Activation of the WNT/β catenin canonical pathway following mechanical injury. (a) Axin-2 and (b) c-JUN mRNAs, two known transcriptional targets of the WNT/β catenin canonical pathway, were upregulated 1 day after injury compared to uninjured controls. (c-f) Paired cartilage explants were cultured in the presence of either 10 mM LiCl or 10 mM NaCl for 1 day and then terminated for gene expression analysis by quantitative real time PCR. Culture in the presence of LiCl induced the upregulation of axin-2 (c) and c-JUN (d) mRNAs, thereby confirming that these two genes are targets of the WNT/β catenin canonical pathway in this experimental system. LiCl treatment also upregulated aggrecan and COL2A1 mRNA (e,f). **p < 0.01. D, day(s); h, hours.