Rheumatoid arthritis, systemic lupus erythematosus and primary Sjögren's syndrome shared megakaryocyte expansion in peripheral blood

OBJECTIVES

Rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS) share many clinical manifestations and serological features. The aim of this study was to identify the common transcriptional profiling and composition of immune cells in peripheral blood in these autoimmune diseases (ADs).

METHODS

We analysed bulk RNA-seq data for enrichment of biological processes, transcription factors (TFs) and deconvolution-based immune cell types from peripheral blood mononuclear cells (PBMCs) in 119 treatment-naive patients (41 RA, 38 pSS, 28 SLE and 12 polyautoimmunity) and 20 healthy controls. The single-cell RNA-seq (scRNA-seq) and flow cytometry had been performed to further define the immune cell subsets on PBMCs.

RESULTS

Similar transcriptional profiles and common gene expression signatures associated with nucleosome assembly and haemostasis were identified across RA, SLE, pSS and polyautoimmunity. Distinct TF ensembles and gene regulatory network were mainly enriched in haematopoiesis. The upregulated cell-lineage-specific TFs PBX1, GATA1, TAL1 and GFI1B demonstrated a strong gene expression signature of megakaryocyte (MK) expansion. Gene expression-based cell type enrichment revealed elevated MK composition, specifically, CD41b⁺CD42b⁺ and CD41b⁺CD61⁺ MKs were expanded, further confirmed by flow cytometry in these ADs. In scRNA-seq data, MKs were defined by TFs PBX1/GATA1/TAL1 and pre-T-cell antigen receptor gene, PTCRA. Cellular heterogeneity and a distinct immune subpopulation with functional enrichment of antigen presentation were observed in MKs.

CONCLUSIONS

The identification of MK expansion provided new insights into the peripheral immune cell atlas across RA, SLE, pSS and polyautoimmunity. Aberrant regulation of the MK expansion might contribute to the pathogenesis of these ADs.

Characterization of Cellular Heterogeneity and an Immune Subpopulation of Human Megakaryocytes

Megakaryocytes (MKs) and their progeny platelets function in a variety of biological processes including coagulation, hemostasis, inflammation, angiogenesis, and innate immunity. However, the divergent developmental and cellular landscape of adult MKs remains mysterious. Here, by deriving the single-cell transcriptomic profiling of MKs from human adult bone marrow (BM), cellular heterogeneity within MKs is unveiled and an MK subpopulation with high enrichment of immune-associated genes is identified. By performing the dynamic single-cell transcriptomic landscape of human megakaryopoiesis in vitro, it is found that the immune signatures of MKs can be traced back to the progenitor stage. Furthermore, two surface markers, CD148 and CD48, are identified for mature MKs with immune characteristics. At the functional level, these CD148+ CD48+ MKs can respond rapidly to immune stimuli both in vitro and in vivo, exhibit high-level expression of immune receptors and mediators, and may function as immune-surveillance cells. The findings uncover the cellular heterogeneity and a novel immune subset of human adult MKs and should greatly facilitate the understanding of the divergent functions of MKs under physiological and pathological conditions.

COVID-19 immune features revealed by a large-scale single-cell transcriptome atlas

A dysfunctional immune response in coronavirus disease 2019 (COVID-19) patients is a recurrent theme impacting symptoms and mortality, yet a detailed understanding of pertinent immune cells is not complete. We applied single-cell RNA sequencing to 284 samples from 196 COVID-19 patients and controls and created a comprehensive immune landscape with 1.46 million cells. The large dataset enabled us to identify that different peripheral immune subtype changes are associated with distinct clinical features, including age, sex, severity, and disease stages of COVID-19. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA was found in diverse epithelial and immune cell types, accompanied by dramatic transcriptomic changes within virus-positive cells. Systemic upregulation of S100A8/A9, mainly by megakaryocytes and monocytes in the peripheral blood, may contribute to the cytokine storms frequently observed in severe patients. Our data provide a rich resource for understanding the pathogenesis of and developing effective therapeutic strategies for COVID-19.

Cytokine Profiling in Myeloproliferative Neoplasms: Overview on Phenotype Correlation, Outcome Prediction, and Role of Genetic Variants

Among hematologic malignancies, the classic Philadelphia-negative chronic myeloproliferative neoplasms (MPNs) are considered a model of inflammation-related cancer development. In this context, the use of immune-modulating agents has recently expanded the MPN therapeutic scenario. Cytokines are key mediators of an auto-amplifying, detrimental cross-talk between the MPN clone and the tumor microenvironment represented by immune, stromal, and endothelial cells. This review focuses on recent advances in cytokine-profiling of MPN patients, analyzing different expression patterns among the three main Philadelphia-negative (Ph-negative) MPNs, as well as correlations with disease molecular profile, phenotype, progression, and outcome. The role of the megakaryocytic clone as the main source of cytokines, particularly in myelofibrosis, is also reviewed. Finally, we report emerging intriguing evidence on the contribution of host genetic variants to the chronic pro-inflammatory state that typifies MPNs.

Cytokine Profiling in Myeloproliferative Neoplasms: Overview on Phenotype Correlation, Outcome Prediction, and Role of Genetic Variants

Among hematologic malignancies, the classic Philadelphia-negative chronic myeloproliferative neoplasms (MPNs) are considered a model of inflammation-related cancer development. In this context, the use of immune-modulating agents has recently expanded the MPN therapeutic scenario. Cytokines are key mediators of an auto-amplifying, detrimental cross-talk between the MPN clone and the tumor microenvironment represented by immune, stromal, and endothelial cells. This review focuses on recent advances in cytokine-profiling of MPN patients, analyzing different expression patterns among the three main Philadelphia-negative (Ph-negative) MPNs, as well as correlations with disease molecular profile, phenotype, progression, and outcome. The role of the megakaryocytic clone as the main source of cytokines, particularly in myelofibrosis, is also reviewed. Finally, we report emerging intriguing evidence on the contribution of host genetic variants to the chronic pro-inflammatory state that typifies MPNs.

Effect of intranasal instillation of Escherichia coli on apoptosis of spleen cells in diet-induced-obese mice

Splenic immune function was enhanced in diet-induced-obese (DIO) mice caused by Escherichia coli. The changes in spleen function on apoptosis were still unknown. Two hundred mice in groups Lean-E. coli and DIO-E. coli were intranasal instillation of E. coli. And another two hundred mice in groups Lean-PBS and DIO-PBS were given phosphate-buffered saline (PBS). Subsequently, spleen histology was analyzed. Then the rates of spleen cell (SC) apoptosis, and expression of the genes and proteins of Bcl-2, Bax, caspase-3 and caspase-9 were quantified in each group at 0 h (uninfected), 12 h, 24 h, and 72 h postinfection. The SC apoptosis rates of the DIO-E. coli groups were lower than those of the DIO-PBS groups at 12, 24 and 72 h (p < 0.05). Anti-apoptotic Bcl-2 expression gene and protein of the DIO-E. coli groups were higher than those of the DIO-PBS groups (p < 0.05). Gene expressions of pro-apoptotic Bax, caspase-3 and caspase-9 of the DIO-E. coli groups were lower than those of DIO-PBS groups at 12, 24 and 72 h (p < 0.05). The SC apoptosis rates of the Lean-E. coli groups were higher than those of the Lean- PBS groups at 12 h and 24 h (p < 0.05). Interestingly, the SC apoptosis rates in the DIO-E. coli groups were lower than those of the Lean-E. coli groups at 12 h (p < 0.05). In conclusion, our results suggested that the DIO mice presented stronger anti-apoptotic abilities than Lean mice in non-fatal acute pneumonia induced by E. coli infection, which is more conducive to protecting the spleen and improving the immune defense ability of the body.

