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BioRxiv : the Preprint Server For... Jun 2024Many aspects of thrombopoiesis, the release of platelets from megakaryocytes (Mks), remain under debate, including where this process occurs. Murine lung -microscopy...
UNLABELLED
Many aspects of thrombopoiesis, the release of platelets from megakaryocytes (Mks), remain under debate, including where this process occurs. Murine lung -microscopy studies suggested that a significant fraction of circulating platelets were released from lung-entrapped, marrow-derived Mks. We now confirm these studies that endogenous mMks are entrapped in the lungs and show that intravenously infused -differentiated, mature murine (m) and human (h) Mks are similarly entrapped followed by shedding of their cytoplasm over ∼30 minutes with a peak number of released platelets occurring 1.5-4 hours later. However, while infused Mks from both species shed large intrapulmonary cytoplasmic fragments that underwent further processing into platelet-sized fragments, the two differed: many mMks escaped from and then recycled back to the lungs, while most hMks were enucleated upon first intrapulmonary passage. Infused immature hMks, inflammatory hMks, umbilical cord-blood-derived hMks and immortalized Mk progenitor cell (imMKCL)-derived hMks were also entrapped in the lung of recipient mice, and released their cytoplasm, but did so to different degrees. Intraarterial infused hMks resulted in few Mks being entrapped in tissues other than the lungs and was accompanied by a blunted and delayed rise in circulating human platelets. These studies demonstrate that the lung entraps and processes both circulating Mks and released large cytoplasmic fragments consistent with a recent lung/heart murine study and support a pulmonary-centric "catch-and-release" model of thrombopoiesis. Thus, thrombopoiesis is a drawn-out process with the majority of cytoplasmic processing derived from Mks occurring in the pulmonary bed.
KEY POINTS
Infused -differentiated megakaryocytes synchronously release cytoplasmic fragments highly selectively in the pulmonary bed. Large, released megakaryocyte fragments recycle to the lungs, undergo further fission, terminally form platelets.
PubMed: 38895231
DOI: 10.1101/2024.06.04.597316 -
Nature Immunology Jun 2024Rare multipotent stem cells replenish millions of blood cells per second through a time-consuming process, passing through multiple stages of increasingly...
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.
Topics: Blood Platelets; Animals; Hematopoietic Stem Cells; Mice; Cell Differentiation; Megakaryocytes; Cell Lineage; Mice, Inbred C57BL; Hematopoiesis; Thrombopoiesis; Mice, Knockout; Humans; Multipotent Stem Cells
PubMed: 38816617
DOI: 10.1038/s41590-024-01845-6 -
ELife May 2024Erythropoiesis and megakaryopoiesis are stringently regulated by signaling pathways. However, the precise molecular mechanisms through which signaling pathways regulate...
Erythropoiesis and megakaryopoiesis are stringently regulated by signaling pathways. However, the precise molecular mechanisms through which signaling pathways regulate key transcription factors controlling erythropoiesis and megakaryopoiesis remain partially understood. Herein, we identified heat shock cognate B (HSCB), which is well known for its iron-sulfur cluster delivery function, as an indispensable protein for friend of GATA 1 (FOG1) nuclear translocation during erythropoiesis of K562 human erythroleukemia cells and cord-blood-derived human CD34+CD90+hematopoietic stem cells (HSCs), as well as during megakaryopoiesis of the CD34+CD90+HSCs. Mechanistically, HSCB could be phosphorylated by phosphoinositol-3-kinase (PI3K) to bind with and mediate the proteasomal degradation of transforming acidic coiled-coil containing protein 3 (TACC3), which otherwise detained FOG1 in the cytoplasm, thereby facilitating FOG1 nuclear translocation. Given that PI3K is activated during both erythropoiesis and megakaryopoiesis, and that FOG1 is a key transcription factor for these processes, our findings elucidate an important, previously unrecognized iron-sulfur cluster delivery independent function of HSCB in erythropoiesis and megakaryopoiesis.
Topics: Erythropoiesis; Humans; Transcription Factors; Phosphatidylinositol 3-Kinases; K562 Cells; Thrombopoiesis; Signal Transduction; Nuclear Proteins; Cell Nucleus; Protein Transport; Hematopoietic Stem Cells; HSC70 Heat-Shock Proteins; Active Transport, Cell Nucleus
PubMed: 38757931
DOI: 10.7554/eLife.95815 -
BioRxiv : the Preprint Server For... Apr 2024Disease-causing missense mutations that occur within structurally and functionally unannotated protein regions can guide researchers to new mechanisms of protein...
