow platelets and whether their contents differ from aging platelets in peripheral blood.

METHODS

In the present study, leukocyte-poor peripheral blood-derived platelets in plasma (LPP) and leukocyte-poor bone marrow platelets in plasma (BMP) were prepared from six donors, activated with calcium chloride, incubated and sampled at day 0, day 3 and day 6. LPP and BMP are platelet preparations intended to evaluate the respective platelet secretomes but are not classified as conventional PRPs, as they are not concentrated to the extent necessary to meet the qualifying criteria. At each time point, 15 growth and immunomodulatory factors were quantitated in LPP and BMP: platelet-derived growth factor AA, basic fibroblast growth factor/fibroblast growth factor 2, granulocyte-macrophage colony-stimulating factor, hepatocyte growth factor, macrophage colony-stimulating factor, stem cell factor, vascular endothelial growth factor, tumor necrosis factor alpha, IL-1β, interferon gamma, IL-4, IL-10, IL-1 receptor antagonist protein, IL-12p40 and arginase-1.

RESULTS

The results illustrate that platelets derived from bone marrow have a unique secretome profile compared with those derived from peripheral blood, with significant differences in anti-inflammatory cytokines, which are associated with monocyte polarization.

CONCLUSIONS

Ultimately, bone marrow-derived platelets may be useful as a stand-alone orthobiologic or as an effective adjuvant to autologous cell therapies where anti-inflammatory and anabolic processes are desired, especially with respect to monocyte function.

Platelet Proteomes, Pathways, and Phenotypes as Informants of Vascular Wellness and Disease

Platelets rapidly undergo responsive transitions in form and function to repair vascular endothelium and mediate hemostasis. In contrast, heterogeneous platelet subpopulations with a range of primed or refractory phenotypes gradually arise in chronic inflammatory and other conditions in a manner that may indicate or support disease. Qualitatively distinguishable platelet phenotypes are increasingly associated with a variety of physiological and pathological circumstances; however, the origins and significance of platelet phenotypic variation remain unclear and conceptually vague. As changes in platelet function in disease exhibit many similarities to platelets following the activation of platelet agonist receptors, the intracellular responses of platelets common to hemostasis and inflammation may provide insights to the molecular basis of platelet phenotype. Here, we review concepts around how protein-level relations-from platelet receptors through intracellular signaling events-may help to define platelet phenotypes in inflammation, immune responses, aging, and other conditions. We further discuss how representing systems-wide platelet proteomics data profiles as circuit-like networks of causally related intracellular events, or, pathway maps, may inform molecular definitions of platelet phenotype. In addition to offering insights into platelets as druggable targets, maps of causally arranged intracellular relations underlying platelet function can also advance precision and interceptive medicine efforts by leveraging platelets as accessible, dynamic, endogenous, circulating biomarkers of vascular wellness and disease. Graphic Abstract: A graphic abstract is available for this article.

Reduced miR-26b Expression in Megakaryocytes and Platelets Contributes to Elevated Level of Platelet Activation Status in Sepsis

In sepsis, platelets may become activated via toll-like receptors (TLRs), causing microvascular thrombosis. Megakaryocytes (MKs) also express these receptors; thus, severe infection may modulate thrombopoiesis. To explore the relevance of altered miRNAs in platelet activation upon sepsis, we first investigated sepsis-induced miRNA expression in platelets of septic patients. The effect of abnormal Dicer level on miRNA expression was also evaluated. miRNAs were profiled in septic vs. normal platelets using TaqMan Open Array. We validated platelet miR-26b with its target SELP (P-selectin) mRNA levels and correlated them with clinical outcomes. The impact of sepsis on MK transcriptome was analyzed in MEG-01 cells after lipopolysaccharide (LPS) treatment by RNA-seq. Sepsis-reduced miR-26b was further studied using Dicer1 siRNA and calpain inhibition in MEG-01 cells. Out of 390 platelet miRNAs detected, there were 121 significantly decreased, and 61 upregulated in sepsis vs. controls. Septic platelets showed attenuated miR-26b, which were associated with disease severity and mortality. SELP mRNA level was elevated in sepsis, especially in platelets with increased mean platelet volume, causing higher P-selectin expression. Downregulation of Dicer1 generated lower miR-26b with higher SELP mRNA, while calpeptin restored miR-26b in MEG-01 cells. In conclusion, decreased miR-26b in MKs and platelets contributes to an increased level of platelet activation status in sepsis.