Clinical impact of dysplastic changes in acquired aplastic anemia: A systematic study of bone marrow biopsies in children and adults

Aplastic anemia (AA) is a rare disorder characterized by suppression of bone marrow function, which can progress to myelodysplastic syndrome (MDS) or to acute myeloid leukemia (AML). To determine if there are characteristics in bone marrow biopsies in children and adults previously diagnosed with acquired AA, which could predict progression to MDS, we evaluated 118 hypocellular bone marrow biopsies from adults (76 patients) and children (42) diagnosed initially with acquired AA previously to any treatment. Histology was reviewed according to a detailed protocol including Bennett and Orazi criteria for hypocellular myelodysplastic syndrome (h-MDS) and Bauman et al. criteria for refractory cytopenia of childhood (RCC). Twelve patients (10.2%; 6 children and 6 adults) progressed to MDS after a median time of 56 months. Criteria described by Bennett and Orazi suggestive of h-MDS in bone marrow biopsies were detected in 16 cases (13.5%; 8 adults and 8 children), and none in patients that progressed to MDS/AML. Twenty adults' biopsies (26.3%) had the histological criteria used for the diagnosis of pediatric RCC, and none showed MDS/AML evolution. Ten children (23.8%) were reclassified morphologically as RCC, and only one progressed to MDS. In this population with acquired aplastic anemia (AAA), no histological/immunohistochemical (H/IHC) bone marrow findings could discriminate patients with higher risk for myeloid clonal progression, which questions the diagnosis of h-MDS/RCC based only on the finding of dysplasia in the cases without increased blasts and/or the characteristic genetic abnormalities.

Activation of toll-like receptors 2 and 4 on CD34+ cells increases human megakaryo/thrombopoiesis induced by thrombopoietin

BACKGROUND

Platelet Toll-like receptor (TLR)2/4 are key players in amplifying the host immune response; however, their role in human megakaryo/thrombopoiesis has not yet been defined.

OBJECTIVES

We evaluated whether Pam3CSK4 or lipopolysaccharide (LPS), TLR2/4 ligands respectively, modulate human megakaryocyte development and platelet production.

METHODS

CD34+ cells from human umbilical cord were stimulated with LPS or Pam3CSK4 with or without thrombopoietin (TPO).

RESULTS

CD34+ cells and megakaryocytes express TLR2 and TLR4 at both RNA and protein level; however, direct stimulation of CD34+ cells with LPS or Pam3CSK4 had no effect on cell growth. Interestingly, both TLR ligands markedly increased TPO-induced CD34+ cell proliferation, megakaryocyte number and maturity, proplatelet and platelet production when added at day 0. In contrast, this synergism was not observed when TLR agonists were added 7 days after TPO addition. Interleukin-6 (IL-6) release was observed upon CD34+ or megakaryocyte stimulation with LPS or Pam3CSK4 but not with TPO and this effect was potentiated in combination with TPO. The increased proliferation and IL-6 production induced by TPO + LPS or Pam3CSK4 were suppressed by TLR2/4 or IL-6 neutralizing antibodies, as well as by PI3K/AKT and nuclear factor-κB inhibitors. Additionally, increased proplatelet and platelet production were associated with enhanced nuclear translocation of nuclear factor-E2. Finally, the supernatants of CD34+ cells stimulated with TPO+LPS-induced CFU-M colonies.

CONCLUSIONS

Our data suggest that the activation of TLR2 and TLR4 in CD34+ cells and megakaryocytes in the presence of TPO may contribute to warrant platelet provision during infection episodes by an autocrine IL-6 loop triggered by PI3K/NF-κB axes.

Primary myelofibrosis marrow-derived CD14+/CD34- monocytes induce myelofibrosis-like phenotype in immunodeficient mice and give rise to megakaryocytes

To confirm that neoplastic monocyte-derived collagen- and fibronectin-producing fibrocytes induce bone marrow (BM) fibrosis in primary myelofibrosis (PMF), we injected PMF BM-derived fibrocyte-precursor CD14⁺/CD34^- monocytes into the tail vein of NOD-SCID-γ (NSG) mice. PMF BM-derived CD14⁺/CD34^- monocytes engrafted and induced a PMF-like phenotype with splenomegaly, myeloid hyperplasia with clusters of atypical megakaryocytes, persistence of the JAK2^V617F mutation, and BM and spleen fibrosis. As control we used normal human BM-derived CD14⁺/CD34^- monocytes. These monocytes also engrafted and gave rise to normal megakaryocytes that, like PMF CD14⁺/CD34^--derived megakaryocytes, expressed HLA-ABC and human CD42b antigens. Using 2 clonogenic assays we confirmed that PMF and normal BM-derived CD14⁺/CD34^- monocytes give rise to megakaryocyte colony-forming cells, suggesting that a subpopulation BM monocytes harbors megakaryocyte progenitor capacity. Taken together, our data suggest that PMF monocytes induce myelofibrosis-like phenotype in immunodeficient mice and that PMF and normal BM-derived CD14⁺/CD34^- monocytes give rise to megakaryocyte progenitor cells.

Rps14, Csnk1a1 and miRNA145/miRNA146a deficiency cooperate in the clinical phenotype and activation of the innate immune system in the 5q- syndrome

RPS14, CSNK1A1, and miR-145 are universally co-deleted in the 5q- syndrome, but mouse models of each gene deficiency recapitulate only a subset of the composite clinical features. We analyzed the combinatorial effect of haploinsufficiency for Rps14, Csnk1a1, and miRNA-145, using mice with genetically engineered, conditional heterozygous inactivation of Rps14 and Csnk1a1 and stable knockdown of miR-145/miR-146a. Combined Rps14/Csnk1a1/miR-145/146a deficiency recapitulated the cardinal features of the 5q- syndrome, including (1) more severe anemia with faster kinetics than Rps14 haploinsufficiency alone and (2) pathognomonic megakaryocyte morphology. Macrophages, regulatory cells of erythropoiesis and the innate immune response, were significantly increased in Rps14/Csnk1a1/miR-145/146a deficient mice as well as in 5q- syndrome patient bone marrows and showed activation of the innate immune response, reflected by increased expression of S100A8, and decreased phagocytic function. We demonstrate that Rps14/Csnk1a1/miR-145 and miR-146a deficient macrophages alter the microenvironment and induce S100A8 expression in the mesenchymal stem cell niche. The increased S100A8 expression in the mesenchymal niche was confirmed in 5q- syndrome patients. These data indicate that intrinsic defects of the 5q- syndrome hematopoietic stem cell directly alter the surrounding microenvironment, which in turn affects hematopoiesis as an extrinsic mechanism.

Human megakaryocytes possess intrinsic antiviral immunity through regulated induction of IFITM3

Evolving evidence indicates that platelets and megakaryocytes (MKs) have unexpected activities in inflammation and infection; whether viral infections upregulate biologically active, antiviral immune genes in platelets and MKs is unknown, however. We examined antiviral immune genes in these cells in dengue and influenza infections, viruses that are global public health threats. Using complementary biochemical, pharmacological, and genetic approaches, we examined the regulation and function of interferon-induced transmembrane protein 3 (IFITM3), an antiviral immune effector gene not previously studied in human platelets and MKs. IFITM3 was markedly upregulated in platelets isolated from patients during clinical influenza and dengue virus (DENV) infections. Lower IFITM3 expression in platelets correlated with increased illness severity and mortality in patients. Administering a live, attenuated DENV vaccine to healthy subjects significantly increased platelet IFITM3 expression. Infecting human MKs with DENV selectively increased type I interferons and IFITM3. Overexpression of IFITM3 in MKs was sufficient to prevent DENV infection. In naturally occurring, genetic loss-of-function studies, MKs from healthy subjects harboring a homozygous mutation in IFITM3 (rs12252-C, a common single-nucleotide polymorphism in areas of the world where DENV is endemic) were significantly more susceptible to DENV infection. DENV-induced MK secretion of interferons prevented infection of bystander MKs and hematopoietic stem cells. Thus, viral infections upregulate IFITM3 in human platelets and MKs, and IFITM3 expression is associated with adverse clinical outcomes. These observations establish, for the first time, that human MKs possess antiviral functions, preventing DENV infection of MKs and hematopoietic stem cells after local immune signaling.

