MEG-01 Cells Research Articles

Compound K Promotes Megakaryocytic Differentiation by NLRP3 Inflammasome Activation.

Platelets are essential blood components that maintain hemostasis, prevent excessive bleeding, and facilitate wound healing. Reduced platelet counts are implicated in various diseases, including leukemia, hepatitis, cancer, and Alzheimer's disease. Enhancing megakaryocytic differentiation is a promising strategy to increase platelet production. Compound K (CK), a major bioactive metabolite of ginsenosides from Panax ginseng, has demonstrated anti-cancer and neuroprotective properties. In this study, we investigated the effects of CK on megakaryocytic differentiation and apoptosis in chronic myeloid leukemia (CML) cell lines K562 and Meg-01. CK treatment significantly upregulated the mRNA expression of key megakaryocytic differentiation markers, including CD61, CD41, and CD42a, and promoted the formation of large, multinucleated cells in K562 cells. Additionally, flow cytometry analysis revealed that CK at 5 µM induced apoptosis, a critical process in thrombocytopoiesis, in both K562 and Meg-01 cells. RT2 Profiler PCR array analysis further identified a marked increase in the expression of genes associated with the activation of the NLRP3 inflammasome in CK-treated K562 and Meg-01 cells. This study is the first to demonstrate that CK promotes megakaryocytic differentiation and apoptosis through the activation of the ERK/EGR1 and NLRP3 inflammasome pathways. These findings suggest that CK may enhance platelet production, indicating its potential as a therapeutic candidate for platelet-related disorders and other associated diseases.

Elevated levels of pro-thrombotic eNOS-negative platelets in COVID-19 patients

BackgroundPlatelet-rich microvascular thrombi are common in severe COVID-19. Endogenous nitric oxide (NO)-signaling limits thrombus formation and previously we identified platelet subpopulations with a differential ability to produce NO based on the presence or absence of endothelial nitric oxide synthase (eNOS). eNOS expression is counter-regulated by cytokines, and COVID-19-associated immune/inflammatory responses may affect the transcriptome profile of megakaryocytes and their platelet progeny. ObjectivesWe investigated whether the percentage of eNOS-negative to eNOS-positive platelets increases in COVID-19 patients and whether this change may be due to the actions of pro-inflammatory cytokines on megakaryocytes. MethodsPlatelets were isolated from hospitalized COVID-19 patients and COVID-19-negative controls. Platelet eNOS was measured by flow cytometry and plasma inflammatory cytokines by ELISA. Megakaryocytes from eNOS-GFP transgenic mice and the Meg-01 cell line were characterized to identify an appropriate model to study eNOS-based platelet subpopulation formation in response to inflammatory cytokines. ResultsCOVID-19 patients demonstrated a significant increase in eNOS-negative and a concomitant decrease in eNOS-positive platelets compared to controls, and this change was associated with disease severity as assessed by ICU admission. A higher eNOS-negative to –positive platelet percentage was associated with enhanced platelet activation as measured by surface CD62P. Accordingly, COVID-19 patients demonstrated higher TNF-α, IL-6, and IL-1β plasma concentrations than controls. Inflammatory cytokines associated with COVID-19 promoted eNOS-negative Meg-01 formation and enhanced subsequent eNOS-negative platelet-like particle formation. ConclusionsCOVID-19 patients have a higher percentage of eNOS-negative to –positive platelets, likely as a result of inflammatory response reducing megakaryocyte eNOS expression, which predisposes to thrombosis.

HIV-1 inhibits IFITM3 expression to promote the infection of megakaryocytes.

Despite an undetectable plasma viral load as a result of antiretroviral therapy, HIV-1-infected individuals with poor immune reconstitution harbor infectious HIV-1 within their platelets. Megakaryocytes, as platelet precursors, are the likely cellular origin of these HIV-1-containing platelets. To investigate the mechanisms that allow megakaryocytes to support HIV-1 infection, we established in vitro models of viral infection using hematopoietic stem cell-derived megakaryocytes and the megakaryocytic MEG-01 cell line. We observed HIV-1 DNA provirus integration into the megakaryocyte cell genome, self-limiting virus production, and HIV-1 protein and RNA compartmentalization, which are hallmarks of HIV-1 infection in myeloid cells. In addition, following HIV-1 infection of megakaryocyte precursors, the expression of interferon-induced transmembrane protein 3 (IFITM3), an antiviral factor constitutively expressed in megakaryocytes, was inhibited in terminally differentiated HIV-1-infected megakaryocytes. IFITM3 knockdown in MEG-01 cells prior to infection led to enhanced HIV-1 infection, indicating that IFITM3 acts as an HIV-1 restriction factor in megakaryocytes. Together, these findings indicate that megakaryocyte precursors are susceptible to HIV-1 infection, leading to terminally differentiated megakaryocytes harboring virus in a process regulated by IFITM3. Megakaryocytes may thus constitute a neglected HIV-1 reservoir that warrants further study in order to develop improved antiretroviral therapies and to facilitate HIV-1 eradication.