The Lipid Composition of Platelets and the Impact of Storage: An Overview

Lipids and bioactive lipid mediators are essential for platelet function. The lipid profile of platelets is highly dynamic due to free exchange of lipids with the plasma, release of extracellular vesicles, and both enzymatic and nonenzymatic lipid conversion. The lipidome of platelets changes in response to activation to accommodate the functional requirements of platelets, particularly for maintenance of hemostasis. Furthermore, when stored at room temperature as a component for transfusion, the lipid profile of platelets is altered. Although there is a growing interest in alternate storage conditions, such as refrigeration and cryopreservation, few contemporary studies have examined the impact of these storage modes on the lipid profile. However, evidence exists that bioactive lipid mediators produced over the storage of blood products may have functional implications once these products are transfused. As such, there is a need to determine the changes occurring to the lipid profile of these products over storage. This review outlines the role of lipids in platelets and discusses the current state of lipidomics for studying platelet components for transfusion in an effort to highlight the necessity for additional transfusion-focused investigations.

The Era of Thromboinflammation: Platelets Are Dynamic Sensors and Effector Cells During Infectious Diseases

Platelets are anucleate cells produced by megakaryocytes. In recent years, a robust body of literature supports the evolving role of platelets as key sentinel and effector cells in infectious diseases, especially critical in bridging hemostatic, inflammatory, and immune continuums. Upon intravascular pathogen invasion, platelets can directly sense viral, parasitic, and bacterial infections through pattern recognition receptors and integrin receptors or pathogen: immunoglobulin complexes through Fc and complement receptors—although our understanding of these interactions remains incomplete. Constantly scanning for areas of injury or inflammation as they circulate in the vasculature, platelets also indirectly respond to pathogen invasion through interactions with leukocytes and the endothelium. Following antigen recognition, platelets often become activated. Through a diverse repertoire of mechanisms, activated platelets can directly sequester or kill pathogens, or facilitate pathogen clearance by activating macrophages and neutrophils, promoting neutrophil extracellular traps (NETs) formation, forming platelet aggregates and microthrombi. At times, however, platelet activation may also be injurious to the host, exacerbating inflammation and promoting endothelial damage and thrombosis. There are many gaps in our understandings of the role of platelets in infectious diseases. However, with the emergence of advanced technologies, our knowledge is increasing. In the current review, we mainly discuss these evolving roles of platelets under four different infectious pathogen infections, of which are dengue, malaria, Esterichia coli (E. coli) and staphylococcus aureus S. aureus, highlighting the complex interplay of these processes with hemostatic and thrombotic pathways.

Platelets as Mediators of Thromboinflammation in Chronic Myeloproliferative Neoplasms

