Absence of JAK2V617F Mutated Endothelial Colony‐Forming Cells in Patients With JAK2V617F Myeloproliferative Neoplasms and Splanchnic Vein Thrombosis

Abstract

P hiladelphia (Ph)-negative myeloproliferative neoplasms (MPN) are acquired hematologic diseases with increased production of mature blood cells. They include polycythemia vera (PV), essential thrombocythemia (ET) and myelofibrosis (MF). The most frequent molecular abnormality found in Ph negative MPN is JAK2V617F, an activating mutation of JAK2 which is responsible for constitutive signaling of various cytokine receptors. Arterial and venous thromboses are the main complications of these diseases and are responsible for high rates of morbidity and mortality. Of note there is a disproportionate incidence of thrombosis at unusual sites including splanchnic vein thrombosis. 1 Splanchnic vein thromboses (SVT) involve one or more abdominal veins, the two most frequent are Portal Vein Thrombosis (PVT) and Budd Chiari Syndrome (BCS). Pathophysiology of thrombosis in MPN is complex and involves abnormalities in blood cells, plasma factors, and endothelial cells (ECs). Several groups, using different techniques, have shown JAK2V617F expression in endothelial cells (Supplemental Fig. 1, http://links.lww.com/HS/ A79). Using laser capture microdissection, JAK2V617F was demonstrated in ECs from hepatic venules in 2 of 3 patients with PV and BCS. 2 JAK2V617F endothelial cells were demonstrated in microdissected splenic capillaries and in ECs cultured from splenic vein in patients with myelofibrosis but without SVT. 3 Although these teams performed experiments to ensure that the DNA they obtained originated from ECs, it is difficult to completely rule out a possible contamination by blood cells. Analysis of endothelial progenitor cells, specifically endothelial colony forming cells (ECFCs), is an alternative way to look for JAK2V617F ECs. Indeed, ECFCs are reported to be the only "true" endothelial progenitor cells, as they are the only ones able to generate blood vessels in vivo: they display clonogenic potential, endothelial but not myeloid cell surface markers, and pronounced postnatal vascularisation ability in vivo. 4,5 ECFCs are a unique tool to investigate endothelial molecular dysfunction in disease, as they give access to endothelial cells from patients in a non-invasive way and a promising tool for vascular regenerative approaches and gene therapy. 6 Yoder et al studied 11 JAK2V617F MPN patients and reported 3 JAK2V617F ECFCs derived from only 1 of 11 patients. Of note, this patient presented with thrombosis and later developed PV. 4 In another study, the JAK2V617F mutation was not detected in any of 75 ECFCs obtained from 57 patients with JAK2V617F MPN but no thrombosis. 7 Teofili et al reported JAK2V617F ECFCs in 5 of 22 MPN patients, all with thrombotic complications including 1 with BCS and 1 with PVT. 8 Lastly, 4 of 5 JAK2V617F-positive patients with BCS but without overt MPN had JAK2V617F ECFCs cultured from the bone marrow. 9 Taken together, these results suggest that the presence of JAK2V617F ECFCs in patients is associated with thrombosis, even in the absence of overt MPN. Our groups have previously demonstr...

The possible role of mutated endothelial cells in myeloproliferative neoplasms

“…The absence of the JAK2 mutation in ECFC from MPN patients was recently confirmed by Guy and colleagues. 13 Teofili et al 12 however, reported that ECFC from patients with MPN were JAK2 V617F + ( Figure 1 ). Almost half of the MPN patients studied were reported to have MPN-like genetic abnormalities in their ECFC, including either SOCS gene hypermethylation or the presence of JAK2 V617F.…”

“…This concept and its implications remain controversial and its significance has been questioned by some investigators. 9 , 11 , 13 The aim of this review is to analyze this evidence in a critical fashion and assess the validity of the link between EC and MPN pathobiology.…”

Exploring the Molecular Aspects of Myeloproliferative Neoplasms Associated with Unusual Site Vein Thrombosis: Review of the Literature and Latest Insights

“…Additionally, JAK2 V617F is not restricted to hematopoietic cells; it is also likely to be present in the endothelial cells of the liver and spleen, thereby promoting the expression of endothelial P-selectin and contributing to thrombosis [23,24]. However, the expression of JAK2 in endothelial cells within the liver has yet to be definitively confirmed [25].…”

Role of Inflammatory Factors during Disease Pathogenesis and Stem Cell Transplantation in Myeloproliferative Neoplasms

“…Thus, depending on the specific microenvironment in MPNs, JAK2V617F + ECs may support anti-thrombotic or pro-thrombotic effects in MPN [ 97 ]. Nevertheless, just recently, Guy et al were not able to detect the JAK2 V617F mutation in PB-derived ECs of two MPN patient cohorts (DNA of 12/31 patients was analyzed), potentially demonstrating a lack of reproducibility of endothelial colony-forming cell (ECFC) cultivation techniques [ 98 ].…”