Platelets Protect From Lipopolysaccharide-Induced Lethal Endotoxemia by Inhibiting Macrophage-Dependent Inflammation Via the Cyclooxygenase 1 (COX1) Signaling Pathway

Abstract Abstract 93 Sepsis is a tremendous burden for health-care systems. Patients with sepsis often have low platelet counts, and septic patients with severe thrombocytopenia have a poor prognosis and higher mortality. However, the role of platelets in the pathogenesis of sepsis has not been well elucidated. We investigated the role of platelets in septic shock using a mouse model of lipopolysaccharide (LPS)-induced endotoxemia. Depletion of platelets by intraperitoneal injection of a rat anti-mouse GPIb monoclonal antibody increased mortality and aggravated organ failure in endotoxemic mice as evident by increases in plasma aminotransferase (ALT), aspartate aminotransferase (AST), Lactate dehydrogenase (LDH), and Creatine kinase (CK) concentrations, while transfusion of platelets reduced mortality. Increases in mortality rate in thrombocytopenic mice by LPS challenge was not due to inflammatory hemorrhage, because there was no significantly hemorrhage observed in brains and lungs from mice pre-treated with either control IgG or the anti-GPIba antibody and blood RBC and Hb concentrations between IgG pre-treated mice and the anti-GPIba antibody pre-treated mice were similar. TNF-a, which is produced mainly by macrophages in vivo, plays critical roles in the development of disseminated intravascular coagulation, acute respiratory distress syndrome and shock in sepsis. Our data indicate that plasma concentrations of proinflammatory cytokines, TNF-a and IL-6, were markedly increased by platelet depletion and decreased by platelet transfusion in the mice challenged with LPS. Effects of platelet depletion on TNF-a production were eliminated in the mice that macrophages were pre-depleted. Furthermore, LPS- or thrombin-activated platelets or releasates from activated platelets inhibited TNF-a and IL-6 production in macrophages in vitro. Inhibition of TNF-a and IL-6 production in macrophages by activated platelets was prevented by pre-incubation of platelets with a COX1 inhibitor aspirin. Moreover, platelets from wild type mice but not COX1 deficient mice inhibited LPS-induced TNF-a and IL-6 production in macrophages. Transfusion of COX1 deficient platelets failed to protect against endotoxemia. Washed platelets from wild-type mice or platelet releasates from thrombin-activated wild-type mice inhibited LPS-induced TNF-a and IL-6 production in macrophages lacking TXA2 receptor, TP, suggesting that a metabolite other than TXA2 is responsible for platelet inhibition of macrophage function. We found that stimulation of platelets with thrombin or LPS induced PGE2 production and pre-incubation of macrophages with an antagonist of PGE2 receptor EP4 reversed platelet inhibition on TNF-a and IL-6 production in macrophages. Our results indicate that platelets protect against septic shock by inhibiting macrophage-dependent inflammatory response via the COX1/PGE2/EP4 dependent pathway. Thus, these findings demonstrate a previously unappreciated role for platelets in septic shock and suggest that platelet transfusion may be effective in treating septic patients. Disclosures: No relevant conflicts of interest to declare.

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A Potential Protective Role of Platelets during Septic Shock Does Not Depend on Their Purinergic Receptors

Blood ◽

10.1182/blood.v128.22.2537.2537 ◽

2016 ◽

Vol 128 (22) ◽

pp. 2537-2537 ◽

Cited By ~ 1

Author(s):

Beatrice Hechler ◽

Chloé Zimmermann ◽

Yannick Rabouel ◽

Stéphanie Magnenat ◽

Mélanie Burban ◽

...

Keyword(s):

