A Jak2-V617F knock-in mouse model for assessing therapeutic efficacy in myeloproliferative neoplasms

Background: Myeloproliferative neoplasms (MPN) are a group of malignant hematological disorders characterized by excessive proliferation of blood cells and are often accompanied by splenomegaly, thrombosis, and bleeding tendencies. The main subtypes of MPN include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). The acquired somatic JAK2-V617F mutation occurs in approximately 95% of PV cases and in about 50% of ET or PMF patients. This mutation results in constitutive activation of the JAK2 kinase signaling pathway, establishing it as a critical therapeutic target in MPNs. Therefore, to enable preclinical evaluation of therapies targeting this mutation, we developed a novel Jak2-V617F knock-in mouse model. Method: Firstly, we generated Jak2-Flox-V617F mice by inserting the inverted exon 14 cassette (carrying the c.1849 G>T, p. V617F mutation) flanked by antiparallel loxp sites into the endogenous Jak2 exon14 locus via ES cell-based gene targeting. These mice were then crossed with Vav1-Cre mice to obtain heterozygous Jak2-Flox-V617F/Vav1-Cre offspring (Jak2-V617F mice), in which Cre-mediated recombination induces Jak2-V617F expression specifically in the hematopoietic cells. The mutant mice were phenotyped using blood routine analysis, flow cytometry, H&E staining and pathology analysis. Finally, we tested the JAK inhibitor Ruxolitinib, a clinical agent for myelofibrosis, for its efficacy in this model. Results: Compared with wild-type mice, Jak2-V617F mice exhibited significantly elevated hemoglobin and hematocrit levels, marked thrombocytosis, increased neutrophils, alopecia and splenomegaly at 8 weeks. By 28 weeks, pathology analysis revealed megakaryocyte hyperplasia and extramedullary hematopoiesis in bone marrow, spleen, and liver in Jak2-V617F mice. Notably, these hematological abnormalities and splenomegaly were significantly mitigated by oral administration of Ruxolitinib. Conclusion: Taken together, our Jak2-V617F mouse model provides a unique platform for studying the mutation of Jak2 in the hematopoietic cells and evaluating the efficacy of potential therapeutic targets in preclinical studies.