[Show abstract][Hide abstract] ABSTRACT: Many chemokines have direct suppressive activity in vitro and in vivo on primitive hematopoietic cells. However, few chemokine-derived peptides have shown a significant activity in inhibiting hematopoiesis. Interestingly, a peptide derived from the 34-58 sequence of the CXC chemokine platelet factor 4 (PF4) produced a 30-40% inhibition of proliferation of murine hematopoietic progenitors (CFU-MK, CFU-GM, and BFU-E) in vitro, at concentrations of 30-60-fold lower than PF4. The aim of the present work was to define the structural parameters and motifs involved in conferring biological activity to the peptide PF4(34-58). Both structural predictions and determinations revealed a new helical motif that was further localized between residues 38 and 46. This helix was necessary for binding of the peptide and for permitting the functional DLQ motif at position 54-56 to activate the putative receptor site. Peptides lacking either the helical or the DLQ motif were devoid of inhibitory activity on the hematopoietic progenitors in vitro. However, among inactive peptides, only those having the helical motif counteracted the inhibition induced by the active peptide PF4(34-58). This suggested that the helix might be required for peptide interactions with a putative receptor site, whereas the DLQ motif would be implicated in the activation of this receptor. These results identify for the first time the dual requirements for the design of chemokine-derived peptides with high suppressive activity on hematopoiesis, as well as for the design of molecules with antagonistic action.
[Show abstract][Hide abstract] ABSTRACT: The use of platelet transfusion to ensure the recovery of thrombopoiesis in patients constitutes high-cost support. The identification and cloning of recombinant human thrombopoietin (TPO) and the development of efficient methods of purification of hematopoietic stem cells and progenitor cells have ameliorated the development of strategies of ex vivo expansion of megakaryocyte (MK) progenitor cells and mature MKs. Synergistic combinations of cytokines including TPO, interleukin (IL)-1, IL-3, IL-11, stem cell factor, and FLT-3 ligand induce the ex vivo expansion of colony-forming unit-MK progenitors and MKs from cytokine-mobilized peripheral blood cells, bone marrow, and cord blood CD34+ cells. Depending on the various culture conditions, i.e., combinations of growth factors, initial concentration of CD34+, serum or serum-free cultures, and/or oxygen tensions, the expansion-fold of MKs and their progenitor cells vary greatly. The clinical applications of the reinfusion of ex vivo-generated MK cells have been investigated successfully in cancer patients following high-dose chemotherapy. This review reports the latest information concerning ex vivo expansion of MKs and the current status of clinical trials.
International Journal of Hematology 05/2000; 71(3):203-10. · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: After 35 years of research, a physiological regulator of platelet production has been identified and the recombinant protein is available. With the discovery of thrombopoietin (TPO), its potential use in a wide variety of clinical megakaryocytic and platelet disorders has been expected and clinical trials have been undertaken. To date, the reported encouraging pre-clinical studies indicate that, as with erythropoietin or G-CSF, minimal toxicity can be expected. A potential limiting side-effect of TPO could be the induction of thrombosis. Nevertheless, it is too early to know whether this cytokine will be of major therapeutic importance for patients with life-threatening thrombocytopenia, such as patients undergoing bone marrow transplantation or subjected to a high dose of chemotherapy. Several experimental and clinical studies are still needed to determine the efficacy of TPO in the prevention or the amelioration of bleeding, which is the ultimate goal for the appropriate use of cytokines with haemostatic benefit. Basic and clinical studies on regulators of megakaryocytopoiesis have rapidly progressed. Now, there is no doubt that some of these regulators are effective in correcting haematopoietic disorders of various aetiologies. Studies on negative regulators not only are important to understand the regulation of megakaryocytopoiesis in normal and pathological states but also have a potential clinical application. Some of these regulators have been shown to be effective in the treatment of essential thrombocythaemia and other myeloproliferative disorders. Platelet factor 4 (PF4) and some other chemokines are also capable of protecting progenitor cells from the cytotoxicity of chemotherapeutic drugs. However, detailed investigations are still required to determine the precise mechanism(s) of action of these regulators and to establish the optimal clinical protocols of negative regulators alone or in association with positive regulators for the treatment of various haematological diseases and cancer.
