The Thrombocytopenia of Wiskott Aldrich Syndrome Is Not Related to a Defect in Proplatelet Formation

Blood ◽  
1999 ◽  
Vol 94 (2) ◽  
pp. 509-518 ◽  
Author(s):  
Elie Haddad ◽  
Elisabeth Cramer ◽  
Christel Rivière ◽  
Philippe Rameau ◽  
Fawzia Louache ◽  
...  
Keyword(s):  
Blood Platelets ◽  
Critical Role ◽  
Consistent Finding ◽  
Cytoskeletal Organization ◽  
Platelet Production ◽  
Wiskott Aldrich Syndrome ◽  
Platelet Size ◽  
Proplatelet Formation ◽  
Small Platelet

The Wiskott-Aldrich syndrome (WAS) is an X-linked hereditary disease characterized by thrombocytopenia with small platelet size, eczema, and increased susceptibility to infections. The gene responsible for WAS was recently cloned. Although the precise function of WAS protein (WASP) is unknown, it appears to play a critical role in the regulation of cytoskeletal organization. The platelet defect, resulting in thombocytopenia and small platelet size, is a consistent finding in patients with mutations in the WASP gene. However, its exact mechanism is unknown. Regarding WASP function in cytoskeletal organization, we investigated whether these platelet abnormalities could be due to a defect in proplatelet formation or in megakaryocyte (MK) migration. CD34+ cells were isolated from blood and/or marrow of 14 WAS patients and five patients with hereditary X-linked thrombocytopenia (XLT) and cultured in serum-free liquid medium containing recombinant human Mpl-L (PEG-rHuMGDF) and stem-cell factor (SCF) to study in vitro megakaryocytopoiesis. In all cases, under an inverted microscope, normal MK differentiation and proplatelet formation were observed. At the ultrastructural level, there was also no abnormality in MK maturation, and normal filamentous MK were present. Moreover, the in vitro produced platelets had a normal size, while peripheral blood platelets of the same patients exhibited an abnormally small size. However, despite this normal platelet production, we observed that F-actin distribution was abnormal in MKs from WAS patients. Indeed, F-actin was regularly and linearly distributed under the cytoplasmic membrane in normal MKs, but it was found concentrated in the center of the WAS MKs. After adhesion, normal MKs extended very long filopodia in which WASP could be detected. In contrast, MKs from WAS patients showed shorter and less numerous filopodia. However, despite this abnormal filopodia formation, MKs from WAS patients normally migrated in response to stroma-derived factor-1 (SDF-1), and actin normally polymerized after SDF-1 or thrombin stimulation. These results suggest that the platelet defect in WAS patients is not due to abnormal platelet production, but instead to cytoskeletal changes occuring in platelets during circulation.

The Thrombocytopenia of Wiskott Aldrich Syndrome Is Not Related to a Defect in Proplatelet Formation

Blood ◽  
1999 ◽  
Vol 94 (2) ◽  
pp. 509-518 ◽  
Author(s):  
Elie Haddad ◽  
Elisabeth Cramer ◽  
Christel Rivière ◽  
Philippe Rameau ◽  
Fawzia Louache ◽  
...  
Keyword(s):  
Blood Platelets ◽  
Critical Role ◽  
Consistent Finding ◽  
Cytoskeletal Organization ◽  
Platelet Production ◽  
Wiskott Aldrich Syndrome ◽  
Platelet Size ◽  
Proplatelet Formation ◽  
Small Platelet

