Post-natal vasculogenesis has been reported to be derived from a hierarchy of circulating endothelial progenitor cells (EPC). Some of these EPC are of myeloid origin while others have a more robust proliferative potential and are solely of endothelial cell (EC) origin. A number of groups have hypothesized that EC dysfunction might contribute to the hypercoagulable state associated with polycythemia vera (PV) by orchestrating the recruitment of blood elements to sites of injury or by regulating vascular tone. The JAK2V617F mutation is present in >95% of patients with PV. In addition, some individuals with normal blood counts who develop splanchnic vein thrombosis, including Budd-Chiari syndrome (BCS) and portal vein thrombosis (PVT) have been reported to have JAK2V617F positive hematopoiesis (45% and 34%, respectively) indicating that this thrombotic tendency might precede the development of PV. We explored whether this activating mutation is present in EC in the vessels of patients with BCS. We tested this hypothesis by studying EC in venules of liver biopsy specimens of patients with BCS with (n=2) or without PV (n=1) and PVT (n=2) without PV using laser capture microdissection (LCM) followed by nested PCR or RT-PCR in order to determine if EC were JAK2V617F positive and were of hematopoietic or EC origin. EC from the hepatic venules of BCS and PVT patients were captured by LCM from hematoxylin and eosin stained sections of archival formalin-fixed paraffin-embedded liver biopsy tissue specimens. EC were identified by their fusiform nuclei and their location along the lining of the hepatic venules. Hepatocytes were identified by their morphology as having round centrally placed nuclei and abundant cytoplasm with a trabecular arrangement. At least 10 EC and 10 hepatocytes from each biopsy specimen were captured and DNA or RNA was extracted. The JAK2V617F mutation was detected using nested allele-specific PCR. The hepatocytes of each patient contained exclusively wild type JAK2 while the EC of the two BCS patients with PV were homozygous for the JAK2V617F. The EC of the other BCS patient and 2 PVT patients who did not have PV contained exclusively wild type JAK2. The EC identity of these cells in the PV patients was confirmed by the presence of the EC transcripts (VE-Cadherin and VEGF-R2) and the absence of hematopoietic cell transcripts (CD45 and CD14). These findings indicate that hepatic venule EC in BCS patients with PV are JAK2V617F positive. The presence of JAK2V617F in both endothelial cells and hematopoietic cells belonging to such patients suggests that PV originates in an adult hemangioblast like cell in such patients. Further studies are required to understand the consequence of JAK2 mutation in EC as related to their propensity to thrombosis in PV.

Disclosures: No relevant conflicts of interest to declare.

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