These data suggest that LRP5 e pression was sufficient to cause chondrocyte dedifferentiation in our e perimental system. Consistent with the unaltered e pression of Lrp6 in vitro, however, LRP6 this site was barely detected in human and mouse OA cartilage samples, and LRP6 overe pression did not alter the e pression levels of the tested genes. Ne t, we e amined the effects of siRNA mediated knockdown of Lrp5 in dedifferentiated chondrocytes. IL 1B is known to trigger the e pression of various catabolic fac tors in primary cultures of articular chondrocytes. Accordingly, we e amined the possibility that LRP5 mediates the IL 1B induced e pression of these catabolic factors in chondrocytes. siRNA induced knockdown of Lrp5 was found to block the IL 1B induced upregulation of Mmp3 and Mmp13, as well as the IL 1B induced downregulation of Col2a1.

To further confirm the effects of LRP5 on Mmp3 and Mmp13 e pression in dedifferentiated chondrocytes, we stimulated the canonical Wnt pathway with recombinant Wnt3a and Wnt7a proteins. Both Wnt3a and Wnt7a induced chondrocyte dedifferentiation by suppressing Col2a1 e pression and concomitantly in creased Lrp5 e pression. However, Wnt3a and Wnt7a had differential effects on MMP e pres sion. Wnt3a triggered the induction Drug_discovery of Mmp13 but not Mmp3, whereas Wnt7a stimulated both Mmp3 and Mmp13. Lrp5 knockout mice show inhibition of e perimental osteoarthritis induced cartilage destruction The specific in vivo functions of LRP5 were evaluated by inducing e perimental OA in Lrp5 mice via aging or by DMM surgery.

Safranin O staining and Mankin score analysis revealed significant cartilage destruction in WT mice subjected to aging or DMM surgery, whereas the degree of cartilage destruction was markedly reduced in Lrp5 mice. Consistent with our results following siRNA media ted knockdown of Lrp5, the IL 1B or Wnt mediated induction of Mmp3 and Mmp13 in articular chondrocytes obtained from LRP5 mice were significantly decreased compared to those from their corresponding WT littermates. To further determine whether the LRP5 mediated regula tion of Mmp3 and Mmp13 e pression occurred via the canonical Wnt B catenin signaling pathway, we e amined the effects of LiCl treatment, which inhibits glycogen synthase kinase 3B. We found that LiCl treat ment of chondrocytes from WT mice further enhanced the Wnt3a mediated upregulation of Mmp13 and the Wnt7a mediated upregulation of Mmp3 and Mmp13, whereas these parameters were unchanged in LiCl treated Lrp5 mice. LRP5 potentiates Wnt B catenin signaling during osteoarthritis pathogenesis Because GSK3B activity is primarily responsible for the degradation of B catenin, Vandetanib we ne t e amined whether the e pression and or activity levels of B catenin could be reg ulated by LRP5.