Inhibition of JAK2V617F-Driven Neoplastic Endothelial Dysfunction by IFNα as a Novel Antifibrotic Mechanism

The vascular niche is a critical regulator of hematopoiesis and disease progression in myeloproliferative neoplasms (MPN). The presence of JAK2V617F+ endothelial cells (EC) in MPN patients and their association with cardiovascular complications highlight the need to understand and therapeutically target this compartment. Using patient-specific induced pluripotent stem cells (iPSC) harboring JAK2 ^WT or the MPN-driver JAK2V617F (heterozygous, JAK2V617F ^HET , or homozygous, JAK2V617F ^HOM ), we identified zygosity-dependent transcriptional profiles in iPSC-derived EC (iEC) at baseline and following interferon-alpha (IFNα) treatment. JAK2V617F ^HET iEC exhibited an endothelial-to-mesenchymal transition (EndMT) signature, while JAK2V617F ^HOM iEC showed suppression of translation and ribosome biogenesis. Leveraging iPSC-based 3D assembloids that mimic the bone marrow (BM) niche, we showed that JAK2V617F-driven EndMT is inhibited by tyrosine kinase inhibitors and IFNα. In both JAK2V617F-driven polycythemia vera and TPO-driven myelofibrosis murine models, scRNA-seq analysis of the BM vascular niche consistently revealed inflammatory and EndMT-associated signatures in arterial and arteriolar EC. Notably, dysregulation of ribosome- and translation-related pathways emerged in the myelofibrosis model and at advanced disease stages in JAK2V617F-driven polycythemia vera, indicating progressive vascular remodeling with disease evolution. Chronic pegylated IFNα treatment in vivo effectively reversed these pathological changes. IFNα’s anti-EndMT activity was further validated in BM biopsies from MPN patients undergoing IFNα therapy. This is the first study to define MPN stage-dependent vascular remodeling and zygosity-specific endothelial effects of JAK2V617F, and to directly link IFNα-mediated EndMT inhibition as a novel antifibrotic mechanism. Our 3D assembloids provide a translational platform for mechanistic studies and therapeutic targeting of the BM microenvironment in MPN.