Disease-causing missense mutations that occur within structurally and functionally unannotated protein regions can guide researchers to new mechanisms of protein regulation and dysfunction. Here, we report that the thrombocytopenia-, myelodysplastic syndromes-, and leukemia-associated P214L mutation in the transcriptional regulator ETV6 creates an XPO1-dependent nuclear export signal to cause protein mislocalization. Strategies to disrupt XPO1 activity fully restore ETV6 P214L protein nuclear localization and transcription regulation activity. Mechanistic insight inspired the design of a 'humanized' ETV6 mice, which we employ to demonstrate that the germline P214L mutation is sufficient to elicit severe defects in thrombopoiesis and hematopoietic stem cell maintenance. Beyond ETV6, we employed computational methods to uncover rare disease-associated missense mutations in unrelated proteins that create a nuclear export signal to disrupt protein function. Thus, missense mutations that operate through this mechanism should be predictable and may suggest rational therapeutic strategies for associated diseases.
PubMed: 38712034
DOI: 10.1101/2024.04.24.590854 -
Biomolecules Apr 2024Thrombopoietin, 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... (Review)
Review
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.
Topics: Thrombopoietin; Humans; Blood Platelets; Animals; Receptors, Thrombopoietin; Thrombopoiesis; Thrombocytopenia; Megakaryocytes
PubMed: 38672505
DOI: 10.3390/biom14040489 -
Cells Apr 2024Platelets are the terminal progeny of megakaryocytes, primarily produced in the bone marrow, and play critical roles in blood homeostasis, clotting, and wound healing.... (Review)
Review
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.
Topics: Animals; Mice; Blood Platelets; Cell Differentiation; Cell Lineage; Hematopoiesis; Hematopoietic Stem Cells; Megakaryocytes; Humans
PubMed: 38667319
DOI: 10.3390/cells13080704 -
Journal of Veterinary Internal Medicine 2024The 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)...
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.
Topics: Animals; Dogs; Cats; Dog Diseases; Thrombocytopenia; Cat Diseases; Retrospective Studies; Female; Male; Diagnosis, Differential; Platelet Count; Blood Platelets; Reference Values
PubMed: 38619127
DOI: 10.1111/jvim.17074 -
International Journal of Biological... 2024Thrombocytopenia, a prevalent hematologic challenge, correlates directly with the mortality of numerous ailments. Current therapeutic avenues for thrombocytopenia are...
Thrombocytopenia, a prevalent hematologic challenge, correlates directly with the mortality of numerous ailments. Current therapeutic avenues for thrombocytopenia are not without limitations. Here, we identify genistin, an estrogen analogue, as a promising candidate for thrombocytopenia intervention, discovered through AI-driven compound library screening. While estrogen's involvement in diverse biological processes is recognized, its role in thrombopoiesis remains underexplored. Our findings elucidate genistin's ability to enhance megakaryocyte differentiation, thereby augmenting platelet formation and production. assessments further underscore genistin's remedial potential against radiation-induced thrombocytopenia. Mechanistically, genistin's efficacy is attributed to its direct interaction with estrogen receptor β (ERβ), with subsequent activation of both ERK1/2 and the Akt signaling pathways membrane ERβ. Collectively, our study positions genistin as a prospective therapeutic strategy for thrombocytopenia, shedding light on novel interplays between platelet production and ERβ.
Topics: Humans; Estrogen Receptor beta; Isoflavones; Thrombocytopenia; Small Molecule Libraries
PubMed: 38617546
DOI: 10.7150/ijbs.90483 -
ELife Apr 2024Thrombocytopenia caused by long-term radiotherapy and chemotherapy exists in cancer treatment. Previous research demonstrates that 5-Hydroxtrayptamine (5-HT) and its...
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.
Topics: Mice; Animals; Vilazodone Hydrochloride; Zebrafish; Receptor, Serotonin, 5-HT1A; Blood Platelets; Thrombocytopenia; Megakaryocytes; Thrombopoiesis
PubMed: 38573820
DOI: 10.7554/eLife.94765