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Objective:During megakaryopoiesis, hematopoietic progenitor cells in the bone marrow proliferate and ultimately differentiate in mature megakaryocytes (MK). We and others have recently described a role for the mammalian target of Rapamycin (mTOR) in proliferation and differentiation of MK cells. Two non-redundant complexes of mTOR have been described; mTORC1 containing rapamycin-associated TOR protein (Raptor) and mTORC2 containing Rapamycin-insensitive companion of mTOR (Rictor). The individual roles of these complexes in MK development have so far not been elucidated, and were investigated in this study.Methods:We have used an siRNA approach to selectively knock down either Rictor or Raptor expression in MO7e megakaryoblastic cells. Using flow cytometry, nuclear ploidity, and cell cycling as assessed by BrdU incorporation were investigated. Electron microscopy and cotransductions with GFP-LC3 were used to quantify autophagy. Activation of intracellular signal transduction pathways was studied by Western blot analysis.Results:We observed a reduced cell cycling upon Rictor siRNA transduction, resulting in decreased numbers of polypoid cells. Knocking down Raptor expression resulted in a reduced expansion and a reduced cell size. In addition, increased autophagy was observed in Raptor siRNA-transduced cells, in correspondence with an attenuation of activation of the p70S6K/S6, and 4E-BP pathways.Conclusions:The current study shows that the mTORC1 and mTORC2 complexes have distinct, non-redundant functions in MO7e MK cell proliferation, and development. The mTOR/Rictor complex affects megakaryopoiesis by regulating nuclear division and subsequent cell cycle progression, whereas Raptor signaling protects MK cells from autophagic cell death, enabling normal megakaryopoiesis to take place.

Mutations in either ABCG5 or ABCG8 cause sitosterolemia, an inborn error of metabolism characterized by high plasma plant sterol concentrations. Recently, macrothrombocytopenia was described in a number of sitosterolemia patients, linking hematological dysfunction to disturbed sterol metabolism. Here, we demonstrate that macrothrombocytopenia is an intrinsic feature of murine sitosterolemia. Abcg5-deficient (Abcg5(-/-)) mice showed a 68% reduction in platelet count, and platelets were enlarged compared with wild-type controls. Macrothrombocytopenia was not due to decreased numbers of megakaryocytes or their progenitors, but defective megakaryocyte development with deterioration of the demarcation membrane system was evident. Lethally irradiated wild-type mice transplanted with bone marrow from Abcg5(-/-) mice displayed normal platelets, whereas Abcg5(-/-) mice transplanted with wild-type bone marrow still showed macrothrombocytopenia. Treatment with the sterol absorption inhibitor ezetimibe rapidly reversed macrothrombocytopenia in Abcg5(-/-) mice concomitant with a strong decrease in plasma plant sterols. Thus, accumulation of plant sterols is responsible for development of macrothrombocytopenia in sitosterolemia, and blocking intestinal plant sterol absorption provides an effective means of treatment.

To investigate underlying mechanisms of thrombocytopenia in myelodysplastic syndrome (MDS), radiolabeled platelet studies were performed in 30 MDS patients with platelets

To investigate whether altered megakaryocyte morphology contributes to reduced platelet production in idiopathic thrombocytopenic purpura (ITP), ultrastructural analysis of megakaryocytes was performed in 11 ITP patients. Ultrastructural abnormalities compatible with (para-)apoptosis were present in 78% ± 14% of ITP megakaryocytes, which could be reversed by in vivo treatment with prednisone and intravenous immunoglobulin. Immunohistochemistry of bone marrow biopsies of ITP patients with extensive apoptosis showed an increased number of megakaryocytes with activated caspase-3 compared with normal (28% ± 4% versus 0%). No difference, however, was observed in the number of bone marrow megakaryocyte colony-forming units (ITP, 118 ± 93/105 bone marrow cells; versus controls, 128 ± 101/105 bone marrow cells; P = .7). To demonstrate that circulating antibodies might affect megakaryocytes, suspension cultures of CD34+ cells were performed with ITP or normal plasma. Morphology compatible with (para-)apoptosis could be induced in cultured megakaryocytes with ITP plasma (2 of 10 samples positive for antiplatelet autoantibodies). Finally, the plasma glycocalicin index, a parameter of platelet and megakaryocyte destruction, was increased in ITP (57 ± 70 versus 0.7 ± 0.2; P = .009) and correlated with the proportion of megakaryocytes showing (para-) apoptotic ultrastructure (P = .02; r = 0.7). In conclusion, most ITP megakaryocytes show ultrastructural features of (para-) apoptosis, probably due to action of factors present in ITP plasma.

