Two novel families with RUNX1 variants indicate glycine 168 as a new mutational hotspot: Implications for FPD/AML diagnosis.

Correct interpretation of the pathogenicity of germline RUNX1 variants is essential for FPD/AML diagnosis, clinical management and leukaemia surveillance. We report two families with clear FPD/AML phenotypic features harbouring missense variants at RHD critical residue Gly168. Although classified as of unknown significance (VUS) by RUNX1-specific curation guidelines, these variants should rather be considered likely pathogenic, as supported by computational tools, structural modelling and dysregulated platelet expression of RUNX1-targets, adding Gly168 among amino acids currently recognised as mutational hotspots. Our data could help reduce the number of variants classified as VUS, providing evidence for updating RUNX1 guidelines, thus improving FPD/AML diagnosis.

Elevated levels of damage-associated molecular patterns HMGB1 and S100A8/A9 coupled with toll-like receptor-triggered monocyte activation are associated with inflammation in patients with myelofibrosis.

Inflammation plays a pivotal role in the pathogenesis of primary and post-essential thrombocythemia or post-polycythemia vera myelofibrosis (MF) in close cooperation with the underlying molecular drivers. This inflammatory state is induced by a dynamic spectrum of inflammatory cytokines, although recent evidence points to the participation of additional soluble inflammatory mediators. Damage-associated molecular patterns (DAMPs) represent endogenous signals released upon cell death or damage which trigger a potent innate immune response. We assessed the contribution of two prototypical DAMPs, HMGB1 and S100A8/A9, to MF inflammation. Circulating HMGB1 and S100A8/A9 were elevated in MF patients in parallel to the degree of systemic inflammation and levels increased progressively during advanced disease stages. Patients with elevated DAMPs had higher frequency of adverse clinical features, such as anemia, and inferior survival, suggesting their contribution to disease progression. Monocytes, which are key players in MF inflammation, were identified as a source of S100A8/A9 but not HMGB1 release, while both DAMPs correlated with cell death parameters, such as serum LDH and cell-free DNA, indicating that passive release is an additional mechanism leading to increased DAMPs. HMGB1 and S100A8/A9 promote inflammation through binding to Toll-like receptor (TLR) 4, whereas the former also binds TLR2. Monocytes from MF patients were shown to be hyperactivated at baseline, as reflected by higher CD11b and tissue factor exposure and increased expression levels of proinflammatory cytokines IL-1ß and IL-6. Patient monocytes showed preserved TLR4 and TLR2 expression and were able to mount normal or even exacerbated functional responses and cytokine upregulation following stimulation of TLR4 and TLR2. Elevated levels of endogenous TLR ligands HMGB1 and S100A8/A9 coupled to the finding of preserved or hyperreactive TLR-triggered responses indicate that DAMPs may promote monocyte activation and cytokine production in MF, fueling inflammation. Plasma IL-1ß and IL-6 were elevated in MF and correlated with DAMPs levels, raising the possibility that DAMPs could contribute to cytokine generation in vivo. In conclusion, this study highlights that, in cooperation with classic proinflammatory cytokines, DAMPs represent additional inflammatory mediators that may participate in the generation of MF inflammatory state, potentially providing novel biomarkers of disease progression and new therapeutic targets.

Toll-like receptor expression and functional behavior in platelets from patients with systemic lupus erythematosus.