Abstract The Wiskott-Aldrich syndrome (WAS) is an X-linked hereditary disease characterized by thrombocytopenia with small platelet size, eczema, and increased susceptibility to infections. The gene responsible for WAS was recently cloned. Although the precise function of WAS protein (WASP) is unknown, it appears to play a critical role in the regulation of cytoskeletal organization. The platelet defect, resulting in thombocytopenia and small platelet size, is a consistent finding in patients with mutations in the WASP gene. However, its exact mechanism is unknown. Regarding WASP function in cytoskeletal organization, we investigated whether these platelet abnormalities could be due to a defect in proplatelet formation or in megakaryocyte (MK) migration. CD34+ cells were isolated from blood and/or marrow of 14 WAS patients and five patients with hereditary X-linked thrombocytopenia (XLT) and cultured in serum-free liquid medium containing recombinant human Mpl-L (PEG-rHuMGDF) and stem-cell factor (SCF) to study in vitro megakaryocytopoiesis. In all cases, under an inverted microscope, normal MK differentiation and proplatelet formation were observed. At the ultrastructural level, there was also no abnormality in MK maturation, and normal filamentous MK were present. Moreover, the in vitro produced platelets had a normal size, while peripheral blood platelets of the same patients exhibited an abnormally small size. However, despite this normal platelet production, we observed that F-actin distribution was abnormal in MKs from WAS patients. Indeed, F-actin was regularly and linearly distributed under the cytoplasmic membrane in normal MKs, but it was found concentrated in the center of the WAS MKs. After adhesion, normal MKs extended very long filopodia in which WASP could be detected. In contrast, MKs from WAS patients showed shorter and less numerous filopodia. However, despite this abnormal filopodia formation, MKs from WAS patients normally migrated in response to stroma-derived factor-1 (SDF-1), and actin normally polymerized after SDF-1 or thrombin stimulation. These results suggest that the platelet defect in WAS patients is not due to abnormal platelet production, but instead to cytoskeletal changes occuring in platelets during circulation.

scholarly journals Platelet-associated immunoglobulin, platelet size, and the effect of splenectomy in the Wiskott-Aldrich syndrome

Blood ◽  
1985 ◽  
Vol 65 (6) ◽  
pp. 1439-1443 ◽  
Author(s):  
L Corash ◽  
B Shafer ◽  
RM Blaese
Keyword(s):  
Platelet Count ◽  
Mean Platelet Volume ◽  
Critical Role ◽  
Volume Distribution ◽  
Normal Range ◽  
Platelet Volume ◽  
Wiskott Aldrich Syndrome ◽  
Platelet Size ◽  
Number Of Patients ◽  
Effect Of Splenectomy

Abstract Wiskott-Aldrich syndrome (WAS) thrombocytopenia is frequently improved by splenectomy, although the mechanism of the thrombocytopenia and its resolution are unknown. Previous studies in two patients have shown that mean platelet volume, which is characteristically reduced in WAS, increased along with platelet count postsplenectomy. Additional studies in a limited number of patients have also demonstrated that platelet- associated immunoglobulin G (PAIgG) is elevated presplenectomy, but to date no postsplenectomy data have been reported. The present study was performed to more fully evaluate the effect of splenectomy on platelet volume and PAIgG in WAS. Before splenectomy, mean platelet volume was reduced but platelet size was broadly distributed with substantial overlap of the normal range. PAIgG was significantly elevated in 13 of 14 presplenectomy WAS patients (means = 78.9 fg per platelet) and fell to normal levels postoperatively (means = 4.0 fg per platelet). Platelet count and clinical status improved postsplenectomy, and mean platelet volume and platelet volume distribution returned to the normal range. WAS subjects who relapsed with recurrent thrombocytopenia redeveloped elevated PAIgG but maintained normal platelet size. The spleen appears to play a critical role in a process that may be immunologically mediated and results in reduced platelet size.

scholarly journals Effects of Cytokines on Platelet Production From Blood and Marrow CD34+ Cells

Blood ◽  
1998 ◽  
Vol 91 (3) ◽  
pp. 830-843 ◽  
Author(s):  
Françoise Norol ◽  
Natacha Vitrat ◽  
Elisabeth Cramer ◽  
Josette Guichard ◽  
Samuel A. Burstein ◽  
...  
Keyword(s):  
Cell Population ◽  
Culture System ◽  
Simple Liquid ◽  
Similar Response ◽  
Platelet Production ◽  
Liquid Culture System ◽  
Cd34 Cells ◽  
Proplatelet Formation ◽  
And Function