A discrepancy exists between basal tissue factor (TF) expression found in endothelial cell cultures and the failure to detect TF in unpertubated endothelial cells in vivo. We demonstrated that basal TF expression in endothelial cell cultures originated from contaminating cells. These cells were ultrastructurally and flowcytometrically identified as smooth muscle cells. The cell cultures had been obtained from collagenase-treated human umbilical cord vessels. Histologic studies revealed that after collagenase treatment the basement membrane was digested and underlying structures were disrupted at some areas of the vein. We selected chymotrypsin as an alternative for the isolation of endothelial cells. Using chymotrypsin, the endothelial lining was selectively lost leaving the basement membrane undisturbed. Furthermore, use of chymotrypsin instead of collagenase minimized the level of basal TF activity. Taken together, we demonstrated that basal TF expression in endothelial cell cultures is caused by contaminating smooth muscle cells. This contamination can strongly be reduced using chymotrypsin instead of collagenase for isolation of endothelial cells.

Natural-food-based compounds show substantial promise for prevention and biotherapy of cancers including leukemia. In general, their mechanism of action remains unclear, hampering rational use of these compounds. Herein we show that the common dietary flavonoid apigenin has anticancer activity, but also may decrease chemotherapy sensitivity, depending on the cell type. We analyzed the molecular consequences of apigenin treatment in two types of leukemia, the myeloid and erythroid subtypes. Apigenin blocked proliferation in both lineages through cell-cycle arrest in G(2)/M phase for myeloid HL60 and G(0)/G(1) phase for erythroid TF1 cells. In both cell lines the JAK/STAT pathway was one of major targets of apigenin. Apigenin inhibited PI3K/PKB pathway in HL60 and induced caspase-dependent apoptosis. In contrast, no apoptosis was detected in TF1 cells, but initiation of autophagy was observed. The block in cell cycle and induction of autophagy observed in this erythroleukemia cell line resulted in a reduced susceptibility toward the commonly used therapeutic agent vincristine. Thus, this study shows that although apigenin is a potential chemopreventive agent due to the induction of leukemia cell-cycle arrest, caution in dietary intake of apigenin should be taken during disease as it potentially interferes with cancer treatment. Cell Death and Disease (2010) 1, e19; doi:10.1038/cddis.2009.18; published online 28 January 2010

Recent studies in erythroid cells have shown that autophagy is an important process for the physiological clearance of mitochondria during terminal differentiation. However, autophagy also plays an important role in removing damaged and dysfunctional mitochondria. Defective mitochondria and impaired erythroid maturation are important characteristics of low-risk myelodysplasia. In this study we therefore questioned whether the autophagic clearance of mitochondria might be altered in erythroblasts from patients with refractory anemia (RA, n=3) and RA with ringed sideroblasts (RARS, n=6). Ultrastructurally, abnormal and iron-laden mitochondria were abundant, especially in RARS patients. A large proportion (52+/-16%) of immature and mature myelodysplastic syndrome (MDS) erythroblasts contained cytoplasmic vacuoles, partly double membraned and positive for lysosomal marker LAMP-2 and mitochondrial markers, findings compatible with autophagic removal of dysfunctional mitochondria. In healthy controls only mature erythroblasts comprised these vacuoles (12+/-3%). These findings were confirmed morphometrically showing an increased vacuolar surface in MDS erythroblasts compared to controls (P