Septic Shock ◽

Platelet Count ◽

Purinergic Receptors ◽

Plasma Concentrations ◽

Protective Role ◽

P2y12 Receptor ◽

Severe Thrombocytopenia ◽

P2y1 Receptor ◽

Tnf Α

Abstract Thrombocytopenia frequently occurs in septic shock patients and is associated with a worsened outcome. Experimental data indicate that platelets may have a protective role during sepsis. Our aims were to i) assess the potential protective role of platelets during septic shock and ii) evaluate the involvement of platelet P2Y1 and P2Y12 purinergic receptors. We used a model of polymicrobial-induced septic shock in mice by cecal ligation below the ileocecal valve and double puncture (CLP). The impact of moderate to severe thrombocytopenia was evaluated using mice deficient for the thrombopoietin receptor (Mpl-R-/-, 80% reduction in platelet count) and intravenous administration of a platelet specific rat anti-GPIbα monoclonal antibody (RAM.6, 2 mg/kg, 93% reduction in platelet count), respectively. To investigate the role of the P2Y12 receptor, WT mice were treated with clopidogrel, an irreversible inhibitor of the P2Y12 receptor, administered per os at 10 mg/kg, the day before and 2 h prior to surgery. Contribution of the P2Y1 receptor was evaluated using mice deficient for the P2Y1 receptor (P2Y1-/-). Mice underwent sham or CLP surgery (6 animals/group). Twenty hours post-surgery, blood and tissue samples were collected to evaluate critical parameters of septic shock. Mortality was recorded in a second group of animals. Twenty hours after CLP, mice with either normal or reduced platelet counts displayed signs of septic shock such as apathy, fur ruffling, conjunctivitis and diarrhea. Their mean arterial blood pressure (MAP) fell by 30% indicating systemic hypotension and organ failure characteristic of shock. Mpl-R-/- mice, displaying moderate thrombocytopenia, showed enhanced plasma concentrations of the pro-inflammatory cytokines TNF-α and IL-6, and of myeloperoxidase (MPO), indicating increased systemic inflammation relative to WT mice. These effects were more pronounced in RAM.6-treated mice displaying severe thrombocytopenia. Thrombin-antithrombin (TAT) complexes, reflecting in vivo thrombin generation, were enhanced in RAM.6-treated mice as compared to Mpl-R-/-mice or WT mice. Thrombocytopenia was also associated with increased plasma levels of aspartate aminotransferase (ASAT) relative to mice with normal platelet count, an effect also more pronounced in severely thrombocytopenic mice. These results indicate that depletion of platelets worsened organ injury during septic shock. Finally, severely thrombocytopenic mice succumbed more rapidly than control mice after CLP. Twenty hours after CLP, clopidogrel-treated mice and P2Y1-/- mice displayed signs of shock attested by a 30% decrease in MAP, similar to that observed in WT mice. Plasma concentrations of TNF-α, IL-6 and MPO were similarly increased in WT, clopidogrel-treated and P2Y1-/- mice. In addition, no differences in TAT levels were observed between the three groups of mice. Finally, the extent of liver damage, as evaluated by measurement of plasma ASAT levels, was similar between clopidogrel-treated mice, P2Y1-/-mice and WT mice. Overall, these results provide evidence for a beneficial role of platelets during experimental septic shock in mice. However, the platelet ADP receptors do not contribute to this effect, suggesting that anti-platelet therapy with P2Y12 receptor antagonists may not be beneficial in patients with septic shock. The mechanisms by which platelets modulate the host response to septic shock remain to be elucidated. Disclosures No relevant conflicts of interest to declare.

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Dual Role for CIB1 in Thrombopoiesis: CIB1 Suppresses Megakaryocyte Quantities but Supports Adhesion, Migration, and Proplatelet Formation

Blood ◽

10.1182/blood.v118.21.2384.2384 ◽

2011 ◽

Vol 118 (21) ◽

pp. 2384-2384

Author(s):

John C Kostyak ◽

Ulhas P Naik

Keyword(s):

