JAK2V617F-Mediated Endothelial Dysfunction Promotes Congestive Heart Failure in a Murine Model of Myeloproliferative Neoplasm
Authors: Castiglione Melissa , Mazzeo Christopher , Jiang Ya-Ping , Chen Juei-Suei , Yin Wei , Lin Richard , Zhan Huichun 
Published: February 2020

Introduction
Cardiovascular complications are the leading cause of morbidity and mortality in patients with myeloproliferative neoplasms (MPNs). The acquired kinase mutation JAK2V617F plays a central role in these disorders. Many studies have established that a significant number of vascular endothelial cells (ECs) in MPN patients carry the mutation.In this study, we tested the hypothesis that the JAK2V617F mutation alters vascular endothelial function to promote cardiovascular complications in patients with MPNs.
Methods
JAK2V617F Flip-Flop (FF1) mice and Tie2-Cre mice were crossed to generate the Tie2FF1 mice, in which human JAK2V617F is expressed specifically in hematopoietic cells and vascular ECs, so as to model the human diseases in which both the hematopoietic stem cells and ECs harbor the mutation. All mice were fed a standard chow diet.
Results
As we previously reported, Tie2FF1 mice develop a myeloproliferative phenotype with leukocytosis, thrombocytosis, significant splenomegaly, and greatly increased numbers of hematopoietic stem cells by 8 wk of age. We observed an increased incidence of sudden death during performance of minor procedures (e.g. submandibular bleeding) in Tie2FF1 mice, especially after 20 wk of age. Transthoracic echocardiography revealed significant decreases in left ventricular ejection fraction and fractional shortening, and increases in left ventricular end-diastolic volume and end-systolic volume in 20-22 wk old Tie2FF1 mice compared to age-matched Tie2-Cre controls, indicative of cardiac dysfunction. Pathological evaluation revealed increased heart size and heart weight, and evidence of pulmonary congestion in Tie2FF1 mice compared to controls, consistent with the diagnosis of congestive heart failure. No atherosclerotic lesions or myocardium infarctions were observed in Tie2FF1 mice. (Figure 1) No significant cardiac dysfunction was observed in Tie2FF1 mice at 10-12 wk of age, suggesting that the heart failure is apparently not present from birth.
Next,we generated a chimeric murine model with JAK2V617F-mutant blood cells and wild-type vascular ECs by transplanting Tie2FF1 marrow cells into wild-type recipients. The transplantation of wild-type marrow cells into wild-type recipients served as a control. Recipients of Tie2FF1 marrow developed myeloproliferation and there was no difference in blood cell counts between these mice and the primary Tie2FF1 mice. However, serial echocardiography evaluation did not reveal any evidence of cardiac dysfunction in recipients of Tie2FF1 marrow. In addition, Ly-6Chighmonocytes, which are important participant at various stages of cardiovascular disease development, were significantly increased in primary Tie2FF1 micecompared to Tie2-Cre controls, but not in wild-type recipients of Tie2FF1 marrow. These observations suggest that JAK2V617F-mutant blood cells alone are not sufficient to generate the spontaneous heart failure phenotype we have observed in Tie2FF1 mice; JAK2V617F-mutant ECs are required, as cardiac dysfunction and inflammatory monocytes are only generated when the ECs bear the JAK2V617F mutation. (Figure 2)
To begin to understand the roles of JAK2V617F-mutant ECs in the development of cardiovascular dysfunction in Tie2FF1 mice, we found that the expression levels of Kruppel-like factors 2 (KLF2) and 4 (KLF4), two important regulators of vascular homeostasis that contribute to an anti-adhesive, anti-thrombotic, and anti-inflammatory endothelial phenotype, as well as thrombomodulin and eNOS, two downstream targets of KLF2/4 signaling, were significantly down-regulated in JAK2V617F-mutant ECs compared to wild-type ECs. In addition, cell surface adhesion molecules PECAM and E-selection were significantly up-regulated in JAK2V617F-mutant ECs compared to wild-type ECs. Both PECAM and E-selectin were further up-regulated in flow sheared (60dyn/cm2) JAK2V617F-mutant ECs compared to un-sheared ECs, while their levels did not change in wild-type ECs. These results indicate that JAK2V617F-mutant ECs display a pro-adhesive phenotype that can contribute to the cardiovascular dysfunction we observed in Tie2FF1 mice. (Figure 3)
Conclusions
In summary, our findings indicate that the JAK2V617F mutation can alter vascular endothelial function to promote cardiovascular complications in a murine model of MPN.

Disclosures
No relevant conflicts of interest to declare.