Anucleate platelets generate progeny

NR4A1 Acts as a Novel Regulator of Platelet Activation and Thrombus Formation

BACKGROUND

Mounting evidence indicates that nuclear receptors play a critical regulatory role in platelet pathophysiology and thrombotic disorders. Although NR4A (the nuclear receptor subfamily 4 group A) plays an important role in cardiovascular pathophysiology, the expression profile and biological function of NR4A member 1 (NR4A1) in platelets have never been reported.

METHODS

We evaluated the functions and the underlying mechanisms of NR4A1 in platelet activation and thrombus formation using platelet-specific NR4A1-deficient mice and NR4A1-specific agonists. Using a hyperlipidemic mouse model and platelets from patients with hypercholesterolemia, we explored the influence of hypercholesterolemia on NR4A1 expression and the effects of NR4A1-specific agonists on platelet hyperreactivity induced by hypercholesterolemia.

RESULTS

NR4A1 was expressed in both human and mouse platelets. Platelet-specific NR4A1 deletion accelerated FeCl3-induced carotid arterial occlusive thrombus formation, enhanced collagen/epinephrine-induced pulmonary thromboembolism, and exacerbated microvascular microthrombi obstruction and infarct expansion in an acute myocardial infarction model. NR4A1-deficient platelets exhibited enhanced agonist-induced aggregation responses, integrin αIIbβ3 activation, dense granule release, α-granule release, platelet spreading, and clot retraction. Consistently, pharmacological activation of NR4A1 by specific agonists decreased platelet activation in both mouse and human platelets. Mechanistically, CAP1 (adenylyl cyclase-associated protein 1) was identified as the direct downstream interacting protein of NR4A1. NR4A1 deletion decreased cAMP levels and phosphorylation of VASP (vasodilator-stimulated phosphoprotein), while NR4A1-specific agonists increased cAMP levels and phosphorylation of VASP in platelets. Importantly, NR4A1 expression in platelets was upregulated in the setting of hypercholesterolemia, which was derived from its upregulation in megakaryocytes in a reactive oxygen species-dependent manner. Platelets from hypercholesterolemic patients and mice exhibited hyperreactivity. However, NR4A1-specific agonists significantly inhibited the activation of hypercholesterolemic platelets to the levels of healthy control platelets.

CONCLUSIONS

We provide the first evidence that nuclear receptor NR4A1 negatively regulates platelet activation and thrombus formation. NR4A1 may serve as a novel therapeutic target for managing thrombosis-based cardiovascular diseases, especially with hypercholesterolemia.

Deciphering Platelets: Are They Cells or an Evolved Form of Extracellular Vesicles?

Platelets are abundant in blood, where they maintain the integrity of the vasculature. Megakaryocytes, the cells responsible for platelet genesis, produce membrane protrusions from which as many as 5000 anucleate platelets can be released into the bloodstream. Platelets lack genomic DNA but contain different molecules, such as RNA, as well as organelles transmitted from the parent megakaryocyte. There is no consensus in the scientific community on whether platelets are cells or not: for example, they are sometimes called cells, small cells, anucleated cells, cell fragments, or megakaryocyte fragments. Extracellular vesicles are particles delimited by a lipid bilayer that are released from cells but cannot replicate on their own. Like platelets, extracellular vesicles lack a nucleus and carry components from their donor cell. Herein, we will explore various viewpoints suggesting that platelets may be cells, albeit not conventional cells, or may be a previously unrecognized type of extracellular vesicle. Beyond a mere debate over terminology, this perspective seeks to help properly define and classify platelets, aiming for better integration into the concept of either cells or extracellular vesicles. This will foster a clearer understanding and drive advances in platelet research.

Activation of AMPK in platelets promotes the production of offspring

Platelets are terminally differentiated anucleated cells, but they still have cell-like functions and can even produce progeny platelets. However, the mechanism of platelet sprouting has not been elucidated so far. Here, we show that when platelet-rich plasma(PRP) was cultured at 37°C, platelets showed a spore phenomenon. The number of platelets increased when given a specific shear force. It is found that AMP-related signaling pathways, such as PKA and AMPK are activated in platelets in the spore state. Meanwhile, the mRNA expression levels of genes, such as CNN3, CAPZB, DBNL, KRT19, and ESPN related to PLS1 skeleton proteins also changed. Moreover, when we use the AMPK activator AICAR(AI) to treat washed platelets, cultured platelets can still appear spore phenomenon. We further demonstrate that washed platelets treated with Forskolin, an activator of PKA, not only platelet sprouting after culture but also the AMPK is activated. Taken together, these data demonstrate that AMPK plays a key role in the process of platelet budding and proliferation, suggesting a novel strategy to solve the problem of clinical platelet shortage.

Mean platelet volume as a prognostic indicator in skin graft viability: A clinical study and retrospective analysis

INTRODUCTION

Skin grafting is the transplantation of partial-thickness or full-thickness skin from the donor to the recipient site, aiming to close tissue defects. However, skin graft transplantation surgery is not always successful and graft loss may occur after a while.

OBJECTIVE

This study aimed to investigate mean platelet volume (MPV) as a prognostic criterion in patients who underwent wound reconstruction with skin graft.

METHOD

This study was cross-sectional and descriptive. The study sample consisted of n = 66 patients who underwent skin grafting for tissue loss. Wound and graft characteristics and some blood parameters were analyzed. Friedman, Kruskal Wallis, and Bonferroni tests were used for data analysis.

RESULTS

The results of this study showed that MPV levels were higher in complex wounds and graft loss than in the others. MPV level was higher in patients with full-thickness skin grafts than in patients with split-thickness grafts. The mean MPV of patients who underwent multiple grafting was higher than single-shot (p < 0.01). There was a positive, strong and statistically significant correlation between serum PCT and MPV in the preoperative period (r = 0.288, p = 0.041) and between MPV and CRP on the 5th postoperative day (r = 0.294, p = 0.045).

CONCLUSION

In this study, MPV increased with increasing wound and graft complexity. Additionally, multiple grafting was statistically associated with an increase in MPV. There was a strong correlation between MPV and serum PCT and CRP at varying measurement times. These results suggest that MPV has the potential to increase in the presence of inflammation just like CRP and serum PCT.

Platelet generation in vivo and in vitro

ABSTRACT

Platelets play crucial roles in hemostasis, thrombosis, and immunity, but our understanding of their complex biogenesis (thrombopoiesis) is currently incomplete. Deeper insight into the mechanisms of platelet biogenesis inside and outside the body is fundamental for managing hematological disorders and for the development of novel cell-based therapies. In this article, we address the current understanding of in vivo thrombopoiesis, including mechanisms of platelet generation from megakaryocytes (proplatelet formation, cytoplasmic fragmentation, and membrane budding) and their physiological location. Progress has been made in replicating these processes in vitro for potential therapeutic application, notably in platelet transfusion and bioengineering of platelets for novel targeted therapies. The current platelet-generating systems and their limitations, particularly yield, scalability, and functionality, are discussed. Finally, we highlight the current controversies and challenges in the field that need to be addressed to achieve a full understanding of these processes, in vivo and in vitro.

