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Hematopoietic stem cell transplantation (HSCT) is pivotal in treating hematologic disorders, yet it poses the risk of post-transplantation pancytopenia. Prophylactic platelet transfusions are often administered to mitigate this risk. Utilizing practical markers, such as immature platelet fraction (IPF), to predict hematopoietic recovery in advance could reduce unnecessary prophylactic transfusions. Our prospective study, involving 53 HSCT patients at Taipei Veterans General Hospital between September 2022 and May 2023, utilized the Sysmex XN analyzer to assess peripheral blood cell parameters. We investigated whether IPF could predict platelet recovery early, determined the optimal cut-off value, and compared platelet usage. Neutrophil and platelet engraftment occurred 10 (median; range: 10–12) and 15 (median; range: 15–18) days post-HSCT. Notably, 71.7% of patients exhibited an IPF increase exceeding 2% before platelet recovery. The optimal cut-off IPF on day 10 for predicting platelet recovery within five days was 2.15% (specificity 0.89, sensitivity 0.65). On average, patients received 3.89 units of post-transplantation platelet transfusion. Our results indicate that IPF serves as a predictive marker for platelet engraftment, peaking before the increase in platelet count. This insight aids clinicians in assessing the need for prophylactic platelet transfusions. Integrating reference IPF values alongside platelet counts enhances the accuracy of evaluating a patient's hematopoietic recovery status. Anticipating the timing of platelet recovery optimizes blood product usage and mitigates transfusion reaction risks. [ABSTRACT FROM AUTHOR]

Harmine (HM), a β‐carboline alkaloid extracted from plants, is a crucial component of traditional Chinese medicine (TCM) known for its diverse pharmacological activities. Thrombocytopenia, a common and challenging hematological disorder, often coexists with serious illnesses. Previous research has shown a correlation between HM and thrombocytopenia, but the mechanism needs further elucidation. The aim of this study was to clarify the mechanisms underlying the effects of HM on thrombocytopenia and to develop new therapeutic strategies. Flow cytometry, Giemsa staining, and Phalloidin staining were used to assess HM's impact on Meg‐01 and HEL cell differentiation and maturation in vitro. A radiation‐induced thrombocytopenic mouse model was employed to evaluate HM's effect on platelet production in vivo. Network pharmacology, molecular docking, and protein blotting were utilized to investigate HM's targets and mechanisms. The results demonstrated that HM dose‐dependently promoted Meg‐01 and HEL cell differentiation and maturation in vitro and restored platelet levels in irradiated mice in vivo. Subsequently, HM was found to be involved in the biological process of platelet production by upregulating the expressions of Rac1, Cdc42, JNK, and 5‐HTR2A. Furthermore, the targeting of HM to 5‐HTR2A and its correlation with downstream Rac1/Cdc42/JNK were also confirmed. In conclusion, HM regulates megakaryocyte differentiation and thrombopoiesis through the 5‐HTR2A and Rac1/Cdc42/JNK pathways, providing a potential treatment strategy for thrombocytopenia. [ABSTRACT FROM AUTHOR]

A key step in platelet production is the migration of megakaryocytes to the vascular sinusoids within the bone marrow. This homing is mediated by the chemokine CXCL12 and its receptor CXCR4. CXCR4 is also a positive regulator of platelet activation and thrombosis. Pim-1 kinase has been shown to regulate CXCR4 signalling in other cell types, and we have previously described how Pim kinase inhibitors attenuate platelet aggregation to CXCL12. However, the mechanism by which Pim-1 regulates CXCR4 signalling in platelets and megakaryocytes has yet to be elucidated. Using human platelets, murine bone marrow-derived megakaryocytes, and the megakaryocyte cell line MEG-01, we demonstrate that pharmacological Pim kinase inhibition leads to reduced megakaryocyte and platelet function responses to CXCL12, including reduced megakaryocyte migration and platelet granule secretion. Attenuation of CXCL12 signalling was found to be attributed to the reduced surface expression of CXCR4. The decrease in CXCR4 surface levels was found to be mediated by rapid receptor internalisation, in the absence of agonist stimulation. We demonstrate that pharmacological Pim kinase inhibition disrupts megakaryocyte and platelet function by reducing constitutive CXCR4 surface expression, decreasing the number of receptors available for agonist stimulation and signalling. These findings have implications for the development and use of Pim kinase inhibitors for the treatment of conditions associated with elevated circulating levels of CXCL12/SDF1α and increased thrombotic risk. [ABSTRACT FROM AUTHOR]

Abstract Background The immature platelet fraction (IPF), a parameter obtained by the Sysmex XN‐1000V analyzer, is used in humans to differentiate between central (CEN) and peripheral (PER) thrombocytopenia (TP) but has not been evaluated in small animals. Objectives Compare IPF between healthy, clinical non‐TP and TP dogs and cats, study IPF in different causes of TP in dogs and cats and, establish IPF reference intervals (RIs), and study the effect of age and sex on IPF in healthy dogs and cats. Animals A total of 3281 dogs and 726 cats. Methods Retrospective review of medical records. Animals were classified as nonthrombocytopenic (healthy group and group of clinical patients without TP [NTP]) or TP. These latter animals were subclassified as pseudothrombocytopenia (PSE), CEN and PER, based on evaluation of platelet clumps, estimated platelet count in blood smears and final diagnosis. Blood samples were evaluated using a Sysmex XN‐1000V with a specific platelet channel (PLT‐F). Results The IPF was significantly different between each subtype of TP in both species. Immature platelet fractions

Background: The immature platelet fraction (IPF), a parameter obtained by the Sysmex XN‐1000V analyzer, is used in humans to differentiate between central (CEN) and peripheral (PER) thrombocytopenia (TP) but has not been evaluated in small animals. Objectives: Compare IPF between healthy, clinical non‐TP and TP dogs and cats, study IPF in different causes of TP in dogs and cats and, establish IPF reference intervals (RIs), and study the effect of age and sex on IPF in healthy dogs and cats. Animals: A total of 3281 dogs and 726 cats. Methods: Retrospective review of medical records. Animals were classified as nonthrombocytopenic (healthy group and group of clinical patients without TP [NTP]) or TP. These latter animals were subclassified as pseudothrombocytopenia (PSE), CEN and PER, based on evaluation of platelet clumps, estimated platelet count in blood smears and final diagnosis. Blood samples were evaluated using a Sysmex XN‐1000V with a specific platelet channel (PLT‐F). Results: The IPF was significantly different between each subtype of TP in both species. Immature platelet fractions <6.9% in dogs or 13.6% in cats, once PSE has been eliminated by review of blood smears, are indicative of CEN. Reference intervals for IPF were 0.5%‐8% in healthy dogs and 1%‐40.3% in healthy cats. Conclusions and Clinical Importance: We determined that IPF can differentiate between CEN and PER in dogs and cats, guiding additional testing and avoiding more invasive procedures (bone marrow sampling). A blood smear always should be evaluated to rule out platelet clumping. [ABSTRACT FROM AUTHOR]

