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Contributions
Abstract: S882
Type: Oral Presentation
Presentation during EHA23: On Saturday, June 16, 2018 from 16:15 - 16:30
Location: Room A8
Background
Myeloproliferative neoplasms are clonal hematopoietic disorders characterized by increased production of terminally differentiated myeloid cells. These diseases that encompass Polycythemia Vera (PV), Primary Myelofibrosis (PMF) and Essential Thrombocythemia (ET) are associated with drivers mutations inducing constitutive activation of JAK2/STAT signaling pathway.
The most prevalent driver mutation is the JAK2V617F mutation. During the last years, murine models of JAK2V617F-induced disease were developed and recapitulate the disease. These models have increased the understanding of the pathogenesis and have provided tools for preclinical testing of new therapies. Among those, interferon (IFN) alpha treatment is widely used in patients and induces significant hematologic and molecular responses. In mouse models, it was shown to target the mutated clone but the mechanism remains unknown.
Aims
STAT2 activation and formation of ISGF3 complex is the hallmark of IFN alpha signaling pathway, while STAT1 homodimer formation is shared by the signaling of many other cytokines and STATs. Thus, we wanted to assess the role of STAT2 in MPN phenotype induced by JAK2 V617F knock-in and to evaluate the role of STAT2 in normal hematopoiesis.
Methods
We crossed our previously described JAK2V617F knock-in mice (based on cre-loxP system, with the use of the vav promoter) with STAT2 knock out mice to obtain STAT2-/- JAK2V617F mice.
Results
The heterozygous KI JAK2V617F homozygous KO STAT2 mice exhibit a stronger myeloproliferative phenotype- regarding the blood counts-, especially on the megakaryocyte lineage. However, mice exhibited a better survival compared to KI JAK2V617F mice, which was surprising, given the very high platelet and granulocyte levels. Myelofibrosis was apparently reduced in mice that do not express STAT2. The study of megakaryopoeisis in STAT2-/- JAK2V617F mice compared to the STAT2+/+ JAK2V617F mice showed no significant increases in CFU-Mk and CD41+CD42+ cell numbers, suggesting that STAT2 deficiency targets the latter stages of megakaryopoeisis. To test whether this late effect on MK differentiation was due to an intrinsic or extrinsic effect, we performed bone marrow reconstitution assays. These experiments showed no differences in blood counts between mice reconstituted with STAT2+/+ JAK2V617F and those reconstituted with STAT2KO/KO JAK2V617F. Thus, the observed impact of STAT2 KO is due to the absence of STAT2 in non-hematopoietic cells. Survival also did not differ between the two types of reconstituted mice and was improved compared to the KI JAK2V617F mice resulting after the vav-cre crossing. The latter result suggests that mortality related to JAK2V617F in our knock-in model is probably related to its expression in endothelial cells (cre expression being under the control of vav promoter).
We will further use these murine models to assess the impact of STAT2 in interferon alpha response via competitive bone marrow reconstitution.
Conclusion
We report that in the vav-dependent JAK2V617F knock-in mouse model, the knock-out of STAT2 protects against myelofbrosis, increases survival, while leading to an increased thrombocytosis. These effects were extrinsic to the hematopoietic system. This raises the possibility that administration of type I IFN, in IFN-resistant patients, may enhance myelofibrosis by activation of STAT2 in non-hematopoietic cells and points to a potential extrinsic pro-inflammatory role of STAT2.
Session topic: 15. Myeloproliferative neoplasms – Biology & Translational Research
Keyword(s): Interferon, Myeloproliferative disorder
Abstract: S882
Type: Oral Presentation
Presentation during EHA23: On Saturday, June 16, 2018 from 16:15 - 16:30
Location: Room A8
Background
Myeloproliferative neoplasms are clonal hematopoietic disorders characterized by increased production of terminally differentiated myeloid cells. These diseases that encompass Polycythemia Vera (PV), Primary Myelofibrosis (PMF) and Essential Thrombocythemia (ET) are associated with drivers mutations inducing constitutive activation of JAK2/STAT signaling pathway.
The most prevalent driver mutation is the JAK2V617F mutation. During the last years, murine models of JAK2V617F-induced disease were developed and recapitulate the disease. These models have increased the understanding of the pathogenesis and have provided tools for preclinical testing of new therapies. Among those, interferon (IFN) alpha treatment is widely used in patients and induces significant hematologic and molecular responses. In mouse models, it was shown to target the mutated clone but the mechanism remains unknown.
Aims
STAT2 activation and formation of ISGF3 complex is the hallmark of IFN alpha signaling pathway, while STAT1 homodimer formation is shared by the signaling of many other cytokines and STATs. Thus, we wanted to assess the role of STAT2 in MPN phenotype induced by JAK2 V617F knock-in and to evaluate the role of STAT2 in normal hematopoiesis.
Methods
We crossed our previously described JAK2V617F knock-in mice (based on cre-loxP system, with the use of the vav promoter) with STAT2 knock out mice to obtain STAT2-/- JAK2V617F mice.
Results
The heterozygous KI JAK2V617F homozygous KO STAT2 mice exhibit a stronger myeloproliferative phenotype- regarding the blood counts-, especially on the megakaryocyte lineage. However, mice exhibited a better survival compared to KI JAK2V617F mice, which was surprising, given the very high platelet and granulocyte levels. Myelofibrosis was apparently reduced in mice that do not express STAT2. The study of megakaryopoeisis in STAT2-/- JAK2V617F mice compared to the STAT2+/+ JAK2V617F mice showed no significant increases in CFU-Mk and CD41+CD42+ cell numbers, suggesting that STAT2 deficiency targets the latter stages of megakaryopoeisis. To test whether this late effect on MK differentiation was due to an intrinsic or extrinsic effect, we performed bone marrow reconstitution assays. These experiments showed no differences in blood counts between mice reconstituted with STAT2+/+ JAK2V617F and those reconstituted with STAT2KO/KO JAK2V617F. Thus, the observed impact of STAT2 KO is due to the absence of STAT2 in non-hematopoietic cells. Survival also did not differ between the two types of reconstituted mice and was improved compared to the KI JAK2V617F mice resulting after the vav-cre crossing. The latter result suggests that mortality related to JAK2V617F in our knock-in model is probably related to its expression in endothelial cells (cre expression being under the control of vav promoter).
We will further use these murine models to assess the impact of STAT2 in interferon alpha response via competitive bone marrow reconstitution.
Conclusion
We report that in the vav-dependent JAK2V617F knock-in mouse model, the knock-out of STAT2 protects against myelofbrosis, increases survival, while leading to an increased thrombocytosis. These effects were extrinsic to the hematopoietic system. This raises the possibility that administration of type I IFN, in IFN-resistant patients, may enhance myelofibrosis by activation of STAT2 in non-hematopoietic cells and points to a potential extrinsic pro-inflammatory role of STAT2.
Session topic: 15. Myeloproliferative neoplasms – Biology & Translational Research
Keyword(s): Interferon, Myeloproliferative disorder