Platelet Indices in Patients With Gram-Negative and Gram-Positive Sepsis: A Retrospective Cross-Sectional Study

OBJECTIVES

Different inflammatory processes and sepsis can significantly affect the number of platelets and platelet indices. Therefore, in this study, total platelet count (PLT), thrombocrit (Pct), platelet distribution width (PDW), mean platelet volume (MPV), and platelet-large cell ratio (P-LCR) were analyzed in patients with Gram-negative and Gram-positive bacterial sepsis and in sterile blood cultures.

MATERIALS AND METHODS

Inclusion criteria were an increased number of inflammatory parameters (elevated values ​​of leukocytes, C-reactive protein (CRP), procalcitonin (PCT), and positive blood culture. Exclusion criteria were patients who did not have elevated values ​​of inflammatory parameters and did not have a positive blood culture. Samples were collected from patients who had sepsis confirmed by blood cultures at the Department of Microbiology and Molecular Diagnostics at University Clinical Hospital Mostar in the period from 2019 to 2022. Three groups were analyzed, patients who had sterile blood cultures, patients with blood cultures with isolated Gram-positive bacteria, and patients with blood cultures with isolated Gram-negative bacteria. Specific infectious agents were identified for each group of patients. In addition to the above, PLT, Pct, MPV, PDW, P-LCR, PCT, CRP, the total number of leukocytes, and the number of neutrophil leukocytes were analyzed in each group.

RESULTS

The values of PCT, CRP, and the number of neutrophile leukocytes were significantly higher in patients with Gram-negative sepsis as compared to Gram-positive sepsis and to control group. Patients with sepsis have decreased PLT and Ptc and increased values of MPV, PDW, and P-LCR. In sepsis caused by the Gram-negative bacteria, i.e., Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii, the values of the same parameters were more changed compared to sepsis caused by Gram-positive bacteria, i.e., Streptococcus pneumoniae, Enterococcus spp., and methicillin-resistant Staphylococcus aureus (MRSA). When comparing Gram-negative negative bacteria, PLT was lowest in sepsis caused by Escherichia coli, the PDW value was highest in sepsis caused by Acinetobacter baumannii, and MPV and P-LCR were the highest in sepsis caused by Klebsiella pneumoniae.

CONCLUSION

Our study showed that platelet indices are significantly changed in patients with sepsis. Patients with sepsis have decreased values of PLT and Pct and increased values of MPV, PDW, and P-LCR, indicating an increase in thrombocyte production. Moreover, the results were more prominent in sepsis caused by Gram-negative bacteria compared to sepsis caused by Gram-positive bacteria.

Association of white blood cell count to mean platelet volume ratio with type 2 diabetic peripheral neuropathy in a Chinese population: a cross-sectional study

BACKGROUND

The white blood cell count to mean platelet volume ratio (WMR) is considered a promising inflammatory marker, and its recognition is increasing. Inflammation is closely related to metabolic diseases such as diabetes and its complications. However, there are currently no reports on the correlation between WMR and type 2 diabetic peripheral neuropathy (DPN). This study aims to explore the correlation between WMR and DPN in type 2 diabetes patients. By understanding this association, we hope to provide a theoretical basis for preventing DPN through the improvement of inflammatory responses.

METHODS

This was a cross-sectional study involving 2515 patients with T2DM. Logistic regression analysis was conducted to assess the associations between WMR and DPN. Finally, the receiver operating characteristic curve (ROC curve) was employed to evaluate the predictive efficacy of WMR for DPN.

RESULTS

Patients in higher WMR quartiles exhibited increased presence of DPN. Additionally, WMR remained significantly associated with a higher odds ratio (OR) of DPN (OR 4.777, 95% confidence interval [CI] 1.296-17.610, P < 0.05) after multivariate adjustment. Moreover, receiver operating characteristic curve analysis indicated that the optimal cutoff value for WMR in predicting DPN presence was 0.5395 (sensitivity: 65.40%; specificity: 41.80%; and area under the curve [AUC]: 0.540).

CONCLUSIONS

In patients with T2DM, WMR was significantly increased in DPN and independently associated with an increased risk of DPN presence in Chinese patients. This suggests that WMR may serve as a useful and reliable biomarker of DPN, highlighting the importance of paying more attention to T2DM patients with high WMR to further prevent and reduce the development of DPN and related unfavorable health outcomes.

Characterization of a novel mouse platelet transfusion model

BACKGROUND AND OBJECTIVES

Platelet transfusions are increasing with medical advances. Based on FDA criteria, platelet units are assessed by in vitro measures; however, it is not known how platelet processing and storage duration affect function in vivo. Our study's aim was to develop a novel platelet transfusion model stored in mouse plasma that meets FDA criteria adapted to mice, and transfused fresh and stored platelets are detectable in clots in vivo.

STUDY DESIGN AND METHODS

Platelet units stored in mouse plasma were prepared using a modified platelet-rich plasma (PRP) collection protocol. Characteristics of fresh and stored units, including pH, cell count, in vitro measures of activity, including activation and aggregation, and post-transfusion recovery (PTR), were determined. Lastly, a tail transection assay was conducted using mice transfused with fresh or stored units, and transfused platelets were identified by confocal imaging.

RESULTS

Platelet units had acceptable platelet and white cell counts and were negative for bacterial contamination. Fresh and 1-day stored units had acceptable pH; the platelets were activatable by thrombin and adenosine diphosphate, agreeable with thrombin, had acceptable PTR, and were present in vivo in clots of recipients after tail transection. In contrast, 2-day stored units had clinically unacceptable quality.

CONCLUSION

We developed mouse platelets for transfusion analogous to human platelet units using a modified PRP collection protocol with maximum storage of 1 day for an 'old' unit. This provides a powerful tool to test how process modifications and storage conditions affect transfused platelet function in vivo.

The association of platelet to white blood cell ratio with diabetes: a nationwide survey in China

Background

Inflammation is integral to diabetes pathogenesis. The novel hematological inflammatory biomarker, platelet to white blood cell ratio (PWR), is linked with various conditions such as chronic kidney disease and stroke. However, the association of this novel clinical indicator with diabetes still remains unclear, which is investigated in this study.

Materials and Methods

A total of 10,973 Chinese participants were included and grouped according to the tertiles of PWR (T1, T2, and T3 groups). Diagnosis of prediabetes and diabetes adhered to American Diabetes Association criteria. Binary logistic regression was adopted to assess the relationship between PWR and both diabetes and prediabetes. The dose-response relationship of PWR and diabetes was examined using restricted cubic spline regression. Subgroup and interaction analyses were conducted to investigate potential covariate interactions.

Results

Individuals with higher PWR had better lifestyles and lipid profiles (all P < 0.05). After adjusting for all the covariates, the T2 group had a 0.83-fold (95% CI: 0.73-0.93, P < 0.01) risk of diabetes and that for the T3 group was 0.68-fold (95% CI: 0.60-0.78. P < 0.001). Dose-response analysis identified non-linear PWR-diabetes associations in the general population and females (both P < 0.05), but absent in males. Participants with prediabetes in the T2 and T3 groups had lower risks of diabetes (OR = 0.80 for the T2 group, P < 0.001 and 0.68 for the T3 group, P < 0.001) in the full models. All the sensitivity analysis support consistent conclusions.

Conclusions

An increase in PWR significantly correlates with reduced diabetes risks. A non-linear PWR-diabetes relationship exists in the general population and females, but not in males. The correlation between PWR and diabetes indicates that PWR holds potentials in early identification and prevention of diabetes.

