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Cell Sep 2023Thrombopoietin (THPO or TPO) is an essential cytokine for hematopoietic stem cell (HSC) maintenance and megakaryocyte differentiation. Here, we report the 3.4 Å...
Thrombopoietin (THPO or TPO) is an essential cytokine for hematopoietic stem cell (HSC) maintenance and megakaryocyte differentiation. Here, we report the 3.4 Å resolution cryoelectron microscopy structure of the extracellular TPO-TPO receptor (TpoR or MPL) signaling complex, revealing the basis for homodimeric MPL activation and providing a structural rationalization for genetic loss-of-function thrombocytopenia mutations. The structure guided the engineering of TPO variants (TPO) with a spectrum of signaling activities, from neutral antagonists to partial- and super-agonists. Partial agonist TPO decoupled JAK/STAT from ERK/AKT/CREB activation, driving a bias for megakaryopoiesis and platelet production without causing significant HSC expansion in mice and showing superior maintenance of human HSCs in vitro. These data demonstrate the functional uncoupling of the two primary roles of TPO, highlighting the potential utility of TPO in hematology research and clinical HSC transplantation.
Topics: Animals; Humans; Mice; Cell Cycle; Cryoelectron Microscopy; Receptors, Thrombopoietin; Thrombopoiesis; Thrombopoietin; DNA Methylation
PubMed: 37633268
DOI: 10.1016/j.cell.2023.07.037 -
Arteriosclerosis, Thrombosis, and... Nov 2023Megakaryocytes are commonly known as large, polyploid, bone marrow resident cells that contribute to hemostasis through the production of platelets. Soon after their... (Review)
Review
Megakaryocytes are commonly known as large, polyploid, bone marrow resident cells that contribute to hemostasis through the production of platelets. Soon after their discovery in the 19th century, megakaryocytes were described in tissue locations other than the bone marrow, specifically in the lungs and the blood circulation. However, the localization of megakaryocytes in the lungs and the contribution of lung megakaryocytes to the general platelet pool has only recently been appreciated. Moreover, the conception of megakaryocytes as uniform cells with the sole purpose of platelet production has been challenged. Here, we review the literature on megakaryocyte cell identity and location with a special focus on recent observations of megakaryocyte subpopulations identified by transcriptomic analyses.
Topics: Megakaryocytes; Blood Platelets; Bone Marrow; Bone Marrow Cells; Thrombopoiesis
PubMed: 37675634
DOI: 10.1161/ATVBAHA.123.318782 -
Journal of Hematology & Oncology Jul 2023Hyperhomocysteinemia (HHcy) is closely associated with thrombotic diseases such as myocardial infarction and stroke. Enhanced platelet activation was observed in animals...
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 × 10/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.
Topics: Humans; Mice; Animals; Thrombopoiesis; Megakaryocytes; Blood Platelets; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Zebrafish; Growth Hormone; Melatonin; Hyperhomocysteinemia; Cell Differentiation
PubMed: 37501059
DOI: 10.1186/s13045-023-01481-x -
Blood Jan 2024Megakaryocytes (MKs) generate thousands of platelets over their lifespan. The roles of platelets in infection and inflammation has guided an interest to the study of...
Megakaryocytes (MKs) generate thousands of platelets over their lifespan. The roles of platelets in infection and inflammation has guided an interest to the study of extramedullary thrombopoiesis and therefore MKs have been increasingly reported within the spleen and lung. However, the relative abundance of MKs in these organs compared to the bone marrow and the scale of their contribution to the platelet pool in a steady state remain controversial. We investigated the relative abundance of MKs in the adult murine bone marrow, spleen, and lung using whole-mount light-sheet and quantitative histological imaging, flow cytometry, intravital imaging, and an assessment of single-cell RNA sequencing (scRNA-seq) repositories. Flow cytometry revealed significantly higher numbers of hematopoietic stem and progenitor cells and MKs in the murine bone marrow than in spleens or perfused lungs. Two-photon intravital and light-sheet microscopy, as well as quantitative histological imaging, confirmed these findings. Moreover, ex vivo cultured MKs from the bone marrow subjected to static or microfluidic platelet production assays had a higher capacity for proplatelet formation than MKs from other organs. Analysis of previously published murine and human scRNA-seq data sets revealed that only a marginal fraction of MK-like cells can be found within the lung and most likely only marginally contribute to platelet production in the steady state.
Topics: Mice; Humans; Animals; Bone Marrow; Thrombopoiesis; Blood Platelets; Megakaryocytes; Spleen
PubMed: 37879046
DOI: 10.1182/blood.2023020895 -
Thrombosis Research Nov 2023Autophagy, the continuous recycling of intracellular building blocks, molecules, and organelles is necessary to preserve cellular function and homeostasis. In this... (Review)
Review
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.
Topics: Humans; Blood Platelets; Megakaryocytes; Thrombopoiesis; Thrombosis; Autophagy; Biology
PubMed: 36058760
DOI: 10.1016/j.thromres.2022.08.019 -
Platelets Dec 2023Inherited thrombocytopenia (IT) is a group of hereditary disorders characterized by a reduced platelet count as the main clinical manifestation, and often with abnormal... (Review)
Review
Inherited thrombocytopenia (IT) is a group of hereditary disorders characterized by a reduced platelet count as the main clinical manifestation, and often with abnormal platelet function, which can subsequently lead to impaired hemostasis. In the past decades, humanized mouse models (HMMs), that are mice engrafted with human cells or genes, have been widely used in different research areas including immunology, oncology, and virology. With advances of the development of immunodeficient mice, the engraftment, and reconstitution of functional human platelets in HMM permit studies of occurrence and development of platelet disorders including IT and treatment strategies. This article mainly reviews the development of humanized mice models, the construction methods, research status, and problems of using humanized mice for the study of human thrombopoiesis.