Platelets are the terminal progeny of megakaryocytes, primarily produced in the bone marrow, and play critical roles in blood homeostasis, clotting, and wound healing. Traditionally, megakaryocytes and platelets are thought to arise from multipotent hematopoietic stem cells (HSCs) via multiple discrete progenitor populations with successive, lineage-restricting differentiation steps. However, this view has recently been challenged by studies suggesting that (1) some HSC clones are biased and/or restricted to the platelet lineage, (2) not all platelet generation follows the "canonical" megakaryocytic differentiation path of hematopoiesis, and (3) platelet output is the default program of steady-state hematopoiesis. Here, we specifically investigate the evidence that in vivo lineage tracing studies provide for the route(s) of platelet generation and investigate the involvement of various intermediate progenitor cell populations. We further identify the challenges that need to be overcome that are required to determine the presence, role, and kinetics of these possible alternate pathways. [ABSTRACT FROM AUTHOR]

Interleukins, a diverse family of cytokines produced by various cells, play crucial roles in immune responses, immunoregulation, and a wide range of physiological and pathological processes. In the context of megakaryopoiesis, thrombopoiesis, and platelet function, interleukins have emerged as key regulators, exerting significant influence on the development, maturation, and activity of megakaryocytes (MKs) and platelets. While the therapeutic potential of interleukins in platelet-related diseases has been recognized for decades, their clinical application has been hindered by limitations in basic research and challenges in drug development. Recent advancements in understanding the molecular mechanisms of interleukins and their interactions with MKs and platelets, coupled with breakthroughs in cytokine engineering, have revitalized the field of interleukin-based therapeutics. These breakthroughs have paved the way for the development of more effective and specific interleukin-based therapies for the treatment of platelet disorders. This review provides a comprehensive overview of the effects of interleukins on megakaryopoiesis, thrombopoiesis, and platelet function. It highlights the potential clinical applications of interleukins in regulating megakaryopoiesis and platelet function and discusses the latest bioengineering technologies that could improve the pharmacokinetic properties of interleukins. By synthesizing the current knowledge in this field, this review aims to provide valuable insights for future research into the clinical application of interleukins in platelet-related diseases. [ABSTRACT FROM AUTHOR]

Selenium deficiency is still a global problem in livestock husbandry, and this micronutrient is commonly supplemented in ruminants around the world, especially during the neonatal period. The aim of this study was to assess the influence of selenium and vitamin E supplementation in young goats in the neonatal period on the activity of the process of thrombopoiesis based on cytological evaluation of bone marrow smears. Twelve clinically healthy goats at the age of 2 days divided into two equal groups (n=6) participated in the study. Only animals from the experimental group received a single dose of Se and vitamin E on the second day of life. Bone marrow was collected three times (2nd day of life and after 15 and 25 days), stained with the MGG method, and subjected to cytological evaluation. Peripheral blood smears were also analyzed three times. The bone marrow cells in the group receiving the supplement absorbed dyes faster and more intensively than the same cells in the control animals. The numbers of megakaryoblasts and megakaryocytes were higher in goats from the experimental group than in the control group, which indicated the intensification of thrombopoiesis in animals supplemented with selenium and vitamin E. The results of the morphological tests clearly indicated an increase in the number of platelets and a higher platelet volume in experimental group. It can be concluded that selenium and vitamin E supplementation has a positive impact on the thrombopoiesis in caprine bone marrow. [ABSTRACT FROM AUTHOR]

Noncoding RNAs (ncRNAs) are a group of RNA molecules that cannot encode proteins, and a better understanding of the complex interaction networks coordinated by ncRNAs will provide a theoretical basis for the development of therapeutics targeting the regulatory effects of ncRNAs. Platelets are produced upon the differentiation of hematopoietic stem cells into megakaryocytes, 1011 per day, and are renewed every 8-9 days. The process of thrombopoiesis is affected by multiple factors, in which ncRNAs also exert a significant regulatory role. This article reviewed the regulatory roles of ncRNAs, mainly microRNAs (miRNAs), circRNAs (circular RNAs), and long non-coding RNAs (lncRNAs), in thrombopoiesis in recent years as well as their roles in primary immune thrombocytopenia (ITP). [ABSTRACT FROM AUTHOR]

Abstract Background Cyclooxygenase (COX)-2 is a rate-limiting enzyme in the biosynthesis of prostanoids, which is mostly inducible by inflammatory cytokines. The participation of COX-2 in the maturation of megakaryocytes has been reported but barely studied in primary immune thrombocytopenia (ITP). Methods The expressions of COX-2 and Caspase-1, Caspase-3 and Caspase-3 p17 subunit in platelets from ITP patients and healthy controls (HC), and the expressions of COX-2 and CD41 in bone marrow (BM) of ITP patients were measured and analyzed for correlations. The effects of COX-2 inhibitor on megakaryopoiesis and thrombopoiesis were assessed by in vitro culture of Meg01 cells and murine BM-derived megakaryocytes and in vivo experiments of passive ITP mice. Results The expression of COX-2 was decreased and Caspase-1 and Caspase-3 p17 were increased in platelets from ITP patients compared to HC. In platelets from ITP patients, the COX-2 expression was positively correlated with platelet count and negatively correlated to the expression of Caspase-1. In ITP patients BM, the expression of CD41 was positively correlated with the expression of COX-2. COX-2 inhibitor inhibited the count of megakaryocytes and impaired the maturation and platelet production in Meg01 cells and bone marrow-derived megakaryocytes. COX-2 inhibitor aggravated thrombocytopenia and damaged megakaryopoiesis in ITP murine model. Conclusion COX-2 plays a vital role in the physiologic and pathologic conditions of ITP by intervening the survival of platelets and impairing the megakaryopoiesis and thrombopoiesis of megakaryocytes.

Abstract Hyperhomocysteinemia (HHcy) is closely associated with thrombotic diseases such as myocardial infarction and stroke. Enhanced platelet activation was observed in animals and humans with HHcy. However, the influence of HHcy on thrombopoiesis remains largely unknown. Here, we reported increased platelet count (PLT) in mice and zebrafish with HHcy. In hypertensive patients (n = 11,189), higher serum level of total Hcy was observed in participants with PLT ≥ 291 × 109/L (full adjusted β, 0.59; 95% CI 0.14, 1.04). We used single-cell RNA sequencing (scRNA-seq) to characterize the impact of Hcy on transcriptome, cellular heterogeneity, and developmental trajectories of megakaryopoiesis from human umbilical cord blood (hUCB) CD34+ cells. Together with in vitro and in vivo analysis, we demonstrated that Hcy promoted megakaryocytes (MKs) differentiation via growth hormone (GH)-PI3K-Akt axis. Moreover, the effect of Hcy on thrombopoiesis is independent of thrombopoietin (TPO) because administration of Hcy also led to a significant increase of PLT in homozygous TPO receptor (Mpl) mutant mice and zebrafish. Administration of melatonin effectively reversed Hcy-induced thrombopoiesis in mice. ScRNA-seq showed that melatonin abolished Hcy-facilitated MK differentiation and maturation, inhibited the activation of GH-PI3K-Akt signaling. Our work reveals a previously unrecognized role of HHcy in thrombopoiesis and provides new insight into the mechanisms by which HHcy confers an increased thrombotic risk. Trial Registration clinicaltrials.gov Identifier: NCT00794885.

