5 research outputs found

    J Thromb Haemost

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    Essentials To reliably study the respective roles of blood and endothelial cells in hemostasis, mouse models with a strong and specific endothelial expression of the Cre recombinase are needed. Using mT/mG reporter mice and conditional JAK2 mice, we compared Pdgfb-iCreERT2 and Cdh5(PAC)-CreERT2 with well-characterized Tie2-Cre mice. Comparison of recombination efficiency and specificity towards blood lineage reveals major differences between endothelial transgenic mice. Cre-mediated recombination occurs in a small number of adult hematopoietic stem cells in Pdgfb-iCreERT2;JAK2 transgenic mice. SUMMARY: Background The vessel wall, and particularly blood endothelial cells (BECs), are intensively studied to better understand hemostasis and target thrombosis. To understand the specific role of BECs, it is important to have mouse models that allow specific and homogeneous expression of genes of interest in all BEC beds without concomitant expression in blood cells. Inducible Pdgfb-iCreERT2 and Cdh5(PAC)-CreERT2 transgenic mice are widely used for BEC targeting. However, issues remain in terms of recombination efficiency and specificity regarding hematopoietic cells. Objectives To determine which mouse model to choose when strong expression of a transgene is required in adult BECs from various organs, without concomitant expression in hematopoietic cells. Methods Using mT/mG reporter mice to measure recombination efficiency and conditional JAK2 mice to assess specificity regarding hematopoietic cells, we compared Pdgfb-iCreERT2 and Cdh5(PAC)-CreERT2 with well-characterized Tie2-Cre mice. Results Adult Cdh5(PAC)-CreERT2 mice are endothelial specific but require a dose of 10 mg of tamoxifen to allow constant Cre expression. Pdgfb-iCreERT2 mice injected with 5 mg of tamoxifen are appropriate for most endothelial research fields except liver studies, as hepatic sinusoid ECs are not recombined. Surprisingly, 2 months after induction of Cre-mediated recombination, all Pdgfb-iCreERT2;JAK2 mice developed a myeloproliferative neoplasm that is related to the presence of JAK2V617F in hematopoietic cells, showing for the first time that Cre-mediated recombination occurs in a small number of adult hematopoietic stem cells in Pdgfb-iCreERT2 transgenic mice. Conclusion This study provides useful guidelines for choosing the best mouse line to study the role of BECs in hemostasis and thrombosis

    Vascular endothelial cell expression of JAK2V617F is sufficient to promote a pro-thrombotic state due to increased P-selectin expression

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    Thrombosis is the main cause of morbidity and mortality in patients with JAK2V617F myeloproliferative neoplasms. Recent studies have reported the presence of JAK2V617F in endothelial cells of some patients with myeloproliferative neoplasms. We investigated the role of endothelial cells that express JAK2V617F in thrombus formation using an in vitro model of human endothelial cells overexpressing JAK2V617F and an in vivo model of mice with endothelial-specific JAK2V617F expression. Interestingly, these mice displayed a higher propensity for thrombus. When deciphering the mechanisms by which JAK2V617F-expressing endothelial cells promote thrombosis, we observed that they have a pro-adhesive phenotype associated with increased endothelial P-selectin exposure, secondary to degranulation of Weibel-Palade bodies. We demonstrated that P-selectin blockade was sufficient to reduce the increased propensity of thrombosis. Moreover, treatment with hydroxyurea also reduced thrombosis and decreased the pathological interaction between leukocytes and JAK2V617F-expressing endothelial cells through direct reduction of endothelial P-selectin expression. Taken together, our data provide evidence that JAK2V617F-expressing endothelial cells promote thrombosis through induction of endothelial P-selectin expression, which can be reversed by hydroxyurea. Our findings increase our understanding of thrombosis in patients with myeloproliferative neoplasms, at least those with JAK2V617F-positive endothelial cells, and highlight a new role for hydroxyurea. This novel finding provides the proof of concept that an acquired genetic mutation can affect the pro-thrombotic nature of endothelial cells, suggesting that other mutations in endothelial cells could be causal in thrombotic disorders of unknown cause, which account for 50% of recurrent venous thromboses

    J Thromb Haemost

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    Neutrophils participate in the pathogenesis of thrombosis through the formation of neutrophil extracellular traps (NETs). Thrombosis is the main cause of morbidity and mortality in patients with myeloproliferative neoplasms (MPNs). Recent studies have shown an increase in NET formation (NETosis) both in patients with JAK2V617F neutrophils and in mouse models, and reported the participation of NETosis in the pathophysiology of thrombosis in mice. This study investigated whether JAK2V617F neutrophils are sufficient to promote thrombosis or whether their cooperation with other blood cell types is necessary. NETosis was studied in PF4iCre;Jak2 mice expressing JAK2V617F in all hematopoietic lineages, as occurs in MPNs, and in MRP8Cre;Jak2 mice in which JAK2V617F is expressed only in leukocytes. In PF4iCre;Jak2 mice, an increase in NETosis and spontaneous lung thrombosis abrogated by DNAse administration were observed. The absence of spontaneous NETosis or lung thrombosis in MRP8Cre;Jak2 mice suggested that mutated neutrophils alone are not sufficient to induce thrombosis. Ex vivo experiments demonstrated that JAK2V617F-mutated platelets trigger NETosis by JAK2V617F-mutated neutrophils. Aspirin treatment in PF4iCre;Jak2 mice reduced NETosis and reduced lung thrombosis. In cytoreductive-therapy-free patients with MPN treated with aspirin, plasma NET marker concentrations were lower than that in patients with MPN not treated with aspirin. Our study demonstrates that JAK2V617F neutrophils alone are not sufficient to promote thrombosis; rather, platelets cooperate with neutrophils to promote NETosis in vivo. A new role for aspirin in thrombosis prevention in MPNs was also identified

    Description of a knock-in mouse model of JAK2V617F MPN emerging from a minority of mutated hematopoietic stem cells

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    The major weakness of most knock-in JAK2V617F mouse models is the presence of the JAK2 mutation in all rather than in a few hematopoietic stem cells (HSC), such as in human "early-stage" myeloproliferative neoplasms (MPN). Understanding the mechanisms of disease initiation is critical as underscored by the incidence of clonal hematopoiesis of indeterminate potential associated with JAK2V617F. Currently, such studies require competitive transplantation. Here, we report a mouse model obtained by crossing JAK2V617F/WT knock-in mice with PF4iCre transgenic mice. As expected, PF4iCre;JAK2V617F/WT mice developed an early thrombocytosis resulting from the expression of JAK2V617F in the megakaryocytes. However, these mice then developed a polycythemia vera-like phenotype at 10 weeks of age. Using mT/mG reporter mice, we demonstrated that Cre recombination was present in all hematopoietic compartments, including in a low number of HSC. The frequency of mutated cells increased along hematopoietic differentiation mimicking the clonal expansion observed in essential thrombocythemia and polycythemia vera patients. This model thus mimics the HSC compartment observed in early-stage MPN, with a small number of JAK2V617F HSC competing with a majority of JAK2WT HSC. PF4iCre;JAK2V617F/WT mice are a promising tool to investigate the mechanisms that regulate clonal dominance and progression to myelofibrosis
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