Role of Primary Cilia in Skeletal Disorders

Figure 2

Cilium in normal and osteoarthritis (OA) articular cartilage tissues. The normal articular cartilage can be divided into superficial, intermediate, and deep zones as shown in figures. In the superficial zone of normal articular cartilage (left), the chondrocytes are ellipsoid. Both chondrocyte and cilia are parallel to the surface of articular cartilage. In intermediate and deep zones, the chondrocytes are irregular, but the cilium orientation is on the medial or lateral cell membranes along the longitudinal axis parallel to the chondrocyte. However, the articular surface is eroding in human OA tissue, and the cilium incidence and length significantly increased compared with normal human articular cartilage [40]. Moreover, the cilia are oriented parallel to the long axis of cells at the articulating surface in normal articular cartilage, but it is oriented to the center of abnormal cell clusters in osteoarthritic cells.