Wnt16 attenuates osteoarthritis progression through a PCP/JNK-mTORC1-PTHrP cascade.

Abstract

Wnt16 is implicated in bone fracture and bone mass accrual both in animals and humans. However, its functional roles and molecular mechanism in chondrocyte differentiation and osteoarthritis (OA) pathophysiology remain largely undefined. In this study, we analysed its mechanistic association and functional relationship in OA progression in chondrocyte lineage. The role of Wnt16 during skeletal development was examined by <i>Col2a1-Wnt16</i> transgenic mice and <i>Wnt16^fl/fl;Col2a1-Cre</i> (Wnt16-cKO) mice. OA progression was assessed by micro-CT analysis and Osteoarthritis Research Society International score after anterior cruciate ligament transection (ACLT) surgery with <i>Wnt16</i> manipulation by <i>adenovirus</i> intra-articular injection. The molecular mechanism was investigated in vitro using 3D chondrocyte pellet culture and biochemical analyses. Histological analysis was performed in mouse joints and human cartilage specimens. <i>Wnt16</i> overexpression in chondrocytes in mice significantly inhibited chondrocyte hypertrophy during skeletal development. <i>Wnt16</i> deficiency exaggerated OA progression, whereas intra-articular injection of <i>Ad-Wnt16</i> markedly attenuated ACLT-induced OA. Cellular and molecular analyses showed that, instead of β-catenin and calcium pathways, Wnt16 activated the planar cell polarity (PCP) and JNK pathway by interacting mainly with AP2b1, and to a lesser extend Ror2 and CD146, and subsequently induced <i>PTHrP</i> expression through phosphor-Raptor mTORC1 pathway. Our findings indicate that Wnt16 activates PCP/JNK and crosstalks with mTORC1-PTHrP pathway to inhibit chondrocyte hypertrophy. Our preclinical study suggests that Wnt16 may be a potential therapeutic target for OA treatment.