A comparative ultrastructural study of the mitotic chondrogenic cells in the mandibular condyle and tibial growth plate of the rat

Localization of CD44 (hyaluronan receptor) and hyaluronan in rat mandibular condyle

CD44 is a multifunctional adhesion molecule that binds to hyaluronan (HA), type I collagen, and fibronectin. We investigated localization of CD44 and HA in mandibular condylar cartilage compared with the growth plate and the articular cartilage, to clarify the characteristics of chondrocytes. We also performed Western blotting using a lysate of mandibular condyle. In mandibular condyle, CD44-positive cells were seen in the surface region of the fibrous cell layer and in the proliferative cell layer. Western blotting revealed that the molecular weight of CD44 in condyle was 78 to 86 kD. Intense reactivity for HA was detected on the surface of the condyle and the lacunae of the hypertrophic cell layer. Moderate labeling was seen in cartilage matrix of the proliferative and maturative layer. Weak labeling was also seen in the fibrous cell layer. In growth plate and articular cartilage, HA was detected in all cell layers. However, chondrocytes of these cartilages did not exhibit reactivity for CD44. These results suggest that chondrocytes in the mandibular condylar cartilage differ in expression of CD44 from those in tibial growth plate and articular cartilage. Cell-matrix interaction between CD44 and HA may play an important role in the proliferation of chondrocytes in the mandibular condyle.