The Role of NFκB in the Pathogenesis of Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPNs) are a group of blood cancers which reduce lifespan and quality of life. Currently, the only curative therapeutic option for patients is allogeneic stem cell transplant which carries a high risk of mortality and is not a viable option for over 90% of patients. The current standard treatment for aggressive MPN disease reduces patient symptoms but does not reduce disease burden. Therefore, new treatment options are needed. Over 90% of MPNs harbor a mutation in one of three genes that all result in JAK-STAT signaling pathway activation. Since the current standard therapy inhibits JAK-STAT signaling but does not reduce disease burden, it is likely that other signaling pathways play a role in disease progression and clonal advantage. Our lab has evaluated a set of MPN patients and found they have elevation of several signaling pathways. One of the most prominent pathways found elevated was NFκB signaling. We also demonstrated that current treatment does not effectively reduce the increase in NFκB signaling. Therefore, the question exists as to whether this retained NFκB increase is contributing to disease phenotype or clonal selection. One way to establish the importance of NFκB signaling in MPNs is by manipulating the pathway in mouse models of MPN. One major component of the canonical NFκB signaling pathway is RELA. We utilized a conditional knockout of this gene in two different MPN mouse models to establish the requirement for canonical NFκB signaling. These two models were disparate in their NFκB pathway activation and exhibited different phenotypes. Myelofibrosis (MF) is the most aggressive chronic MPN subtype and the retroviral MPL W515L mouse model recapitulates several phenotypes typically seen in MF patients. These mice demonstrated increased NFκB signaling measured by mass cytometry, NFκB-GFP reporter, and qPCR analysis. By transplanting cells with the MPL W515L mutation and knockout of Rela, we established that loss of Rela prevented expansion of the MPL W515L cells. The loss of MPL W515L cell expansion prevented the leukocytosis, thrombocytosis, erythrocytosis, and bone marrow fibrosis typically observed in the model. Our data support the possibility that Rela is a critical component of the disease development pathway for MPL W515L model mice. Our second model is a Jak2 V617F knock-in model that closely resembles characteristics of polycythemia vera (PV) patients. We did not detect increased NFκB signaling compared to wild type mice as examined by mass cytometry, GSEA, and qPCR analysis. The loss of Rela in Jak2 V617F mice did not eliminate their hallmark erythrocytosis or extramedullary hematopoiesis and causes only a small transient decrease in the extent of leukocytosis. The data presented in this dissertation supports the possibility that NFκB plays a role in MPN disease but the extent of that role may be dependent on the severity of disease and the level of NFκB pathway elevation present. These experiments support further exploration of inhibiting NFκB in MPN patients