Abstract The late stages of megakaryocytopoiesis, consisting of the terminal processes of cytoplasmic maturation and platelet shedding, remain poorly understood. A simple liquid culture system using CD34+ cells in serum-free medium has been developed to study the regulation of platelet production in vitro. Platelets produced in vitro were enumerated by flow cytometry. A truncated form of human Mpl-Ligand conjugated to polyethylene glycol (PEG-rHuMGDF) played a crucial role in both proplatelet formation and platelet production. A combination of stem cell factor (SCF), interleukin-3 (IL-3), and IL-6 was as potent as PEG-rHuMGDF for the growth of megakaryocytes (MKs). However, the number of proplatelet-displaying MKs and platelets was increased 10-fold when PEG-rHuMGDF was used. Peripheral blood mobilized CD34+ cells gave rise to a threefold augmentation of platelets compared with marrow CD34+ cells. This finding was related to the higher proliferative capacity of the former population because the proportion of proplatelet-displaying MKs was similar for both types of CD34+ cells. The production of platelets per MK from CD34+ cells was low, perhaps because of the low ploidy of the cultured MKs. This defect in polyploidization correlated with the degree of proliferation of MK progenitors induced by cytokines. In contrast, ploidy development closer to that observed in marrow MKs was observed in MKs derived from the low proliferative CD34+CD41+ progenitors and was associated with a twofold to threefold increment in platelet production per MK. As shown using this CD34+ CD41+ cell population, PEG-rHuMGDF was required throughout the culture period to potently promote platelet production, but was not involved directly in the process of platelet shedding. IL-3, SCF, and IL-6 alone had a very weak effect on proplatelet formation and platelet shedding. Surprisingly, when used in combination, these cytokines elicited a degree of platelet production which was decreased only 2.4-fold in comparison with PEG-rHuMGDF. This suggests that proplatelet formation may be inhibited by non-MK cells which contaminate the cultures when the entire CD34+ cell population is used. Cultured platelets derived from PEG-rHuMGDF– or cytokine combination-stimulated cultures had similar ultrastructural features and a nearly similar response to activation by thrombin. The data show that this culture system may be useful to study the effects of cytokines and the role of polyploidization on platelet production and function.

scholarly journals Effects of Cytokines on Platelet Production From Blood and Marrow CD34+ Cells

Blood ◽  
1998 ◽  
Vol 91 (3) ◽  
pp. 830-843 ◽  
Author(s):  
Françoise Norol ◽  
Natacha Vitrat ◽  
Elisabeth Cramer ◽  
Josette Guichard ◽  
Samuel A. Burstein ◽  
...  
Keyword(s):  
Cell Population ◽  
Culture System ◽  
Simple Liquid ◽  
Similar Response ◽  
Platelet Production ◽  
Liquid Culture System ◽  
Cd34 Cells ◽  
Proplatelet Formation ◽  
And Function

The late stages of megakaryocytopoiesis, consisting of the terminal processes of cytoplasmic maturation and platelet shedding, remain poorly understood. A simple liquid culture system using CD34+ cells in serum-free medium has been developed to study the regulation of platelet production in vitro. Platelets produced in vitro were enumerated by flow cytometry. A truncated form of human Mpl-Ligand conjugated to polyethylene glycol (PEG-rHuMGDF) played a crucial role in both proplatelet formation and platelet production. A combination of stem cell factor (SCF), interleukin-3 (IL-3), and IL-6 was as potent as PEG-rHuMGDF for the growth of megakaryocytes (MKs). However, the number of proplatelet-displaying MKs and platelets was increased 10-fold when PEG-rHuMGDF was used. Peripheral blood mobilized CD34+ cells gave rise to a threefold augmentation of platelets compared with marrow CD34+ cells. This finding was related to the higher proliferative capacity of the former population because the proportion of proplatelet-displaying MKs was similar for both types of CD34+ cells. The production of platelets per MK from CD34+ cells was low, perhaps because of the low ploidy of the cultured MKs. This defect in polyploidization correlated with the degree of proliferation of MK progenitors induced by cytokines. In contrast, ploidy development closer to that observed in marrow MKs was observed in MKs derived from the low proliferative CD34+CD41+ progenitors and was associated with a twofold to threefold increment in platelet production per MK. As shown using this CD34+ CD41+ cell population, PEG-rHuMGDF was required throughout the culture period to potently promote platelet production, but was not involved directly in the process of platelet shedding. IL-3, SCF, and IL-6 alone had a very weak effect on proplatelet formation and platelet shedding. Surprisingly, when used in combination, these cytokines elicited a degree of platelet production which was decreased only 2.4-fold in comparison with PEG-rHuMGDF. This suggests that proplatelet formation may be inhibited by non-MK cells which contaminate the cultures when the entire CD34+ cell population is used. Cultured platelets derived from PEG-rHuMGDF– or cytokine combination-stimulated cultures had similar ultrastructural features and a nearly similar response to activation by thrombin. The data show that this culture system may be useful to study the effects of cytokines and the role of polyploidization on platelet production and function.