BACKGROUND: Multiple blood cell abnormalities participate in the development of inflammation in systemic lupus erythematosus (SLE). Although platelets have been suggested as one of these contributors through the release of their content during activation, there are limited specific data about their role as immune players in SLE. MATERIALS AND METHODS: Thirteen SLE patients were included. Flow cytometry was used to measure Toll-like receptors (TLR) 2, 4, and 9 in resting platelets, platelet-activation markers (PAC-1 binding, P-selectin, CD63, and CD40 ligand -L) and platelet-leukocyte aggregates before and after specific TLR stimulation. Soluble CD40L and von Willebrand factor (vWf) release from stimulated platelets was measured using ELISA. RESULTS: In resting conditions, SLE platelets showed normal expression levels of TLR 2, 4 and 9. Platelet surface activation markers, soluble CD40L, and vWf release were normal at baseline and after TLR stimulation. Platelet-monocyte aggregates were elevated in resting conditions in SLE samples and showed only a marginal increase after TLR stimulation, while baseline and stimulated platelet-neutrophil and platelet-lymphocyte aggregates were normal. C-reactive protein levels positively correlated with platelet-monocyte aggregates both at baseline and after stimulation with the TLR-2 agonist PAM3CSK4, suggesting these complexes could reflect the inflammatory activity in SLE. In our cohort, 12 of 13 patients received treatment with hydroxychloroquine (HCQ), a known inhibitor of endosomal activity and a potential inhibitor of platelet activation. The fact that SLE platelets showed an adequate response to TLR agonists suggests that, despite this treatment, they retain the ability to respond to the increased levels of damage-associated molecular patterns (DAMPs), which represent known TLR ligands, present in the circulation of SLE patients. Interestingly, elevated plasma levels of high mobility group box 1 (HMGB1), a classical DAMP, correlated with vWf release from TLR-stimulated platelets, suggesting that HMGB1 may also be released by platelets, thereby creating a positive feedback loop for platelet activation that contributes to inflammation. CONCLUSION: Our study demonstrates normal platelet TLR expression and function together with increased circulating platelet-monocyte aggregates. In addition, a direct correlation was observed between plasma HMGB1 levels and platelet vWf release following TLR2 stimulation. This platelet behavior in a group of patients undergoing HCQ treatment suggests that platelets could play a role in the inflammatory state of SLE.

High cell-free DNA is associated with disease progression, inflammasome activation and elevated levels of inflammasome-related cytokine IL-18 in patients with myelofibrosis.

Myelofibrosis (MF) is a clonal hematopoietic stem cell disorder classified among chronic myeloproliferative neoplasms, characterized by exacerbated myeloid and megakaryocytic proliferation and bone marrow fibrosis. It is induced by driver (JAK2/CALR/MPL) and high molecular risk mutations coupled to a sustained inflammatory state that contributes to disease pathogenesis. Patient outcome is determined by stratification into risk groups and refinement of current prognostic systems may help individualize treatment decisions. Circulating cell-free (cf)DNA comprises short fragments of double-stranded DNA, which promotes inflammation by stimulating several pathways, including inflammasome activation, which is responsible for IL-1ß and IL-18 maturation and release. In this work, we assessed the contribution of cfDNA as a marker of disease progression and mediator of inflammation in MF. cfDNA was increased in MF patients and higher levels were associated with adverse clinical outcome, a high-risk molecular profile, advanced disease stages and inferior overall survival, indicating its potential value as a prognostic marker. Cell-free DNA levels correlated with tumor burden parameters and markers of systemic inflammation. To mimic the effects of cfDNA, monocytes were stimulated with poly(dA:dT), a synthetic double-stranded DNA. Following stimulation, patient monocytes released higher amounts of inflammasome-processed cytokine, IL-18 to the culture supernatant, reflecting enhanced inflammasome function. Despite overexpression of cytosolic DNA inflammasome sensor AIM2, IL-18 release from MF monocytes was shown to rely mainly on the NLRP3 inflammasome, as it was prevented by NLRP3-specific inhibitor MCC950. Circulating IL-18 levels were increased in MF plasma, reflecting in vivo inflammasome activation, and highlighting the previously unrecognized involvement of this cytokine in MF cytokine network. Monocyte counts were higher in patients and showed a trend towards correlation with IL-18 levels, suggesting monocytes represent a source of circulating IL-18. The close correlation shown between IL-18 and cfDNA levels, together with the finding of enhanced DNA-triggered IL-18 release from monocytes, suggest that cfDNA promotes inflammation, at least in part, through inflammasome activation. This work highlights cfDNA, the inflammasome and IL-18 as additional players in the complex inflammatory circuit that fosters MF progression, potentially providing new therapeutic targets.