Conflicts Of Interest ◽

Dual Role ◽

Wild Type ◽

Hematopoietic Stem ◽

Platelet Recovery ◽

Proplatelet Formation ◽

And Migration ◽

Platelet Depletion ◽

Defective Clearance

Abstract Abstract 2384 Megakaryocytes (MKs) are large polyploid cells that produce platelets through a process known as thrombopoiesis. Thrombopoietin (Tpo) is the major cytokine that regulates a variety of steps in this process, including hematopoietic stem cell (HSC) differentiation to MKs, proplatelet formation, and platelet release into the circulation. However, the molecular mechanism of thrombopoiesis is poorly understood. We have previously reported that calcium- and integrin-binding protein 1 (CIB1) regulates endomitosis in Dami cells. To further characterize the role of CIB1 in thrombopoiesis, we utilized a Cib1−/− mouse model. We observed that Cib1−/− mice have a slightly elevated number of platelets and bone marrow (BM)-derived MKs than wild-type (WT) controls (p<0.05). Rate of platelet clearance was comparable in Cib1−/− and WT mice, suggesting that the defective clearance is not the cause of the observed elevated platelet number. In order to determine if the HSC differentiation is dysregulated by the ablation of Cib1, we analyzed MK-colony forming unit production, which revealed an increase in the colony forming cells with Cib1 deletion compared to WT (p<0.05). Additionally, BM from Cib1−/− mice, cultured with Tpo for 24 hours, produced more highly polyploid MKs than WT BM (p<0.05). These results suggest that Cib1 may negatively regulate initial steps of megakaryopoiesis. Subsequent analysis of Tpo signaling revealed that activation of FAK, a known suppresser of Tpo signaling, is attenuated, as indicated by reduced FAKY925 phosphorylation in Cib1−/− BM-derived MKs treated with Tpo. Consequently, Akt and ERK1/2 activation downstream of Tpo was enhanced. These results suggested that Cib1 inhibits Tpo signaling by augmenting FAK activation. Interestingly, platelet recovery in Cib1−/− mice following platelet depletion by experimental immunothrombocytopenia was attenuated compared to WT (p<0.05). This could be due to impaired adhesion and migration of MKs on the extracellular matrix. Consistent with this notion, adhesion to fibrinogen and fibronectin and migration towards an SDF-1α gradient were significantly reduced in Cib1−/− MKs compared to WT (p<0.05). Additionally, Cib1−/− MKs formed fewer proplatelets compared to WT (p<0.05), when plated on fibrinogen. These data suggest that CIB1 plays a dual role in thrombopoiesis, initially by negatively regulating Tpo signaling, and later by supporting MK migration and proplatelet production. Disclosures: No relevant conflicts of interest to declare.

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Impact of Platelet Count on Bleeding in the Setting of Anti-Platelet Therapy

Blood ◽

10.1182/blood-2020-142893 ◽

2020 ◽

Vol 136 (Supplement 1) ◽

pp. 18-18

Author(s):

Robert Hugh Lee ◽

Wolfgang Bergmeier

Keyword(s):

Real Time ◽

Conflicts Of Interest ◽

Thrombotic Event ◽

Platelet Inhibition ◽

Intravital Imaging ◽

Severe Thrombocytopenia ◽

Platelet Counts ◽

Anti Platelet Therapy ◽

The Impact

Anti-platelet therapy (APT) is used for secondary prevention of thrombosis. The most commonly prescribed anti-platelet drugs are aspirin and P2Y12 inhibitors, including clopidogrel, prasugrel and ticagrelor. Dual anti-platelet therapy (DAPT) consisting of aspirin and a P2Y12 inhibitor is often used in the first 1-12 months after an initial thrombotic event and has a greater anti-thrombotic effect than single agents, but is also associated with a higher risk of bleeding. Due to this risk of hemorrhage, the appropriate use of DAPT in patients requiring percutaneous coronary intervention (PCI) with baseline or periprocedural thrombocytopenia remains unclear. To study the impact of thrombocytopenia on bleeding with APT, we used intravital imaging in a murine hemostasis model and adoptive platelet transfer to generate mice with specific platelet counts with or without platelet inhibition. To generate experimental mice, we used transgenic mice in which platelets express a chimeric GPIb receptor with the extracellular domain replaced with a domain of the human IL-4R (hIL-4R/GPIb-Tg). Endogenous platelets were depleted by injection of anti-hIL-4R antibody, and the recipient mice were then transfused with wild-type (WT) platelets from donor mice treated, or not, with single or dual APT (aspirin 20 mg/kg; clopidogrel 25 mg/kg) to achieve specific platelet counts ranging from 50,000 to 400,000 platelets/μL. We also compared these mice with WT mice (with normal platelet counts, ~1,200,000 platelets/μL) treated with APT. Platelet inhibition was confirmed prior to performing in vivo experiments. Hemostasis was determined by intravital imaging in our saphenous vein laser injury model, in which a 50 μm injury was induced by laser ablation. Real-time top-down epifluorescence imaging was used to determine time to initial hemostasis, rebleeding events, and platelet and fibrin accumulation. In each mouse, 3-5 injuries were induced at different sites and each injury was visualized for 10 minutes. Following real-time imaging, spinning disk confocal Z-stacks of platelet plugs were obtained for 3D reconstruction to compare platelet plug volume. In untreated WT mice, hemostasis was achieved in ~20 seconds. In WT mice treated with DAPT, initial hemostasis was often rapidly achieved but this was followed by significant rebleeding events. Paradoxically, platelet accumulation was increased in WT + DAPT mice due to extravascular accumulation of platelets which occurred during bleeding. However, in plugs that stabilized, plug volume was reduced in WT + DAPT mice. In hIL-4R/GPIb-Tg mice with reduced platelet counts, untreated platelets were able to form a stable hemostatic plug even at 50,000/μL, although time to hemostasis was slightly prolonged. However, as platelet counts decreased in mice with DAPT-treated platelets, initial hemostasis became more prolonged and many injuries never achieved initial hemostasis. These results suggest that DAPT may not be safe in the setting of severe thrombocytopenia. Disclosures No relevant conflicts of interest to declare.