[Show abstract][Hide abstract] ABSTRACT: Platelet factor 4 (PF-4) inhibits angiogenesis in vitro and in vivo. The mechanism of inhibition is poorly understood. We have investigated the mechanism of inhibition by examining the interaction of PF-4 and the fibroblast growth factor-2 (FGF-2)/fibroblast growth factor receptor (FGFR) system. PF-4 inhibited the binding of FGF-2 to high-affinity and low-affinity binding sites in murine microvascular endothelial cells (LEII cells) and proliferation. Maximum inhibition of binding to endothelial FGF receptors was observed at PF-4 concentrations between 5 and 10 microg/mL (half maximum inhibition at 0.6 micro/mL), and proliferation was completely inhibited at 2 microg/mL. At this concentration, PF-4 reduced internalization of 125I-FGF-2 by threefold and delayed degradation. To gain insight into the mechanism of inhibition, we have analyzed the interaction of PF-4 with FGF-2/FGFR by using mutant heparan sulfate-deficient Chinese hamster ovary (CHO) cells transfected with the FGFR-1 cDNA (CHOm-FGFR-1) and by examining the direct interaction with FGF-2. In the absence of heparin, PF-4 inhibited binding of 125I-FGF-2 to CHOm-FGFR-1 cells in a concentration-dependent manner, although not completely. In the presence of heparin, PF-4 abolished totally the stimulatory effect of heparin. Furthermore, PF-4 complexed to FGF-2 and inhibited endogenous or heparin-induced FGF-2 dimerization. These results indicate that PF-4 interacts with FGF-2 by complex formation, inhibiting FGF-2 dimerization, binding to FGF receptors, and internalization. This mechanism most likely contributes to the antiangiogenic properties of PF-4.
[Show abstract][Hide abstract] ABSTRACT: Platelet factor 4 (PF4) has been recognized as an inhibitor of myeloid progenitors. However, the mechanism of action of this chemokine remains poorly understood. The present study was designed to determine its structure/function relationship. A series of peptides overlapping the C-terminal and central regions of PF4 were analyzed in vitro for their action on murine hematopoietic progenitor growth to assess the minimal sequence length required for activity. The peptides p17-58 and p34-58 possessed an increased hematopoietic inhibitory activity when compared with PF4, whereas the shorter peptides p47-58 and p47-70 were equivalent to the native molecule and the peptide p58-70 was inactive. The PF4 functional motif DLQ located in 54-56 was required for the activity of these peptides. The peptide p34-58 impaired to a similar extent the growth of colony-forming unit-megakaryocyte (CFU-MK) as well as burst-forming unit-erythroid (BFU-E) and colony-forming unit-granulocyte-macrophage (CFU-GM), whereas PF4 was more active on CFU-MK. In the experiments using purified murine CD34(+) marrow cells, statistically significant inhibition induced by p34-58 was shown at concentrations of 2.2 nmol/L or greater for progenitors of the three lineages, whereas that induced by PF4 was seen at 130 nmol/L for CFU-MK and 650 nmol/L for CFU-GM and BFU-E, indicating that the p34-58 acts directly on hematopoietic progenitors and its activity is approximately 60- to 300-fold higher than PF4. The p34-58, unlike PF4, lacked affinity for heparin and its inhibitory activity could not be abrogated by the addition of heparin. In addition, an antibody recognizing p34-58 neutralized the activity of p34-58 but not whole PF4 molecule. These results demonstrate that PF4 contains a functional domain in its central region, which is independent of the heparin binding properties, and provide evidence for a model of heparin-dependent and independent pathways of PF4 in inhibiting hematopoiesis.
