scholarly journals Bleeding diathesis in mice lacking JAK2 in platelets

2021 ◽  
Vol 5 (15) ◽  
pp. 2969-2981
Author(s):  
Nathan Eaton ◽  
Saravanan Subramaniam ◽  
Marie L. Schulte ◽  
Caleb Drew ◽  
David Jakab ◽  
...  
Keyword(s):  
Intracellular Signaling ◽  
Myeloproliferative Neoplasms ◽  
Jak2 V617f ◽  
Cytokine Signaling ◽  
Hematopoietic Stem ◽  
Shear Rates ◽  
Granule Secretion ◽  
Static Conditions ◽  
Activation Motif

Abstract The tyrosine kinase JAK2 is a critical component of intracellular JAK/STAT cytokine signaling cascades that is prevalent in hematopoietic cells, such as hematopoietic stem cells and megakaryocytes (MKs). Individuals expressing the somatic JAK2 V617F mutation commonly develop myeloproliferative neoplasms (MPNs) associated with venous and arterial thrombosis, a leading cause of mortality. The role of JAK2 in hemostasis remains unclear. We investigated the role of JAK2 in platelet hemostatic function using Jak2fl/fl Pf4-Cre (Jak2Plt−/−) mice lacking JAK2 in platelets and MKs. Jak2Plt−/− mice developed MK hyperplasia and splenomegaly associated with severe thrombocytosis and bleeding. This notion was supported by failure to occlude in a ferric chloride carotid artery injury model and by a cremaster muscle laser-induced injury assay, in which Jak2Plt−/− platelets failed to form stable thrombi. Jak2Plt−/− platelets formed thrombi poorly after adhesion to type 1 collagen under arterial shear rates. Jak2Plt−/− platelets spread poorly on collagen under static conditions or on fibrinogen in response to the collagen receptor GPVI-specific agonist, collagen-related peptide (CRP). After activation with collagen, CRP, or the CLEC-2 agonist rhodocytin, Jak2Plt−/− platelets displayed decreased α-granule secretion and integrin αIIbβ3 activation or aggregation, but showed normal responses to thrombin. Jak2Plt−/− platelets had impaired intracellular signaling when activated via GPVI, as assessed by tyrosine phosphorylation. Together, the results show that JAK2 deletion impairs platelet immunoreceptor tyrosine-based activation motif signaling and hemostatic function in mice and suggest that aberrant JAK2 signaling in patients with MPNs affects GPVI signaling, leading to hemostatic platelet function.

scholarly journals Bleeding Diathesis in Mice Lacking JAK2 in Platelets

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 12-12
Author(s):  
Nathan Eaton ◽  
Saravanan Subramaniam ◽  
Marie L Schulte ◽  
Caleb Drew ◽  
David Jakab ◽  
...  
Keyword(s):  
Intracellular Signaling ◽  
Arterial Thrombosis ◽  
Myeloproliferative Neoplasms ◽  
Critical Role ◽  
Cytokine Signaling ◽  
Severe Bleeding ◽  
Type I ◽  
Bleeding Diathesis ◽  
Hematopoietic Stem ◽  
Injury Model

The tyrosine kinase JAK2 is a critical component of intracellular JAK/STAT cytokine signaling cascades that is prevalent in hematopoietic cells such as hematopoietic stem and progenitor cells (HSPCs), megakaryocytes (MKs), and platelets. Individuals expressing somatic activating JAK2 mutations such as JAK2V617F commonly develop myeloproliferative neoplasms (MPNs) associated with serious complications, including venous and arterial thrombosis, a leading cause of mortality. Here, we investigated the role of JAK2 in hemostasis and thrombosis using Jak2fl/flPf4-Cre (Jak2Plt-/-) mice specifically lacking JAK2 within the platelet lineage. Jak2Plt-/- mice developed severe thrombocytosis with a 5-fold increase in circulating platelet number, MK hyperplasia, and splenomegaly. Jak2Plt-/-platelets were of normal size and the expression of major membrane surface glycoproteins was indistinguishable from controls, except for the integrin β3, which was reduced by 20%. Despite the thrombocytosis, Jak2Plt-/- mice had a severe bleeding diathesis, as evidenced by: 1) prolonged tail bleeding time; 2) failure to occlude in a ferric chloride-induced carotid artery injury model; and 3) failure to form stable thrombi in a laser-induced cremaster muscle injury model. Jak2Plt-/- platelets spread poorly on immobilized collagen or on immobilized fibrinogen following GPVI stimulation with the collagen-related peptide (CRP). Jak2Plt-/- platelets had defective α-granule secretion and integrin αIIbβ3 activation following stimulation with CRP, but not thrombin, and showed aggregation defects with low-doses of CRP. Together, the data support a GPVI-specific impairment in platelets lacking JAK2, a notion that was supported by impaired intracellular signaling following GPVI stimulation, as assessed by protein tyrosine phosphorylation. Jak2Plt-/- platelets adhered poorly to type I collagen under arterial shear rates in whole blood. However, JAK2 deletion in platelets did not alter plasma von Willebrand factor (VWF) levels or botrocetin-mediated binding of plasma VWF to GPIbα. Together, the results underline a critical role for JAK2 in platelet GPVI signaling and hemostatic function, which likely contributes to venous and arterial thrombosis observed in patients with MPNs with the activating JAK2V617F mutation. Disclosures No relevant conflicts of interest to declare.