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PSGL-1 regulates platelet P-selectin-mediated endothelial activation and shedding of P-selectin from activated platelets

Thrombosis and Haemostasis ◽

10.1160/th07-03-0207 ◽

2007 ◽

Vol 98 (10) ◽

pp. 806-812 ◽

Cited By ~ 46

Author(s):

Vandana Dole ◽

Wolfgang Bergmeier ◽

Ian Patten ◽

Junichi Hirahashi ◽

Tanya Mayadas ◽

...

Keyword(s):

Endothelial Activation ◽

Leukocyte Rolling ◽

Wild Type ◽

Platelet Surface ◽

Activated Platelets ◽

And Function ◽

Body Secretion

SummaryWe have previously shown that activated platelets in circulation stimulate release of endothelial Weibel-Palade bodies thus increasing leukocyte rolling in venules. P-selectin on the activated platelets mediates adhesion to leukocytes via PSGL-1 and is rapidly shed into plasma. We were interested in studying the role of PSGL-1 in regulating expression and function of platelet P-selectin. We show here that PSGL-1 is critical for the activation of endothelial cells in venules of mice infused with activated platelets. The interaction of platelet P-selectin with PSGL-1 is also required for P-selectin shedding, as P-selectin was retained significantly longer on the surface of activated platelets infused into PSGL-1-/- compared to wild-type mice. The leukocyte integrin αMβ2 (Mac-1) was not required for P-selectin shedding. In addition to shedding, P-selectin can be downregulated from the platelet surface through internalization and this is the predominant mechanism in the absence of PSGL-1. We demonstrate that leukocyte- neutrophil elastase,known to cleave P-selectin in vitro, is not the major sheddase for P-selectin in vivo. In conclusion, interaction of platelet P-selectin with PSGL-1 is crucial for activation of the endothelium andWeibel-Palade body secretion. The interaction with PSGL-1 also results in rapid shedding of P-selectin thus downregulating the inflammatory potential of the platelet.

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Targeting myeloid-cell specific integrin α9β1 inhibits arterial thrombosis in mice

Blood ◽

10.1182/blood.2019002846 ◽

2020 ◽

Vol 135 (11) ◽

pp. 857-861 ◽

Cited By ~ 2

Author(s):

Nirav Dhanesha ◽

Manasa K. Nayak ◽

Prakash Doddapattar ◽

Manish Jain ◽

Gagan D. Flora ◽

...

Keyword(s):

Arterial Thrombosis ◽

Potential Role ◽

Myeloid Cell ◽

Neutrophil Extracellular Traps ◽

Cathepsin G ◽

Wild Type ◽

Extracellular Traps ◽

Laser Injury ◽

Activated Platelets

Abstract Evidence suggests that neutrophils contribute to thrombosis via several mechanisms, including neutrophil extracellular traps (NETs) formation. Integrin α9β1 is highly expressed on neutrophils when compared with monocytes. It undergoes affinity upregulation on neutrophil activation, and stabilizes adhesion to the activated endothelium. The role of integrin α9 in arterial thrombosis remains unexplored. We generated novel myeloid cell-specific integrin α9−/− mice (α9fl/flLysMCre+) to study the role of integrin α9 in arterial thrombosis. α9fl/fl littermates were used as controls. We report that α9fl/flLysMCre+ mice were less susceptible to arterial thrombosis in ferric chloride (FeCl3) and laser injury-induced thrombosis models with unaltered hemostasis. Neutrophil elastase-positive cells were significantly reduced in α9fl/flLysMCre+ mice concomitant with reduction in neutrophil count, myeloperoxidase levels, and red blood cells in the FeCl3 injury-induced carotid thrombus. The percentage of cells releasing NETs was significantly reduced in α9fl/flLysMCre+ mouse neutrophils stimulated with thrombin-activated platelets. Furthermore, we found a significant decrease in neutrophil-mediated platelet aggregation and cathepsin-G secretion in α9fl/flLysMCre+ mice. Transfusion of α9fl/fl neutrophils in α9fl/flLysMCre+ mice restored thrombosis similar to α9fl/fl mice. Treatment of wild-type mice with anti-integrin α9 antibody inhibited arterial thrombosis. This study identifies the potential role of integrin α9 in modulating arterial thrombosis.