Autoantibody against integrin αv β3 contributes to thrombocytopenia by blocking the migration and adhesion of megakaryocytes

Essentials The pathogenesis of immune thrombocytopenia (ITP) has not been fully clarified. We analyzed the role of anti-αvβ3 autoantibody in the pathogenesis of ITP in patients. Anti-αvβ3 autoantibody impeded megakaryocyte migration and adhesion to the vascular niche. Anti-αv β3 autoantibody potentially contributes to the pathogenesis of refractory ITP.

SUMMARY

Background The pathogenesis of immune thrombocytopenia (ITP) has not been fully clarified. Anti-αvβ3 integrin autoantibody is detected in chronic ITP patients, but its contribution to ITP is still unclear. Objectives To clarify the potential role of anti-αvβ3 integrin autoantibody in chronic ITP and the related mechanism. Methods Relationship between levels of anti-αvβ3 autoantibody and platelets in chronic ITP patients was evaluated. The influence of anti-αvβ3 antibody on megakaryocyte (MK) survival, differentiation, migration and adhesion was assessed, and the associated signal pathways were investigated. Platelet recovery and MKs' distribution were observed in an ITP mouse model pretreated with different antibodies. Result In this study, we showed that the anti-αvβ3 autoantibody usually coexists with anti-αIIbβ3 autoantibody in chronic ITP patients, and patients with both autoantibodies have lower platelets. In in vitro studies, we showed that the anti-αvβ3 antibody had no significant effect on the survival and proliferation of MKs, whereas it decreased formations of proplatelet significantly. Anti-αvβ3 antibody impeded stromal cell derived facor-1 alpha (SDF-1α)- mediated migration and inhibited the phosphorylation of protein kinase B. Anti-αvβ3 antibody significantly inhibited MKs' adhesion to endothelial cells and Fibrogen. The phosphorylation of focal adhesion kinase and proto-oncogene tyrosine-protein kinase Src induced by adhesion was inhibited when MKs were pretreated with anti-αvβ3 antibody. In in vivo studies, we showed that injection with anti-αv antibody delayed platelet recovery in a mouse model of ITP. Conclusions These findings demonstrate that the autoantibody against integrin αv β3 may aggravate thrombocytopenia in ITP patients by impeding MK migration and adhesion to the vascular niche, which provides new insights into the pathogenesis of ITP.

Thrombocytopenia and Anemia with Anti-c-Mpl antibodies Effectively Treated with Cyclosporine in a Patient with Rheumatoid Arthritis and Chronic Renal Failure

A 61-year-old woman with rheumatoid arthritis who was undergoing hemodialysis for end-stage renal failure was transferred to our hospital due to severe thrombocytopenia and anemia. A bone marrow biopsy showed the complete absence of megakaryocytes and erythroblasts. Cyclosporine treatment resulted in the improvement of her megakaryocyte and erythroblast levels, and a decrease in her serum level of anti-c-Mpl (thrombopoietin receptor) antibodies. After this initial improvement, her anemia progressively worsened, despite the continuous administration of immunosuppressive therapy with cyclosporine. Her platelet and leukocyte counts remained stable. This is the first report of a probable case of anti-c-Mpl antibody-associated pure red cell aplasia and acquired amegakaryocytic thrombocytopenic purpura.

Semaphorin 7A inhibits platelet production from CD34+ progenitor cells

BACKGROUND

The multifunctional protein semaphorin 7A (Sema7A) may have regulatory effects on blood cell differentiation via its receptors β1-integrin and plexin C1. As thrombocytopenia can be treated with transfusion of ex vivo CD34(+) cell-derived megakaryocytes, we investigated the effect of Sema7A on differentiation of CD34(+) progenitor cells into megakaryocytes and platelets.

METHODS

Megakaryocytes and platelets were differentiated with a specific cytokine cocktail (CC) from CD34(+) progenitor cells in the presence or absence of Sema7A. Expression of cell markers CD41, CD42a and CD61 or detection of the activation of the signal mediator focal adhesion kinase (FAK) was performed by flow cytometry, cytokine secretion by Luminex technology, and megakaryocyte cell density and morphology by microscopic studies. Sema7A levels in vivo were assessed by real-time PCR and ELISA in hematological patients undergoing chemotherapy.

RESULTS

CD34(+) progenitor cells expressed the receptors for Sema7A. Expression of CD41, CD42a and CD61 was markedly reduced in the presence of Sema7A, after CC-dependent platelet production from CD34(+) progenitor cells. As revealed by microscopic analysis, megakaryocyte cell density was significantly lower in the presence of Sema7A as compared with controls. Blocking of CD29 abrogated the Sema7A-mediated inhibition. Sema7A activated FAK in CD34(+) progenitor cells and significantly increased secretion of the proinflammatory cytokines IL-6, IL-8 and GM-CSF. Finally, Sema7A levels were up-regulated in 50% of patients after chemotherapy.

CONCLUSIONS

Sema7A markedly reduces the production rates of megakaryocytes and platelets from CD34(+) progenitor cells. Hence, up-regulation of Sema7A may be a major risk factor for a reduced platelet repopulation after hematopoietic stem cell transplantation.

[Detecting anti-megakaryocyte antibodies in serum of systemic lupus erythematosus patients by indirect immunofluorescence]

This study was purposed to investigate the mechanism of thrombocytopenia in patients with systemic lupus erythematosus (SLE) through detecting anti-megakaryocyte antibodies in SLE patients. The serum anti-megakaryocyte antibodies in 36 SLE cases with thrombocytopenia were detected by using indirect immunofluorescence, the detected results were compared with detected results of 30 SLE cases without thrombocytopenia and 30 healthy persons. The results showed that the positive incidences of anti-megakaryocyte antibody in serum of 36 SLE cases with thrombocytopenia, 30 SLE cases without thrombocytopenia and 30 healthy persons were 19.4% (7/36), 6.7% (2/30) and 3.3% (1/30) respectively. As compared with SLE patients without thrombocytopenia and healthy persons, SLE patients with thrombocytopenia had higher incidence of anti-megakaryocyte antibodies, moreover there was significant difference between SLE patients with thrombocytopenia and healthy persons (p < 0.05), while there was no significant difference between SLE patients with or without thrombocytopenia (p > 0.05). It is concluded that autoantibodies against megakaryocytes exist in SLE patients and may partially contribute to the incidence of thrombocytopenia in SLE patients. The detection of anti-megakaryocyte antibodies with a enough case number is needed to make a final conclusion on thrombocytopenia pathogenesis in SLE.

Platelet alpha-granules: basic biology and clinical correlates

alpha-Granules are essential to normal platelet activity. These unusual secretory granules derive their cargo from both regulated secretory and endocytotic pathways in megakaryocytes. Rare, inheritable defects of alpha-granule formation in mice and man have enabled identification of proteins that mediate cargo trafficking and alpha-granule formation. In platelets, alpha-granules fuse with the plasma membrane upon activation, releasing their cargo and increasing platelet surface area. The mechanisms that control alpha-granule membrane fusion have begun to be elucidated at the molecular level. SNAREs and SNARE accessory proteins that control alpha-granule secretion have been identified. Proteomic studies demonstrate that hundreds of bioactive proteins are released from alpha-granules. This breadth of proteins implies a versatile functionality. While initially known primarily for their participation in thrombosis and hemostasis, the role of alpha-granules in inflammation, atherosclerosis, antimicrobial host defense, wound healing, angiogenesis, and malignancy has become increasingly appreciated as the function of platelets in the pathophysiology of these processes has been defined. This review will consider the formation, release, and physiologic roles of alpha-granules with special emphasis on work performed over the last decade.