Chronic myeloproliferative neoplasms (MPN) are stem cell disorders driven by mutations in JAK2, CALR, or MPL genes and characterized by myeloid proliferation and increased blood cell counts. They encompass three closely related conditions, including essential thrombocythemia, polycythemia vera, and primary myelofibrosis. Elevated levels of cytokines released by clonal and non-clonal cells generate a chronic proinflammatory state that contributes to disease pathogenesis. Thrombosis represents the most common cause of morbidity and mortality in MPN, although paradoxically, patients may also present with a bleeding diathesis. The mechanisms leading to thrombosis are complex and multiple and include increased blood cells together with qualitative abnormalities of red cells, leukocytes, and platelets that favor a prothrombotic activated phenotype. The functional interplay between blood cells, the clotting cascade, and dysfunctional endothelium contributes to hypercoagulability and this process is perpetuated by the effect of inflammatory cytokines. In addition to their well-known function in hemostasis, platelets contribute to innate immunity and inflammation and play a key role in MPN thromboinflammatory state. In vivo platelet activation leads to platelet aggregate formation and exposure of adhesion molecules which favor their interaction with activated neutrophils and monocytes leading to circulating platelet-leukocyte heterotypic aggregates. Platelets are recruited to the activated endothelium further enhancing the reciprocal activation of both cell types. Crosstalk between activated cells drives cytokine production, further fuelling the self-reinforcing thromboinflammatory loop. In addition, MPN platelets provide a procoagulant scaffold which triggers the coagulation cascade and platelet-derived microparticles amplify this response. Markers of platelet, leukocyte, endothelial and coagulation activation are increased in MPN patients although prospective studies are required to determine the potential value of these parameters for identifying patients at increased thrombotic risk. Thrombosis remains the main complication of MPN patients, with a high risk of recurrence despite adequate cytoreductive and antithrombotic treatment. Deeper insight into the mechanism favoring thrombosis development in this setting may lead to novel therapeutic approaches for MPN thrombosis. Considering the critical role of inflammation in the vascular risk, concomitant targeting of inflammatory pathways could potentially impact on primary or secondary prevention strategies.

Hyaluronan in inflammatory bowel disease: Cross-linking inflammation and coagulation

Hyaluronan, a major extracellular matrix component, is an active participant in many disease states, including inflammatory bowel disease (IBD). The synthesis of this dynamic polymer is increased at sites of inflammation. Hyaluronan together with the enzymes responsible for its synthesis, degradation, and its binding proteins, directly modulates the promotion and resolution of disease by controlling recruitment of immune cells, by release of inflammatory cytokines, and by balancing hemostasis. This review discusses the functional significance of hyaluronan in the cells and tissues involved in inflammatory bowel disease pathobiology.

Megakaryocytes in Bone Metastasis: Protection or Progression?

Bone is the primary site where some cancers develop secondary growth, particularly those derived from breast and prostate tissue. The spread of metastasis to distant sites relies on complex mechanisms by which only cells endowed with certain characteristics are able to reach secondary growth sites. Platelets play a pivotal role in tumour growth, by conferring resistance to shear stress to the circulating tumour cells and protection against natural killer cell attack. Mature polyploid megakaryocytes (MKs) reside in close proximity to the vascular sinusoids of bone marrow, where their primary function is to produce platelets. Emerging evidence has demonstrated that MKs are essential for skeletal homeostasis, due to the expression and production of the bone-related proteins osteocalcin, osteonectin, bone morphogenetic protein, osteopontin, bone sialoprotein, and osteoprotegerin. Debate surrounds the role that MKs play in the development of bone metastasis, which is the topic of this mini-review.

Megakaryocyte Contribution to Bone Marrow Fibrosis: many Arrows in the Quiver

In Primary Myelofibrosis (PMF), megakaryocyte dysplasia/hyperplasia determines the release of inflammatory cytokines that, in turn, stimulate stromal cells and induce bone marrow fibrosis. The pathogenic mechanism and the cells responsible for progression to bone marrow fibrosis in PMF are not completely understood. This review article aims to provide an overview of the crucial role of megakaryocytes in myelofibrosis by discussing the role and the altered secretion of megakaryocyte-derived soluble factors, enzymes and extracellular matrices that are known to induce bone marrow fibrosis.