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Negative Effects of GM-CSF Signaling In t(8;21)-Induced Leukemia

Blood ◽

10.1182/blood.v116.21.3163.3163 ◽

2010 ◽

Vol 116 (21) ◽

pp. 3163-3163

Author(s):

Shinobu Matsuura ◽

Ming Yan ◽

Eun-Young Ahn ◽

Miao-Chia Lo ◽

David Dangoor ◽

...

Keyword(s):

Myeloid Leukemia ◽

Sex Chromosome ◽

De Novo ◽

Conflicts Of Interest ◽

Hematopoietic Cells ◽

Receptor Activation ◽

Pseudoautosomal Region ◽

Wild Type ◽

Gm Csf

Abstract Abstract 3163 The t(8;21)(q22;q22) translocation is one of the most common chromosomal translocations in de novo acute myeloid leukemia (AML). The 8;21 translocation is often associated with additional cytogenetic abnormalities. The loss of the sex chromosome (LOS) is by far the most frequent abnormality found in association with the t(8;21) leukemia, accounting for 32–59% of patients, in contrast to other types of AML in which the LOS occurs in less than 5% of patients. To evaluate the role of sex chromosome deletion in t(8;21)-related leukemogenesis, hematopoietic cells from a mouse line with only one sex chromosome were used in retrovirus-mediated t(8;21) (AML1-ETO) expression and transplantation assays. The absence of leukemia in those animals suggested that a gene present in the pseudoautosomal region of sex chromosomes in humans but not in mice may be the target gene in LOS. The granulocyte-macrophage colony-stimulating factor receptor α (GM-CSFRα) gene is one such gene and is also known to be involved in myeloid cell survival, proliferation and differentiation. The GM-CSFRα gene is specifically down-regulated in AML patients with t(8;21), but not in other common translocations (Valk PJM et al, NEJM, 2004). The GM-CSFR complex is composed of α and βc subunits that assemble into a complex for receptor activation and signaling. To investigate the role of GM-CSFR signaling in t(8;21)-mediated leukemogenesis, GM-CSFR common β subunit knockout (GM-CSFRβc-/-) mice were used in our studies as a model for deficient GM-CSFR signaling. Transduction of AML1-ETO in hematopoietic cells from GM-CSFRβc-/- resulted in myeloid leukemia of a median survival time of 225 days, high percentage of blasts in peripheral blood and bone marrow, anemia, thrombocytopenia, hepatomegaly and splenomegaly. Comparison of wild-type and GM-CSFRβc-/- cells in the same transplantation resulted in development of AML1-ETO-induced leukemia at higher penetrance in GM-CSFRβc-/- cells (28.5% vs 100%). Moreover, the latency of leukemia was shorter in GM-CSFRβc-/- cells than in wild-type cells after transduction of AML1-ETO9a. Analysis of the hematopoietic compartment of healthy GM-CSFRβc-/- mice detected no significant abnormalities in the immature hematopoietic compartment (LSK, CMP, GMP, MEP), suggesting that AML1-ETO expression is required for leukemia to occur. In vitro, expression of AML1-ETO alone is sufficient for the immortalization of normal hematopoietic cells, as demonstrated by serial replating capacity of cells in methylcellulose colony assay. Addition of mGM-CSF to the basic cytokine cocktail (mIL-3, hIL-6, mSCF, hEPO) did not significantly affect number, type, size, and cell composition of colony cells. In contrast, the addition of mGM-CSF eliminated the replating capacity of AML1-ETO expressing cells, although they survived longer than control vector-infected cells. The results suggest that activation of GM-CSF signaling can specifically abrogate the self-renewal ability of potential leukemic stem cells in the early immortalization phase. These results support a possible tumor suppressor role of GM-CSF in leukemogeneis by AML1-ETO and may provide clues to understand how AML1-ETO corrupts normal GM-CSF signals to its own advantage for leukemogenic transformation. Disclosures: No relevant conflicts of interest to declare.

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Desialylated Platelets Are Cleared From the Circulation by the Hepatic Asialoglycoprotein Receptor,

Blood ◽

10.1182/blood.v118.21.3257.3257 ◽

2011 ◽

Vol 118 (21) ◽

pp. 3257-3257

Author(s):

Renata Grozovsky ◽

Silvia Giannini ◽

Karin M. Hoffmeister

Keyword(s):

