Fig. 5. Postnatal RUNX2 overexpression induces MMP13 expression in unmineralized articular chondrocytes prior to accelerating articular cartilage degeneration following MLI.

(A) Safranin O/Fast green staining of knee joint sections from R26^Runx2/+ (Control) and Acan^CreERT2/+; R26^Runx2/+ (RUNX2 OE) mice injected with tamoxifen at 2 months of age and subjected to sham or MLI at 2.5 months of age. Joints were harvested one month following injury. Top panels are 5X images of the knee joint; bottom panels are high magnification images (20X) of the boxed regions. (B) Cartilage degeneration in Control (n = 6) and RUNX2 OE (n = 6) mice was evaluated by modified OARSI scoring (top graph) and quantitative histomorphometric analysis (bottom graph, data normalized to contralateral sham control sample). (C) MMP13 (left panels) and COL10A1 (right panels) immunohistochemistry of knee joint sections from Control or RUNX2 OE mice subjected to sham or MLI at 2.5 months of age and harvested 1 month following injury (20X images). (D) Quantification of MMP13⁺ cell number as percentage of total cell number from Control and RUNX2 OE mice (MLI samples only, n = 4 for both groups). (E) Quantification of COL10A1⁺ cartilage area as percentage of total cartilage area from Control and RUNX2 OE mice (MLI samples only, n = 4 for both groups). *p < 0.05, Student’s t-test.