Angiogenic Factors eNOS and VEGF Have Increased Expression in Granulocytes of JAK2V617F Homozygous Forms of Polycythemia Vera,

Abstract 3847

The microvessel density of bone marrow is increased in myeloproliferative neoplasms (MPN) parallel with vascular endothelial growth factor (VEGF). VEGF-mediated angiogenesis requires nitric oxide (NO) production from activated endothelial NO synthase (eNOS). NO as well as hypoxia stimulate the VEGF gene expression and angiogenesis by enhancing hypoxia inducible factor (HIF)-1 activity. We studied 126 newly diagnosed patients with BCR-ABL⁻ MPN: 64 polycythemia vera (PV), 36 essential thrombocythemia (ET), 26 primary myelofibrosis (PMF) and 12 healthy individuals. We performed a combined analysis of hematopoietic CD34⁺ progenitor cells and granulocytes in peripheral blood of these individuals. The eNOS protein level is more than three-fold elevated in granulocytes of JAK2V617F homozygous PV patients. The essential inducer of angiogenesis VEGF-A has also about three-fold elevation at the protein level in granulocytes of PV patients, with major increases in JAK2V617F homozygous forms. Immunohistochemical analysis reveal that the percentage of VEGF-A-positive cells is increased in bone marrow of PV (5.58±0.7%) compared to normal controls (2.78±0.7%) and VEGF-A mRNA levels are increased in hematopoietic progenitor cells of PV origin. Transcription factor HIF-1α gene expression is decreased in hematopoietic progenitor cells and increased in granulocytes of PV patients. Negative regulator of HIF-1α activity, a transcription factor HIF-3α, has decreased expression in hematopoietic progenitor cells and not changed in granulocytes. In contrast to PV patients, PMF and ET disorders with a minor JAK2 mutation burden demonstrate reduced eNOS and VEGF protein levels and decreased HIF-1a gene expression in peripheral blood granulocytes, although the increase in percentage of VEGF-A-positive cells in bone marrow observed in PV patients is also evident. The present results expand the significance of JAK2V617F mutation in induction of angiogenic factors eNOS and VEGF in granulocytes of PV patients with enhanced HIF-1α presence. Moreover, the stromal and hematopoietic cells also show increased VEGF protein expression in bone marrow of PV patients. Therefore, we find that variations in angiogenic factors expression among MPN patients appear to be related to JAK2V617F mutation allele burden.