Pathogenic mechanisms contributing to thrombocytopenia in patients with systemic lupus erythematosus.

SummarySystemic lupus erythematosus (SLE) is an autoimmune condition developing thrombocytopenia in about 10-15% of cases, however, mechanisms leading to low platelet count were not deeply investigated in this illness. Here we studied possible causes of thrombocytopenia, including different mechanisms of platelet clearance and impairment in platelet production. Twenty-five SLE patients with and without thrombocytopenia were included. Platelet apoptosis, assessed by measurement of loss of mitochondrial membrane potential, active caspase 3 and phosphatidylserine exposure, was found to increase in thrombocytopenic patients. Plasma from 67% SLE patients (thrombocytopenic and non-thrombocytopenic) induced loss of sialic acid (Ricinus communis agglutinin I and/or Peanut agglutinin binding) from normal platelet glycoproteins. Concerning platelet production, SLE plasma increased megakaryopoiesis (evaluated using normal human cord blood CD34+ hematopoietic progenitors), but inhibited thrombopoiesis (proplatelet count). Anti-platelet autoantibody depletion from SLE plasma reverted this inhibition. Overall, abnormalities were more frequently observed in thrombocytopenic than non-thrombocytopenic SLE patients and in those with active disease (SLEDAI≥5). In conclusion, platelet clearance due to apoptosis and desialylation, and impaired platelet production mainly due to inhibition of thrombopoiesis, could be relevant mechanisms leading to thrombocytopenia in SLE. These findings could provide a rational basis for the choice of proper therapies to correct platelet counts in these patients.[Figure: see text].

Platelet Toll-Like Receptors Mediate Thromboinflammatory Responses in Patients With Essential Thrombocythemia.

Essential thrombocythemia (ET) is comprised among chronic myeloproliferative neoplasms (MPN) and is caused by driver mutations in JAK2, CALR, and MPL, which lead to megakaryocyte proliferation and prominent thrombocytosis. Thrombosis remains the main cause of morbidity in ET and is driven by the interplay between blood cells, the endothelium, the clotting cascade, and host-derived inflammatory mediators. Platelet activation plays a key role in the thrombotic predisposition, although the underlying mechanisms remain poorly defined. In addition to their role in hemostasis, platelets participate in innate immunity and inflammation owing to the expression of toll-like receptors (TLR), which recognize inflammatory signals, triggering platelet functional responses. Considering the impact of inflammation on ET procoagulant state, we assessed the contribution of TLR2 and TLR4 to platelet hemostatic and inflammatory properties in ET patients, by using Pam3CSK4 and lipopolysaccharide (LPS) as specific TLR2 and TLR4 ligands, respectively. TLR2 ligation induced increased surface translocation of α-granule-derived P-selectin and CD40L, which mediate platelet interaction with leukocytes and endothelial cells, respectively, and higher levels of dense granule-derived CD63 in patients, whereas PAC-1 binding was not increased and LPS had no effect on these platelet responses. Platelet-neutrophil aggregate formation was elevated in ET at baseline and after stimulation of both TLR2 and TLR4. In addition, ET patients displayed higher TLR2- and TLR4-triggered platelet secretion of the chemokine RANTES (CCL5), whereas von Willebrand factor release was not enhanced, revealing a differential releasate pattern for α-granule-stored inflammatory molecules. TLR-mediated hyperresponsiveness contrasted with impaired or preserved responses to classic platelet hemostatic agonists, such as TRAP-6 and thrombin. TLR2 and TLR4 expression on the platelet surface was normal, whereas phosphorylation of downstream effector ERK1/2 was higher in patients at baseline and after incubation with Pam3CSK4, which may partly explain the enhanced TLR2 response. In conclusion, exacerbated response to TLR stimulation may promote platelet activation in ET, boosting platelet/leukocyte/endothelial interactions and secretion of inflammatory mediators, overall reinforcing the thromboinflammatory state. These findings highlight the role of platelets as inflammatory sentinels in MPN prothrombotic scenario and provide additional evidence for the close intertwining between thrombosis and inflammation in this setting.