Harmine promotes megakaryocyte differentiation and thrombopoiesis by activating the Rac1/Cdc42/JNK pathway through a potential target of 5-HTR2A.

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.

Oxymatrine, a novel TLR2 agonist, promotes megakaryopoiesis and thrombopoiesis through the STING/NF-ĸB pathway

Radiation-induced thrombocytopenia (RIT) faces a perplexing challenge in the clinical treatment of cancer patients, and current therapeutic approaches are inadequate in the clinical settings. In this researsh, oxymatrine, a new molecule capable of healing RIT was screened out, and the underlying regulatory mechanism associated with magakaryocyte (MK) differentiation and thrombopoiesis was demonstrated. The capacity of oxymatrine to induce MK differentiation was verified in K-562 and Meg-01 cells in vitro. The ability to induce thrombopoiesis was subsequently demonstrated in Tg (cd41:eGFP) zebrafish and RIT model mice. In addition, we carried out network pharmacological prediction, drug affinity responsive target stability assay (DARTS) and cellular thermal shift assay (CETSA) analyses to explore the potential targets of oxymatrine. Moreover, the pathway underlying the effects of oxymatrine was determined by Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, Western blot, and immunofluorescence. Oxymatrine markedly promoted MK differentiation and maturation in vitro. Moreover, oxymatrine induced thrombopoiesis in Tg (cd41:eGFP) zebrafish and accelerated thrombopoiesis and platelet function recovery in RIT model mice. Mechanistically, oxymatrine directly binds to toll-like receptor 2 (TLR2) and further regulates the downstream pathway stimulator of interferon genes (STING)/nuclear factor-kappaB (NF-κB), which can be blocked by C29 and C-176, which are specific inhibitors of TLR2 and STING, respectively. Taken together, we demonstrated that oxymatrine , a novel TLR2 agonist, plays a critical role in accelerating MK differentiation and thrombopoiesis via the STING/NF-κB axis, suggesting that oxymatrine is a promising candidate for RIT therapy.

The Expression of Cell Cycle Cyclins in a Human Megakaryoblast Cell Line Exposed to Simulated Microgravity.

The study of the physiological and pathophysiological processes under extreme conditions facilitates a better understanding of the state of a healthy organism and can also shed light on the pathogenesis of diseases. In recent years, it has become evident that gravitational stress affects both the whole organism and individual cells. We have previously demonstrated that simulated microgravity inhibits proliferation, induces apoptosis, changes morphology, and alters the surface marker expression of megakaryoblast cell line MEG-01. In the present work, we investigate the expression of cell cycle cyclins in MEG-01 cells. We performed several experiments for 24 h, 72 h, 96 h and 168 h. Flow cytometry and Western blot analysis demonstrated that the main change in the levels of cyclins expression occurs under conditions of simulated microgravity after 96 h. Thus, the level of cyclin A expression showed an increase in the RPM group during the first 4 days, followed by a decrease, which, together with the peak of cyclin D, may indicate inhibition of the cell cycle in the G2 phase, before mitosis. In addition, based on the data obtained by PCR analysis, we were also able to see that both cyclin A and cyclin B expression showed a peak at 72 h, followed by a gradual decrease at 96 h. STED microscopy data also confirmed that the main change in cyclin expression of MEG-01 cells occurs at 96 h, under simulated microgravity conditions, compared to static control. These results suggested that the cell cycle disruption induced by RPM-simulated microgravity in MEG-01 cells may be associated with the altered expression of the main regulators of the cell cycle. Thus, these data implicate the development of cellular stress in MEG-01 cells, which may be important for proliferating human cells exposed to microgravity in real space.