Current Strategies to Guide the Antiplatelet Therapy in Acute Coronary Syndromes

The role of antiplatelet therapy in patients with acute coronary syndromes is a moving target with considerable novelty in the last few years. The pathophysiological basis of the treatment depends on platelet biology and physiology, and the interplay between these aspects and clinical practice must guide the physician in determining the best therapeutic options for patients with acute coronary syndromes. In the present narrative review, we discuss the latest novelties in the antiplatelet therapy of patients with acute coronary syndromes. We start with a description of platelet biology and the role of the main platelet signal pathways involved in platelet aggregation during an acute coronary syndrome. Then, we present the latest evidence on the evaluation of platelet function, focusing on the strengths and weaknesses of each platelet's function test. We continue our review by describing the role of aspirin and P2Y12 inhibitors in the treatment of acute coronary syndromes, critically appraising the available evidence from clinical trials, and providing current international guidelines and recommendations. Finally, we describe alternative therapeutic regimens to standard dual antiplatelet therapy, in particular for patients at high bleeding risk. The aim of our review is to give a comprehensive representation of current data on antiplatelet therapy in patients with acute coronary syndromes that could be useful both for clinicians and basic science researchers to be up-to-date on this complex topic.

Reproducibility and stability of the immature platelet fraction using Sysmex XN-10

BACKGROUND

The Immature Platelet Fraction (IPF) is an indicator of thrombopoiesis which is a useful parameter in thrombocytopenia. It demonstrates compensatory mechanisms in production of platelets, but currently not implemented in routine clinical practice. The aim of this study was to establish the reproducibility and stability of IPF, for both percentage (%-IPF) and absolute (A-IPF) measurements.Material/methods: A total of 71 samples, of which 45 for reproducibility and 26 for stability analysis, were assayed for full blood count using the Sysmex XN-10 analyser at room temperature (RT:19-25 °C). For reproducibility analysis, IPF measurements were analysed 11 times by different appraisers using the same sample, while for stability analysis, IPF was measured over fourteen hourly-intervals up to 24 h (n = 21) and then separately extended beyond the point of stability to 72 h (n = 5).

RESULTS

Reproducibility analysis of %-IPF and A-IPF (n = 45) showed very reliable results, with the range of mean CV% values between 1.25-8.90% and 1.70-9.96%, respectively. On the other hand, overall, stability analysis of %-IPF and A-IPF (n = 21) at RT over 24 h showed reliable results, with pooled mean CV% values of 1.32% and 1.43%, respectively, with no significant difference between %-IPF and A-IPF (p = 0.767 and p = 0.821). All %-IPF and A-IPF values had exceeded the set acceptance criterion of stability (CV% ≥ 10.0%) before 72 h.

CONCLUSIONS

Overall, %-IPF and A-IPF reproducibility and storage at RT for 24 h predominantly demonstrates the suitability of their usage for testing on the Sysmex XN-series analysers.

Non-canonical non-genomic morphogen signaling in anucleate platelets: a critical determinant of prothrombotic function in circulation

Circulating platelets derived from bone marrow megakaryocytes play a central role in thrombosis and hemostasis. Despite being anucleate, platelets express several proteins known to have nuclear niche. These include transcription factors and steroid receptors whose non-genomic functions are being elucidated in platelets. Quite remarkably, components of some of the best-studied morphogen pathways, namely Notch, Sonic Hedgehog (Shh), and Wnt have also been described in recent years in platelets, which regulate platelet function in the context of thrombosis as well as influence their survival. Shh and Notch pathways in stimulated platelets establish feed-forward loops of autocrine/juxtacrine/paracrine non-canonical signaling that helps perpetuate thrombosis. On the other hand, non-canonical Wnt signaling is part of a negative feedback loop for restricting platelet activation and possibly limiting thrombus growth. The present review will provide an overview of these signaling pathways in general. We will then briefly discuss the non-genomic roles of transcription factors and steroid receptors in platelet activation. This will be followed by an elaborate description of morphogen signaling in platelets with a focus on their bearing on platelet activation leading to hemostasis and thrombosis as well as their potential for therapeutic targeting in thrombotic disorders.

Phosphoinositides take a central stage in regulating blood platelet production and function

Blood platelets are produced by megakaryocytes through a complex program of differentiation and play a critical role in hemostasis and thrombosis. These anucleate cells are the target of antithrombotic drugs that prevent them from clumping in cardiovascular disease conditions. Platelets also significantly contribute to various aspects of physiopathology, including interorgan communications, healing, inflammation, and thromboinflammation. Their production and activation are strictly regulated by highly elaborated mechanisms. Among them, those involving inositol lipids have drawn the attention of researchers. Phosphoinositides represent the seven combinatorially phosphorylated forms of the inositol head group of inositol lipids. They play a crucial role in regulating intracellular mechanisms, such as signal transduction, actin cytoskeleton rearrangements, and membrane trafficking, either by generating second messengers or by directly binding to specific domains of effector proteins. In this review, we will explore how phosphoinositides are implicated in controlling platelet production by megakaryocytes and in platelet activation processes. We will also discuss the diversity of phosphoinositides in platelets, their role in granule biogenesis and maintenance, as well as in integrin signaling. Finally, we will address the discovery of a novel pool of phosphatidylinositol 3-monophosphate in the outerleaflet of the plasma membrane of human and mouse platelets.

Autophagy and its consequences for platelet biology

Autophagy, the continuous recycling of intracellular building blocks, molecules, and organelles is necessary to preserve cellular function and homeostasis. In this context, it was demonstrated that autophagy plays an important role in megakaryopoiesis, the development and differentiation of hematopoietic progenitor cells into megakaryocytes. Furthermore, in recent years, autophagic proteins were detected in platelets, anucleate cells generated by megakaryocytes, responsible for hemostasis, thrombosis, and a key cell in inflammation and host immune responses. In the last decade studies have indicated the occurrence of autophagy in platelets. Moreover, autophagy in platelets was subsequently demonstrated to be involved in platelet aggregation, adhesion, and thrombus formation. Here, we review the current knowledge about autophagy in platelets, its function, and clinical implications. However, at the advent of platelet autophagy research, additional discoveries derived from evolving work will be required to precisely define the contributions of autophagy in platelets, and to expand the ever increasing physiologic and pathologic roles these remarkable and versatile blood cells play.

High ploidy large cytoplasmic megakaryocytes are hematopoietic stem cells regulators and essential for platelet production

Megakaryocytes (MK) generate platelets. Recently, we and others, have reported MK also regulate hematopoietic stem cells (HSC). Here we show high ploidy large cytoplasmic megakaryocytes (LCM) are critical negative regulators of HSC and critical for platelet formation. Using a mouse knockout model (Pf4-Srsf3^Δ/Δ) with normal MK numbers, but essentially devoid of LCM, we demonstrate a pronounced increase in BM HSC concurrent with endogenous mobilization and extramedullary hematopoiesis. Severe thrombocytopenia is observed in animals with diminished LCM, although there is no change in MK ploidy distribution, uncoupling endoreduplication and platelet production. When HSC isolated from a microenvironment essentially devoid of LCM reconstitute hematopoiesis in lethally irradiated mice, the absence of LCM increases HSC in BM, blood and spleen, and the recapitulation of thrombocytopenia. In contrast, following a competitive transplant using minimal numbers of WT HSC together with HSC from a microenvironment with diminished LCM, sufficient WT HSC-generated LCM regulates a normal HSC pool and prevents thrombocytopenia. Importantly, LCM are conserved in humans.