Downregulation of TREM-like transcript-1 and collagen receptor α2 subunit, two novel RUNX1-targets, contributes to platelet dysfunction in familial platelet disorder with predisposition to acute myelogenous leukemia.

Germline RUNX1 mutations lead to thrombocytopenia and platelet dysfunction in familial platelet disorder with predisposition to acute myelogenous leukemia (AML). Multiple aspects of platelet function are impaired in these patients, associated with altered expression of genes regulated by RUNX1 We aimed to identify RUNX1-targets involved in platelet function by combining transcriptome analysis of patient and shRUNX1-transduced megakaryocytes (MK). Down-regulated genes included TREM-like transcript (TLT)-1 (TREML1) and the integrin subunit alpha (α)-2 (ITGA2) of collagen receptor α2-beta (ß)-1, which are involved in platelet aggregation and adhesion, respectively. RUNX1 binding to regions enriched for H3K27Ac marks was demonstrated for both genes using chromatin immunoprecipitation. Cloning of these regions upstream of the respective promoters in lentivirus allowing mCherry reporter expression showed that RUNX1 positively regulates TREML1 and ITGA2, and this regulation was abrogated after deletion of RUNX1 sites. TLT-1 content was reduced in patient MK and platelets. A blocking anti-TLT-1 antibody was able to block aggregation of normal but not patient platelets, whereas recombinant soluble TLT-1 potentiated fibrinogen binding to patient platelets, pointing to a role for TLT-1 deficiency in the platelet function defect. Low levels of α2 integrin subunit were demonstrated in patient platelets and MK, coupled with reduced platelet and MK adhesion to collagen, both under static and flow conditions. In conclusion, we show that gene expression profiling of RUNX1 knock-down or mutated MK provides a suitable approach to identify novel RUNX1 targets, among which downregulation of TREML1 and ITGA2 clearly contribute to the platelet phenotype of familial platelet disorder with predisposition to AML.

Differential expression of SDF-1 receptor CXCR4 in molecularly defined forms of inherited thrombocytopenias.

The SDF-1-CXCR4 axis plays an essential role in the regulation of platelet production, by directing megakaryocyte (MK) migration toward the vascular niche, thus allowing terminal maturation and proplatelet formation, and also regulates platelet function in an autocrine manner. Inherited thrombocytopenias (IT) comprise a spectrum of diverse clinical conditions caused by mutations in genes involved in platelet production and function. We assessed CXCR4 expression and SDF-1 levels in a panel of well-characterized forms of IT. Decreased surface CXCR4 levels were found in 8 of 27 (29.6%) IT patients by flow cytometry, including 4 of 6 patients with ANKRD26-RT, 3 of 3 patients with GPS and 1 of 6 patients with FPD/AML. Low CXCR4 levels were associated with impaired SDF-1-triggered platelet aggregation, indicating that this decrease is functionally relevant, whereas a normal platelet response was shown in patients harbouring preserved membrane CXCR4. Reduced CXCR4 was not due to decreased gene expression, as platelet RNA levels were normal or increased, suggesting a post-transcriptional defect. Increased ligand-induced receptor internalization was ruled out, as circulating SDF-1 levels were similar to controls. MK CXCR4 expression was normal, indicating that the defect in CXCR4 arises after the step of platelet biogenesis. In conclusion, the finding of defective CXCR4 expression specifically associated with certain IT disorders highlights the fact that abnormalities in several megakaryocytic regulators underlie IT pathogenesis and further reveal the heterogeneous nature of these conditions.

Neutrophil extracellular trap formation and circulating nucleosomes in patients with chronic myeloproliferative neoplasms.