Bone Marrow ◽

Conflicts Of Interest ◽

Fold Increase ◽

Asialoglycoprotein Receptor ◽

Regulatory Mechanisms ◽

Wild Type ◽

Cell Counts ◽

Blood Cell Counts ◽

Terminal Galactose

Abstract Abstract 3257 The regulatory mechanisms of platelet homeostasis remain elusive. We investigated here the role of hepatic asialoglycoprotein receptor (a.k.a. Ashwell-Morell receptor) in platelet clearance. Mice lacking the hepatic asialoglycoprotein receptor Asgpr2 subunit had increased platelet survivals (T1/2 = 49.5±2h) when compared to wild type (WT, T1/2 = 31±4h) mice. Consequently, Asgpr2−/− mice had platelet counts increased by ∼20%, compared to WT, with increased terminal galactose exposure, as demonstrated using the galactose specific lectin RCA1. Bone marrow and spleen megakaryocyte numbers were reduced by ∼15% and ∼20% in Asgpr2−/− mice, compared to WT mice. Sialidase (NA, Clostidium perfringens, 50mU/mice) maximally desialylated circulating platelets when injected intravenously, as evidenced by increased RCA1 binding. Sialidase injection resulted in a ∼60% depletion of circulating platelets after 24h in Asgpr2−/− mice, compared to >90% in WT mice, indicating that desialylated platelets were partially removed by Asgpr1/2. In contrast to platelets, red blood cell counts were unaffected by sialidase treatment. Sialidase injection for 72h resulted in a 2.3-fold and 1.2-fold increase in megakaryocyte numbers in the spleen and bone marrow of WT mice, respectively, but not in Asgpr2−/− mice. In contrast to sialidase treatment, injections of rabbit anti-mouse platelet serum (RAMPS) depleted >95% of circulating platelets and increased by 70% bone marrow, but not spleen MK numbers in both WT and Asgpr2−/− mice. The data shows that removal of desialylated, i.e, senescent, platelets by the hepatic Ashwell-Morell receptor differs to that of antibody-mediated platelet clearance. Disclosures: No relevant conflicts of interest to declare.

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Non-Canonical NF-Kb Signaling Regulates Hematopoietic Stem Cell Self-Renewal and Microenvironment Interactions

Blood ◽

10.1182/blood.v118.21.859.859 ◽

2011 ◽

Vol 118 (21) ◽

pp. 859-859 ◽

Cited By ~ 1

Author(s):

Chen Zhao ◽

Yan Xiu ◽

John M Ashton ◽

Lianping Xing ◽

Yoshikazu Morita ◽

...

Keyword(s):

Bone Marrow ◽

Bone Marrow Cells ◽

Conflicts Of Interest ◽

Wild Type ◽

Double Knockout ◽

Self Renewal ◽

Hematopoietic Stem ◽

Physiological Processes ◽

Marrow Cells

Abstract Abstract 859 RelB and NF-kB2 are the main effectors of NF-kB non-canonical signaling and play critical roles in many physiological processes. However, their role in hematopoietic stem/progenitor cell (HSPC) maintenance has not been characterized. To investigate this, we generated RelB/NF-kB2 double-knockout (dKO) mice and found that dKO HSPCs have profoundly impaired engraftment and self-renewal activity after transplantation into wild-type recipients. Transplantation of wild-type bone marrow cells into dKO mice to assess the role of the dKO microenvironment showed that wild-type HSPCs cycled more rapidly, were more abundant, and had developmental aberrancies: increased myeloid and decreased lymphoid lineages, similar to dKO HSPCs. Notably, when these wild-type cells were returned to normal hosts, these phenotypic changes were reversed, indicating a potent but transient phenotype conferred by the dKO microenvironment. However, dKO bone marrow stromal cell numbers were reduced, and bone-lining niche cells supported less HSPC expansion than controls. Further, increased dKO HSPC proliferation was associated with impaired expression of niche adhesion molecules by bone-lining cells and increased inflammatory cytokine expression by bone marrow cells. Thus, RelB/NF-kB2 signaling positively and intrinsically regulates HSPC self-renewal and maintains stromal/osteoblastic niches and negatively and extrinsically regulates HSPC expansion and lineage commitment through the marrow microenvironment. Disclosures: No relevant conflicts of interest to declare.

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The Clinical Role of Micrornas (miRs) in Cytogenetically Normal (CN) Acute Myeloid Leukemia (AML): miR-155 Upregulation Independently Identifies High-Risk Patients (Pts)

Blood ◽

10.1182/blood.v120.21.1387.1387 ◽

2012 ◽

Vol 120 (21) ◽

pp. 1387-1387 ◽

Cited By ~ 1

Author(s):

Guido Marcucci ◽

Kati Maharry ◽

Klaus H. Metzeler ◽

Stefano Volinia ◽

Yue-Zhong Wu ◽

...