Direct Cryo-ET observation of platelet deformation induced by SARS-CoV-2 spike protein

SARS-CoV-2 is a novel coronavirus responsible for the COVID-19 pandemic. Its high pathogenicity is due to SARS-CoV-2 spike protein (S protein) contacting host-cell receptors. A critical hallmark of COVID-19 is the occurrence of coagulopathies. Here, we report the direct observation of the interactions between S protein and platelets. Live imaging shows that the S protein triggers platelets to deform dynamically, in some cases, leading to their irreversible activation. Cellular cryo-electron tomography reveals dense decorations of S protein on the platelet surface, inducing filopodia formation. Hypothesizing that S protein binds to filopodia-inducing integrin receptors, we tested the binding to RGD motif-recognizing platelet integrins and find that S protein recognizes integrin α_vβ₃. Our results infer that the stochastic activation of platelets is due to weak interactions of S protein with integrin, which can attribute to the pathogenesis of COVID-19 and the occurrence of rare but severe coagulopathies.

Association Between Platelet Indices and Preoperative Deep Vein Thrombosis in Elderly Patients Undergoing Total Joint Arthroplasty: A Retrospective Study

To investigate the association between platelet (PLT) indices and preoperative deep vein thrombosis (DVT) in elderly patients undergoing total joint arthroplasty (TJA). A total of 1391 patients were enrolled. We created receiver operator characteristic (ROC) curve using the ratio of PLT indices to DVT before TJA, divided the enrolled patients into groups based on the cut-off value, and then analyzed risk factors for DVT before TJA in the multivariate binary logistic regression analysis. Preoperative DVT occurred in 103 cases. Based on the ROC curve, we determined that the cut-off values for PLT, mean platelet volume (MPV), platelet distribution width (PDW), platelet large cell ratio (P-LCR), and plateletcrit (PCT) were 202 × 109/L, 11.4 fL, 13.2 fL, 34.6%, and 0.228%. And the areas under the curve were 0.606, 0.605, 0.617, 0.616, and 0.598. Multivariate binary regression analysis revealed that the risk of preoperative DVT in TJA patients with PLT≥202 × 109/L, MPV≤11.4 fL, PDW≤13.2 fL, P-LCR≤34.6%, and PCT≥0.228% increased by 2.32 (P < .001, 95% confidence interval [CI] [1.50-3.60]), 1.86 (P < .001, 95% CI [1.22-2.83]), 2.17 (P < .001, 95% CI [1.43-3.31]), 2.27 (P < .001, 95% CI [1.50-3.45]), and 1.76 times (P = .013, 95% CI [1.13-2.76]), respectively. Age, P < .001, odds ratio (OR) = 1.08, 95% CI [1.04-1.11]; corticosteroid use, P = .011, OR = 3.66, 95% CI [1.34-9.96]. We found that increased PLT count and PCT, decreased MPV, PDW, and P-LCR, old age, and corticosteroid use were independent risk factors for preoperative DVT in elderly TJA patients.

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.

A New Role of NAP1L1 in Megakaryocytes and Human Platelets

Platelets (PLTs) are anucleate and considered incapable of nuclear functions. Contrastingly, nuclear proteins were detected in human PLTs. For most of these proteins, it is unclear if nuclear or alternatively assigned functions are performed, a question we wanted to address for nuclear assembly protein 1like 1 (NAP1L1). Using a wide array of molecular methods, including RNAseq, co-IP, overexpression and functional assays, we explored expression pattern and functionality of NAP1L1 in PLTs, and CD34⁺-derived megakaryocytes (MKs). NAP1L1 is expressed in PLTs and MKs. Co-IP experiments revealed that dihydrolipolylysine-residue acetyltransferase (DLAT encoded protein PDC-E2, ODP2) dynamically interacts with NAP1L1. PDC-E2 is part of the mitochondrial pyruvate-dehydrogenase (PDH) multi-enzyme complex, playing a crucial role in maintaining cellular respiration, and promoting ATP-synthesis via the respiratory chain. Since altered mitochondrial function is a hallmark of infectious syndromes, we analyzed PDH activity in PLTs from septic patients demonstrating increased activity, paralleling NAP1L1 expression levels. MKs PDH activity decreased following an LPS-challenge. Furthermore, overexpression of NAP1L1 significantly altered the ability of MKs to form proplatelet extensions, diminishing thrombopoiesis. These results indicate that NAP1L1 performs in other than nucleosome-assembly functions in PTLs and MKs, binding a key mitochondrial protein as a potential chaperone, and gatekeeper, influencing PDH activity and thrombopoiesis.

Direct Cryo-ET observation of platelet deformation induced by SARS-CoV-2 Spike protein

SARS-CoV-2 is a novel coronavirus responsible for the COVID-19 pandemic. Its high pathogenicity is due to SARS-CoV-2 spike protein (S protein) contacting host-cell receptors. A critical hallmark of COVID-19 is the occurrence of coagulopathies. Here, we report the direct observation of the interactions between S protein and platelets. Live imaging showed that the S protein triggers platelets to deform dynamically, in some cases, leading to their irreversible activation. Strikingly, cellular cryo-electron tomography revealed dense decorations of S protein on the platelet surface, inducing filopodia formation. Hypothesizing that S protein binds to filopodia-inducing integrin receptors, we tested the binding to RGD motif-recognizing platelet integrins and found that S protein recognizes integrin α _v β ₃ . Our results infer that the stochastic activation of platelets is due to weak interactions of S protein with integrin, which can attribute to the pathogenesis of COVID-19 and the occurrence of rare but severe coagulopathies.

The white blood cell count to mean platelet volume ratio for ischemic stroke patients after intravenous thrombolysis

Background and Purpose

White blood cell count to mean platelet volume ratio (WMR) is increasingly recognized as a promising biomarker. However, its predictive capability for acute ischemic stroke (AIS) patients is relatively less researched. The primary aim of this study is to explore its prognostic value in AIS patients after reperfusion regarding 3-month poor functional outcome.

Methods

A total of 549 AIS patients who had undergone vascular reperfusion procedure with complete 3-month follow-up were retrospectively recruited in this study. White blood cell count, mean platelet volume at 24 h of admission were recorded. Stroke severity had been estimated using the National Institutes of Health Stroke Scale (NIHSS) and poor outcome was defined as modified Rankin Scale (mRS) 3–6 at 3 months.

Results

AIS patients with poor functional outcome at 3 months displayed higher WMR. A positive correlation between WMR and NIHSS score was found (r = 0.334, p < 0.001). After adjusting potential confounders, WMR was still an independent risk factor for poor prognosis at 3 months (OR = 2.257, 95% CI [1.117-4.564], p = 0.023) in multivariate logistic regression model. Subgroup analyses further suggested a significant association between WMR and poor outcome in high baseline NIHSS (per 0.1-point increase: OR = 1.153, 95% CI [1.014-1.312], p = 0.030) group. Receiver operating characteristic (ROC) curves analysis was utilized to assess the predictive ability of WMR, indicating a cut-off value of 0.86. A nomogram that includes age, sex, NIHSS on admission, high WMR for predicting 1-year all-cause survival was also developed (C-index = 0.628).