Patients with myelodysplasia (MDS) show an impaired reactive oxygen species (ROS) production in response to fMLP stimulation of GM-CSF-primed neutrophils. In this study, we investigated the involvement of lipid rafts in this process and showed that treatment of neutrophils with the lipid raft-disrupting agent methyl-β-cyclodextrin abrogates fMLP-induced ROS production and activation of ERK1/2 and protein kinase B/Akt, two signal transduction pathways involved in ROS production in unprimed and GM-CSF-primed neutrophils. We subsequently showed that there was a decreased presence of Lyn, gp91phox, and p22phox in lipid raft fractions from neutrophils of MDS. Furthermore, the plasma membrane expression of the lipid raft marker GM1, which increases upon stimulation of GM-CSF-primed cells with fMLP, was reduced significantly in MDS patients. By electron microscopy, we showed that the fMLP-induced increase in GM1 expression in GM-CSF-primed cells was a result of de novo synthesis, which was less efficient in MDS neutrophils. Taken together, these data indicate an involvement of lipid rafts in activation of signal transduction pathways leading to ROS production and show that in MDS neutrophils, an impaired lipid raft formation in GM-CSF-primed cells results in an impaired ROS production.

Platelet production requires compartmentalized caspase activation within megakaryocytes. This eventually results in platelet release in conjunction with apoptosis of the remaining megakaryocyte. Recent studies have indicated that in low-risk myelodysplastic syndromes (MDS) and idiopathic thrombocytopenic purpura (ITP), premature cell death of megakaryocytes may contribute to thrombocytopenia. Different cell death patterns have been identified in megakaryocytes in these disorders. Growing evidence suggests that, besides apoptosis, necrosis and autophagic cell death, may also be programmed. Therefore, programmed cell death (PCD) can be classified in apoptosis, a caspase-dependent process, apoptosis-like, autophagic and necrosis-like PCD, which are predominantly caspase-independent processes. In MDS, megakaryocytes show features of necrosis-like PCD, whereas ITP megakaryocytes demonstrate predominantly characteristics of apoptosis-like PCD ( para-apoptosis). Triggers for these death pathways are largely unknown. In MDS, the interaction of Fas/Fas-ligand might be of importance, whereas in ITP antiplatelet autoantibodies recognizing common antigens on megakaryocytes and platelets might be involved. These findings illustrate that cellular death pathways in megakaryocytes are recruited in both physiological and pathological settings, and that different forms of cell death can occur in the same cell depending on the stimulus and the cellular context. Elucidation of the underlying mechanisms might lead to novel therapeutic interventions.

To investigate the ultrastructural characteristics of erythroblasts in myelodysplasia (MDS) which might be of additional importance in understanding its pathogenesis.22 patients were classified according to FAB (French-American-British classification), IPSS (international prognostic score system), cytogenetic risk factors and transfusion dependency. Using electron microscopy, in 77% of the cases, nuclear abnormalities consisting of disrupted membranes and cystic/dilated perinuclear spaces were noted. In a limited number of patients (n=7), a low percentage of apoptosis in the erythroid lineage (mean 3.1+/-1.6%; median 3%: range 1-6) (normal controls:0.5%) could be noted, primarily in mature erythroblasts and significantly associated with spongiform nuclear features. In all patients extensive cytoplasmic vacuolization and myelin figures in erythroblasts were demonstrated. In 55% of the cases, enlarged and abnormal mitochondria were observed, significantly associated with iron-accumulation. A significant inverse relation existed between the absence of apoptosis and more advanced, or high risk disease and cytogenetic risk factors. Mitochondrial abnormalities were significantly correlated with high risk disease as well with an increase in transfusion dependency.These data indicate that in MDS apoptosis may play a role in early stages of disease. The overall prominent defects in mitochondria might be an additional defect that is involved in ineffective erythropoiesis.