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. • Autophagy plays an important role in megakaryopoiesis. • Autophagosome formation and autophagy are essential in platelet biology. • Autophagy in platelets is involved in platelet aggregation, adhesion, and thrombus formation. • The importance of platelet autophagic functions is demonstrated in clinically relevant conditions and disease states, such as diabetes, hypoxia/ischemia, ITP, and sepsis. • Elaborate methods are available to study autophagy in platelets reliably and in great detail. [ABSTRACT FROM AUTHOR]

Platelets are generated by specialized cells called megakaryocytes (MKs). However, MK's origin and platelet release mode have remained incompletely understood. Here, we established direct visualization of embryonic thrombopoiesis in vivo by combining multiphoton intravital microscopy (MP-IVM) with a fluorescence switch reporter mouse model under control of the platelet factor 4 promoter (Pf4CreRosa26mTmG). Using this microscopy tool, we discovered that fetal liver MKs provide higher thrombopoietic activity than yolk sac MKs. Mechanistically, fetal platelets were released from MKs either by membrane buds or the formation of proplatelets, with the former constituting the key process. In E14.5 c-Myb-deficient embryos that lack definitive hematopoiesis, MK and platelet numbers were similar to wild-type embryos, indicating the independence of embryonic thrombopoiesis from definitive hematopoiesis at this stage of development. In summary, our novel MP-IVM protocol allows the characterization of thrombopoiesis with high spatio-temporal resolution in the mouse embryo and has identified membrane budding as the main mechanism of fetal platelet production. [ABSTRACT FROM AUTHOR]

Platelets are the terminal progeny of megakaryocytes, primarily produced in the bone marrow, and play critical roles in blood homeostasis, clotting, and wound healing. Traditionally, megakaryocytes and platelets are thought to arise from multipotent hematopoietic stem cells (HSCs) via multiple discrete progenitor populations with successive, lineage-restricting differentiation steps. However, this view has recently been challenged by studies suggesting that (1) some HSC clones are biased and/or restricted to the platelet lineage, (2) not all platelet generation follows the “canonical” megakaryocytic differentiation path of hematopoiesis, and (3) platelet output is the default program of steady-state hematopoiesis. Here, we specifically investigate the evidence that in vivo lineage tracing studies provide for the route(s) of platelet generation and investigate the involvement of various intermediate progenitor cell populations. We further identify the challenges that need to be overcome that are required to determine the presence, role, and kinetics of these possible alternate pathways.

Background: Cyclooxygenase (COX)-2 is a rate-limiting enzyme in the biosynthesis of prostanoids, which is mostly inducible by inflammatory cytokines. The participation of COX-2 in the maturation of megakaryocytes has been reported but barely studied in primary immune thrombocytopenia (ITP). Methods: The expressions of COX-2 and Caspase-1, Caspase-3 and Caspase-3 p17 subunit in platelets from ITP patients and healthy controls (HC), and the expressions of COX-2 and CD41 in bone marrow (BM) of ITP patients were measured and analyzed for correlations. The effects of COX-2 inhibitor on megakaryopoiesis and thrombopoiesis were assessed by in vitro culture of Meg01 cells and murine BM-derived megakaryocytes and in vivo experiments of passive ITP mice. Results: The expression of COX-2 was decreased and Caspase-1 and Caspase-3 p17 were increased in platelets from ITP patients compared to HC. In platelets from ITP patients, the COX-2 expression was positively correlated with platelet count and negatively correlated to the expression of Caspase-1. In ITP patients BM, the expression of CD41 was positively correlated with the expression of COX-2. COX-2 inhibitor inhibited the count of megakaryocytes and impaired the maturation and platelet production in Meg01 cells and bone marrow-derived megakaryocytes. COX-2 inhibitor aggravated thrombocytopenia and damaged megakaryopoiesis in ITP murine model. Conclusion: COX-2 plays a vital role in the physiologic and pathologic conditions of ITP by intervening the survival of platelets and impairing the megakaryopoiesis and thrombopoiesis of megakaryocytes. [ABSTRACT FROM AUTHOR]

Hyperhomocysteinemia (HHcy) is closely associated with thrombotic diseases such as myocardial infarction and stroke. Enhanced platelet activation was observed in animals and humans with HHcy. However, the influence of HHcy on thrombopoiesis remains largely unknown. Here, we reported increased platelet count (PLT) in mice and zebrafish with HHcy. In hypertensive patients (n = 11,189), higher serum level of total Hcy was observed in participants with PLT ≥ 291 × 109/L (full adjusted β, 0.59; 95% CI 0.14, 1.04). We used single-cell RNA sequencing (scRNA-seq) to characterize the impact of Hcy on transcriptome, cellular heterogeneity, and developmental trajectories of megakaryopoiesis from human umbilical cord blood (hUCB) CD34+ cells. Together with in vitro and in vivo analysis, we demonstrated that Hcy promoted megakaryocytes (MKs) differentiation via growth hormone (GH)-PI3K-Akt axis. Moreover, the effect of Hcy on thrombopoiesis is independent of thrombopoietin (TPO) because administration of Hcy also led to a significant increase of PLT in homozygous TPO receptor (Mpl) mutant mice and zebrafish. Administration of melatonin effectively reversed Hcy-induced thrombopoiesis in mice. ScRNA-seq showed that melatonin abolished Hcy-facilitated MK differentiation and maturation, inhibited the activation of GH-PI3K-Akt signaling. Our work reveals a previously unrecognized role of HHcy in thrombopoiesis and provides new insight into the mechanisms by which HHcy confers an increased thrombotic risk. Trial Registration clinicaltrials.gov Identifier: NCT00794885. [ABSTRACT FROM AUTHOR]

The use of messenger RNA (mRNA) enables the transient production of therapeutic proteins with stable and predictable translational kinetics and without the risk of insertional mutagenesis. Recent findings highlight the enormous potential of mRNA-based therapeutics. Here, we describe the synthesis of chemically modified thrombopoietin (TPO) mRNA through in vitro transcription and in vivo delivery via lipid nanoparticles (LNPs). After delivery of TPO mRNA in mice, compared with normal physiological values, plasma TPO protein levels increased over 1000-fold in a dose-dependent manner. Moreover, through a single intravenous dose of TPO mRNA-loaded LNPs, both reticulated and total platelet count increased significantly in mice, demonstrating that TPO protein derived from the exogenous mRNA was able to maintain normal activity. Submicrogram quantity of N1-methylpseudouridine-modified TPO mRNA showed a similar effect in promoting thrombopoiesis as that by the TPO receptor agonist romiplostim. In addition, a therapeutic value was established in anti-GPIbα (CD42b) antibody-induced thrombocytopenia mouse models that showed a fast recovery of platelet count. Our study demonstrated chemically modified in-vitro-transcribed TPO mRNA as a potentially safe therapeutic intervention to stimulate thrombopoiesis.