The mechanisms underlying increased thrombotic risk in chronic myeloproliferative neoplasms (MPN) are incompletely understood. We assessed whether neutrophil extracellular traps (NETs), which promote thrombosis, contribute to the procoagulant state in essential thrombocythemia, polycythemia vera and myelofibrosis (MF) patients. Although MPN neutrophils showed increased basal reactive oxygen species (ROS), enhanced NETosis by unstimulated neutrophils was an infrequent finding, whereas PMA-triggered NETosis was impaired, particularly in MF, due to decreased PMA-triggered ROS production. Elevated circulating nucleosomes were a prominent finding and were higher in patients with advanced disease, which may have potential prognostic implication. Histone-MPO complexes, proposed as specific NET biomarker, were seldomly detected, suggesting NETs may not be the main source of nucleosomes in most patients, whereas their correlation with high LDH points to increased cell turn-over as a plausible origin. Lack of association of nucleosomes or NETs with thrombosis or activation markers does not support their use as predictors of thrombosis although prospective studies in a larger cohort may help define their potential contribution to MPN thrombosis. These results do not provide evidence for relevant in vivo NETosis in MPN patients under steady state conditions, although availability of standardized NET biomarkers may contribute to further research in this field.

Long-term follow-up of essential thrombocythemia patients treated with anagrelide: subgroup analysis according to JAK2/CALR/MPL mutational status.

BACKGROUND: Anagrelide represents a treatment option for essential thrombocythemia, although its place in therapy remains controversial. AIM: To assess the impact of mutational status in response rates and development of adverse events during long-term use of anagrelide. METHODS: We retrospectively evaluated 67 patients with essential thrombocythemia treated with anagrelide during 68 (4-176) months. RESULTS: Mutational frequencies were 46.3%, 28.3%, and 1.5% for JAK2V617F, CALR and MPL mutations. Anagrelide yielded a high rate of hematologic responses, which were complete in 49.25% and partial in 46.25%, without differences among molecular subsets. The rate of thrombosis during treatment was one per 100 patient-years, without excess bleeding. Anemia was the major adverse event, 30.3% at 5-yr follow-up, being more frequent in CALR(+) (P < 0.05). Myelofibrotic transformation developed in 14.9% (12.9%, 21%, and 12.5% in JAK2V617F(+), CALR(+), and triple-negative patients, respectively, P = NS) and those treated >60 months were at higher risk, OR (95% CI) 9.32 (1.1-78.5), P < 0.01, indicating the need for bone marrow monitoring during prolonged treatment. CONCLUSION: Although CALR(+) patients were at higher risk of developing anemia, anagrelide proved effective among all molecular subsets, indicating that mutational status does not seem to represent a major determinant of choice of cytoreductive treatment among essential thrombocythemia therapies.

Abnormal regulation of soluble and anchored IL-6 receptor in monocytes from patients with essential thrombocythemia.

OBJECTIVE: In a previous study, we found increased plasma soluble receptor for interleukin-6 (sIL-6R) levels in patients with essential thrombocythemia (ET) that could promote megakaryopoiesis through IL-6 binding and further interaction with the signal transducer gp130. Here we have searched for the cell source of sIL-6R within mononuclear cells in these patients and the underlying abnormalities involved in its overproduction. MATERIALS AND METHODS: Thirty patients with the diagnosis of ET were studied. sIL-6R levels were measured by enzyme-linked immunosorbent assay technique in the supernatants of peripheral monocyte and lymphocyte cultures. Expression of membrane-anchored IL-6R was determined by flow cytometry. In order to study the mechanism of sIL-6R production, tumor necrosis factor-α protease inhibitor was added to specifically block IL-6R shedding. Gene expression of sIL-6R levels were evaluated by reverse transcription polymerase chain reaction. RESULTS: Monocytes were the main source of sIL-6R. Besides, in ET patients, monocyte sIL-6R release was higher than that of controls (p = 0.0014). Lymphocytes enhanced monocyte sIL-6R production by cell-mediated contact in normal controls, but this cooperation could not be seen in patients. Membrane expression of IL-6R was increased after monocyte adhesion in ET. sIL-6R synthesis was upregulated in most patients, while messenger RNA was normal. CONCLUSIONS: Our results indicate that ET monocytes are responsible for sIL-6R overproduction within mononuclear cells through synthesis upregulation. In addition, the lack of cooperation of lymphocytes in monocyte sIL-6R production in ET could be due to a monocyte abnormality. The agonistic effect of sIL-6R on IL-6 action could contribute to the exacerbated megakaryocytic growth in ET.