Abstract 138: Platelet RIPK1 Promotes Platelet Activation And Aggregation In Arteriolar Thrombosis And Ischemic Stroke

Receptor-interacting protein Ser/Thr kinase 1 (RIPK1) is a molecular switch for inflammation and cell death in nucleated cells, and its function is controlled by phosphorylation at the Ser166 residue. However, it is unknown whether RIPK1 regulates platelet function in arterial thrombosis. Intravital microscopy using megakaryocyte-specific Ripk1 conditional knockout (CKO) mice ( Ripk1 fl/fl;Pf4-cre ) revealed that platelet Ripk1 promoted platelet thrombus formation at sites of laser-induced cremaster arteriolar thrombosis. Deletion of platelet Ripk1 prolonged the time to occlusion in FeCl 3 -induced carotid arterial thrombosis without affecting tail bleeding times. Further, compared to wild-type (WT) mice, Ripk1 CKO mice exhibited improved neurological deficits and reduced infarct volume in ischemic stroke induced by transient middle cerebral artery occlusion. Flow cytometry and aggregation assays showed that deletion of platelet Ripk1 reduced P-selectin exposure, αIIbβ3 integrin activation, and platelet aggregation induced by thrombin, collagen-related peptides (CRP), and U46619, but not ADP. Pretreatment of Ripk1-null platelets with ADP rescued the aggregation defect. Treatment of platelets with Nec-1s, a RIPK1 inhibitor that blocks RIPK1-Ser166 phosphorylation, did not affect platelet activation and aggregation. Instead, RIPK1-Ser320/321 was rapidly phosphorylated in thrombin- or CRP-stimulated human and mouse platelets. Treatment of platelets with an inhibitor of phospholipase C, p38, or MAPK-activated protein kinase 2 (MK2), but not a protein kinase C inhibitor, decreased RIPK1-Ser320/321 phosphorylation after thrombin or CRP stimulation, implying that the p38-MK2 axis phosphorylates RIPK1-Ser320/321. Using a genetic approach in human megakaryoblastic MEG-01 cells, we found that RIPK1 knockdown reduced granule secretion from stimulated MEG-01 cells, which was rescued by overexpressing WT RIPK1, but not mutant RIPK1-Ser320Ala, in the RIPK1 knockdown MEG-01 cells. These results suggest that platelet RIPK1 enhances granule secretion during platelet activation through p38-MK2-mediated phosphorylation of RIPK1-Ser320/321, thereby contributing to the pathology of thrombotic disease.

Clusterin can mediate apoptosis-induced molecular mechanisms in immune thrombocytopenia

AbstractAbnormalities in the apoptosis pathway have been implicated into the pathogenesis of various autoimmune diseases, including immune thrombocytopenia (ITP). Our data suggest that mechanisms associated with impaired clusterin-mediated apoptosis might play a role in the pathophysiology of ITP platelets and their production by MKs. Platelet-rich plasma from 10 patients with ITP compared with healthy controls was used for the apoptosis proteomic profiling and clusterin (CLU) expression validation by reverse transcription polymerase chain reaction. We used the megakaryoblastic (MEG-01) cell line, treated for 2 hours with plasma from patients with newly diagnosed ND), chronic ITP or healthy controls and pan-caspase inhibitor (Z-VAD-FMK), apoptosis inducer ABT-737, rotenone (Rot), or rapamycin (Rap). Our apoptosis proteomic profiling revealed significantly increased expression levels of certain apoptotic genes such as CLU, phospho-p53 (S46), procaspase-3, and cleaved caspase 3 (CASP-3) in patients with ITP compared with healthy controls. Treatment with pan-caspase inhibitor or Rap had a significant downregulatory effect at messenger RNA (mRNA) level for CLU; CASP-3, -8, and -9; p53; and B-cell lymphoma-2–associated X protein (BAX) in ITP plasma–treated cells in comparison with control plasma–treated MEG-01 cells, whereas Rot or ABT-737 had opposite effects. We observed a significant downregulation of mRNA expression levels of these apoptotic markers in ITP plasma–treated and CLU or glucose-regulated protein 78 small interfering RNA–transfected MEG-01 cells. Our results indicate an upregulation of CLU and BAX in platelets and MKs which may contribute to deciphering the cause of platelet destruction in ITP disease.

Activating SRC/MAPK signaling via 5-HT1A receptor contributes to the effect of vilazodone on improving thrombocytopenia.

