Pharmacological neutralization of the Rspo2/Wnt axis preserves subchondral bone plate and vascular niche integrity to attenuate cartilage degeneration in osteoarthritis.

OBJECTIVES

Osteoarthritis (OA) involves the structural failure of the joint unit, where the subchondral bone plate and associated vascular niche serve as a critical barrier and mechanical support for articular cartilage. This study investigates R-spondin 2 (Rspo2) as a mediator of instability within the subchondral bone plate-associated vascular niche and evaluates whether its pharmacological neutralization attenuates niche disruption and preserves osteochondral integrity.

METHOD: Human tibial-plateau subchondral bone scRNA-seq (GSE196678) and clinical specimens were analyzed to identify Wnt-related pathways. OA was induced in mice via ACLT + DMM surgery. Weekly intra-articular administration of recombinant Rspo2, an Rspo2-neutralizing antibody (Rspo2-NAb), or the Wnt inhibitor DKK1 began on postoperative day 3. Subchondral bone remodeling and cartilage degeneration were assessed in separate groups of mice at postoperative days 30 and 60.

RESULTS

The scRNA-seq analysis identified Wnt-related expression patterns in OA subchondral endothelial cells (ECs). Histology showed a higher percentage of CD31+/p-β-catenin (Ser675)+ cells in OA specimens than in controls. In vitro, rhRspo2 enhanced endothelial proliferation and tube formation, whereas conditioned medium from Rspo2-overexpressing ECs promoted osteogenic and osteoclastic differentiation and disrupted chondrocyte homeostasis; these effects were attenuated by Rspo2-NAb or DKK1, consistent with involvement of Wnt/β-catenin signaling. Early postoperative administration of Rspo2-NAb or DKK1 reduced subchondral bone plate remodeling and the proportion of CD31+EMCN+ cells, and attenuated cartilage degeneration in vivo.

CONCLUSIONS

These findings support a paracrine role for endothelial-derived Rspo2 in vitro and the potential of early Rspo2 neutralization to attenuate bone remodeling and cartilage degeneration in experimental OA.