[Correlation between CD34+CD61+ megakaryocyte precursors and platelet engraftment in allogeneic hematopoietic stem cell transplantation]

This study was purposed to investigate the correlation between the dose infused megakaryocytic precursors (CD34+, CD34+CD61+) and recovery time of platelet count following an allogeneic PBSCT and/or BMT through quantitative detection of CD34+ and its subpopulation in peripheral blood and BM mobilized by G-CSF. 24 patients with various hematologic malignancies received PBSCT/BMT from their HLA matched or unrelated donors and haploidentical siblings in April-December 2007. 20 evaluated patients were divided into 2 groups according to different transplant schemes. HLA matched group received PBSCT regime and haploidentical group received PBSCT combined with BMT. CD34+CD61+ subpopulations in sample from patients receiving PBSCT/BMT were measured by flow cytometry immediately or storage over night. The results showed that the median number of infused CD34+, CD34+CD61+ and CD34-CD61+ cells in haploidentical group were 6.24x10(6)/kg (1.53-20.48), 66.19x10(4)/kg (8.16-493.83), and 34.38x10(6)/kg (14.71-109.16) respectively, in HLA matched group those were 4.88x10(6)/kg (1.00-8.24), 14.16x10(4)/kg (11.63-96.87), and 13.50x10(6)/kg (1.74-35.61), respectively. Median days of ANCs>0.5x10(9)/L and platelets>20x10(9)/L were 18.5 (11.0-29.0) days and 16.5 (9.0-35.0) days in haploidentical group respectively; in HLA matched group those were 14.5 (9.0-24.0) and 10.5 (6.0-37.0) respectively. A significance difference of median days for ANC engraftment presented between two groups (p=0.048). There was no significant difference of time for platelet engraftment between 2 groups. For patients with CD34+ cell dose>2x10(6)/kg there was significant difference of time of platelet engraftment between HLA matched and haploidentical groups (p=0.006). The number of CD34+CD61+ cells infused in 12 haploidentical patients or in 8 HLA matched patients were much better correlated with the time of platelet recovery up to 20x10(9)/L than that of number of CD34+ cells infused in total 20 patients (r=-0.768 and p=0.004 for haploidentical CD34+CD61+ cells, r=-0.747 and p=0.033 for HLA matched CD34+ CD61+ cells, r=-0.449 and p=0.047 for CD34+ cells). There was an inverse correlation between the number of infused CD34+ CD61+ cells and time of platelet engraftment. Therefore, as the number of CD34+ CD61+ cells increased, duration of platelet engraftment (time to reach platelet count of 20x10(9)/L) shortened significantly. It is concluded that the determining the number of megakaryocytic precursor by flow cytometry may predict the platelet reconstitutive capacity of the allogeneic hematopoietic stem cell transplantation, which is in haploidentical PBSCT and in BMT.

[hNUDC promotes proliferation and differentiation of megakaryocytopoiesis on human CD341+ cells]

AIM

aTo study the effect of human nuclear distribution C èhNUDCé on human megakaryocyte proliferation and differentiation from cord blood CD34(+) cells in vitro.

METHODS

aHuman CD34(+) cells were isolated using the Dynal CD34 Progenitor Cell Selection System from umbilical cord blood. The CD34(+) cells were then cultured in serum free methylcellulose semi-solid media, the morphologic aspects and number of small, medium and large CFU-MK colonies were observed and scored on the day12 by microscopy analysis. The CD34(+) cells were cultured in serum free liquid media, cells were removed on day 10 and formation of CD41(+) in human megakaryocyte and its DNA polyploidization of nuclear were analyzed on a FACsort flowcytometer.

RESULTS

ahNUDC supported the formation of small and medium CFU-MK colony in serum free semi-solid media. Furthermore, hNUDC induced a remarkable increase in expression of the megakaryocyte cell surface marker CD41(+) and stimulated the CD41(+) DNA polyploidization more effectively than TPO.

CONCLUSION

hNUDC may play an important role in megakaryocyte proliferation and differentiation.

Effects of inhibitor of Src kinases, SU6656, on differentiation of megakaryocytic progenitors and activity of alpha1,6-fucosyltransferase

alpha1,6-fucosyltransferase (FUT8) attaches fucose residues via an alpha1,6 linkage to the innermost N-acetylglucosamine residue of N-linked glycans. Glycans with this type of structure are present in GpIIb/GpIIIa complex (CD41a) which is present on megakaryocytes (Mks) and platelets. CD41a is the earliest marker of megakaryocytopoiesis. The aim of this study was to analyse the morphology, phenotype, ploidy level and activity of FUT8 during induced differentiation/maturation of Mk progenitor cells in ex vivo culture. We used SU6656, a selective inhibitor of Src tyrosine kinases, as differentiation-inducing agent for Mks. The addition of SU6656 to the culture system of megakaryocytic progenitors from cord blood CD34(+) cells and Meg-01 cell line induced their maturation towards later stages of Mk differentiation with increased activity of FUT8. We suggest FUT8 as a candidate for an early marker of differentiation and possibly of the ploidy level of Mks. We confirm a special status of FUT8 in megakaryocytopoiesis.

[Preparation of monoclonal antibody against human hNudC and its expression in human megakaryocytes]

AIM

To prepare and characterize the monoclonal antibody (mAB) against human nuclear distribution C (hNudC).

METHODS

The coding region of hNudC was amplified from human embryo liver tissue and the recombinant prokaryotic expression vector pET28b was constructed. hNudC protein was expressed as a fusion protein with an N-terminal 6-His tag. The purified recombinant hNudC protein was used to immunize BALB/c mice for preparing mAb. The hybridoma cells produced from mAB were screened by ELISA and the specificity of mAb was analyzed by immunohistochemical staining and Western blot.

RESULTS

Two hybridoma cells (2C16 and 2D8) secreting mAb against hNudC were developed. The isotypes of the two mABs were IgGI and IgM, respectively. ELISA detection showed that the titer of mABs, 2C16 and 2D8 was 1:64, 1:32 in cultured supernatant and 1:1 x 10(5), 1:5 x 10(4) in ascites, respectively. They could specifically bind to recombinant hNudC. The results of immunohistochemical staining and Western blot indicated that mAb could specifically recognize hNudC in human Dami, Meg-01 cell lines and human marrow CD41+ megakaryocytes generated from umbilical core blood.

CONCLUSION

Monoclonal antibodies against hNudC with high titers and specificity have been successfully prepared, which will be useful for assessing the function, native distribution and aberrant expression of hNudC protein.

Comparative, genome-scale transcriptional analysis of CHRF-288-11 and primary human megakaryocytic cell cultures provides novel insights into lineage-specific differentiation

OBJECTIVES

Little is known about the transcriptional events underlying megakaryocytic (Mk) differentiation. We sought to identify genes and pathways previously unassociated with megakaryopoiesis and to evaluate the CHRF-288-11 (CHRF) megakaryoblastic cell line as a model system for investigating megakaryopoiesis.

METHODS

Using DNA microarrays, Q-RT-PCR, and protein-level assays, we compared the dynamic gene expression pattern of phorbol ester-induced differentiation of CHRF cells to cytokine-induced Mk differentiation of human mobilized peripheral blood CD34(+) cells.

