Investigation of the molecular and functional pathophysiology of polycythaemia vera

• Main Author: Everington, Tamara
• Published: University College London (University of London) 2009
• Subjects: 616.15
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505136

This thesis explores the pathophysiological mechanisms underlying the myeloproliferative disease, Polycythaemia Vera (PV). PV is characterised by clonal red cell expansion with a tendency for leukaemic transformation. This study focuses on primary erythroid progenitor cells derived from 27 PV patients and 49 control subjects with non-clonal red cell expansion or normal red cell mass providing insight into survival, signal transduction & the molecular signature of these cells. The erythropoietin independent colonies (EECs) characteristic of PV were detected in 93% PV, the V617F Jak2 mutation was present in 93% PV and marked upregulation of PV1 mRNA which can be associated with PV was found in 89% PV. None of the control subjects showed these features. PV erythroid progenitors showed increased proliferation with relative resistance to cytokine deprivation when 14 PV samples were compared with 10 controls. Apoptosis was not found to be increased in PV. In over 40 experiments PV erythroid progenitors showed aberrant signalling with constitutive and stimulated increases in activation of the PI3K, MAPK and Jak/STAT pathways. Activation of each pathway was reduced with specific small molecule inhibitors. Use of PI3K & Jak2 inhibitors caused comparable reduction between PV & control samples in 40 erythroid colony assays and 20 survival experiments using erythroid progenitors. However, there was some evidence to suggest that the Jak2 inhibitors used were less effective in PV with homozygous expression of V617F Jak2. EECs from PV samples were, however, greatly reduced with inhibitors. RNA from 14 erythroid progenitor samples including 6 PV were hybridised onto Affymetrix GeneChip microarrays. There was segregration of signature between subject groups. The array data was validated by real-time quantitative PCR and this technique was further used to show that 2/4 genes identified as upregulated in PV were not Jak2 dependent but that the well recognised Jak/STAT target, Pim-1 was.