Escaping the nuclear confines: signal-dependent pre-mRNA splicing in anucleate platelets

Comprehensive comparison of neonate and adult human platelet transcriptomes

Understanding the underlying mechanisms of the well-substantiated platelet hyporeactivity in neonates is of interest given their implications for the clinical management of newborns, a population at higher bleeding risk than adults (especially sick and preterm infants), as well as for gaining insight into the regulatory mechanisms of platelet biology. Transcriptome analysis is useful in identifying mRNA signatures affecting platelet function. However, human fetal/neonatal platelet transcriptome analysis has never before been reported. We have used mRNA expression array for the first time to compare platelet transcriptome changes during development. Microarray analysis was performed in pure platelet RNA obtained from adult and cord blood, using the same platform in two independent laboratories. A high correlation was obtained between array results for both adult and neonate platelet samples. There was also good agreement between results in our adult samples and outcomes previously reported in three different studies. Gene enrichment analysis showed that immunity- and platelet function-related genes are highly expressed at both developmental stages. Remarkably, 201 genes were found to be differentially expressed throughout development. In particular, neonatal platelets contain higher levels of mRNA that are associated with protein synthesis and processing, while carrying significantly lower levels of genes involved in calcium transport/metabolism and cell signaling (including GNAZ). Overall, our results point to variations in platelet transcriptome as possibly underlining the hypo-functional phenotype of neonatal platelets and provide further support for the role of platelets in cellular immune response. Better characterization of the platelet transcriptome throughout development can contribute to elucidate how transcriptome changes impact different pathological conditions.

Swarm Intelligence-Enhanced Detection of Non-Small-Cell Lung Cancer Using Tumor-Educated Platelets

Blood-based liquid biopsies, including tumor-educated blood platelets (TEPs), have emerged as promising biomarker sources for non-invasive detection of cancer. Here we demonstrate that particle-swarm optimization (PSO)-enhanced algorithms enable efficient selection of RNA biomarker panels from platelet RNA-sequencing libraries (n = 779). This resulted in accurate TEP-based detection of early- and late-stage non-small-cell lung cancer (n = 518 late-stage validation cohort, accuracy, 88%; AUC, 0.94; 95% CI, 0.92-0.96; p < 0.001; n = 106 early-stage validation cohort, accuracy, 81%; AUC, 0.89; 95% CI, 0.83-0.95; p < 0.001), independent of age of the individuals, smoking habits, whole-blood storage time, and various inflammatory conditions. PSO enabled selection of gene panels to diagnose cancer from TEPs, suggesting that swarm intelligence may also benefit the optimization of diagnostics readout of other liquid biopsy biosources.

Platelet-Eosinophil Interactions As a Potential Therapeutic Target in Allergic Inflammation and Asthma

The importance of platelet activation during hemostasis is well understood. An understanding of these mechanisms has led to the use of several classes of anti-platelet drugs to inhibit aggregation for the prevention of thrombi during cardiovascular disease. It is now also recognized that platelets can function very differently during inflammation, as part of their role in the innate immune response against pathogens. This dichotomy in platelet function occurs through distinct physiological processes and alternative signaling pathways compared to that of hemostasis (leading to platelet aggregation) and is manifested as increased rheological interactions with leukocytes, the ability to undergo chemotaxis, communication with antigen-presenting cells, and direct anti-pathogen responses. Mounting evidence suggests platelets are also critical in the pathogenesis of allergic diseases such as asthma, where they have been associated with antigen presentation, bronchoconstriction, bronchial hyperresponsiveness, airway inflammation, and airway remodeling in both clinical and experimental studies. In particular, platelets have been reported bound to eosinophils in the blood of patients with asthma and the incidence of these events increases after both spontaneous asthma attacks in a biphasic manner, or after allergen challenge in the clinic. Platelet depletion in animal models of allergic airway inflammation causes a profound reduction in eosinophil recruitment to the lung, suggesting that the association of platelets with eosinophils is indeed an important event during eosinophil activation. Furthermore, in cases of severe asthma, and in animal models of allergic airways inflammation, platelet–eosinophil complexes move into the lung through a platelet P-selectin-mediated, eosinophil β1-integrin activation-dependent process, while platelets increase adherence of eosinophils to the vascular endothelium in vitro, demonstrating a clear interaction between these cell types in allergic inflammatory diseases. This review will explore non-thrombotic platelet activation in the context of allergy and the association of platelets with eosinophils, to reveal how these phenomena may lead to the discovery of novel therapeutic targets.

Patterns and functional implications of platelets upon tumor "education"

While platelets are traditionally recognized to play a predominant role in hemostasis and thrombosis, increasing evidence verifies its involvement in malignancies. As a component of the tumor microenvironment, platelets influence carcinogenesis, tumor metastasis and chemotherapy efficiency. Platelets status is thus predictable as a hematological biomarker of cancer prognosis and a hot target for therapeutic intervention. On the other hand, the role of circulating tumor cells (CTCs) as an inducer of platelet activation and aggregation has been well acknowledged. The cross-talk between platelets and CTCs is reciprocal on that the CTCs activate platelets while platelets contribute to CTCs' survival and dissemination. This review covers some of the current issues related to the loop between platelets and tumor aggression, including the manners of tumor cells in "educating" platelets and biofunctional alterations of platelets upon tumor "education". We also highlight the potential clinical applications on the interplay between tumors and platelets. Further studies with well-designed prospective multicenter trials may contribute to clinical "liquid biopsy" diagnosis by evaluating the global changes of platelets.

The determinants of alternative RNA splicing in human cells

Alternative splicing represents an important level of the regulation of gene function in eukaryotic organisms. It plays a critical role in virtually every biological process within an organism, including regulation of cell division and cell death, differentiation of tissues in the embryo and the adult organism, as well as in cellular response to diverse environmental factors. In turn, studies of the last decade have shown that alternative splicing itself is controlled by different mechanisms. Unfortunately, there is no clear understanding of how these diverse mechanisms, or determinants, regulate and constrain the set of alternative RNA species produced from any particular gene in every cell of the human body. Here, we provide a consolidated overview of alternative splicing determinants including RNA-protein interactions, epigenetic regulation via chromatin remodeling, coupling of transcription-to-alternative splicing, effect of secondary structures in pre-RNA, and function of the RNA quality control systems. We also extensively and critically discuss some mechanistic insights on coordinated inclusion/exclusion of exons during the formation of mature RNA molecules. We conclude that the final structure of RNA is pre-determined by a complex interplay between cis- and trans-acting factors. Altogether, currently available empirical data significantly expand our understanding of the functioning of the alternative splicing machinery of cells in normal and pathological conditions. On the other hand, there are still many blind spots that require further deep investigations.

