ROR1/STAT3 positive feedback loop facilitates cartilage degeneration in Osteoarthritis through activation of NF-κB signaling pathway.

Background: Osteoarthritis (OA) is a chronic joint disorder with a serious impact on society. The main pathological change in OA is articular cartilage degeneration, which is directly associated with imbalance of anabolic and catabolic activities in chondrocytes.

Objective: To evaluate the expression and biological effects of ROR1 in OA cartilage and determine whether knockdown of ROR1 attenuates cartilage degeneration.

Methods: ROR1 expression in OA clinical specimens was evaluated by western blotting and immunohistochemistry. The effects of ROR1 on anabolic and catabolic activities were evaluated in Wnt5a-treated human primary chondrocytes by western blotting, immunofluorescence, and luciferase assay. The effects of ROR1 knockdown on cartilage degeneration in a surgical OA mouse model were examined by X-ray imaging and Safranin O-Fast Green histological staining.

Results: ROR1 was considerably upregulated in cartilage tissues of OA patients. ROR1 knockdown alleviated the activation of the NF-κB signaling pathway and reversed the suppression of collagen II and aggrecan by Wnt5a, as well as upregulation of ADAMTS-5 and MMP-13 in chondrocytes. In addition, ROR1 knockdown significantly reduced Wnt5a-induced STAT3 nuclear translocation. STAT3 binding to the ROR1 promoter indicated a positive feedback loop between ROR1 and STAT3. ROR1 knockdown was confirmed to dramatically alleviate cartilage degradation in the DMM induced-OA mouse model.

Conclusion: Increased expression of ROR1 in OA cartilage tissues leads to a positive feedback loop with STAT3, which activates the NF-κB signaling pathway, resulting in an imbalance between chondrocyte anabolism and catabolism. These results indicate a potential new therapeutic target for the treatment of OA.