RESULTS

Transcriptional patterns of well-known Mk genes were similar between the two systems. CHRF cells constitutively express some early Mk genes including GATA-1. Expression patterns of apoptosis-related genes suggested that increased p53 activity is involved in Mk apoptosis, and this was confirmed by p53-DNA-binding activity data and flow-cytometric analysis of the p53 target gene BBC3. Certain Rho and G-protein-coupled-receptor signaling pathway components were upregulated, including genes not previously associated with Mk cells. Ontological analysis revealed upregulation of defense-response genes, including both known and candidate platelet-derived contributors to inflammation. Upregulation of interferon-responsive genes occurred in the cell line, but not in the primary cells, likely due to a known genetic mutation in the JAK2/STAT5 signaling pathway.

CONCLUSIONS

This analysis of megakaryopoiesis, which integrates dynamic gene expression data with protein abundance and activity assays, has identified a number of genes and pathways that may help govern megakaryopoiesis. Furthermore, the transcriptional data support the hypothesis that CHRF cells resemble an early Mk phenotype and, with certain limitations, exhibit genuine transcriptional features of Mk differentiation upon treatment with phorbol esters.

Sites and kinetics of donor thrombopoiesis following transplantation of whole bone marrow and progenitor subsets

INTRODUCTION

Little is known about the sites and kinetics of thrombopoiesis following bone marrow transplant. The spleen is a site of hematopoiesis in a healthy mouse, and hematopoietic activity increases in response to stress. We hypothesized that the spleen is a major site of early post-transplant thrombopoiesis.

METHODS

We transplanted whole bone marrow (WBM) or lineage depleted progenitor subsets fractionated based on expression of c-kit and Sca-1 from transgenic mice expressing green fluorescent protein into lethally irradiated C57BL/6 recipients. We also transplanted whole bone marrow cells into healthy and splenectomized mice. Post-transplant megakaryopoiesis was assessed by measuring circulating platelet number, percent donor-derived platelets, bone marrow cellularity, splenic weight, megakaryocyte size, and megakaryocyte concentration from hour 3 to day 28 post transplant.

RESULTS

Following transplant, circulating donor-derived platelets were derived only from c-kit expressing subsets. Donor-derived platelets first appeared on post-transplant day five. Splenectomy reduced the number of these earliest circulating platelets. Splenic megakaryopoiesis increased dramatically from day 7-14 post-transplant. However, splenectomy accelerated platelet engraftment during this time frame.

CONCLUSION

Overall, these results demonstrate that the first platelets are produced by c-kit expressing megakaryocyte progenitors in the bone marrow and spleen. After post-transplant day 5, the net effect of the spleen on thrombopoiesis is to slow engraftment due to immune effects or hypersplenism.

CD41+/CD45+Cells Without Acetylcholinesterase Activity Are Immature and a Major Megakaryocytic Population in Murine Bone Marrow

Murine megakaryocytes (MKs) are defined by CD41/CD61 expression and acetylcholinesterase (AChE) activity; however, their stages of differentiation in bone marrow (BM) have not been fully elucidated. In murine lineage-negative (Lin(-))/CD45(+) BM cells, we found CD41(+) MKs without AChE activity (AChE(-)) except for CD41(++) MKs with AChE activity (AChE(+)), in which CD61 expression was similar to their CD41 level. Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs could differentiate into AChE(+), with an accompanying increase in CD41/CD61 during in vitro culture. Both proplatelet formation (PPF) and platelet (PLT) production for Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs were observed later than for Lin(-)/CD41(++)/CD45(+)/AChE(+) MKs, whereas MK progenitors were scarcely detected in both subpopulations. GeneChip and semiquantitative polymerase chain reaction analyses revealed that the Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs are assigned at the stage between the progenitor and PPF preparation phases in respect to the many MK/PLT-specific gene expressions, including beta1-tubulin. In normal mice, the number of Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs was 100 times higher than that of AChE(+) MKs in BM. When MK destruction and consequent thrombocytopenia were caused by an antitumor agent, mitomycin-C, Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs led to an increase in AChE(+) MKs and subsequent PLT recovery with interleukin-11 administration. It was concluded that MKs in murine BM at least in part consist of immature Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs and more differentiated Lin(-)/CD41(++)/CD45(+)/AChE(+) MKs. Immature Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs are a major MK population compared with AChE(+) MKs in BM and play an important role in rapid PLT recovery in vivo.

CD41-YFP mice allow in vivo labeling of megakaryocytic cells and reveal a subset of platelets hyperreactive to thrombin stimulation

OBJECTIVE

Development of a mouse line permitting live imaging of cells expressing CD41/GpIIb as a means to study megakaryopoiesis.

MATERIALS AND METHODS

The gene encoding yellow fluorescent protein (eyfp) was inserted by homologous recombination into embryonic stem cells at the start site of the gpIIb locus. A knockin mouse line, designated CD41-yellow fluorescent protein (YFP), was developed and was characterized by fluorescence microscopy and flow cytometry. Activity of YFP(+) platelets was determined by induction of P-selectin expression in response to thrombin stimulation.

RESULTS

CD41-YFP mice contained YFP-labeled megakaryocytes and platelets, the proportions of which varied, depending on the genotype and individual animal, while lymphoid, myelomonocytic, and erythroid lineages were negative. In addition, a fraction of hematopoietic stem cells and intermediate progenitors expressed YFP at low levels. Crossing CD41-YFP mice with lysozyme green fluorescent protein and globin cyan fluorescent protein mice, followed by in vivo imaging of fetal liver, revealed megakaryocytic cells as a subset distinct from myeloid and erythroid cells. This experiment is also the first to show the distribution of three hematopoietic lineages in a minimally perturbed organ. Surprisingly, analysis of CD41-YFP platelets showed that the YFP(+) subset is more responsive to thrombin stimulation than the YFP(-) subset. Experiments aimed at determining the stability of the YFP(+) platelets showed that after lethal irradiation of CD41-YFP mice, the proportion of labeled platelets in the blood declines more rapidly than the bulk of the platelets.

CONCLUSION

The newly developed mouse line should become useful not only for in vivo imaging experiments of megakaryocytes and platelets, but also for studies on platelet aging and function. Our irradiation experiments suggest that the YFP(+) platelets are enriched for newly made cells because YFP has a shorter half-life than platelets. Therefore, the finding that YFP(+) platelets are more responsive to thrombin stimulation raises the possibility that platelet activity decreases rapidly during physiological aging.

HIV-1 negatively affects the survival/maturation of cord blood CD34(+) hematopoietic progenitor cells differentiated towards megakaryocytic lineage by HIV-1 gp120/CD4 membrane interaction

To investigate the mechanisms involved in the human immunodeficiency virus type 1 (HIV-1)-related thrombocytopenia (TP), human umbilical cord blood (UCB) CD34(+) hematopoietic progenitor cells (HPCs) were challenged with HIV-1(IIIb) and then differentiated by thrombopoietin (TPO) towards megakaryocytic lineage. This study showed that HIV-1, heat-inactivated HIV-1, and HIV-1 recombinant gp120 (rgp120) activated apoptotic process of megakaryocyte (MK) progenitors/precursors and decreased higher ploidy MK cell fraction. All these inhibitory effects on MK survival/maturation and platelets formation were elicited by the interaction between gp120 and CD4 receptor on the cell membrane in the absence of HIV-1 productive infection. In fact, in our experimental conditions, HPCs were resistant to HIV-1 infection and no detectable productive infection was observed. We also evaluated whether the expression of specific cytokines, such as TGF-beta1 and APRIL, involved in the regulation of HPCs and MKs proliferation, was modulated by HIV-1. The specific protein and mRNA detection analysis, during TPO-induced differentiation, demonstrated that HIV-1 upregulates TGF-beta1 and downregulates APRIL expression through the CD4 engagement by gp120. Altogether, these data suggest that survival/differentiation of HPCs committed to MK lineage is negatively affected by HIV-1 gp120/CD4 interaction. This long-term inhibitory effect is also correlated to specific cytokines regulation and it may represent an additional mechanism to explain the TP occurring in HIV-1 patients.

