Articular cartilage thickness and Mig6 localization. (A-D) Sections of 12-week-old normal Mig-6-flox (A, C) and Mig-6-flox;Prx1Cre conditional knockout (Mig-6-cko) knees (B, D) stained with Safranin-O to detect proteoglycan (red) and counterstained with Fast Green (tibia is at the bottom, femur is at the top). The articular cartilage of the tibial and femoral surfaces (boxed areas in A, B, shown at high magnification in C, D) is dramatically thickened in the Mig-6-cko knee (B, D). In addition, reduced Safranin-O staining is observed in the the superficial zone of the Mig-6-cko articular cartilage (* in D), which is highly cellular and contains numerous rounded chondrocytes often appearing as doublets (arrowheads in D). Note also the thickened ligaments (lg) and menisci (m); abundant connective tissue (ct), and thin subchondral bone (sb) in Mig-6-cko knee joint (compare A to B). (E) Immunohistochemical detection of Mig-6 protein in 12-week-old normal Mig-6-flox tibial articular cartilage, showing Mig-6-positive chondrocytes (brown stain, arrows) mainly in the superficial zone. Some Mig-6-positive chondrocytes were also present in deeper zones (arrowhead) in the articular cartilage adjacent to the tidemark. (F) Measurement of the widths of the normal and Mig-6-cko tibial articular cartilages (for example, see bars in C, D) shows that the Mig-6-cko articular cartilage is dramatically thicker than normal articular cartilage. The articular cartilage of Mig-6-cko mice was more than 1.5-fold thicker than normal articular cartilage at 12 weeks of age (P <0.01). (G, H) Sections of six-week normal Mig-6-flox (G) and Mig-6-cko knees (H) stained with Safranin-O/Fast Green. The articular cartilage of Mig-6-cko joints is also dramatically thickened at six weeks of age (compare bars in G vs. H). (I) Measurement of the widths of the normal and Mig-6-cko tibial articular cartilages shows that the Mig-6-cko articular cartilage is nearly two-fold thicker at six weeks of age (P <.001). Scale Bar = 500 μm (A, B); 200 μm (C, D); 100 μm (E, G, H).
Shepard et al. Arthritis Research & Therapy 2013 15:R60 doi:10.1186/ar4233