Protein glycosylation, including sialylation, involves complex and frequent post-translational modifications, which play a critical role in different biological processes. The conjugation of carbohydrate residues to specific molecules and receptors is critical for normal hematopoiesis, as it favors the proliferation and clearance of hematopoietic precursors. Through this mechanism, the circulating platelet count is controlled by the appropriate platelet production by megakaryocytes, and the kinetics of platelet clearance. Platelets have a half-life in blood ranging from 8 to 11 days, after which they lose the final sialic acid and are recognized by receptors in the liver and eliminated from the bloodstream. This favors the transduction of thrombopoietin, which induces megakaryopoiesis to produce new platelets. More than two hundred enzymes are responsible for proper glycosylation and sialylation. In recent years, novel disorders of glycosylation caused by molecular variants in multiple genes have been described. The phenotype of the patients with genetic alterations in GNE, SLC35A1, GALE and B4GALT is consistent with syndromic manifestations, severe inherited thrombocytopenia, and hemorrhagic complications. [ABSTRACT FROM AUTHOR]

Interleukins, a diverse family of cytokines produced by various cells, play crucial roles in immune responses, immunoregulation, and a wide range of physiological and pathological processes. In the context of megakaryopoiesis, thrombopoiesis, and platelet function, interleukins have emerged as key regulators, exerting significant influence on the development, maturation, and activity of megakaryocytes (MKs) and platelets. While the therapeutic potential of interleukins in platelet-related diseases has been recognized for decades, their clinical application has been hindered by limitations in basic research and challenges in drug development. Recent advancements in understanding the molecular mechanisms of interleukins and their interactions with MKs and platelets, coupled with breakthroughs in cytokine engineering, have revitalized the field of interleukin-based therapeutics. These breakthroughs have paved the way for the development of more effective and specific interleukin-based therapies for the treatment of platelet disorders. This review provides a comprehensive overview of the effects of interleukins on megakaryopoiesis, thrombopoiesis, and platelet function. It highlights the potential clinical applications of interleukins in regulating megakaryopoiesis and platelet function and discusses the latest bioengineering technologies that could improve the pharmacokinetic properties of interleukins. By synthesizing the current knowledge in this field, this review aims to provide valuable insights for future research into the clinical application of interleukins in platelet-related diseases.

Platelets are the second most abundant blood component after red blood cells and can participate in a variety of physiological and pathological functions. Beyond its traditional role in hemostasis and thrombosis, it also plays an indispensable role in inflammatory diseases. However, thrombocytopenia is a common hematologic problem in the clinic, and it presents a proportional relationship with the fatality of many diseases. Therefore, the prevention and treatment of thrombocytopenia is of great importance. The expression of Toll-like receptors (TLRs) is one of the most relevant characteristics of thrombopoiesis and the platelet inflammatory function. We know that the TLR family is found on the surface or inside almost all cells, where they perform many immune functions. Of those, TLR2 and TLR4 are the main stress-inducing members and play an integral role in inflammatory diseases and platelet production and function. Therefore, the aim of this review is to present and discuss the relationship between platelets, inflammation and the TLR family and extend recent research on the influence of the TLR2 and TLR4 pathways and the regulation of platelet production and function. Reviewing the interaction between TLRs and platelets in inflammation may be a research direction or program for the treatment of thrombocytopenia-related and inflammatory-related diseases. [ABSTRACT FROM AUTHOR]

Platelets, generated from precursor megakaryocytes (MKs), are central mediators of hemostasis and thrombosis. The process of thrombopoiesis is extremely complex, regulated by multiple factors, and related to many cellular events including apoptosis. However, the role of apoptosis in thrombopoiesis has been controversial for many years. Some researchers believe that apoptosis is an ally of thrombopoiesis and platelets production is apoptosis-dependent, while others have suggested that apoptosis is dispensable for thrombopoiesis, and is even inhibited during this process. In this review, we will focus on this conflict, discuss the relationship between megakaryocytopoiesis, thrombopoiesis and apoptosis. In addition, we also consider why such a vast number of studies draw opposite conclusions of the role of apoptosis in thrombopoiesis, and try to figure out the truth behind the mystery. This review provides more comprehensive insights into the relationship between megakaryocytopoiesis, thrombopoiesis, and apoptosis and finds some clues for the possible pathological mechanisms of platelet disorders caused by abnormal apoptosis. [ABSTRACT FROM AUTHOR]

In recent years, there has been interest in the study of platelets, the functions of which, as it turned out, are not limited to their involvement in the mechanism of blood coagulation. Many works are devoted to the study of the functional state of platelets under conditions of acute and chronic alcohol exposure. The results of such studies can be useful in the development of new markers of the degree of alcohol intoxication of the body for the subsequent choice of a method for drug correction of disorders caused by acute or chronic alcohol effects. The review summarizes the results of studies on the effect of ethanol on the platelet biogenesis, abundance, morphology, and biochemistry. An analysis of studies performed both in vitro and in experimental animals in vivo, as well as the results of clinical observations, is presented. [ABSTRACT FROM AUTHOR]

Platelets are generated by specialized cells called megakaryocytes (MKs). However, MK’s origin and platelet release mode have remained incompletely understood. Here, we established direct visualization of embryonic thrombopoiesis in vivo by combining multiphoton intravital microscopy (MP-IVM) with a fluorescence switch reporter mouse model under control of the platelet factor 4 promoter (Pf4CreRosa26mTmG). Using this microscopy tool, we discovered that fetal liver MKs provide higher thrombopoietic activity than yolk sac MKs. Mechanistically, fetal platelets were released from MKs either by membrane buds or the formation of proplatelets, with the former constituting the key process. In E14.5 c-Myb-deficient embryos that lack definitive hematopoiesis, MK and platelet numbers were similar to wild-type embryos, indicating the independence of embryonic thrombopoiesis from definitive hematopoiesis at this stage of development. In summary, our novel MP-IVM protocol allows the characterization of thrombopoiesis with high spatio-temporal resolution in the mouse embryo and has identified membrane budding as the main mechanism of fetal platelet production.

Thrombocytopenia is one of the most common complications of cancer therapy. Until now, there are still no satisfactory medications to treat chemotherapy and radiation-induced thrombocytopenia (CIT and RIT, respectively). Caulis Polygoni Multiflori (CPM), one of the most commonly used Chinese herbs, has been well documented to nourish blood for tranquilizing the mind and treating anemia, suggesting its beneficial effect on hematopoiesis. However, it is unknown whether CPM can accelerate megakaryopoiesis and thrombopoiesis. Here, we employ a UHPLC Q–Exactive HF-X mass spectrometer (UHPLC QE HF-X MS) to identify 11 ingredients in CPM. Then, in vitro experiments showed that CPM significantly increased megakaryocyte (MK) differentiation and maturation but did not affect apoptosis and lactate dehydrogenase (LDH) release of K562 and Meg-01 cells. More importantly, animal experiments verified that CPM treatment markedly accelerated platelet recovery, megakaryopoiesis and thrombopoiesis in RIT mice without hepatic and renal toxicities in vivo. Finally, RNA-sequencing (RNA-seq) and western blot were used to determine that CPM increased the expression of proteins related to PI3K/Akt and MEK/ERK (MAPK) signaling pathways. On the contrary, blocking PI3K/Akt and MEK/ERK signaling pathways with their specific inhibitors suppressed MK differentiation induced by CPM. In conclusion, for the first time, our study demonstrates that CPM may be a promised thrombopoietic agent and provide an experimental basis for expanding clinical use. [ABSTRACT FROM AUTHOR]

Thrombocytopenia is a common symptom and one of the warning signs of dengue virus (DENV) infection. Platelet depletion is critical as it may lead to other severe dengue symptoms. Understanding the molecular events of this condition during dengue infection is challenging because of the multifaceted factors involved in DENV infection and the dynamics of the disease progression. Platelet levels depend on the balance between platelet production and platelet consumption or clearance. Megakaryopoiesis and thrombopoiesis, two interdependent processes in platelet production, are hampered during dengue infection. Conversely, platelet elimination via platelet activation, apoptosis and clearance processes are elevated. Together, these anomalies contribute to thrombocytopenia in dengue patients. Targeting the molecular events of dengue-mediated thrombocytopenia shows great potential but still requires further investigation. Nonetheless, the application of new knowledge in this field, such as immature platelet fraction analysis, may facilitate physicians in monitoring the progression of the disease.

