Promotes Megakaryocyte Differentiation Research Articles

Daucosterol regulates JAK2-STAT3 signaling pathway to promote megakaryocyte differentiation

Immune thrombocytopenia (ITP) is an autoimmune disease caused by the loss of immune tolerance to platelet autoantigens, resulting in reduced platelet production and increased platelet destruction. Impaired megakaryocyte differentiation and maturation is a key factor in the pathogenesis and treatment of ITP. Sarcandra glabra, a plant of the Chloranthaceae family, is commonly used in clinical practice to treat ITP, and daucosterol (Dau) is one of its active ingredients. However, whether Dau can treat ITP and the key mechanism of its effect are still unclear. In this study, we found that Dau could effectively promote the differentiation and maturation of megakaryocytes and the formation of polyploidy in the megakaryocyte differentiation disorder model constructed by co-culturing Dami and HS-5 cells. In vivo experiments showed that Dau could not only increase the number of polyploidized megakaryocytes in the ITP rat model, but also promote the recovery of platelet count. In addition, through network pharmacology analysis, we speculated that the JAK2-STAT3 signaling pathway might be involved in the process of Dau promoting megakaryocyte differentiation. Western blot results showed that Dau inhibited the expression of P-JAK2 and P-STAT3. In summary, these results provide a basis for further studying the pharmacological mechanism of Dau in treating ITP.

Alnustone promotes megakaryocyte differentiation and platelet production via the interleukin-17A/interleukin-17A receptor/Src/RAC1/MEK/ERK signaling pathway

ObjectivesThrombocytopenia is a disease in which the number of platelets in the peripheral blood decreases. It can be caused by multiple genetic factors, and numerous challenges are associated with its treatment. In this study, the effects of alnustone on megakaryocytes and platelets were investigated, with the aim of developing a new therapeutic approach for thrombocytopenia. MethodsRandom forest algorithm was used to establish a drug screening model, and alnustone was identified as a natural active compound that could promote megakaryocyte differentiation. The effect of alnustone on megakaryocyte activity was determined using cell counting kit-8. The effect of alnustone on megakaryocyte differentiation was determined using flow cytometry, Giemsa staining, and phalloidin staining. A mouse model of thrombocytopenia was established by exposing mice to X-rays at 4 Gy and was used to test the bioactivity of alnustone in vivo. The effect of alnustone on platelet production was determined using zebrafish. Network pharmacology was used to predict targets and signaling pathways. Western blotting and immunofluorescence staining determined the expression levels of proteins. ResultsAlnustone promoted the differentiation and maturation of megakaryocytes in vitro and restored platelet production in thrombocytopenic mice and zebrafish. Network pharmacology and western blotting showed that alnustone promoted the expression of interleukin-17A and enhanced its interaction with its receptor, and thereby regulated downstream MEK/ERK signaling and promoted megakaryocyte differentiation. ConclusionsAlnustone can promote megakaryocyte differentiation and platelet production via the interleukin-17A/interleukin-17A receptor/Src/RAC1/MEK/ERK signaling pathway and thus provides a new therapeutic strategy for the treatment of thrombocytopenia.

Integration of transcription regulation and functional genomic data reveals lncRNA SNHG6’s role in hematopoietic differentiation and leukemia

BackgroundLong non-coding RNAs (lncRNAs) are pivotal players in cellular processes, and their unique cell-type specific expression patterns render them attractive biomarkers and therapeutic targets. Yet, the functional roles of most lncRNAs remain enigmatic. To address the need to identify new druggable lncRNAs, we developed a comprehensive approach integrating transcription factor binding data with other genetic features to generate a machine learning model, which we have called INFLAMeR (Identifying Novel Functional LncRNAs with Advanced Machine Learning Resources).MethodsINFLAMeR was trained on high-throughput CRISPR interference (CRISPRi) screens across seven cell lines, and the algorithm was based on 71 genetic features. To validate the predictions, we selected candidate lncRNAs in the human K562 leukemia cell line and determined the impact of their knockdown (KD) on cell proliferation and chemotherapeutic drug response. We further performed transcriptomic analysis for candidate genes. Based on these findings, we assessed the lncRNA small nucleolar RNA host gene 6 (SNHG6) for its role in myeloid differentiation. Finally, we established a mouse K562 leukemia xenograft model to determine whether SNHG6 KD attenuates tumor growth in vivo.ResultsThe INFLAMeR model successfully reconstituted CRISPRi screening data and predicted functional lncRNAs that were previously overlooked. Intensive cell-based and transcriptomic validation of nearly fifty genes in K562 revealed cell type-specific functionality for 85% of the predicted lncRNAs. In this respect, our cell-based and transcriptomic analyses predicted a role for SNHG6 in hematopoiesis and leukemia. Consistent with its predicted role in hematopoietic differentiation, SNHG6 transcription is regulated by hematopoiesis-associated transcription factors. SNHG6 KD reduced the proliferation of leukemia cells and sensitized them to differentiation. Treatment of K562 leukemic cells with hemin and PMA, respectively, demonstrated that SNHG6 inhibits red blood cell differentiation but strongly promotes megakaryocyte differentiation. Using a xenograft mouse model, we demonstrate that SNHG6 KD attenuated tumor growth in vivo.ConclusionsOur approach not only improved the identification and characterization of functional lncRNAs through genomic approaches in a cell type-specific manner, but also identified new lncRNAs with roles in hematopoiesis and leukemia. Such approaches can be readily applied to identify novel targets for precision medicine.

