Activation of JAK/STAT Signaling in Megakaryocytes Sustains Myeloproliferation In Vivo

The myeloproliferative neoplasms (MPN), including polycythemia vera, essential thrombocythemia, and primary myelofibrosis, are characterized by the expansion of the erythroid, megakaryocytic, and granulocytic lineages. A common feature of these disorders is the presence of abnormal megakaryocytes, which have been implicated as causative agents in the development of bone marrow fibrosis. However, the specific contributions of megakaryocytes to MPN pathogenesis remain unclear. We used transgenic mice to drive expression of in megakaryocyte lineage-committed hematopoietic cells. We also assessed the critical role of mutant megakaryocytes in MPN maintenance through cell ablation studies in and BMT models of MPN. -mutant presence in megakaryocytes was sufficient to induce enhanced erythropoiesis and promote fibrosis, which leads to a myeloproliferative state with expansion of mutant and nonmutant hematopoietic cells. The increased erythropoiesis was associated with elevated IL6 level, which was also required for aberrant erythropoiesis . Furthermore, depletion of megakaryocytes in the and BMT models ameliorated polycythemia and leukocytosis in addition to expected effects on megakaryopoiesis. Our observations reveal that JAK/STAT pathway activation in megakaryocytes induces myeloproliferation and is necessary for MPN maintenance . These observations indicate that MPN clone can influence the behavior of the wild-type hematopoietic milieu, at least, in part, via altered production of proinflammatory cytokines and chemokines. Our findings resonate with patients who present with a clinical MPN and a low allele burden, and support the development of MPN therapies aimed at targeting megakaryocytes.