In mammalian hematopoiesis, megakaryocytes mature and become polyploid in the bone marrow before releasing platelets into circulation. In contrast, fish produce thrombocytes in kidney marrow, where young thrombocytes undergo maturation in circulation, akin to platelets. Despite morphological differences, our single-cell sequencing revealed significant gene expression similarities between fish thrombocytes and mammalian megakaryocytes, including Nfe2, which is crucial in platelet production. In addition to nfe2 expression, we found four nfe2-related genes, nfe2I1a, nfe2I1b, nfe2I2a, and nfe2I3, were expressed in mature thrombocytes. However, only nfe2, nfe2l2a, and nfe2l3 are expressed in young thrombocytes. Thus, we hypothesized that Nfe2-related factors may also be involved in thrombocyte production. To address this, we knocked down the four novel nfe2-related genes by the piggyback method and found both young and mature thrombocytes reduced when nfe2, nfe2l1a, and nfe2l3 were knocked down. They also exhibited greater gill bleeding and prolonged time to occlusion (TTO) compared to controls. In summary, our study shows Nfe2I1a and Nfe2l3 as novel transcription factors that are positive regulators influencing adult zebrafish thrombopoiesis., Competing Interests: Declaration of competing interest The authors report no conflict of interest., (Copyright © 2024. Published by Elsevier Inc.)

Background:  Specifically positioned negatively charged residues within the cytoplasmic domain of the adaptor protein, linker for the activation of T cells (LAT), have been shown to be important for efficient phosphorylation of tyrosine residues that function to recruit cytosolic proteins downstream of immunoreceptor tyrosine-based activation motif (ITAM) receptor signaling. LAT tyrosine 132-the binding site for PLC-γ2-is a notable exception, preceded instead by a glycine, making it a relatively poor substrate for phosphorylation. Mutating Gly 131 to an acidic residue has been shown in T cells to enhance ITAM-linked receptor-mediated signaling. Whether this is generally true in other cell types is not known., Methods:  To examine whether LAT Gly 131 restricts ITAM signaling in cells of the megakaryocyte lineage, we introduced an aspartic acid at this position in human induced pluripotent stem cells (iPSCs), differentiated them into megakaryocytes, and examined its functional consequences., Results:  iPSCs expressing G131D LAT differentiated and matured into megakaryocytes normally, but exhibited markedly enhanced reactivity to glycoprotein VI (GPVI)-agonist stimulation. The rate and extent of LAT Tyr 132 and PLC-γ2 phosphorylation, and proplatelet formation on GPVI-reactive substrates, were also enhanced., Conclusion:  These data demonstrate that a glycine residue at the -1 position of LAT Tyr 132 functions as a kinetic bottleneck to restrain Tyr 132 phosphorylation and signaling downstream of ITAM receptor engagement in the megakaryocyte lineage. These findings may have translational applications in the burgeoning field of in vitro platelet bioengineering., Competing Interests: None declared., (Thieme. All rights reserved.)

Platelets are generated and released into the bloodstream from their precursor cells, megakaryocytes that reside in the bone marrow. Though platelets have no nucleus or DNA, they contain a full transcriptome that, during platelet formation, is transported from the megakaryocyte to the platelet. It has been described that transcripts in platelets can be translated into proteins that influence platelet response. The platelet transcriptome is highly dynamic and has been extensively studied using microarrays and, more recently, RNA sequencing (RNA-seq) in relation to diverse conditions (inflammation, obesity, cancer, pathogens and others). In this review, we focus on bulk and single-cell RNA-seq studies that have aimed to characterize the coding transcriptome of healthy megakaryocytes and platelets in humans. It has been noted that bulk RNA-seq has limitations when studying in vitro-generated megakaryocyte cultures that are highly heterogeneous, while single-cell RNA-seq has not yet been applied to platelets due to their very limited RNA content. Next, we illustrate how these methods can be applied in the field of inherited platelet disorders for gene discovery and for unraveling novel disease mechanisms using RNA from platelets and megakaryocytes and rare disease bioinformatics. Next, future perspectives are discussed on how this field of coding transcriptomics can be integrated with other next-generation technologies to decipher unexplained inherited platelet disorders in a multiomics approach. [ABSTRACT FROM AUTHOR]

Abivertinib, a third-generation tyrosine kinase inhibitor, is originally designed to target epidermal growth factor receptor (EGFR)-activating mutations. Previous studies have shown that abivertinib has promising antitumor activity and a well-tolerated safety profile in patients with non-small-cell lung cancer. However, abivertinib also exhibited high inhibitory activity against Bruton's tyrosine kinase and Janus kinase 3. Given that these kinases play some roles in the progression of megakaryopoiesis, we speculate that abivertinib can affect megakaryocyte (MK) differentiation and platelet biogenesis. We treated cord blood CD34+ hematopoietic stem cells, Meg-01 cells, and C57BL/6 mice with abivertinib and observed megakaryopoiesis to determine the biological effect of abivertinib on MK differentiation and platelet biogenesis. Our in vitro results showed that abivertinib impaired the CFU-MK formation, proliferation of CD34+ HSC-derived MK progenitor cells, and differentiation and functions of MKs and inhibited Meg-01-derived MK differentiation. These results suggested that megakaryopoiesis was inhibited by abivertinib. We also demonstrated in vivo that abivertinib decreased the number of MKs in bone marrow and platelet counts in mice, which suggested that thrombopoiesis was also inhibited. Thus, these preclinical data collectively suggested that abivertinib could inhibit MK differentiation and platelet biogenesis and might be an agent for thrombocythemia. [ABSTRACT FROM AUTHOR]

Abstract Background Although airborne fine particulate matter (PM) pollution has been demonstrated as an independent risk factor for pulmonary and cardiovascular diseases, their currently-available toxicological data is still far from sufficient to explain the cause-and-effect. Platelets can regulate a variety of physiological and pathological processes, and the epidemiological study has indicated a positive association between PM exposure and the increased number of circulative platelets. As one of the target organs for PM pollution, the lung has been found to be involved in the storage of platelet progenitor cells (i.e. megakaryocytes) and thrombopoiesis. Whether PM exposure influences thrombopoiesis or not is thus explored in the present study by investigating the differentiation of megakaryocytes upon PM treatment. Results The results showed that PM exposure promoted the thrombopoiesis in an exposure concentration-dependent manner. PM exposure induced the megakaryocytic maturation and development by causing cell morphological changes, occurrence of DNA ploidy, and alteration in the expressions of biomarkers for platelet formation. The proteomics assay demonstrated that the main metabolic pathway regulating PM-incurred alteration of megakaryocytic maturation and thrombopoiesis was the mitochondrial oxidative phosphorylation (OXPHOS) process. Furthermore, airborne PM sample promoted-thrombopoiesis from megakaryocytes was related to particle size, but independent of sampling filters. Conclusion The findings for the first time unveil the potential perturbation of haze exposure in thrombopoiesis from megakaryocytes by regulating mitochondrial OXPHOS. The substantial evidence on haze particle-incurred hematotoxicity obtained herein provided new insights for assessing the hazardous health risks from PM pollution.