[Show abstract][Hide abstract] ABSTRACT: Mouse embryonic stem (ES) cells transfected with a 1.7 kb cDNA of porcine transforming growth factor type beta1 (TGFbeta1), known as ES-T cells, were found to be able to differentiate in vitro into cystic embryonic bodies (EBs) with outspread tubular structures. Morphological analysis using light, phase-contrast and electron microscopes revealed that in culture, the EBs of ES-T cells initially developed some flat endothelial-like cells which further proliferated and migrated to form thread structures. At 8-10 days after EB formation, these thread structures further developed into net-like and tubular structures connecting directly to EBs. Immunofluorescent assays using antibodies against Flk-1 and von Willebrand factor (vWF) indicated that these net-like and tubular structures of ES-T cells consisted of vascular endothelial cells. Further analysis by RT-PCR revealed that the EBs with tubular structures expressed the mRNA of other markers of vascular endothelial cells, including VE-cadherin and platelet-endothelial cell adhesion molecule (PECAM). Cells of hematopoietic origin were not detected on the outside of EBs by immunostaining using several antibodies specific for granulocytes, macrophages and lymphocytes as well as by benzidine staining for erythroid cells on the outside of EBs. Our data demonstrates that the transfer of TGFbeta1 into ES cells results in a significant vasculogenesis without concomitant hematopoiesis. ES-T cells could therefore provide an excellent model for studying blood vessel formation and vasculogenic and hematopoietic interactions.
[Show abstract][Hide abstract] ABSTRACT: A computer-assisted automatic image procedure was karyocytopoiesis in culture. This analysis system was based on acetylcholinesterase staining, a specific staining for murine bone marrow megakaryocytes, and an image capturing instrument with a computer program. Two kinds of routine megakaryocyte culture methods were used, the plasma clot and the serum-free agar systems. A comparison between manual counting and the instrument was made. The image analysis software was able to distinguish between megakaryocytes (MK) at different stages of maturation. The results show that this analysis system can simultaneously detect not only the number of megakaryocytes and their colonies in each dish, but also the surface area of individual megakaryocytes. In addition, this analysis system functions automatically 24 hours a day and the results obtained are reproducible. Using this system, we have confirmed previous observations that thrombopoietin (TPO) and heparin stimulate both proliferation and maturation of megakaryocytes. In addition, we found that platelet factor 4 (PF-4) significantly reduced the number of megakaryocytes but not their cell surface area, whereas TGFbeta1 decreased both number and surface area of megakaryocytes, suggesting that PF4 and TGFbeta1 negatively regulate megakaryocytopoiesis by different mechanisms. We noticed that megakaryocytes grown under agar culture conditions regularly had an increased size in comparison with those grown in a plasma clot system, which may be an indication that the plasma clot culture media contains an inhibitor(s) of megakaryocyte maturation. Our data indicate that this image analysis system, in addition to its automatic and reproducible features, is more efficient and allows detection of more parameters than routine manual microscopic detection.
[Show abstract][Hide abstract] ABSTRACT: Chemokines are a large family of cytokines that act not only as immune and inflammatory regulators but also as regulators of hematopoiesis. Two major subfamilies of chemokines are distinguished on the basis of whether the first two cysteines are separated by a single residue (CXC) or three residues (CX3C) or they are adjacent (CC) or there is a single C. The Macrophage Inflammatory Protein 1 alpha (MIP-1 alpha), which belongs to CC family is a powerful inhibitor of hematopoisis in vitro and in vivo. The sub-family CXC comprises two main groups. The first sub-group includes the ELR chemokines, in which interleukin-8 (IL-8) is the most prototypic and possesses suppressive activities on hematopoiesis. Platelet Factor 4 (PF4) belongs to the sub-group of non-ELR CXC chemokines. PF4 acts as an inhibitor of hematopoiesis, particularly of the megakaryocytopoiesis. Recently, it has been shown that a peptide of PF4, 34-58 which does not contain the site of heparin binding, is able to inhibit the growth of hematopoietic progenitors in vitro, providing evidence for a model of heparin dependent and independent pathways of PF4 action on hematopoiesis. PF4 can reduce the chimiosensitivity of hematopoietic cells in mice treated by the cytotoxic drug 5-Fluorouracyl, suggesting a potential clinical application of PF4 in cancer therapy.