Single-Cell Transcriptomics Reveal Altered Hematopoietic Mechanisms Driven By T21 and GATA1s

Introduction Trisomy 21 (T21) is associated with baseline erythrocytosis and thrombocytopenia and risk of transient abnormal myelopoiesis (TAM) and acute megakaryoblastic leukemia of Down syndrome (ML-DS). TAM and ML-DS are characterized by mutations in the transcription factor GATA1, resulting in the truncated isoform GATA1s (G1S). We previously found that T21 increases erythropoiesis, while G1S severely impairs erythroid development but enhances megakaryocyte (MK) proliferation (Byrska-Bishop et al, JCI 2015). To better understand how T21 and G1S each impact hematopoiesis, we performed single-cell RNA sequencing (scRNA-seq) of multipotent and late hematopoietic progenitor cells (HPCs) differing only by chromosome 21 and/or G1S status. Methods Four isogenic human induced pluripotent stem cell (iPSC) lines differing only by chromosome 21 (euploid vs. T21) and/or GATA1 (WT vs. G1S) status underwent hematopoietic differentiation by embryoid body formation. Cells were collected at 3 timepoints: on day 7 (D7), CD41 +235 + multipotent HPCs were purified by flow cytometry and on days 9 (D9) and 11 (D11), late HPCs biased to a single lineage were collected. Cells were sequenced by scRNA-seq and underwent quality control followed by clustering and analysis using Seurat. Clusters were manually annotated based on expression of 141 key hematopoietic genes, including aggregated expression of lineage markers. Early vs. committed lineage clusters were determined based on the relative expression of lineage-specific markers. Within each lineage, differentially expressed genes (DEGs) associated with a genetic background were assessed using the Wilcoxon rank-sum test. The χ² test was used to compare categorical data. A 2-tailed p or adjusted p <0.05 was considered statistically significant. Results Cluster annotation revealed HPC, early and committed erythroid and MK, and myeloid cells (Figure 1). D7 T21/G1S HPCs surprisingly showed an erythroid bias, with upregulation of genes such as GYPA and AHSP, while euploid/G1S HPCs showed a MK bias, with upregulation of genes including PF4V1 and PF4. With wtGATA1, neither euploid nor T21 D7 HPCs showed a significant lineage skew. On D9 and D11, the euploid/WT, T21/WT, and T21/G1S cells developed subpopulations committing to the erythroid lineage, while the euploid/G1S cells demonstrated minimal erythroid potential (Figure 1). Across all 3 timepoints, early and committed erythrocytes from T21 and euploid cells with G1S had a greater number of combined DEGs than their wtGATA1 counterparts (G1S vs. WT, T21: 692 vs. 378; euploid: 1235 vs. 599). On D9, T21 was associated with a greater erythroid skew (38.6% of T21/WT and 32.2% of T21/G1S cells vs. 27.8% of euploid/WT cells; p <0.00001). By D11, this erythroid drive was no longer apparent, and the T21/G1S erythrocytes were significantly less mature (Table 1; p <0.00001). These data suggest that T21 initially enhances erythropoietic drive, while G1S results in a near-complete erythroid block in euploid cells but an incomplete developmental block with T21. All 4 genotypes yielded MK subpopulations on D9 and D11 (Figure 1). With wtGATA1, euploid and T21 MKs were predominantly early MKs by D11 (Table 1). Interestingly, G1S was associated with enhanced MK commitment and maturation in the euploid context but arrest at the early stage with T21 (Table 1; p <0.00001). G1S was again associated with increased DEGs compared to wtGATA1 (G1S vs. WT, T21: 594 vs. 454; euploid: 1689 vs. 1310). These data suggest that G1S in a euploid background promotes MK differentiation, but T21 and G1S cooperate to generate immature, abnormal MKs. Conclusions Although the hematopoietic abnormalities and leukemic risk of T21 have been well-described, the underlying developmental events remain unclear. This scRNA-seq timecourse of HPCs differentiated from isogenic iPSCs reveals the individual and synergistic effects of T21 and G1S. Overall, T21 enhances erythropoietic drive while G1S alone suppresses erythropoiesis. G1S in euploid cells enhances megakaryopoiesis, but with T21, megakaryopoietic commitment and maturation are uncoupled with a strong bias to early MKs. Together, the competing effects of T21 and G1S appear to result in abnormal, immature erythrocytes and MKs with impaired lineage commitment, consistent with a pro-leukemic phenotype.

