Fig 2: Sclerostin upregulates in the articular cartilage post‐injury. Sost immunostaining was conducted on contralateral WT (A) and SOSTTG (E and I) joints at 1 day after injury. Injured WT joints had elevated levels of Sost (B and C), while injured SOSTTG joints had elevated expression of both mouse (F and G) and human Sclerostin (J and K) 1 day after injury. No differences were observed in Sclerostin expression in the osteocytes of injured animals (D, H, and L). Real‐time quantitative PCR (qPCR) analysis of whole‐joint RNA of WTs at 1, 2, 3, and 4 days after injury (M). All images are at ×20 magnification. *p < 0.05, **p < 0.01.

Fig 3: Moderate PTOA phenotype in SOSTTG compared with WT and Sost‐/‐. Histological staining of Safranin‐O and Fast Green on contralateral (left knee) at 16 weeks post‐injury (A). Cartilage integrity scoring using three distinct regions: femoral surface (I); anterior tibial surface (II); and the posterior tibial surface (III). Lower magnification (×5) of whole joint overview between C57Bl/6 (a, e), Sost‐/‐ (i, m), and SOSTTG (q, u); higher‐resolution (×20) images are provided for all other images. Injured and contralateral joints were examined and scored in three distinct regions using a modified OARSI scoring method (OA severity: 0∼2, mild; 3∼4, moderate; and 5∼6, severe). Uninjured control (UIC) and contralateral (left knee) were utilized as controls. Scale bar = 0.2 mm. *p < 0.05, ***p < 0.001. Erosion to the growth plate is marked by asterisks (e, m). Black arrows indicated regions of erosion.

Fig 4: Sost activation in the injured joint is TNFα and NF‐κB dependent. Time line for IA administration of NF‐κB inhibitor (BAY‐11‐7082) and TNFα inhibitor (neutralizing antibody) (A). Immunohistochemical staining of cartilage (Col2a; green), Sost (red), and nucleus (DAPI; blue) between vehicle (DMSO or PBS) and BAY‐11‐7082 (B) or TNFα antibody (C) treated injured joints.

Fig 5: SOSTTG and WT injured joints treated with recombinant Sost (rmSost) protein have reduced levels of activated MMPs post‐injury. MMPSense was administered IV 5 hours post‐injury; rmSost was delivered IA post‐injury, and mean fluorescence intensity was measured 3 days post‐injury as depicted in A. SOSTTG‐ and rmSost‐treated injured joints displayed significantly less fluorescence than Sost‐/‐ or WT control joints (B). Representative ex vivo images of WT uninjured (C) and injured WT (D), Sost‐/‐ (E), and SOSTTG (F). Injured joints show reduced fluorescence in SOSTTG (F). Similarly, rmSost‐treated injured joints (H) show less fluorescence than PBS controls (G). **p < 0.01, ***p < 0.001.