Screening for MPL mutations in essential thrombocythemia and primary myelofibrosis: normal Mpl expression and absence of constitutive STAT3 and STAT5 activation in MPLW515L-positive platelets.

OBJECTIVES: To evaluate the frequency of MPL W515L, W515K and S505N mutations in essential thrombocythemia (ET) and primary myelofibrosis (PMF) and to determine whether MPLW515L leads to impaired Mpl expression, constitutive STAT3 and STAT5 activation and enhanced response to thrombopoietin (TPO). METHODS: Mutation detection was performed by allele-specific PCR and sequencing. Platelet Mpl expression was evaluated by flow cytometry, immunoblotting and real-time RT-PCR. Activation of STAT3 and STAT5 before and after stimulation with increasing concentrations of TPO was studied by immunoblotting. Plasma TPO was measured by ELISA. RESULTS: MPLW515L was detected in 1 of 100 patients with ET and 1 of 11 with PMF. Platelets from the PMF patient showed 100% mutant allele, which was <50% in platelets from the ET patient, who also showed the mutation in granulocytes, monocytes and B cells. Mpl surface and total protein expression were normal, and TPO levels were mildly increased in the MPLW515L-positive ET patient, while MPL transcripts did not differ from controls in both MPLW515L-positive patients. Constitutive STAT3 and STAT5 phosphorylation was absent and dose response to TPO-induced phosphorylation was not enhanced. CONCLUSIONS: The low frequency of MPL mutations in this cohort is in agreement with previous studies. The finding of normal Mpl levels in MPLW515L-positive platelets indicates this mutation does not lead to dysregulated Mpl expression, as frequently shown for myeloproliferative neoplasms. The lack of spontaneous STAT3 and STAT5 activation and the normal response to TPO is unexpected as MPLW515L leads to constitutive receptor activation and hypersensitivity to TPO in experimental models.

Dysregulation of stromal derived factor 1/CXCR4 axis in the megakaryocytic lineage in essential thrombocythemia.

This study investigated the involvement of chemokines including stromal derived factor 1 (SDF-1), interleukin 8 (IL-8), growth-related oncogene alpha (GRO-alpha) and their receptors, CXCR4, CXCR2 and CXCR1 in essential thrombocythemia (ET), a chronic myeloproliferative disease characterized by megakaryocytic hyperplasia and high platelet count. Fifty-three ET patients were studied. Plasma levels of SDF-1, IL-8 and GRO-alpha, evaluated by enzyme-linked immunosorbent assay, and flow cytometric analysis of CXCR1 and CXCR2 on the platelet membrane, were found to be normal in ET patients. CXCR4 expression on platelet surface as well as platelet CXCR4 mRNA detected by real-time reverse transcription polymerase chain reaction, were decreased. Platelet CXCR4 internalization rate was normal while SDF-1-induced platelet aggregation was delayed, decreased or absent. Immunohistochemical staining revealed that megakaryocytes were also affected. CXCR4 decrease was not observed either in peripheral white blood cells or in circulating CD34(+) precursors. These results show that CXCR4 is decreased in the megakaryocytic lineage in ET, mainly due to a reduced CXCR4 production, and an abnormal platelet response to SDF-1. This report is the first to describe platelet and megakaryocytic CXCR4 deficiency in a human disease and the presence of this abnormality in a megakaryocytic-related illness highlights the important role of SDF-1/CXCR4 axis in platelet development.

JAK2V617F mutation in platelets from essential thrombocythemia patients: correlation with clinical features and analysis of STAT5 phosphorylation status.