Critical shifts in lipid metabolism promote megakaryocyte differentiation and proplatelet formation

During megakaryopoiesis, megakaryocytes (MKs) undergo cellular morphological changes with strong modification of membrane composition and lipid signaling. Here, we adopt a lipid-centric multiomics approach to create a quantitative map of the MK lipidome during maturation and proplatelet formation. Data reveal that MK differentiation is driven by an increased fatty acyl import and de novo lipid synthesis, resulting in an anionic membrane phenotype. Pharmacological perturbation of fatty acid import and phospholipid synthesis blocked membrane remodeling and directly reduced MK polyploidization and proplatelet formation, resulting in thrombocytopenia. The anionic lipid shift during megakaryopoiesis was paralleled by lipid-dependent relocalization of the scaffold protein CKIP-1 and recruitment of the kinase CK2α to the plasma membrane, which seems to be essential for sufficient platelet biogenesis. Overall, this study provides a framework to understand how the MK lipidome is altered during maturation and the effect of MK membrane lipid remodeling on MK kinase signaling involved in thrombopoiesis.

Xanthotoxin, a novel inducer of platelet formation, promotes thrombocytopoiesis via IL-1R1 and MEK/ERK signaling

BackgroundThrombocytopenia is a common hematological disease caused by many factors. It usually complicates critical diseases and increases morbidity and mortality. The treatment of thrombocytopenia remains a great challenge in clinical practice, however, its treatment options are limited. In this study, the active monomer xanthotoxin (XAT) was screened out to explore its medicinal value and provide novel therapeutic strategies for the clinical treatment of thrombocytopenia. MethodsThe effects of XAT on megakaryocyte differentiation and maturation were detected by flow cytometry, Giemsa and phalloidin staining. RNA-seq identified differentially expressed genes and enriched pathways. The signaling pathway and transcription factors were verified through WB and immunofluorescence staining. Tg (cd41: eGFP) transgenic zebrafish and mice with thrombocytopenia were used to evaluate the biological activity of XAT on platelet formation and the related hematopoietic organ index in vivo. ResultsXAT promoted the differentiation and maturation of Meg-01 cells in vitro. Meanwhile, XAT could stimulate platelet formation in transgenic zebrafish and recover platelet production and function in irradiation-induced thrombocytopenia mice. Further RNA-seq prediction and WB verification revealed that XAT activates the IL-1R1 target and MEK/ERK signaling pathway, and upregulates the expression of transcription factors related to the hematopoietic lineage to promote megakaryocyte differentiation and platelet formation. ConclusionXAT accelerates megakaryocyte differentiation and maturation to promote platelet production and recovery through triggering IL-1R1 and activating the MEK/ERK signaling pathway, providing a new pharmacotherapy strategy for thrombocytopenia.

Ormeloxifene, a nonsteroidal antifertility drug promotes megakaryocyte differentiation in leukemia cell line K562.

Ormeloxifene (ORM) (3,4-trans-2,2-dimethyl-3-phenyl-4-p-(β-pyrrolidinoethoxy) phenyl-7-methoxychroman), world's first nonsteroidal selective estrogen receptor modulatorapproved for contraception in India has been shown to have potential anticancer activities. Here, we show that ORMcan induce megakaryocyte and myeloid (granulocytic) but not erythroid differentiation in multipotent human myeloid leukemia cell line K562. We show that ORM at an IC50 of 7.5 µM can induce morphological changes similar to megakaryocytes in K562 cells. ORM led to increase in levels of megakaryocytic differentiation markers (CD41 and CD61) as well as key transcription factors GATA1 and AML1. We further show that ORM induces megakaryocytic differentiation in K562 cells through ERK activation and induction of autophagy in a fashion similar to other known inducers of megakaryocytic differentiation such as phorbol esters. In addition, as shown earlier, we yet again observed that ORM led to activation of caspases since their inhibition through pan-caspase inhibitor mitigated megakaryocytic differentiation as they led to significant decrease in CD41 and CD61. Because induction of megakaryocytic differentiation in K562 involves growth arrest and exit from cell cycle, we also observed an increase in levels of p21 and p27 with decrease in c-Myc protein levels in K562 cells treated with 7.5 µM ORM for 24 and 48 h,respectively. Taken together, these findings indicate that ORM can markedly induce megakaryocytic differentiation in K562 cells.

Targeting a thrombopoietin-independent strategy in the discovery of a novel inducer of megakaryocytopoiesis, DMAG, for the treatment of thrombocytopenia.

Thrombocytopenia is a thrombopoietin (TPO)-related disorder with very limited treatment options, and can be lifethreatening. There are major problems with typical thrombopoietic agents targeting TPO signaling, so it is urgent to discover a novel TPO-independent mechanism involving thrombopoiesis and potential druggable targets. We developed a drug screening model by the multi-grained cascade forest (gcForest) algorithm and found that 3,8-di-O-methylellagic acid 2- O-glucoside (DMAG) (10, 20 and 40 μM) promoted megakaryocyte differentiation in vitro. Subsequent investigations revealed that DMAG (40 mM) activated ERK1/2, HIF-1b and NF-E2. Inhibition of ERK1/2 blocked megakaryocyte differentiation and attenuated the upregulation of HIF-1b and NF-E2 induced by DMAG. Megakaryocyte differentiation induced by DMAG was inhibited via knockdown of NF-E2. In vivo studies showed that DMAG (5 mg/kg) accelerated platelet recovery and megakaryocyte differentiation in mice with thrombocytopenia. The platelet count of the DMAG-treated group recovered to almost 72% and 96% of the count in the control group at day 10 and 14, respectively. The platelet counts in the DMAG-treated group were almost 1.5- and 1.3-fold higher compared with those of the irradiated group at day 10 and 14, respectively. Moreover, DMAG (10, 25 and 50 mM) stimulated thrombopoiesis in zebrafish. DMAG (5 mg/kg) could also increase platelet levels in c-MPL knockout (c-MPL-/-) mice. In summary, we established a drug screening model through gcForest and demonstrated that DMAG promotes megakaryocyte differentiation via the ERK/HIF1/NF-E2 pathway which, importantly, is independent of the classical TPO/c-MPL pathway. The present study may provide new insights into drug discovery for thrombopoiesis and TPO-independent regulation of thrombopoiesis, as well as a promising avenue for thrombocytopenia treatment.

