Abstract

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 JAK2WT or the MPN-driver JAK2V617F (heterozygous, JAK2V617FHET, or homozygous, JAK2V617FHOM), we identified zygosity-dependent transcriptional profiles in iPSC-derived EC (iEC) at baseline and following interferon-alpha (IFN) treatment. JAK2V617FHET iEC exhibited an endothelial-to-mesenchymal transition (EndMT) signature, while JAK2V617FHOM 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 IFN. 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 IFN treatment in vivo effectively reversed these pathological changes. IFNs anti-EndMT activity was further validated in BM biopsies from MPN patients undergoing IFN therapy. This is the first study to define MPN stage-dependent vascular remodeling and zygosity-specific endothelial effects of JAK2V617F, and to directly link IFN-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. Bullet PointsO_LIArterial vascular remodeling emerges as a novel hallmark of MPN, characterized by TNF-inflammation, ribosomal dysregulation and EndMT. C_LIO_LIIFN restores neoplastic endothelial dysfunction, highlighting its role as a vascular niche-modulating and anti-fibrotic agent in MPN. C_LI