Abstract 2932 Several studies have shown that hematopoietic precursor cells in low-risk myelodysplastic syndromes (MDS) undergo premature cell death. The mode of cell death is cell type specific and might include apoptosis, necrosis, and/or autophagy. Studies in MDS erythroblasts have shown enhanced apoptosis and enhanced autophagy (Houwerzijl EJ et al. Leukemia 2009), while megakaryocytes undergo a caspase-3 independent nonapoptotic cell death (Houwerzijl EJ et al. Blood 2005). Increasing data suggest that in MDS the bone marrow microenvironment is also affected. Some stromal cells, including mesenchymal and circulating endothelial cells, can carry similar chromosomal abnormalities as the neoplastic hematopoietic clone (Della Porta MG et al. Leukemia 2008, Lopez-Villar O et al. Leukemia 2009). In addition, recent data show that hematopoietic and endothelial cells have a common precursor, the hemangioblast (Lancrin C et al. Nature 2009). These findings raise the question whether endothelial cells in MDS also die prematurely. To define in more detail the underlying cell death pathways in MDS endothelial cells and to quantify vascularisation, immunohistochemical staining and electron microscopic analysis were performed on bone marrow samples of patients with refractory anemia (RA, n=6) and RA with ringed sideroblasts (RARS, n=6), and healthy controls (n=4). According to the MDS International Prognostic Scoring System (IPSS) the patients were categorized as low risk (n=6) and intermediate risk-1 (n=6). Immunohistochemistry of the MDS bone marrow biopsies demonstrated increased bone marrow microvessel density (MVD) determined by FVIII staining. In both RA and RARS MVD was increased compared to normal (number of vessels: 4 ± 1.6 and 3.8 ± 1.1/powerfield respectively, versus 0.4 ± 0.5 in healthy controls, magnification × 400). The increased number of endothelial cells stained strongly positive for VEGF in both RA and RARS compared to normal bone marrow. The elevated VEGF expression of these cells might be related to a significantly enhanced expression of hypoxia inducible factor-2α (HIF-2α) compared to normal controls, which was especially found in RARS endothelial cells. In contrast, immunostaining for HIF-1α was negative in MDS patients as well as controls. To expand these results ultrastructural analysis was performed on hematons of a subgroup of these patients (n=10). Hematons are compact spherical particles which contain hematopoietic progenitor cells residing within a finely arborized stromal framework, including adipocytes, mesenchymal cells, resident macrophages and endothelial cells (Blazsek I et al. Blood 2000). Hematons can be isolated from the bone marrow aspirate light density fraction. The ultrastructural analysis revealed irregularly shaped endothelial cells without pericytes and degradation of the basal membrane. Cytoplasmic vacuolization was present in endothelial cells, especially in RARS patients. The majority of these vacuoles were double membraned, a main characteristic of autophagy. Mitochondria were normal. No features of apoptosis were found, which was confirmed by a negative immunostaining for caspase-3 and caspase-8. Microvessels were irregularly shaped and showed frequent sprouting. These results indicate that endothelial cells from low-risk MDS patients are ultrastructurally abnormal, showing features of autophagy, but no apoptosis. Autophagy in these cells may be a type of cell death or a cell-rescue reaction to nutrient- and/or growth factor depletion in the microenvironment. On the other hand, in agreement with previous studies, angiogenesis, in low-risk MDS is increased, and appears to be HIF-2α and not HIF-1α mediated. Together, these findings may suggest that endothelial cells in MDS, similar to hematopoietic cells, show a high rate of cellular proliferation, which coincides with an increased susceptibility for premature cell death, i.e. autophagy. The findings might contribute to knowledge of the defective make-up of the stem cell compartment in MDS which requires a strong interaction between hematopoietic stem cells and the microenvironment. Disclosures: No relevant conflicts of interest to declare.

Single donor platelets (SDPC) were collected by the elutriation technique in a closed-system integrated with large storage containers. Seven runs of SDPC were stored in a 1.5 liter polyvinyl-chloride trimellitate (PVC-TOTM) storage container, making the ratio of platelet concentrate volume to container volume 1:4.5. An equal volume of pooled multiple donor platelet concentrates (MDPC) was stored in parallel under the same conditions. All haematological data were comparable for both products, except for the degree of leukocyte contamination (5-fold increase in the pool). Under these conditions, the functional, morphological, and metabolic characteristics of elutriated platelets throughout 7-day storage were superior to those of pooled platelets. Although the platelet count was not significantly different in both types of concentrates, the mean pH of pooled MDPC fell to 6.0 on day 5 of storage. Leukocytes were shown to contribute to this pH fall. The extent of cell damage, however, as evidenced by LDH leakage (42.7 LDH units/1011 platelets/day by differential centrifugation, compared to 5.3 units by elutriation) could not be explained solely on the basis of the leukocyte effect. This indicated that the processing method itself influences the platelet quality. By increasing the surface/volume ratio of SDPC, the initial pH of 7.1 was well maintained throughout storage, platelet metabolic rate was slowed, and the function and ultrastructure improved significantly. © 1992 Wiley-Liss, Inc.