Comptes rendus des séances de la Société de biologie et de ses filiales 02/1998; 192(5):917-23.
[Show abstract][Hide abstract] ABSTRACT: We have recently reported that platelet factor 4 (PF4), a megakaryocyte-platelet protein, is a potent inhibitor of human and murine megakaryocytopoiesis. In addition, PF4 accelerated the recovery of the marrow precursor cells in 5-fluorouracil (5-FU) treated mice. We show in this study that a slight modification of the C-terminal peptide related to PF4 (C13-24DE), which was previously reported as the carboxy terminal region of PF4 implicated in PF4 inhibitory activity, is also able to significantly increase murine high proliferating-potential-colony forming cells (HPP-CFC), colony-forming-unit megakaryocyte (CFU-MK) and colony-forming unit granulocyte-macrophage (CFU-GM) progenitor number, eight days after 5-FU administration, when it was given intraperitoneally twice a day (200 micrograms/kg/inj) prior to 5-FU administration (150 mg/kg). Furthermore, the C13-24DE pretreatment enhanced both the number and the diameter of single megakaryocyte (MK) by day 8. These data indicate that the C13-24DE peptide related to PF4 accelerated the in vivo recovery of stem cells, progenitors (CFU-GM, CFU-MK) and single MK after 5-FU treatment and may have a hemoprotective effect against chemotherapeutic agents.
International Journal of Hematology 01/1998; 66(4):435-44. · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effects of platelet factor 4 (PF4) on the viability and chemosensitivity of normal hematopoietic cells and cancer cell lines were studied to determine the mechanisms whereby PF4 functions as either an inhibitor or a protector and to evaluate its clinical significance. Two other chemokines, interleukin-8 (IL-8) and neutrophil-activating peptide-2 (NAP-2), were also studied in comparison to PF4. Using a tetrazolium salt assay for cell viability, we observed that PF4 at 1 to 50 microg/mL supported the viability of normal human bone marrow cells. Approximately 45% of cells cultured for 48 hours survived, whereas 80% or more survived in the presence of PF4 5 microg/mL. PF4 also supported the viability of CD34+ cord blood (CB) cells and protected them from apoptosis induced by transforming growth factor beta1 (TGFbeta1) and cytotoxic drugs. Pretreatment of CD34+ cells by PF4, but not by TGFbeta1, caused an increase in the number of megakaryocyte colonies after these cells were replated in secondary cultures. Flow cytometry analysis showed that when CD34+ cells were preincubated with PF4 or TGFbeta1 for 12 days in hematopoietic growth factor-rich medium, an increased number of remaining CD34+ cells was observed only for PF4-treated cells. Furthermore, PF4 significantly reduced the chemosensitivity of bone marrow cells, as shown by its ability to increase the 50% inhibition concentration (IC50) of several cytotoxic agents. Like PF4, IL-8 and NAP-2 at 0.1, 0.6, and 1 microg/mL supported the survival of myeloid progenitors, including colony-forming units granulocyte, erythroblast, monocyte, megakaryocyte (CFU-GEMM), CFU-megakaryocyte (CFU-MK), CFU-granulocyte/macrophage (CFU-GM), and burst-forming units-erythroblast (BFU-E), and reduced their sensitivity to the toxicity of etoposide (ETP). Protamine sulfate at 1 to 100 microg/mL showed no such activity of PF4. Interestingly, the three chemokines failed to affect significantly the viability and chemosensitivity of three leukemic and two other tumor cell lines. Based on these results, we conclude for the first time that PF4 and IL-8 and NAP-2 support the survival of normal hematopoietic precursors and protect them from the toxicity of chemotherapeutic agents. Because such activities are unique to normal hematopoietic cells but not to the cancer cell lines evaluated, a potential clinical application of these molecules in the treatment of cancer is suggested.