This research presents the first findings on thrombopoiesis for Wistar rats. Haemopoietic cells from the femur and the sternum were analysed by light microscopy in combination with infrared and near-ultraviolet light for fine cytoplasmic structure analysis. Five main types of thrombocyte precursor cells were identified in the bone marrow samples: megakaryoblast, promegakaryocyte and megakaryocyte (basophilic, acidophilic and thrombocytogenic). More intensive thrombopoiesis and morphologically differentiated cells were found in sternum samples.

The dynamics of platelet formation could only be investigated since the development of two-photon microscopy in combination with suitable fluorescent labeling strategies. In this review paper, we give an overview of recent advances in fluorescence imaging of the bone marrow that have contributed to our understanding of platelet biogenesis during the last decade. We make a brief survey through the perspectives and limitations of today’s intravital imaging, but also discuss complementary methods that may help to piece together the puzzle of megakaryopoiesis and platelet formation.

Many lung immune cells are known to respond to inhaled particulate matter. However, current known responses cannot explain how particles induce thrombosis in the lung and how they translocate to distant organs. Here, we demonstrate that lung megakaryocytes (MKs) in the alveolar and interstitial regions display location-determined characteristics and act as crucial responders to inhaled particles. They move rapidly to engulf particles and become activated with upregulation in inflammatory responses and thrombopoiesis. Comprehensive in vivo, in vitro and ex vivo results unraveled that MKs were involved in particle-induced lung damages and shed particle-containing platelets into blood circulation. Moreover, MK-derived platelets exhibited faster clotting, stronger adhesion than normal resting platelets, and inherited the engulfed particles from parent MKs to assist in extrapulmonary particle transportation. Our findings collectively highlight that the specific responses of MKs towards inhaled particles and their roles in facilitating the translocation of particles from the lungs to extrapulmonary organs for clearance., (© 2024. The Author(s).)

In contrast to most hematopoietic lineages, megakaryocytes (MKs) can derive rapidly and directly from hematopoietic stem cells (HSCs). The underlying mechanism is unclear, however. Here, we show that DNA damage induces MK markers in HSCs and that G2 arrest, an integral part of the DNA damage response, suffices for MK priming followed by irreversible MK differentiation in HSCs, but not in progenitors. We also show that replication stress causes DNA damage in HSCs and is at least in part due to uracil misincorporation in vitro and in vivo. Consistent with this notion, thymidine attenuated DNA damage, improved HSC maintenance, and reduced the generation of CD41 + MK-committed HSCs. Replication stress and concomitant MK differentiation is therefore one of the barriers to HSC maintenance. DNA damage-induced MK priming may allow rapid generation of a lineage essential to immediate organismal survival, while also removing damaged cells from the HSC pool., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Platelet homeostasis is essential for vascular integrity and immune defence 1,2 . Although the process of platelet formation by fragmenting megakaryocytes (MKs; thrombopoiesis) has been extensively studied, the cellular and molecular mechanisms required to constantly replenish the pool of MKs by their progenitor cells (megakaryopoiesis) remains unclear 3,4 . Here we use intravital imaging to track the cellular dynamics of megakaryopoiesis over days. We identify plasmacytoid dendritic cells (pDCs) as homeostatic sensors that monitor the bone marrow for apoptotic MKs and deliver IFNα to the MK niche triggering local on-demand proliferation and maturation of MK progenitors. This pDC-dependent feedback loop is crucial for MK and platelet homeostasis at steady state and under stress. pDCs are best known for their ability to function as vigilant detectors of viral infection 5 . We show that virus-induced activation of pDCs interferes with their function as homeostatic sensors of megakaryopoiesis. Consequently, activation of pDCs by SARS-CoV-2 leads to excessive megakaryopoiesis. Together, we identify a pDC-dependent homeostatic circuit that involves innate immune sensing and demand-adapted release of inflammatory mediators to maintain homeostasis of the megakaryocytic lineage., (© 2024. The Author(s).)

Rare multipotent stem cells replenish millions of blood cells per second through a time-consuming process, passing through multiple stages of increasingly lineage-restricted progenitors. Although insults to the blood-forming system highlight the need for more rapid blood replenishment from stem cells, established models of hematopoiesis implicate only one mandatory differentiation pathway for each blood cell lineage. Here, we establish a nonhierarchical relationship between distinct stem cells that replenish all blood cell lineages and stem cells that replenish almost exclusively platelets, a lineage essential for hemostasis and with important roles in both the innate and adaptive immune systems. These distinct stem cells use cellularly, molecularly and functionally separate pathways for the replenishment of molecularly distinct megakaryocyte-restricted progenitors: a slower steady-state multipotent pathway and a fast-track emergency-activated platelet-restricted pathway. These findings provide a framework for enhancing platelet replenishment in settings in which slow recovery of platelets remains a major clinical challenge., (© 2024. The Author(s).)

Thrombocytopenia is one of the most common complications of cancer therapy. Until now, there are still no satisfactory medications to treat chemotherapy and radiation-induced thrombocytopenia (CIT and RIT, respectively). Caulis Polygoni Multiflori (CPM), one of the most commonly used Chinese herbs, has been well documented to nourish blood for tranquilizing the mind and treating anemia, suggesting its beneficial effect on hematopoiesis. However, it is unknown whether CPM can accelerate megakaryopoiesis and thrombopoiesis. Here, we employ a UHPLC Q–Exactive HF-X mass spectrometer (UHPLC QE HF-X MS) to identify 11 ingredients in CPM. Then, in vitro experiments showed that CPM significantly increased megakaryocyte (MK) differentiation and maturation but did not affect apoptosis and lactate dehydrogenase (LDH) release of K562 and Meg-01 cells. More importantly, animal experiments verified that CPM treatment markedly accelerated platelet recovery, megakaryopoiesis and thrombopoiesis in RIT mice without hepatic and renal toxicities in vivo. Finally, RNA-sequencing (RNA-seq) and western blot were used to determine that CPM increased the expression of proteins related to PI3K/Akt and MEK/ERK (MAPK) signaling pathways. On the contrary, blocking PI3K/Akt and MEK/ERK signaling pathways with their specific inhibitors suppressed MK differentiation induced by CPM. In conclusion, for the first time, our study demonstrates that CPM may be a promised thrombopoietic agent and provide an experimental basis for expanding clinical use.

Objective: Immature platelet counts (IPC) may prove useful in guiding platelet transfusion management in preterm neonates. However, the relationship between IPCs and thrombopoietin (Tpo) concentrations has not been evaluated in preterm neonates.Methods: Prospective cohort study in thrombocytopenic (n = 31) and non-thrombocytopenic very low birth weight (VLBW) infants (n = 38), and healthy term neonates (controls; n = 41). Absolute platelet counts (APCs), IPCs, and Tpo concentrations were assessed by a fully-automated hematological analyzer (IPC, APC) and by ELISA (Tpo concentrations) in parallel on day 1 of life (d1), d3, and d7.Results: In healthy term neonates, APCs remained stable between d1 and d3. In non-thrombocytopenic VLBW infants, APCs increased from d1 to d7, while in the thrombocytopenia group, APCs declined from d1 to d3, before they slightly increased again by d7. Median IPCs were similar in healthy term vs. non-thrombocytopenic VLBW infants and remained stable between d1 and d3 (p > 0.05). Notably, IPCs significantly increased between d3 and d7 in both non-thrombocytopenic and thrombocytopenic VLBW infants. However, in thrombocytopenic VLBW infants, IPC values were significantly lower at each time point as compared to non-thrombocytopenic VLBWs (p < 0.001). In each subgroup, Tpo concentrations increased from d1 to d3. The median Tpo concentrations were significantly higher in thrombocytopenic as compared to non-thrombocytopenic VLBW infants at d3 (p = 0.01) and d7 (p = 0.002).Discussion: Term infants, thrombocytopenic, and non-thrombocytopenic preterm infants display similar developmental changes in indices of megakaryopoietic activity. In thrombocytopenic preterm infants, however, the responsive increases in Tpo and immature platelets appear to be developmentally limited.