Conditional CRISPR-Mediated Deletion of Lyn Kinase Promotes Megakaryocyte Differentiation, Platelet Production and Function

Thrombocytopenia leading to life-threatening excessive bleeding can be caused by defects in megakaryocyte/platelet production, platelet depletion by platelet-specific auto- or allo-antibodies, blood loss following trauma or surgery, or as a result of damage to bone marrow blood stem cells induced by chemo- or radiation therapy. Currently, platelets available for transfusion are entirely dependent on volunteer blood donation, which are often in short supply, carry a risk of infection, and often unable to be antigen-matched for alloimmunized patients. Thus, maintaining an adequate supply of platelets for transfusion is often a challenge. In response to this growing clinical need, a number of laboratories have started differentiating human induced pluripotent stem cells (iPSCs) into megakaryocytes, with the long-term goal of creating a readily available supply of antigen-matched, highly functional platelets. Current methods for generating platelets from iPS cell-derived megakaryocytes have been improved to produce enough platelets in vitro to begin phase I safety trials in humans; however, modifying the iPS cell genome has the potential to further improve both the yield and function of in vitro-generated platelets. The purpose of this investigation, therefore, was to combine recent advances in gene editing technology with iPS cell differentiation techniques to improve the yield and/or functionality of in vitro-derived platelet products. As a start, we sought to examine whether disruption of negative regulators of platelet production and/or activation might allow the generation of increased numbers of platelets with improved hemostatic effectiveness. One such negative regulator of platelet function is the Src family kinase, Lyn. Previous studies using pharmacologic inhibitors and global Lyn knockout mice have shown that that disrupting Lyn activity leads to mild thrombocytosis and megakaryocytosis. The effects of specifically targeting Lyn in human megakaryocytes and platelets, however, are not known. We hypothesized that conditionally disrupting Lyn during the process of iPSC to megakaryocyte differentiation might be an effective way to enhance megakaryocyte differentiation, platelet production, and hemostatic function. Using CRISPR/Cas9 gene editing technology, we generated a temporally controllable, tamoxifen-inducible Lyn-KO iPS cell line system that allowed us to conditionally delete Lyn at any desired stage of the iPSC→hematopoietic stem cell (HSC)→megakaryocyte→platelet differentiation process. We found tamoxifen efficiently disrupted Lyn expression at any of these stages within 24-48 hours after addition of the drug to the cell culture, and also improved the efficiency and yield of the iPSC→megakaryocyte→proplatelet differentiation process. Lyn-deficient human megakaryocytes prepared in this fashion exhibited enhanced reactivity, as reported by increased Erk phosphorylation in response to thrombopoietin stimulation, and by an improved ability to support hemostasis in human blood in vitro, as determined using thromboelastometry (ROTEM). Taken together, these data suggest that temporal disruption of Lyn kinase might represent an effective strategy for the engineering and manufacture of in vitro-derived platelets for both diagnostic and future therapeutic use. Disclosures Newman: NIH: Research Funding; Bloodworks Northwest: Membership on an entity's Board of Directors or advisory committees; Rallybio Corporation: Consultancy.

MicroRNA-22 promotes megakaryocyte differentiation through repression of its target, GFI1

AbstractThe role of microRNAs in a number of tissue differentiation processes including hematopoiesis is an area of active investigation with biological and clinical amplifications. Weiss and Ito explore the impact of microRNA-22 in megakaryocytic differentiation, demonstrating a major role for this microRNA.

Tetrandrine antagonizes acute megakaryoblastic leukaemia growth by forcing autophagy-mediated differentiation.