Conclusions

WMR is significantly correlated with stroke severity on admission and is proved to be an important prognostic indicator for AIS outcomes, especially in high NIHSS on admission group. Additionally, the developed nomogram that includes high WMR for predicting 1-year survival provides us with an effective visualization tool.

Human platelets display dysregulated sepsis-associated autophagy, induced by altered LC3 protein-protein interaction of the Vici-protein EPG5

Platelets mediate central aspects of host responses during sepsis, an acute profoundly systemic inflammatory response due to infection. Macroautophagy/autophagy, which mediates critical aspects of cellular responses during inflammatory conditions, is known to be a functional cellular process in anucleate platelets, and is essential for normal platelet functions. Nevertheless, how sepsis may alter autophagy in platelets has never been established. Using platelets isolated from septic patients and matched healthy controls, we show that during clinical sepsis, the number of autophagosomes is increased in platelets, most likely due to an accumulation of autophagosomes, some containing mitochondria and indicative of mitophagy. Therefore, autophagy induction or early-stage autophagosome formation (as compared to decreased later-stage autophagosome maturation or autophagosome-late endosome/lysosome fusion) is normal or increased. This was consistent with decreased fusion of autophagosomes with lysosomes in platelets. EPG5 (ectopic P-granules autophagy protein 5 homolog), a protein essential for normal autophagy, expression did increase, while protein-protein interactions between EPG5 and MAP1LC3/LC3 (which orchestrate the fusion of autophagosomes and lysosomes) were significantly reduced in platelets during sepsis. Furthermore, data from a megakaryocyte model demonstrate the importance of TLR4 (toll like receptor 4), LPS-dependent signaling for regulating this mechanism. Similar phenotypes were also observed in platelets isolated from a patient with Vici syndrome: an inherited condition caused by a naturally occurring, loss-of-function mutation in EPG5. Together, we provide evidence that autophagic functions are aberrant in platelets during sepsis, due in part to reduced EPG5-LC3 interactions, regulated by TLR4 engagement, and the resultant accumulation of autophagosomes.Abbreviations: ACTB: beta actin; CLP: cecal ligation and puncture; Co-IP: co-immunoprecipitation; DAP: death associated protein; DMSO: dimethyl sulfoxide; EPG5: ectopic P-granules autophagy protein 5 homolog; ECL: enhanced chemiluminescence; HBSS: Hanks' balanced salt solution; HRP: horseradish peroxidase; ICU: intensive care unit; LPS: lipopolysaccharide; LAMP1: lysosomal associated membrane protein 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; MKs: megakaryocytes; PFA: paraformaldehyde; PBS: phosphate-buffered saline; PLA: proximity ligation assay; pRT-PCR: quantitative real-time polymerase chain reaction; RT: room temperature; SQSTM1/p62: sequestosome 1; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TLR4: toll like receptor 4; TEM: transmission electron microscopy; WGA: wheat germ agglutinin.

Analysis of preplatelets and their barbell platelet derivatives by imaging flow cytometry

Circulating large "preplatelets" undergo fission via barbell platelet intermediates into two smaller, mature platelets. In this study, we determine whether preplatelets and/or barbells are equivalent to reticulated/immature platelets by using ImageStream flow cytometry and super-resolution microscopy. Immature platelets, preplatelets, and barbells were quantified in healthy and thrombocytopenic mice, healthy human volunteers, and patients with immune thrombocytopenia or undergoing chemotherapy. Preplatelets and barbells were 1.9% ± 0.18%/1.7% ± 0.48% (n = 6) and 3.3% ± 1.6%/0.5% ± 0.27% (n = 12) of total platelet counts in murine and human whole blood, respectively. Both preplatelets and barbells exhibited high expression of major histocompatibility complex class I with high thiazole orange and Mitotracker fluorescence. Tracking dye experiments confirmed that preplatelets transform into barbells and undergo fission ex vivo to increase platelet counts, with dependence on the cytoskeleton and normal mitochondrial respiration. Samples from antibody-induced thrombocytopenia in mice and patients with immune thrombocytopenia had increased levels of both preplatelets and barbells correlating with immature platelet levels. Furthermore, barbells were absent after chemotherapy in patients. In mice, in vivo biotinylation confirmed that barbells, but not all large platelets, were immature. This study demonstrates that a subpopulation of large platelets are immature preplatelets that can transform into barbells and undergo fission during maturation.

Sepsis and Thrombocytopenia: A Nowadays Problem

Sepsis is a life-threatening organ failure produced by a dysregulated host response to infection that involves 15.6% of hospital mortality. The most common signs and symptoms of sepsis are hypotension, tachypnea, fever, and leukocytosis, whether suspected or confirmed. Including a major one, thrombocytopenia is a sign that is an independent predictor of poor outcomes in patients with sepsis, increasing their mortality rate and their length of stay in the intensive care unit (ICU). So far, the ongoing treatment for this problem is securing the airway, treating hypoxemia, and providing vascular access for hydration, antibiotic delivery, and vasopressors, if needed. This article has reviewed the different possible mechanisms found for sepsis-associated thrombocytopenia, going from the most acknowledged one as decreased platelet production to the potential aftermath of sepsis itself as disseminated intravascular coagulation (DIC). This article has also discussed the future treatment for patients suffering from thrombocytopenia and sepsis, going from phase I and II trials as GI antagonists to the well-known drug aspirin as a possible treatment for this problem.

The GPIb-IX complex on platelets: insight into its novel physiological functions affecting immune surveillance, hepatic thrombopoietin generation, platelet clearance and its relevance for cancer development and metastasis

The glycoprotein (GP) Ib-IX complex is a platelet receptor that mediates the initial interaction with subendothelial von Willebrand factor (VWF) causing platelet arrest at sites of vascular injury even under conditions of high shear. GPIb-IX dysfunction or deficiency is the reason for the rare but severe Bernard-Soulier syndrome (BSS), a congenital bleeding disorder. Although knowledge on GPIb-IX structure, its basic functions, ligands, and intracellular signaling cascades have been well established, several advances in GPIb-IX biology have been made in the recent years. Thus, two mechanosensitive domains and a trigger sequence in GPIb were characterized and its role as a thrombin receptor was deciphered. Furthermore, it became clear that GPIb-IX is involved in the regulation of platelet production, clearance and thrombopoietin secretion. GPIb is deemed to contribute to liver cancer development and metastasis. This review recapitulates these novel findings highlighting GPIb-IX in its multiple functions as a key for immune regulation, host defense, and liver cancer development.

Platelet-Therapeutics to Improve Tissue Regeneration and Wound Healing-Physiological Background and Methods of Preparation

Besides their function in primary hemostasis, platelets are critically involved in the physiological steps leading to wound healing and tissue repair. For this purpose, platelets have a complex set of receptors allowing the recognition, binding, and manipulation of extracellular structures and the detection of pathogens and tissue damage. Intracellular vesicles contain a huge set of mediators that can be released to the extracellular space to coordinate the action of platelets as other cell types for tissue repair. Therapeutically, the most frequent use of platelets is the intravenous application of platelet concentrates in case of thrombocytopenia or thrombocytopathy. However, there is increasing evidence that the local application of platelet-rich concentrates and platelet-rich fibrin can improve wound healing and tissue repair in various settings in medicine and dentistry. For the therapeutic use of platelets in wound healing, several preparations are available in clinical practice. In the present study we discuss the physiology and the cellular mechanisms of platelets in hemostasis and wound repair, the methods used for the preparation of platelet-rich concentrates and platelet-rich fibrin, and highlight some examples of the therapeutic use in medicine and dentistry.