Keyword(s):

Clinical Outcome ◽

Conflicts Of Interest ◽

Disease Free Survival ◽

Gene Expression Signature ◽

White Blood Count ◽

Categorical Variables ◽

Prognostic Impact ◽

Continuous Variables ◽

Wild Type

Abstract Abstract 1387 miR-155 is upregulated in aggressive subtypes of solid tumors and leukemia. In AML, higher miR-155 expression is associated with FLT3-ITD. However, whether miR-155 upregulation impacts on clinical outcome independently from FLT3-ITD and other prognosticators is unknown. We evaluated the prognostic impact of miR-155 in 363 CN-AML pts (153 age <60 y; 210 age ≥60 y) that were treated with cytarabine-daunorubicin-based regimens and had a median follow-up of 7.9 y (range, 2.3–12.9). miR-155 levels were measured in pretreatment marrow or blood by the NanoString nCounter assay quantifying expression of the encoding gene MIR155HG; other molecular markers were assessed centrally. High miR-155 expressers (miR-155) had higher WBC (P<.001) and were more often FLT3-ITD-positive (pos; P<.001), RUNX1-mutated (mut; <.001), WT1-mut (P=.03), ↑ ERG (P=.02) and ↑ BAALC (P=.002), and less often CEBPA-mut (P=.003), IDH2-mut (P=.004) and FLT3-TKD-pos (P=.08) than low expressers (↓ miR-155). ↑ miR-155 had lower CR rates (P<.001), shorter DFS (P=.001) and OS (P<.001), than ↓ miR-155. In multivariable analyses (MVA; Table), ↑ miR-155 was associated with lower CR rates (P=.007) and shorter OS (P<.001). Among younger pts, ↑ miR-155 had lower CR rates (P=.03) and shorter DFS (P<.001) and OS (P<.001) than ↓ miR-155. In MVA (Table), ↑ miR-155 status remained associated with worse CR rate (P=.06), shorter DFS (P=.003) and OS (P=.01). Among older pts, ↑ miR-155 had lower CR rates (P=.008) and shorter OS (P<.001); in MVA (Table), ↑ miR-155 remained associated with worse CR (P=.03) and shorter OS (P=.05). In the European LeukemiaNet classification, younger ↑ miR-155 in the Favorable (Fav) Genetic Group (GG; CEBPA-mut and/or NPM1-mut without FLT3-ITD) had lower CR rates (P=.03) and shorter DFS (P=.04) and OS (P=.02) than ↓ miR-155. In the younger Intermediate-I (Int-I) GG pts (with wild-type CEBPA, NPM1-mut with FLT3-ITD, or wild-type NPM1), miR-155 expression did not impact independently on outcome. In older pts, ↑ miR-155 had a shorter OS both in the Fav (P=.06) and Int-I GGs (P=.05) than ↓ miR-155. To gain biologic insights, we derived an Affymetrix gene-expression signature that comprised 196 mRNAs significantly correlated with miR-155 expression. Consistent with previous mechanistic studies, Gene Ontology analysis revealed that the ↑ miR-155-associated signature was enriched for genes involved in anti-apoptotic, proliferative and inflammatory activities (FDR<0.05). ↑ miR-155 was not significantly correlated with that of any other microRNAs (miRs) thereby supporting the unique role of miR-155 among the miRs in AML. In summary, miR-155 expression is independently associated with clinical outcome in CN-AML and may allow for better evaluation of molecular risk, especially in pts lacking FLT3-ITD, like those in the ELN Fav GG. Moreover, given its role in deregulation of fundamental mechanisms of cell homeostasis and the emergence of miR inhibitors, miR-155 may become a novel therapeutic target. Table. MVA in pts with primary CN-AML Group CR DFS OS OR P HR P HR P All pts miR-155 expression not significantly associated with DFS a miR-155, ↑ v ↓ 0.46 .007 1.62 <.001 NPM1, mut v wt 2.42 .005 BAALC, ↑ v ↓ 0.37 .002 2.16 <.001 WBC, each 50 units 0.65 <.001 Age group, older v younger 0.43 .003 2.38 <.001 FLT3-ITD, pos v neg 1.78 <.001 Race, white v nonwhite 1.62 .03 Pts age < 60 y miR-155, ↑ v ↓ 0.39 .06 2.13 .003 1.84 .01 RUNX1, mut v wt 0.21 .01 Age, each 10 y increase 0.45 .004 WBC, each 50 units 1.49 <.001 FLT3-ITD, pos v neg 2.82 <.001 1.82 .01 FLT3-TKD, pos v neg 3.27 <.001 BAALC, ↑ v ↓ 2.66 <.001 2.33 <.001 Race, white v nonwhite 2.81 .02 CEBPA, mut v wt 0.47 .02 WT1, mut v wt 2.25 .005 Pts age ≥ 60 y miR-155 expression not significantly associated with DFS miR-155, ↑ v ↓ 0.46 .03 1.36 .05 NPM1, mut v wt 2.45 .03 BAALC, ↑ v ↓ 0.32 .004 2.18 <.001 WBC, each 50 units 0.65 .005 Age, each 10 y increase 0.48 .02 FLT3-ITD, pos v neg 1.56 .006 ↑, high expression; ↓, low expression; CR, complete remission; DFS, disease-free survival; HR, hazard ratio; mut, mutated; neg, negative; OR, odds ratio; OS, overall survival; pos, positive; WBC, white blood count; wt, wild-type. Odds ratios > (<) 1.0 mean higher (lower) CR rate and HRs > (<) 1.0 mean higher (lower) risk of relapse or death (DFS) or death (OS) for the higher values of continuous variables and the 1st category listed for categorical variables. Disclosures: No relevant conflicts of interest to declare.