The poor prognosis of acute megakaryoblastic leukaemia (AMKL) means there is a need to develop novel therapeutic methods to treat this condition. It was recently shown that inducing megakaryoblasts to undergo terminal differentiation is effective as a treatment for AMKL. This encouraged us to identify a compound that induces megakaryocyte differentiation, which could then act as a potent anti-leukaemia agent. The effects of tetrandrine on the expression of CD41 and cell morphology were investigated in AMKL cells. We used CRISPR/Cas9 knockout system to knock out ATG7 and verify the role of autophagy in tetrandrine-induced megakaryocyte differentiation. shNotch1 and CA-Akt were transfected into K562 cells to examine the downstream pathways of ROS signalling and the mechanistic basis of the tetrandrine-induced megakaryocyte differentiation. The anti-leukaemia effects of tetrandrine were analysed both in vitro and in vivo. A low dose of tetrandrine induced cell cycle arrest and megakaryocyte differentiation in AMKL cells via activation of autophagy. Molecularly, we demonstrated that this effect is mediated by activation of Notch1 and Akt and subsequent accumulation of ROS. In contrast, in normal mouse fetal liver cells, although tetrandrine induced autophagy, it did not affect cell proliferation or promote megakaryocyte differentiation, suggesting a specific effect of tetrandrine in malignant megakaryoblasts. Finally, tetrandrine also showed in vivo efficacy in an AMKL xenograft mouse model. Modulating autophagy-mediated differentiation may be a novel strategy for treating AMKL, and tetrandrine has the potential to be developed as a differentiation-inducing agent for AMKL chemotherapy.

ZNF300 Promotes Megakaryocytic Differentiation

To study the function of ZNF300 in the megakaryocytes differentiation and proliferation. Public data analysis of ZNF300 expression and megakaryocyte culture were used to reveal the correlation of ZNF300 expression with leukemia and megakaryocyte differetniation; ZNF300 overexpression was mediated by lentiviral or retroviral infection, and the differentiation and proliferation of K562 cells and primary mouse bone marrow cells to magekaryocytes were measured by flow cytometry, MTT assay and colony-forming test; the ZNF300 subcellular localization was tested by separating cytosolic and nuclear extracts combined with Western blotting. The dual-luciferase assay and ChIP-qPCR were used to study ZNF300 target gene. ZNF300 expression upregulation correlated with megakaryoyte differentiation; over-expression of ZNF300 promoted CD41 and CD61 expression, inhibited cell cycle progress, and could reduce colony-forming unit. The ZNF300 locolized in nuclear and regulated C-MYC expression. ZNF300 promotes megakaryocyte differentiation.

The TAL1 Short Isoform Generated By PRMT1-Mediated Alternative RNA Splicing Promotes Erythroid Differentiation

The isoforms of key transcription factors in hematopoiesis such as TAL1, GATA1 and RUNX1 are generated through alternative RNA splicing regulated by the PRMT1-RBM15 axis (Zhang et al. 2015). The functions of short isoforms of GATA1 (GATA1s) and RUNX1 (RUNX1a) are well characterized, yet it is unknown how the short isoform of TAL1 (TAL1s) regulates hematopoiesis. In this presentation, we report that the short isoform of TAL1, i.e. TAL1s, is generated via alternative RNA splicing as detected by isoform specific real-time PCR reactions using RNA isolated from leukemia cell lines and primary human cord blood cells. RBM15, an RNA binding protein, which is involved in chromosome translocation to produce RBM15-MKL1 fusion protein in acute megakaryocytic leukemia, regulates the alternative RNA splicing of TAL1. RBM15 promotes the production of full-length TAL1 mRNA, while reduction of RBM15 protein level via PRMT1-mediated degradation pathway favors the production of TAL1s. RBM15 directly binds to intronic regions on TAL1 pre-mRNA. Binding of RBM15 is responsible for recruiting SF3B1-associated RNA splicing complex. Given that PRMT1 senses the hypoxia status of hematopoietic cells, the changing of TAL1s/TAL1fl ratio by PRMT1 activity may be an adaptive response of hematopoietic cells to hypoxia status. The short form TAL1s still contains the helix-loop-helix DNA binding domain but not the N terminal regions upstream of the DNA binding domain. Thus, the TAL1s may act as a dominant negative mutant of the full-length TAL1fl to block TAL1fl-regulated transcription. We demonstrated that overexpression of TAL1s not the full-length TAL1promotes the erythroid differentiation of K562 cells. Although TAL1 gene is required for both erythroid and megakaryocyte differentiation at early stage of hematopoiesis, TAL1s does not promote megakaryocyte differentiation. Therefore, fine-tuning the TAL1 isoforms by the PRMT1-RBM15 axis determine the cell fate of a MEP progenitor cell. Using immunoprecipitation assays and mass spectrometry analysis, we identified proteins specifically associated with the N terminal region of TAL1. How unique TAL1s-associated transcriptional regulatory complex plays in erythroid differentiation will be discussed in the presentation in comparison with the Tal1fl-asociated protein complex. In summary, our findings stratify another new layer of regulation by PRMT1, which relays extracellular signals (such as hypoxia signal) to transcriptional regulatory program. Given that PRMT1 is often constitutively highly expressed in leukemia cells, how overproduction of short form TAL1 interferes with normal hematopoiesis may help to explain the molecular mechanisms of many hematological malignancies associated with dysregulation of TAL1 expression. DisclosuresNo relevant conflicts of interest to declare.