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.

Activating SRC/MAPK signaling via 5-HT1A receptor contributes to the effect of vilazodone on improving thrombocytopenia

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.

Polyamine release and vesicular polyamine transporter expression in megakaryoblastic cells and platelets

Polyamines not only play essential roles in cell growth and function of living organisms but are also released into the extracellular space and function as regulators of chemical transduction, although the cells from which they are released and their mode of release are not well understood. The vesicular polyamine transporter (VPAT), encoded by the SLC18B1 is responsible for the vesicular storage of spermine and spermidine, followed by their vesicular release from secretory cells. Focusing on VPAT will help identify polyamine-secreting cells and new polyamine functions. In this study, we investigated the possible involvement of VPAT in vesicular release of polyamines in MEG-01 clonal megakaryoblastic cells and platelets. RT-PCR, western blotting, and immunohistochemistry revealed VPAT expression in MEG-01 cells. MEG-01 cells secreted polyamines upon A23187 stimulation in the presence of Ca2+, which is temperature-dependent and sensitive to bafilomycin A1. A23187-induced polyamine secretion from MEG-01 cells was reduced by treatment with reserpine, VPAT inhibitors, or VPAT RNA interference. Platelets also expressed VPAT, displaying a punctate distribution, and released spermidine upon A23187 and thrombin stimulation. These findings have demonstrated VPAT-mediated vesicular polyamine release from MEG-01 cells, suggesting the presence of similar vesicular polyamine release mechanisms in platelets.

Abstract 1381: Characterization of the 12-lipoxygenase expression in the megakaryoblastic cell line, Dami

Abstract Megakaryocytes are myeloid cells produced primarily in the bone marrow and are best known for releasing platelets in the blood stream. In the platelet production process, megakaryocytes transfer their bioactive content, including the 12-lipoxygenase (12-LO) enzyme, into newly formed platelets. The 12-LO has been shown to be implicated in platelet activation and is overexpressed in several chronic inflammatory conditions, including several types of cancers. The 12-LO is responsible for the conversion of the arachidonic acid into the 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), a key lipid mediator implicated in several steps of the metastatic cascade. While 12-LO is expressed in mature human megakaryocytes, we recently identified two megakaryoblast cell lines isolated from leukemia patients lacking 12-LO expression. However, only one of the two cell lines expresses functional 12-LO protein upon megakaryocyte maturation. The goal of this study is to characterize the 12-LO expression during the megakaryocyte maturation process. We hypothesize that 12-LO expression is increased during cell maturation and that inhibition of the 12-LO expression will result in dysfunctional platelets. Both the Dami cell and MEG-01 cells were induced with the co-incubation of both phorbol myristate acetate and eltrombopag, a thrombopoietin receptor agonist. The maturation and viability of the cells were confirmed by flow cytometry. Expression of the 12-LO was assessed by RT-qPCR and immunoblot. Quantification of the 12(S)-HETE was performed by reversed-phase high performance liquid chromatography. Platelet release was quantified by flow cytometry using CD41 fluorescent labelled antibodies. We observed a 3-fold increase in 12-LO protein expression following cell maturation in the Dami cell line. Interestingly, mRNA expression between the undifferentiated Dami cells and mature Dami cells remained unchanged. Furthermore, we did not detect any 12-LO protein expression in the MEG-01 after the cell’s maturation. Finally, we identified a specific 12-LO antisens non-coding RNA that is implicated in the regulation of the protein expression in megakaryocytes. Our study reports the first mechanistic regulation of 12-LO expression implicated in the megakaryocyte maturation process. Since both platelets and platelet-specific 12-LO play an important role in cancer biology, it is important to better understand how megakaryocytes package the enzyme inside these small cells. It remains elusive whether 12-LO enrichment in platelet correlates with the disease severity. Citation Format: Luc H. Boudreau, Vanessa L. Gauvin, Jaël Richard, Marie-France N. Soucy, Mathieu P.A. Hébert, Eric P. Allain. Characterization of the 12-lipoxygenase expression in the megakaryoblastic cell line, Dami [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1381.

