Treatment of chondrocytes from WT mice with IL 1B, Wnt3a or Wnt7a also increased the transcrip tional activity of the B catenin Tcf Lef comple , whereas this activity was completely blocked in cells from Lrp5 mice. Consistent with these observations, the e pression useful site levels of B catenin and LRP5 were remarkably increased in OA cartilage induced by DMM surgery, and the B catenin e pressing cells largely overlapped with the LRP5 e pressing cells. Moreover, the e pression levels of B catenin and MMP13 were increased in OA affected human cartilage compared to healthy control cartilage. Interestingly, the increases in B catenin, MMP3 and MMP13 found in the OA cartilage of WT mice subjected to aging or DMM sur gery were not observed in e perimental OA cartilage samples from Lrp5 mice.

To control for une pected effects from the lack of Lrp5 in noncartilage tissues, we generated chondrocyte specific conditional KO mice, whereby the cre recombinase gene specifically deleted the Lrp5 gene from cartilage, but not other tissues, such as brain, heart and bone. Lrp5fl fl.Col2a1 cre and correspon ding Lrp5fl fl control mice were subjected to induced OA by DMM surgery. Consistent with our data from the total KO mice, Lrp5fl fl.Col2a1 cre mice e hibited significantly reduced cartilage destruction following DMM surgery compared with control Lrp5fl fl mice and did not show DMM surgery induced upregulation of B catenin, MMP3 and MMP13 e pression levels in OA cartil age samples. We also e amined whether the upregulation of LRP5 could potentiate chondrocyte apop tosis and found that chondrocyte apoptosis induced by 1 ug ml anti Fas antibody was not altered by Lrp5 defi ciency.

However, stimulation of apoptosis by IL 1B treatment Brefeldin_A in the presence of a low concentration of anti Fas antibody was slightly but signifi cantly reduced in Lrp5 deficient chondrocytes. As determined by TUNEL assay, apoptotic cells were also relatively reduced in DMM induced OA cartilage from Lrp5fl fl.Col2a1 cre mice compared to Lrp5fl fl mice. Taken together, our results suggest that LRP5 induces chondrocyte dedifferentiation and promotes the e pression of catabolic genes by potentiating the Wnt B catenin signaling pathway. Discussion Disturbance of cartilage homeostasis is a main cause of OA pathogenesis.

In OA, cartilage destruction is initiated by defects in joint biomechanics in conjunction with predisposing factors, leading to an imbalance of anabolic and catabolic molecular weight calculator factors. Various biochemical pathways are modulated, resulting in the insufficient synthesis of cartilage matri by chondrocytes, increased numbers of apoptotic chondrocytes and degradation of the ECM due to increased production of MMPs and ADAMTS. In this study, we demonstrate that Lrp5 is a crucial catabolic regulator of Wnt B catenin sig naling mediated OA cartilage destruction.