scholarly journals Genome editing to model and reverse a prevalent mutation associated with myeloproliferative neoplasms

PLoS ONE ◽  
2021 ◽  
Vol 16 (3) ◽  
pp. e0247858
Author(s):  
Ron Baik ◽  
Stacia K. Wyman ◽  
Shaheen Kabir ◽  
Jacob E. Corn
Keyword(s):  
Myeloproliferative Neoplasms ◽  
Jak2 V617f ◽  
Cytokine Signaling ◽  
Competitive Growth ◽  
Erythroid Progenitors ◽  
Erythroid Progenitor ◽  
Hematopoietic Stem ◽  
Stem And Progenitor Cells

Myeloproliferative neoplasms (MPNs) cause the over-production of blood cells such as erythrocytes (polycythemia vera) or platelets (essential thrombocytosis). JAK2 V617F is the most prevalent somatic mutation in many MPNs, but previous modeling of this mutation in mice relied on transgenic overexpression and resulted in diverse phenotypes that were in some cases attributed to expression level. CRISPR-Cas9 engineering offers new possibilities to model and potentially cure genetically encoded disorders via precise modification of the endogenous locus in primary cells. Here we develop “scarless” Cas9-based reagents to create and reverse the JAK2 V617F mutation in an immortalized human erythroid progenitor cell line (HUDEP-2), CD34+ adult human hematopoietic stem and progenitor cells (HSPCs), and immunophenotypic long-term hematopoietic stem cells (LT-HSCs). We find no overt in vitro increase in proliferation associated with an endogenous JAK2 V617F allele, but co-culture with wild type cells unmasks a competitive growth advantage provided by the mutation. Acquisition of the V617F allele also promotes terminal differentiation of erythroid progenitors, even in the absence of hematopoietic cytokine signaling. Taken together, these data are consistent with the gradually progressive manifestation of MPNs and reveals that endogenously acquired JAK2 V617F mutations may yield more subtle phenotypes as compared to transgenic overexpression models.

scholarly journals Genome editing to model and reverse a prevalent mutation associated with myeloproliferative neoplasms

2019 ◽  
Author(s):  
Ron Baik ◽  
Stacia K. Wyman ◽  
Shaheen Kabir ◽  
Jacob E. Corn
Keyword(s):  
Myeloproliferative Neoplasms ◽  
Jak2 V617f ◽  
Cytokine Signaling ◽  
Competitive Growth ◽  
Erythroid Progenitors ◽  
Erythroid Progenitor ◽  
Hematopoietic Stem ◽  
Stem And Progenitor Cells

AbstractMyeloproliferative neoplasms (MPNs) cause the over-production of blood cells such as erythrocytes (polycythemia vera) or platelets (essential thrombocytosis). JAK2 V617F is the most prevalent somatic mutation in many MPNs, but previous modeling of this mutation in mice relied on transgenic overexpression and resulted in diverse phenotypes that were in some cases attributed to expression level. CRISPR-Cas9 engineering offers new possibilities to model and potentially cure genetically encoded disorders via precise modification of the endogenous locus in primary cells. Here we develop “scarless” Cas9-based reagents to create and reverse the JAK2 V617F mutation in an immortalized human erythroid progenitor cell line (HUDEP-2), CD34+ adult human hematopoietic stem and progenitor cells (HSPCs), and immunophenotypic long-term hematopoietic stem cells (LT-HSCs). We find no overt in vitro increase in proliferation associated with an endogenous JAK2 V617F allele, but co-culture with wild type cells unmasks a competitive growth advantage provided by the mutation. Acquisition of the V617F allele also promotes terminal differentiation of erythroid progenitors, even in the absence of hematopoietic cytokine signaling. Taken together, these data are consistent with the gradually progressive manifestation of MPNs and reveals that endogenously acquired JAK2 V617F mutations may yield more subtle phenotypes as compared to transgenic overexpression models.