Topics: Animals; Mice; Humans; Disease Models, Animal; Blood Platelets; Thrombopoiesis; Thrombocytopenia; Blood Platelet Disorders; Hematopoietic Stem Cell Transplantation
PubMed: 37849076
DOI: 10.1080/09537104.2023.2267676 -
Nature Communications Jul 2023Platelets, small hemostatic blood cells, are derived from megakaryocytes. Both bone marrow and lung are principal sites of thrombopoiesis although underlying mechanisms...
Platelets, small hemostatic blood cells, are derived from megakaryocytes. Both bone marrow and lung are principal sites of thrombopoiesis although underlying mechanisms remain unclear. Outside the body, however, our ability to generate large number of functional platelets is poor. Here we show that perfusion of megakaryocytes ex vivo through the mouse lung vasculature generates substantial platelet numbers, up to 3000 per megakaryocyte. Despite their large size, megakaryocytes are able repeatedly to passage through the lung vasculature, leading to enucleation and subsequent platelet generation intravascularly. Using ex vivo lung and an in vitro microfluidic chamber we determine how oxygenation, ventilation, healthy pulmonary endothelium and the microvascular structure support thrombopoiesis. We also show a critical role for the actin regulator Tropomyosin 4 in the final steps of platelet formation in lung vasculature. This work reveals the mechanisms of thrombopoiesis in lung vasculature and informs approaches to large-scale generation of platelets.
Topics: Mice; Animals; Blood Platelets; Microfluidics; Megakaryocytes; Thrombopoiesis; Lung
PubMed: 37419900
DOI: 10.1038/s41467-023-39598-9 -
Journal of Thrombosis and Haemostasis :... Nov 2023Megakaryocyte differentiation and platelet production disorders are the main causes of thrombocythemia and thrombocytopenia and lead to thrombosis or hemorrhage....
BACKGROUND
Megakaryocyte differentiation and platelet production disorders are the main causes of thrombocythemia and thrombocytopenia and lead to thrombosis or hemorrhage. Branched-chain amino acids (BCAAs) are essential nutrients that regulate important metabolic signals. BCAA administration could also increase platelet activation and promote the risk of thrombosis.
OBJECTIVES
To unveil the role of BCAAs in thrombocytopoiesis.
METHODS
BCAA-fed mice and megakaryocyte/platelet-specific branched-chain α-keto acid dehydrogenase E1α subunit-deficient mice were used to study the role of BCAAs in thrombocytopoiesis.
RESULTS
In this study, we found that BCAA diet could facilitate megakaryocyte differentiation and platelet production. Meanwhile, megakaryocyte/platelet-specific branched-chain α-keto acid dehydrogenase E1α subunit-deficient mice developed thrombocythemia, which was mainly caused by the excessive differentiation of megakaryocytes and proplatelet biogenesis. Moreover, the use of BT2, the agonist of BCAA catabolism, could affect proplatelet formation (PPF) and megakaryocyte polyploidization, as well as ameliorating the thrombocythemia of BCAA-fed mice.
CONCLUSION
We found that deficiency in BCAA catabolism led to the activation of p70S6K/mammalian target of rapamycin (mTOR) signaling, megakaryocyte over differentiation, and the acceleration of PPF. Activating BCAA metabolism with BT2 could inhibit mTOR signaling, reduce PPF, and ameliorate thrombocythemia in BCAA-fed mice. Therefore, this study reveals a novel role of BCAAs in megakaryocyte differentiation and platelet production, suggesting that targeting BCAA-mediated p70S6K/mTOR signaling may be a potential strategy for the treatment of thrombocytopenia or thrombocythemia.
Topics: Mice; Animals; Amino Acids, Branched-Chain; Ribosomal Protein S6 Kinases, 70-kDa; Thrombopoiesis; 3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); TOR Serine-Threonine Kinases; Thrombocytosis; Thrombocytopenia; Thrombosis; Mammals
PubMed: 37473846
DOI: 10.1016/j.jtha.2023.06.039 -
International Journal of Biological... 2023Abnormal megakaryocyte maturation and platelet production lead to platelet-related diseases and impact the dynamic balance between hemostasis and bleeding. Cellular...
Abnormal megakaryocyte maturation and platelet production lead to platelet-related diseases and impact the dynamic balance between hemostasis and bleeding. Cellular repressor of E1A-stimulated gene 1 (CREG1) is a glycoprotein that promotes tissue differentiation. However, its role in megakaryocytes remains unclear. In this study, we found that CREG1 protein is expressed in platelets and megakaryocytes and was decreased in the platelets of patients with thrombocytopenia. A cytosine arabinoside-induced thrombocytopenia mouse model was established, and the mRNA and protein expression levels of CREG1 were found to be reduced in megakaryocytes. We established megakaryocyte/platelet conditional knockout () and transgenic mice (tg-). Compared to mice, mice exhibited thrombocytopenia, which was mainly caused by inefficient bone marrow (BM) thrombocytopoiesis, but not by apoptosis of circulating platelets. Cultured -megakaryocytes exhibited impairment of the actin cytoskeleton, with less filamentous actin, significantly fewer proplatelets, and lower ploidy. CREG1 directly interacts with MEK1/2 and promotes MEK1/2 phosphorylation. Thus, our study uncovered the role of CREG1 in the regulation of megakaryocyte maturation and thrombopoiesis, and it provides a possible theoretical basis for the prevention and treatment of thrombocytopenia.
Topics: Animals; Mice; Blood Platelets; Bone Marrow; Megakaryocytes; Mice, Transgenic; Thrombocytopenia; Thrombopoiesis; Humans
PubMed: 37496998
DOI: 10.7150/ijbs.78660