OBJECTIVE: JAK2V617F mutation rate in granulocytes from essential thrombocythemia (ET) patients ranges from 12% to 57%. Our aim was to evaluate the frequency of this mutation in the megakaryocyte/platelet lineage, and to analyze its clinical associations in ET. In addition, we determined whether this mutation leads to constitutive phosphorylation of STAT5 in platelets. MATERIALS AND METHODS: Consecutive patients with ET were included and clinical features were retrospectively reviewed. Mutation detection was performed by allele specific RT-PCR (AS-RT-PCR) and Restriction fragment length polymorphism (RFLP) analysis of platelet RNA. Constitutive phosphorylation of STAT5 in platelets was studied by Western blot. RESULTS: Fifty patients were included, 24 (48%) were JAK2V617F-positive by both AS-RT-PCR and RFLP. Patients with the mutation were older, had significantly higher hemoglobin levels, and lower platelet counts. Besides, higher frequency of thrombotic events was found in JAK2V617F-positive patients younger than 60, 53% vs. 4%, P = 0.0008. In addition, constitutive STAT5 phosphorylation was not detected in platelets from 12 patients. CONCLUSIONS: The frequency of the JAK2V617F mutation in platelets was similar to that reported in granulocytes in the literature, suggesting this mutation does not occur as an isolated event in the megakaryocyte lineage. If confirmed in a larger study, the observed higher frequency of thrombosis in patients younger than 60 might be a useful predictive marker for thrombosis in this subset of patients. Even though this mutation has been predicted to constitutively activate the JAK2 kinase, spontaneous phosphorylation of STAT5 does not seem to be a frequent finding in platelets from ET patients.

[Megakaryopoietic cytokine levels in patients with essential thrombocythemia and their relationship with clinical and biochemical features]. / Niveles de citoquinas megacariocitopoyeticas en pacientes con trombocitemia esencial y su relacion con caracteristicas clinicas y bioquimicas.

Megakaryopoiesis and platelet production are driven by transcription factors and cytokines present in bone marrow environment. Essential thrombocythemia (ET) is a chronic myeloproliferative disorder characterized by high platelet count and megakaryocytic hyperplasia. In the present work we evaluated plasmatic levels of cytokines involved in megakaryocytic development in a group of patients with ET that were not on treatment, as well as thrombopoietin (TPO) levels before and during anagrelide treatment. The assays were carried out using ELISA techniques. Among the cytokines mainly involved in proliferation of megakaryocytic progenitors, interleukin 3 (IL-3) levels were found increased in patients compared to normal controls (p = 0.0383). Granulocyte-macrophage colony stimulating factor and stem cell factor levels were normal. Interleukin 6, as well as interleukin 11 and erythropoietin (EPO), cytokines mainly related to megakaryocytic maturation, were normal. Plasma TPO levels before treatment were within the normal range and increased during treatment but the difference was not statistically significant. Patients who displayed spontaneous platelet aggregation had higher plasma TPO levels compared to those who did not (p = 0.049). We did not find any relationship between cytokine levels and clinical or laboratory parameters. The high IL-3 levels seen in some patients with ET could contribute to megakaryocytic proliferation. The simultaneous occurrence of higher TPO levels and elevated platelet count could be a predisposing factor for the development of spontaneous platelet aggregation in ET patients.

Niveles de citoquinas megacariocitopoyéticas en pacientes con trombocitemia esencial y su relación con características clínicas y bioquímicas / Megakaryopoietic cytokine levels in patients with essential thrombocythemia and their relationship with clinical and biochemical features