Platelet RNA as a circulating biomarker trove for cancer diagnostics

Platelets are multifunctional cell fragments, circulating in blood in high abundance. Platelets assist in thrombus formation, sensing of pathogens entering the blood stream, signaling to immune cells, releasing vascular remodeling factors, and, negatively, enhancing cancer metastasis. Platelets are 'educated' by their environment, including in patients with cancer. Cancer cells appear to initiate intraplatelet signaling, resulting in splicing of platelet pre-mRNAs, and enhance secretion of cytokines. Platelets can induce leukocyte and endothelial cell modeling factors, for example, through adenine nucleotides (ATP), thereby facilitating extravasation of cancer cells. Besides releasing factors, platelets can also sequester RNAs and proteins released by cancer cells. Thus, platelets actively respond to queues from local and systemic conditions, thereby altering their transcriptome and molecular content. Platelets contain a rich repertoire of RNA species, including mRNAs, small non-coding RNAs and circular RNAs; although studies regarding the functionality of the various platelet RNA species require more attention. Recent advances in high-throughput characterization of platelet mRNAs revealed 10 to > 1000 altered mRNAs in platelets in the presence of disease. Hence, platelet RNA appears to be dynamically affected by pathological conditions, thus possibly providing opportunities to use platelet RNA as diagnostic, prognostic, predictive, or monitoring biomarkers. In this review, we cover the literature regarding the platelet RNA families, processing of platelet RNAs, and the potential application of platelet RNA as disease biomarkers.

MicroRNA profiling of platelets from immune thrombocytopenia and target gene prediction

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by a low platelet count and insufficient platelet production. Previous studies identified that microRNAs (miRNAs/miRs) are important for platelet function. However, the regulatory role of miRNAs in the pathogenesis of thrombocytopenia in ITP remains unclear. The aim of the present study is to isolate differentially expressed miRNAs, and identify their roles in platelets from ITP. A total of 5 ml blood from 22 patients with ITP and 8 healthy controls was isolated for platelet collection. A microarray assay was performed to analyze the differentially expressed miRNAs in the patients with ITP and healthy patients. Furthermore, the expression of differentially expressed miRNAs was verified by reverse transcription‑quantitative polymerase chain reaction. In addition, the target mRNAs of the differentially expressed miRNAs were predicted via miRWalk databases, and the target genes and miRNAs were classified by Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes analyses. In the present study, 115 miRNAs were identified to be differentially expressed in platelets from patients with ITP compared with the healthy controls (>3‑fold alteration; P<0.05). Among them, 57 miRNAs were upregulated in ITP, while 58 miRNAs were downregulated. Bioinformatic prediction demonstrated that hsa‑miR‑548a‑5p, hsa‑miR‑1185‑2‑3p, hsa‑miR‑30a‑3p, hsa‑miR‑6867‑5p, hsa‑miR‑765 and hsa‑miR‑3125 were associated with platelet apoptosis and adhesion in ITP. The present study performed miRNA profiling of platelets from patients with ITP and the results may aid in the understanding of the regulatory mechanism of ITP.

Platelet proteome reveals novel pathways of platelet activation and platelet-mediated immunoregulation in dengue

Dengue is the most prevalent human arbovirus disease worldwide. Dengue virus (DENV) infection causes syndromes varying from self-limiting febrile illness to severe dengue. Although dengue pathophysiology is not completely understood, it is widely accepted that increased inflammation plays important roles in dengue pathogenesis. Platelets are blood cells classically known as effectors of hemostasis which have been increasingly recognized to have major immune and inflammatory activities. Nevertheless, the phenotype and effector functions of platelets in dengue pathogenesis are not completely understood. Here we used quantitative proteomics to investigate the protein content of platelets in clinical samples from patients with dengue compared to platelets from healthy donors. Our assays revealed a set of 252 differentially abundant proteins. In silico analyses associated these proteins with key molecular events including platelet activation and inflammatory responses, and with events not previously attributed to platelets during dengue infection including antigen processing and presentation, proteasome activity, and expression of histones. From these results, we conducted functional assays using samples from a larger cohort of patients and demonstrated evidence for platelet activation indicated by P-selectin (CD62P) translocation and secretion of granule-stored chemokines by platelets. In addition, we found evidence that DENV infection triggers HLA class I synthesis and surface expression by a mechanism depending on functional proteasome activity. Furthermore, we demonstrate that cell-free histone H2A released during dengue infection binds to platelets, increasing platelet activation. These findings are consistent with functional importance of HLA class I, proteasome subunits, and histones that we found exclusively in proteome analysis of platelets in samples from dengue patients. Our study provides the first in-depth characterization of the platelet proteome in dengue, and sheds light on new mechanisms of platelet activation and platelet-mediated immune and inflammatory responses.

Dengue is the most frequent hemorrhagic viral disease and re-emergent infection in the world. Recent decades were marked by a progressive global expansion of the infection including a higher frequency of severe dengue. Currently there is no effective vaccinal coverage or specific therapies, while efforts aimed at vector control have failed to stop the progression of epidemics and expansion of the disease. An increased understanding of the molecular physiology is of paramount importance for the establishment of new therapeutic targets and better clinical management. Dengue fever is characterized by thrombocytopenia and vascular leak. Although thrombocytopenia is a hallmark of dengue, the molecular phenotype and activities of platelets in the pathogenesis of dengue is not well elucidated. This work characterizes the proteome of platelets isolated from patients with dengue and includes validation of functionally-linked protein networks that we identified, using samples from a larger cohort of dengue patients. Moreover, in vitro experiments revealed activities of platelets that have recognized importance to dengue pathogenesis, including chemokine release, antigen presentation, and proteasome activity. Finally, our results identify circulating histones as a novel mechanism of platelet activation in dengue. These findings provide new evidence for platelet immune activities in dengue illness, and mark an advance in the understanding of this disease.

Platelet factor XI: intracellular localization and mRNA splicing following platelet activation

BACKGROUND

The structure and function of platelet factor XI (FXI) protein and the presence of F11 mRNA in platelets are controversial. Although platelets are anucleated cells they contain spliceosome components and pre-mRNAs. Three platelet proteins have been demonstrated to be spliced upon platelet activation.

OBJECTIVE

To determine whether FXI is also spliced upon activation and to discern the localization of FXI in platelets.

METHODS

Localization of FXI in platelets was assessed by confocal immunofluorescence staining. ELISA, chromogenic assay and western blot analyses were used to measure antigen levels, activity levels and size of FXI in platelets, respectively. Splicing patterns of F11 mRNA were assessed in three states of platelet activation: activated platelets, resting platelets and αIIbβ3-integrin activated platelets.

