Load-induced glycosaminoglycan release and matrix metalloproteinase activity in mouse cartilage explants from FrzB−/−and wild-type mice. Explants were subjected to dynamic compression for 6 hours (0.5 Hz, 1 MPa). FrzB−/− cartilage explants (black bars, n = 4) or wild-type (WT) explants (gray bars, n = 4) were loaded. Results from the loaded cartilage explants were normalized to those from the corresponding nonloaded explants (Ctrl), so that the graphs represent the fold-induction in response to compression. (A) Amount of glycosaminoglycan (GAG) released from cartilage explants into culture supernatant. (B) Matrix metalloproteinase (MMP) enzymatic activity was measured in the culture supernatant of cartilage explants. Load-induced MMP activity tends to be enhanced in FrzB−/− explants compared with WT (P = 0.17). Bars represent the mean ± standard error of the mean. *P ≤ 0.05 versus Ctrl. FrzB, frizzled-related protein B; KO, knockout.