Deletion of SOST increased damage to joint cartilage. (A) Safranin O staining of wild-type (WT) and SOST-knockout (SOST-KO) mice after destabilization of the medial meniscus (DMM) or sham operation at weeks 4 and 6. Bar, 100 nm. Osteoarthritis (OA) score in DMM and sham-operated knees of WT and SOST-KO mice at each time point. (B) Immunohistochemistry of Adamts5/4 of WT and SOST-KO mice at weeks 4 and 6. Bar, 50 nm. (C) Quantification of information represented in (B). (D) Immunohistochemistry of type X collagen in WT and SOST-KO mice 4 weeks after OA induction. Bar, 50 nm. (E) SOST-KO increased chondrocyte apoptosis in non-calcified and calcified cartilage. Bar, 50 nm. Data are means ± SEM.*P < 0.05 compared with sham-operated mice. #P < 0.05 (n = 5 animals for each genotype).