[Show abstract][Hide abstract] ABSTRACT: Heparin, a glycosaminoglycan (GAG) derivative has been widely used as an anticoagulation agent for more than 50 years. This study was conducted to demonstrate that, due to their modulatory effect on cytokines, heparin and other GAGs can favor megakaryocytopoiesis both in vitro and in vivo in mice. In vitro addition of heparin and other GAGs (excepting keratane sulfate) into plasma clot cultures induces a significant increase in the number of megakaryocyte colonies. Optimal heparin and GAG concentrations for maximal effect are approximately 50-100 micrograms/ml. In agar culture without serum, all GAGs do not have this stimulating effect on megakaryocyte colonies. This would suggest that the GAG action depends on the presence of one or more plasma factors. Interactions between GAGs and cytokines such as IL3, IL6, G-SCF, GM-CSF, aFGF, TPO and EPO as well as PF4 and TGFB1 were also conducted. The results demonstrate that heparin and chondroitin sulfate significantly increases the action of TPO, IL6 and aFGF but not the action of IL3, G-SCF and EPO. Heparin and other GAGs can also neutralize PF4 and TGFB1 inhibitory action. In vivo, the effect of low-molecular-weight heparin (Fraxiparine) injected in normal mice treated with 5-fluorouracil increases megakaryocytopoiesis. The findings demonstrate that heparin and its derivatives have a potentializing effect on megakaryocytopoiesis and could be used as therapeutic agents in the treatment of thrombocytopenia.
Annales de medecine interne 02/1997; 148(2):150-3.
[Show abstract][Hide abstract] ABSTRACT: We have previously reported that heparin is capable of stimulating in vitro and in vivo megakaryocytopoiesis in mice and has a thrombopoietic effect when given in chronic immune thrombocytopenic purpura and that heparin and several other glycosaminoglycans (GAGs) promote the growth of human megakaryoblastic cell lines in the presence of serum. We show here that GAGs, including heparan sulfate (HS), chondroitin sulfate (CS), dermatan sulfate (DS), and hyaluronic acid (HA), also stimulate in vitro growth of murine megakaryocyte progenitors and augment the diameter of individual megakaryocytes in the presence of serum. However, in a serum-free agar system, the GAGs alone had no effect on megakaryocyte colony formation, suggesting that GAGs cooperate with some serum factor(s) to exert their activity. We also show that heparin significantly potentiates the megakaryocytopoietic activity of C-Mpl ligand and interleukin (IL)-6 but not IL3, GM-CSF, SCF, and Epo. In addition, the GAGs significantly neutralize the inhibitory action of platelet factor 4 (PF4) and transforming growth factor beta 1 (TGF beta 1) on megakaryocyte colony growth. These results demonstrate a stimulating activity of GAGs on megakaryocytopoiesis by modifying the activity of several growth-regulating factors.
[Show abstract][Hide abstract] ABSTRACT: Megakaryocytopoiesis concerns the commitment of hematopoietic stem cells towards the megakaryocyte lineage, the proliferation and maturation of megakaryocyte progenitors, leading to platelet formation. Normal megakaryocytopoiesis requires an equilibrium between positive and negative regulators. Thrombopoietin, recently cloned, is the main growth factor for the megakaryocyte lineage, enhancing all the steps of megakaryocyte development: proliferation, maturation, ploidisation, platelet formation. Several other factors have a direct (interleukin 3, 6, 11, 13, GMCSF, erythropoietin) or indirect (interleukin 1, stem cell factor) positive effect. Factors inhibiting megakaryocytopoiesis are synthetized by the megakaryocytes themselves (platelet factor 4, transforming growth factor beta), or have many other effects (alpha-interferon, thrombin) or correspond to a novel molecule (anagrelide). Heparin and other glycosaminoglycans positively modulate megakaryocytopoiesis by acting synergistically with some growth factors and by neutralizing some inhibitors. These progresses in the knowledge of normal and pathological megakaryocytopoiesis should lead to considerable therapeutic advances.
Comptes rendus des séances de la Société de biologie et de ses filiales 02/1996; 190(5-6):515-32.
