Vascular and lymphatic dysregulation via non-EndoMT Col2a1 signaling in bisphosphonate-related osteonecrosis of the jaw

Abstract Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a severe complication of antiresorptive therapy with poorly understood vascular mechanisms. Here, we integrate whole-organ tissue-clearing imaging, single-cell transcriptomics, and proteomics to construct a multimodal atlas of the mouse and human BRONJ mandibular microenvironment. We identify gross vascular and lymphatic rarefaction and four endothelial subtypes with aberrant Col2a1 upregulation. Fibroblasts and macrophages emerge as key endothelial interactors, highlighting dysregulation of the endothelium-matrix-immune axis. Unlike homeostatic Dmp1⁺/Tfap2a⁺ fibroblasts and Stab1⁺ macrophages, BRONJ lesions feature pathological Lrrc15⁺/Chad⁺ fibroblasts and Il6⁺ macrophages, driving ectopic chondrogenesis and inflammation. Mechanistically, the COL2A1-CD44 axis (EC-to-fibroblast/macrophage signaling) and COL2A1-SDC4 axis (EC-to-fibroblast signaling) are upregulated in BRONJ disease condition, while lineage tracing excludes EndoMT, implicating extracellular matrix remodeling. We functionally validate this axis via localized Col2a1 siRNA silencing and endothelial-specific genetic deletion. Cross-species validation in human mandibles confirms vascular-lymphatic dysregulation, inflammation, and chondrogenesis. Overall, we establish vascular and lymphatic dysregulation as a BRONJ hallmark and identify the COL2A1-CD44/SDC4 axis as a therapeutic target.