MiR-494-3p Overexpression Leads to SOCS6 Downregulation and Supports Megakaryocytopoiesis in Primary Myelofibrosis CD34+ Hematopoietic Stem/Progenitor Cells

Primary Myelofibrosis (PMF) belongs to the Philadelphia negative Myeloproliferative Neoplasms (MPNs) and is characterized by hematopoietic stem-cell derived clonal myeloproliferation, involving especially megakaryocyte (MK) lineage, bone marrow fibrosis and extramedullary hematopoiesis. Recent studies have suggested that alterations in miRNAs expression could play a critical role in MPN's pathogenesis. In order to shed some light on this issue, we have previously performed the integrative analysis (IA) of gene and miRNA expression profiles of PMF CD34+ hematopoietic stem/progenitor cells (HSPCs) isolated from 42 PMF patients compared with 31 healthy donors (R. Norfo et al., Blood, 2014). IA identified miR-494-3p as one of the most upregulated miRNAs in PMF CD34+ cells associated to the highest number of downregulated predicted targets (eighty-six, Fig. 1).In order to study the role of miR-494-3p in hematopoietic commitment and differentiation, and to elucidate its possible involvement in PMF pathogenesis, we performed miRNA overexpression experiments in cord blood (CB) CD34+ cells through miRNA mimic electroporation. The data showed that miR-494-3p promotes MK differentiation of HSPCs. Indeed, the fraction of cells expressing MK surface antigen CD41 was steadily increased in miR-494-3p overexpressing samples compared with controls (75.4±0.3% vs 53.2±3.5% at day 8, 82.6±1.3% vs 60.4±4.3% at day 10 of culture, p<0.05), as well as the percentage of cells expressing the late MK antigen CD42b was similarly increased. Furthermore, the percentage of MK colonies was increased in collagen-based clonogenic assay upon miR-494-3p overexpression compared to control (44.8±4.1% vs 24.1±2.1%, p<0.05). Next, to better characterize the molecular mechanisms underlying megakaryocytopoiesis stimulation by miR-494-3p, we profiled CB CD34+ cells overexpressing this miRNA using the Affymetrix HG-U219 microarray platform. Gene Expression profile analysis allowed the identification of 134 differentially expressed genes between cells overexpressing miR-494-3p and controls. In particular, we highlighted the presence of 13 genes downregulated both upon miRNA overexpression and in PMF CD34+ cells. Among them, Suppressor of Cytokine Signaling 6 (SOCS6) turned out to be the miR-494-3p predicted target associated to the most favorable prediction scores according to TargetScan, microRNA.org and miRDB prediction algorithms. Furthermore, 3’ UTR luciferase reporter assays, performed in K562 cell line, proved the predicted interaction between miR-494-3p and SOCS6 3’UTR. Subsequently, we studied the role of SOCS6 in HSPCs differentiation by inhibiting its expression in CB CD34+ cells through small interfering RNAs. SOCS6 silencing stimulated megakaryocytopoiesis in CB CD34+ cells, as demonstrated by the expansion of CD41+ and CD42b+ cell fractions in SOCS6 silenced samples compared with controls (52.8±7.0% vs 37.7±4.5% at day 8, 66.9±7.2% vs 50.7±7.2% at day 10 for CD41+ cells, p<0.05). Moreover, MK colonies were increased upon SOCS6 silencing in collagen-based clonogenic assays (62.4±7.7% vs 51.3±6.5%, p<0.05) and morphological analysis further supported these results. Finally, in order to study the possible contribution of miR-494-3p overexpression to PMF pathogenesis, we performed inhibition experiments in PMF CD34+ cells by means of miR-494-3p antagomiR. As a result, miR-494-3p silencing led to SOCS6 upregulation and impaired MK differentiation in PMF HSPCs as demonstrated by the decrease in CD41+ cell fraction in silenced samples compared with controls (28.6±7.1% vs 39.2±7.7% at day 12 of culture, p<0.05) and by the reduction of MK colonies in collagen-based clonogenic assay (44.4±3.6% vs 54.7±2.5%, p<0.05). The values are reported as mean±S.E.M from 3 independent experiments.Taken together, our results showed that miR-494-3p overexpression promotes megakaryocytopoiesis in HSPCs. Moreover, we demonstrated for the first time that SOCS6 is a direct target of miR-494-3p. Since SOCS6 downregulation promotes MK differentiation of HSPCs, SOCS6 could be considered, at least in part, responsible for the biological effects observed after miR-494-3p overexpression. As miR-494-3p and SOCS6 showed the same expression trend in PMF CD34+ cells, our results could suggest that miR-494-3p/SOCS6 axis is involved in the induction of MK hyperplasia typically observed in PMF patients. [Display omitted] DisclosuresVannucchi:Novartis: Consultancy, Research Funding, Speakers Bureau; Baxalta: Speakers Bureau; Shire: Speakers Bureau.

Whole-Exome Sequencing Identifies Loci Associated with Blood Cell Traits and Reveals a Role for Alternative GFI1B Splice Variants in Human Hematopoiesis

Circulating blood cell counts and indices are important indicators of hematopoietic function and a number of clinical parameters, such as blood oxygen-carrying capacity, inflammation, and hemostasis. By performing whole-exome sequence association analyses of hematologic quantitative traits in 15,459 community-dwelling individuals, followed by insilico replication in up to 52,024 independent samples, we identified two previously undescribed coding variants associated with lower platelet count: a common missense variant in CPS1 (rs1047891, MAF = 0.33, discovery + replication p = 6.38× 10(-10)) and a rare synonymous variant in GFI1B (rs150813342, MAF = 0.009, discovery + replication p = 1.79× 10(-27)). By performing CRISPR/Cas9 genome editing in hematopoietic cell lines and follow-up targeted knockdown experiments in primary human hematopoietic stem and progenitor cells, we demonstrate an alternative splicing mechanism by which the GFI1B rs150813342 variant suppresses formation of a GFI1B isoform that preferentially promotes megakaryocyte differentiation and platelet production. These results demonstrate how unbiased studies of natural variation in blood cell traits can provide insight into the regulation of human hematopoiesis.

