age samples were frozen, sectioned at a thickness of 6 um and subjected to Alcian blue and immunohistochemical stain ing. Mouse cartilage was fi ed in 4% paraformaldehyde, decalcified in 0. 5 M ethylenediaminetetraacetic acid, embedded in paraffin and sectioned at a thick ness of 6 um. Cartilage destruction was evaluated by Safranin O staining and scored according to Mankins method. Immunostaining of LRP5, MMP3, MMP13 and B catenin in human and mouse cartilage was per formed using standard techniques. RT PCR and quantitative RT PCR Total RNA isolated from mouse articular chondrocytes and OA cartilage tissues was reverse transcribed, and the resulting cDNA was PCR amplified. The PCR primers and conditions used for mouse Col2a1, Mmp3, Mmp13, Ptgs2, Nos2 and Gapdh were previously described.

Western blot analysis Total cell lysates were prepared with lysis buffer containing 150 mM NaCl, 1% Nonidet P 40, 50 mM Tris, 0. 2% SDS, 5 mM NaF, a protease inhibitor cocktail and a phosphatase inhibitor cocktail. Proteins were resolved by SDS PAGE, transferred GSK-3 to nitrocellulose membranes, de tected by incubation with the appropriate primary antibody and a pero idase conjugated secondary antibody and visualized using an enhanced chemiluminescence system. The primary antibodies used were purchased from ABGENT, EMD Millipore, BD Biosciences, 610408. B catenin, 610154 Santa Cruz Biotechnology and Cell Signaling Technology, 9252. and phosphorylated JNK, 9255. Danvers, MA, USA.

Transfection and reporter gene assay Mouse articular chondrocytes were cultured for 3 days, transfected for 4 hours with Lrp5 small interfering RNA or pSPORT6 Lrp5 using Lipofectamine 2000 reagent, then treated with IL 1B, Wnt3a or Wnt7a. A nonsilencing control siRNA and empty vector were used as the negative controls. To deter mine the transcriptional activity of B catenin Tcf Lef, we used a reporter gene assay. Chondrocytes were transfected with 1 ug of reporter gene or control gene and 1 ug of pCMV B galactosidase using Lipofectamine 2000. The transfected cells were treated with IL 1B, Wnt3a or Wnt7a for 24 hours, then luciferase acti vity was measured and normalized with respect to transfec tion efficiency. Statistical analysis The nonparametric Mann Whitney U test was used to analyze data based on ordinal grading systems, such as International Cartilage Repair Society and Mankin scores.

For qRT PCR results and apoptotic cell numbers, the data were first tested for conformation to a normal distribution using the Shapiro Wilk test, then analyzed by Students t test or analysis of variance with post hoc tests as ap propriate. Significance was accepted at the 0. 05 level of probability. Results Lrp5 is upregulated via JNK and NF ��B pathways during IL 1B mediated pathogenesis of chondrocytes We first e amined the e pression levels of Lrp5 and Lrp6 during the chondrogenic differentiation of mesen chymal cells obtained from mouse embryonic limb buds and subjected to micromass culture. We found th