RESULTS

Platelet FXI was exhibited in platelet granules. Activated platelets exhibited higher levels of mature F11 mRNA and protein and lower levels of F11 pre-mRNA compared to resting or αIIbβ3-integrin activated platelets.

CONCLUSIONS

We confirmed the presence of FXI in platelets and showed that it is localized in granules but is not restricted to the same α-granule subtype as von-Willebrand factor and p-selectin. Our study also shows that F11 is present in platelets as pre-mRNA and is spliced upon platelet activation.

Activation of NLRP3 inflammasome complex potentiates venous thrombosis in response to hypoxia

Venous thromboembolism (VTE), caused by altered hemostasis, remains the third most common cause of mortality among all cardiovascular conditions. In addition to established genetic and acquired risk factors, low-oxygen environments also predispose otherwise healthy individuals to VTE. Although disease etiology appears to entail perturbation of hemostasis pathways, the key molecular determinants during immediate early response remain elusive. Using an established model of venous thrombosis, we here show that systemic hypoxia accelerates thromboembolic events, functionally stimulated by the activation of nucleotide binding domain, leucine-rich-containing family, pyrin domain containing 3 (NLRP3) inflammasome complex and increased IL-1β secretion. Interestingly, we also show that the expression of NLRP3 is mediated by hypoxia-inducible factor 1-alpha (HIF-1α) during these conditions. The pharmacological inhibition of caspase-1, in vivo knockdown of NLRP3, or HIF-1α other than IL-1β-neutralizing antibodies attenuated inflammasome activation and curtailed thrombosis under hypoxic conditions. We extend the significance of these preclinical findings by studying modulation of this pathway in patients with altitude-induced venous thrombosis. Our results demonstrate distinctive, increased expression of NLRP3, caspase-1, and IL-1β in individuals with clinically established venous thrombosis. We therefore propose that an early proinflammatory state in the venous milieu, orchestrated by the HIF-induced NLRP3 inflammasome complex, is a key determinant of acute thrombotic events during hypoxic conditions.

Intron retention as a component of regulated gene expression programs

Intron retention has long been an exemplar of regulated splicing with case studies of individual events serving as models that provided key mechanistic insights into the process of splicing control. In organisms such as plants and budding yeast, intron retention is well understood as a major mechanism of gene expression regulation. In contrast, in mammalian systems, the extent and functional significance of intron retention have, until recently, remained greatly underappreciated. Technical challenges to the global detection and quantitation of transcripts with retained introns have often led to intron retention being overlooked or dismissed as “noise”. Now, however, with the wealth of information available from high-throughput deep sequencing, combined with focused computational and statistical analyses, we are able to distinguish clear intron retention patterns in various physiological and pathological contexts. Several recent studies have demonstrated intron retention as a central component of gene expression programs during normal development as well as in response to stress and disease. Furthermore, these studies revealed various ways in which intron retention regulates protein isoform production, RNA stability and translation efficiency, and rapid induction of expression via post-transcriptional splicing of retained introns. In this review, we highlight critical findings from these transcriptomic studies and discuss commonalties in the patterns prevalent in intron retention networks at the functional and regulatory levels.

SMN deficiency in severe models of spinal muscular atrophy causes widespread intron retention and DNA damage

Spinal muscular atrophy (SMA), an autosomal recessive neuromuscular disease, is the leading monogenic cause of infant mortality. Homozygous loss of the gene survival of motor neuron 1 (SMN1) causes the selective degeneration of lower motor neurons and subsequent atrophy of proximal skeletal muscles. The SMN1 protein product, survival of motor neuron (SMN), is ubiquitously expressed and is a key factor in the assembly of the core splicing machinery. The molecular mechanisms by which disruption of the broad functions of SMN leads to neurodegeneration remain unclear. We used an antisense oligonucleotide (ASO)-based inducible mouse model of SMA to investigate the SMN-specific transcriptome changes associated with neurodegeneration. We found evidence of widespread intron retention, particularly of minor U12 introns, in the spinal cord of mice 30 d after SMA induction, which was then rescued by a therapeutic ASO. Intron retention was concomitant with a strong induction of the p53 pathway and DNA damage response, manifesting as γ-H2A.X positivity in neurons of the spinal cord and brain. Widespread intron retention and markers of the DNA damage response were also observed with SMN depletion in human SH-SY5Y neuroblastoma cells and human induced pluripotent stem cell-derived motor neurons. We also found that retained introns, high in GC content, served as substrates for the formation of transcriptional R-loops. We propose that defects in intron removal in SMA promote DNA damage in part through the formation of RNA:DNA hybrid structures, leading to motor neuron death.

Principal Components Analysis Based Unsupervised Feature Extraction Applied to Gene Expression Analysis of Blood from Dengue Haemorrhagic Fever Patients

Dengue haemorrhagic fever (DHF) sometimes occurs after recovery from the disease caused by Dengue virus (DENV), and is often fatal. However, the mechanism of DHF has not been determined, possibly because no suitable methodologies are available to analyse this disease. Therefore, more innovative methods are required to analyse the gene expression profiles of DENV-infected patients. Principal components analysis (PCA)-based unsupervised feature extraction (FE) was applied to the gene expression profiles of DENV-infected patients, and an integrated analysis of two independent data sets identified 46 genes as critical for DHF progression. PCA using only these 46 genes rendered the two data sets highly consistent. The application of PCA to the 46 genes of an independent third data set successfully predicted the progression of DHF. A fourth in vitro data set confirmed the identification of the 46 genes. These 46 genes included interferon- and heme-biosynthesis-related genes. The former are enriched in binding sites for STAT1, STAT2, and IRF1, which are associated with DHF-promoting antibody-dependent enhancement, whereas the latter are considered to be related to the dysfunction of spliceosomes, which may mediate haemorrhage. These results are outcomes that other type of bioinformatic analysis could hardly achieve.

Activated Platelets Induce Endothelial Cell Activation via an Interleukin-1β Pathway in Systemic Lupus Erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) is associated with the premature development of cardiovascular disease. The platelet-endothelium interaction is important in the pathogenesis of cardiovascular disease. In this study, we investigated the platelet phenotype from patients with SLE and matched controls, and their effect on endothelial cells.