The sticky truth about angiogenesis and thrombospondins

The formation of new blood vessels, a process known as angiogenesis, is important for embryonic development and wound healing as well as the development of cancer and inflammation; therefore, angiogenesis is a valuable target for clinical intervention. Both logic and empiricism suggest that a balance of stimulatory and inhibitory switches is required for orderly formation of blood vessels. Thrombospondins 1 and 2 were among the first natural angiogenesis inhibitors to be identified. However, the cellular origins and mechanisms of action of these important proteins during angiogenesis have remained largely unknown. Studies by Kopp et al., presented in this issue of the JCI, clarify some of these issues by revealing that megakaryocytes and their "sticky" wound-healing progeny, platelets, are important sources of thrombospondins 1 and 2 and that these thrombopoietic cells play key roles in controlling blood vessel formation during hematopoiesis and ischemic wound healing (see the related article beginning on page 3277).

Thrombospondins deployed by thrombopoietic cells determine angiogenic switch and extent of revascularization

Thrombopoietic cells may differentially promote or inhibit tissue vascularization by releasing both pro- and antiangiogenic factors. However, the molecular determinants controlling the angiogenic phenotype of thrombopoietic cells remain unknown. Here, we show that expression and release of thrombospondins (TSPs) by megakaryocytes and platelets function as a major antiangiogenic switch. TSPs inhibited thrombopoiesis, diminished bone marrow microvascular reconstruction following myelosuppression, and limited the extent of revascularization in a model of hind limb ischemia. We demonstrate that thrombopoietic recovery following myelosuppression was significantly enhanced in mice deficient in both TSP1 and TSP2 (TSP-DKO mice) in comparison with WT mice. Megakaryocyte and platelet levels in TSP-DKO mice were rapidly restored, thereby accelerating revascularization of myelosuppressed bone marrow and ischemic hind limbs. In addition, thrombopoietic cells derived from TSP-DKO mice were more effective in supporting neoangiogenesis in Matrigel plugs. The proangiogenic activity of TSP-DKO thrombopoietic cells was mediated through activation of MMP-9 and enhanced release of stromal cell-derived factor 1. Thus, TSP-deficient thrombopoietic cells function as proangiogenic agents, accelerating hemangiogenesis within the marrow and revascularization of ischemic hind limbs. As such, interference with the release of cellular stores of TSPs may be clinically effective in augmenting neoangiogenesis.

Impaired megakaryopoiesis in patients with chronic idiopathic neutropenia is associated with increased transforming growth factor β1 production in the bone marrow

Patients with chronic idiopathic neutropenia (CIN) display relatively low peripheral blood platelet counts and hypo-lobulated megakaryocytes in the bone marrow (BM). The underlying pathogenetic mechanismswere probed by studying the reserves and clonogenic potential of BM megakaryocytic progenitor cells using flow-cytometry and a collagen-based clonogenic assay for the identification of megakaryocyte colony-forming units (CFU-Meg). Thrombopoietin (TPO) and transforming growth factor-beta1 (TGFbeta1) levels were also evaluated in long-term BM culture supernatants using an enzyme-linked immunosorbent assay. CIN patients (n = 39) showed a low proportion of BM CD34(+)/CD61(+) megakaryocytic progenitor cells and low frequency of early and mixed CFU-Meg in the BM mononuclear, but not CD34(+), cell fraction, compared with healthy controls (n = 20). TPO and TGFbeta1 levels were significantly higher in patients compared with controls. TPO levels inversely correlated with platelet counts whereas TGFbeta1 values correlated inversely with CD34(+)/CD61(+) and CFU-Meg megakaryocytic progenitor cell numbers and positively with TPO levels. The addition of an anti-TGFbeta1 neutralising antibody significantly increased the numbers of CFU-Meg in CIN patients but not in controls, compared with baseline. These data suggest that increased local production of TGFbeta1 probably affects the BM megakaryocytic progenitor cell growth in CIN whereas the compensatory production of TPO finally balances the TGFbeta1-induced inhibitory effect.

[Effect of GM-CSF on expansion and differentiation of CD34+ megakaryocyte progenitor cells from cord blood in vitro]

To study the effect of GM-CSF on in vitro expansion of megakaryocyte progenitor cells from cord blood, CD34(+) cells isolated by magnetic cell sorting system (MACS) were cultured in serum-free medium containing TPO, IL-3, SCF and with or without various concentrations of GM-CSF (5, 20, 100 ng/ml). The numbers of MNC, proportion of CD34(+)CD41(+) cells and CFU-MK were measured at 6, 10 and 14 days. The results showed that the expansion of MNC and proportion of CD41(+) cells was accelerated distinctly by various concentrations of GM-CSF after 14 days, while 20 and 100 ng/ml GM-CSF exhibited higher expansion effect than that of 5 ng/ml. TPO + IL-3 + SCF with 5 ng/ml or 20 ng/ml GM-CSF could stimulate the formation of CFU-MK, while TPO + IL-3 + SCF with 100 ng/ml GM-CSF could inhibit it. It is concluded that GM-CSF can accelerate the expansion of megakaryocyte progenitor cells from CD34(+) cells in cord blood in the serum-free medium containing TPO + IL-3 + SCF.

Optimizing therapy for myeloid disorders of Down syndrome

Children with Down syndrome (DS) are at increased risk of leukaemia. Myeloid disorders include transient abnormal myelopoiesis (TAM), myelodysplasia (MDS) and acute myeloid leukaemia (AML). Mutations in the GATA-1 gene, which encodes for a transcription factor central to the normal development of the erythroid and megakaryocytic lineages, are found in cases of TAM, MDS and AML in DS children. DS children with MDS/AML mostly present between the ages of 1 and 4 years, and have a large predominance of megakaryoblastic disease (French-American-British type M7). The MDS and AML are part of a single disease entity (myeloid leukaemia of Down syndrome) that is extremely sensitive to chemotherapy. Resistant disease and relapse are rare, but treatment-related toxicity is high, and deaths in remission have exceeded those due to disease in most series. Accordingly, controlled dosage reduction is the focus of contemporary treatment studies.

Mechanisms of thrombopoiesis

Megakaryocytes (MKs) expand and differentiate over several days in response to thrombopoietin (Tpo) before releasing innumerable blood platelets. The final steps in platelet assembly and release represent a unique cellular transformation that is orchestrated by a range of transcription factors, signaling molecules, and cytoskeletal elements. Here we review recent advances in the physiology and molecular basis of MK differentiation. Genome-wide approaches, including transcriptional profiling and proteomics, have been used to identify novel platelet products and differentiation markers. The extracellular factors, stromal-derived factor (SDF)-1 chemokine and fibroblast growth factor (FGF)-4 direct MK interactions with the bone marrow stroma and regulate cytokine-independent cell maturation. An abundance of bone marrow MKs induce pathologic states, including excessive bone formation and myelofibrosis, and the basis for these effects is now better appreciated. We review the status of transcription factors that control MK differentiation, with special emphasis on nuclear factor-erythroid 2 (NF-E2) and its two putative target genes, beta1-tubulin and 3-beta-hydroxysteroid reductase. MKs express steroid receptors and some estrogen ligands, which may constitute an autocrine loop in formation of proplatelets, the cytoplasmic protrusions within which nascent blood platelets are assembled. Finally, we summarize our own studies on cellular and molecular facets of proplatelet formation and place the findings within the context of outstanding questions about mechanisms of thrombopoiesis.