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Gtpase Immunity-Associated Protein Family Member 4 Contributes to the Enhanced Expansion of HSPCs in RUNX1 Deficient Mice

Blood ◽

10.1182/blood.v124.21.4344.4344 ◽

2014 ◽

Vol 124 (21) ◽

pp. 4344-4344

Author(s):

Amanda Scholl ◽

Kentson Lam ◽

Alex Muselman ◽

Tingdong Tang ◽

Shinobu Matsuura ◽

...

Keyword(s):

Family Member ◽

Conflicts Of Interest ◽

Protein Family ◽

Dominant Negative ◽

Negative Regulator ◽

Wild Type ◽

Double Knockout ◽

Hematopoietic Stem ◽

Myeloid Progenitor

Abstract RUNX1 is the transcription factor described as the master regulator of hematopoiesis. Due to its central role during blood development, numerous RUNX1 mutations have been reported in hematologic abnormalities. Mice null for Runx1 die during embryogenesis, lacking definitive HSCs. Conditional Runx1Δ/Δ mice are viable, but exhibit a variety of blood abnormalities. The most salient defect in these Runx1Δ/Δ mice is expansion of the hematopoietic stem and progenitor cell (HSPC) population, measured as an increase in number of lineage negative, Sca1 positive, cKit positive (LSK) cells. A shortened form of RUNX1 (RUNX1SF) lacking the C-terminal and part of the N-terminal domain (41-214) acts as a dominant negative regulator of RUNX1 and hence also models RUNX1 loss-of-function. A differential gene expression analysis of HSPCs derived from Runx1Δ/Δ compared to wild type mice uncovered GTPase immunity-associated protein family member 4 (GIMAP4) as one of the genes most highly upregulated. Previous studies have focused almost exclusively on the role of GIMAP4 as a pro-apoptotic protein during T-cell development. This study illuminates a novel non-apoptotic role of GIMAP4 in a formerly unstudied HSPC context. Runx1Δ/Δ mice were crossed with Gimap4-/- mice to generate a double knockout (dKO) mouse line. These dKO mice exhibited attenuated HSPC proliferation in comparison to Runx1Δ/Δ mice, suggesting that GIMAP4 functions in this HSPC expansion phenotype. BMT experiments using lethally irradiated C57 mice and RUNX1SF transduced wild type versus Gimap4-/-bone marrow confirmed this result. GIMAP4 also worked independently and coordinately with RUNX1 to influence individual progenitor populations. Common lymphoid progenitors (CLP) were affected only by GIMAP4. Gimap4-/- mice exhibited an expansion of the CLP population, consistent with its pro-apoptotic role in lymphoid populations. Conversely, both RUNX1 and GIMAP4 coordinately exerted an effect on myeloid progenitor populations. Runx1Δ/Δ mice harbored expanded granulocyte-macrophage progenitor (GMP) and common myeloid progenitor (CMP) populations. This expansion was not observed when GIMAP4 was also ablated. This suggests a pro-proliferative role of GIMAP4 specifically in myeloid populations. These opposing roles of GIMAP4 in lymphoid versus myeloid cells suggest a more contextual, cell-specific role of this GTPase protein. Ultimately, this study provides insight into how RUNX1 and GIMAP4 may coordinate to maintain HSPC homeostasis. Disclosures No relevant conflicts of interest to declare.

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