APPROACH AND RESULTS

Platelet aggregability was measured in 54 SLE subjects off antiplatelet therapy (mean age 40.1±12.8 years; 82% female; 37% white) with age- and sex-matched controls. Platelets were coincubated with human umbilical vein endothelial cells (HUVECs) and changes to gene expression assessed by an RNA array and quantitative reverse transcription polymerase chain reaction. SLE disease activity index ranged from 0 to 22 (mean 5.1±3.9). Compared with controls, patients with SLE had significantly increased monocyte and leukocyte-platelet aggregation and platelet aggregation in response to submaximal agonist stimulation. An agnostic microarray of HUVECs cocultured with SLE platelets found a platelet-mediated effect on endothelial gene pathways involved in cell activation. Sera from SLE versus control subjects significantly increased (1) activation of control platelets; (2) platelet adhesion to HUVECs; (3) platelet-induced HUVEC gene expression of interleukin-8, and intercellular adhesion molecule 1; and (4) proinflammatory gene expression in HUVECs, mediated by interleukin-1β-dependent pathway. Incubation of SLE-activated platelets with an interleukin-1β-neutralizing antibody or HUVECs pretreated with interleukin-1 receptor antibodies attenuated the platelet-mediated activation of endothelial cells.

CONCLUSIONS

Platelet activity measurements and subsequent interleukin-1β-dependent activation of the endothelium are increased in subjects with SLE. Platelet-endothelial interactions may play a role in the pathogenesis of cardiovascular disease in patients with SLE.

Cancer and Thrombosis: The Platelet Perspective

Platelets are critical to hemostatic and immunological function, and are key players in cancer progression, metastasis, and cancer-related thrombosis. Platelets interact with immune cells to stimulate anti-tumor responses and can be activated by immune cells and tumor cells. Platelet activation can lead to complex interactions between platelets and tumor cells. Platelets facilitate cancer progression and metastasis by: (1) forming aggregates with tumor cells; (2) inducing tumor growth, epithelial-mesenchymal transition, and invasion; (3) shielding circulating tumor cells from immune surveillance and killing; (4) facilitating tethering and arrest of circulating tumor cells; and (5) promoting angiogenesis and tumor cell establishment at distant sites. Tumor cell-activated platelets also predispose cancer patients to thrombotic events. Tumor cells and tumor-derived microparticles lead to thrombosis by secreting procoagulant factors, resulting in platelet activation and clotting. Platelets play a critical role in cancer progression and thrombosis, and markers of platelet-tumor cell interaction are candidates as biomarkers for cancer progression and thrombosis risk.

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.

Platelets in infectious disease

Sepsis is a dynamic, acute, infectious disease syndrome characterized by dysregulated thrombo-inflammatory responses. The high mortality associated with sepsis has been recognized since the earliest clinicians' writings. Despite this, advances in the treatment of sepsis have been more modest. This is limited, in part, by the heterogeneity in the definition, population, presentation, and causal factors of infectious syndromes. Given the persistently high morbidity and mortality associated with sepsis, a better understanding of the dysregulated cellular biology underpinning sepsis is needed. Platelets are small, anucleate cells that have hemostatic, inflammatory, and immune-mediating properties. Platelets are the second most common circulating blood cell, and emerging evidence suggests that platelets serve as sentinel and effector cells during infectious syndromes. Nevertheless, the molecular and functional changes that occur in platelets during sepsis, and their impact on the clinical course of infected patients, remain incompletely understood. In this review, we first highlight the complex and dynamic pathophysiology characteristics of acute, systemic infections and we then discuss established and emerging evidence of the roles of platelets in sepsis.

Perfect timing: splicing and transcription rates in living cells

An important step toward understanding gene regulation is the elucidation of the time necessary for the completion of individual steps. Measurement of reaction rates can reveal potential nodes for regulation. For example, measurements of in vivo transcription elongation rates reveal regulation by DNA sequence, gene architecture, and chromatin. Pre-mRNA splicing is regulated by transcription elongation rates and vice versa, yet the rates of RNA processing reactions remain largely elusive. Since the 1980s, numerous model systems and approaches have been used to determine the precise timing of splicing in vivo. Because splicing can be co-transcriptional, the position of Pol II when splicing is detected has been used as a proxy for time by some investigators. In addition to these 'distance-based' measurements, 'time-based' measurements have been possible through live cell imaging, metabolic labeling of RNA, and gene induction. Yet splicing rates can be convolved by the time it takes for transcription, spliceosome assembly and spliceosome disassembly. The variety of assays and systems used has, perhaps not surprisingly, led to reports of widely differing splicing rates in vivo. Recently, single molecule RNA-seq has indicated that splicing occurs more quickly than previously deduced. Here we comprehensively review these findings and discuss evidence that splicing and transcription rates are closely coordinated, facilitating the efficiency of gene expression. On the other hand, introduction of splicing delays through as yet unknown mechanisms provide opportunity for regulation. More work is needed to understand how cells optimize the rates of gene expression for a range of biological conditions. WIREs RNA 2017, 8:e1401. doi: 10.1002/wrna.1401 For further resources related to this article, please visit the WIREs website.

Properties of donated red blood cell components from patients with hereditary hemochromatosis

BACKGROUND

Red blood cells (RBCs) contain large amounts of iron, and periodic therapeutic phlebotomy is thus the main treatment for hereditary hemochromatosis (HH). However, the donation of therapeutic phlebotomy products from asymptomatic patients for transfusion purposes remains controversial. In this study, we compared the quality of RBCs obtained from HH patients with those of non-HH RBCs, within the allowed 42-day storage period.

STUDY DESIGN AND METHODS

RBCs were obtained from HH patient donors and random regular blood donors by whole blood collection. RBCs were stored for up to 42 days, according to national regulations and standard blood bank conditions in France. The following variables were assessed: hematologic and biochemical results, RBC membrane and soluble inflammatory markers, and the proinflammatory potential of HH RBC supernatant toward endothelial cells in an in vitro model.

RESULTS

There were no major differences between the two groups in terms of biophysical, biochemical, or soluble immunomodulatory factors. However, we observed small but significant differences in changes in RBC membrane proteins during storage, including increased phosphatidylserine expression and decreased hemolysis in HH compared with normal RBCs. However, there were no differences in terms of bioactivity of soluble immunomodulatory factors in the RBC supernatant during storage between HH and control donors, as determined by their effects on endothelial cells in vitro.

CONCLUSIONS

These in vitro studies suggest that RBCs from HH patients appear, while exhibiting subtle differences, to be suitable for transfusion purposes according to currently accepted criteria.

The proteasome regulates collagen-induced platelet aggregation via nuclear-factor-kappa-B (NFĸB) activation

INTRODUCTION

Platelets possess critical hemostatic functions in the system of thrombosis and hemostasis, which can be affected by a multitude of external factors. Previous research has shown that platelets have the capacity to synthesize proteins de novo and more recently a multicatalytic protein complex, the proteasome, has been discovered in platelets. Due to its vital function for cellular integrity, the proteasome has become a therapeutic target for anti-proliferative drug therapies in cancer. Clinically thrombocytopenia is a frequent side-effect, but the aggregatory function of platelets also appears to be affected. Little is known however about underlying regulatory mechanisms and functional aspects of proteasome inhibition on platelets. Our study aims to investigate the role of the proteasome in regulating collagen-induced platelet aggregation and its interaction with NFkB in this context.

