RSPO2 and osteoarthritis: Okura et al. found that the content of R-spondin 2 in synovial fluid of patients with osteoarthritis gradually increased with the severity of OA, and mianserin could prevent and improve articular cartilage degradation in a mouse model of knee OA with medial meniscus instability by inhibiting R-spondin 2-induced Wnt/β-catenin signaling pathway in chondrocytes (Okura et al., 2019).