Tiki2 maintains articular cartilage homeostasis and protects against osteoarthritis by inhibiting Wnt/β-catenin signaling

Osteoarthritis (OA) is a serious degenerative joint disease with high morbidity and is currently incurable because of its poorly defined underlying molecular basis. Here, we demonstrated that Tiki2, a membrane-tethered proteolytic Wnt inhibitor, is highly expressed in the articular chondrocytes of hyaline cartilage and that its expression negatively correlates with osteoarthritis. Tiki2 haploinsufficiency in mice causes spontaneous articular cartilage degeneration. Tiki2 deletion in chondrocytes accelerates instability-induced knee joint osteoarthritis progression in mice. Mechanistically, Tiki2 antagonizes Wnt signaling in chondrocytes and maintains chondrocyte anabolic gene expression. Moreover, intra-articular administration of a TIKI2-expressing adeno-associated virus significantly alleviated OA progression in mice, and expressing TIKI2 promoted chondrogenesis and chondrocyte redifferentiation and inhibited hypertrophic differentiation in vitro. Our results reveal the function of Tiki2 in articular cartilage homeostasis and osteoarthritis and suggest that Tiki2 is a potential target for osteoarthritis therapy.