MATERIAL AND METHODS

Using fluorescence activity assays, platelet aggregometry and immunoblotting, we investigate regulatory interactions of the proteasome and Nuclear-factor-kappa-B (NFkB) in collagen-induced platelet aggregation.

RESULTS

We show that collagen induces proteasome activation in platelets and collagen-induced platelet aggregation can be reduced with proteasome inhibition by the specific inhibitor epoxomicin. This effect does not depend on Rho-kinase/ROCK activation or thromboxane release, but rather depends on NFkB activation. Inhibition of the proteasome prevented cleavage of NFκB-inhibitor protein IκBα and decreased NFκB activity after collagen stimulation. Inhibition of the NFκB-pathway in return reduced collagen-induced platelet proteasome activity and cleavage of proteasome substrates.

CONCLUSIONS

This work offers novel explanations how the proteasome influences collagen-dependent platelet aggregation by involving non-genomic functions of NFkB.

RGDfK-functionalized gold nanorods bind only to activated platelets

Integrin-targeting peptide RGDfK-labeled gold nanorods (GNR) seek to improve hyperthermia targeted to solid tumors by exploiting the known up-regulation of integrin αvβ3 cell membrane proteins on solid tumor vasculature surfaces. Tumor binding specificity might be expected since surrounding tissues and endothelial cells have limited numbers of these receptors. However, RGD peptide binding to many proteins is promiscuous, with known affinity to several families of cell integrin receptors, and also possible binding to platelets after intravenous infusion via a different integrin receptor, αIIbβ3, on platelets. Binding of RGDfK-targeted GNR could considerably impact platelet function, ultimately leading to increased risk of bleeding or thrombosis depending on the degree of interaction. We sought to determine if RGDfK-labeled GNR could interact with platelets and alter platelet function. Targeted and untargeted nanorods exhibited little interaction with resting platelets in platelet rich plasma (PRP) preparations. However, upon platelet activation, peptide-targeted nanorods bound actively to platelets. Addition of RGDfK-GNR to unactivated platelets had little effect on markers of platelet activation, indicating that RGDfK-nanorods were incapable of inducing platelet activation. We next tested whether activated platelet function was altered in the presence of peptide-targeted nanorods. Platelet aggregation in whole blood and PRP in the presence of targeted nanorods had no significant effect on platelet aggregation. These data suggest that RGDfK-GNR alone have little impact on platelet function in plasma. However, nonspecific nanorod binding may occur in vascular beds where activated platelets are normally cleared, such as the spleen and liver, producing a possible toxicity risk for these nanomaterials. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 209-217, 2017.

Farnesoid X Receptor and Its Ligands Inhibit the Function of Platelets

OBJECTIVE

Although initially seemingly paradoxical because of the lack of nucleus, platelets possess many transcription factors that regulate their function through DNA-independent mechanisms. These include the farnesoid X receptor (FXR), a member of the superfamily of ligand-activated transcription factors, that has been identified as a bile acid receptor. In this study, we show that FXR is present in human platelets and FXR ligands, GW4064 and 6α-ethyl-chenodeoxycholic acid, modulate platelet activation nongenomically.

APPROACH AND RESULTS

FXR ligands inhibited the activation of platelets in response to stimulation of collagen or thrombin receptors, resulting in diminished intracellular calcium mobilization, secretion, fibrinogen binding, and aggregation. Exposure to FXR ligands also reduced integrin α_IIbβ₃ outside-in signaling and thereby reduced the ability of platelets to spread and to stimulate clot retraction. FXR function in platelets was found to be associated with the modulation of cyclic guanosine monophosphate levels in platelets and associated downstream inhibitory signaling. Platelets from FXR-deficient mice were refractory to the actions of FXR agonists on platelet function and cyclic nucleotide signaling, firmly linking the nongenomic actions of these ligands to the FXR.

CONCLUSIONS

This study provides support for the ability of FXR ligands to modulate platelet activation. The atheroprotective effects of GW4064, with its novel antiplatelet effects, indicate FXR as a potential target for the prevention of atherothrombotic disease.

Platelets in Pulmonary Immune Responses and Inflammatory Lung Diseases

Platelets are essential for physiological hemostasis and are central in pathological thrombosis. These are their traditional and best known activities in health and disease. In addition, however, platelets have specializations that broaden their functional repertoire considerably. These functional capabilities, some of which are recently discovered, include the ability to sense and respond to infectious and immune signals and to act as inflammatory effector cells. Human platelets and platelets from mice and other experimental animals can link the innate and adaptive limbs of the immune system and act across the immune continuum, often also linking immune and hemostatic functions. Traditional and newly recognized facets of the biology of platelets are relevant to defensive, physiological immune responses of the lungs and to inflammatory lung diseases. The emerging view of platelets as blood cells that are much more diverse and versatile than previously thought further predicts that additional features of the biology of platelets and of megakaryocytes, the precursors of platelets, will be discovered and that some of these will also influence pulmonary immune defenses and inflammatory injury.

Determinants of effective lentivirus-driven microRNA expression in vivo

Manipulation of microRNA (miRNA) levels, including overexpression of mature species, has become an important biological tool, even motivating miRNA-based therapeutics. To assess key determinants of miRNA overexpression in a mammalian system in vivo, we sought to bypass the laborious generation of a transgenic animal by exploiting placental trophoblast-specific gene manipulation using lentiviral vectors, which has been instrumental in elucidating trophoblast biology. We examined the impact of several key components of miRNA stem loops and their flanking sequences on the efficiency of mature miRNA expression in vivo. By combining established and novel approaches for miRNA expression, we engineered lentivirus-driven miRNA expression plasmids, which we tested in the mouse placenta. We found that reverse sense inserts minimized single-strand splicing and degradation, and that maintaining longer, poly-A-containing arms flanking the miRNA stem-loop markedly enhanced transgenic miRNA expression. Additionally, we accomplished overexpression of diverse mammalian, drosophila, or C. elegans miRNAs, either based on native context or using a “cassette” replacement of the mature miRNA sequence. Together, we have identified primary miRNA sequences that are paramount for effective expression of mature miRNAs, and validated their role in mice. Principles established by our findings may guide the design of efficient miRNA vectors for in vivo use.

