Mechanical stress and inflammation have opposite effects on Wnt signaling in human chondrocytes.

Dysregulation of Wnt signaling has been strongly associated with development and progression of osteoarthritis (OA). Here, we set out to investigate the independent effects of either mechanical stress or inflammation on Wnt signaling in human neo-cartilage pellets, and to relate this Wnt signaling to OA pathophysiology. OA synovium conditioned media (OAS-CM) was collected after incubating synovium from human end-stage OA joints for 24 hours in medium. Cytokine levels in the OAS-CM were determined with a multiplex immunoassay (Luminex). Human neo-cartilage pellets were exposed to 20% mechanical stress, 2% OAS-CM or 1 ng/ml IL-1β. Effects on expression levels of Wnt signaling members were determined by RT-qPCR. Additionally, expression of these members in articular cartilage from human OA joints was analyzed in association to joint space narrowing (JSN) and osteophyte scores. Protein levels of IL-1β, IL-6, IL-8, IL-10, TNF-α and GM-CSF positively correlated with each other. Mechanical stress increased non-canonical WNT5A and FOS expression. In contrast, these genes were downregulated upon stimulation with OAS-CM or IL-1β. Furthermore, Wnt inhibitors DKK1 and FRZB decreased in response to OAS-CM or IL-1β exposure. Finally, expression of WNT5A in OA articular cartilage was associated with increased JSN scores, but not osteophyte scores. Our results demonstrate that mechanical stress and inflammatory stimuli have opposite effects on canonical and non-canonical Wnt signaling in human neo-cartilage. Considering the extent to which mechanical stress and inflammation contribute to OA in individual patients, we hypothesize that targeting specific Wnt pathways offers a more effective, individualized approach. This article is protected by copyright. All rights reserved.