A single JAK2V617F driver mutation induces spatially segregated and ontogeny-dependent skeletal remodeling in myeloproliferative neoplasms, causing coexisting osteosclerosis and bone loss through a conserved osteochondral injury program mediated by THBS1+ stromal cells that undergo pathological lineage plasticity with ectopic chondrogenesis, and combined pharmacological inhibition of THBS1 and JAK signaling simultaneously suppresses myeloproliferation, halts fibrosis, and restores bone homeostasis across developmentally distinct skeletal compartments.

Myelofibrosis in patients with myeloproliferative neoplasms (MPNs) is traditionally characterized by bone marrow fibrosis and osteosclerosis, with de novo bone formation commonly attributed to impaired osteoclast-mediated resorption. Here, we challenge this paradigm by demonstrating that a solitary clonal driver mutation simultaneously induces pathological bone formation and resorption, with osteosclerosis acting to conceal localized and active bone destruction rather than inhibiting it. Through population analysis; clinical imaging; patient-derived multi-tissue sequencing; murine models and organ-on-a-chip systems, we demonstrate that spatial and ontogeny-dependent remodeling in mesoderm- and neural crest–derived bones is mechanistically interconnected via a previously unidentified osteochondral stromal injury program. Neural crest–derived stromal cells suppress osteogenic programs and undergo injury-induced lineage plasticity with ectopic chondrogenesis, mirroring pathological remodeling in mesoderm-derived growth plate regions. This shared injury response promotes osteoclastogenesis and is mediated by a conserved Thrombospondin 1+ (THBS1+) stromal population that links fibrotic remodeling to bone loss. Combined pharmacological inhibition of THBS1 and JAK signaling reduces myeloproliferation, halts fibrosis progression, and restores two developmentally distinct bones, establishing THBS1 as a unifying therapeutic target in myelofibrosis.