Metabolic state of hematopoietic stem cells (HSCs) is an important regulator of self‐renewal and lineage‐specific differentiation. Posttranslational modification of proteins via O‐GlcNAcylation is an ideal metabolic sensor, but how it contributes to megakaryopoiesis and thrombopoiesis remains unknown. Here, we reveal for the first time that cellular O‐GlcNAcylation levels decline along the course of megakaryocyte (MK) differentiation from human‐derived hematopoietic stem and progenitor cells (HSPCs). Inhibition of O‐GlcNAc transferase (OGT) that catalyzes O‐GlcNAcylation prolongedly decreases O‐GlcNAcylation and induces the acquisition of CD34+CD41a+ MK‐like progenitors and its progeny CD34−CD41a+/CD42b+ megakaryoblasts (MBs)/MKs from HSPCs, consequently resulting in increased CD41a+ and CD42b+ platelets. Using correlation and co‐immunoprecipitation analyses, we further identify c‐Myc as a direct downstream target of O‐GlcNAcylation in MBs/MKs and provide compelling evidence on the regulation of platelets by novel O‐GlcNAc/c‐Myc axis. Our data indicate that O‐GlcNAcylation posttranslationally regulates c‐Myc stability by interfering with its ubiquitin‐mediated proteasomal degradation. Depletion of c‐Myc upon inhibition of OGT promotes platelet formation in part through the perturbation of cell adhesion molecules, that is, integrin‐α4 and integrin‐β7, as advised by gene ontology and enrichment analysis for RNA sequencing and validated herein. Together, our findings provide a novel basic knowledge on the regulatory role of O‐GlcNAcylation in megakaryopoiesis and thrombopoiesis that could be important in understanding hematologic disorders whose etiology are related to impaired platelet production and may have clinical applications toward an ex vivo platelet production for transfusion. [ABSTRACT FROM AUTHOR]

Abstract Patients suffering from acute or sustained thrombocytopenia require platelet transfusions, which are entirely donor‐based and limited by challenges related to storage and fluctuating supply. Developing cell‐culture technologies will enable ex vivo and donor‐independent platelet production. However, critical advancements are needed to improve scalability and increase megakaryocyte (Mk) culture productivity. To address these needs, we evaluated Mk production from mobilized peripheral blood CD34+ cells cultured on a commercially available gas‐permeable silicone rubber membrane, which provides efficient gas exchange, and investigated the use of fed‐batch media dilution schemes. Starting with a cell‐surface density of 40 × 103 CD34+ cells per cm2 (G40D), culturing cells on the membrane for the first 5 days and employing media dilutions yielded 39 ± 19 CD41+CD42b+ Mks per input CD34+ cell by day 11—a 2.2‐fold increase compared with using standard culture surfaces and full media exchanges. By day 7, G40D conditions generated 1.5‐fold more CD34+ cells and nearly doubled the numbers of Mk progenitors. The increased number of Mk progenitors coupled with media dilutions, potentially due to the retention of interleukin (IL)‐3, increased Mk production in G40D. Compared with controls, G40D had higher viability, yielded threefold more Mks per milliliter of media used and exhibited lower mean ploidy, but had higher numbers of high‐ploidy Mks. Finally, G40D‐Mks produced proplatelets and platelet‐like‐particles that activate and aggregate upon stimulation. These results highlight distinct improvements in Mk cell‐culture and demonstrate how new technologies and techniques are needed to enable clinically relevant production of Mks for platelet generation and cell‐based therapies.

Abstract Methods to deepen clinical responses to ibrutinib are needed to improve outcomes for patients with chronic lymphocytic leukemia (CLL). This study aimed to determine the safety and efficacy of combining a janus kinase (JAK)‐inhibitor with ibrutinib because JAK‐mediated cytokine‐signals support CLL cells and may not be inhibited by ibrutinib. The JAK1/2 inhibitor ruxolitinib was prescribed to 12 CLL patients with abnormal serum beta‐2 microglobulin levels after 6 months or persistent lymphadenopathy or splenomegaly after 12 months on ibrutinib using a 3 + 3 phase 1 trial design (NCT02912754). Ibrutinib was continued at 420 mg daily and ruxolitinib was added at 5, 10, 15, or 20 mg BID for 3 weeks out of five for seven cycles. The break was mandated to avoid anemia and thrombocytopenia observed with ruxolitinib as a single agent in CLL. The combination was well‐tolerated without dose‐limiting toxicities. Cyclic changes in platelets, lymphocytes, and associated chemokines and thrombopoietic factors were observed and partial response criteria were met in 2 of 12 patients. The results suggest that JAK‐signaling helps CLL cells persist in the presence of ibrutinib and ruxolitinib with ibrutinib is well‐tolerated and may be a useful regiment to use in combination therapies for CLL.

Introduction: Statins are pharmacological agents commonly used to lower serum cholesterol level. The aim of the experiment was to investigate the effect of the statin simvastatin on thrombopoiesis in the porcine model because it is the closest to the human one regarding physiological and genetic similarities.

Background: Although airborne fine particulate matter (PM) pollution has been demonstrated as an independent risk factor for pulmonary and cardiovascular diseases, their currently-available toxicological data is still far from sufficient to explain the cause-and-effect. Platelets can regulate a variety of physiological and pathological processes, and the epidemiological study has indicated a positive association between PM exposure and the increased number of circulative platelets. As one of the target organs for PM pollution, the lung has been found to be involved in the storage of platelet progenitor cells (i.e. megakaryocytes) and thrombopoiesis. Whether PM exposure influences thrombopoiesis or not is thus explored in the present study by investigating the differentiation of megakaryocytes upon PM treatment. Results: The results showed that PM exposure promoted the thrombopoiesis in an exposure concentration-dependent manner. PM exposure induced the megakaryocytic maturation and development by causing cell morphological changes, occurrence of DNA ploidy, and alteration in the expressions of biomarkers for platelet formation. The proteomics assay demonstrated that the main metabolic pathway regulating PM-incurred alteration of megakaryocytic maturation and thrombopoiesis was the mitochondrial oxidative phosphorylation (OXPHOS) process. Furthermore, airborne PM sample promoted-thrombopoiesis from megakaryocytes was related to particle size, but independent of sampling filters. Conclusion: The findings for the first time unveil the potential perturbation of haze exposure in thrombopoiesis from megakaryocytes by regulating mitochondrial OXPHOS. The substantial evidence on haze particle-incurred hematotoxicity obtained herein provided new insights for assessing the hazardous health risks from PM pollution. [ABSTRACT FROM AUTHOR]