La megacariocitopoyesis y la producción de plaquetas están regidas por factores de transcripción y citoquinas presentes en el microambiente medular. La trombocitemia esencial (TE) es una enfermedad mieloproliferativa crónica caracterizada por aumento del recuento de plaquetas e hiperplasia megacariocítica. En el presente trabajo se evaluaron los niveles de las citoquinas que participan en el desarrollo megacariocítico en plasma de pacientes con TE que se encontraban sin tratamiento y los de trombopoyetina (TPO) antes y durante el tratamiento con anagrelide. Las determinaciones se realizaron por técnica de ELISA. Dentro de las citoquinas involucradas en la etapa de proliferación, los niveles de interleuquina 3 (IL-3) se encontraron aumentados en los pacientes (p=0.0383) respecto al grupo control. Los niveles de factor estimulante de colonias granulocito-macrofágico y stem cell factor fueron normales. Dentro de las citoquinas con acción sobre la maduración megacariocítica, tanto la interleuquina 6 como la interleuquina 11 y la eritropoyetina estuvieron normales. Los niveles de TPO antes del tratamiento no difirieron del grupo control y durante el tratamiento aumentaron de manera no significativa. Los pacientes que presentaron agregación espontánea tuvieron niveles más altos de TPO que los que no lo hicieron (p=0.049). Los niveles de las citoquinas no tuvieron relación con ninguno de los parámetros clínicos ni de laboratorio evaluados. El aumento de los niveles de IL-3 podría contribuir al incremento en la proliferación megacariocítica en este grupo. La presencia simultánea de niveles más altos de TPO y trombocitosis sería un factor predisponente para la ocurrencia de agregación espontánea en los pacientes con TE

Megakaryopoiesis and platelet production are driven by transcription factors and cytokines present in bone marrow environment. Essential thrombocythemia (ET) is a chronic myeloproliferative disorder characterized by high platelet count and megakaryocytic hyperplasia. In the present work we evaluated plasmatic levels of cytokines involved in megakaryocytic development in a group of patients with ET that were not on treatment, as well as thrombopoietin (TPO) levels before and during anagrelide treatment. The assays were carried out using ELISA techniques. Among the cytokines mainly involved in proliferation of megakaryocytic progenitors, interleukin 3 (IL-3) levels were found increased in patients compared to normal controls (p=0.0383). Granulocyte-macrophage colony stimulating factor and stem cell factor levels were normal. Interleukin 6, as well as interleukin 11 and erythropoietin (EPO), cytokines mainly related to megakaryocytic maturation, were normal. Plasma TPO levels before treatment were within the normal range and increased during treatment but the difference was not statistically significant. Patients who displayed spontaneous platelet aggregation had higher plasma TPO levels compared to those who did not (p=0.049). We did not find any relationship between cytokine levels and clinical or laboratory parameters. The high IL-3 levels seen in some patients with ET could contribute to megakaryocytic proliferation. The simultaneous occurrence of higher TPO levels and elevated platelet count could be a predisposing factor for the development of spontaneous platelet aggregation in ET patients

Low Mpl receptor expression in a pedigree with familial platelet disorder with predisposition to acute myelogenous leukemia and a novel AML1 mutation.

Germ-line heterozygous mutations in the hematopoietic transcription factor AML1 (RUNX1) have been identified in patients with familial platelet disorder with predisposition to acute myelogenous leukemia (FPD/AML), which is characterized by thrombocytopenia, abnormal platelet function, and propensity to myeloid malignancies. We identified a novel mutation in the AML1 gene in an FPD/AML pedigree characterized by a single nucleotide deletion that generates a frameshift and premature chain termination (Pro218fs-Ter225). Both wild-type and mutant transcripts were expressed in affected individuals by allele-specific reverse transcriptase-polymerase chain reaction (RT-PCR). Thrombopoietin (TPO) binds to the Mpl receptor and is the major regulator of megakaryopoiesis. To explore the mechanisms underlying thrombocytopenia, we studied the TPO/Mpl pathway in this newly identified pedigree. TPO levels were mildly to moderately elevated. On flow cytometry and immunoblotting, Mpl receptor expression was decreased and TPO-induced signaling was impaired. While no mutations were identified in the MPL gene by sequence analysis, low MPL mRNA levels were found, suggesting decreased gene expression. Of particular interest, several AML1-binding motifs are present in the MPL promoter, suggesting MPL is an AML1 target. In conclusion, we identified a C-terminal AML1 mutation that leads to a decrease in Mpl receptor expression, providing a potential explanation for thrombocytopenia in this FPD/AML pedigree.