Relative platelet reductions provide better pathophysiologic signatures of coagulopathies in sepsis

In sepsis-associated coagulopathies and disseminated intravascular coagulation, relative platelet reductions may reflect coagulopathy severity. However, limited evidence supports their clinical significance and most sepsis-associated coagulopathy criteria focus on the absolute platelet counts. To estimate the impact of relative platelet reductions and absolute platelet counts on sepsis outcomes. A multicenter retrospective observational study was performed using the eICU Collaborative Research Database, comprising 335 intensive care units (ICUs) in the United States. Patients with sepsis and an ICU stay > 2 days were included. Estimated effects of relative platelet reductions and absolute platelet counts on mortality and coagulopathy-related complications were evaluated. Overall, 26,176 patients were included. Multivariate mixed-effect logistic regression analysis revealed marked in-hospital mortality risk with larger platelet reductions between days one and two, independent from the resultant absolute platelet counts. The adjusted odds ratio (OR) [95% confidence intervals (CI)] for in-hospital mortality was 1.28[1.23–1.32], 1.86[1.75–1.97], 2.99[2.66–3.36], and 6.05[4.40–8.31] for 20–40%, 40–60%, 60–80%, and > 80% reductions, respectively, when compared with a < 20% decrease in platelets (P < 0.001 for each). In the multivariate logistic regression analysis, platelet reductions ≥ 11% and platelet counts ≤ 100,000/μL on day 2 were associated with high coagulopathy-related complications (OR [95%CI], 2.03 and 1.18; P < 0.001 and P < 0.001), while only platelet reduction was associated with thromboembolic complications (OR [95%CI], 1.43 [1.03–1.98], P < 0.001). The magnitude of platelet reductions represent mortality risk and provides a better signature of coagulopathies in sepsis; therefore, it is a plausible criterion for sepsis-associated coagulopathies.

Super-resolution imaging reveals cytoskeleton-dependent organelle rearrangement within platelets at intermediate stages of maturation

A steady supply of platelets maintains their levels in the blood, and this is achieved by the generation of progeny from platelet intermediates. Using systematic super-resolution microscopy, we examine the ultrastructural organization of various organelles in different platelet intermediates to understand the mechanism of organelle redistribution and sorting in platelet intermediate maturation as the early step of platelet progeny production. We observe the dynamic interconversion between the intermediates and find that microtubules are responsible for controlling the overall shape of platelet intermediates. Super-resolution images show that most of the organelles are located near the cell periphery in oval preplatelets and confined to the bulbous tips in proplatelets. We also find that the distribution of the dense tubular system and α granules is regulated by actin, whereas that of mitochondria and dense granules is governed by microtubules. Altogether, our results call for a reassessment of organelle redistribution in platelet intermediates.

EVALUATION OF THE RELATIONSHIP OF MPV, RDW AND PVI PARAMETERS WITH DISEASE SEVERITY IN COVID-19 PATIENTS

Coronavirus was first detected in three severe pneumonia cases in Wuhan, China, in December 2019. Studies on red cell distribution width (RDW-CV) and mean platelet volume (MPV) laboratory parameters, which can be examined in complete blood count in COVID-19 patients, are still very limited. However, to the best of our knowledge, there are no studies examining the relationship between platelet volume index (PVI) and disease severity in COVID-19 patients, which was evaluated in this study. The aim of this study was to evaluate the relationship of disease severity in COVID-19 patients with their MPV, RDW, and PVI parameters. The study included 92 COVID-19 patients as a study group and 84 healthy individuals as control group. All laboratory data and radiological images were scanned retrospectively from patient files and hospital information system. Evaluation of the RDW-CV and MPV blood parameters, and PVI measured in COVID-19 patients yielded statistically significant differences according to the disease severity. We suggest that RDW-CV and PVI, evaluated within the scope of the study, may be the parameters that should be considered in the early diagnosis of the disease, from the initial stages of COVID-19. In addition, we think that the RDW-CV and MPV laboratory parameters, as well as PVI, which all are simple, inexpensive and widely used hematologic tests, can be used as important biomarkers in determining COVID-19 severity and mortality.

Role of oculocerebrorenal syndrome of Lowe (OCRL) protein in megakaryocyte maturation, platelet production and functions: a study in patients with Lowe syndrome

Lowe syndrome (LS) is an oculocerebrorenal syndrome of Lowe (OCRL1) genetic disorder resulting in a defect of the OCRL protein, a phosphatidylinositol-4,5-bisphosphate 5-phosphatase containing various domains including a Rho GTPase-activating protein (RhoGAP) homology domain catalytically inactive. We previously reported surgery-associated bleeding in patients with LS, suggestive of platelet dysfunction, accompanied with a mild thrombocytopenia in several patients. To decipher the role of OCRL in platelet functions and in megakaryocyte (MK) maturation, we conducted a case-control study on 15 patients with LS (NCT01314560). While all had a drastically reduced expression of OCRL, this deficiency did not affect platelet aggregability, but resulted in delayed thrombus formation on collagen under flow conditions, defective platelet spreading on fibrinogen and impaired clot retraction. We evidenced alterations of the myosin light chain phosphorylation (P-MLC), with defective Rac1 activity and, inversely, elevated active RhoA. Altered cytoskeleton dynamics was also observed in cultured patient MKs showing deficient proplatelet extension with increased P-MLC that was confirmed using control MKs transfected with OCRL-specific small interfering(si)RNA (siOCRL). Patients with LS also had an increased proportion of circulating barbell-shaped proplatelets. Our present study establishes that a deficiency of the OCRL protein results in a defective actomyosin cytoskeleton reorganisation in both MKs and platelets, altering both thrombopoiesis and some platelet responses to activation necessary to ensure haemostasis.

Current understanding and future implications of sepsis-induced thrombocytopenia

Sepsis is a global health burden that needs intensive medical care. Thrombocytopenia in sepsis is well known to increase morbidity as well as mortality. Several studies have been performed both in animal models and in humans to understand the mechanism by which sepsis causes thrombocytopenia. Recent studies have shown that inhibiting thrombocytopenia improves outcomes in sepsis patients. Understanding these mechanisms to identify targets in use of newer treatment modalities besides using resuscitation measures, antibiotics and removal of thrombocytopenia inducing agent could potentially help us improve outcomes in sepsis.

Post-Transcriptional Expression Control in Platelet Biogenesis and Function

Platelets are highly abundant cell fragments of the peripheral blood that originate from megakaryocytes. Beside their well-known role in wound healing and hemostasis, they are emerging mediators of the immune response and implicated in a variety of pathophysiological conditions including cancer. Despite their anucleate nature, they harbor a diverse set of RNAs, which are subject to an active sorting mechanism from megakaryocytes into proplatelets and affect platelet biogenesis and function. However, sorting mechanisms are poorly understood, but RNA-binding proteins (RBPs) have been suggested to play a crucial role. Moreover, RBPs may regulate RNA translation and decay following platelet activation. In concert with other regulators, including microRNAs, long non-coding and circular RNAs, RBPs control multiple steps of the platelet life cycle. In this review, we will highlight the different RNA species within platelets and their impact on megakaryopoiesis, platelet biogenesis and platelet function. Additionally, we will focus on the currently known concepts of post-transcriptional control mechanisms important for RNA fate within platelets with a special emphasis on RBPs.