The discovery of iPSCs has led to the ex vivo production of differentiated cells for regenerative medicine. In the case of transfusion products, the derivation of platelets from iPSCs is expected to complement our current blood-donor supplied transfusion system through donor-independent production with complete pathogen-free assurance. This derivation can also overcome alloimmune platelet transfusion refractoriness by resulting in autologous, HLA-homologous or HLA-deficient products. Several developments were necessary to produce a massive number of platelets required for a single transfusion. First, expandable megakaryocytes were established from iPSCs through transgene expression. Second, a turbulent-type bioreactor with improved platelet yield and quality was developed. Third, novel drugs that enabled efficient feeder cell-free conditions were developed. Fourth, the platelet-containing suspension was purified and resuspended in an appropriate buffer. Finally, the platelet product needed to be assured for competency and safety including non-tumorigenicity through in vitro and in vivo preclinical tests. Based on these advancements, a clinical trial has started. The generation of human iPSC-derived platelets could evolve transfusion medicine to the next stage and assure a ubiquitous, safe supply of platelet products. Further, considering the feasibility of gene manipulations in iPSCs, other platelet products may bring forth novel therapeutic measures. [ABSTRACT FROM AUTHOR]

This research presents the first findings on thrombopoiesis for Wistar rats. Haemopoietic cells from the femur and the sternum were analysed by light microscopy in combination with infrared and nearultraviolet light for fine cytoplasmic structure analysis. Five main types of thrombocyte precursor cells were identified in the bone marrow samples: megakaryoblast, promegakaryocyte and megakaryocyte (basophilic, acidophilic and thrombocytogenic). More intensive thrombopoiesis and morphologically differentiated cells were found in sternum samples. [ABSTRACT FROM AUTHOR]

Thrombopoietin, the primary regulator of blood platelet production, was postulated to exist in 1958, but was only proven to exist when the cDNA for the hormone was cloned in 1994. Since its initial cloning and characterization, the hormone has revealed many surprises. For example, instead of acting as the postulated differentiation factor for platelet precursors, megakaryocytes, it is the most potent stimulator of megakaryocyte progenitor expansion known. Moreover, it also stimulates the survival, and in combination with stem cell factor leads to the expansion of hematopoietic stem cells. All of these growth-promoting activities have resulted in its clinical use in patients with thrombocytopenia and aplastic anemia, although the clinical development of the native molecule illustrated that "it's not wise to mess with mother nature", as a highly engineered version of the native hormone led to autoantibody formation and severe thrombocytopenia. Finally, another unexpected finding was the role of the thrombopoietin receptor in stem cell biology, including the development of myeloproliferative neoplasms, an important disorder of hematopoietic stem cells. Overall, the past 30 years of clinical and basic research has yielded many important insights, which are reviewed in this paper.

Thrombocytopenia caused by long-term radiotherapy and chemotherapy exists in cancer treatment. Previous research demonstrates that 5-Hydroxtrayptamine (5-HT) and its receptors induce the formation of megakaryocytes (MKs) and platelets. However, the relationships between 5-HT1A receptor (5-HTR1A) and MKs is unclear so far. We screened and investigated the mechanism of vilazodone as a 5-HTR1A partial agonist in promoting MK differentiation and evaluated its therapeutic effect in thrombocytopenia. We employed a drug screening model based on machine learning (ML) to screen the megakaryocytopoiesis activity of Vilazodone (VLZ). The effects of VLZ on megakaryocytopoiesis were verified in HEL and Meg-01 cells. Tg (itga2b: eGFP) zebrafish was performed to analyze the alterations in thrombopoiesis. Moreover, we established a thrombocytopenia mice model to investigate how VLZ administration accelerates platelet recovery and function. We carried out network pharmacology, Western blot, and immunofluorescence to demonstrate the potential targets and pathway of VLZ. VLZ has been predicted to have a potential biological action. Meanwhile, VLZ administration promotes MK differentiation and thrombopoiesis in cells and zebrafish models. Progressive experiments showed that VLZ has a potential therapeutic effect on radiation-induced thrombocytopenia in vivo. The network pharmacology and associated mechanism study indicated that SRC and MAPK signaling are both involved in the processes of megakaryopoiesis facilitated by VLZ. Furthermore, the expression of 5-HTR1A during megakaryocyte differentiation is closely related to the activation of SRC and MAPK. Our findings demonstrated that the expression of 5-HTR1A on MK, VLZ could bind to the 5-HTR1A receptor and further regulate the SRC/MAPK signaling pathway to facilitate megakaryocyte differentiation and platelet production, which provides new insights into the alternative therapeutic options for thrombocytopenia., Competing Interests: LZ, CN, RL, XT, TY, MR, MH, RL, XZ, DQ, LW, FH, XX, YW, JL, YW, JW No competing interests declared, (© 2024, Zhou, Ni, Liao et al.)

A State of the Art lecture titled "Immune Attack on Megakaryocytes in ITP: The Role of Megakaryocyte Impairment" was presented at the International Society on Thrombosis and Haemostasis Congress in 2023. Immune thrombocytopenia (ITP) is an acquired autoimmune disorder caused by autoantibodies against platelet surface glycoproteins that provoke increased clearance of circulating platelets, leading to reduced platelet number. However, there is also evidence of a direct effect of antiplatelet autoantibodies on bone marrow megakaryocytes. Indeed, immunologic cells responsible for autoantibody production reside in the bone marrow; megakaryocytes progressively express during their maturation the same glycoproteins against which ITP autoantibodies are directed, and platelet autoantibodies have been detected in the bone marrow of patients with ITP. In vitro studies using ITP sera or monoclonal antibodies against platelet and megakaryocyte surface glycoproteins have shown an impairment of many steps of megakaryopoiesis and thrombopoiesis, such as megakaryocyte differentiation and maturation, migration from the osteoblastic to the vascular niche, adhesion to extracellular matrix proteins, and proplatelet formation, resulting in impaired and ectopic platelet production in the bone marrow and diminished platelet release in the bloodstream. Moreover, cytotoxic T cells may target bone marrow megakaryocytes, resulting in megakaryocyte destruction. Altogether, these findings suggest that antiplatelet autoantibodies and cellular immunity against bone marrow megakaryocytes may significantly contribute to thrombocytopenia in some patients with ITP. Finally, we summarize relevant new data on this topic presented during the 2023 International Society on Thrombosis and Haemostasis Congress. The complete unraveling of the mechanisms of immune attack-induced impairment of megakaryopoiesis and thrombopoiesis may open the way to new therapeutic approaches., (© 2024 The Author(s).)

Emerging evidence has revealed a direct differentiation route from hematopoietic stem cells to megakaryocytes (direct route), in addition to the classical differentiation route through a series of restricted hematopoietic progenitors (stepwise route). This raises the question of the importance of two alternative routes for megakaryopoiesis. Here, we developed fate-mapping systems to distinguish the two routes, comparing their quantitative and functional outputs. We found that megakaryocytes were produced through the two routes with comparable kinetics and quantity under homeostasis. Single-cell RNA sequencing of the fate-mapped megakaryocytes revealed that the direct and stepwise routes contributed to the niche-supporting and immune megakaryocytes, respectively, but contributed to the platelet-producing megakaryocytes together. Megakaryocytes derived from the two routes displayed different activities and were differentially regulated by chemotherapy and inflammation. Our work links differentiation route to the heterogeneity of megakaryocytes. Alternative differentiation routes result in variable combinations of functionally distinct megakaryocyte subpopulations poised for different physiological demands., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)