[Study on the expansion of megakaryocyte progenitors in vitro from cord blood]

This study was aimed to investigate the effect of various cytokines on megakeryocytes expansion in vitro from human cord blood CD34(+) cells in order to establish an optimal culture system for MK expansion. Mononuclear cells were obtained by Ficoll-Hapaque density gradient separation. CD34(+) cells were positively isolated using a CD34 progenitor cell isolation kit. CD34(+) cells were placed into 24 well plates at a concentration of 2 x 10(4) per well. Each well contained 1 ml of IMDM with the present of effective MK cells growth cytokines. Clonogenic potentials of MK progenitor were assayed using a methylcellulose cultures system. The results suggested that four cytokines (IL-3 + IL-6 + TPO + FLT3L) culture system could effectively induce and expand cord blood CD41(+) MK cells. The number of CD41(+) cells expanded 154.67 +/- 32.21-fold on day 7, and 193.23 +/- 25.24-fold on day 14. In conclusion, established expansion system in vitro for MK cells provides experimental foundation for recovery of platelets after cord blood transplantation.

Characterization of banked umbilical cord blood hematopoietic progenitor cells and lymphocyte subsets and correlation with ethnicity, birth weight, sex, and type of delivery: a Cord Blood Transplantation (COBLT) Study report

BACKGROUND

The Cord Blood Transplantation (COBLT) Study banking program was initiated in 1996. The study goals were to develop standard operating procedures for cord blood (CB) donor recruitment and banking and to build an ethnically diverse unrelated CB bank to support a transplantation protocol.

STUDY DESIGN AND METHODS

The hematopoietic progenitor cell (HPC) and lymphocyte subset (LS) content of approximately 8000 CB units were characterized, and these results were correlated with donor ethnicity, birth weight, gestational age, sex, and type of delivery.

RESULTS

There was a significant correlation of CD34+ cell count with colony-forming unit (CFU)-granulocyte-macrophage (r=0.68, p<0.001), CFU-granulocyte-erythroid-macrophage-megakaryocyte (r=0.52, p<0.001), burst-forming unit-erythroid (BFU-E; r=0.61, p<0.001), and total CFUs (r=0.67, p<0.001). Nucleated red blood cell count was significantly correlated with total CD34+ (r=0.56, p<0.001), total CFU (r=0.50, p<0.001), BFU-E (r=0.48, p<0.001), and counts of CD34+ subsets (p<0.001). Caucasian ethnicity was significantly correlated with higher CD3+/CD4+, CD19+, and CD16+/CD56+ LSs. Furthermore, CD34+/CD38- and CD34+/CD61+ CB units (HPC-C) were significantly lower in African American and Asian persons compared to Caucasian and Hispanic persons. Male sex was associated with significantly fewer CD3+/CD4+, CD19+, and CD16+/CD56+ but increased CD3+/CD8+ LSs (p<0.001). Finally, cesarean section was associated with significantly higher total CFU and CD16+/CD56+ but lower CD3+/CD4+, CD3+/CD8+, and CD19+ LSs.

CONCLUSION

These results provide a standard and range for uniformly processed HPC-C progenitor cells and LSs. CB progenitor cells and/or LSs may in the future predict for rapidity of engraftment, incidence of graft-versus-host disease, speed and quality of immunore- constitution, graft-versus-tumor effects, and/or success of gene transfection after CB transplantation.

[In vitro expansion of cord blood megakaryocyte progenitor]

OBJECTIVE

To expand cord blood megakaryocyte progenitor cells in vitro.

METHODS

Cord blood CD34+ cells were selected by magnetic cell sorting (MACS), and thrombopoietin (TPO), interleukin-11 (IL-11), and heparin were used in the expansion system of megakaryocyte progenitor. The expansion efficiency was measured by fluorescence-activated cell sorting (FACS) using the megakaryocytic specific monoclonal antibodies (CD34+, CD41a+, CD61+, CD34+CD41a+, CD41a+CD61+) and colony-forming units-megakaryocyte (CFU-MK) analysis. The expanded megakaryocyte progenitor were determined by histochemistry staining using CD41a and the observation of the ultrastructure of megakaryocyte (MK) by electron microscopy. The megakaryocyte function were examined by the platelet activation in vitro and nonobese diabetic/severe combined immunodifficiency (NOD/SCID) mice transplantation in vivo.

RESULTS

CD34+CD41a+ cells was expanded (4.0 +/- 1.7) folds on day 7 in TPO (50 ng/ml) group and (10.5 +/- 4.8) fold in TPO combined with IL-11 group; after heparin was joined in on day 0, a more significantly elevated expansion was found in the heparin, TPO, and IL-11 group [(29.9 +/- 6.4) folds than the above two groups; P < 0.05]. Meanwhile, the large CFU-MK colony (> 50 cells/colony) was (106.8 +/- 26.9) folds on day 7 (P < 0.05). The megakaryocyte expanding with TPO, IL-11 and heparin for 7 days in vitro transplanted the NOD/SCID mice fasten the recovery of platelet and white blood cell account and improved the survival. Megakaryocyte under culture displayed certain development of territories membrane. Platelet activation test comfirmed that the expanding megakaryocyte progenitor had the normal function.

CONCLUSION

TPO, IL-11, and heparin combination system for ex vivo expansion is an effective expansion system of megakaryocyte progenitor.

Fast but durable megakaryocyte repopulation and platelet production in NOD/SCID mice transplanted with ex-vivo expanded human cord blood CD34+ cells

We have previously established a stroma-free culture with Flt-3 ligand (FL), stem cell factor (SCF), and thrombopoietin (TPO) that allows the maintenance and the expansion for several weeks of a cord blood (CB) CD34+ cell population capable of multilineage and long-lasting hematopoietic repopulation in non-obese diabetic/ severe combined immunodeficient (NOD/SCID) mice. In this work the kinetics of megakarocyte (Mk)-engraftment that is often poor and delayed in CB transplantation, and human platelet (HuPlt) generation in NOD/SCID mice of baseline CD34+ cells (b34+), and of CD34+ cells reisolated after a 4-week expansion with FL+SCF+TPO (4w34+) were compared. With b34+ cells Mk-engraftment was first seen at week 3 (CD41+: 0.4%); 4w34+ cells allowed a more rapid Mk-engraftment (at weeks 2 and 3 the CD41+ cells were 0.3% and 0.8%). Circulating HuPlts were first seen at weeks 2 and 1, respectively. Mk-engraftment levels of b34+ and 4w34+ cells 6-8 weeks after transplantation were similar (12 +/- 3.5 versus 15 +/- 5% CD45+; 1.3 +/- 0.5 versus 1.8 +/- 0.5% CD41+ cells). Also serial transplant experiments were performed with expanded and reselected CB cells. In secondary and tertiary recipients the Mk population was detected with bone marrow fluorescence-activated cell sorter analysis; these experiments indicate the effective long-term repopulation of expanded cells. Selected CD34+ cells after a 4-week expansion with FL+SCF+TPO are more efficient in Mk engraftment than the same number of unmanipulated cells.

Expression of protease activated receptor 3 (PAR3) is upregulated by induction of megakaryocyte phenotype in human erythroleukemia (HEL) cells

OBJECTIVE

Two major protease-activated receptors (PARs), PAR1 and PAR4, are involved in the activation of human platelets by thrombin. A third, PAR3, is preferentially expressed by tissues of hematopoietic origin and megakaryocytes. Although PAR3 is also a thrombin substrate, its low-level expression on human platelets suggests a function distinct from that of PAR1, the major receptor involved in thrombin-mediated platelet activation. We studied the expression of PARs during megakaryocyte differentiation of human erythroleukemia (HEL) cells in order to determine the role of PAR3 in megakaryocytopoiesis.