Integrating network pharmacology with microRNA microarray analysis to identify the role of miRNAs in thrombosis treated by the Dahuang Zhechong pill

Background:Thrombotic diseases are the leading causes of death worldwide, urging for improvements in treatment strategies. Dahuang Zhechong pill (DHZCP) is a traditional Chinese medicine widely used for treating thrombotic diseases; however, the underlying mechanisms remain unclear. This study aimed to explore the potential mechanisms of DHZCP in treating thrombosis with a focus on bioinformatics and miRNAs. Methods:We used network pharmacology to explore the targets of thrombosis treated with DHZCP and performed microarray analysis to acquire miRNA profiles and predict the target genes in thrombin-stimulated MEG-01 cells treated with DHZCP. Based on the overlapping of targets, we carried out a component-target-miRNA network and enrichment analysis and validated the selected miRNAs and mRNAs using quantitative reverse transcription-polymerase chain reaction. Results:Our data showed 850 targets of 230 active ingredients of DHZCP and 1214 thrombosis-related genes; 235 targets were common. We identified 32 miRNAs that were regulated by thrombin stimulation but regulated reversely by DHZCP treatment in MEG-01 cells, and predicted 1846 targets with function annotation. We analyzed conjointly 23 integrating targets from network pharmacology and microarray. HIF1A, PIK3CA, MAPK1 and BCL2L1 emerged as key nodes in the network diagrams. We confirmed the differential expression of seven miRNAs, one mRNA (BCL2L1) and platelet surface protein. Conclusions:This study showed that miRNAs and their targets, such as BCL2L1, played crucial roles in platelet activation during DHZCP intervention in thrombosis, highlighting their potential to alleviate platelet activation and increase cell apoptosis. The study’s findings could help develop new strategies for improving thrombosis treatment.

Combined Delivery of miR-15/16 through Humanized Ferritin Nanocages for the Treatment of Chronic Lymphocytic Leukemia.

Chronic lymphocytic leukemia (CLL) is a widespread type of leukemia that predominantly targets B lymphocytes, undermining the balance between cell proliferation and apoptosis. In healthy B cells, miR-15/16, a tandem of microRNAs, functions as a tumor suppressor, curbing the expression of the antiapoptotic B cell lymphoma 2 protein (Bcl-2). Conversely, in CLL patients, a recurring deletion on chromosome 13q14, home to the miR15-a and miR16-1 genes, results in Bcl-2 overexpression, thereby fostering the onset of the pathology. In the present research, a novel approach utilizing humanized ferritin-based nanoparticles was employed to successfully deliver miR15-a and miR-16-1 into MEG01 cells, a model characterized by the classic CLL deletion and overexpression of the human ferritin receptor (TfR1). The loaded miR15-a and miR16-1, housed within modified HumAfFt, were efficiently internalized via the MEG01 cells and properly directed into the cytoplasm. Impressively, the concurrent application of miR15-a and miR16-1 demonstrated a robust capacity to induce apoptosis through the reduction in Bcl-2 expression levels. This technology, employing RNA-loaded ferritin nanoparticles, hints at promising directions in the battle against CLL, bridging the substantial gap left by traditional transfection agents and indicating a pathway that may offer hope for more effective treatments.

Gestodene, a novel positive allosteric modulator of PAR1, enhances PAR1-mediated human platelet aggregation.

Background: Protease-activated receptor 1 (PAR1) is expressed in human platelets and can be activated by low concentrations of thrombin. Vorapaxar, a selective antagonist of PAR1, inhibits thrombin-induced calcium mobilization in human platelet, which is associated with an increased risk of bleeding. Conversely, the administration of a positive allosteric modulator (PAM) of PAR1 may pose a substantial risk of thrombosis due to inducing excessive platelet activation. In this study, we discovered a novel PAM of PAR1 and investigated the effect of enhanced PAR1 activation by PAM of PAR1 on platelet activation. Methods: To find PAMs of PAR1, a cell-based screen was performed in HT29 cells, and finally, gestodene, an oral contraceptive drug (OC), was identified as a novel PAM of PAR1. The mechanism of action of gestodene and its effects on platelet activation were investigated in human megakaryocytic leukemia cell line MEG-01 cells and human platelet. Results: Gestodene enhanced both thrombin- and PAR1-activating peptide (AP)-induced intracellular calcium levels in a dose-dependent manner without altering PAR2 and PAR4 activity. Gestodene significantly increased PAR1-AP-induced internalization of PAR1 and phosphorylation of ERK1/2, and the enhancing effects were significantly blocked by vorapaxar. Furthermore, gestodene potently increased PAR1-AP induced morphological changes in MEG-01 cells. Remarkably, in human blood, gestodene exerted a robust augmentation of PAR1-AP-induced platelet aggregation, and vorapaxar effectively attenuated the gestodene-induced enhancement of platelet aggregation mediated by PAR1. Conclusion: Gestodene is a selective PAM of PAR1 and suggest one possible mechanism for the increased risk of venous thromboembolism associated with OCs containing gestodene.