[Show abstract][Hide abstract] ABSTRACT: We have previously shown that platelet factor 4 (PF 4) is a potent inhibitor of megakaryocytopoiesis and that it may protect stem cells from 5-fluorouracil (5-FU) cytotoxicity. In the present work, the effects of human PF 4 on megakaryocyte (MK) growth from human CD34+ cord blood (CB) cells were studied in comparison with transforming growth factor beta 1 (TGF-beta 1). Development of MK from CD34+ cells in both plasma clot culture and liquid culture was significantly inhibited by PF 4 (5 micrograms/ml) and TGF beta 1 (1 ng/ml). Inhibition of cell growth by PF 4 was reversible judging from the fact that the CD34+ cells preincubated with PF 4 could regenerate colonies after washing and replating into the cultures. By contrast, TGF-beta 1 pretreated CD34+ cells gave rise to few colonies following replating. Moreover, incubation of CD34+ cells with PF 4 in liquid culture caused an increase in the number of both stem cell factor (SCF)-binding cells and CD34 antigen-bearing cells, and exhibited greater capacity to form MK colonies than control after the treatment of 5-FU. In vivo in mice, twice injections of PF 4 at 40 micrograms/kg with an interval of 6 h followed by one injection of 5-FU at 150 mg/kg resulted in a significant increase in the number of colony-forming cells with high proliferative potential (HPP-CFC) and colony-forming unit-megakaryocyte (CFU-MK) in bone marrow. In exponentially growing human erythroleukemia cells (HEL), the addition of PF 4 prolonged cell cycle progression and therefore resulted in an increased cell population in S phase, as determined by flow cytometric analysis. Different from PF 4, TGF-beta 1 blocked more cells in G 1 phase. These results demonstrate that PF 4 and TFG-beta 1 inhibit MK development from CD34+ CB cells by different mechanisms and suggest that PF 4, unlike TGF-beta 1, exerts its inhibitory effect on cell growth in a reversible and S phasespecific manner by which it protects stem cells and MK progenitor cells from 5-FU cytotoxicity.
[Show abstract][Hide abstract] ABSTRACT: Development of megakaryocyte (MK) from CD34+ cord blood (CB) cells in both plasma clot culture and liquid culture was significantly inhibited by human platelet factor 4 (PF4) and human transforming growth factor beta 1 (TGF beta 1). Inhibition of cell growth by PF4 was reversible judging from the fact that the CD34+ cells preincubated with PF4 could regenerate colonies after washing and replating into the cultures. By contrast, TGF beta 1-pretreated CD34+ cells gave rise to few colonies following replating. Moreover, incubation of CD34+ cells with PF4 in liquid culture caused an increase in the number of both stem cell factor (SCF)-binding cells and CD34 antigen-bearing cells, and exhibited greater capacity to form MK colonies than control after the treatment of 5-FU. In vivo in mice, twice injections of PF4 at 40 micrograms/kg resulted in a significant increase in the number of colony-forming cells with high proliferative potential (HPP-CFC) and colony-forming unit-megakaryocyte (CFU-MK) in bone marrow. In exponentially growing human erythroleukemia cells (HEL), the addition of PF4 prolonged cell cycle progression and therefore resulted in an increased cell population in S phase, as determined by flow cytometric analysis. Different from PF4, TGF beta 1 blocked more cells in G1 phase. These results demonstrate that PF4 and TGF beta 1 inhibit MK development from CD34+ CB cells by different mechanisms and suggest that PF4, unlike TGF beta 1, exerts its inhibitory effect on cell growth in a reversible and S phase-specific manner by which it protects stem cells and MK progenitor cells from 5-FU cytotoxicity.
Bulletin de l'Académie nationale de médecine 12/1995; 179(8):1657-70. · 0.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Our previous in-vitro and in-vivo studies showed that heparin enhanced murine and human megakaryocytopoiesis. 20 patients with chronic immune thrombocytopenic purpura were randomly divided into two groups and given 10 mg per day of prednisone for 30 days, for haemostatic purposes. One group received in addition heparin (1250 IU twice a day subcutaneously for 30 days). From day 10, a significant increase in platelet count was observed in eight of the ten patients treated with heparin (p < 0.05), with return to the initial value after heparin cessation in six of the responders. These data demonstrate the effectiveness of heparin and suggest its use or that of other related compounds for therapy of chronic immune thrombocytopenic purpura.