scholarly journals The Power of Extracellular Vesicles in Myeloproliferative Neoplasms: “Crafting” a Microenvironment That Matters

Cells ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 2316
Author(s):  
Lucia Catani ◽  
Michele Cavo ◽  
Francesca Palandri
Keyword(s):  
Extracellular Vesicles ◽  
Immune Escape ◽  
Myeloproliferative Neoplasms ◽  
Cell Communication ◽  
Bioactive Molecules ◽  
Driver Genes ◽  
Hematopoietic Stem ◽  
Increased Risk ◽  
Patients Experience

Myeloproliferative Neoplasms (MPN) are acquired clonal disorders of the hematopoietic stem cells and include Essential Thrombocythemia, Polycythemia Vera and Myelofibrosis. MPN are characterized by mutations in three driver genes (JAK2, CALR and MPL) and by a state of chronic inflammation. Notably, MPN patients experience increased risk of thrombosis, disease progression, second neoplasia and evolution to acute leukemia. Extracellular vesicles (EVs) are a heterogeneous population of microparticles with a role in cell-cell communication. The EV-mediated cross-talk occurs via the trafficking of bioactive molecules such as nucleic acids, proteins, metabolites and lipids. Growing interest is focused on EVs and their potential impact on the regulation of blood cancers. Overall, EVs have been suggested to orchestrate the complex interplay between tumor cells and the microenvironment with a pivotal role in “education” and “crafting” of the microenvironment by regulating angiogenesis, coagulation, immune escape and drug resistance of tumors. This review is focused on the role of EVs in MPN. Specifically, we will provide an overview of recent findings on the involvement of EVs in MPN pathogenesis and discuss opportunities for their potential application as diagnostic and prognostic biomarkers.

scholarly journals JAK2 V617F impairs hematopoietic stem cell function in a conditional knock-in mouse model of JAK2 V617F–positive essential thrombocythemia

Blood ◽  
2010 ◽  
Vol 116 (9) ◽  
pp. 1528-1538 ◽  
Author(s):  
Juan Li ◽  
Dominik Spensberger ◽  
Jong Sook Ahn ◽  
Shubha Anand ◽  
Philip A. Beer ◽  
...  
Keyword(s):  
Stem Cell ◽  
Hematopoietic Stem Cell ◽  
Essential Thrombocythemia ◽  
Cell Function ◽  
Myeloproliferative Neoplasms ◽  
Myeloproliferative Neoplasm ◽  
Jak2 V617f ◽  
Transgenic Models ◽  
Disease Phenotype ◽  
Hematopoietic Stem

The JAK2 V617F mutation is found in most patients with a myeloproliferative neoplasm and is sufficient to produce a myeloproliferative phenotype in murine retroviral transplantation or transgenic models. However, several lines of evidence suggest that disease phenotype is influenced by the level of mutant JAK2 signaling, and we have therefore generated a conditional knock-in mouse in which a human JAK2 V617F is expressed under the control of the mouse Jak2 locus. Human and murine Jak2 transcripts are expressed at similar levels, and mice develop modest increases in hemoglobin and platelet levels reminiscent of human JAK2 V617F–positive essential thrombocythemia. The phenotype is transplantable and accompanied by increased terminal erythroid and megakaryocyte differentiation together with increased numbers of clonogenic progenitors, including erythropoietin-independent erythroid colonies. Unexpectedly, JAK2V617F mice develop reduced numbers of lineage−Sca-1+c-Kit+ cells, which exhibit increased DNA damage, reduced apoptosis, and reduced cell cycling. Moreover, competitive bone marrow transplantation studies demonstrated impaired hematopoietic stem cell function in JAK2V617F mice. These results suggest that the chronicity of human myeloproliferative neoplasms may reflect a balance between impaired hematopoietic stem cell function and the accumulation of additional mutations.