Amicus or Adversary Revisited: Platelets in Acute Lung Injury and Acute Respiratory Distress Syndrome

Platelets are essential cellular effectors of hemostasis and contribute to disease as circulating effectors of pathologic thrombosis. These are their most widely known biologic activities. Nevertheless, recent observations demonstrate that platelets have a much more intricate repertoire beyond these traditional functions and that they are specialized for contributions to vascular barrier integrity, organ repair, antimicrobial host defense, inflammation, and activities across the immune continuum. Paradoxically, on the basis of clinical investigations and animal models of disease, some of these newly discovered activities of platelets appear to contribute to tissue injury. Studies in the last decade indicate unique interactions of platelets and their precursor, the megakaryocyte, in the lung and implicate platelets as essential effectors in experimental acute lung injury and clinical acute respiratory distress syndrome. Additional discoveries derived from evolving work will be required to precisely define the contributions of platelets to complex subphenotypes of acute lung injury and to determine if these remarkable and versatile blood cells are therapeutic targets in acute respiratory distress syndrome.

MiR-21 role in aspirin-dependent PPARα and multidrug resistance protein 4 upregulation

BACKGROUND

A mechanism involved in high on-aspirin treatment residual platelet reactivity is platelet multidrug resistance protein 4 (MRP4) overexpression. Aspirin enhances platelet MRP4 expression with a PPARα-dependent mechanism and reduces miR-21 expression that, in turn, downregulates PPARα expression.

OBJECTIVE

The aim of our study was to verify the relationship between miR-21 and MRP4-PPARα levels induced by aspirin treatment.

METHODS

We evaluated the changes in MRP4-PPARα, mRNA, MRP4 protein, and miR-21 expression induced by aspirin in: (i) in vitro-treated megakaryoblastic cell line (DAMI), (ii) primary megakaryocytes cultures and derived platelets, (iii) healthy volunteers' platelets treated with aspirin, and (iv) aspirinated patients (aspirin-treated patients) and in a control population (control).

RESULTS

We observed an aspirin-induced reverse relationship between the expression of miR-21 and PPARα-MRP4. In DAMI cells the miR-21 mimic transfection reduces PPARα and MRP4 expression, even if cells were treated with aspirin after transfection. MiR-21 inhibitor transfection induces PPARα and MRP4 expression that are not enhanced by aspirin treatment. In human megakaryocytes, aspirin treatment lead to a miR-21 downregulation and a MRP4 upregulation and this trend is confirmed in derived platelets. In aspirin-treated volunteers, an inverse relationship between miR-21 and MRP4 platelet expression was found after aspirin treatment. A similar negative relationship was found in aspirin-treated patients vs the control population.

CONCLUSION

The results reported in this study provide information that aspirin induces the modulation of platelet miR-21 expression levels and this modulation can be responsible for MRP4 enhancement in circulating platelets.

Tumor-Educated Platelets as a Noninvasive Biomarker Source for Cancer Detection and Progression Monitoring

Liquid biopsies represent a potential revolution in cancer diagnostics as a noninvasive method for detecting and monitoring diseases, complementary to or even replacing current tissue biopsy approaches. Several blood-based biosources and biomolecules, such as cell-free DNA and RNA, proteins, circulating tumor cells, and extracellular vesicles, have been explored for molecular test development. We recently discovered the potential of tumor-educated blood platelets (TEP) as a noninvasive biomarker trove for RNA biomarker panels. TEPs are involved in the progression and spread of several solid tumors, and spliced TEP RNA surrogate signatures can provide specific information on the presence, location, and molecular characteristics of cancers. So far, TEP samples from patients with different tumor types, including lung, brain, and breast cancers, have been tested, and it has been shown that TEPs from patients with cancer are distinct from those with inflammatory and other noncancerous diseases. It remains to be investigated how platelets are "educated," which mechanisms cause intraplatelet RNA splicing, and whether the relative contribution of specific platelet subpopulations changes in patients with cancer. Ultimately, TEP RNA may complement currently used biosources and biomolecules employed for liquid biopsy diagnosis, potentially enhancing the detection of cancer in an early stage and facilitating noninvasive disease monitoring. Cancer Res; 78(13); 3407-12. ©2018 AACR.

