Osteoblast-Derived HIF-1α Drives Compartment-Specific H-Type Angiogenesis in Knee Osteoarthritis via VEGFA Signaling

Introduction: Pathological H-type angiogenesis in medial subchondral bone plays a critical role in Knee Osteoarthritis (KOA); however, the cellular crosstalk remains unclear. We investigated whether osteoblast-derived hypoxia-inducible factor-1 alpha (HIF-1α) drives medial vascular remodeling via vascular Endothelial Growth Factor A (VEGFA) paracrine signaling to Endothelial Cells (ECs). Methods: The bulk and single-cell RNA sequencing (scRNA-seq) data for KOA and control samples were collected from the Gene Expression Omnibus (GEO) databases. Differential expression analysis was performed using the limma R package. scRNA-seq analysis was performed using the Seurat package, HIF-1α activity was scored by AUCell, and cell-cell communication was inferred using CellChat. An osteoblast-EC Transwell co-culture system was established to explore the role of osteoblast-derived HIF-1α in regulating endothelial function under inflammatory conditions. After HIF-1α knockdown in osteoblasts, we performed quantitative Polymerase Chain Reaction (qPCR) and Western blotting, and assessed tube formation ability. Results: Integrated bulk RNA-seq analysis revealed significant upregulation of HIF-1α signaling and Extracellular Matrix (ECM)-related pathways in medial subchondral bone of KOA patients. scRNA-seq analysis further revealed distinct osteoblast and endothelial cell populations in the medial compartment, with AUCell scoring confirming higher HIF-1α pathway activity in medial osteoblasts. CellChat analysis computationally inferred VEGF-mediated macrophage-EC communication, including VEGFA-VEGFR2 and VEGFB-VEGFR1 interactions. In functional validation, HIF-1α knockdown in osteoblasts reduced VEGFA expression, attenuated the levels of H-type vessel markers CD31 and EMCN in ECs, and impaired capillary tube formation. Discussion: This study revealed a compartment-specific HIF-1α signaling that drove KOA pathological angiogenesis in medial subchondral bone via an osteoblast-endothelial feed-forward axis, providing a targeted therapeutic strategy Conclusion: The findings suggest that osteoblast-derived HIF-1α drives compartment-specific H-type angiogenesis in KOA via VEGFA-dependent endothelial activation, highlighting the osteoblast-endothelial axis as a therapeutic target.