Platelet WDR1 suppresses platelet activity and is associated with cardiovascular disease

Platelet activity plays a major role in hemostasis with increased platelet activity likely contributing to the pathogenesis of atherothrombosis. We sought to identify associations between platelet activity variability and platelet-related genes in healthy controls. Transcriptional profiling of platelets revealed that WD-40 repeat domain 1 (WDR1), an enhancer of actin-depolymerizing factor activity, is downregulated in platelet messenger RNA (mRNA) from subjects with a hyperreactive platelet phenotype. We used the human megakaryoblastic cell line MEG-01 as an in vitro model for human megakaryocytes and platelets. Stimulation of MEG-01 with thrombin reduced levels of WDR1 transcripts and protein. WDR1 knockdown (KD) in MEG-01 cells increased adhesion and spreading in both the basal and activated states, increased F-actin content, and increased the basal intracellular calcium concentration. Platelet-like particles (PLPs) produced by WDR1 KD cells were fewer in number but larger than PLPs produced from unmodified MEG-01 cells, and had significantly increased adhesion in the basal state and upon thrombin activation. In contrast, WDR1 overexpression reversed the WDR1 KD phenotype of megakaryocytes and PLPs. To translate the clinical significance of these findings, WDR1 expression was measured in platelet RNA from subjects with established cardiovascular disease (n = 27) and age- and sex-matched controls (n = 10). The WDR1 mRNA and protein level was significantly lower in subjects with cardiovascular disease. These data suggest that WDR1 plays an important role in suppressing platelet activity, where it alters the actin cytoskeleton dynamics, and downregulation of WDR1 may contribute to the platelet-mediated pathogenesis of cardiovascular disease.

Maternal extracellular vesicles and platelets promote preeclampsia via inflammasome activation in trophoblasts

Preeclampsia (PE) is a placenta-induced inflammatory disease associated with maternal and fetal morbidity and mortality. The mechanisms underlying PE remain enigmatic and delivery of the placenta is the only known remedy. PE is associated with coagulation and platelet activation and increased extracellular vesicle (EV) formation. However, thrombotic occlusion of the placental vascular bed is rarely observed and the mechanistic relevance of EV and platelet activation remains unknown. Here we show that EVs induce a thromboinflammatory response specifically in the placenta. Following EV injection, activated platelets accumulate particularly within the placental vascular bed. EVs cause adenosine triphosphate (ATP) release from platelets and inflammasome activation within trophoblast cells through purinergic signaling. Inflammasome activation in trophoblast cells triggers a PE-like phenotype, characterized by pregnancy failure, elevated blood pressure, increased plasma soluble fms-like tyrosine kinase 1, and renal dysfunction. Intriguingly, genetic inhibition of inflammasome activation specifically in the placenta, pharmacological inhibition of inflammasome or purinergic signaling, or genetic inhibition of maternal platelet activation abolishes the PE-like phenotype. Inflammasome activation in trophoblast cells of women with preeclampsia corroborates the translational relevance of these findings. These results strongly suggest that EVs cause placental sterile inflammation and PE through activation of maternal platelets and purinergic inflammasome activation in trophoblast cells, uncovering a novel thromboinflammatory mechanism at the maternal-embryonic interface.

Platelets enrich their transcriptome circle

In this issue of Blood, Alhasan et al report the existence of circular RNAs (circRNAs) in circulating human platelets, thereby revealing yet another facet of their already diverse transcriptome.

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.

The prowess of platelets in immunity and inflammation

Platelets not only serve as essential haemostatic cells, they also have important roles in immune defence and inflammation. Despite not having a nucleus, platelets contain physiologically relevant amounts of RNA, which can be spliced and translated into functional proteins. In addition, platelets have the ability to bind to numerous other cells, such as leukocytes and vascular cells. During those interactions, platelets can modulate cellular responses, resulting in e. g. inflammatory activation or apoptosis. Recent studies have demonstrated that platelets can influence the outcomes of bacterial and viral infection, as well as the extent of tissue injury after ischaemia. Platelets also carry considerable amounts of cytokines and growth factors in their secretory granules, preformed for rapid secretion. Those properties in combination with the sheer amount of platelets circulating in the blood stream make them an important force in the immune response during health and disease. In this overview, recent findings concerning those interesting properties of platelets beyond haemostasis are discussed.

A brief review on the mechanisms of aspirin resistance

Aspirin is the most widely prescribed drug for the primary and secondary prevention of cardiovascular and cerebrovascular diseases. However, a large number of patients continue to experience thromboembolic events despite aspirin therapy, a phenomenon referred to as aspirin resistance or treatment failure. Aspirin resistance is often observed along with a high incidence of unstable plaque, cardiovascular events and cerebrovascular accident. Studies have shown that aspirin reduces the production of TXA2, but not totally inhibits the activation of platelets. In this review, we analyze current and past research on aspirin resistance, presenting important summaries of results regarding the potential contributive roles of single nucleotide polymorphisms, inflammation, metabolic syndrome and miRNAs. The aim of this article is to provide a brief review on aspirin resistance and platelet function, which will provide important insights into the research of aspirin resistance.

Normalization of qPCR in platelets - YWHAE a potential genericreference gene

The mRNA of human platelets has been extensively studied and it is generally appreciated that platelets contain mRNA transcripts derived from the megakaryocytes, and they have the ability to translate it into proteins. Additionally, platelets contain microRNA (miRNA) that has been shown to potentially regulate the translation of certain proteins. When quantifying gene expression by quantitative real-time polymerase chain reaction (qPCR), a valid normalization method is required and the use of reference genes is a common and robust approach. It is recommended to perform a proper validation of potential reference genes for each individual experimental setup. Previous studies have mainly been performed using commonly used reference genes for nucleated cells, and to our knowledge there are no global evaluations of the stability of transcripts in platelets. Finding a stable transcript would be valuable for inter-study comparisons, and the aim of this study was to identify one or more stable mRNA transcripts suitable as generic reference genes for mRNA gene expression studies in platelets. Platelets were incubated for 24 h and microarray of platelet mRNA revealed that the levels of YWHAE, B2M, ITM2B, H3F3A, PF4V1 remained similar between 0 and 24 h. Further validation of the stability of these genes together with GAPDH, RN18S1, and PPIA, genes frequently used as reference genes in platelet studies, was performed using qPCR after different in vitro conditions. In addition, inter-individual stability of the genes was analyzed in diabetic patients compared with healthy matched controls. Analysis of gene stability by the software RefFinder revealed that YWHAE, PF4V1, and B2M were the most stable genes in platelets from healthy donors. In addition, YWHAE was stable between subjects. Furthermore, the potential influence of miRNA on the selected genes was investigated by knockdown of Dicer1 in the megakaryocytic cell line MEG01. YWHAE, H3F3A, B2M, and GAPDH remained unchanged over time in MEG01 cells indicating that these genes are not regulated by miRNA and hence are more stably expressed. In conclusion, YWHAE is a stable transcript in platelets and we suggest the use of YWHAE as a generic reference gene in mRNA gene expression studies.