Translational Implications of Platelets as Vascular First Responders

Platelets play a vital role in normal hemostasis to stem blood loss at sites of vascular injury by tethering and adhering to sites of injury, recruiting other platelets and blood cells to the developing clot, releasing vasoactive small molecules and proteins, and assembling and activating plasma coagulation proteins in a tightly regulated temporal and spatial manner. In synchrony with specific end products of coagulation, primarily cross-linked fibrin, a stable thrombus quickly forms. Far beyond physiological hemostasis and pathological thrombosis, emerging evidence supports platelets playing a pivotal role in vascular homeostasis, inflammation, cellular repair, regeneration, and wide range of autocrine and paracrine functions. In essence, platelets play both structural and functional roles as reporters, messengers, and active transporters surveying the vasculature for cues of environmental or developmental stimuli and participating as first responders.1 In this review, we will provide a contemporary perspective of platelet physiology, including fundamental, translational, and clinical constructs that apply directly to human health and disease.

An update on factor XI structure and function

Factor XI (FXI) is the zymogen of a plasma protease, factor XIa (FXIa), that contributes to thrombin generation during blood coagulation by proteolytic activation of several coagulation factors, most notably factor IX (FIX). FXI is a homolog of prekallikrein (PK), a component of the plasma kallikrein-kinin system. While sharing structural and functional features with PK, FXI has undergone adaptive changes that allow it to contribute to blood coagulation. Here we review current understanding of the biology and enzymology of FXI, with an emphasis on structural features of the protein as they relate to protease function.

Small but mighty: Platelets as central effectors of host defense

Platelets actively participate in inflammatory processes and drive diseases such as atherosclerosis, rheumatoid arthritis and cancer metastasis. However, platelets also have anti-inflammatory and anti-infective properties, which have received less consideration in the past. In this review, we highlight recent findings on the role of platelets in host defense and describe regulatory pathways modulating immuneresponses. Furthermore, we discuss the role of platelets for the resolution of inflammation and tissue repair. These conceptual changes contribute to our understanding of platelet biology in disease.

Platelet functional and transcriptional changes induced by intralipid infusion

Multiple studies have shown the effects of long-term exposure to high-fat or western diets on the vascular system. There is limited knowledge on the acute effects of high circulating fat levels, specifically on platelets, which have a role in many processes, including thrombosis and inflammation. This study investigated the effects of acute, high-fat exposure on platelet function and transcript profile. Twenty healthy participants were given an intravenous infusion of 20% Intralipid emulsion and heparin over 6 hours. Blood samples were taken prior to and the day after infusion to measure platelet function and transcript expression levels. Platelet aggregation was not significantly affected by Intralipid infusion, but, when mitochondria function was inhibited by carbonyl cyanide 3-chlorophenylhydrazone (CCCP) or oligomycin, platelet aggregation was higher in the post-infusion state compared to baseline. Through RNA sequencing, and verified by RT-qPCR, 902 miRNAs and 617 mRNAs were affected by Intralipid infusion. MicroRNAs increased include miR-4259 and miR-346, while miR-517b and miR-517c are both decreased. Pathway analysis identified two clusters significantly enriched, including cell motility. In conclusion, acute exposure to high fat affects mitochondrial-dependent platelet function, as well as the transcript profile.

Platelet populations and priming in hematological diseases

In healthy subjects and patients with hematological diseases, platelet populations can be distinguished with different response spectra in hemostatic and vascular processes. These populations partly overlap, and are less distinct than those of leukocytes. The platelet heterogeneity is linked to structural properties, and is enforced by inequalities in the environment. Contributing factors are variability between megakaryocytes, platelet ageing, and positive or negative priming of platelets during their time in circulation. Within a hemostatic plug or thrombus, platelet heterogeneity is enhanced by unequal exposure to agonists, with populations of contracted platelets in the thrombus core, discoid platelets at the thrombus surface, patches of ballooned and procoagulant platelets forming thrombin, and coated platelets binding fibrin. Several pathophysiological hematological conditions can positively or negatively prime the responsiveness of platelet populations. As a consequence, in vivo and in vitro markers of platelet activation can differ in thrombotic and hematological disorders.