Getting a good view: in vitro imaging of platelets under flow

As the anucleate cells responsible for hemostasis and thrombosis, platelets are exposed to a myriad of biophysical and biochemical stimuli within vasculature and heterogeneous blood clots. Highly controlled, reductionist in vitro imaging studies have been instrumental in providing a detailed and quantitative understanding of platelet biology and behavior, and have helped elucidate some surprising functions of platelets. In this review, we highlight the tools and approaches that enable visualization of platelets in conjunction with precise control over the local biofluidic and biochemical microenvironment. We also discuss next generation tools that add further control over microenvironment cell stiffness or enable visualization of the interactions between platelets and endothelial cells. Throughout the review, we include pragmatic knowledge on imaging systems, experimental conditions, and approaches that have proved to be useful to our in vitro imaging studies of platelets under flow.

Megakaryocyte and Platelet Transcriptomics for Discoveries in Human Health and Disease

Anucleate platelets, long viewed as merely cell fragments with a limited repertoire of rapid-acting hemostatic functions, are now recognized to have a complex and dynamic transcriptome mirroring that of many nucleated cells. The field of megakaryocyte and platelet transcriptomics has been rapidly growing, particularly with the advent of newer technologies such as next-generation RNA-sequencing. Studies interrogating the megakaryocyte and platelet transcriptome have led to a number of key insights into human health and disease. In this brief focused review, we will discuss some of the recent discoveries made through transcriptome analysis of megakaryocytes and platelets. We will also highlight the utility of integrating ribosome footprint analysis to augment discoveries. Both bulk and single-cell sequencing approaches will be reviewed, along with comparative studies between human and murine platelets under basal healthy settings and during acute systemic inflammatory diseases.

Presence of intra-tumoral CD61+ megakaryocytes predicts poor prognosis in non-small cell lung cancer

Background

Lung is a reservoir for megakaryocytes (MKs). The relationship between intra-tumoral MKs and non-small cell lung cancer (NSCLC) is unknown. We investigate relationship between high intra-tumoral MKs with the recurrence of NSCLC.

Methods

The tissue sections of 629 patients with resected NSCLC were stained with hematoxylin, anti-CD61, anti-CD34 and stromal cell-derived factor-1 (SDF-1). CD61+ giant cells localized in CD34+ capillaries were identified as MKs. The impact of MKs and preoperative platelet count on disease-free survival (DFS) was investigated.

Results

Overall, 18.9% of patients were positive for the presence of MKs. In univariate analysis, the median DFS of the MK+ group was shorter than the median DFS of the MK- group (69.1 vs. 80.5 months; P=0.021). Multivariate analysis indicated that MKs in tumor tissue was an unfavorable prognostic factor for DFS (HR 1.351, P=0.065), the impact of which was more significant in non-squamous cell carcinoma (NSCC) (HR 1.710, P=0.008) and in patients with N0 (HR 1.883, P=0.009). Although systemic platelet count of the MK+ group was significantly higher than the MK- group (270.6×10⁹ vs. 243.6×10⁹/L, P=0.007), the stratified subgroup DFS curves (P=0.003) showed that the effect of MKs on prognosis was independent of the blood platelet count.

Conclusions

Our results demonstrate that CD61+ MKs in tumor tissue predict unfavorable prognosis in NSCLC.

Investigation of calmodulin-like and rod domain mutations suggests common molecular mechanism for α-actinin-1-linked congenital macrothrombocytopenia

Actinin-1 mutations cause dominantly inherited congenital macrothrombocytopenia (CMTP), with mutations in the actin-binding domain increasing actinin's affinity for F-actin. In this study, we examined nine CMTP-causing mutations in the calmodulin-like and rod domains of actinin-1. These mutations increase, to varying degrees, actinin's ability to bundle actin filaments in vitro. Mutations within the calmodulin-like domain decrease its thermal stability slightly but do not dramatically affect calcium binding, with mutant proteins retaining calcium-dependent regulation of filament bundling in vitro. The G764S and E769K mutations increase cytoskeletal association of actinin in cells, and all mutant proteins colocalize with F-actin in cultured HeLa cells. Thus, CMTP-causing actinin-1 mutations outside the actin-binding domain also increase actin association, suggesting a common molecular mechanism underlying actinin-1 related CMTP.

Mean Platelet Volume (MPV): New Perspectives for an Old Marker in the Course and Prognosis of Inflammatory Conditions

Platelet size has been demonstrated to reflect platelet activity and seems to be a useful predictive and prognostic biomarker of cardiovascular events. It is associated with a variety of prothrombotic and proinflammatory diseases. The aim is a review of literature reports concerning changes in the mean platelet volume (MPV) and its possible role as a biomarker in inflammatory processes and neoplastic diseases. PubMed database was searched for sources using the following keywords: platelet activation, platelet count, mean platelet volume and: inflammation, cancer/tumor, cardiovascular diseases, myocardial infarction, diabetes, lupus disease, rheumatoid arthritis, tuberculosis, ulcerative colitis, renal disease, pulmonary disease, influencing factors, age, gender, genetic factors, oral contraceptives, smoking, lifestyle, methods, standardization, and hematological analyzer. Preference was given to the sources which were published within the past 20 years. Increased MPV was observed in cardiovascular diseases, cerebral stroke, respiratory diseases, chronic renal failure, intestine diseases, rheumatoid diseases, diabetes, and various cancers. Decreased MPV was noted in tuberculosis during disease exacerbation, ulcerative colitis, SLE in adult, and different neoplastic diseases. The study of MPV can provide important information on the course and prognosis in many inflammatory conditions. Therefore, from the clinical point of view, it would be interesting to establish an MPV cut-off value indicating the intensity of inflammatory process, presence of the disease, increased risk of disease development, increased risk of thrombotic complications, increased risk of death, and patient's response on applied treatment. Nevertheless, this aspect of MPV evaluation allowing its use in clinical practice is limited and requires further studies.

The Birth and Death of Platelets in Health and Disease

Blood platelets are involved in a wide range of physiological responses and pathological processes. Recent studies have considerably advanced our understanding of the mechanisms of platelet production and clearance, revealing new connections between the birth and death of these tiny, abundant cells. Key insights have also been gained into how physiological challenges such as inflammation, infection, and chemotherapy can affect megakaryocytes, the cells that produce platelets.

Autophagy in Platelets

Anucleate platelets are produced by fragmentation of megakaryocytes. Platelets circulate in the bloodstream for a finite period: upon vessel injury, they are activated to participate in hemostasis; upon senescence, unused platelets are cleared. Platelet hypofunction leads to bleeding. Conversely, pathogenic platelet activation leads to occlusive events that precipitate strokes and heart attacks. Recently, we and others have shown that autophagy occurs in platelets and is important for platelet production and normal functions including hemostasis and thrombosis. Due to the unique properties of platelets, such as their lack of nuclei and their propensity for activation, methods for studying platelet autophagy must be specifically tailored. Here, we describe useful methods for examining autophagy in both human and mouse platelets.