Towards understanding pre-mRNA splicing mechanisms and the role of SR proteins

Alternative pre-mRNA splicing provides a source of vast protein diversity by removing non-coding sequences (introns) and accurately linking different exonic regions in the correct reading frame. The regulation of alternative splicing is essential for various cellular functions in both pathological and physiological conditions. In eukaryotic cells, this process is commonly used to increase proteomic diversity and to control gene expression either co- or post-transcriptionally. Alternative splicing occurs within a megadalton-sized, multi-component machine consisting of RNA and proteins; during the splicing process, this complex undergoes dynamic changes via RNA-RNA, protein-protein and RNA-protein interactions. Co-transcriptional splicing functionally integrates the transcriptional machinery, thereby enabling the two processes to influence one another, whereas post-transcriptional splicing facilitates the coupling of RNA splicing with post-splicing events. This review addresses the structural aspects of spliceosomes and the mechanistic implications of their stepwise assembly on the regulation of pre-mRNA splicing. Moreover, the role of phosphorylation-based, signal-induced changes in the regulation of the splicing process is demonstrated.

Non-genomic activities of retinoic acid receptor alpha control actin cytoskeletal events in human platelets

Essentials Platelets employ proteins/signaling pathways traditionally thought reserved for nuclear niche. We determined retinoic-acid-receptor alpha (RARα) expression and function in human platelets. RARα/actin-related protein-2/3 complex (Arp2/3) interact via non-genomic signaling in platelets. RARα regulates Arp2/3-mediated actin cytoskeletal dynamics and platelet spreading.

SUMMARY

Background Platelets utilize proteins and pathways classically reserved for the nuclear niche. Methods We determined whether human platelets express retinoic-acid-receptor family members, traditionally thought of as nuclear transcription factors, and deciphered the function of RARα. Results We found that RARα is robustly expressed in human platelets and megakaryocytes and interacts directly with actin-related protein-2/3 complex (Arp2/3) subunit 5 (Arp2/3s5). Arp2/3s5 co-localized with RARα in situ and regulated platelet cytoskeletal processes. The RARα ligand all-trans retinoic acid (atRA) disrupted RARα-Arp2/3 interactions. When isolated human platelets were treated with atRA, rapid cytoskeletal events (e.g. platelet spreading) were inhibited. In addition, when platelets were cultured for 18 h in the presence of atRA, actin-dependent morphological changes (e.g. extended cell body formation) were similarly inhibited. Using in vitro actin branching assays, RARα and Arp2/3-regulated complex actin branch formation was demonstrated. Consistent with inhibition of cytoskeletal processes in platelets, atRA, when added to this branching assay, resulted in dysregulated actin branching. Conclusion Our findings identify a previously unknown mechanism by which RARα regulates Arp2/3-mediated actin cytoskeletal dynamics through a non-genomic signaling pathway. These findings have broad implications in both nucleated and anucleate cells, where actin cytoskeletal events regulate cell morphology, movement and division.

A dynamic intron retention program in the mammalian megakaryocyte and erythrocyte lineages

Intron retention (IR) is a form of alternative splicing that can impact mRNA levels through nonsense-mediated decay or by nuclear mRNA detention. A complex, dynamic IR pattern has been described in maturing mammalian granulocytes, but it is unknown whether IR occurs broadly in other hematopoietic lineages. We globally assessed IR in primary maturing mammalian erythroid and megakaryocyte (MK) lineages as well as their common progenitor cells (MEPs). Both lineages exhibit an extensive differential IR program involving hundreds of introns and genes with an overwhelming loss of IR in erythroid cells and MKs compared to MEPs. Moreover, complex IR patterns were seen throughout murine erythroid maturation. Similarly complex patterns were observed in human erythroid differentiation, but not involving the murine orthologous introns or genes. Despite the common origin of erythroid cells and MKs, and overlapping gene expression patterns, the MK IR program is entirely distinct from that of the erythroid lineage with regards to introns, genes, and affected gene ontologies. Importantly, our results suggest that IR serves to broadly regulate mRNA levels. These findings highlight the importance of this understudied form of alternative splicing in gene regulation and provide a useful resource for studies on gene expression in the MK and erythroid lineages.

SMN Protein Can Be Reliably Measured in Whole Blood with an Electrochemiluminescence (ECL) Immunoassay: Implications for Clinical Trials

Spinal muscular atrophy (SMA) is caused by defects in the survival motor neuron 1 (SMN1) gene that encodes survival motor neuron (SMN) protein. The majority of therapeutic approaches currently in clinical development for SMA aim to increase SMN protein expression and there is a need for sensitive methods able to quantify increases in SMN protein levels in accessible tissues. We have developed a sensitive electrochemiluminescence (ECL)-based immunoassay for measuring SMN protein in whole blood with a minimum volume requirement of 5μL. The SMN-ECL immunoassay enables accurate measurement of SMN in whole blood and other tissues. Using the assay, we measured SMN protein in whole blood from SMA patients and healthy controls and found that SMN protein levels were associated with SMN2 copy number and were greater in SMA patients with 4 copies, relative to those with 2 and 3 copies. SMN protein levels did not vary significantly in healthy individuals over a four-week period and were not affected by circadian rhythms. Almost half of the SMN protein was found in platelets. We show that SMN protein levels in C/C-allele mice, which model a mild form of SMA, were high in neonatal stage, decreased in the first few weeks after birth, and then remained stable throughout the adult stage. Importantly, SMN protein levels in the CNS correlated with SMN levels measured in whole blood of the C/C-allele mice. These findings have implications for the measurement of SMN protein induction in whole blood in response to SMN-upregulating therapy.

[The molecular mechanisms of platelets activation in patients with cerebrovascular disease]

Cerebrovascular disease is a main cause of mortality and one of the big medical problems. After the vascular wall's damage the endothelial cells secrete the von Willebrand factor which then connects with its platelet's receptor GP Ib-V-IX. There are two polymorphisms Thr145Met and T(-5)C of the GP Iba gene associated with arterial thrombosis development. Also the difference in platelets' genes expressions was shown in patients with various clinical course of ischemic heart disease. The aim of this study was to investigate the role of platelet's receptor for von Willebrand factor in platelets' activation in patients with cerebrovascular disease. 123 patients with cerebrovascular disease and 97 healthy donors were included into the study. We analyzed the level of receptor for von Willebrand factor on platelet's membrane by flow cytometry, Thr145Met and T(-5)C GP Iba polymorphiams by PCR-RFLP, the GP Iba gene expression by RT-PCR and ADP-induced platelet aggregation by Born method. We have shown: 1) the 145Met GP Iba allele prevalence in patients with atherotrombotic stroke development due to macroangiopathy; 2) the pre-mRNA transform into the mature mRNA in activated platelets and this process may be stopped by the antiplatelet therapy by acetylsalicylic acid.