Megakaryocytes in Myeloproliferative Neoplasms Have Unique Somatic Mutations

Myeloproliferative neoplasms (MPNs) are a group of related clonal hemopoietic stem cell disorders associated with hyperproliferation of myeloid cells. They are driven by mutations in the hemopoietic stem cell, most notably JAK2^V617F, CALR, and MPL. Clinically, they have the propensity to progress to myelofibrosis and transform to acute myeloid leukemia. Megakaryocytic hyperplasia with abnormal features are characteristic, and it is thought that these cells stimulate and drive fibrotic progression. The biological defects underpinning this remain to be explained. In this study we examined the megakaryocyte genome in 12 patients with MPNs to determine whether there are somatic variants and whether there is any association with marrow fibrosis. We performed targeted next-generation sequencing for 120 genes associated with myeloid neoplasms on megakaryocytes isolated from aspirated bone marrow. Ten of the 12 patients had genomic defects in megakaryocytes that were not present in nonmegakaryocytic hemopoietic marrow cells from the same patient. The greatest allelic burden was in patients with increased reticulin deposition. The megakaryocyte-unique mutations were predominantly in genes that regulate chromatin remodeling, chromosome alignment, and stability. These findings show that genomic abnormalities are present in megakaryocytes in MPNs and that these appear to be associated with progression to bone marrow fibrosis.

The clinical significance of platelet microparticle-associated microRNAs

Circulating blood platelets play a central role in the maintenance of hemostasis. They adhere to subendothelial extracellular matrix proteins that become exposed upon vessel wall damage, which is followed by platelet activation, further platelet recruitment, platelet aggregation and formation of an occlusive, or non-occlusive, platelet thrombus. Platelets host a surprisingly diverse transcriptome, which is comprised of ~9500 messenger RNAs (mRNAs) and different classes of non-coding RNAs, including microRNAs, as well as a significant repertoire of proteins that contribute to their primary (adhesion, aggregation, granule secretion) and alternative (RNA transfer, mRNA translation, immune regulation) functions. Platelets have the propensity to release microparticles (MPs; 0.1–1 μm in diameter) upon activation, which may mediate inflammatory responses and contribute to exacerbate inflammatory diseases and conditions. Carrying components of the platelets’ cytoplasm, platelet MPs may exert their effects on recipient cells by transferring their content in platelet-derived bioactive lipid mediators, cytokines, mRNAs and microRNAs. Platelet MP-associated microRNAs may thus function also outside of platelets and play an important role in intercellular signaling and gene expression programming across the entire circulatory system. The role and importance of platelet MP-associated microRNAs in various aspects of biology and pathophysiology are increasingly recognized, and now provide the scientific basis and rationale to support further translational research and clinical studies. The clinical significance, pathophysiological role as well as the diagnostic and therapeutic potential of platelet MP-associated microRNAs in cardiovascular diseases, platelet transfusion and cancer will be discussed.

Hyperglycaemia suppresses microRNA expression in platelets to increase P2RY12 and SELP levels in type 2 diabetes mellitus

Megakaryocyte (MK)-derived miRNAs have been detected in platelets. Here, we analysed the expression of platelet and circulating miR-223, miR-26b, miR-126 and miR-140 that might be altered with their target mRNAs in type 2 diabetes mellitus (DM2). MiRNAs were isolated from leukocyte-depleted platelets and plasma samples obtained from 28 obese DM2, 19 non-DM obese and 23 healthy individuals. The effect of hyperglycaemia on miRNAs was also evaluated in MKs using MEG-01 and K562 cells under hyperglycaemic conditions after 8 hours up to four weeks. Quantitation of mature miRNA, pre-miRNAs and target mRNA levels (P2RY12 and SELP) were measured by RT-qPCR. To prove the association of miR-26b and miR-140 with SELP (P-selectin) mRNA level, overexpression or inhibition of these miRNAs in MEG-01 MKs was performed using mimics or anti-miRNAs, respectively. The contribution of calpain substrate Dicer to modulation of miRNAs was studied by calpain inhibition. Platelet activation was evaluated via surface P-selectin by flow cytometry. Mature and pre-forms of investigated miRNAs were significantly reduced in DM2, and platelet P2RY12 and SELP mRNA levels were elevated by two-fold at increased platelet activation compared to controls. Significantly blunted miRNA expressions were observed by hyperglycaemia in MEG-01 and K562-MK cells versus baseline values, while the manipulation of miR-26b and miR-140 expression affected SELP mRNA level. Calpeptin pretreatment restored miRNA levels in hyperglycaemic MKs. Overall, miR-223, miR-26b, miR-126 and miR-140 are expressed at a lower level in platelets and MKs in DM2 causing upregulation of P2RY12 and SELP mRNAs that may contribute to adverse platelet function.

