Bone Abstracts

Aim: Wnt/β-catenin pathway promotes cartilage breakdown in osteoarthritis. We have previously shown that sclerostin preserves chondrocyte maintenance in vitro by reducing chondrocyte catabolism through the inhibition of Wnt/β-catenin pathway. However, sclerostin restores partially the expression of the anabolic genes. We therefore investigated the effect of sclerostin in the activation of Wnt non canonical pathways mediated by Ca²⁺/CaMKII, JNK, and PKC proteins.

Methods: Primary murine chondrocyte were cultured in the presence of Wnt3a and sclerostin. Effect of JNK and PKC pathways in the chondrocyte phenotype were investigated using SP600125 and Staurosporin inhibitors respectively. Chondrocyte differentiation was investigated by RT-qPCR and western blotting through the expression of type II collagen, Sox9, Aggrecan, MMP-3, 13, and ADAMTS4 and 5. Alcian blue staining was used for analyzing the accumulation of highly sulphated GAG in chondrocytes.

Results: Wnt3a increased the expression of metalloproteinases such as ADAMTS and MMP, which was totally abolished by sclerostin. Moreover, sclerostin restored partially the expression of type II Collagen, Sox9 and Aggrecan induced by Wnt3a. Wnt3a promoted the phosphorylation of JNK and PKC but not the phosphorylation of CaMKβII. Sclerostin inhibited the phosphorylation of JNK but not PKC. We found that Wnt3a decreased the accumulation of highly sulphated GAG. Interestingly, sclerostin rescued the accumulation of highly sulphated GAG and the expression of the anabolic genes through the inhibition of JNK pathway.

Conclusions: Wnt3a inhibits anabolism in chondrocytes by activating the JNK pathways and prevented by sclerostin. These results show that Sclerostin may play a role in cartilage homeostasis through both canonical and non canonical pathways.