Anemia in myelodysplasia (MDS) is partially ascribed to enhanced programmed cell death (PCD) of committed erythroid cells in the bone marrow compartment. Especially, enhanced apoptosis has been described. However, nonapoptotic forms of PCD have been demonstrated in MDS megakaryocytes characterized by the absence of chromatin condensation and caspase-3 and -8 activation (Houwerzijl EJ et al. Blood2005;105:3472–3479). Recent studies have indicated that besides apoptosis, necrosis and autophagic cell death can be recognized as PCD, whereby cells are capable to switch between the different types of PCD dependent on their cellular context. To define in more detail the underlying cell death pathways in MDS erythroblasts, immunohistochemical staining and ultrastructural and immunolabeling analysis were performed on bone marrow samples of low-risk MDS patients and normal controls (n=4). Immunohistochemistry of MDS bone marrow biopsies (n=23) demonstrated no positive staining of the erythroblasts for active caspase -3 and -8. To confirm these results ultrastructural analysis and immunoelectron microscopy was performed on mononuclear cells (MNC) and hematons of a subgroup of these patients (n=9). Hematons are compact hematopoietic complexes in which hematopoietic cells, including erythroblasts, are embedded in their own microenvironment. The ultrastructural analysis revealed that only a small fraction of erythroid cells of the MNC and hematon fraction of both MDS patients and healthy controls demonstrated features of apoptosis (2 ± 2% vs 0%). However, 52 ± 16% of immature and mature MDS erythroblasts contained cytoplasmic vacuoles in contrast to normal erythroblasts, in which vacuoles were only shown in the matured stage (12 ± 3%). These vacuoles were partly double-membraned and stained positive for the lysosomal marker LAMP (lysosome associated membrane protein)-2, catalase and the mitochondrial inner membrane protein (immunogold staining) underscoring the presence of autophagy of mitochondria and other cytoplasmic components. Morphometric analysis confirmed that the vacuolar surface in the cytoplasm of MDS erythroblasts was increased compared to controls (P

Anemia in myelodysplasia (MDS) is partially ascribed to enhanced cell death of committed erythroid cells in the bone marrow compartment. To define in more detail the underlying type of cell death in MDS, immunohistochemical staining and ultrastructural analysis were performed on MDS and normal bone marrow samples. Immunohistochemistry of MDS bone marrow biopsies (n=20) demonstrated no positive staining of the erythroid lineage for active caspase -3 or -8. Ultrastructural analysis was performed in low-risk MDS patients (Refractory anemia (RA; n=3); RA with ringed sideroblasts (RARS; n=4) on isolated bone marrow hematons, which are compact hematopoietic complexes containing adipocytes, mesenchymal and endothelial cells, and hematopoietic cells. In vitro culture assays have demonstrated that these hematons contain a high number of progenitor and primitive cells. Ultrastructural analysis of the hematons of the MDS patients as well as the healthy controls demonstrated no signs of apoptosis in erythroid cells. In contrast, abnormalities compatible with autophagy were present in >60% of the MDS cells. Especially, cytoplasmic vacuoles with double membranes were noticed in basophilic and polychromatic normoblasts. Morphometric analysis of the erythroid cells showed no differences between healthy controls and MDS patients with regard to cell volume, mitochondria content or nuclear surface, but a significant increase was shown for the ratio area of vacuoles/cytoplasm in the MDS basophilic and polychromatic normoblasts (healthy controls vs MDS: 0.003 vs 0.013 (p

In isolation procedures for lymphocytes, isotonic ammonium chloride buffers are frequently used to lyse erythrocytes. In addition to evidence for an effect on lymphocyte function we now report a morphological alteration after treatment of lymphocytes with ammonium chloride buffer. Expression of parallel tubular structures was lost and only amorphous, electron-dense granules could be observed.