DREAM plays an important role in platelet activation and thrombogenesis

Downstream regulatory element antagonist modulator (DREAM), a transcriptional repressor, is known to modulate pain responses. However, it is unknown whether DREAM is expressed in anucleate platelets and plays a role in thrombogenesis. By using intravital microscopy with DREAM-null mice and their bone marrow chimeras, we demonstrated that both hematopoietic and nonhematopoietic cell DREAMs are required for platelet thrombus formation following laser-induced arteriolar injury. In a FeCl₃-induced thrombosis model, we found that compared with wild-type (WT) control and nonhematopoietic DREAM knockout (KO) mice, DREAM KO control and hematopoietic DREAM KO mice showed a significant delay in time to occlusion. Tail bleeding time was prolonged in DREAM KO control mice, but not in WT or DREAM bone marrow chimeric mice. In vivo adoptive transfer experiments further indicated the importance of platelet DREAM in thrombogenesis. We found that DREAM deletion does not alter the ultrastructural features of platelets but significantly impairs platelet aggregation and adenosine triphosphate secretion induced by numerous agonists (collagen-related peptide, adenosine 5'-diphosphate, A23187, thrombin, or U46619). Biochemical studies revealed that platelet DREAM positively regulates phosphoinositide 3-kinase (PI3K) activity during platelet activation. Using DREAM-null platelets and PI3K isoform-specific inhibitors, we observed that platelet DREAM is important for α-granule secretion, Ca²⁺ mobilization, and aggregation through PI3K class Iβ (PI3K-Iβ). Genetic and pharmacological studies in human megakaryoblastic MEG-01 cells showed that DREAM is important for A23187-induced Ca²⁺ mobilization and its regulatory function requires Ca²⁺ binding and PI3K-Iβ activation. These results suggest that platelet DREAM regulates PI3K-Iβ activity and plays an important role during thrombus formation.

Platelets as immune-sensing cells

Publisher's Note: This article has a companion Point by Brass et al. Publisher's Note: Join in the discussion of these articles at Blood Advances Community Conversations.

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.

Human Platelet Lipidomics: Variance, Visualization, Flux, and Fuel

The cardioprotection afforded by low-dose aspirin reflects the biological importance of the platelet lipid thromboxane A2. In this issue of Cell Metabolism, Slatter et al. (2016) illuminate the breadth, complexity, and variability of the human platelet lipidome under conditions of thrombin activation and aspirin suppression, potentially facilitating the pursuit of precision medicine.

The nonhemostatic immune functions of platelets

Platelets are megakaryocyte-derived cellular fragments, which lack a nucleus and are the smallest circulating cells and are classically known to have a major role in supporting hemostasis. Apart from this well-established role, it is now becoming evident that platelets are also capable of conveying other important functions, such as during infection and inflammation. This paper will outline these nonhemostatic functions in two major sections termed "Platelets versus pathogens" and "Platelet-target cell communication". Platelets actively contribute to protection against invading pathogens and are capable of regulating immune functions in various target cells, all through sophisticated and efficient mechanisms. These relatively novel features will be highlighted, illustrating the multifunctional role of platelets in inflammation.