Suppression of age-related hypertrophic differentiation of deep-zone articular chondrocytes by overexpression of CCN2.

<p>Immunohistochemical staining of type X collagen in frontal sections of knee joint. (A) Typical staining of type X collagen of the TG (left) and WT (right) joints from 21-month-old mice. Bars: 100 µm. a and b: type X collagen staining of the medial portion of knee joint in the load-bearing region. Femora (f) and tibia (t) are presented. a’ and b’: higher magnification of load-bearing region indicated by the dotted box in a and b, respectively. Type X collagen-positive cells (arrowheads in b’) were observed in the deep zone of WT tibial articular cartilage, but not in those of TG cartilage. (B) Type X collagen staining of articular cartilage (knee joints) from 21- and 18-month-old littermates. Bars: 200 µm. (C) Results of densitometric analysis of type X collagen staining of tibial articular cartilage. Left: staining intensity of individual medial cartilage samples of tibia. Right: mean value. TG cartilage showed a significantly lower accumulation of type X collagen compared with the WT cartilage. ***: <i>p</i><0.01.