Fyn and Lyn phosphorylate the Fc receptor γ chain downstream of glycoprotein VI in murine platelets, and Lyn regulates a novel feedback pathway

Blood ◽  
2000 ◽  
Vol 96 (13) ◽  
pp. 4246-4253 ◽  
Author(s):  
Lynn S. Quek ◽  
Jean-Max Pasquet ◽  
Ingeborg Hers ◽  
Richard Cornall ◽  
Graham Knight ◽  
...  
Keyword(s):  
Tyrosine Phosphorylation ◽  
Fc Receptor ◽  
Inhibitory Pathway ◽  
Functional Responses ◽  
Glycoprotein Vi ◽  
Granule Secretion ◽  
Activation Motif ◽  
Additional Role ◽  
Feedback Pathway

Abstract Activation of platelets by collagen is mediated by the complex glycoprotein VI (GPVI)/Fc receptor γ (FcRγ chain). In the current study, the role of 2 Src family kinases, Fyn and Lyn, in GPVI signaling has been examined using murine platelets deficient in one or both kinases. In the fyn−/−platelets, tyrosine phosphorylation of FcRγ chain, phopholipase C (PLC) activity, aggregation, and secretion are reduced, though the time of onset of response is unchanged. In the lyn−/−platelets, there is a delay of up to 30 seconds in the onset of tyrosine phosphorylation and functional responses, followed by recovery of phosphorylation and potentiation of aggregation and α-granule secretion. Tyrosine phosphorylation and aggregation in response to stimulation by collagen-related peptide is further attenuated and delayed in fyn−/−lyn−/−double-mutant platelets, and potentiation is not seen. This study provides the first genetic evidence that Fyn and Lyn mediate FcR immune receptor tyrosine-based activation motif phosphorylation and PLCγ2 activation after the ligation of GPVI. Lyn plays an additional role in inhibiting platelet activation through an uncharacterized inhibitory pathway.

scholarly journals CALR mutations in a cohort of JAK2 V617F negative patients with suspected myeloproliferative neoplasms

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Tanja Belcic Mikic ◽  
Tadej Pajic ◽  
Matjaz Sever
Keyword(s):  
Sanger Sequencing ◽  
Blood Count ◽  
Mutation Detection ◽  
Myeloproliferative Neoplasms ◽  
Jak2 V617f ◽  
Frameshift Mutations ◽  
Secondary Conditions ◽  
Non Invasive ◽  
Calr Mutations

AbstractSuspicion of myeloproliferative neoplasms (MPNs) and especially essential thrombocythemia (ET) in primary care is often based solely on blood counts, with patients referred to a haematologist without a thorough evaluation. We retrospectively assessed the role of calreticulin gene (CALR) mutations in the diagnosis of MPN in this population. We studied CALR mutations in 524 JAK2 V617F-negative patients with suspected MPN. Uncommon CALR mutations were confirmed by Sanger sequencing and searched for in the COSMIC or HGMD database. Mutations were defined as frameshift or non-frameshift mutations. CALR mutations were detected in 23 patients (23/524 = 4.4%). Four mutations detected in our study were newly identified mutations. Non-frameshift mutations were detected in two patients. Most patients (380/524 = 72.5%) were diagnosed with secondary conditions leading to blood count abnormalities such as iron deficiency, inflammatory and infectious diseases, malignancy and hyposplenism. Nine patients (9/23 = 39%) were retrospectively diagnosed with ET based on CALR mutation confirmation. Two patients with non-frameshift CALR mutations were diagnosed with reactive thrombocytosis and MPN unclassifiable, respectively. Our study showed that CALR mutations are important, non-invasive diagnostic indicators of ET and can aid in its diagnosis. Moreover, the type of CALR mutation must be accurately defined, as non-frameshift mutations may not be associated with ET. Finally, CALR mutation detection should be reserved for patients with high suspicion of clonal haematological disease.

Direct Activation of STAT5 by TEL-Lyn Fusion Protein Promotes Induction of Myeloproliferative Neoplasms with Myelofibrosis

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 4114-4114
Author(s):  
Yusuke Takeda ◽  
Chiaki Nakaseko ◽  
Hiroaki Tanaka ◽  
Masahiro Takeuchi ◽  
Makiko Yui ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Myeloproliferative Neoplasms ◽  
Jak2 V617f ◽  
Signaling Molecules ◽  
Janus Kinase ◽  
Idiopathic Myelofibrosis ◽  
Lyn Kinase