scholarly journals In vivo stimulation of megakaryocytopoiesis by recombinant murine granulocyte-macrophage colony-stimulating factor

Blood ◽  
1990 ◽  
Vol 76 (8) ◽  
pp. 1473-1480
Author(s):  
AM Vannucchi ◽  
A Grossi ◽  
D Rafanelli ◽  
PR Ferrini
Keyword(s):  
Bone Marrow ◽  
Blood Platelets ◽  
Colony Stimulating Factor ◽  
Platelet Production ◽  
Macrophage Colony Stimulating Factor ◽  
Macrophage Colony ◽  
Stimulating Factor ◽  
Stimulation Of

Murine recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) was injected in mice, and the effects on bone marrow, splenic megakaryocytes, megakaryocyte precursors (megakaryocyte colony-forming units [CFU-Meg]) were evaluated. In mice injected three times a day for 6 days with 12,000 to 120,000 U rGM-CSF, no significant modification of both platelet levels and mean platelet volume was observed, while there was a twofold increase in blood neutrophils. However, the rate of platelet production, as assessed by the measurement of 75selenomethionine incorporation into blood platelets, was On the contrary, administration of up to 384,000 U rGM-CSF two times a day for 2 days, as for a typical “thrombopoietin assay,” failed to modify platelet production. A significant dose-related increase in the number of splenic megakaryocytes occurred in mice receiving 60,000 to 120,000 U rGM-CSF, while a slight increase in the number of bone marrow megakaryocytes was observed in mice injected with 120,000 U rGM-CSF. The proportion of bone marrow megakaryocytes with a size less than 18 microns and greater than 35 microns resulted significantly higher in mice receiving rGM-CSF in comparison with controls; an increase in the percentage of splenic megakaryocytes greater than 35 microns was also observed. A statistically significant increase in the total spleen content of CFU-Meg was observed after administration of 90,000 and 120,000 U rGM-CSF three times a day for 6 days, while no effect on bone marrow CFU-Meg was recorded, irrespective of the dose delivered. Finally, 24 hours after a single intravenous injection of rGM-CSF, there was a significant increase in the proportion of CFU-Meg in S- phase, with the splenic progenitors being more sensitive than bone marrow-derived CFU-Meg. These data indicate that rGM-CSF has in vivo megakaryocyte stimulatory activity, and are consistent with previous in vitro observations. However, an effective stimulation of megakaryocytopoiesis in vivo, bringing about an increase in the levels of blood platelets, may require interaction of rGM-CSF with other cytokines.

scholarly journals Analysis of clinical and molecular genetic characteristics of Wiskott-Aldrich syndrome and X-linked thrombocytopenia