Cold temperature induces a TRPM8-independent calcium release from the endoplasmic reticulum in human platelets.

The detection of temperature by the human sensory system is life-preserving and highly evolutionarily conserved. Platelets are sensitive to temperature changes and are activated by a decrease in temperature, akin to sensory neurons. However, the molecular mechanism of this temperature-sensing ability is unknown. Yet, platelet activation by temperature could contribute to numerous clinical sequelae, most importantly to reduced quality of ex vivo-stored platelets for transfusion. In this multidisciplinary study, we present evidence for the expression of the temperature-sensitive ion channel transient receptor potential cation channel subfamily member 8 (TRPM8) in human platelets and precursor cells. We found the TRPM8 mRNA and protein in MEG-01 cells and platelets. Inhibition of TRPM8 prevented temperature-induced platelet activation and shape change. However, chemical agonists of TRPM8 did not seem to have an acute effect on platelets. When exposing platelets to below-normal body temperature, we detected a cytosolic calcium increase which was independent of TRPM8 but was completely dependent on the calcium release from the endoplasmic reticulum. Because of the high interindividual variability of TRPM8 expression, a population-based approach should be the focus of future studies. Our study suggests that the cold response of platelets is complex and TRPM8 appears to play a role in early temperature-induced activation of platelets, while other mechanisms likely contribute to later stages of temperature-mediated platelet response.

Thrombopoietin-independent generation of platelet-like particles from megakaryoblastic cells

The use of megakaryoblastic leukemia MEG-01 cells can help reveal the mechanisms of thrombopoiesis. However, conventional in vitro activation of platelet release from MEG-01 cells requires thrombopoietin, which is costly. Here, we aim to develop a more straightforward and affordable method. Synchronization of the MEG-01 cells was initially performed using serum-free culture, followed by spontaneous cell differentiation in the presence of serum. Different stages of megakaryoblast differentiation were classified based on cell morphology, DNA content, and cell cycle. The MEG-01 cells released platelet-like particles at a level comparable to that of the thrombopoietin-activated MEG-01 cells. The platelet-like particles were distinguishable from PLP-derived extracellular vesicles and could express P-selectin following ADP activation. Importantly, the platelet-like particles induced fibrin clotting in vitro using platelet-poor plasma. Therefore, this thrombopoietin-independent cell synchronization method is an effective and straightforward method for studying megakaryopoiesis and thrombopoiesis.

SARAF overexpression impairs thrombin-induced Ca2+ homeostasis in neonatal platelets.

Neonatal platelets present a reduced response to the platelet agonist, thrombin (Thr), thus resulting in a deficient Thr-induced aggregation. These alterations are more pronounced in premature newborns. Here, our aim was to uncover the causes underneath the impaired Ca2+ homeostasis described in neonatal platelets. Both Ca2+ mobilization and Ca2+ influx in response to Thr are decreased in neonatal platelets compared to maternal and control woman platelets. In neonatal platelets, we observed impaired Ca2+ mobilization in response to the PAR-1 agonist (SFLLRN) or by blocking SERCA3 function with tert-butylhydroquinone. Regarding SOCE, the STIM1 regulatory protein, SARAF, was found overexpressed in neonatal platelets, promoting an increase in STIM1/SARAF interaction even under resting conditions. Additionally, higher interaction between SARAF and PDCD61/ALG2 was also observed, reducing SARAF ubiquitination and prolonging its half-life. These results were reproduced by overexpressing SARAF in MEG01 and DAMI cells. Finally, we also observed that pannexin 1 permeability is enhanced in response to Thr in control woman and maternal platelets, but not in neonatal platelets, hence, leading to the deregulation of the Ca2+ entry found in neonatal platelets. Summarizing, we show that in neonatal platelets both Ca2+ accumulation in the intracellular stores and Thr-evoked Ca2+ entry through either capacitative channels or non-selective channels are altered in neonatal platelets, contributing to deregulated Ca2+ homeostasis in neonatal platelets and leading to the altered aggregation observed in these subjects.