The Lancet 08/1995; 346(8969):220-1. DOI:10.1016/S0140-6736(95)91269-X · 45.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of a low-molecular-weight heparin, faxiparin (Nadroparin), on murine megakaryocytopoiesis in vitro and in vivo was studied in comparison with unfractionated heparin. The addition of fraxiparin at 1-20 IU/ml into plasma clot cultures but not serum-free agar culture significantly enhanced MK colony growth. Furthermore, fraxiparin was found to potentiate the stimulating activity of aplastic anaemia serum (AAS) but not stem cell factor (SCF), interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF) and erythropoietin (Epo), on MK colony growth in vitro, and to neutralize the inhibitory effect of platelet factor 4 (PF4) in vitro and in vivo. Fraxiparin also acted synergistically with heparin cofactor II and antithrombin III to promote megakaryocyte colony formation. Intraperitoneal administration of fraxiparin twice daily for 4 d at 0.1-25 IU/injection increased in mice the level of blood platelet counts and the number of single MKs and CFU-MK in bone marrow. These data demonstrate that fraxiparin is able to positively regulate megakaryocytopoiesis.
British Journal of Haematology 12/1994; 88(3):608-12. DOI:10.1111/j.1365-2141.1994.tb05080.x · 4.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Angiogenic factors are potent growth factors promoting proliferation and differentiation of vascular endothelial cells. Recent evidence suggest that these factors also promote hematopoietic cell growth. The major group of angiogenic growth factors is the fibroblast growth factor (FGF) family. Two prototypes, acidic FGF and basic FGF, have been demonstrated to interact with granulopoiesis and megakaryocytopoiesis. Basic FGF stimulates granulopoiesis in long term bone marrow cultures while acidic and basic FGF promote megakaryocytopoiesis. These effects are presumably mediated via specific FGF receptors, that have been identified in bone marrow and leukemia cell lines. Besides the FGF family, angiogenic inhibitors such as platelet factor-4 (PF-4) have been found to exhibit an inhibitory effect on megakaryocytopoiesis. In contrast, it has been demonstrated that hematopoietic growth factors including granulocyte-macrophage colony-stimulating factor (GM-CSF), or erythropoietin promote angiogenesis in vivo and in vitro. In light of these recent observations and the common origin of endothelial cells and hematopoietic cells, it is suggested that angiogenic factors are hematopoietic growth factors and vice versa. However, these data must be interpreted with caution and a careful in vivo evaluation should be done before these observed in vivo effects are proven to be significant to the physiopathology of hematopoiesis or angiogenesis.
[Show abstract][Hide abstract] ABSTRACT: Megakaryocytes are normal bone marrow cells which have the unique ability to become polyploid. This phenomenon is termed endomitosis and its mechanism remains poorly understood at present. It is known that the cell cycle of eukaryotes, particularly at G2/M transition, is regulated by a complex with histone H1 kinase activity, the maturation- or M-phase promoting factor (MPF). We have therefore studied the expression of subunits of MPF, the p34cdc2 and cyclin B in normal bone marrow culture megakaryocytic cells, blood leukocytes and platelets as well as in human megakaryoblastic cell lines Dami, Meg-01, HEL and the promyelocytic cell line HL60. Using immunohistochemistry and electron microscopy we have observed that cyclin B was virtually undetectable in megakaryocytes and platelets, but was abundant in granulocytes, monocytes/macrophages and HL60. Studies by RT-PCR showed the presence in large quantities of mRNA of cyclin B in all cell types studied, even in megakaryocytic-like cells. These observations suggest some important implications in the understanding of the mechanisms of megakaryocyte polyploidization and related endomitosis.
Comptes Rendus de l Académie des Sciences - Series III - Sciences de la Vie 01/1994; 316(12):1438-45.