2021 ◽  
Vol 2 (3) ◽  
pp. 61-66
Author(s):  
Doina TURCAN ◽  
Lucia ANDRIES ◽  
Alexandr DORIF ◽  
Victoria SACARA
Keyword(s):  
Actin Polymerization ◽  
Wide Spectrum ◽  
Molecular Genetic ◽  
Clinical Findings ◽  
Recurrent Infections ◽  
Genetic Characteristics ◽  
Wiskott Aldrich Syndrome ◽  
Platelet Size ◽  
First Case ◽  
Small Platelet

Introduction. Wiskott-Aldrich syndrome is a rare X-linked disorder characterized by microthrombocytopenia, eczema, and recurrent infections. It is caused by mutations of the WAS gene which encodes the WAS protein (WASp) – a key regulator of actin polymerization in hematopoietic cells. Mutations within the WASp gene result in a wide heterogeneity of clinical disease, ranging from ‘classical WAS’ to mild asymptomatic thrombocytopenia (X-linked thrombocytopenia [XLT]), or congenital neutropenia (X-lined neutropenia [XLN]).Case presentation. This present paper reports a phenotypical and laboratory description of two children diagnosed with WAS and one child diagnosed with XLT. The first case was a six months old male with septicemia, thrombocytopenia, eczema and petechial rash. The second case was a 2 years old boy presenting with complaints of recurrent infections, eczema and thrombocytopenia with small platelet size. The third case was a 16 years old boy who presented with thrombocytopenia and recurrent sinopulmonary infections.Conclusions. Due to a wide spectrum of clinical findings, the diagnosis of WAS/XLT should be considered in any male patient presenting with petechiae, bruises, and congenital or early-onset thrombocytopenia associated with small platelet size.

scholarly journals M6PR-Specific Targeting of Lysosomal Heparanase Regulates Platelet Hemostatic Function in Mice

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 1059-1059
Author(s):  
Nathan Eaton ◽  
Caleb Drew ◽  
Theresa A. Dlugi ◽  
Karin M. Hoffmeister ◽  
Hervé Falet
Keyword(s):  
Platelet Function ◽  
Conflicts Of Interest ◽  
Blood Platelets ◽  
Critical Role ◽  
Fluorescent Microscopy ◽  
Type I ◽  
Dense Granules ◽  
Specific Targeting

Besides α-granules and dense granules, which play critical roles in and beyond hemostasis, circulating blood platelets and their precursor cells megakaryocytes contain lysosomes, the contents of which are also secreted during platelet activation. In their delivery to the lysosome, acid hydrolases bearing phosphomannosyl residues are trafficked from the trans-Golgi network to the acidic late-endosomal compartment via the mannose 6-phosphate receptor (M6PR) pathway. To determine the role of M6PR-specific targeting of lysosomal enzymes in platelet function, platelet parameters were investigated in M6pr-/- mice lacking the 46-kDa M6PR, the physiological role of which is unclear. M6pr-/- mice had normal platelet count but displayed an increased number of distinct proplatelet-like cells compared to control mice, as determined by immunofluorescent microscopy. Moreover, transmission electron microscopy revealed the presence of abnormal membrane tubulations, elongated and electron-dense granules, and large vacuole-like structures within resting M6pr-/- platelets. M6pr-/- platelets expressed normally major glycoproteins on their surface and von Willebrand factor and fibrinogen in their α-granules. M6pr-/- mice were hyper-thrombotic, as assessed by tail bleeding time, and M6pr-/- platelets adhered to type I collagen with a significantly greater propensity than control platelets under arterial shear in in vitro flow experiments. Heparanase, an endo-β-glucuronidase that cleaves extracellular matrix heparan sulfate proteoglycans, is the most abundant lysosomal enzyme in platelets. Thus, its contribution to the phenotype of M6pr-/- mice was investigated further. Heparanase expression was decreased in the bone marrow megakaryocytes and blood platelets of M6pr-/- mice and increased in M6pr-/- plasma, as evidenced by immunoblot and fluorescent microscopy analysis, consistent with its mistargeting in the absence of M6PR. Interestingly, pharmacological inhibition of heparanase with OGT 2115 normalized the adhesion of M6pr-/- platelets to collagen in vitro, indicating that increased plasma heparanase contributes to the thrombotic phenotype of M6pr-/- mice. Taken together, the data suggest that the M6PR-specific targeting of lysosomal heparanase plays a critical role in platelet function, thereby regulating hemostasis. Disclosures No relevant conflicts of interest to declare.