METHODS

HEL cells exposed to phorbol 12-myristate 13-acetate (PMA) to induce megakaryocyte differentiation were examined by light microscopy and flow cytometry (DNA ploidy, surface expression of PAR1, PAR3, GPIIb-IIIa). Northern blot, RT-PCR, and quantitative RT-PCR were used to evaluate the expression of PARs 1, 3, and 4 mRNA. HEL cells were also exposed to thrombin and thrombopoietin (TPO).

RESULTS

In baseline studies, unstimulated HEL cells were found to express comparable levels of PAR1 and PAR3 by Northern blot. Minimal expression of PAR4 was detected by RT-PCR, but not by Northern analysis. Exposure to PMA, but not thrombin or TPO, resulted in megakaryocytic differentiation as evident by increased cell size and nuclear complexity, increased ploidy, and enhanced expression of GPIIb-IIIa, a specific marker of megakaryocytes/platelets. PMA-stimulated HEL cells showed enhanced PAR3 cell-surface expression (approximately threefold increase by day 2) by flow cytometry. In contrast, there was no change in cell-surface PAR1 expression. Northern blot analysis (approximately 10-fold) and quantitative RT-PCR (approximately threefold) confirmed the upregulation of PAR3 mRNA expression (by 24 hours) in cells exposed to PMA. This did not occur with exposure to TPO.

CONCLUSION

These data demonstrate increased expression of PAR3 mRNA and protein in HEL cells undergoing megakaryocytic maturation following PMA exposure, suggesting a developmental role for PAR3. Furthermore, regulation of PAR3 expression appears to be specifically coupled to the protein kinase C system, but independent of the Ras/Raf/MAP kinase pathway.

Acquired amegakaryocytic thrombocytopenia associated with proliferation of γ/δ TCR+ T-lymphocytes and a BCR-ABL (p210) fusion transcript

Acquired amegakaryocytic thrombocytopenia (AATP) in adults is a rare disorder characterized by severe thrombocytopenia and decreased or absent megakaryocytes in an otherwise normal bone marrow. We present a 44-yr-old man in whom the diagnosis of AATP was established in January 2001. Immunophenotyping of the peripheral blood lymphocytes showed a relative increase in the subpopulation of gamma/delta T-cell receptor (TCR) positive (gamma/delta TCR(+)) and (CD4, CD8) negative T lymphocytes, and PCR suggested a monoclonal pattern of TCR gamma chain gene rearrangement. Cytogenetic examination of his bone marrow cells showed a normal male karyotype but RT-PCR analysis revealed a BCR-ABL (p210) fusion transcript. The inhibition of CFU-Mk growth mediated by the patient's T lymphocytes indicated that the pathogenic mechanism for AATP could be an immunological attack on megakaryocyte progenitors where the gamma/delta TCR-positive T lymphocytes are directly involved. The case emphasizes the complex association of T-lymphocyte monoclonal proliferation and AATP.

Gene expression profile of primary human CD34+CD38lo cells differentiating along the megakaryocyte lineage

OBJECTIVE

To identify genes involved in megakaryopoiesis, high-density oligonucleotide microarrays were used to compare transcript profiles from undifferentiated CD34+CD38lo cells and culture-derived megakaryocytes (MKs).

MATERIALS AND METHODS

Megakaryocyte differentiation was achieved in vitro by inducing primary human CD34+CD38lo cells in serum-deprived media supplemented with the cytokine combination of interleukin-3, interleukin-6, stem cell factor, and thrombopoietin for 10 days. Three replicate microarray experiments were performed using hematopoietic cells isolated from three different organ donors and high-density oligonucleotide microarrays.

RESULTS

Analysis of gene array data resulted in 304 differentially expressed genes (p < or = 0.001, fold change > or = 3). A third of the 25 most highly up-regulated genes were known to participate in hemostasis (z = 6.75), and no genes known to be associated with MKs were among the down-regulated genes. We also found a large proportion of up-regulated transcripts in gene ontology categories of adhesion and receptor activity (85%) and signal transduction activity (68%). At the same time, 70% of genes within transcription factor functions were down-regulated. Confirmatory studies indicated that the array results correlated with mRNA and protein expression levels in primary MKs.

CONCLUSION

This study provides a global expression profile of human MKs and a list of novel and previously uncharacterized candidate genes that are important components of megakaryopoiesis.

Extracellular signal-regulated kinase induces the megakaryocyte GPIIb/CD41 gene through MafB/Kreisler

Extracellular signal-regulated kinase (ERK) facilitates cell cycle progression in most mammalian cells, but in certain cell types prolonged signaling through this pathway promotes differentiation and lineage-specific gene expression through mechanisms that are poorly understood. Here, we characterize the transcriptional regulation of platelet GPIIb integrin (CD41) by ERK during megakaryocyte differentiation. ERK-dependent transactivation involves the proximal promoter of GPIIb within 114 bp upstream of the transcriptional start site. GATA, Ets, and Sp1 consensus sequences within this region are each necessary and function combinatorially in ERK-activated transcription. MafB/Kreisler is induced in response to ERK and synergizes with GATA and Ets to enhance transcription from the proximal promoter. The requirement for MafB in promoter regulation is demonstrated by inhibition of transactivation following dominant-negative or antisense suppression of MafB function. Thus, ERK promotes megakaryocyte differentiation by coordinate regulation of nuclear factors that synergize in GPIIb promoter regulation. These results establish a novel role for MafB as a regulator of ERK-induced gene expression.

Additional transplantation of ex vivo generated megakaryocytic cells after high-dose chemotherapy

The additional transplantation of ex vivo generated hematopoietic (post)-progenitor cells represents a possible approach to ameliorate high-dose chemotherapy induced cytopenia. We investigated the feasibility of the large-scale expansion and transplantation of autologous megakaryocytic cells in four patients with advanced solid tumors. Up to 1,460x10(6) ex vivo generated cells were administered without adverse effects but no clear cut effect on platelet recovery was observed.

[A study on micromegakaryocyte in children with idiopathic thrombocytopenic purpura]

OBJECTIVE

Bone marrow megakaryocytes overly proliferate and abnormally develop among patients with idiopathic thrombocytopenic purpura (ITP). Previous studies showed that it resulted from the abnormal immune function of the body. But the changes in megakaryocytes, especially in micromegakaryocytes in this disease are unclear. The present study was designed to explore the growth and development status of megakaryocytes and the significance of changes in micromegakaryocytes in pediatric cases.

METHODS

Routine bone marrow smears assay and enzyme labeling for micromegakaryocytes with CD41 monoclonal antibody (McAb) were performed in 46 children with ITP. The level of platelet-associated immunoglobulin (PA-Ig) was measured with ELISA.

RESULTS

Among 46 children, 36 had acute ITP (AITP)and 10 chronic ITP (CITP). The number of megakaryocytes increased or was normal in 45 patients, but decreased only in 1 case of CITP. The positive rate of micromegakaryocytes and type I micromegakaryocytes was 98% (45/46) and 35% (16/46), respectively. The positive rate of type I micromegakaryocytes was higher in CITP (50%) cases than that in AITP (31%) cases, but the median of the other three types of micromegakaryocytes in CITP cases (159) was lower than that in the AITP cases (336). There was no relationship between the numbre of all types of megakaryocytes and the level of PA-Ig.

CONCLUSION

Majority of patients with ITP showed an increase in micromegakaryocytes, especially in type II, III and IV. The immune disturbance might not be the only reason for ITP. The abnormality of quality of megakaryocytes might be one of the potential causes for thrombocytopenia in some cases of ITP, especially in those of CITP. The appearance and the number of type I micromegakaryocytes might reflect the prognosis of cases of ITP.