JAK2V617F leads to intrinsic changes in platelet formation and reactivity in a knock-in mouse model of essential thrombocythemia

Abstract

The principal morbidity and mortality in patients with essential thrombocythemia (ET) and polycythemia rubra vera (PV) stems from thrombotic events. Most patients with ET/PV harbor a JAK2V617F mutation, but its role in the thrombotic diathesis remains obscure. Platelet function studies in patients are difficult to interpret because of interindividual heterogeneity, reflecting variations in the proportion of platelets derived from the malignant clone, differences in the presence of additional mutations, and the effects of medical treatments. To circumvent these issues, we have studied a JAK2V617F knock-in mouse model of ET in which all megakaryocytes and platelets express JAK2V617F at a physiological level, equivalent to that present in human ET patients. We show that, in addition to increased differentiation, JAK2V617F-positive megakaryocytes display greater migratory ability and proplatelet formation. We demonstrate in a range of assays that platelet reactivity to agonists is enhanced, with a concomitant increase in platelet aggregation in vitro and a reduced duration of bleeding in vivo. These data suggest that JAK2V617F leads to intrinsic changes in both megakaryocyte and platelet biology beyond an increase in cell number. In support of this hypothesis, we identify multiple differentially expressed genes in JAK2V617F megakaryocytes that may underlie the observed biological differences.

Gray platelet syndrome: proinflammatory megakaryocytes and α-granule loss cause myelofibrosis and confer metastasis resistance in mice

“…Platelet preparation, culture of bone marrow-derived MKs, proplatelet assays, flow cytometry analysis, and generation of cell lysates for western blot analysis have been described before and are detailed elsewhere 24 and in the supplemental Methods.…”

“…Data processing and analysis were performed as described elsewhere. 24 Gene set enrichment analysis was carried out using Gene Set Enrichment Analysis. 26 Version 4 gene sets of Gene Ontology (GO) molecular function were used with a weighted scoring scheme of the Student t scores.…”

Lysyl oxidase is associated with increased thrombosis and platelet reactivity

“…Platelets from JAK2V617F knock-in mice showed increased activation in response to CRP-XL, thrombin, collagen, and fibrinogen. 57 In another model transplanted with JAK2V617F knock-in cells, time to occlusion after FeCl 3 treatment was decreased as compared with controls, but formed thrombi were unstable, which was attributed to reduced levels of GPVI. 58 Analysis of thrombosis in vivo in the GATA-1 low mouse model is precluded by the extreme thrombocytopenia observed in those animals.…”

Bone marrow fibrosis in myelofibrosis: pathogenesis, prognosis and targeted strategies

“…Fos is a regulator of TGF-β signaling. 32 Previously Muth et al studied patients with MPN and reported that proplatelet numbers were higher in patients with essential thrombocythemia and pre-fibrotic MF than in controls. 33 Proplatelets were even more abundant in patients with fibrotic MF compared to those with pre-fibrotic MF or essential thrombocythemia.…”