Abstract Abstract 4114 Background Myeloproliferative neoplasms (MPN), a group of hematopoietic stem cell (HSC) disorders, are often accompanied by myelofibrosis. The V617F somatic mutation in the Janus kinase 2 (JAK2) gene has recently been found in the majority of patients with polycythemia vera (PV) and more than half of patients with essential thrombocythemia (ET) and idiopathic myelofibrosis (IMF). The expression of JAK2 V617F causes a PV-like disease with myelofibrosis in a murine bone marrow (BM) transplant model. In addition, a gain-of-function c-MPL W515 mutation was described in nearly 10% of patients with JAK2 V617F-negative IMF. However, the mechanism responsible for MPD and the formation of myelofibrosis in patients without JAK2 or c-MPL mutations is still unclear. We previously identified the fusion of the TEL gene to the Lyn gene (TEL-Lyn) in idiopathic myelofibrosis with ins(12;8)(p13;q11q21). The introduction of TEL-Lyn into HSCs resulted in fatal MPN with massive myelofibrosis in mice, implicating the rearranged Lyn kinase in the pathogenesis of MPN with myelofibrosis. However, the signaling molecules directly downstream from and activated by TEL-Lyn remain unknown. Design and Methods We examined the signaling pathways activated by TEL-Lyn by Western blotting, immunoprecipitation, and in vitro kinase assay using a TEL-Lyn kinase-dead mutant as a control. We further characterized the functional properties of Stat5-deficient HSCs transduced with TEL-Lyn by colony-forming assay and bone marrow transplantation to evaluate the role of STAT5 in TEL-Lyn-induced MPN. Results TEL-Lyn was demonstrated to be constitutively active as a kinase through autophosphorylation. In TEL-Lyn-expressing cells, STAT5, STAT3, and Akt were constitutively activated. Among these signaling molecules, STAT5 was activated most prominently and this occurred without the activation of Jak2, the major kinase for STAT5. TEL-Lyn was co-immunoprecipitated with STAT5, and STAT5 was phosphorylated when incubated with TEL-Lyn, but not with TEL-Lyn kinase-dead mutant. These results indicate that TEL-Lyn interacts with STAT5 and directly activates STAT5 both in vitro and in vivo. Of note, the capacity of TEL-Lyn to support the formation of hematopoietic colonies under cytokine-free conditions in vitro and to induce MPN with myelofibrosis in vivo was profoundly attenuated in a Stat5-null background. Conclusions In this study, we clearly showed that TEL-Lyn directly activates STAT5 and the capacity of TEL-Lyn to induce MPN with myelofibrosis was profoundly attenuated in the absence of STAT5. Our findings of TEL-Lyn in this study support the role of the Src family kinases in the regulation of STAT pathways and implicate active Lyn in the alternative pathway for STAT activation in pathological cytokine signaling. Our mouse model of MPD with myelofibrosis would be beneficial for the analysis of therapeutic approaches for myelofibrosis. Disclosures: No relevant conflicts of interest to declare.

JAK2 Signaling Specifies Phenotypic Pleiotropy In Myeloproliferative Neoplasms

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 1608-1608
Author(s):  
Lily Huang ◽  
Huiyu Yao ◽  
Yue Ma
Keyword(s):  
Bone Marrow ◽  
Conflicts Of Interest ◽  
Phenotypic Diversity ◽  
Myeloproliferative Neoplasms ◽  
Jak2 V617f ◽  
Wild Type ◽  
Gain Of Function ◽  
Hematopoietic Stem ◽  
Phenotypic Differences ◽  
V617f Mutation