RBM15-Mediated RNA Splicing Fine-Tunes Epigenetic Program through Interaction with SF3B1

Abstract RBM15, an RNA binding protein belongs to the SPEN family, which is evolutionally conserved from plant to mammals. The relevance of RBM15 to blood diseases came to spot light when RBM15 was discovered to be involved in chromosome translocation t(1;22) in acute megakaryoblastic leukemia. RBM15 is indispensible for the self-renewal of hematopoietic stem cells in response to stress and for megakaryocyte terminal differentiation. RBM15 knockdown results in the unchecked generation of megakaryocyte progenitors in mouse models. At the molecular level, RBM15 have been shown to be a transcriptional repressor in NOCTH signaling pathway by recruiting HDAC complexes like another family member SHARP. RBM15 interacts with transcriptional coactivator SET1/ASH2. RBM15 controls the alternative splicing of thrombopoietin receptor (MPL). However, the molecular mechanisms on how RBM15 regulates alternative RNA splicing is less known. We identified the RBM15-associated proteins with mass spectrometry analysis. Pathway analysis found that RBM15 is mainly associated with proteins involved in RNA splicing, which is also validated by immune-fluorescent microscopy with anti-RBM15 antibody. Among the RBM15-associated proteins are SF3B1 and U2AF, which are heavily mutated in myeloid dysplasia syndrome and chronic lymphocytic leukemia. The interaction between RBM15 and SF3B1 is further validated by co-immunoprecipitation assays. Furthermore, we found that RBM15-SF3B1 interaction is regulated by protein arginine methylation of RBM15. RBM15 is responsible for recruiting SF3B1 complex to the pre-mRNA intronic regions with weak U2snRNP binding sites. We did pair-end, 100bp read RNA-seq of RNA isolated from RBM15 knockdown leukemia cells, and used RBM15 antibody to immunoprecipiate sonicated RNAs to identify intronic regions bound by RBM15. Combining these next generation sequencing data, we found about 50% of the RBM15 binding sites are in the intronic regions and 45% of the RBM15 binding sites are in the 3'UTR regions. RBM15 regulates alternative splicing of a few known transcription factors involved in hematopoiesis such as GATA1, Fli1, GFIb, and RUNX1 as well as chromatin binding proteins such as BRD4, HDAC7 etc.. Therefore, RBM15-SF3B1 interaction fine-tunes the optimal dose of transcription factors needed for the generation of blood lineages in response to environmental stress. How the mutant SF3B1 proteins disrupt its interaction with RBM15 will be discussed. In addition to RBM15-mediated RNA splicing, we also found that RBM15 per se is regulated by its antisense counterpart (AS-RBM15). AS-RBM15 is a long non-coding RNA whose transcription is activated by RUNX1. AS-RBM15 promotes megakaryocyte differentiation by activating RBM15 protein translation. Therefore, RBM15 and AS-RBM15 are at the center of a RNA regulatory network, which is linked to epigenetic programs regulated by RUNX1 and GATA1. Given that both RUNX1 and SF3B1 are often mutated in myeloid dysplasia syndrome, understanding RBM15-mediated gene regulation offers much needed knowledge for understanding MDS. Disclosures No relevant conflicts of interest to declare.

Risk of thromboembolism with thrombopoietin receptor agonists in adult patients with thrombocytopenia: Systematic review and meta-analysis of randomized controlled trials

Background and objectiveRomiplostim and eltrombopag are thrombopoietin receptor (TPOr) agonists that promote megakaryocyte differentiation, proliferation and platelet production. In 2012, a systematic review and meta-analysis reported a non-statistically significant increased risk of thromboembolic events for these drugs, but analyses were limited by lack of statistical power. Our objective was to update the 2012 meta-analysis examining whether TPOr agonists affect thromboembolism occurrence in adult thrombocytopenic patients. Materials and methodsWe conducted a systematic review and meta-analysis of randomized controlled trials (RCTs). Updated searches were conduced on PubMed, Cochrane Central, and publicly available registries (up to December 2014). RCTs using romiplostim or eltrombopag in at least one group were included. Relative risks (RR), absolute risk ratios (ARR) and number needed to harm (NNH) were estimated. Heterogeneity was analyzed using Cochran's Q test and I2 statistic. ResultsFifteen studies with 3026 adult thrombocytopenic patients were included. Estimated frequency of thromboembolism was 3.69% (95% CI: 2.95–4.61%) for TPOr agonists and 1.46% (95% CI: 0.89–2.40%) for controls. TPOr agonists were associated with a RR of thromboembolism of 1.81 (95% CI: 1.04–3.14) and an ARR of 2.10% (95% CI: 0.03–3.90%) meaning a NNH of 48. Overall, we did not find evidence of statistical heterogeneity (p=0.43; I2=1.60%). ConclusionsOur updated meta-analysis suggested that TPOr agonists are associated with a higher risk of thromboemboembolic events compared with controls, and supports the current recommendations included in the European product information on this respect.