Development Of 3D Models For Studying Megakaryopoiesis In Vitro

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 3696-3696
Author(s):  
Lindsay Wray ◽  
Christian A Di Buduo ◽  
David L. Kaplan ◽  
Alessandra Balduini
Keyword(s):  
Mechanical Properties ◽  
Bone Marrow ◽  
Extracellular Matrix ◽  
Endothelial Cells ◽  
Peripheral Blood ◽  
Platelet Production ◽  
Vascular Niche ◽  
Proplatelet Formation ◽  
Bone Marrow Vascular Niche

Abstract Introduction Silk fibroin, derived from Bombyx mori silkworm cocoons, is used extensively in biomaterials and regenerative medicine. The useful characteristics of this protein include self-assembly, robust mechanical properties, biocompatibility and biodegradability. Moreover, silk can be enhanced through a variety of chemical modifications that affect cell attachment, growth and differentiation. Thrombocytopenia occurs when a patient suffers from an abnormally low platelet count in the peripheral blood; usually a result of disease, trauma, or cancer treatment. To treat these patients, it is estimated that two million platelet transfusions are performed in the U.S. each year. This high demand for platelets has created a clinical demand for studying the causes of thrombocytopenia and alternative routes for treatment. Platelets are anuclear cells that are released into the bloodstream in the bone marrow by megakaryocytes via the extension of long filaments called proplatelets. It is hypothesized that platelet production from megakaryocytes is regulated by environmental factors at the site of bone marrow vascular niche. Studies of megakaryopoiesis are typically performed on extracellular matrix protein-coated culture plates and transwell membranes. While these initial studies have provided invaluable insight into the process of megakaryopoiesis, the goal of the present project was to create a bone marrow model that mimics the vascular niche for functional in vitro platelet production. We hypothesized that a silk-based in vitro tissue model would allow the effects of substrate surface properties and endothelial co-culture on megakaryopoiesis to be studied in a holistic manner, thereby enabling further elucidation of the mechanisms involved in the process of platelet production. Results In order to more closely mimic the bone marrow vascular niche structure, a porous silk sponge was assembled around the silk vessel-like tubes. Megakarycytes seeded in the porous silk sponge migrated toward the silk tube and released platelets into the tube lumen. The perfusion bioreactor moved the platelets into the platelet collecting bags. After perfusion the platelets were collected and analyzed by flow cytometry. The bioreactor platelets exhibited similar morphology, CD41 positive staining, and activation compared to peripheral blood platelet controls. Megakaryocyte attachment and proplatelet formation through the silk vascular wall were improved by altering the silk properties. Silk functionalized by entrapping extracellular matrix proteins within the tube membrane resulted in increased megakaryocyte attachment and proplatelet compared to unfunctionalized silk tube controls. Silk surface roughness improved megakaryocyte attachment compared to the control but did not affect proplatelets. Decreasing the silk stiffness improved proplatelets, but did not significantly affect megakaryocyte attachment. Co-culture with endothelial cells improved megakaryocyte attachment while maintaining a high level of proplatelet formation. Additionally, megakaryocyte and endothelial cell co-culture on the silk vessel model resulted in an icreased platelet production compared to megakaryocytes cultured alone. Conclusions The goal of this project was to develop an in vitro model of megakaryopoiesis using a tissue engineering approach. Using human megakaryocytes and endothelial cells, we demonstrate the following advanced features of the silk-based model: (1) immobilization of extracellular matrix components within the membrane, (2) tunable surface topography, (3) tunable mechanical properties, (4) physiologically relevant thickness for appropriate proplatelet extension, and (5) controlled localization of a vascular endothelium. Thus, by functionalizing silk, we can control megakaryocyte function on silk. The broader impact of this work offers a versatile new tool for studying megakaryocyte development and platelet production in vitro. Disclosures: No relevant conflicts of interest to declare.

