Fig. 6.

Knees of non-injured MMP13^ocy−/− mice show more cartilage damage than wild-type mice. a–c Safranin-O stained joints of 16-week-old wild-type mice show intact cartilage, while MMP13^ocy−/− mice have areas of cartilage surface irregularity and proteoglycan depletion (a), leading to significantly higher OARSI (b) and modified Mankin (c) scores (n = 6). d–f In sham-injured joints, MMP13-dependent proteoglycan loss is still apparent, and meniscal-ligamentous injury (MLI) induces severe cartilage damage in both groups (d). On OARSI (e) and modified Mankin (f) grading scales, sham-injured MMP13^ocy−/− mice score significantly higher than wild-type mice (n = 10), but scores are equivalent after MLI (n = 10 for wild-type, n = 11 for MMP13^ocy−/−). Arrows denote cartilage damage in non-injured joints. Scale bars are 100 μm. Graphs show mean ± SEM. *P < 0.05 between genotypes by unpaired t test