Biometric Image Analysis for Quantitation of Dividing Platelets

(1) Background: Quantification of platelet division is challenging because automated Coulter cell counters produce equivocal platelet counts. (2) Methods: We applied the flow cytometric cell tracking dye dilution assay as a popular immunological method to evaluate lymphocyte proliferation to prove and quantitate platelet division. We also devised a method relying on platelet culture in a semisolid medium which enabled dividing platelets to be identified by limiting the diffusive movement of platelets. Mixing platelets of different labeling colors in semisolid medium and counting the platelet doublets of each color combination enabled us to prove and quantitate platelet division. (3) Results: The tracking dye dilution assay revealed that 75.5 to 85.6% of platelets were dividing after 20 hours in culture. Platelets labeled with two different tracking dyes were mixed and cultured in semisolid medium for differential doublet counting. We counted platelet singlets and doublets of each color and color combination using confocal microscopy after six hours of culture and compared the relative number of two-colored doublets with binomial prediction to prove platelet division (P < 0.01). Division was suppressed by taxol, nocodazole, or cytochalasin D treatment. We derived a formula for determining the fraction of dividing platelets using the numbers of singlets and doublets of each color and color combination. The platelet division fraction ranged from 8.8 to 17.5%. (4) Conclusion: We successfully measured platelet division using a simple biometric image analysis method with possible future application to microfluidic devices.

Cellular and Molecular Networking Within the Ecosystem of Cancer Cell Communication via Tunneling Nanotubes

Intercellular communication is vital to the ecosystem of cancer cell organization and invasion. Identification of key cellular cargo and their varied modes of transport are important considerations in understanding the basic mechanisms of cancer cell growth. Gap junctions, exosomes, and apoptotic bodies play key roles as physical modalities in mediating intercellular transport. Tunneling nanotubes (TNTs)-narrow actin-based cytoplasmic extensions-are unique structures that facilitate direct, long distance cell-to-cell transport of cargo, including microRNAs, mitochondria, and a variety of other sub cellular components. The transport of cargo via TNTs occurs between malignant and stromal cells and can lead to changes in gene regulation that propagate the cancer phenotype. More notably, the transfer of these varied molecules almost invariably plays a critical role in the communication between cancer cells themselves in an effort to resist death by chemotherapy and promote the growth and metastases of the primary oncogenic cell. The more traditional definition of "Systems Biology" is the computational and mathematical modeling of complex biological systems. The concept, however, is now used more widely in biology for a variety of contexts, including interdisciplinary fields of study that focus on complex interactions within biological systems and how these interactions give rise to the function and behavior of such systems. In fact, it is imperative to understand and reconstruct components in their native context rather than examining them separately. The long-term objective of evaluating cancer ecosystems in their proper context is to better diagnose, classify, and more accurately predict the outcome of cancer treatment. Communication is essential for the advancement and evolution of the tumor ecosystem. This interplay results in cancer progression. As key mediators of intercellular communication within the tumor ecosystem, TNTs are the central topic of this article.

Differential Expression Profile of MicroRNAs During Prolonged Storage of Platelet Concentrates As a Quality Measurement Tool in Blood Banks

Platelet concentrate (PC) is a key blood component, which even in good storage conditions, susceptible to cellular damage over time. Hence, blood banks discard unused PC bags after 5 days of storage. Biomarkers of PC quality are therefore highly sought after in blood bank governance. We used the data (Gene Expression Omnibus: GSE61856) generated with next-generation sequencing to examine the expression profiles of microRNAs (miRNAs) from PCs that were stored for 6 days in a blood bank, that is, 1 day longer than is normally stored PC. We identified the 14 most differentially expressed miRNAs by comparing a control PC on the first day of storage with the PCs on each of the subsequent 5 days of storage from day 1 to 6. In all, we identified nine miRNAs with the downregulated profile (miR-145-5p, miR-150-5p, miR-183-5p, miR-26a-5p, miR-331-3p, miR-338-5p, miR-451a, miR-501-3p, and miR-99b-5p) and five upregulated miRNAs (miR-1304-3p, miR-411-5p, miR-432-5p, miR-668-3p, and miR-939-5p). These miRNAs were validated by real-time quantitative PCR in 100 PC units. As each PC unit is composed of platelets of five individuals, the validation was thus performed in 500 individuals (250 men and 250 women, comprised 18-40 years old adults). The data were analyzed with hierarchical clustering and principal component analysis, which revealed the variation of mean relative expression and the instability of miRNAs half-life on the fourth day of PC storage, which coincides with time of onset of platelet storage lesions. These new observations can usefully inform future decision-making and governance in blood banks concerning PC quality.

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.

Imaging platelet biogenesis in vivo

In this review paper, we give a historical perspective of the development of imaging modalities to visualize platelet biogenesis and how this contributed to our current understanding of megakaryopoiesis and thrombopoiesis. We provide some insight how distinct in vivo and in situ imaging methods, including ultramicrographs, have contributed to the current concepts of platelet formation. The onset of intravital microscopy into the mouse bone marrow has markedly modified and challenged our thinking of platelet biogenesis during the last decade. Finally, we discuss ongoing work, which was presented at the recent International Society on Thrombosis and Haemostasis (ISTH) meeting.

Biomolecular Consequences of Platelet Pathogen Inactivation Methods

Pathogen inactivation (PI) for platelet concentrates (PC) is a fairly recent development in transfusion medicine that is intended to decrease infectious disease transmission from the donor to the receiving patient. Effective inactivation of viruses, bacteria and eukaryotic parasites adds a layer of safety, protecting the blood supply against customary and emerging pathogens. Three PI methods have been described for platelets. These are based on photochemical damage of nucleic acids which prevents replication of most infectious pathogens and contaminating donor leukocytes. Because platelets do not replicate, the collateral damage to platelet function is considered low to non-existing. This is disputable however because photochemistry is not specific for nucleic acids and significantly affects platelet biomolecules as well. The impact of these biomolecular changes on platelet function and hemostasis is not well understood, but is increasingly being studied. The results of these studies can help explain current and future clinical observations with PI platelets, including the impact on transfusion yield and bleeding. This review summarizes the biomolecular effects of PI treatment on platelets. We conclude that despite a comparable principle of photochemical inactivation, all three methods affect platelets in different ways. This knowledge can help blood banks and transfusion specialists to guide their choice when considering the implementation or clinical use of PI treated platelets.

Deletion of GLUT1 and GLUT3 Reveals Multiple Roles for Glucose Metabolism in Platelet and Megakaryocyte Function

Anucleate platelets circulate in the blood to facilitate thrombosis and diverse immune functions. Platelet activation leading to clot formation correlates with increased glycogenolysis, glucose uptake, glucose oxidation, and lactic acid production. Simultaneous deletion of glucose transporter (GLUT) 1 and GLUT3 (double knockout [DKO]) specifically in platelets completely abolished glucose uptake. In DKO platelets, mitochondrial oxidative metabolism of non-glycolytic substrates, such as glutamate, increased. Thrombosis and platelet activation were decreased through impairment at multiple activation nodes, including Ca²⁺ signaling, degranulation, and integrin activation. DKO mice developed thrombocytopenia, secondary to impaired pro-platelet formation from megakaryocytes, and increased platelet clearance resulting from cytosolic calcium overload and calpain activation. Systemic treatment with oligomycin, inhibiting mitochondrial metabolism, induced rapid clearance of platelets, with circulating counts dropping to zero in DKO mice, but not wild-type mice, demonstrating an essential role for energy metabolism in platelet viability. Thus, substrate metabolism is essential for platelet production, activation, and survival.