Pericyte coverage of abnormal blood vessels in myelofibrotic bone marrows

Background and Objectives Myelofibrotic bone marrow displays abnormal angiogenesis but the pathogenic mechanisms of this are poorly understood. Since pericyte abnormalities are described on solid tumor vessels we studied whether vessel morphology and pericyte coverage in bone marrow samples from patients with myelofibrosis differed from that in samples from controls. Design and Methods We assessed the microvascular density (MVD), vessel morphology and pericyte coverage in bone marrows from 19 myelofibrosis patients and nine controls. We also studied the same parameters in two mouse models of myelofibrosis, with genetic alterations affecting megakaryocyte differentiation (i.e. one model with low GATA-1 expression and the other with over-expression of thrombopoietin). Results In myelofibrotic marrows, MVD was 3.8-fold greater than in controls ( p p JAK2 V617F-positive than in negative patients ( p =0.026). Moreover, 92±11 % of vessels in patients with myelofibrosis were pericyte-coated but only 51±20 % of vessels in controls ( p Interpretation and Conclusions We conclude that angiogenesis is similarly abnormal in human and murine myelofibrosis with intense pericyte coating, presumably related to abnormal megakaryocytopoiesis.