Risk of thromboembolism with thrombopoietin receptor agonists in adult patients with thrombocytopenia: Systematic review and meta-analysis of randomized controlled trials

Background and objectiveRomiplostim and eltrombopag are thrombopoietin receptor (TPOr) agonists that promote megakaryocyte differentiation, proliferation and platelet production. In 2012, a systematic review and meta-analysis reported a non-statistically significant increased risk of thromboembolic events for these drugs, but analyses were limited by lack of statistical power. Our objective was to update the 2012 meta-analysis examining whether TPOr agonists affect thromboembolism occurrence in adult thrombocytopenic patients. Materials and methodsWe conducted a systematic review and meta-analysis of randomized controlled trials (RCTs). Updated searches were conduced on PubMed, Cochrane Central, and publicly available registries (up to December 2014). RCTs using romiplostim or eltrombopag in at least one group were included. Relative risks (RR), absolute risk ratios (ARR) and number needed to harm (NNH) were estimated. Heterogeneity was analyzed using Cochran's Q test and I2 statistic. ResultsFifteen studies with 3026 adult thrombocytopenic patients were included. Estimated frequency of thromboembolism was 3.69% (95% CI: 2.95–4.61%) for TPOr agonists and 1.46% (95% CI: 0.89–2.40%) for controls. TPOr agonists were associated with a RR of thromboembolism of 1.81 (95% CI: 1.04–3.14) and an ARR of 2.10% (95% CI: 0.03–3.90%) meaning a NNH of 48. Overall, we did not find evidence of statistical heterogeneity (p=0.43; I2=1.60%). ConclusionsOur updated meta-analysis suggested that TPOr agonists are associated with a higher risk of thromboemboembolic events compared with controls, and supports the current recommendations included in the European product information on this respect.

Novel function of PITH domain-containing 1 as an activator of internal ribosomal entry site to enhance RUNX1 expression and promote megakaryocyte differentiation.

Altered gene expression coincides with leukemia development and may affect distinct features of leukemic cells. PITHD1 was significantly downregulated in leukemia and upregulated upon PMA induction in K562 cells undergoing megakaryocyte differentiation. We aimed to study the function of PITHD1 in megakaryocyte differentiation. K562 cells and fetal liver cells were used for either overexpression or downregulation of PITHD1 by retroviral or lentiviral transduction. FACS was used to detect the expression of CD41 and CD42 to measure megakaryocyte differentiation in these cells. Western blot and quantitative RT-PCR were used to measure gene expression. Dual luciferase assay was used to detect promoter or internal ribosomal entry site (IRES) activity. Ectopic expression of PITHD1 promoted megakaryocyte differentiation and increased RUNX1 expression while PITHD1 knockdown showed an opposite phenotype. Furthermore, PITHD1 efficiently induced endogenous RUNX1 expression and restored megakaryocyte differentiation suppressed by a dominant negative form of RUNX1. PITHD1 regulated RUNX1 expression at least through two distinct mechanisms: increasing transcription activity of proximal promoter and enhancing translation activity of an IRES element in exon 3. Finally, we confirmed the function of PITHD1 in regulating RUNX1 expression and megakaryopoiesis in mouse fetal liver cells. PITHD1 was a novel activator of IRES and enhanced RUNX1 expression that subsequently promoted megakaryocyte differentiation. Our findings shed light on understanding the mechanisms underlying megakaryopoiesis or leukemogenesis.

HGH promotes megakaryocyte differentiation and exerts a complementary effect with c-Mpl ligands on thrombopoiesis

AbstractHuman growth hormone (hGH) is known to play a functional role in regulating hematopoiesis, although its direct effect on thrombopoiesis is unclear. In this study, we show for the first time that hGH has a distinct capacity to promote the differentiation of human primary megakaryocytes derived from umbilical cord blood CD34+ cells. In particular, hGH is potent in facilitating proplatelet formation and platelet production from cultured megakaryocytes. The stage- and time-specific activations of extracellular signal-regulated kinase 1/2 and protein kinase B signaling pathways are involved in the action of hGH. Fusion with hGH enhances the effect of a tandem dimer of thrombopoietin mimetic peptide (dTMP) on thrombopoiesis, manifested by a significant acceleration and increase of platelet production, indicating that hGH may exert a complementary and synergistic effect with c-Mpl ligands on thrombopoiesis. Accordingly, the administration of dTMP-growth hormone fusion protein led to a rapid platelet recovery in mice with severe thrombocytopenia induced by 6.5 Gy total body irradiation, thereby markedly abridging the duration of thrombocytopenia crisis (platelets <150 × 109/L), in comparison with high doses of dTMP. These findings demonstrate the functional role of growth hormone in promoting thrombopoiesis and provide a promising avenue for the treatment of severe thrombocytopenia.