A novel role for PECAM-1 in megakaryocytokinesis and recovery of platelet counts in thrombocytopenic mice

Blood ◽  
2007 ◽  
Vol 109 (10) ◽  
pp. 4237-4244 ◽  
Author(s):  
Tarvinder S. Dhanjal ◽  
Caroline Pendaries ◽  
Ewan A. Ross ◽  
Mark K. Larson ◽  
Majd B. Protty ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Spatial Localization ◽  
Matrix Proteins ◽  
Platelet Production ◽  
Stromal Microenvironment ◽  
Proplatelet Formation ◽  
Stromal Cell Derived Factor ◽  
Deficient Mice

Abstract During thrombopoiesis, maturing megakaryocytes (MKs) migrate within the complex bone marrow stromal microenvironment from the proliferative osteoblastic niche to the capillary-rich vascular niche where proplatelet formation and platelet release occurs. This physiologic process involves proliferation, differentiation, migration, and maturation of MKs before platelet production occurs. In this study, we report a role for the glycoprotein PECAM-1 in thrombopoiesis. We show that following induced thrombocytopenia, recovery of the peripheral platelet count is impaired in PECAM-1–deficient mice. Whereas MK maturation, proplatelet formation, and platelet production under in vitro conditions were unaffected, we identified a migration defect in PECAM-1–deficient MKs in response to a gradient of stromal cell–derived factor 1 (SDF1), a major chemokine regulating MK migration within the bone marrow. This defect could be explained by defective PECAM-1−/− MK polarization of the SDF1 receptor CXCR4 and an increase in adhesion to immobilized bone marrow matrix proteins that can be explained by an increase in integrin activation. The defect of migration and polarization was confirmed in vivo with demonstration of altered spatial localization of MKs within the bone marrow in PECAM-1–deficient mice, following immune-induced thrombocytopenia. This study identifies a novel role for PECAM-1 in regulating MK migration and thrombopoiesis.

Production of functional platelets by differentiated embryonic stem (ES) cells in vitro

Blood ◽  
2003 ◽  
Vol 102 (12) ◽  
pp. 4044-4051 ◽  
Author(s):  
Tetsuro-Takahiro Fujimoto ◽  
Satoshi Kohata ◽  
Hidenori Suzuki ◽  
Hiroshi Miyazaki ◽  
Kingo Fujimura
Keyword(s):  
Stromal Cells ◽  
Culture Medium ◽  
Es Cells ◽  
Blood Platelets ◽  
Embryonic Stem ◽  
Clinical Applications ◽  
Platelet Production ◽  
Transmission Electron ◽  
Second Wave

Abstract Megakaryocytes and functional platelets were generated in vitro from murine embryonic stem (ES) cells with the use of a coculture system with stromal cells. Two morphologically distinctive megakaryocytes were observed sequentially. Small megakaryocytes rapidly produced proplatelets on day 8 of the differentiation, and large hyperploid megakaryocytes developed after day 12, suggesting primitive and definitive megakaryopoiesis. Two waves of platelet production were consistently observed in the culture medium. A larger number of platelets was produced in the second wave; 104 ES cells produced up to 108 platelets. By transmission electron microscopy, platelets from the first wave were relatively rounder with a limited number of granules, but platelets from the second wave were discoid shaped with well-developed granules that were indistinguishable from peripheral blood platelets. ES-derived platelets were functional since they bound fibrinogen, formed aggregates, expressed P-selectin upon stimulation, and fully spread on immobilized fibrinogen. These results show the potential utility of ES-derived platelets for clinical applications. Furthermore, production of gene-transferred platelets was achieved by differentiating ES cells that were transfected with genes of interest. Overexpression of the cytoplasmic domain of integrin β3 in the ES-derived platelets prevented the activation of αIIbβ3, demonstrating that this system will facilitate functional platelet studies. (Blood. 2003;102:4044-4051)

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