Time-Dependent Decay of mRNA and Ribosomal RNA during Platelet Aging and Its Correlation with Translation Activity

Previous investigations have indicated that RNAs are mostly present in the minor population of the youngest platelets, whereas translation in platelets could be biologically important. To attempt to solve this paradox, we studied changes in the RNA content of reticulated platelets, i.e., young cells brightly stained by thiazole orange (TO^bright), a fluorescent probe for RNAs. We provoked in mice strong thrombocytopenia followed by dramatic thrombocytosis characterized by a short period with a vast majority of reticulated platelets. During thrombocytosis, the TO^bright platelet count rapidly reached a maximum, after which TO^dim platelets accumulated, suggesting that most of the former were converted into the latter within 12 h. Experiments on platelets, freshly isolated or incubated ex vivo at 37°C, indicated that their “RNA content”, here corresponding to the amounts of extracted RNA, and the percentage of TO^bright platelets were positively correlated. The “RNA Content” normalized to the number of platelets could be 20 to 40 fold higher when 80–90% of the cells were reticulated (20–40 fg/platelet), than when only 5–10% of control cells were TO^bright (less than 1fg/platelet). TO^bright platelets, incubated ex vivo at 37°C or transfused into mice, became TO^dim within 24 h. Ex vivo at 37°C, platelets lost about half of their ribosomal and beta actin RNAs within 6 hours, and more than 98% of them after 24 hours. Accordingly, fluorescence in situ hybridization techniques confirmed the presence of beta actin mRNAs in most reticulated-enriched platelets, but detected them in only a minor subset of control platelets. In vitro, constitutive translation decreased considerably within less than 6 hours, questioning how protein synthesis in platelets, especially in non-reticulated ones, could have a biological function in vivo. Nevertheless, constitutive transient translation in young platelets under pathological conditions characterized by a dramatic increase in circulating reticulated platelets could deserve to be investigated.

Maternal Plasma DNA and RNA Sequencing for Prenatal Testing

Cell-free DNA (cfDNA) testing has recently become indispensable in diagnostic testing and screening. In the prenatal setting, this type of testing is often called noninvasive prenatal testing (NIPT). With a number of techniques, using either next-generation sequencing or single nucleotide polymorphism-based approaches, fetal cfDNA in maternal plasma can be analyzed to screen for rhesus D genotype, common chromosomal aneuploidies, and increasingly for testing other conditions, including monogenic disorders. With regard to screening for common aneuploidies, challenges arise when implementing NIPT in current prenatal settings. Depending on the method used (targeted or nontargeted), chromosomal anomalies other than trisomy 21, 18, or 13 can be detected, either of fetal or maternal origin, also referred to as unsolicited or incidental findings. For various biological reasons, there is a small chance of having either a false-positive or false-negative NIPT result, or no result, also referred to as a "no-call." Both pre- and posttest counseling for NIPT should include discussing potential discrepancies. Since NIPT remains a screening test, a positive NIPT result should be confirmed by invasive diagnostic testing (either by chorionic villus biopsy or by amniocentesis). As the scope of NIPT is widening, professional guidelines need to discuss the ethics of what to offer and how to offer. In this review, we discuss the current biochemical, clinical, and ethical challenges of cfDNA testing in the prenatal setting and its future perspectives including novel applications that target RNA instead of DNA.

Circular RNA enrichment in platelets is a signature of transcriptome degradation

In platelets, splicing and translation occur in the absence of a nucleus. However, the integrity and stability of mRNAs derived from megakaryocyte progenitor cells remain poorly quantified on a transcriptome-wide level. As circular RNAs (circRNAs) are resistant to degradation by exonucleases, their abundance relative to linear RNAs can be used as a surrogate marker for mRNA stability in the absence of transcription. Here we show that circRNAs are enriched in human platelets 17- to 188-fold relative to nucleated tissues and 14- to 26-fold relative to samples digested with RNAse R to selectively remove linear RNA. We compare RNAseq read depths inside and outside circRNAs to provide in silico evidence of transcript circularity, show that exons within circRNAs are enriched on average 12.7 times in platelets relative to nucleated tissues and identify 3162 genes significantly enriched for circRNAs, including some where all RNAseq reads appear to be derived from circular molecules. We also confirm that this is a feature of other anucleate cells through transcriptome sequencing of mature erythrocytes, demonstrate that circRNAs are not enriched in cultured megakaryocytes, and demonstrate that linear RNAs decay more rapidly than circRNAs in platelet preparations. Collectively, these results suggest that circulating platelets have lost >90% of their progenitor mRNAs and that translation in platelets occurs against the backdrop of a highly degraded transcriptome. Finally, we find that transcripts previously classified as products of reverse transcriptase template switching are both enriched in platelets and resistant to decay, countering the recent suggestion that up to 50% of rearranged RNAs are artifacts.

RNA-Seq of Tumor-Educated Platelets Enables Blood-Based Pan-Cancer, Multiclass, and Molecular Pathway Cancer Diagnostics

Tumor-educated blood platelets (TEPs) are implicated as central players in the systemic and local responses to tumor growth, thereby altering their RNA profile. We determined the diagnostic potential of TEPs by mRNA sequencing of 283 platelet samples. We distinguished 228 patients with localized and metastasized tumors from 55 healthy individuals with 96% accuracy. Across six different tumor types, the location of the primary tumor was correctly identified with 71% accuracy. Also, MET or HER2-positive, and mutant KRAS, EGFR, or PIK3CA tumors were accurately distinguished using surrogate TEP mRNA profiles. Our results indicate that blood platelets provide a valuable platform for pan-cancer, multiclass cancer, and companion diagnostics, possibly enabling clinical advances in blood-based "liquid biopsies".

Alternatively spliced, spliceosomal twin introns in Helminthosporium solani

Spliceosomal twin introns, "stwintrons", have been defined as complex intervening sequences that carry a second intron ("internal intron") interrupting one of the conserved sequence domains necessary for their correct splicing via consecutive excision events. Previously, we have described and experimentally verified stwintrons in species of Sordariomycetes, where an "internal intron" interrupted the donor sequence of an "external intron". Here we describe and experimentally verify two novel stwintrons of the potato pathogen Helminthosporium solani. One instance involves alternative splicing of an internal intron interrupting the donor domain of an external intron and a second one interrupting the acceptor domain of an overlapping external intron, both events leading to identical mature mRNAs. In the second case, an internal intron interrupts the donor domain of the external intron, while an alternatively spliced intron leads to an mRNA carrying a premature chain termination codon. We thus extend the stwintron concept to the acceptor domain and establish a link of the occurrence of stwintrons with that of alternative splicing.