Abstract Myeloproliferative neoplasms (MPNs) are a phenotypically diverse group of pre-leukemic diseases characterized by overproduction of one or more of the myeloid cell lineages. Gain-of -function mutations in the Janus tyrosine kinase 2 (JAK2) are major determinants in MPNs, These include the V617F mutation and mutations in exon 12. Interestingly, MPN phenotype in patients with exon 12 mutations is distinct from that of patients with the V617F mutation. Mechanisms underlying the phenotypic differences are not well understood. We performed an unbiased screen for residues essential for JAK2 auto-inhibition, and identified a panel of novel gain-of-function mutations. Interestingly, three of them with similar kinase activities in vitro elicited distinctive hematopoietic abnormalities in mice. Specifically, JAK2(K539I) results primarily in erythrocytosis, JAK2(N622I) predominantly granulocytosis, and JAK2(V617F) in both. These phenotypes are consistent with clinical data showing that patients with the V617F mutation exhibit erythrocytosis and granulocytosis, whereas those with mutations in exon 12 (where K539 resides) exhibit erythrocytosis only. To determine the mechanisms underlying the phenotypic differences by different JAK2 mutants, we characterized hematopoietic progenitors and precursor subsets in these mice for their proliferation, apoptosis and differentiation. Quantification of the hematopoietic stem and progenitor population showed an increased percentage of granulocyte-monocyte progenitors (GMP) and skewing of differentiation towards the granulocytic lineage in JAK2(V617F) and JAK2(N622I) mice compared to JAK2(K539I) or wild-type JAK2 mice. Because no difference was observed in the proliferation or apoptosis of bone marrow progenitors from JAK2 mutant mice, differentiation of the common myeloid progenitors (CMP) was likely skewed towards GMP by JAK2(V617F) and JAK2(N622I). Consistent with this hypothesis, similar results were observed in colony forming assays from sorted CMP populations. In the spleen, a decrease in GMP apoptosis and an increase in apoptosis of the megakaryocyte-erythrocyte progenitors (MEP) also contributed to the skewing towards the granulocytic lineage in JAK2(N622I) mice. Similar to MPN patients, mice expressing JAK2 mutants exhibited splenomegaly. We found that JAK2 mutants caused redistribution of hematopoietic stem and progenitors from the bone marrow to spleen. As a result, more differentiated precursors were expanded in the spleens of JAK2 mutants mice compared to mice expressing wild-type JAK2. Consistent with their phenotypes, the percentage of Annexin V＋7AAD－erythroblasts in JAK2(K539I) and JAK2(V617F) mice was significantly less than in JAK2(N622I) or wild-type JAK2 mice. On the other hand, both proliferation and apoptosis contribute to the differential degrees of granulocytosis among mice expressing different JAK2 mutants. In line with the different effects elicited by different JAK2 mutants in progenitor and precursor cells, signal transduction pathways were differentially activated downstream of different JAK2 mutants. In summary, our results showed that JAK2 mutants differentially skew differentiation in early stem and progenitor compartments, and also regulate apoptosis and proliferation of distinct precursor subsets to cause erythrocytosis or granulocytosis in mice. These results provide the mechanistic basis for the phenotypic diversity observed in MPNs with different JAK2 mutants. Disclosures: No relevant conflicts of interest to declare.

PRMT5 Methyltransferase Activity Is Required to Sustain Adult Hematopoiesis

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 4335-4335
Author(s):  
Fan LIU ◽  
Guoyan Cheng ◽  
Fabiana Perna ◽  
Xu Haiming ◽  
Pierre-Jacques Hamard ◽  
...  
Keyword(s):  
Cell Biology ◽  
Conflicts Of Interest ◽  
Critical Role ◽  
Conditional Knockout ◽  
Major Type ◽  
Cytokine Signaling ◽  
Methyltransferase Activity ◽  
Hematopoietic Stem ◽  
Arginine Residues

Abstract Epigenetic regulators have been shown to play critical roles in normal hematopoiesis, and their activity is frequently altered in hematopoietic cancers. Protein arginine methyltransferase 5 (PRMT5) is the major type II PRMTs, catalyzing the symmetric di-methylation of arginine residues in histones (H2A, H3 and H4) and non-histone proteins. PRMT5 is over-expressed in several cancers, including acute leukemia and non-Hodgkin’s lymphoma. To define the role of PRMT5 in normal adult hematopoiesis, we generated PRMT5 conditional knockout mice using Mx1-cre. The induced deletion of both alleles of PRMT5 leads to severe pancytopenia and bone marrow aplasia with subsequent lethality in two weeks. First, loss of PRMT5 triggers the impaired proliferation and rapid disappearance of progenitor cells. At the same time, PRMT5 deficient HSCs show increased cell cycling and a transient HSC accumulation, which is rapidly followed by stem cell exhaustion. Mechanistically, we show that deletion of PRMT5 severely impairs cytokine signaling. It also up-regulates p53 protein level and the expression of p53 target genes. These effects likely account for the critical role of PRMT5 in HSPCs. We have conducted many additional experiments to show that these effects of PRMT5 deletion on hematopoiesis are cell autonomous; and also that the methyltransferase activity of PRMT5 is required to sustain normal hematopoiesis. Thus, we identify PRMT5 as a critical regulator of normal hematopoietic stem and progenitor cell biology. Disclosures No relevant conflicts of interest to declare.

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