Qing-Fei-Pai-Du Decoction ameliorated coagulopathy and thrombocytopenia in endotoxaemia rats and enhanced platelet production from megakaryocytes

BackgroundsThe Qing-Fei-Pai-Du Decoction (QFPDD) was reported to ameliorate the inflammatory coagulopathy and thrombocytopenia in COVID-19 patients. This work investigated the effects of QFPDD in endotoxaemia rats and then further studied its influence on platelet production using cultured megakaryocytes. MethodsThe coagulation indexes and platelet aggregation reactivity of LPS-induced endotoxemia rats with or without QFPDD treatment were analyzed. The platelet parameters, the expression of thrombopoietin (TPO) in the liver and the kidney, number of the megakaryocytes in bone marrow smear of rats were checked. The maturation and platelet production of human megakaryoblastic MEG-01 cells treated with QFPDD or isochlorogenic acid A (ISA), an active component of QFPDD, were observed. ResultsQFPDD improved the coagulation indexes of LPS-induced endotoxaemia rats and decreased the hyper-reactivity of platelets. QFPDD ameliorated LPS-induced decrease in platelet number, partially alleviated increase in liver TPO expression and exhibited no influence on increase in the number of bone marrow megakaryocytes. QFPDD promoted maturation and production of platelet-like particles of MEG-01 megakaryocytes. The effects of QFPDD on MEG-01 megakaryocytes might be related to activation of AKT pathway and up-regulation of related transcription factors. ISA also could induce the maturation of MEG-01 cells. ConclusionsQFPDD effectively ameliorated coagulopathy and thrombocytopenia in rats under inflammatory state. The mechanisms of QFPDD in ameliorating thrombocytopenia might be based on both decreasing effects on platelet depletion in coagulation and inducing effects on maturation and platelet production of megakaryocytes. ISA might be one of the components which contribute to the effects of QFPDD on megakaryocytes.

TRPM8 Contributes to Early Temperature-Induced Platelet Activation

Background: Like sensory neurons, platelets are activated by a decrease in temperature. However, the molecular mechanism of this temperature-sensing ability is unknown. Platelet activation by temperature could contribute to numerous clinical observations, most importantly to the well-known reduced lifespan of ex vivo-stored platelets for transfusion. In this study, we sought to dissect the molecular basis of the cold-induced platelet activation response and specifically, evaluate the role of the thermosensitive ion channel transient receptor potential cation channel subfamily member 8 (TRPM8) in platelets and their precursor cells. Methods: We tested for the presence of TRPM8 on the megakaryocytic cell line MEG-01 and human platelets by immunoblotting, confocal microscopy, and imaging flow cytometry. The effect of TRPM8 on platelets was evaluated using the commercially available TRPM8 inhibitor PF-05105679. In addition, we used TRPM8 agonists such as menthol, WS-12, and icilin. Platelet shape change and αIIbβ3 integrin activation were assessed by imaging flow cytometry and conventional flow cytometry. We tested for platelet aggregation using light transmission aggregometry and for intracellular calcium by reading fluorescence on a plate reader after loading platelets with Fura-2-AM. Calcium release in response to temperature decrease was assessed after loading platelets or TRPM8-transfected HEK293T/17 and reading fluorescence in a Real-Time PCR Detection System. Results: We detected TRPM8 mRNA and protein in MEG-01 cells and platelets but there was a remarkable variability among donors. Further evidence for TRPM8's presence in platelets came from the fact that inhibitors of TRPM8 prevented early temperature-induced platelet activation events, such as αIIbβ3 integrin activation and shape change. Unlike temperature changes, chemical agonists of TRPM8 did not seem to have an acute effect on platelets. Platelets exposed to below-normal body temperature displayed a cytosolic calcium increase, but this was independent of TRPM8 and entirely dependent on the calcium release from the endoplasmic reticulum. Conclusion: We found evidence for TRPM8 expression in platelets but the expression varies greatly between individuals and is of unclear physiologic significance. Our study suggests that the cold response of platelets is complex, and TRPM8 appears to play a calcium-independent role in the early temperature-induced activation of platelets, while other mechanisms likely contribute to later stages of temperature-mediated platelet response. Because of the high interindividual variability of TRPM8 expression, a population-based approach should be the focus of future studies.